The Nitty-Gritty of Community Ecology and Biogeography
Whenever I tell people that I am a research assistant in the primatology lab at UMass, I get a few responses:
“The what lab?” (“Primatology—I can tell you a ton of fun facts about different kinds of monkeys if you’re interested!”)
“Wait, there’s monkeys on campus?!” (“No, but I do look at pictures of them!)
This is usually followed by: “So… what exactly do you do?” This is a little bit more difficult to answer.
One project we are currently working on in the lab focuses on primate biogeography and community ecology. Biogeography is defined as the distribution of organisms through space, in this case, specifically primates. Community ecology is the study of interactions between all living inhabitants in an area (e.g. park); this includes the plants, other animals, and even the insects. Basically, we are trying to understand all of the factors that can affect primate distribution and their community structure.
To understand community ecology, it is important to ask: how do primates compete with other animals? There are various ways animals can compete with each other, including the popular "simulated' competition that occurs every year during March Mammal Madness. Though in real life, food is a main reason why animals compete with each other. Diet in primates varies from species to species; most species will fall into several categories. They can be frugivory (they eat fruit), folivory (leaves), gumnivory (tree gum), granivory (seeds), insectivory (it means what you think it means), and faunivory (animals). For the most part, primates get a majority of their energy from plants, with some exceptions.
The only fully carnivorous primates are tarsiers. They are primarily insectivorous, but have also been documented eating birds, lizards, snakes, and even bats! Tarsiers are a part of the Asian primates being analyzed in the biogeography project, and are only found on islands of Southeast Asia.
But, what happens if you're not an exception (like tarsiers) and you like the same food as your neighbor?
Interspecific (between species) dietary competition puts greater pressure on frugivores than folivores. Trees can only produce so much fruit. Once the fruit is gone, it's gone until the tree fruits again. Leaves, on the other hand, are a bit easier to come by. In some places, a dietary niche can only be utilized by one species; another cannot coexist there. For example, it has been suggested that in the Neotropics, sloths may fulfill the folivore niche that folivorous primates fill in other regions of the world.
To analyze this community dynamic, the lab is first identifying which species of primates, civets, and giant squirrels are found at various sites all around Asia.
Civets are small mammals (which I think look like an adorable cross between a cat and a weasel) that are often omnivorous. You can think of them as similar to the North American raccoon--they eat a wide range of things. The golden palm civet, for example, eats fruits and berries along with invertebrates and a range of small vertebrates.
I mentioned that the lab is also looking into giant squirrels. I didn't stutter; giant squirrels are real. And, they're also pretty cute!
The photo to the left shows the Indian giant squirrel, or, Ratufa indica. Fun fact: their tails alone can be up to two feet long! Indian giant squirrels are seed dispersers in their communities; just like many primates. They are omnivorous, eating fruits, flowers, nuts, bark, bird eggs, and insects. Just like the civets, these mammals are potential competitors for food.
Besides eating the same things, how exactly does food competition work? Direct interactions can include displacement at food sources (i.e. pushing another animal out of the way or, simply, making them move away). Indirect interactions can involve scramble competition, consuming as much food as possible before competitors arrive (think about a piñata at a kid's birthday party and the mayhem that ensues after its burst).
There's a lot more that can be said about dietary competition, but... I'm hungry.
Primates also interact with other animals through a communal sort of security system: alarm calls! Alarm calls are vocalizations that detail information about a predator to the group. They can convey predator size, distance, threat level, and category. In some primates, they can even identify a specific predator. A recent 2013 study, Cäsar et al., looked at black-fronted titi monkey alarm calls and found that the calls identify not only the type of predator, but its location as well.
Among others, vervet monkeys are known to make predator-specific alarm calls (listen to some calls
here). On the other hand, yellow-casqued hornbills (a species of bird) have been documented to be able to distinguish between predator-specific alarm calls from Diana monkeys.
By examining whether or not these non-primate animals are more or less likely to live with with particular primate species , we can begin to look into how they affect primate community structures. Why is it important in the first place, though? Recent studies support the idea that similar vegetation leads to similar mammalian community structure across continents (Louys et al. 2011). This may also occur in a temporal context. Are certain primate communities associated with specific types of habitats in the fossil record?
This matters because we ourselves are also primates and descendants of extinct primates. If we can begin to piece together the community structures of our human ancestors, then not only can we begin to understand our origins, but, we can begin to understand ourselves in the present. Were there changes in environment around the same time as major advances in our evolution--for example, larger brain size and tool making--and can we determine this from environmental factors? How did these ancestors affect primate community structure? Could these factors happen again? Have they already?
Tarsier photo by Peter Slavik
Golden Palm Civet photo by Anjitha Senarath - http://www.fluidr.com/photos/anjitha/31914993403/
Indian Giant Squirrel photo by Vijay Cavale - http://www.arkive.org/indian-giant-squirrel/ratufa-indica/image-G37587.html
Vervet monkey photo - https://the100countriesplan.com/2015/05/30/zimbabwe/