Wednesday, September 21, 2016

How Different is Different Enough?

By Jordan Daley
Science Outreach Coordinator



Photo by Michael Butler Brown
At first, I jumped for joy when I read this NY Times Science article the other day: A Quadruple Take on the Giraffe: There are four species, not one? It's fascinating! It's exciting! It sounds great: new species! Then I did my own double take, asking what does it really mean?

The premise of the study, published in Current Biology, is simple. The authors performed genetic tests on 200 individual giraffes from the existing 9 subspecies of Giraffa camelopardalis. Their findings show that some of the subspecies are far more different than we initially thought. The genetics show as much difference as a brown bear and a polar bear. So now we're looking at 4 separate species of giraffe, the Maasai, Northern, Southern, and Reticulated Giraffes, and among them, numerous subspecies.

This past spring VINS hosted a Brain Buzz event with our friends at the Dartmouth Graduate Office and the Upper Valley Food Coop. Michael B. Brown spoke to us about wildlife and energy development and offered us insight into one particular subspecies of the then singular giraffe species, Rothschild's giraffe. Michael described how this subspecies lives largely in isolation in very specific areas of Uganda and their numbers are low, only an estimated 1500. The IUCN classifies them as endangered. 

As if being endangered wasn't enough, the Rothschild's giraffe now finds it in another precarious situation- taxonomically confused. The authors of the September 2016 study suggest that the Rothschild's giraffe is actually so similar to the Nubian giraffe that we should consider them all just one species of Northern giraffe. 

Yet, this whole "how many giraffe species are there?" thing isn't entirely new. An earlier study published in BMC Biology in December 2007 indicates that giraffes might be as different as 6 or even 11 different species! That study gives the Rothschild's giraffe a whole species unto itself.

Bouncing around from subspecies, to species, back to subspecies, and now nothing very special at all, might seem like a downgrade for the Rothschild's giraffe, but what will the new taxonomy really change? I reached out to Dr. Doug Bolger, Professor of Environmental Studies at Dartmouth College, to learn more. Doug and Michael work together and both are interested in populations of animals and how they're effected by human impacts, including land use and development. 


When I first asked about the implications of this study, Dr. Bolger's first answer was to be expected, "Well, it's complicated." Sifting through the nitty gritty, we quickly settled into this question of "how different is different enough?" This is really at the root of all our taxonomic questions. 

As Dr. Bolger explained, there are lots of ways to determine the question of "how different is different enough?" There are theories that value geography, or ability to reproduce sexually, physical form, or any number of different characteristics. Carl Linneaus began to systematize our categories of species in the early 1700s, making observations of an animal's physical and behavioral forms. Since then we've found better and better ways to observe differences between animals. This 2016 giraffe study does the same thing Linneaus did when he first described the giraffe in 1758, but rather than describing physical features, it looks at the genetics. Naturally, when we zoom in closer and closer, we start to see different things, and our existing categories don't seem to fit anymore. 

These categories don't always work because they're static. Evolution, on the other hand, is constantly acting on the species. As observers, we're inspecting the ongoing billion year old process of evolution from just one point in time. Just like a photograph, our perspective doesn't really reveal the whole situation. Our categories are affected by that perspective. They can't really accurately reflect the diversity of species because that diversity is still undergoing a slow but constant evolutionary process. 

Of course, that doesn't mean we should just chuck them out the window- they're still useful because our human impacts act much more quickly than evolution. And however imperfect, they help us understand the needs of different animals, how they interact with each other, and what measures we can take to protect them. An example: red tailed hawks and Cooper's hawks both belong to the hawk family, Accipitridae, but the red tail is in the genus Buteo and the Cooper's belongs to Accipiter. Their different categories correspond to their body and tail shapes, hunting behaviors, and habitats. They have different needs and we need to protect habitat that is suitable for each species to thrive. We need categories to help us create achievable conservation goals that respond to human impacts. We need to understand the imperfect nature of those categories, so that we can be adaptable to new findings.

So for a giraffe like the Rothschild's, not having a category designation like subspecies, might mean that their specific conservation needs get over looked in the larger picture of Nubian or Northern giraffes. (For now, the IUCN still lists the Rothschild's giraffe as endangered and conservation efforts continue.) And yet, breaking down the larger genus of giraffes into four smaller and more precise species might mean that conservation efforts can have an even greater impact on each species. So whatever we decide about which groups are different enough, Dr. Bolger says, "What is clear is that the evolutionary histories of these four categories are longer and more distinct than we ever thought, and that is worthy of conservation." Here at VINS, we agree. 


Photo by Michael Butler Brown


No comments:

Post a Comment