Having just learnt about the Grants in community ecology class, who famously continued Darwin’s work in studying the finches of Galapagos Islands for some 36 years, I was bemused and surprised when WIRED reported a new species discovered by them yesterday. Topics brought up in community ecology class keep popping up in the news! Read about it here.
So what is it with all this species talk? Here’s some quick background.
The systems of classification we have today in biological science for living organisms have many levels. They start from Domain, Kingdom, Phylum, Class, Order, Family, Genus and finally Species. Of all of these levels, note that the only “natural” classification is species – why? Because we recognise the individual for itself, and the species is a fundamental unit that is not grouped together with other individuals based on a set of characteristics that people think is important, because this can be flawed. Note that classifications are a human construct after all, just as the theoretical science we make our rules in the world by are simply hypotheses that have yet to be proven wrong.
Scientists in the past first started classifying animals much like how a 5 year old kid naturally learns to put things together. If they look like the same thing, it makes sense that they are the same kind of thing. Fishes look like fishes, and insects look like insects. We call this morphology (structure, or external form). Are things really that simple though?
As the earth aged and thousands and millions of years passed, species on different continents adapted to the different conditions present there. In certain parts of the world however, this set of abiotic conditions (things like amount of moisture, air, temperature, nutrients, etc) were similar – and living organisms living by this same set of conditions may have adapted to this set of conditions, growing to have the same kind of external form, and thus looking the same. We call this convergent evolution. Click here for more examples of convergent evolution.
Source: Ivana Stehlik’s lecture notes for Environmental Biology, University of Toronto.
Lineage-wise though, they may come from extremely different ancestors. Cacti are one example. Desert conditions are so harsh that only a certain set of characteristics have prevailed, and plants from different families (DNA-wise) in different deserts have the same characteristics: needle-like leaves, succulence, deep roots, etc. On the other hand, two individuals that look completely different can be the same species: a few cases in point are ants and termites. Ever see how different soldier ants are from worker ants? And look at the queen!
Soldier termite with big bulbous red head; alate reproductive is whitish in colour, worker termites are the rest in dull grey and cream colour. Picture by Nuwan, from my collection (for more termites, see my page here)
Okay, so we know morphology isn’t enough. So what exactly is a species? This kinda seems pretty clear cut, doesn’t
it? Well it actually is kind of fuzzy – though most scientists agree on
using the Ernst Mayr biological species concept:
“Groups of populations that can actually or potentially exchange genes with one another and that are reproductively isolated from other such groups”
Why is that unclear? It sounds like its pretty clear-cut. Theoretically, that is. Realistically, its difficult to actually determine if individuals from two populations are capable of reproducing together and producing viable offspring. Take for example some common birds of Singapore. To test with certainty if the mynahs, crows, sparrows and pigeons are different species (setting aside structural differences), one would have to place them together in a setting and allow for enough time to see if they would breed together. If they breed and produce infertile offspring, it’s ruled out. But if they do produce viable offspring, one would then have to follow the case back to the wild, to see if their territories overlap enough that copulation is possible, and then observe if breeding between the two occurs. Extrapolate that to birds of a country. To test this with all the birds of a country, would be a nightmare. Read more about other species concepts here.
It’s not so clear after all, and there are many other things to take into account. What about organisms that breed asexually, such as fungi and aphids? Or living things that hybridise? The picture gets more fuzzy as we consider more things. Remember though, that this is a human construct, and we can keep coming up definitions that fit best as they can; sometimes they don’t fit for all cases, and we may need separate definitions for others. It’s not made in stone! For a quick, easily absorbed lesson in speciation, go here (recommended!).