If you’re a prey animal, you spend an awful lot of your time trying to not wind up like this:
As we’ve talked about an awful lot on this blog (here, here, and here, for example), the same holds true for a lot of predators. Just because you kill and eat other animals, doesn’t mean you don’t have to worry about being killed yourself (as this hyena so unceremoniously discovered).
But, what we haven’t talked so much about, is that the same holds true for plants. If you’re a plant, you get eaten by these terrifying animals:
But, just like prey animals and mesopredators can change their behaviour to minimise the risk of being killed, plants have a few tricks up their sleeves. They can spend a lot of energy growing big thorns, for example, that makes them less delectable.
Or! They can grow in places that their predators avoid — the places where their predators’ predators hang out. Got that? It’s a trickle-down landscape of fear, which had, until now, only been really well documented in small experimental systems with critters like spiders and grasshoppers. But researcher Dr. Adam Ford and colleagues just published an elegant paper in Science showing that leopards and African wild dogs can make the Kenyan savanna less thorny through this cascade. Basically, leopards and wild dogs eat impala. Impala eat Acacia trees. Impala much prefer to eat acacias with fewer thorns (because really, who doesn’t?) – and, if given the opportunity, impala will can eat these small-thorned acacias so much that they can suppress the acacia population.
But! Leopards and wild dogs seem to be offering these tasty small-thorned acacias a refuge. Leopards and wild dogs spend most of their time in denser thickets, where they have more cover to hunt. Impala avoid these thickets and rarely venture in — when they do, however, they have a much higher probability of being killed. And this creates this spiral – those tasty small-thorned trees survive and grow in these thickets because predators scare impala away.
So it’s a trickle down landscape of fear – a compelling and really exciting story. But, what sets Adam’s paper apart from many other attempts to document this effect in large predators, is the series of elegant experiments in which he and colleagues explicitly tested each step in this cascade. Controlling for habitat use to confirm that impala aren’t getting killed in the woods simply because they spend more time there (and in fact, they get killed more even though the spend less time there). Adding and removing thorns to acacias to see if it was really the thorns that mattered. Creating herbivore exclosures to measure whether impala could really suppress acacia density. I spent my entire time reading the article alternating between saying “This is so cool!” and “I am so jealous!” It’s an amazing story. Read more about it here (or here, or or here)!
You’ve undoubtedly seen it: Grass. Tall waving grass. Lots of it. From here to the horizon. If you’re itching to get images of animals to classify, the “nothing here” grass images can seem annoying. Some people find the grass images soothing. The animals themselves, well, a lot of them seem to like it.
Some animals find that tall grass is nice for concealing themselves from predators, like these guys:
Or this impala:
And some animals think the grass is nice for eating, like here:
This post is brought to you by Faulty Cameras that switch unexpectedly to video mode when they’re not supposed to. These Season 5 videos have no sound, but capture some of the movement you don’t get with the photographs, so I thought you might like them.
Imagine you are an impala.
You’re hungry. You want to go find some lovely nice grass to graze, and you know where the tastiest grass is. The only problem is that every time you go over to taste that best grass, you smell lion. And, well, that’s a little scary. So what do you do? Take the chance and go nibble the tastiest of tasty grasses? Or go elsewhere where the grass isn’t quite as nice?
This conflict for herbivores between finding the most nutritious food available and not becoming food is the basis for some of our research questions. We know that lions prioritize certain areas for hunting. In fact, former Lion Research Center researcher Anna Mosser discovered that lions set up their territories near where rivers and streams come together. Here there is open water where herbivores may come to drink and lots of green coffee leaves and vegetation (which is good eating for herbivores, but also provides a place for lions to hide and stalk those herbivores).
We know what the lions do. But what we don’t really know is what sort of decisions the herbivores make. The answer to this question likely depends on the answers to some other questions. We might first ask: what does the distribution of grass look like out in the Serengeti? If it’s the wet season and there’s good grass all around, perhaps we’d expect that herbivores would tend to avoid places with lots of lions. But if it’s the dry season and the only good places to eat are near rivers, then maybe the herbivores are forced to eat near lions so they don’t starve.
Or, we might ask: for any given herbivore species, how likely is it to be attacked by lions? Very large herbivores – like hippos, elephants, and giraffes – are a lot less likely to be attacked by lions than their mid-sized relatives. So maybe these big herbivores don’t care very much about whether they’re eating near lions or not.
We also have to ask the question of whether the herbivores can even tell which areas have a lot of lions and which don’t. If they can’t tell where the lions are, then we’d expect them to spread out, with more herbivores in areas of better foliage and fewer animals where the foliage isn’t so good.
The data you’re giving us through Snapshot Serengeti will help us understand the choices herbivores are making. We’ll be able to map the distributions of lots of different herbivore species. Then we’ll compare the distributions with the areas with the best greenery and the areas where lions congregate. We’ll be able to see if different herbivore species distribute themselves in different ways. And we’ll be able to see, over time, how these herbivore distributions change with dry season, wet season, droughts, and floods.