February 27, 2026 • 40 mins
Biodiversity loss is an ongoing challenge, but some of the language we use to describe it may be on shakier ground than we realize. Are we really living through a “sixth mass extinction”? What does that phrase technically imply, and how well is it supported by the data? And what about climate change: how much species-level extinction can credibly be attributed to warming so far, and how do you attribute causes when multiple threats interact?
To explore these questions, I spoke with John Wiens, an ecologist at the University of Arizona whose work focuses on extinction rates and climate-driven range losses. We discuss what the evidence suggests about acceleration (or the lack thereof) in extinction in recent decades, why documented extinctions have been concentrated on islands and in freshwater systems, and how climate change is expected to reshape extinction risk through mechanisms like heat extremes, shifting range limits, and disease dynamics. The thread running through it all is credibility and ambition: how to communicate urgency without overclaiming, and why a stronger conservation goal is not “avoiding a mass extinction,” but preventing extinctions wherever we still can.
Links to resources
- Future threats to biodiversity and pathways to their prevention - The 2017 Tilman et al. article that John referred to in our discussion
- Questioning the sixth mass extinction - A 2025 article by John and colleague
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
SPEAKER_00 (00:00):
And the truth is that I think, you know, we
shouldn't stop species loss uhbecause it's part of a mass
extinction.
We should stop species lossbecause it's wrong to drive
other species to extinction.
SPEAKER_01 (00:19):
Welcome to the Case for Conservation podcast, where
we make the case for conservingnature and its biodiversity by
building a robust, credibleargument, one that sometimes
requires us to re-examineconventional wisdom.
I'm your host, Andre Moder.
Biodiversity loss is an ongoingchallenge, but some of the
language you use to describe itmay be on shakier ground than we
(00:41):
realize.
Are we really living through asuccess mass extinction?
What does that phrasetechnically imply?
And how well is it supported bythe data?
And what about climate change?
How many species levelextinctions can credibly be
attributed to warming so far?
And how do you attribute causeswhen multiple threats interact?
(01:02):
To explore these questions, Ispoke with John Weens, an
ecologist at the University ofArizona, whose work focuses on
extinction rates andclimate-driven range losses.
We discussed what the evidencesuggests about acceleration or
lack thereof in extinction inrecent decades, why documented
extinctions have becomeconcentrated on islands and in
(01:24):
freshwater systems, and howclimate change is expected to
reshape extinction risk throughmechanisms like heat extremes,
shifting range limits, anddisease dynamics.
The thread running through itall is credibility and ambition.
How to communicate urgencywithout overclaiming, and why a
stronger conservation goal isnot avoiding a mass extinction,
(01:46):
but preventing extinctionswherever we still can.
I began by asking John the basicoverarching question.
SPEAKER_00 (02:05):
I think the evidence is not there to support it at
this point.
I think it's sort of been takenas dogma for a few decades now.
But I think that the theoriginal evidence was was never
very strong to support that.
So basically you say it is aclearly there's a biodiversity
crisis.
Hundreds of species have goneextinct, you know, if not
(02:26):
thousands.
But to be, you know, it needs torank, it needs to be in the top
six mass extinctions that everhappened.
And and I think what what'slagging from that literature is
is generally sort of a you knowputting the current crisis uh on
a quantitative basis andcomparing it to those past ones.
And I think that just tends notto happen.
(02:48):
So for example, the thebackground extinction rate, this
idea that we're exceeding thebackground extinctions, well, of
course we are.
Humans are causing extinctions,but you know, the background
extinction rate is basically amean.
And so if it's a mean, sometimesyou're above the mean and
sometimes you're below it.
And and you can make a big dealabout how far above that that
mean we are, but that's usuallybased on comparing the time
(03:09):
scale of hundreds of years tomillions of years.
And you can expect you know hugedifferences like that when
you're comparing these verydifferent timescales.
SPEAKER_01 (03:17):
It reminds me a bit, I interviewed Earl Ellis uh a
while ago about the idea of theAnthropocene.
And and he, I think a similarkind of idea, his argument, if I
remember correctly, I'm I hopeI'm not mischaracterizing it,
but his argument was that theterminology is simply incorrect.
It's just technically it's notit's not right.
(03:39):
And so I guess that's the casehere as well.
But it it sort of makes mewonder, you know, at the
technical level, I I understand,but then just as a PR tool uh
and a way of of addressing theas you use the word biodiversity
crisis, right?
The term biodiversity crisis.
I guess my question would belike, what's wrong with using
sixth extinction as a marketingtool?
(04:01):
Or is it because of the clashwith the technical yeah?
SPEAKER_00 (04:05):
Well, so so part of the I think that there is a
potential, there is a potentialcollision with the marketing and
the technical side of it.
So so one thing is so what iswhat is our goal in should be
our goal in conservation be?
You see, it's to stop the sixthmass extinction.
That's an incredibly weak goal,right?
(04:34):
I'd say, come on, can we dobetter than that?
I mean, I I really prefer these,you know, these people who are
saying, okay, we're, you know,the zero extinction people, the
people that are focused on,okay, what's let's find the next
thing that's going to go extinctand stop it from going extinct.
And I think that needs to be themindset and not this, you know,
this incredibly lazy andunambitious idea of stopping 75%
(04:57):
species loss over hundreds orthousands of years.
SPEAKER_01 (04:59):
Right.
I suppose that it works on, youknow, most people they hear the
word and it sort of has itsdesired effect.
The problem is if someone wantsto dig more deeply into it, and
then they sort of then there's acredibility problem, right?
Because so you look deeply intoit and you see, well, actually,
that's not correct.
So then you start wondering whatelse is not accurate.
SPEAKER_00 (05:20):
Yeah, and and and it's I think it matters that
it's not it's not accurate.
You know, so questions, I meanit's fundamental questions.
So how you know what percentageof species have gone extinct?
And in terms of documented ones,it's it's less than one percent.
And so is you know, arguing thatwe're in the midst of 75%
species loss is like, you know,it doesn't take much digging to
(05:42):
see the problem, right?
SPEAKER_01 (05:43):
Yeah, um, and I guess another thing is that, and
I remember talking to MariaDonilas about this, is that we
human beings tend to focus onvertebrates, right?
And especially mammals and andbirds, but vertebrates, let's
say, as a as a whole.
Among vertebrates, theextinction rate is higher than
among species in general.
(06:05):
Is that correct or or notnecessarily?
SPEAKER_00 (06:07):
Um it's it's the highest is in is in tetrapods
and in uh molluscs.
And and so those have been hitthe hardest, it seems.
SPEAKER_01 (06:17):
Okay, and can you just just for for those who are
not sure, can you just explaintetrapods and mollusks?
What do those include?
What do those groups?
SPEAKER_00 (06:23):
Oh, so the tetrapods is basically just land
vertebrates.
So we think of amphibians,birds, mammals, and and
reptiles, you know, whichincludes turtles, lizards, and
snakes.
Um and so that that would be allvertebrates except for fish,
basically.
And mollusks would be you know,in terms of the the conservation
aspects, you know, mollusks endsup being mostly snails and then
(06:45):
bivalves as some um mussels, forexample.
SPEAKER_01 (06:48):
Right, marine and freshwater bivalves.
SPEAKER_00 (06:51):
Yeah, and and those have been those have been hit
really hard.
SPEAKER_01 (06:55):
So most of those are vertebrates, right?
So the tetrapods are allvertebrates.
SPEAKER_00 (07:01):
They're there are about um half of vertebrates.
SPEAKER_01 (07:04):
Right.
And what would you say?
I don't think I've ever seenthis written anywhere, but what
would you say to the statementthat there's a there's a
six-math extinction when you'relooking at tetrapods or
vertebrates?
SPEAKER_00 (07:15):
The the numbers are still way below.
SPEAKER_01 (07:18):
Right.
SPEAKER_00 (07:19):
What happens is it is that you know, things are
definitely bad for birds andmammals, and and then with you
know, for reptiles less so.
And even for amphibians, youknow, even there's there's a lot
of possibly extinct species fromKitrid, but not you know, not
ones that are definitelyextinct.
And so it's it's just not youknow, it's nothing like it's
(07:40):
nothing like 10%, it's nothinglike 75%, it's you know, more
like barely one percent.
SPEAKER_01 (07:46):
And a kytrid is the fungus, right?
The amphibian fungus.
SPEAKER_00 (07:50):
Yeah, and it really horrific, you know, just just
causing these horrific declinesand crashes.
SPEAKER_01 (07:56):
Right.
Yeah, it's interesting.
Amphibians, and the other onethat comes to mind is insects as
a very broad group.
I interviewed Jane Hill a whileago.
She's a an entomologist whoworks on butterflies
specifically.
And this is a bit too far backfor me to remember the details,
but essentially the the shortanswer to the question, is there
an insect to get in underway?
(08:17):
The short answer is no.
Um and there's just a lot ofvariability between groups.
Um, and she's lookingspecifically at at butterflies.
And so it's kind of like a, youknow, depending on the scale
that you look at and which partof the world you look at, and
and all these differentvariables, you know, once you
take all of those intoconsideration, as you said,
there are declines, but they'renot at the you know, the six
(08:41):
mass extinction kind of level,exactly as you were saying for
for vertebrates and and speciesmore more generally.
But then what about the theelement of acceleration?
You know, the the trend ratherthan the status.
So, you know, because I thinkyou'd be for people would be
forgiven for declaring asix-mass extinction if the rate
of of species loss isaccelerating in in a direction
(09:03):
that you you can extrapolate.
Uh what do you say then?
SPEAKER_00 (09:06):
Yeah, so so that's something that we looked at.
This this is work that I didwith um uh this great uh student
named Kristen Saban.
And specifically the the paperthat Kristen led in in
Proceedings B last fall, um, welooked, we looked at these
rates.
And basically there's thisliterature that says these rates
are are you know rapidlyaccelerating.
(09:27):
And that's true at the scale ofcenturies, but I think when we
think of rapid acceleration, itshould be at the scale of
decades at the least.
And when you look at decades,the last few hundred years, you
don't see that.
And in fact, for a lot ofgroups, the peak was like 100
years ago.
The peak extinction rate perdecade was uh around 100 years
(09:47):
ago.
So that's the case for plants,it's the case for arthropods,
and you know, tetrapods alsohave generally the extinction
rates have actually beendeclining recently.
And you know, there's when youlook really recently, there's
definitely the potential forartifacts in terms of things
aren't getting documented, theextinctions aren't being
documented.
(10:08):
But when we're looking over thetime scale of hundreds of years,
that seems less likely.
SPEAKER_02 (10:12):
Right.
SPEAKER_00 (10:13):
Um and and so I think you know, there's there's
definitely a reasonable argumentas to whether it's things are
actually decelerating or whetherthey're just more or less
constant.
But I just the the evidence forthis claim of rapid acceleration
is is just not supported at thescale of decades.
SPEAKER_02 (10:30):
I see.
SPEAKER_00 (10:31):
Um, mollusks show this this pretty this pretty
recent peak, and andactinopterygians also show a
more a more recent peak.
So there's definitely some thatthat variability kind of
contributes to what looks like amore a more constant pattern
when you look across everything.
Um but it's definitely not rapidaccelerations.
(10:52):
And even though folks haveclaimed it, you know, what I
think in cases they they seem tohave done is is to take the
cumulative number and call thatthe rate.
And the, you know, as you know,the distance traveled is not the
is not the velocity.
So they basically confuse thoseand it's just kind of gone into
the literature as as and justpeople have sort of taken it to
(11:13):
be true.
SPEAKER_01 (11:14):
What do you think the motivation is?
I often ask this sort ofquestion in these discussions.
What do you think is themotivation for that kind of
approach, that flawed approach?
SPEAKER_00 (11:24):
Uh I mean, I think it's good intentions, you know.
I think that, you know, and andI definitely appreciate the
desire to create urgency, but Ithink, you know, we have to tell
the truth.
And the truth is that I think,you know, we shouldn't stop
species loss uh because it'spart of a mass extinction.
(11:46):
We should stop species lossbecause it's wrong to drive
other species to extinction.
We shouldn't be considering anyhuman-caused extinctions to be
acceptable, in my opinion.
We should stop them all.
And we, you know, I think weneed to be more aggressive about
it and saying, you know, stopthem all.
I don't care if it's a massextinction, it's not a mass
extinction.
(12:06):
And and, you know, we again setmuch more aggressive and
ambitious goals about stoppingextinction.
SPEAKER_01 (12:14):
It's also, don't you think, a much more robust way of
viewing things, you know, to saythat, you know, we just want to
stop extinctions, because youknow, that's that's sort of
constant under any conditionsthat that's that's approach
works.
Whereas uh the idea that youhave to wait until things get
really bad before you dosomething, that depends on
(12:35):
things being really bad, right?
It's sort of yeah, yeah.
SPEAKER_00 (12:37):
And and I think also one important aspect is you
know, part of the reason why Ithink it's declining.
So in a group like tetrapods isthat people are doing great
conservation work.
And there's been some you knowexcellent studies before ours
showing that like in birds andmammals, conservation work has
actually slowed the rate ofextinction.
And you know, we should becelebrating that and uh you
(13:02):
know, just not sort ofextrapolating doom and gloom.
If you actually look at thedata, it's like, wow, you know,
this conservation stuff worksand we need to do more of it.
SPEAKER_01 (13:13):
Yeah.
So the rates are are declining.
Um, I was going to ask whetheryou think that the the drivers
of biodiversity loss are lessintense than they were sort of
you know at the peak of speciesloss.
Because so you mentionedconservation now.
So I guess the question would beto what extent is the slowing
(13:34):
down or the decrease in speciesloss due to conservation as
opposed to just, you know, thedrivers are just less intense
than they have been in the past?
SPEAKER_00 (13:43):
It's a great question.
And and we don't, we definitelydon't, based on our stuff, we
don't know the answer to that.
I would place good money thatit's it's a bit of both.
And maybe just something topoint out, right?
Just when we talk about thesepast extinctions, it's a lot uh
on islands.
It's about 65% on islands, andthen what's on the mainland is
dominated by fresh water.
(14:05):
And so, you know, it's easy tothink about the rainforest being
cut down and we're losing allthe species from that.
Um, but that's not that's notthe big driver of documented
extinctions.
It's a lot of invasive specieson islands and then creating uh
dams and fresh water on themainland.
SPEAKER_01 (14:23):
Right.
So dam creation is the mainreason for freshwater
extinctions on uh on land, onsort of land in general.
SPEAKER_00 (14:30):
I I think it's a big part of it, but it's definitely
fresh water.
It's definitely um on themainland among again, among the
extinctions that have happenedin the last 500 years, it's a
lot, a lot of fresh water.
And some of these dams have beenabsolutely devastating.
There's the one in Alabama thatwas just you know catastrophic.
SPEAKER_01 (14:48):
Yeah, and that's because it just completely
changes the entire structure ofthe of the system, right?
And the regimes and everything.
SPEAKER_00 (14:56):
You know, sort of like a um, you can imagine
something that was in a smallriver-y stream and suddenly
that's replaced by a lake, youknow, um, you know, the
reservoir backing up and justdestroys those habitats and
things can't, no, no way thatthey can adapt to those sorts of
changes.
SPEAKER_01 (15:13):
It's kind of like the equivalent of a forest being
replaced by a savannahovernight.
SPEAKER_00 (15:18):
Totally.
Yeah, yeah.
Or even worse.
SPEAKER_01 (15:22):
And then in terms of islands, I think the I'm sure
the ecologists and others amongus will will know, but can you
just explain for for those whodon't know why islands are such
hot spots of extinction?
SPEAKER_00 (15:34):
Yeah, there's I mean, there's a lot of things
that seem to be driving that.
I mean, so uh one is seems to bethe lack of of anti-predator
mechanisms, but and it also itit's you know typically driven
by invasive species.
So a kind of a classic example,you know, would be the brown
tree snakes introduced on Guam.
And they just the birds don'thave never seen a snake before.
(15:57):
They don't recognize it as apredator, and they just go and
they just gobble everything up.
SPEAKER_01 (16:02):
Um and the birds don't learn or have the birds
learned at all to evade them, ordo they just continue sort of
following their evolutionaryhardwiring and continue being
easy targets?
SPEAKER_00 (16:15):
Is that well that's that's a great question.
And I don't I don't know enoughabout the details of the system
to know that, but it's it's agreat question.
But I think that there are sortof mismatches like this that are
that are very common.
Yeah uh and then the islandspecies, they just tend to have
tiny ranges and they're veryvulnerable.
SPEAKER_01 (16:33):
Right.
And what about habitats?
So you've spoken aboutgeographical features, I
suppose, but or I supposefreshwater is a habitat as well.
But what else can you say abouthow extinctions vary according
to habitats?
SPEAKER_00 (16:46):
Um the main things that we did, you know, was sort
of island versus mainland, andso it's definitely driven by
island, and then we looked atterrestrial freshwater marine.
And marine is so far has hasmostly been unscathed relatively
unscathed.
And what's you know, the themajor driver of extinction there
is just direct exploitation.
SPEAKER_02 (17:06):
Right.
SPEAKER_00 (17:07):
So things could change very much if we, you
know, put enough carbon in theatmosphere and basically turn
the oceans into a giant can ofCoca-Cola, you know, highly
acidic.
But uh but you know, sort ofknock on wood so far, not that
bad.
SPEAKER_01 (17:22):
And in terms of drivers, you know, I spoke about
drivers in general uh a momentago, but um just wanted to sort
of outline that there are thereare according to IPES again and
other sources, there are fivemain drivers of extinction.
So number one is uh habitatdestruction or or uh alteration,
and then climate change,invasive species, pollution, and
(17:46):
exploitation, as you were sayingin the case of fisheries, right?
Those are kind of the big five.
But just as a general question,what is causing extinctions?
And especially I'm interested inwhat role climate change has to
play or has played.
Perhaps we can talk about how ithas to play in the future.
We can that can be the nextquestion.
SPEAKER_00 (18:03):
Yeah, so that's definitely something that we
specifically looked at was whatwere the biggest drivers of
these extinctions over the past500 years.
And invasive species is thebiggest.
SPEAKER_02 (18:14):
Okay.
SPEAKER_00 (18:14):
Um, and that's particularly on islands, and
then habitat destruction is isnext.
And then there's sort of directexploitation is also there on
and you know, pollution andclimate change.
But I would say so theseinvasive species are sort of the
past.
(18:35):
They are what caused the youknow the biggest loss of species
of uh in the past.
In the future, you know, thecurrently we look at what's
currently threatened, thebiggest threat is is habitat
destruction.
Um if you look, I think decadesin the future, a few decades in
the future, it's I think it'sgoing to be climate change.
And and so we've estimated youknow, like 20 to 30 percent in
(18:57):
in various papers, about 20 to30 percent species loss under
more pessimistic scenarios.
Right now, that hasn't, youknow, it's not happened yet.
And in fact, the a weird factaway is that if you look at the
last few hundred years, there'sno significant increase in
actual species level extinctionsfrom climate change.
And that doesn't mean it's not athreat.
(19:19):
It just means it hasn't hit yet.
SPEAKER_02 (19:22):
Right.
SPEAKER_00 (19:22):
Yeah.
And that's you know, because thepredictions are like you know,
for 2070, 20, you know, 2100,that sort of thing.
And that's so it doesn't meanthat you know everyone's wrong
that there's not extensivespecies loss from climate
change.
It means it's not here yet.
It's you know, under these morepessimistic scenarios.
SPEAKER_01 (19:39):
Right.
But that's a very importantpoint because you know, just
like your sixth mass extinctionpoint, you know, this is
something important and uh and amajor threat uh predicted for
the future.
But you very often see andincreasingly recently from some
pretty what I would haveregarded as credible sources,
you see claims of species havinggone extinct already from
(20:02):
climate change at a fairly largescale.
Um and this is especially in themedia, but you do see it in
peer-reviewed journals as well,in sort of commentaries mostly,
not really empirical studies.
So I guess the question therewould be the same is you know,
what's the problem with thatwith that if it raises
awareness?
But I guess the credibility isthe problem, right?
SPEAKER_00 (20:22):
Yeah, I mean, I think I think that things are
going uh things are goingextinct from climate change.
Already?
Yeah, I think that's the case.
Yeah, you know, uh there's amammal, a s uh a mammal on a
small island in Australiarecently went extinct, and and
it's sort of been happening at acertain level, you know, for
decades now.
And also when we talk aboutkitrid, kitrid is it often seems
(20:46):
to be when it drives things toextinction, it's it's sort of uh
an interaction between thefungus and and climate change.
So it has driven things toextinction, but it but it's not
it's not the big driver yet.
SPEAKER_01 (20:59):
Right.
Yeah, so you said invasive alienspecies in the past, uh land
change in the present, andpossibly climate change in the
future.
SPEAKER_00 (21:07):
Actually, I I just found I found the table.
So if you if you look at thatsort of the breakdown among the
the 615 with identified causes,it's uh 38% invasive, 31%
habitat loss, 20% directexploitation, 5% pollution,
everything else is much smaller,so less than 5%.
SPEAKER_01 (21:28):
Okay.
How easy, I'm sure the answer isnot very easy, but how easy is
it to attribute these causes toextinctions?
I guess in the case of invasivealien species, it's probably
relatively easy, right?
SPEAKER_00 (21:41):
Oh, I think it's I think they're all tough.
And I'm probably I've been tooglib already, you know, and I
should have cautioned, you know,that that it is really hard to
say this.
And and you know, we are we'rebasing this on the IUCN
database, and and they're verythey often will attribute
multiple causes.
And so we get these persons.
Precise numbers by saying, okay,well, people thought it was
(22:03):
this, this, and this.
So we you know assign each ofthem 0.33.
And so I, you know, I think I'mI may be making it sound more
clear-cut than it's justified.
SPEAKER_01 (22:12):
Right.
SPEAKER_00 (22:13):
So it there's a lot of uncertainty.
And then I mean the joke that Imake is, you know, if if we
could do a carefully controlledexperiment, they wouldn't be
extinct, right?
Like, you know, if they're theywere around and that these are
things that often they wentextinct a hundred years ago,
people don't know exactly why.
Um, so so that's very common.
SPEAKER_01 (22:31):
Especially in the case of climate change, though,
I'm wondering do you know how itis even possible to attribute an
extinction to climate changewhen there are so many other
interacting factors?
SPEAKER_00 (22:42):
Yeah, no, this is something we think about a lot.
So a lot of the work that thatmy collaborators and I do on
climate change, we focus onthese surveys over time and we
look for these ones wherethere's been no other, no
obvious changes in habitat.
You know, so things, so we thinkwe can isolate it being from
climate change.
And kind of world these we makethese projections of like, you
(23:04):
know, 15 to 30 percent speciesloss and things like that.
And it's based on extrapolatingfrom these studies where you
know these resurveys over timeand and um yeah, and I've I've
done some of this myself.
You know, so I've done theseresurveys in my our local lizard
species here, and um, you know,I've seen really dramatic
changes.
And I know, I know these placeslike the back of my hand, and
(23:26):
nothing's changed, but they'restill disappearing.
SPEAKER_01 (23:29):
So I suppose it's a case of sort of eliminating all
the other possible causes one byone and you know, becoming more
and more certain that uh theclimate change is the is the
issue if nothing else is showingup.
SPEAKER_00 (23:42):
Yeah, and and it's a very widespread pattern at sort
of at the warm edge of speciesranges that they things are are
disappearing and the numbersaround, you know, like around
45% looked over time in theserelatively unmodified habitats
that around 45% of the speciesthat people have looked at, they
have their, they've kind of losttheir warmest edge populations
(24:03):
to sort of exactly what youexpect from climate change.
Add the climatic data in there,and yes, it's these patterns are
predicted by the increase intemperatures and other factors.
SPEAKER_01 (24:13):
Yeah, I was just about to ask sort of what the
actual mechanics of it is.
So, I mean, some people mightthink you know sea level rise
actually like lit physicallydrowns out the species, but
that's not really how it works,right?
It's much more subtle than that.
So, what what would be theactual mechanisms?
Is it sort of simple temperaturechange or change in humidity, or
certain species are favored overothers because of the of the
(24:37):
change in these conditions?
SPEAKER_00 (24:40):
It's a great question.
And I will say that there's manylayers to that onion.
So one layer, uh one layer is toidentify which climatic
variables are related to the tothe extinctions.
And um, so you know, one thingthat we we published on a few
years ago in in PNAS is um, youknow, that it seems to be
maximum yearly temperatures.
(25:01):
So generally we often thinkabout, you know, we talk about
climate change, we sort of talkabout the mean annual
temperatures, and you know, wesort of in some ways, maybe the
obvious thing is that it seemsto be maximum annual
temperatures that are that areoften the best predictor.
Okay, so that's one layer of theonion.
And the next layer of onion, sobut what's actually happening on
the ground?
And we did a study on that a fewyears ago, just sort of a
(25:24):
review, and it it does seem tobe species interactions more
often, but you know, still a lotof a lot of things uncertain.
But species interactions, youthink about okay, so what are
the, you know, what are theworst hit organisms?
And I think the two that reallyspring to mind are amphibians
and coral.
And amphibians, what's going on?
It's the kidrid fungus.
(25:44):
It's this interaction betweenclimate change and the kidrid
fungus.
Of course, but corals, it's themejecting their, they get
stressed, they heat stressed,then they eject the Nidarians
eject their zocenthelae, andthen they die.
So, but then there's other lotsof other examples like this,
like really strange ones withbirds where their their food
supply rots, things like that,and and so all sorts of
(26:07):
different things.
SPEAKER_01 (26:07):
Um just to take the kitrid fungus example a little
bit further, because I thinkthat's probably one that's
relatively easy to to grasp.
Would that be just a case oflike warmer conditions simply
make uh make it easier forfungus to spread, to grow and to
spread?
SPEAKER_00 (26:24):
Is no, I'm afraid it's not that simple.
And I'm not really an expert onit, but but I can just tell you
for sure that it's montanespecies in the tropics.
And so it's the species that Ithink are adapted to cooler
temperatures, uh to relativelyconstant cooler temperatures,
and then it gets warmer and thenthe Kitrid hits.
(26:45):
Um that seems to be what'shappening, and I it even there I
may be oversimplifying greatly,but but it it's it's very
complicated.
It's not so, for example, youyou go in the lowlands, like in
the you know, it's sort of alowland jungle, the Amazon or
something, everything's finefrom Kitrid, and then you but
you go up into the Andes andthen it's it's uh um it's a real
(27:08):
shit show.
SPEAKER_01 (27:10):
And and so would you would it be reasonable to
speculate that things are finein the lowlands because under
those conditions the fungus hasalways been able to spread and
therefore the organisms areadapted to deal with it?
SPEAKER_00 (27:21):
Or now we're definitely at the limits of my
of my knowledge.
SPEAKER_01 (27:25):
That's okay.
I don't expect you to knoweverything.
I'm just kind of wondering, Imean, just theoretically
speaking, is that sort of areasonable hypothesis?
It might have already beenproven or disproven.
But is that sort of a reasonableway to think about it?
Is it I I guess maybe anotherway of asking the question is is
Kitrid a an invasive species, oris it a in what sense is it an
invasive species?
(27:46):
Is it invasive because climatehas enabled it to spread, or has
it been brought in by some othermeans?
SPEAKER_00 (27:51):
It's no, it's a great question.
And and it's really it's it'sreally complicated.
And they've they've folks havehad a lot of trouble figuring
out where it's from.
But it it mine mine is it is anit is an invasive species.
And and so, and just to clarify,right, it's it's just focus,
it's amphibians, right?
It's just amphibians that thisis hitting.
And and the frog one, you know,people think it may be spread by
(28:14):
bullfrog.
So that's an invasive frogspecies that's fairly tolerant
of the kitrid.
And so the bullfrogs then spreadit to, you know, other species
that are more sensitive to it.
Basically, it's like these um,you know, a tropical montane
species are sort of cool adaptedand they're sort of temperature
(28:36):
specialists.
And I think they sort of get itwarms up and they get stressed,
and then the kitrid gets them.
SPEAKER_02 (28:43):
Right.
SPEAKER_00 (28:44):
I do I do want to point out there's actually been
some some actually some some ofmy favorite papers.
Uh my favorite paper justshowing that, you know, all the
these bouncing back.
Some of the frogs are are arebouncing back from it, which is
just fantastic.
SPEAKER_01 (28:58):
Uh yeah.
Which suggests that that thatthere's just sort of a how do
you say, like a ceiling ofresilience, right?
Or sort of a maybe a floor ofresilience, um, and and that's
been reached, you know, beforethe population get gets wiped
out, um, that that's reached,and then the population is sort
of able to continue and and uhpotentially actually resist
(29:19):
future uh infestations of thefungus, right?
SPEAKER_00 (29:22):
Yeah, there may be there seems to be some evolution
going on in in in some cases.
So it's it's it's really greatbecause I I remember in the
early aughts and and even theyou know the the 90s and stuff,
traveling around and and lookinglooking for frogs in these
montane tropical areas, and itwas it was horrible.
Um so it's it's really wonderfulto hear that that you know at
least some of them are arebouncing back somewhat.
SPEAKER_01 (29:44):
Yeah, that's fantastic news.
But but just to and I justwanted to sort of push back a
little bit, uh, you know, beingdevil's advocate at the climate
change as a cause of extinctionsidea.
And this is you know not basedon any empirical evidence, but
just sort of l logic kind ofworking here.
So so far the increase intemperature has only been one or
(30:04):
two degrees over the pasthundred years or so, right?
So and that seems and I I knowthat's variable in some habitats
that can be gr more or less, butnot it not by a huge amount.
So I'm just sort of wondering,you know, what is the likelihood
that that that is causingextinctions again versus all
these other factors?
You know, you mentioned thatbullfrogs might be carrying the
(30:24):
fungus, uh, for example, youknow, but what's what's the
chance of that being the causeas opposed to just something
else that we haven't noticedyet?
SPEAKER_00 (30:32):
So so the the big you know part of it is that we
do see these correlationsbetween these local extinctions
and climate change.
Right.
And and so it's not just random.
SPEAKER_01 (30:45):
Um You said at the warmer edges of the ranges, you
said as well, right?
So there's sort of worldwide,there's sort of a a pattern
emerging there.
SPEAKER_00 (30:54):
Absolutely, absolutely.
And that's yeah, so so so thisis something I published on like
in 10 years ago now, and it wasjust a literature review, but
just looking at these warm edgesover time, and and it was about
I think 47% of out of 976species, and that was all over
the world, all these differentgroups of organisms, you know,
(31:14):
marine, freshwater, terrestrial.
Um, and then you know, a fewyears later we go back and we
look at that with the climatedata added, and we can show that
yes, it's related tospecifically to climate change.
SPEAKER_01 (31:26):
Right.
So there's a correlationessentially.
SPEAKER_00 (31:29):
Yes, yes.
Um, and and when these and thesestudies that we're using are
ones where you know we'vealready tossed out the ones
where it seems like there'smodified habitat or something
like that.
Um so I think it's it's real.
You know, I think thatdefinitely the the local
extinctions from climate changeare you know, I think it's very
much real.
SPEAKER_01 (31:48):
And I suppose becoming more accurate over
time, right?
As more studies are done, yousort of eliminating all these
other potential factors andarriving at a more accurate
picture of things.
SPEAKER_00 (31:59):
Definitely.
And um and I think that that youknow sort of 45% thing is is
actually holding up as thousandsof more species are being added.
My my former postdoc, uh GopalMorale, um, we have this data
set of over 5,000 species, andit's very similar to the 976
species data set, and that it'syou know around 45, 50 percent
(32:21):
for these warm edge localextinctions.
And that's that's part of thething, also.
It's like, well, you know, it itwould be weird that there would
be, you know, sort of it's thisvery broad pattern.
And with these 5,000 speciesalso, we have the correlations
with climate change, also.
Um so I think I think that'svery much real.
SPEAKER_01 (32:41):
Right.
So I suppose just just sort of afinal Dill's advocate comment
would be I suppose that you cansay that there's you know,
correlation is not causation,but the correlation is becoming
increasingly convincing overtime.
Is that is that reasonable?
SPEAKER_00 (32:56):
Yeah, I I think so.
Yeah.
And and and also the other Ijust don't see any other
plausible mechanisms.
So for example, it's it'sterrestrial, it's freshwater,
it's marine, it's all thesedifferent groups of organisms.
Uh, it's correlated with thechange in in climate.
And and many of the patterns aresort of what you would expect
from what we know about speciesniches and things like that.
SPEAKER_01 (33:19):
Right.
When you write about this, youknow, climate-caused extinction
phenomenon and just extinctionsin general, perhaps, do you
often include recommendations topolicymakers and and others and
sort of what to do about this?
And if so, what do you say?
SPEAKER_00 (33:36):
Yeah, no, that's a great, it's a great question.
I've definitely been been askedthis before you know, recently,
if like, okay, so what if youknow, I'm a conservation person
and what are we supposed to do?
And here's my three wordrecommendation stop climate
change, right?
I mean, because it's it's sortof, you know, like moving
species A to a cooler place.
(33:56):
It's it's not enough.
I mean, it's a whole community.
So it's really um it's the greatquestion.
It's kind of the question, but II don't I don't think there's a
satisfying answer.
Yeah, and I should also say thatthat um one one thing that we
found from this is that you sortof expect species just to move
(34:18):
naturally and track theirclimactic niches, but they
generally don't.
They do they're supposed to sortof be moving up at their cool
edges, right?
Moving into higher elevationsand stuff, and the majority of
them just aren't moving at all.
SPEAKER_01 (34:30):
You know, that that that doesn't surprise me.
That idea of you know justallowing protected areas to
stretch up slopes and and up youknow altitudes and latitudes
basically just has never reallymade sense to me.
And that's partly because thereare already other species there,
right?
So, but also, I mean, you know,the soil structure can be
(34:50):
different, uh, vegetation, youknow, plants might not move at
the same rate as as animals, andso the the there's a completely
different habitat there, even ifthe temperature is you know
constant with what they wereused to.
There's so many other factorsthat that change.
So that never made a lot ofsense to me.
I don't I don't know howprominent that idea still is in
the literature.
SPEAKER_00 (35:08):
I think I mean it maybe they will kind of catch
up.
Maybe, maybe it's just thatextinction is happening more
quickly than the dispersal is.
You know, I think we stillshould allow for it.
It's just um, I don't know, saysomewhere between disappointing
and alarming that things aren'tmoving like they should.
Um and the thing is, you know,they're animals or they're
(35:30):
plants.
They don't know that they're,hey, you need to go and move to
a higher elevation.
They don't know that.
I mean, it's it does, itdoesn't, it's not how they work,
right?
So it's not, yeah, like I say,it's not entirely surprising.
SPEAKER_01 (35:40):
But yeah.
And uh would a more sort ofrobust strategy maybe be just to
ensure that other factors arenot complicating the matter.
So, you know, for example, youknow, expand the quantity and
quality of protected areas sothat, you know, for example,
invasive alien species aren'tmaking matters worse.
(36:01):
That will help, right?
Maybe that's the best thing wecan do short of stopping climate
change.
SPEAKER_00 (36:06):
Yeah, I mean, maybe, maybe it's certainly beyond my
knowledge or or you know levelof creativity.
Um, but I definitely think thatlike, yeah, stopping every other
threat, I mean, protecting thehabitats, stopping the invasive
species, you know, it's like doeverything we can.
And and you know, and and thesethese bad scenarios, the bad
(36:26):
climate scenarios haven'thappened yet.
And and maybe, maybe they won't,you know, maybe you know, we'll
sort of make the make the energyconversion and things like that.
And and uh so so I think it itis good.
Uh but we could with this, wecould still also we could we
could stop climate change andstill lose you know 30, 40
percent of the species out therefrom from other factors like
(36:49):
habitat production and thingslike that.
Um so I think that it's it's umyou know question, we have to
protect all the habitats, stopthe invasive species, do all
those things, and stop climatechange.
SPEAKER_01 (37:03):
Yeah, it's a multi, multi-war front, or multi-front
war rather.
And I just had one otherquestion to add, but maybe we've
already covered it.
But um is there anything moreyou can say or that you'd like
to say about how we canextrapolate recent extinctions
into the future?
Not just climate-causedextinctions, but extinctions in
general.
SPEAKER_00 (37:24):
Yeah, so we've definitely worked on on the
climate change one, and that'syou know, again, like 20 to 30
percent of species.
And you know, and of course, thethe the bad thing is we know we
could lose a lot of the speciesthat are currently listed as
endangered or or threatened, wecould, you know, there's a
potential to lose all or most ofthose.
But I mean, I I think there'ssome people have done nice, uh,
(37:47):
you know, there's possible touse approaches looking at
protected habitats and speciesthat aren't in protected
habitats and the potential oflosing those ones and say, okay,
what if we lose everythingthat's not in the protected
habitat?
You know, do those sorts ofanalyses.
And I think there was maybesomething done like that for
tetrapods a few years ago, and Ithink I think we we've cited,
(38:08):
and and they sort of talkedabout losing 10%, you know,
additional 10% of species.
SPEAKER_01 (38:17):
Another interesting thing about what you said about
climate change being the futurethreat and land change the
current threat and invasivealien species the past threat is
that uh when it comes to landchange or habitat transformation
or whatever you want to call it,we have reached sort of peak
land use globally.
And although that's varied, youknow, in the tropics we continue
(38:38):
to lose a lot of land.
Um, but uh that's sort ofslowing as well to some extent.
So we can hopefully look forwardto a future where the
transformation of habitat is isalmost a non-issue.
I mean, that's sort of somethingwhich seems doable, right, in
the in the not too distantfuture, or perhaps I'm looking
at several decades rather thanthan several years.
(38:58):
But then you are left with theseremaining threats like like
climate change.
Invasive alien species, althoughyou said that that was the the
the past cause of majorextinction, that continues to be
a big problem, doesn't it?
I mean, there are still a lot ofspecies that haven't yet been
tried as invasive species.
SPEAKER_00 (39:16):
You know, they've been Yeah, I know that's that's
a good point.
Yeah.
And also I would say in terms ofhabitat destruction, there's a
great paper from David Tillmanfrom many years ago, sort of
talking about how things arechanging and sort of like like
how how Asia went through this,you know, lost a lot of this
habitat, and and you know, andnow sort of people have of how
(39:38):
do I put this sort of kind ofleveling up people in terms of
getting people out of extremepoverty and and um and sort of
Africa hasn't gone through thatyet.
And Africa, you know, sort ofpresumably will go through that
and is likely to lose a lot ofhabitat in the in the process.
Right.
Um so it's kind of like the ideathat it's the these things are
(39:59):
sort of maybe changing acrossacross the globe over time.
And the truth is that I think, you know, we
shouldn't stop species loss uhbecause it's part of a mass
extinction.
We should stop species lossbecause it's wrong to drive
other species to extinction.
SPEAKER_01 (00:19):
Welcome to the Case for Conservation podcast, where
we make the case for conservingnature and its biodiversity by
building a robust, credibleargument, one that sometimes
requires us to re-examineconventional wisdom.
I'm your host, Andre Moder.
Biodiversity loss is an ongoingchallenge, but some of the
language you use to describe itmay be on shakier ground than we
(00:41):
realize.
Are we really living through asuccess mass extinction?
What does that phrasetechnically imply?
And how well is it supported bythe data?
And what about climate change?
How many species levelextinctions can credibly be
attributed to warming so far?
And how do you attribute causeswhen multiple threats interact?
(01:02):
To explore these questions, Ispoke with John Weens, an
ecologist at the University ofArizona, whose work focuses on
extinction rates andclimate-driven range losses.
We discussed what the evidencesuggests about acceleration or
lack thereof in extinction inrecent decades, why documented
extinctions have becomeconcentrated on islands and in
(01:24):
freshwater systems, and howclimate change is expected to
reshape extinction risk throughmechanisms like heat extremes,
shifting range limits, anddisease dynamics.
The thread running through itall is credibility and ambition.
How to communicate urgencywithout overclaiming, and why a
stronger conservation goal isnot avoiding a mass extinction,
(01:46):
but preventing extinctionswherever we still can.
I began by asking John the basicoverarching question.
SPEAKER_00 (02:05):
I think the evidence is not there to support it at
this point.
I think it's sort of been takenas dogma for a few decades now.
But I think that the theoriginal evidence was was never
very strong to support that.
So basically you say it is aclearly there's a biodiversity
crisis.
Hundreds of species have goneextinct, you know, if not
(02:26):
thousands.
But to be, you know, it needs torank, it needs to be in the top
six mass extinctions that everhappened.
And and I think what what'slagging from that literature is
is generally sort of a you knowputting the current crisis uh on
a quantitative basis andcomparing it to those past ones.
And I think that just tends notto happen.
(02:48):
So for example, the thebackground extinction rate, this
idea that we're exceeding thebackground extinctions, well, of
course we are.
Humans are causing extinctions,but you know, the background
extinction rate is basically amean.
And so if it's a mean, sometimesyou're above the mean and
sometimes you're below it.
And and you can make a big dealabout how far above that that
mean we are, but that's usuallybased on comparing the time
(03:09):
scale of hundreds of years tomillions of years.
And you can expect you know hugedifferences like that when
you're comparing these verydifferent timescales.
SPEAKER_01 (03:17):
It reminds me a bit, I interviewed Earl Ellis uh a
while ago about the idea of theAnthropocene.
And and he, I think a similarkind of idea, his argument, if I
remember correctly, I'm I hopeI'm not mischaracterizing it,
but his argument was that theterminology is simply incorrect.
It's just technically it's notit's not right.
(03:39):
And so I guess that's the casehere as well.
But it it sort of makes mewonder, you know, at the
technical level, I I understand,but then just as a PR tool uh
and a way of of addressing theas you use the word biodiversity
crisis, right?
The term biodiversity crisis.
I guess my question would belike, what's wrong with using
sixth extinction as a marketingtool?
(04:01):
Or is it because of the clashwith the technical yeah?
SPEAKER_00 (04:05):
Well, so so part of the I think that there is a
potential, there is a potentialcollision with the marketing and
the technical side of it.
So so one thing is so what iswhat is our goal in should be
our goal in conservation be?
You see, it's to stop the sixthmass extinction.
That's an incredibly weak goal,right?
(04:34):
I'd say, come on, can we dobetter than that?
I mean, I I really prefer these,you know, these people who are
saying, okay, we're, you know,the zero extinction people, the
people that are focused on,okay, what's let's find the next
thing that's going to go extinctand stop it from going extinct.
And I think that needs to be themindset and not this, you know,
this incredibly lazy andunambitious idea of stopping 75%
(04:57):
species loss over hundreds orthousands of years.
SPEAKER_01 (04:59):
Right.
I suppose that it works on, youknow, most people they hear the
word and it sort of has itsdesired effect.
The problem is if someone wantsto dig more deeply into it, and
then they sort of then there's acredibility problem, right?
Because so you look deeply intoit and you see, well, actually,
that's not correct.
So then you start wondering whatelse is not accurate.
SPEAKER_00 (05:20):
Yeah, and and and it's I think it matters that
it's not it's not accurate.
You know, so questions, I meanit's fundamental questions.
So how you know what percentageof species have gone extinct?
And in terms of documented ones,it's it's less than one percent.
And so is you know, arguing thatwe're in the midst of 75%
species loss is like, you know,it doesn't take much digging to
(05:42):
see the problem, right?
SPEAKER_01 (05:43):
Yeah, um, and I guess another thing is that, and
I remember talking to MariaDonilas about this, is that we
human beings tend to focus onvertebrates, right?
And especially mammals and andbirds, but vertebrates, let's
say, as a as a whole.
Among vertebrates, theextinction rate is higher than
among species in general.
(06:05):
Is that correct or or notnecessarily?
SPEAKER_00 (06:07):
Um it's it's the highest is in is in tetrapods
and in uh molluscs.
And and so those have been hitthe hardest, it seems.
SPEAKER_01 (06:17):
Okay, and can you just just for for those who are
not sure, can you just explaintetrapods and mollusks?
What do those include?
What do those groups?
SPEAKER_00 (06:23):
Oh, so the tetrapods is basically just land
vertebrates.
So we think of amphibians,birds, mammals, and and
reptiles, you know, whichincludes turtles, lizards, and
snakes.
Um and so that that would be allvertebrates except for fish,
basically.
And mollusks would be you know,in terms of the the conservation
aspects, you know, mollusks endsup being mostly snails and then
(06:45):
bivalves as some um mussels, forexample.
SPEAKER_01 (06:48):
Right, marine and freshwater bivalves.
SPEAKER_00 (06:51):
Yeah, and and those have been those have been hit
really hard.
SPEAKER_01 (06:55):
So most of those are vertebrates, right?
So the tetrapods are allvertebrates.
SPEAKER_00 (07:01):
They're there are about um half of vertebrates.
SPEAKER_01 (07:04):
Right.
And what would you say?
I don't think I've ever seenthis written anywhere, but what
would you say to the statementthat there's a there's a
six-math extinction when you'relooking at tetrapods or
vertebrates?
SPEAKER_00 (07:15):
The the numbers are still way below.
SPEAKER_01 (07:18):
Right.
SPEAKER_00 (07:19):
What happens is it is that you know, things are
definitely bad for birds andmammals, and and then with you
know, for reptiles less so.
And even for amphibians, youknow, even there's there's a lot
of possibly extinct species fromKitrid, but not you know, not
ones that are definitelyextinct.
And so it's it's just not youknow, it's nothing like it's
(07:40):
nothing like 10%, it's nothinglike 75%, it's you know, more
like barely one percent.
SPEAKER_01 (07:46):
And a kytrid is the fungus, right?
The amphibian fungus.
SPEAKER_00 (07:50):
Yeah, and it really horrific, you know, just just
causing these horrific declinesand crashes.
SPEAKER_01 (07:56):
Right.
Yeah, it's interesting.
Amphibians, and the other onethat comes to mind is insects as
a very broad group.
I interviewed Jane Hill a whileago.
She's a an entomologist whoworks on butterflies
specifically.
And this is a bit too far backfor me to remember the details,
but essentially the the shortanswer to the question, is there
an insect to get in underway?
(08:17):
The short answer is no.
Um and there's just a lot ofvariability between groups.
Um, and she's lookingspecifically at at butterflies.
And so it's kind of like a, youknow, depending on the scale
that you look at and which partof the world you look at, and
and all these differentvariables, you know, once you
take all of those intoconsideration, as you said,
there are declines, but they'renot at the you know, the six
(08:41):
mass extinction kind of level,exactly as you were saying for
for vertebrates and and speciesmore more generally.
But then what about the theelement of acceleration?
You know, the the trend ratherthan the status.
So, you know, because I thinkyou'd be for people would be
forgiven for declaring asix-mass extinction if the rate
of of species loss isaccelerating in in a direction
(09:03):
that you you can extrapolate.
Uh what do you say then?
SPEAKER_00 (09:06):
Yeah, so so that's something that we looked at.
This this is work that I didwith um uh this great uh student
named Kristen Saban.
And specifically the the paperthat Kristen led in in
Proceedings B last fall, um, welooked, we looked at these
rates.
And basically there's thisliterature that says these rates
are are you know rapidlyaccelerating.
(09:27):
And that's true at the scale ofcenturies, but I think when we
think of rapid acceleration, itshould be at the scale of
decades at the least.
And when you look at decades,the last few hundred years, you
don't see that.
And in fact, for a lot ofgroups, the peak was like 100
years ago.
The peak extinction rate perdecade was uh around 100 years
(09:47):
ago.
So that's the case for plants,it's the case for arthropods,
and you know, tetrapods alsohave generally the extinction
rates have actually beendeclining recently.
And you know, there's when youlook really recently, there's
definitely the potential forartifacts in terms of things
aren't getting documented, theextinctions aren't being
documented.
(10:08):
But when we're looking over thetime scale of hundreds of years,
that seems less likely.
SPEAKER_02 (10:12):
Right.
SPEAKER_00 (10:13):
Um and and so I think you know, there's there's
definitely a reasonable argumentas to whether it's things are
actually decelerating or whetherthey're just more or less
constant.
But I just the the evidence forthis claim of rapid acceleration
is is just not supported at thescale of decades.
SPEAKER_02 (10:30):
I see.
SPEAKER_00 (10:31):
Um, mollusks show this this pretty this pretty
recent peak, and andactinopterygians also show a
more a more recent peak.
So there's definitely some thatthat variability kind of
contributes to what looks like amore a more constant pattern
when you look across everything.
Um but it's definitely not rapidaccelerations.
(10:52):
And even though folks haveclaimed it, you know, what I
think in cases they they seem tohave done is is to take the
cumulative number and call thatthe rate.
And the, you know, as you know,the distance traveled is not the
is not the velocity.
So they basically confuse thoseand it's just kind of gone into
the literature as as and justpeople have sort of taken it to
(11:13):
be true.
SPEAKER_01 (11:14):
What do you think the motivation is?
I often ask this sort ofquestion in these discussions.
What do you think is themotivation for that kind of
approach, that flawed approach?
SPEAKER_00 (11:24):
Uh I mean, I think it's good intentions, you know.
I think that, you know, and andI definitely appreciate the
desire to create urgency, but Ithink, you know, we have to tell
the truth.
And the truth is that I think,you know, we shouldn't stop
species loss uh because it'spart of a mass extinction.
(11:46):
We should stop species lossbecause it's wrong to drive
other species to extinction.
We shouldn't be considering anyhuman-caused extinctions to be
acceptable, in my opinion.
We should stop them all.
And we, you know, I think weneed to be more aggressive about
it and saying, you know, stopthem all.
I don't care if it's a massextinction, it's not a mass
extinction.
(12:06):
And and, you know, we again setmuch more aggressive and
ambitious goals about stoppingextinction.
SPEAKER_01 (12:14):
It's also, don't you think, a much more robust way of
viewing things, you know, to saythat, you know, we just want to
stop extinctions, because youknow, that's that's sort of
constant under any conditionsthat that's that's approach
works.
Whereas uh the idea that youhave to wait until things get
really bad before you dosomething, that depends on
(12:35):
things being really bad, right?
It's sort of yeah, yeah.
SPEAKER_00 (12:37):
And and I think also one important aspect is you
know, part of the reason why Ithink it's declining.
So in a group like tetrapods isthat people are doing great
conservation work.
And there's been some you knowexcellent studies before ours
showing that like in birds andmammals, conservation work has
actually slowed the rate ofextinction.
And you know, we should becelebrating that and uh you
(13:02):
know, just not sort ofextrapolating doom and gloom.
If you actually look at thedata, it's like, wow, you know,
this conservation stuff worksand we need to do more of it.
SPEAKER_01 (13:13):
Yeah.
So the rates are are declining.
Um, I was going to ask whetheryou think that the the drivers
of biodiversity loss are lessintense than they were sort of
you know at the peak of speciesloss.
Because so you mentionedconservation now.
So I guess the question would beto what extent is the slowing
(13:34):
down or the decrease in speciesloss due to conservation as
opposed to just, you know, thedrivers are just less intense
than they have been in the past?
SPEAKER_00 (13:43):
It's a great question.
And and we don't, we definitelydon't, based on our stuff, we
don't know the answer to that.
I would place good money thatit's it's a bit of both.
And maybe just something topoint out, right?
Just when we talk about thesepast extinctions, it's a lot uh
on islands.
It's about 65% on islands, andthen what's on the mainland is
dominated by fresh water.
(14:05):
And so, you know, it's easy tothink about the rainforest being
cut down and we're losing allthe species from that.
Um, but that's not that's notthe big driver of documented
extinctions.
It's a lot of invasive specieson islands and then creating uh
dams and fresh water on themainland.
SPEAKER_01 (14:23):
Right.
So dam creation is the mainreason for freshwater
extinctions on uh on land, onsort of land in general.
SPEAKER_00 (14:30):
I I think it's a big part of it, but it's definitely
fresh water.
It's definitely um on themainland among again, among the
extinctions that have happenedin the last 500 years, it's a
lot, a lot of fresh water.
And some of these dams have beenabsolutely devastating.
There's the one in Alabama thatwas just you know catastrophic.
SPEAKER_01 (14:48):
Yeah, and that's because it just completely
changes the entire structure ofthe of the system, right?
And the regimes and everything.
SPEAKER_00 (14:56):
You know, sort of like a um, you can imagine
something that was in a smallriver-y stream and suddenly
that's replaced by a lake, youknow, um, you know, the
reservoir backing up and justdestroys those habitats and
things can't, no, no way thatthey can adapt to those sorts of
changes.
SPEAKER_01 (15:13):
It's kind of like the equivalent of a forest being
replaced by a savannahovernight.
SPEAKER_00 (15:18):
Totally.
Yeah, yeah.
Or even worse.
SPEAKER_01 (15:22):
And then in terms of islands, I think the I'm sure
the ecologists and others amongus will will know, but can you
just explain for for those whodon't know why islands are such
hot spots of extinction?
SPEAKER_00 (15:34):
Yeah, there's I mean, there's a lot of things
that seem to be driving that.
I mean, so uh one is seems to bethe lack of of anti-predator
mechanisms, but and it also itit's you know typically driven
by invasive species.
So a kind of a classic example,you know, would be the brown
tree snakes introduced on Guam.
And they just the birds don'thave never seen a snake before.
(15:57):
They don't recognize it as apredator, and they just go and
they just gobble everything up.
SPEAKER_01 (16:02):
Um and the birds don't learn or have the birds
learned at all to evade them, ordo they just continue sort of
following their evolutionaryhardwiring and continue being
easy targets?
SPEAKER_00 (16:15):
Is that well that's that's a great question.
And I don't I don't know enoughabout the details of the system
to know that, but it's it's agreat question.
But I think that there are sortof mismatches like this that are
that are very common.
Yeah uh and then the islandspecies, they just tend to have
tiny ranges and they're veryvulnerable.
SPEAKER_01 (16:33):
Right.
And what about habitats?
So you've spoken aboutgeographical features, I
suppose, but or I supposefreshwater is a habitat as well.
But what else can you say abouthow extinctions vary according
to habitats?
SPEAKER_00 (16:46):
Um the main things that we did, you know, was sort
of island versus mainland, andso it's definitely driven by
island, and then we looked atterrestrial freshwater marine.
And marine is so far has hasmostly been unscathed relatively
unscathed.
And what's you know, the themajor driver of extinction there
is just direct exploitation.
SPEAKER_02 (17:06):
Right.
SPEAKER_00 (17:07):
So things could change very much if we, you
know, put enough carbon in theatmosphere and basically turn
the oceans into a giant can ofCoca-Cola, you know, highly
acidic.
But uh but you know, sort ofknock on wood so far, not that
bad.
SPEAKER_01 (17:22):
And in terms of drivers, you know, I spoke about
drivers in general uh a momentago, but um just wanted to sort
of outline that there are thereare according to IPES again and
other sources, there are fivemain drivers of extinction.
So number one is uh habitatdestruction or or uh alteration,
and then climate change,invasive species, pollution, and
(17:46):
exploitation, as you were sayingin the case of fisheries, right?
Those are kind of the big five.
But just as a general question,what is causing extinctions?
And especially I'm interested inwhat role climate change has to
play or has played.
Perhaps we can talk about how ithas to play in the future.
We can that can be the nextquestion.
SPEAKER_00 (18:03):
Yeah, so that's definitely something that we
specifically looked at was whatwere the biggest drivers of
these extinctions over the past500 years.
And invasive species is thebiggest.
SPEAKER_02 (18:14):
Okay.
SPEAKER_00 (18:14):
Um, and that's particularly on islands, and
then habitat destruction is isnext.
And then there's sort of directexploitation is also there on
and you know, pollution andclimate change.
But I would say so theseinvasive species are sort of the
past.
(18:35):
They are what caused the youknow the biggest loss of species
of uh in the past.
In the future, you know, thecurrently we look at what's
currently threatened, thebiggest threat is is habitat
destruction.
Um if you look, I think decadesin the future, a few decades in
the future, it's I think it'sgoing to be climate change.
And and so we've estimated youknow, like 20 to 30 percent in
(18:57):
in various papers, about 20 to30 percent species loss under
more pessimistic scenarios.
Right now, that hasn't, youknow, it's not happened yet.
And in fact, the a weird factaway is that if you look at the
last few hundred years, there'sno significant increase in
actual species level extinctionsfrom climate change.
And that doesn't mean it's not athreat.
(19:19):
It just means it hasn't hit yet.
SPEAKER_02 (19:22):
Right.
SPEAKER_00 (19:22):
Yeah.
And that's you know, because thepredictions are like you know,
for 2070, 20, you know, 2100,that sort of thing.
And that's so it doesn't meanthat you know everyone's wrong
that there's not extensivespecies loss from climate
change.
It means it's not here yet.
It's you know, under these morepessimistic scenarios.
SPEAKER_01 (19:39):
Right.
But that's a very importantpoint because you know, just
like your sixth mass extinctionpoint, you know, this is
something important and uh and amajor threat uh predicted for
the future.
But you very often see andincreasingly recently from some
pretty what I would haveregarded as credible sources,
you see claims of species havinggone extinct already from
(20:02):
climate change at a fairly largescale.
Um and this is especially in themedia, but you do see it in
peer-reviewed journals as well,in sort of commentaries mostly,
not really empirical studies.
So I guess the question therewould be the same is you know,
what's the problem with thatwith that if it raises
awareness?
But I guess the credibility isthe problem, right?
SPEAKER_00 (20:22):
Yeah, I mean, I think I think that things are
going uh things are goingextinct from climate change.
Already?
Yeah, I think that's the case.
Yeah, you know, uh there's amammal, a s uh a mammal on a
small island in Australiarecently went extinct, and and
it's sort of been happening at acertain level, you know, for
decades now.
And also when we talk aboutkitrid, kitrid is it often seems
(20:46):
to be when it drives things toextinction, it's it's sort of uh
an interaction between thefungus and and climate change.
So it has driven things toextinction, but it but it's not
it's not the big driver yet.
SPEAKER_01 (20:59):
Right.
Yeah, so you said invasive alienspecies in the past, uh land
change in the present, andpossibly climate change in the
future.
SPEAKER_00 (21:07):
Actually, I I just found I found the table.
So if you if you look at thatsort of the breakdown among the
the 615 with identified causes,it's uh 38% invasive, 31%
habitat loss, 20% directexploitation, 5% pollution,
everything else is much smaller,so less than 5%.
SPEAKER_01 (21:28):
Okay.
How easy, I'm sure the answer isnot very easy, but how easy is
it to attribute these causes toextinctions?
I guess in the case of invasivealien species, it's probably
relatively easy, right?
SPEAKER_00 (21:41):
Oh, I think it's I think they're all tough.
And I'm probably I've been tooglib already, you know, and I
should have cautioned, you know,that that it is really hard to
say this.
And and you know, we are we'rebasing this on the IUCN
database, and and they're verythey often will attribute
multiple causes.
And so we get these persons.
Precise numbers by saying, okay,well, people thought it was
(22:03):
this, this, and this.
So we you know assign each ofthem 0.33.
And so I, you know, I think I'mI may be making it sound more
clear-cut than it's justified.
SPEAKER_01 (22:12):
Right.
SPEAKER_00 (22:13):
So it there's a lot of uncertainty.
And then I mean the joke that Imake is, you know, if if we
could do a carefully controlledexperiment, they wouldn't be
extinct, right?
Like, you know, if they're theywere around and that these are
things that often they wentextinct a hundred years ago,
people don't know exactly why.
Um, so so that's very common.
SPEAKER_01 (22:31):
Especially in the case of climate change, though,
I'm wondering do you know how itis even possible to attribute an
extinction to climate changewhen there are so many other
interacting factors?
SPEAKER_00 (22:42):
Yeah, no, this is something we think about a lot.
So a lot of the work that thatmy collaborators and I do on
climate change, we focus onthese surveys over time and we
look for these ones wherethere's been no other, no
obvious changes in habitat.
You know, so things, so we thinkwe can isolate it being from
climate change.
And kind of world these we makethese projections of like, you
(23:04):
know, 15 to 30 percent speciesloss and things like that.
And it's based on extrapolatingfrom these studies where you
know these resurveys over timeand and um yeah, and I've I've
done some of this myself.
You know, so I've done theseresurveys in my our local lizard
species here, and um, you know,I've seen really dramatic
changes.
And I know, I know these placeslike the back of my hand, and
(23:26):
nothing's changed, but they'restill disappearing.
SPEAKER_01 (23:29):
So I suppose it's a case of sort of eliminating all
the other possible causes one byone and you know, becoming more
and more certain that uh theclimate change is the is the
issue if nothing else is showingup.
SPEAKER_00 (23:42):
Yeah, and and it's a very widespread pattern at sort
of at the warm edge of speciesranges that they things are are
disappearing and the numbersaround, you know, like around
45% looked over time in theserelatively unmodified habitats
that around 45% of the speciesthat people have looked at, they
have their, they've kind of losttheir warmest edge populations
(24:03):
to sort of exactly what youexpect from climate change.
Add the climatic data in there,and yes, it's these patterns are
predicted by the increase intemperatures and other factors.
SPEAKER_01 (24:13):
Yeah, I was just about to ask sort of what the
actual mechanics of it is.
So, I mean, some people mightthink you know sea level rise
actually like lit physicallydrowns out the species, but
that's not really how it works,right?
It's much more subtle than that.
So, what what would be theactual mechanisms?
Is it sort of simple temperaturechange or change in humidity, or
certain species are favored overothers because of the of the
(24:37):
change in these conditions?
SPEAKER_00 (24:40):
It's a great question.
And I will say that there's manylayers to that onion.
So one layer, uh one layer is toidentify which climatic
variables are related to the tothe extinctions.
And um, so you know, one thingthat we we published on a few
years ago in in PNAS is um, youknow, that it seems to be
maximum yearly temperatures.
(25:01):
So generally we often thinkabout, you know, we talk about
climate change, we sort of talkabout the mean annual
temperatures, and you know, wesort of in some ways, maybe the
obvious thing is that it seemsto be maximum annual
temperatures that are that areoften the best predictor.
Okay, so that's one layer of theonion.
And the next layer of onion, sobut what's actually happening on
the ground?
And we did a study on that a fewyears ago, just sort of a
(25:24):
review, and it it does seem tobe species interactions more
often, but you know, still a lotof a lot of things uncertain.
But species interactions, youthink about okay, so what are
the, you know, what are theworst hit organisms?
And I think the two that reallyspring to mind are amphibians
and coral.
And amphibians, what's going on?
It's the kidrid fungus.
(25:44):
It's this interaction betweenclimate change and the kidrid
fungus.
Of course, but corals, it's themejecting their, they get
stressed, they heat stressed,then they eject the Nidarians
eject their zocenthelae, andthen they die.
So, but then there's other lotsof other examples like this,
like really strange ones withbirds where their their food
supply rots, things like that,and and so all sorts of
(26:07):
different things.
SPEAKER_01 (26:07):
Um just to take the kitrid fungus example a little
bit further, because I thinkthat's probably one that's
relatively easy to to grasp.
Would that be just a case oflike warmer conditions simply
make uh make it easier forfungus to spread, to grow and to
spread?
SPEAKER_00 (26:24):
Is no, I'm afraid it's not that simple.
And I'm not really an expert onit, but but I can just tell you
for sure that it's montanespecies in the tropics.
And so it's the species that Ithink are adapted to cooler
temperatures, uh to relativelyconstant cooler temperatures,
and then it gets warmer and thenthe Kitrid hits.
(26:45):
Um that seems to be what'shappening, and I it even there I
may be oversimplifying greatly,but but it it's it's very
complicated.
It's not so, for example, youyou go in the lowlands, like in
the you know, it's sort of alowland jungle, the Amazon or
something, everything's finefrom Kitrid, and then you but
you go up into the Andes andthen it's it's uh um it's a real
(27:08):
shit show.
SPEAKER_01 (27:10):
And and so would you would it be reasonable to
speculate that things are finein the lowlands because under
those conditions the fungus hasalways been able to spread and
therefore the organisms areadapted to deal with it?
SPEAKER_00 (27:21):
Or now we're definitely at the limits of my
of my knowledge.
SPEAKER_01 (27:25):
That's okay.
I don't expect you to knoweverything.
I'm just kind of wondering, Imean, just theoretically
speaking, is that sort of areasonable hypothesis?
It might have already beenproven or disproven.
But is that sort of a reasonableway to think about it?
Is it I I guess maybe anotherway of asking the question is is
Kitrid a an invasive species, oris it a in what sense is it an
invasive species?
(27:46):
Is it invasive because climatehas enabled it to spread, or has
it been brought in by some othermeans?
SPEAKER_00 (27:51):
It's no, it's a great question.
And and it's really it's it'sreally complicated.
And they've they've folks havehad a lot of trouble figuring
out where it's from.
But it it mine mine is it is anit is an invasive species.
And and so, and just to clarify,right, it's it's just focus,
it's amphibians, right?
It's just amphibians that thisis hitting.
And and the frog one, you know,people think it may be spread by
(28:14):
bullfrog.
So that's an invasive frogspecies that's fairly tolerant
of the kitrid.
And so the bullfrogs then spreadit to, you know, other species
that are more sensitive to it.
Basically, it's like these um,you know, a tropical montane
species are sort of cool adaptedand they're sort of temperature
(28:36):
specialists.
And I think they sort of get itwarms up and they get stressed,
and then the kitrid gets them.
SPEAKER_02 (28:43):
Right.
SPEAKER_00 (28:44):
I do I do want to point out there's actually been
some some actually some some ofmy favorite papers.
Uh my favorite paper justshowing that, you know, all the
these bouncing back.
Some of the frogs are are arebouncing back from it, which is
just fantastic.
SPEAKER_01 (28:58):
Uh yeah.
Which suggests that that thatthere's just sort of a how do
you say, like a ceiling ofresilience, right?
Or sort of a maybe a floor ofresilience, um, and and that's
been reached, you know, beforethe population get gets wiped
out, um, that that's reached,and then the population is sort
of able to continue and and uhpotentially actually resist
(29:19):
future uh infestations of thefungus, right?
SPEAKER_00 (29:22):
Yeah, there may be there seems to be some evolution
going on in in in some cases.
So it's it's it's really greatbecause I I remember in the
early aughts and and even theyou know the the 90s and stuff,
traveling around and and lookinglooking for frogs in these
montane tropical areas, and itwas it was horrible.
Um so it's it's really wonderfulto hear that that you know at
least some of them are arebouncing back somewhat.
SPEAKER_01 (29:44):
Yeah, that's fantastic news.
But but just to and I justwanted to sort of push back a
little bit, uh, you know, beingdevil's advocate at the climate
change as a cause of extinctionsidea.
And this is you know not basedon any empirical evidence, but
just sort of l logic kind ofworking here.
So so far the increase intemperature has only been one or
(30:04):
two degrees over the pasthundred years or so, right?
So and that seems and I I knowthat's variable in some habitats
that can be gr more or less, butnot it not by a huge amount.
So I'm just sort of wondering,you know, what is the likelihood
that that that is causingextinctions again versus all
these other factors?
You know, you mentioned thatbullfrogs might be carrying the
(30:24):
fungus, uh, for example, youknow, but what's what's the
chance of that being the causeas opposed to just something
else that we haven't noticedyet?
SPEAKER_00 (30:32):
So so the the big you know part of it is that we
do see these correlationsbetween these local extinctions
and climate change.
Right.
And and so it's not just random.
SPEAKER_01 (30:45):
Um You said at the warmer edges of the ranges, you
said as well, right?
So there's sort of worldwide,there's sort of a a pattern
emerging there.
SPEAKER_00 (30:54):
Absolutely, absolutely.
And that's yeah, so so so thisis something I published on like
in 10 years ago now, and it wasjust a literature review, but
just looking at these warm edgesover time, and and it was about
I think 47% of out of 976species, and that was all over
the world, all these differentgroups of organisms, you know,
(31:14):
marine, freshwater, terrestrial.
Um, and then you know, a fewyears later we go back and we
look at that with the climatedata added, and we can show that
yes, it's related tospecifically to climate change.
SPEAKER_01 (31:26):
Right.
So there's a correlationessentially.
SPEAKER_00 (31:29):
Yes, yes.
Um, and and when these and thesestudies that we're using are
ones where you know we'vealready tossed out the ones
where it seems like there'smodified habitat or something
like that.
Um so I think it's it's real.
You know, I think thatdefinitely the the local
extinctions from climate changeare you know, I think it's very
much real.
SPEAKER_01 (31:48):
And I suppose becoming more accurate over
time, right?
As more studies are done, yousort of eliminating all these
other potential factors andarriving at a more accurate
picture of things.
SPEAKER_00 (31:59):
Definitely.
And um and I think that that youknow sort of 45% thing is is
actually holding up as thousandsof more species are being added.
My my former postdoc, uh GopalMorale, um, we have this data
set of over 5,000 species, andit's very similar to the 976
species data set, and that it'syou know around 45, 50 percent
(32:21):
for these warm edge localextinctions.
And that's that's part of thething, also.
It's like, well, you know, it itwould be weird that there would
be, you know, sort of it's thisvery broad pattern.
And with these 5,000 speciesalso, we have the correlations
with climate change, also.
Um so I think I think that'svery much real.
SPEAKER_01 (32:41):
Right.
So I suppose just just sort of afinal Dill's advocate comment
would be I suppose that you cansay that there's you know,
correlation is not causation,but the correlation is becoming
increasingly convincing overtime.
Is that is that reasonable?
SPEAKER_00 (32:56):
Yeah, I I think so.
Yeah.
And and and also the other Ijust don't see any other
plausible mechanisms.
So for example, it's it'sterrestrial, it's freshwater,
it's marine, it's all thesedifferent groups of organisms.
Uh, it's correlated with thechange in in climate.
And and many of the patterns aresort of what you would expect
from what we know about speciesniches and things like that.
SPEAKER_01 (33:19):
Right.
When you write about this, youknow, climate-caused extinction
phenomenon and just extinctionsin general, perhaps, do you
often include recommendations topolicymakers and and others and
sort of what to do about this?
And if so, what do you say?
SPEAKER_00 (33:36):
Yeah, no, that's a great, it's a great question.
I've definitely been been askedthis before you know, recently,
if like, okay, so what if youknow, I'm a conservation person
and what are we supposed to do?
And here's my three wordrecommendation stop climate
change, right?
I mean, because it's it's sortof, you know, like moving
species A to a cooler place.
(33:56):
It's it's not enough.
I mean, it's a whole community.
So it's really um it's the greatquestion.
It's kind of the question, but II don't I don't think there's a
satisfying answer.
Yeah, and I should also say thatthat um one one thing that we
found from this is that you sortof expect species just to move
(34:18):
naturally and track theirclimactic niches, but they
generally don't.
They do they're supposed to sortof be moving up at their cool
edges, right?
Moving into higher elevationsand stuff, and the majority of
them just aren't moving at all.
SPEAKER_01 (34:30):
You know, that that that doesn't surprise me.
That idea of you know justallowing protected areas to
stretch up slopes and and up youknow altitudes and latitudes
basically just has never reallymade sense to me.
And that's partly because thereare already other species there,
right?
So, but also, I mean, you know,the soil structure can be
(34:50):
different, uh, vegetation, youknow, plants might not move at
the same rate as as animals, andso the the there's a completely
different habitat there, even ifthe temperature is you know
constant with what they wereused to.
There's so many other factorsthat that change.
So that never made a lot ofsense to me.
I don't I don't know howprominent that idea still is in
the literature.
SPEAKER_00 (35:08):
I think I mean it maybe they will kind of catch
up.
Maybe, maybe it's just thatextinction is happening more
quickly than the dispersal is.
You know, I think we stillshould allow for it.
It's just um, I don't know, saysomewhere between disappointing
and alarming that things aren'tmoving like they should.
Um and the thing is, you know,they're animals or they're
(35:30):
plants.
They don't know that they're,hey, you need to go and move to
a higher elevation.
They don't know that.
I mean, it's it does, itdoesn't, it's not how they work,
right?
So it's not, yeah, like I say,it's not entirely surprising.
SPEAKER_01 (35:40):
But yeah.
And uh would a more sort ofrobust strategy maybe be just to
ensure that other factors arenot complicating the matter.
So, you know, for example, youknow, expand the quantity and
quality of protected areas sothat, you know, for example,
invasive alien species aren'tmaking matters worse.
(36:01):
That will help, right?
Maybe that's the best thing wecan do short of stopping climate
change.
SPEAKER_00 (36:06):
Yeah, I mean, maybe, maybe it's certainly beyond my
knowledge or or you know levelof creativity.
Um, but I definitely think thatlike, yeah, stopping every other
threat, I mean, protecting thehabitats, stopping the invasive
species, you know, it's like doeverything we can.
And and you know, and and thesethese bad scenarios, the bad
(36:26):
climate scenarios haven'thappened yet.
And and maybe, maybe they won't,you know, maybe you know, we'll
sort of make the make the energyconversion and things like that.
And and uh so so I think it itis good.
Uh but we could with this, wecould still also we could we
could stop climate change andstill lose you know 30, 40
percent of the species out therefrom from other factors like
(36:49):
habitat production and thingslike that.
Um so I think that it's it's umyou know question, we have to
protect all the habitats, stopthe invasive species, do all
those things, and stop climatechange.
SPEAKER_01 (37:03):
Yeah, it's a multi, multi-war front, or multi-front
war rather.
And I just had one otherquestion to add, but maybe we've
already covered it.
But um is there anything moreyou can say or that you'd like
to say about how we canextrapolate recent extinctions
into the future?
Not just climate-causedextinctions, but extinctions in
general.
SPEAKER_00 (37:24):
Yeah, so we've definitely worked on on the
climate change one, and that'syou know, again, like 20 to 30
percent of species.
And you know, and of course, thethe the bad thing is we know we
could lose a lot of the speciesthat are currently listed as
endangered or or threatened, wecould, you know, there's a
potential to lose all or most ofthose.
But I mean, I I think there'ssome people have done nice, uh,
(37:47):
you know, there's possible touse approaches looking at
protected habitats and speciesthat aren't in protected
habitats and the potential oflosing those ones and say, okay,
what if we lose everythingthat's not in the protected
habitat?
You know, do those sorts ofanalyses.
And I think there was maybesomething done like that for
tetrapods a few years ago, and Ithink I think we we've cited,
(38:08):
and and they sort of talkedabout losing 10%, you know,
additional 10% of species.
SPEAKER_01 (38:17):
Another interesting thing about what you said about
climate change being the futurethreat and land change the
current threat and invasivealien species the past threat is
that uh when it comes to landchange or habitat transformation
or whatever you want to call it,we have reached sort of peak
land use globally.
And although that's varied, youknow, in the tropics we continue
(38:38):
to lose a lot of land.
Um, but uh that's sort ofslowing as well to some extent.
So we can hopefully look forwardto a future where the
transformation of habitat is isalmost a non-issue.
I mean, that's sort of somethingwhich seems doable, right, in
the in the not too distantfuture, or perhaps I'm looking
at several decades rather thanthan several years.
(38:58):
But then you are left with theseremaining threats like like
climate change.
Invasive alien species, althoughyou said that that was the the
the past cause of majorextinction, that continues to be
a big problem, doesn't it?
I mean, there are still a lot ofspecies that haven't yet been
tried as invasive species.
SPEAKER_00 (39:16):
You know, they've been Yeah, I know that's that's
a good point.
Yeah.
And also I would say in terms ofhabitat destruction, there's a
great paper from David Tillmanfrom many years ago, sort of
talking about how things arechanging and sort of like like
how how Asia went through this,you know, lost a lot of this
habitat, and and you know, andnow sort of people have of how
(39:38):
do I put this sort of kind ofleveling up people in terms of
getting people out of extremepoverty and and um and sort of
Africa hasn't gone through thatyet.
And Africa, you know, sort ofpresumably will go through that
and is likely to lose a lot ofhabitat in the in the process.
Right.
Um so it's kind of like the ideathat it's the these things are
(39:59):
sort of maybe changing acrossacross the globe over time.
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