This course is an introduction to ecology and ecosystem dynamics using a systems thinking lens. Through a case study on Mozambique's Gorongosa National Park, learners will explore how scientists study ecosystems, and investigate the complex array of factors that inform management efforts. At the end of the course, learners will be able to grapple with real-world conservation questions, such as whether an ecosystem can recover from anthropogenic disruption and what role humans can, and should, play in that recovery.
Conserving and Restoring Ecosystems
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来自 American Museum of Natural History 的课程
Ecology: Ecosystem Dynamics and Conservation
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从本节课中
Can an Ecosystem Recover?
This week we conclude by focusing on the role of humans in ecosystems: how humans interact with and are shaped by their environments. We explore the meaning of the “anthropocene” (the title given to the current geological age in recognition of significant impact of human activities) and investigate management approaches that balance human needs and biodiversity. We also return to Gorongosa National Park to wrap up the course, shifting the conversation from "Can an ecosystem recover?" to "Should it recover?" and "What does a successful recovery look like?" We explore how conservation might have to adjust to future challenges such as climate change, extinctions, and human population growth. We also introduce the idea that a spectrum of conservation approaches is necessary, from the preservation of land and species, to the integration of biodiversity into market economies, to the creation and management of “novel” ecosystems.
与讲师见面
Ana Luz PorzecanskiDirector
Center for Biodiversity and Conservation
Welcome to HHMI's 2015
Holiday Lectures on Science.
This year's lectures, Patterns and Processes in Ecology,
will be given by two leaders in ecological research,
Dr. Robert Pringle and Dr. Corina Tarnita of Princeton University.
The sixth lecture is titled Conserving and Restoring Ecosystems.
And now, Dr. Robert Pringle.
All right.
So, it's the last lecture before lunch and you guys are all still with
us and asking the most amazing questions,
so we love you for that.
And this lecture is, in many ways,
to me, the most important.
But unfortunately, I only have really 15 minutes to give it.
And it's important because it's about taking,
and I hope we've been able to convince you,
Corina and I, over the course of the morning,
that by coupling kind of creative problem solving approaches,
new technologies, mathematical models,
and experimental tests, we can understand a lot about how ecosystems actually work,
and that's a new thing in ecology,
which is a relatively young science.
But this lecture is about how can we take that kind of knowledge and apply it to
the restoration of a severely degraded ecosystem that we've been
talking about all morning, Gorongosa National Park.
Okay. So, the collapse of
large wildlife is not unique to Gorongosa or at any other system.
So, here's a heat map showing where there are the most species of large mammals.
Not surprisingly, that map concentrated in Africa,
Eastern and Southern Africa.
And here is species that are threatened.
This is a map of a number of threatened species.
Point being there really quite a few.
And actually, Africa is doing reasonably well.
Three or four severely threatened species like our Grévy's zebra,
for example, black rhino, white rhino, elephants.
So, large mammals are just vulnerable because people like to eat them.
They often have parts like ivory,
tusks, and horn that people,
for whatever reason, like to harvest and sell for extraordinary amounts of money.
And I've already showed you that
these largest mammals are really important players in the ecosystem.
They are setting limits
on the abundance of other species and they're influencing the diversity of
other species and a variety of ecosystem functions that we're not
showing on this graph like how the nutrient cycle and how much carbon gets stored.
That's a big one, right? It's like large mammals influencing
how much carbon gets stored in the ecosystem versus goes up into the atmosphere.
So, it's a big deal that these herbivore populations are declining.
That map that Corina showed in the previous lecture with
the range map shrinkage of those three species is a reason for serious concern,
not just because we love those species,
but also because we love the ecosystems that they come from.
So, here's Gorongosa National Park in Southeastern Africa.
Mozambique is shaped like a Y. Gorongosa is pretty much at the center of that.
And I would say that the real heart
ecologically of Gorongosa National Park is this Lake Urema.
That's a flood plain or called the lake.
In the wet season, it's a lake. It gets huge in a day or so most of the park.
In the dry season, it shrinks,
and what it leaves behind is this really like nutrient rich silt
and mud that can grow very nutritious plant communities.
And so Gorongosa was established in 1960
and it was immediately heralded as one of Africa's greatest game parks.
And you can see that in this headline,
this is from a defunct newspaper called The Daily News from South Africa,
and they're saying this new national park in Gorongosa could be Africa's greatest.
Just quite a big statement especially from
a country where you have Kruger National Park and of course the Serengeti.
So, it's quite a strong statement here about Gorongonsa.
And the reason why it inspired so much excitement is shown in this photo.
It may look like a bunch of black blobs and white speckles.
But what it really is is a herd of probably a thousand buffalo on the Urema floodplain.
So this is that floodplain I told you about.
The floodwaters recede and it leaves behind grasses and the herbivores move in.
So, here's just a ton of buffalos and these are
actually cattle egrets that are following them.
Here's what it looks like today, same place.
And those are not buffalos. These are water buck.
So what happened? Well, you already know what happened.
The tragic history of this place,
and it's an interesting history to read some time.
Also, didn't have time to go into all of the social causes of it,
but it's really heartrending,
and not least for the effect that it had on wildlife.
Not most of the effect it had on wildlife either,
but it really devastated this national park.
And you can see here, this is actually post-war.
This is 1994, two years after the cessation of
hostilities and in a place that has been economically
and just had the soul ripped out of it by
15 years of the most grotesque kind of war imaginable.
And people are starving.
Naturally, they go in and they eat.
And so this guy has got a bike full of duikers and headed home to cook.
This is Lichtenstein's hartebeest and waterbuck,
and here are some bones littering the park.
Two years after the war,
still hunting going on at very high levels.
Now, since about 2004,
unofficially and officially since 2007,
there's been an effort to restore Gorongosa National Park,
and we call it the Gorongosa Restoration Project,
and I'm a part of it,
and it is spearheaded by this fellow,
Greg Carr, up in the top left reading a speech to
a community meeting of community members.
Here is a planning meeting that happened in
2010 about how the restorations should proceed.
Here is the chief park warden,
Mateos Matombo, sharing a ceremonial beverage with local communities.
And this is all part of the restoration process.
This is the social and political embedding of
the national park in the culture of the local place. And that's important.
And of course, this is the hippo house.
I could show you a historical photo where people were
sitting out on this balcony drinking cocktails,
watching the hippos graze and the elephants trumpet and, all that kind of stuff.
Now, we have a single bushbuck.
I don't know if you can see it down there by the third pillar.
And this is what it looks like today. It's a ruin.
And so if we're going to do this,
we're going to spend probably $80 to
about $100 million to restore this ecosystem over 20 years.
We need to ask ourselves some questions,
and we need to hold our own feet to the fire.
So, the philosophical question we need to ask is what's the right baseline?
Do we try to restore how the ecosystem looked in 1977 right before the war?
Do we try to make it look like it did before the scramble for Africa?
Can we take it back to pre-European times?
Well, those can be debated,
and ultimately, it's a bit of a subjective question that science can't answer.
But science does have a role here.
Okay? So, the practical question I want to ask is how
can science help achieve whatever goal is chosen?
And then I'll just say that the goal that the restoration project has decided on is to
try to restore the pre-war state as the goal.
Okay. So, you guys have seen a piece of this story already in
Corina's lecture that the flood plain grazer community, so here,
we're talking about hippo, buffalo, wildebeest, zebra,
and waterbuck were disproportionately dominated in terms of biomass by hippo, buffalo,
and to some extent,
wildebeest and zebra, and then you had this kind of waterbuck,
which was hanging around there,
following the near extinction of all these other species.
Wildebeest is zero. Wildebeests were counted in 2002.
It's just six zebra.
The waterbuck have assumed outsize importance and that has continued to the present day.
Even as some of the other species numbers have started to increase a little bit,
we have all these waterbuck.
And we have a lot and a lot of individuals
of species that were never counted before the war
so we don't know what their baseline is,
but we just know that there's a lot and I've been in some African ecosystems.
I've never been to a place with more warthog running around than Gorongosa.
It's almost pestilential there in the camp.
They're everywhere.
And so, it's a little bit pathological.
Now we've also noticed,
people in my lab,
my graduate students and postdocs,
who have gone out and we
have systematically surveyed the vegetation
of the floodplain and found that it has changed,
too, not just the animals.
So, this very palatable grass, Cynodon dactylon,
has decreased in relative abundance since 1972,
and this rather unpalatable forb has increased in abundance since 1972,
and this invasive South-American non-native woody plant which has choke
many floodplain ecosystems has increased pretty dramatically as well.
So, this looks like a degradation
of the plant community from the point of view of grazers.
So, these are observations.
We know that the bulk grazers have been replaced by smaller, selective herbivores.
We know that the previous vegetation community which was dominated
by grasses like this Cynodon dactylon and it had relatively few forbs,
is now in a situation where the grasses are few and the forbs are many.
So what do we need to know from a restoration perspective?
We need to know if this is going to naturally revert this current situation today.
Is it going to naturally revert to the pre-war state that we had over there in 1972?
Or alternatively, has it changed to a new stable state
that will not change without heavy perturbation, heavy human intervention?
Okay. And now how do we figure that out?
Well, first of all,
we do have to understand exactly what processes are driving these changes, right?
So, I'm going to outline three hypotheses for you guys and then I'll
present you a little bit of evidence in support of each.
But I should note that we are just starting this,
this is very new science and so this data hot off the press.
I don't have nice tight conclusions for you.
All I have is, am opening up the hood and you guys are seeing science in action and data
that am literally getting by email two days ago so that I could put it in this talk.
So, the first hypothesis is that,
these smaller selective grazers that are dominant today are suppressing grasses,
maybe they are too abundant,
maybe they feed selectively and they go and they avoid these nasty forbs,
and they are going directly for the palatable plants.
And because there's 35,000 of them out there on the floodplain,
35,000 or more, they're eating up all the grasses.
Alternatively, maybe it was that these bulk grazers which are not particularly selective,
like a hippo has a wide mouth it eats everything that's in the path
of that mouth and it can eat a lot of forbs
and it can eat a lot of grasses and generally,
they tend to crop it like a golf course.
And what do you do when you don't mow the yard?
It gets weeds, right?
So maybe these animals are functioning like big,
biotic lawnmowers that are skipping the weeds out and maintaining the grass lawn.
And then the third question is really whether
these herbivores are competing with each other or not and
whether that might impede the recovery of the pre-war fauna?
Okay, so how do we test this first one,
that these smaller selective grazers
are negatively impacting the grasses and benefiting the forbs?
Well, to do that, we have,
this is an exclosure fence so much like the one we described in the previous lecture.
This one is keeping out waterbuck and reedbuck and other sort of the species that have
increased in recent years and we're going to be able to track how the vegetation changes.
And if this hypothesis is true, that well,
this hypothesis represented here if that's true,
we should see a reversion,
we should see grass increase in abundance inside the fences.
Okay, and for abundance and woody plant abundance decline.
Now, if my other hypothesis is true,
that these are basically the lawnmower hypothesis, how can we test that?
We can test that by mowing the lawn at a very large scale.
And so this is actually not Gorongosa.
This is the Welgevonden reserve,
private reserve in South Africa where they did a similar kind of range and experiment.
They mowed and they added fertilizer.
So, that's basically simulating the effect of a hippo or a buffalo, right?
You're clipping the grass and then you're adding fertilizer, manure fertilizer.
And what they found is,
you can see those green patches, right?
Now, you can, if you couldn't before.
That's where they had mowed and fertilized and what's really cool is,
they found that if you do this, mow and fertilize,
you can create a grazing lawn which is nutritious like
grass-based patch that will expand and grow.
And so, this could be a way of seeding these environments, okay?
And then the last hypothesis,
how do we test herbivore-herbivore competition?
We've already talked about one way,
the DNA metabarcoding data analysis.
And I showed you that, in fact,
we're finding this emerging generality that
in these large mammal species really partition the dietary niche,
so they should not be competing
strongly because they eat lots of largely different foods.
And this is from Kenya not from Gorongosa,
and I wish we had the hippo,
and buffalo, and waterbuck data to show you there,
those samples are still being processed.
But I do have samples for waterbuck and warthog and show you that they
also are partitioning the niche in a very similar way. Same exact story.
So I expect this story to be general, generally true.
Now, we can use these critter cam data so here we are back in the mind of a waterbuck,
seeing what it's seeing, and looking at what it's foraging.
See, it's actually not going for necessarily.
It is foraging at a very low and selective level,
but it's not going for grasses.
It's eating actually a lot of forbs.
So, to me, the notion that waterbuck are
actually overgrazing the grasses and that's why you're getting all these forbs,
doesn't really hold up.
And in fact, when you analyze the waterbuck feces with the metabarcoding,
you find that they're eating more than 50 percent forbs and Mimosa.
They love some of the forbs and the Mimosa plants and don't need grazers.
Now if you contrast that,
here's a critter cam around the neck of a buffalo and look what it's eating.
That's tall fit grass, okay?
And that's very different from the previous clip.
We've got a sample size of one year but I would expect this to be fairly represented.
So another indication that these things are not strongly competing,
they're eating different kinds of food, all right?
And so, my assessment is as follows,
that my hypothesis one is unlikely,
that I do not think it is the overgrazing.
Really, there's no more biomass of
large herbivore in the floodplain Gorongosa now than there was.
It just happens to be a different species and that probably
has a big effect of some kind or at least a temporary one,
but I don't think it's causing the vegetation changes as we've observed.
My second hypothesis I think is quite likely.
Actually, I think that these big mammals
act as biotic lawnmowers and that when you pull them out of the system,
the forbs get a competitive edge,
and we have actually seen this in long term data from some of
those herbivore exclusion experiments in Kenya,
that when you put all the large mammals away,
forbs start to replace grasses.
So, we're looking forward to testing this using that mowing experiment,
seeing if we can revert using mowing fertilizing.
Finally, the data we have do not really suggest any strong role
for a competition between these two groups of organisms.
So, my overall prediction is that,
this system will revert, right?
That is, Karina implied with her lecture,
waterbuck are just going through this exponential phase and there's logistic growth,
and sooner or later they're gonna hit that carrying capacity,
start to decline as the other species
like buffalo and zebras start to become more abundant,
and then they will be competing,
and the system will start to shift back into it.
So, that is nice because it suggests that we don't have to do necessarily this.
What this is, is these are
some potential restoration actions depending on the answers of the science.
This is how you translate the science into management,
and this is showing that you could introduce a bunch of buffalo if you wanted,
but it costs at a cost of hundreds of thousands of dollars,
and a great stress to the animals,
and lots of time involved.
So, maybe you don't need to do that, right?
This is why we need to understand this stuff because that's a lot of money to invest,
if you're going to do it, you should only do it because you know it's going to work.
Another thing we could do is go out and call waterbuck, go out and shoot a bunch,
and reduce their numbers, and again,
falling from Karina's very nice lecture,
basically, is a strong argument for why that's not necessary.
They just haven't reached their current capacity and
they aren't in competition with other species,
so don't go out and do the ethically dubious thing of calling
wildlife inside a national park because
you're freaking out that things aren't recovering the way they should.
Now, here's the one that I actually think we should consider,
which is to re-introduce some key predators, right?
Right now, in Gorongosa,
we have lions, but we have no hyenas,
we have no wild dogs,
we have no jackal's,
and we have, probably, no leopards.
Nobody has seen a leopard, anyway.
If there are leopards around,
there are certainly not many of them because we've been looking pretty hard.
Bringing those animals back,
the hyenas is an important competitor of waterbuck, in particular.
Then, here's the management action that I find,
certainly as an experiment, fairly appealing,
is to go in with a fertilizer bag,
and a tractor, and try to create some grazing lands.
And lastly, one that I find not solved.
If we cannot get a reversion of this system,
if we think that we're in a new stable state,
we might try to apply herbicide that is specific to woody plants and
won't hurt the grass as a way of bringing the system back into equilibrium.
Hopefully, that won't be necessary because the biology and
restoration often does a really good job of correcting itself.
If you understand enough about the biology,
to facilitate the biology in doing that.
That's all. I'll take a couple of questions.
So, how does the positive reversion
to the mean affect the continuity of ecological succession?
Yes, that's really interesting. So, ecological succession is the idea that
the system will go through a kind of
characteristic set of changes as it reaches a climax or equilibrium community.
And I guess, what I would say is that,
this recovery process would be the equivalent of succession.
So, what's happened is you've taken
the Gorongosa ecosystem and you've swung a wrecking ball at it,
and change it all around.
And the successional process is the process of re-equilibration that will happen if
the animals are adequately protected from hunting and the system is preserved.
Then the natural successional processes should help restore the balance.
More in the back.
What will "re-introducing the predators," what effect will that have?
Great question.
I don't know exactly,
but there are several things that we've noticed.
One, is that hyenas,
for example, to take one species that is not really functionally present in Gorongosa,
are big predators on waterbuck and
they may help keep the waterbuck population
a little bit more in check which may help hasten the recovery of other species.
Remember my wolf trophic cascade?
That was an effect not of the wolves eating
so many elk but of the fear that the wolves induced in the elk.
So, there is a sort of fear that's
missing in the Gorongosa herbivores and it feels amiss when you're there.
You see, for example,
we have a GPS collar on a bushbuck which is a shy forest antelope and this animal
lives out on the edge of a floodplain and goes on
these foraging journeys out into the middle of the floodplain where there's no bushes,
and it would not do that, I think,
if there were predators around,
because it would be very vulnerable.
In addition to whatever kind of population level effects that it has,
restoring predators would have the benefit of
putting a healthy respect back into the herbivores to
modify their behavior in ways that
would basically bring it to a closer approximation of what it used to be.
And the last benefit which is that,
I don't know if you guys know the sound of a hyena,
this spotted hyena calling at night,
it's a very distinctive sound.
And if you spend your time in Savannah's,
or camping in Savannah's, then,
you know that sound and it's kind of beautiful, right?
You'd be out of your campfire and hear that sound all around you.
Right now, Gorongosa does not have that sound.
So, it is sonically incomplete,
and it sounds funny but it's actually matters
because the whole plan for restoring Gorongosa
is based on revitalizing a tourism industry
that can help pay the bills of the park which are substantial, right?
And so, if you don't have some of the elements that the safari goer wants to experience,
that would enrich their experience,
then you're missing something that's economically hurting you as well.
