I’m in South Africa, getting a feel for the ongoing Panthera camera trapping surveys, collating data, falling madly in love with the country and South African bush, and scheming for how I need to find a way to come back.
Things are a bit of a whirlwind, but so far I am amazed and excited about the amount of monitoring that many of the small private and state-run reserves have been doing. There is an extraordinary amount of information that has been collected over the last decade on how all of the top predators move and live across these parks. There are parks with and without lions. Parks with and without hyenas. With and without wild dogs. Some parks are big and some are small. Some are very thickly treed, others are somewhat open. (Note that one thing I discovered very quickly is that pretty much all South African habitat, even the grassland, would equate to “woodland” in the Serengeti. So…”open” is a relative term.)
The amount of data here is enough to get any science nerd’s heart a flutter. But I am trying to focus on what is out the window instead of what’s on the computer for now. I’ve only a few days in South Africa, and endless time to analyze the data.
In the meanwhile, I thought I’d share one of my new favorite animals: the nyala.
These cousins to the waterbuck we capture in camera on Serengeti, and you can see it a bit in their pretty faces. But these animals are far more stunning than anything I’ve ever seen in Serengeti. The females are small and sport bright white stripes on their red fur, and the males have these incredible “manes” that run down the undersides of their necks and to their bellies. They are pretty awesome. As is everything I’ve experienced in South Africa so far. Yep, definitely need to find a way back!
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.
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!
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.
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.
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.
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!
Last week I wrote about using really simple approaches to interpret camera trap data. Doing so makes the cameras a really powerful tool that virtually any research team around the world can use to quickly survey an ecosystem.
Existing monitoring projects in Serengeti give us a really rare opportunity to actually validate our results from Snapshot Serengeti: we can compare what we’re seeing in the cameras to what we see, say, from radio-tracking collared lions, or to the number of buffalo and elephants counted during routine flight surveys.
One of the things we’ve been hoping to do with the cameras is to use them to understand where species are, and how those distributions change. As you know, I’ve struggled a bit with matching lion photographs to known lion ranging patterns. Lions like shade, and because of that, they are drawn to camera traps on lone, shady trees on the plains from miles and miles away.
But I’ve finally been able to compare camera trap captures to know distributions for other animals. Well, one other animal: giraffes. From 2008-2010, another UMN graduate student, Megan Strauss, studied Serengeti giraffes and recorded where they were. By comparing her data with camera trap data, we can see that the cameras do okay.
The graph below compares camera trap captures to known densities of giraffes and lions. Each circle represents a camera trap; the bigger the circle, the more photos of giraffes (top row) or lions (bottom row). The background colors reflect known relative densities measured from long-term monitoring: green means more giraffes or lions; tan/white means fewer. For giraffes, on the whole, we get more giraffe photos in places that have more giraffes. That’s a good sign. The scatterplot visualizes the map in a different way, showing the number of photos on the y-axis vs. the known relative densities on the x-axis.
What we see is that cameras work okay for giraffes, but not so much for lions. Again, I suspect that this has a lot to do with the fact that lions are incredibly heat stressed, and actively seek out shade (which they then sleep in for 20 hours!). But lions are pretty unique in their extreme need for shade, so cameras probably work better for most other species. We see the cameras working better for giraffes, which is a good sign.
We’ve got plans to explore this further. In fact, Season 7 will overlap with a wildebeest study that put GPS collars on a whole bunch of migratory wildebeest. For the first time, we’ll be able to compare really fine scale data on the wildebeest movements to the camera trap photos, and we can test even more precisely just how well the cameras work for tracking large-scale animal movements. Exciting!
Over the last few weeks, I’ve shared some of our preliminary findings from Seasons 1-6 here and here. As we’re still wrapping up the final stages of preparation for Season 7, I thought I’d continue in that vein.
One of the coolest things about camera traps is our ability to simultaneously monitor many different animal species all at once. This is a big deal. If we want to protect the world around us, we need to understand how it works. But the world is incredibly complex, and the dynamics of natural systems are driven by many different species interacting with many others. And since some of these critters roam for hundreds or thousands of miles, studying them is really hard.
I have for a while now been really excited about the ability of camera traps to help scientists study all of these different species all at once. But cameras are tricky, because turning those photographs into actual data on species isn’t always straightforward. Some species, for example, seem to really like cameras,
so we see them more often than we really should — meaning we might think there are more of that critter than there really are. There are statistical approaches to deal with this kind of bias in the photos, but these statistics are really complex and time consuming.
This has actually sparked a bit of a debate among researchers who use camera traps. Researchers and conservationists have begun to advocate camera traps as a cost-effective, efficient, and accessible way to quickly survey many understudied, threatened ecosystems around the world. They argue that basic counting of photographs of different species is okay as a first pass to understand what animals are there and how many of them there are. And that requiring the use of the really complex stats might hinder our ability to quickly survey threatened ecosystems.
So, what do we do? Are these simple counts of photographs actually any good? Or do we need to spend months turning them into more accurate numbers?
Snapshot Serengeti is really lucky in that many animals have been studied in Serengeti over the years. Meaning that unlike many camera trap surveys, we can actually check our data against a big pile of existing knowledge. In doing so, we can figure out what sorts of things cameras are good at and what they’re not.
Comparing the raw photographic capture rates of major Serengeti herbivores to their population sizes as estimated in the early 2000’s, we see that the cameras do an okay job of reflecting the relative abundance of different species. The scatterplot below shows the population sizes of 14 major herbivores estimated from Serengeti monitoring projects on the x-axis, and camera trap photograph rates of those herbivores on the y-axis. (We take the logarithm of the value for statistical reasons.) There are really more wildebeest than zebra than buffalo than eland, and we see these patterns in the number of photographs taken.
Like we saw the other week, monthly captures shows that we can get a decent sense of how these relative abundances change through time.
So, by comparing the camera trash photos to known data, we see that they do a pretty good job of sketching out some basics about the animals. But the relationship also isn’t perfect.
So, in the end, I think that our Snapshot Serengeti data suggests that cameras are a fantastic tool and that raw photographic capture rates can be used to quickly develop a rough understanding of new places, especially when researchers need to move quickly. But to actually produce specific numbers, say, how many buffalo per square-km there are, we need to dive in to the more complicated statistics. And that’s okay.
You’ve got to check out this game: http://nightjar.exeter.ac.uk/story/nightjar_game
Scientists from the University of Exeter are trying to understand camouflage. Specifically, they want to understand how camouflage helps protect animals from being eaten for dinner, and they’re doing this by studying ground nesting birds in South Africa & Zambia.
Like Snapshot Serengeti, these guys use camera traps too, to figure out whose munching on birds and their nests. Unlike Snapshot Serengeti, however, they aren’t asking for help IDing the photos: instead, they’re asking for help figuring out how predators see, and how different types of camouflage work better or worse against predators with different types of vision.
Humans have trichromatic vision, meaning we have three different types of receptors (light sensitive cells in the eye) that can process color: red (longwave), green (mediumwave), and blue (shortwave). Some animals only have two receptor types and can only see one or two colors, whereas other animals have four, allowing them to see wavelengths such as infrared or ultraviolet that are invisible to people. Thus, what camouflages eggs against one predator might not work so well against another predator.
What these researchers have done is create a game that mimics the vision of other predators. So you get to see the world through the eyes of either a genet cat (with dichromatic vision) or a vervet monkey (with trichromatic vision), and “hunt” for birds or their nests in a series of pictures. This helps scientists understand how perception changes among different animals, and how camouflage works against different perception types.
So go check it out! But don’t forget to come back and then help us classify Season 7! We’ll announce its debut on the blog soon!
Look at this picture of the world – it’s blue, it’s green, it’s dynamic. It is covered in swirling clouds beneath which we can see hints of landforms, their shapes and their colors. Satellites tireless orbiting the Earth gathered the information to construct this image. And every pixel of this this awe-inspiring rendition of our planetary home is packed with data on geology, topography, climatology, and broad-scale biological processes.
I still find it funny that I can sit in my office and watch weather patterns in Asia, cloud formation over the Pacific, or even examine the contours of the moon in minute detail, thanks to remote sensing programs. Not that lunar geomorphology is particularly pertinent to lion behavior, at least, in any way we’ve discovered so far. Still, an incredible amount of information on the Serengeti landscape can be collected by remote sensing and incorporated into our research. “Remote sensing” simply refers to gathering information from an object without actually making physical contact with the object itself. Primarily, this involves the use of aerial platforms (some kind of satellite or aircraft) carrying sensor technologies that detect and classify objects by means of propagated signals. Most people are passingly familiar with RADAR (“radio detection and ranging”) and SONAR (“sound navigation and ranging”), both examples of remote sensing technologies where radio waves and sound, respectively, are emitted and information retrieved from the signal bouncing back off of other objects. The broad-scale biotic or abiotic environmental information gathered can then be used in our analyses to help predict and explain patterns of interest. People are using remote sensing to monitor monitoring deforestation in Amazon Basin, glacial features in Arctic and Antarctic regions, and processes in coastal and deep oceans. Here are brief vignettes of several kinds of remote sensing data we draw upon for our own biological studies.
NDVI: Normalized Difference Vegetation Index
NDVI is collected using the National Oceanic and Atmospheric Administration (NOAA)’s Advanced Very High Resolution Radiometer and is an assessment of whether a bit of landscape in question contains live green vegetation or not. And yes, it’s far more complicated than simply picking out the color “green”. In live plants, chlorophyll in the leaves absorbs solar radiation in the visible light spectrum as a source of energy for the process of photosynthesis. Light in the near-infrared spectral region, however, is much higher in energy and if the plant were to absorb these wavelengths, it would overheat and become damaged. These wavelengths are reflected away. This means that if you look at the spectral readings from vegetation, live green plants appear relatively dark in the visible light spectral area and bright in the near-infrared. You can exploit the strong differences in plant reflectance to determine their distribution in satellite images. Clever, right? NDVI readings are normalized on a scale of -1 to 1, where negative values correspond to water, values closer to zero indicate barren areas of tundra, desert, or barren rock, and increasingly positive values represent increasing vegetated areas. As you can see in the image above, we have NDVI readings for our study sites which can be used to examine temporal and spatial patterns of vegetation cover, biomass, or productivity — factors important in driving herbivore distribution patterns.
MODIS: Moderate-resolution Imaging Spectroradiometer
The MODIS monitoring system is being carried in orbit aboard a pair of satellites, the Terra and Aqua spacecraft, launched by NASA in the early 2000s. The two instruments image the entire surface of the Earth every 1 to 2 days, collecting measurements on a range of spectral bands and spatial resolutions. Their readings provide information on large-scale global processes, including pretty much anything that can occur in the oceans, on land, or throughout the lower atmosphere. Many of the beautiful Earth images, such as the one at the head of this post, are constructed using MODIS data. We hope to use MODIS information for the detection and mapping of wildlife fires, which impact organisms at every level of the Serengeti food web.
LiDAR: Apparently, a common misnomer is that “LiDAR” is an acronym for Light Detection and Ranging, while the official Oxford English Dictionary (the be-all-end-all for etymology) maintains that the word is merely a combination of light and radar. Either way, it’s less of a mouthful than the other two techniques just discussed!
LiDAR is quite well-known for its applications in homing missiles and weapons ranging, and was used in the 1971 Apollo 15 mission to map the surface of the moon. We also use this for biology, I promise. What LiDAR does, and does far better than RADAR technology, is to calculate distances by illuminating a target with a laser and measuring the amount of time it takes for the reflected signal to return. High resolution maps can be produced detailing heights of objects and structural features of any material that can reflect the laser, including metallic and non-metallic objects, rocks, rain, clouds, and even, get this, single molecules. There are two types of LiDAR: topographic, for mapping land, and bathymetric, which can penetrate water. To acquire these types of data for your site, you load up your sensors into an airplane, helicopter, or drone and use these aerial platforms to cover broad areas of land. I first became aware of LiDAR from a study that used this technology in South Africa to map lion habitat and correlate landscape features with hunting success. I’ve also seen it used to map habitat for wolves and elk, determine canopy structure, and, interestingly enough, to remotely distinguish between different types of fish (weird, and also really neat). Now we don’t have LiDAR information for the Serengeti, so keep an eye out for anyone who might be able to lend us a couple of small aircraft and some very expensive sensing equipment!