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Species, Part One

February 25, 2017

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Darwin’s Finches, courtesy of Welcome Images

In the next few posts we’ll be discussing the concept of species and why that’s important to urban biodiversity conservation. I think a common conception of conservation work is that it’s all about protecting species, but that isn’t quite right. Conservation projects actually target three levels of diversity: species, yes, but also genetic and ecosystem diversity. However, being humans, we’re attracted to things we can relate to, and most of us can relate better to organisms than to genes (and even more so to individuals), and perhaps this is why there is so much focus on species.

Many people remember the definition of a species that they learned in high school biology: members of a species can interbreed with each other and produce viable (i.e., alive and non-sterile) offspring. This is what’s commonly termed the biological definition of a species. But the concept of a species is actually quite slippery – and that’s not even going into the differences between a species and a subspecies (deciding whether two populations are different enough from each other to belong to different species, or just different enough to belong to separate subspecies of the same species, can be quite the debate).

Canids provide a good example of why the biological definition of a species can be problematic. No one would argue that a wolf is not a dog, which is not a coyote, but all three can interbreed and produce viable offspring.

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Thomas Brown, 1829. In the Public Domain.

So, how else might we go about defining the concept? Traditionally, the morphology of animals was considered, with like grouped with like. This was done by looking at the color of specimens, taking measurements of various body parts (skulls, other bones, wingspan, and so on), body parts, and other physical components of organisms that can be measured and quantified. Statistical tests were then done to look at how these measurements could be best grouped together. If a bunch of specimens best group together into two groups and not only one, the theory goes, then you’re looking at two separate species.

These days we can also look at this from the molecular level, through genetic analysis of a specimen (or, rather, of a very small piece of a specimen – hair and scat can be used for non-invasive testing). In some ways this is similar to looking at the morphology of a specimen – you’re basically counting genes and seeing how many differences there are between one specimen and the other. That’s of course an over-simplification of both the process and the analysis, but for the purposes of our discussion, we’ll leave it at that.

On a tangent, I highly recommend a book that came out last year, The Dragon Behind the Glass: A True Story of Power, Obsession, and the World’s Most Coveted Fish, by Emily Voigt. The book isn’t entirely relevant to the urban wildlife world (and yet is entirely relevant in some ways), but it does a great job of discussing the slipperiness of the species concept and the benefits and drawbacks of using a molecular definition.

More on species to come!

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