More results!
As I’m writing up my dissertation (ahh!), I’ve been geeking out with graphs and statistics (and the beloved/hated stats program R). I thought I’d share a cool little tidbit.
Full disclosure: this is just a bit of an expansion on something I posted back in March about how well the camera traps reflect known densities. Basically, as camera traps become more popular, researchers are increasingly looking for simple analytical techniques that can allow them to rapidly process data. Using the raw number of photographs or animals counted is pretty straightforward, but is risky because not all animals are equally “detectable”: some animals behave in ways that make them more likely to be seen than other animals. There are a lot of more complex methods out there to deal with these detectability issues, and they work really well — but they are really complex and take a long time to work out. So there’s a fair amount of ongoing debate about whether or not raw capture rates should ever be used even for quick and dirty rapid assessments of an area.
Since the Serengeti has a lot of other long term monitoring, we were able to compare camera trap capture rates (# of photographs weighted by group size) to actual population sizes for 17 different herbivores. Now, it’s not perfect — the “known” population sizes reflect herbivore numbers in the whole park, and we only cover a small fraction of the park. But from the graph below, you’ll see we did pretty well.
Actual herbivore densities (as estimated from long-term monitoring) are given on the x-axis, and the # photographic captures from our camera survey are on the y-axis. Each species is in a different color (migratory animals are in gray-scale). Some of the species had multiple population estimates produced from different monitoring projects — those are represented by all the smaller dots, and connected by a line for each species. We took the average population estimate for each species (bigger dots).
We see a very strong positive relationship between our photos and actual population sizes: we get more photos for species that are more abundant. Which is good! Really good! The dashed line shows the relationship between our capture rates and actual densities for all species. We wanted to make sure, however, that this relationship wasn’t totally dependent on the huge influx of wildebeest and zebra and gazelle — so we ran the same analysis without them. The black line shows that relationship. It’s still there, it’s still strong, and it’s still statistically significant.
Now, the relationship isn’t perfect. Some species fall above the line, and some below the line. For example, reedbuck and topi fall below the line – meaning that given how many topi really live in Serengeti, we should have gotten more pictures. This might be because topi mostly live in the northern and western parts of Serengeti, so we’re just capturing the edge of their range. And reedbuck? This might be a detectability issue — they tend to hide in thickets and so might not pass in front of cameras as often as animals that wander a little more actively.
Ultimately, however, we see that the cameras do a good overall job of catching more photos of more abundant species. Even though it’s not perfect, it seems that raw capture rates give us a pretty good quick look at a system.
Giraffe battle
I thought I would share these video clips from my camera trap with you. During my research using camera traps in South Africa I mostly used the picture mode but in the early days when I was trying to figure out what the camera trap was capable of and what was most valuable from my research point of view I messed around with the video option.
From my research perspective it wasn’t that great, I found that the camera was slower to trigger in video mode and so particularly at night I was left with lots of footage of nothing. But from pure interest value it sometimes proved very interesting.
On this occasion I had set up the camera on a sand road hoping to capture the leopard who frequently passed that way leaving its pug marks for all to see. I was pretty sure of capturing the leopard. What I didn’t bank on was getting a full 17 minutes of footage of two giraffe battling it out. Nor was I expecting the unique perspective from which the camera shot the footage. Oh and the leopard never showed. Typical!
I hope you enjoy the following three short clips.
Fieldwork on the horizon
In news not quite as exciting as Ali’s (congratulations again!), I have just gotten word from the Tanzanian research institute that the proposal I submitted for summer research have been approved! It looks like I’ll be heading out to Dar es Salaam and Arusha in the next three weeks to get the rest of my permits sorted out, and then head into the field immediately afterward. Definitely looking forward to seeing this amazing system first-hand — I’m sure it will be a surreal experience, after becoming so familiar with the animals and landscape through the camera trap images. Added bonus: I get to leave Minnesota, where it is still snowing. Hurrah!
Lions and cheetahs and dogs, oh my! (final installment)
I’ve written a handful of posts (here and here and here) about how lions are big and mean and nasty…and about how even though they are nasty enough to keep wild dog populations in check, they don’t seem to be suppressing cheetah numbers.
Well, now that research is officially out! It’s just been accepted by the Journal of Animal Ecology and is available here. Virginia Morrell over at ScienceNews did a nice summary of the story and it’s conservation implications here.
One dissertation chapter down, just two more to go!
A different way to see the world
I posted a little while ago about the applications of remote sensing technology in biological research. Here’s a TED talk by one of the authors of the South African study I mentioned with some fascinating visuals showing the level of detail these technologies can reveal to us. While the talk starts off flying you through a “lion’s-eye” view of hunting terrain, Greg Asner goes on to reveal some of the other ecological and conservation implications of these technologies and how they can help us do things from finding illegal goldmines and documenting species composition in the Amazon to tracking habitat changes by elephants and fire back in Africa.
South Africa, here I come.
Back in October, I wrote about how a grant proposal was turning me into a zombie.
Well, much to my surprise, turns out that my foray into the world of the walking dead was worth the effort. I’ve just heard that the National Science Foundation does, indeed, want to send me to South Africa to carry out this research!
Basically, I’m interested in how the other big carnivores (hyenas, leopards, cheetahs, and wild dogs) manage to live with lions. And I think that one of the keys to their coexistence has to do with how the other carnivores distribute themselves across the landscape to avoid being killed or harassed by lions. Do they avoid huge tracts of land and lose access to the valuable resources within? Or are they able to fine-tune their behavior and still use those areas without getting into trouble?
As you know, I’m using the camera traps to try and figure out these patterns of habitat use by the major carnivores. But that still just tells me what they do in a place (the Serengeti) where there are lions, and I don’t know if the lions are directly causing these patterns. I can’t, for obvious reasons, do an experiment where I take out all the lions and see if the rest of the animals change their behaviors, which would help me identify such a causal relationship.
But in South Africa, there are two virtually identical reserves — they have the same habitat, the same prey animals, and the same carnivores…except that one has lions and one does not. These reserves are right next to each other and surrounded by fencing. So they are pretty much the perfect experimental system where I can actually answer whether or not the patterns we see in predator behavior are caused by lions. What’s even better is that there are already ongoing research projects there that are running camera trap surveys very similar to Snapshot Serengeti. So most of my work will be doing some measurements of the vegetation and working with the researchers in South Africa to compile their data in a way that we can draw these comparisons.
Comparison of Serengeti (left) and Phinda/Mkhuze (right). Phinda and Mkhuze are two virtually identical reserves in South Africa, except that lions have historically been excluded from Mkhuze.
It’s going to be a *lot* of computer work with a *little* bit of getting out into the bush, but the questions are so cool and the ability to effectively isolate the effect of a single top predator (lions) in a natural ecosystem is so rare, that I couldn’t be more excited about it.
The History of Lions
Barbary Lion, BBC
Here’s a great post by the BBC about some genetic work that has just been done to shed light on the evolutionary history of lions. Apparently, it’s a bit tricky reconstructing lion history due to the fact that they don’t fossilize particularly well (generally not conducive conditions in lion habitat) and that humans create giant holes in the record by wiping out entire sub-population.
However, from genetic analyses of living lions and museum specimens, these authors have determined that there are two evolutionary groups of lions – those in India and Central/West Africa and those in Eastern/Southern Africa. This happens to have some interesting implications for lion conservation and reintroduction — check out the article!
The legend of wolves and wapiti
The story of how reintroduced wolves transformed Yellowstone is now well known. According to the story, wolves scared elk away from the riversides, which allowed the willows and aspen to recover, allowing beavers to come back because they had home-building material big enough to use, and the beaver dams restored the health of the watershed.
I remember reading this story in college. I was sitting at a computer in UVA’s Alderman Library, digging up articles for a class presentation, when I stumbled on the now highly controversial article, “Wolves and the Ecology of Fear.” It blew my mind: right then and there, at the beginning of my last year of college, I knew I wanted to study how predators drove ecosystem dynamics.
It’s a beautiful story, and one that changed the trajectory of my career. And it’s one that’s been very hard to let go of, despite mounting evidence over the last decade that this story might not be more than a myth.
Dr. Arthur Middleton a post-doc at Yale and former graduate student at UWyoming, recently penned a fantastic op-ed about this in the NYtimes.
I had the good fortune of meeting Arthur at the Ecological Society of America talk last summer. I was a big fan of the work that he’d done, and that of his Ph.D. advisor, Dr. Matt Kaufman. But I didn’t envy either of them as they stepped into the fire of trying to take down what has become a beloved, monumental, epic tale. There’s no doubt that behaviorally-mediated trophic cascades do exist, and that predators can have profound influences on ecosystems, but the long-standing poster child for this simply isn’t real.
If you do one thing on your coffee break today, read his piece. While I could summarize the debate here, I couldn’t begin to do justice to Arthur’s eloquent argument.
Scratch that. If there’s one thing you do today, read Arthur’s piece. Not only will it make you think about wolves and ecology, but it will make you think about what nature we save, why we save it, and why that matters.
Interesting finds from Season 7!
Season 7 is up and running, and we’re already running into some interesting critters!
melanistic serval
No, that’s not a house cat wandering through the middle of the savanna. If you check out the gigantic ears, it appears that we’ve caught sight of a melanistic serval! Melanism involves a genetic mutation that causes the development of dark pigments in the skin, like a reverse albinism. For comparison, these guys normally look like this:
regular ol’ serval
According to our field assistant, Daniel, the serval population is booming in the Serengeti at the moment. Perhaps with so many animals, it’s not entirely unexpected to find one or two odd cases like this.
Let’s see what other interesting finds pop up in the latest season of Snapshot Serengeti!
Season 7
It’s been a long time coming, but it’s really and truly here.
First, we have to reiterate that Season 7 would never have been possible without your help. Last summer, our long-term National Science Foundation funding ran out and we were facing a gap in funding that could have closed down the camera survey forever. We launched the Save Snapshot Serengeti campaign to make sure that Season 7 happened — and because of your support, it did. Thank you, again, for making this project possible in so many ways.
And now! The hard won photos of Season 7 are here.
Season 7 is a big one, running from May 2013 all the way through to the end of November. That’s 7 months! In that time, the long rains faded and the roads became dusty. Stan, whose face you’ve seen so many times checking cams
Stan
began a master’s program in Dar es Salaam, and Norbert took over checking the cameras in his place.
Norbert!
Back in Minnesota, Margaret defended her dissertation and began a new post doc at Harvard working with the Phenocam project. I’ve been frantically analyzing data from Seasons 1-6 to finish my dissertation. And Meredith became the newest member of the Snapshot Serengeti team.
So, stop whatever you’re doing for a few minutes and go check out Season 7. Because really, whose day *isn’t* brightened by photos like this?
Teehee…warthog nose!
Snapshot Serengeti 