Are Human-Caused Ecological Invasions Good for Evolution and Diversity?
Burmese Python in Florida
Today I read of another huge snake finding in Florida that got me thinking once again about invasive species and evolution, as did the original story from earlier this year in which I learned of the invasion. ((python image copyright Key West Magazine))
Over the past eight years, a population of Burmese pythons has been exploding in the Florida everglades. As of 2007, the population had risen from essentially none (other than the occasional recaptured pet) to an estimated 30,000 pythons (also see this report from the University of Florida).
We often hear in the news about some invasive species or another and how the state involved is seeking to exterminate or halt the invasion. Obviously, many of these invasions can have disastrous consequences on the local ecology. The pythons may endanger many threatened birds of the everglades as well as everything else small enough to fit through the giant python maw. However, as we heard in this incredibly interesting study from August, some of these invasions may actually trigger bursts of increased biodiversity.
Timber Rattlesnake in the Ozark Mountains
To be upfront, I am not an ecologist, though I have studied ecology a fair bit during my earlier years in biology (I actually once spent a summer radio-tracking timber rattlesnakes in the Ozark Mountains). Thus, I certainly wouldn’t claim enough expertise to suggest anything about the true effects of ecological invasions.
But I do wonder about the type of world we as humans wish to create and maintain around ourselves with our increasing ecological understanding. It seems to me that the picture often painted by ecologists and conservationists is one in which every species on the planet right now becomes saved, in its current habitat and in defined “healthy” and “stable” ecosystems. Of course, none of us believes that we can save all ecosystems, or perhaps even most of them – what with the rampant destruction and fracturing of almost every habitat in every corner of the planet. Nonetheless, even if we could, is that really the goal we should be reaching for?
Do we want every current species to continue its existence in its current form? Is not extinction of some species necessary for the “progress” ((by progress I just mean change. Obviously there is no such thing as “progress” from some lower quality to a higher one when it comes to evolution – except in fitness in a given niche)) of others?
Rocky invades my porch. I couldn't resist giving him a cracker.
Unfortunately, the positive or negative effects of a particular invasion or ecosystem change can never be fully understood except in hindsight – and even then, our understanding of the outcome is only tenuous. So how are we to decide which species we should consider lost causes? Which are too specialized to survive long term on an inherently changing planet? Which should we support?
Granted, all of these questions rest on the assumption that our own species will be a long-lived one – long-lived on evolutionary time scales, which seems to me an extreme unlikelihood. But suspend your disbelief and imagine that our species continues to be the caretaker of this fragile little ball in space for eons to come, in some form or another. What do we wish to become of the varied ecosystems of our world? Do we wish to simply maintain the life and habitats in the still-natural parts of our lands, and allow the species to evolve within the limits of those fractured areas? Or should we allow any species to gain holds on whatever niches they can, and allow natural selection to work its magic as it has for 3.7 billion years?
We know that the vast majority of these invasions occurring in ecosystems across the planet are due to our own machinations. Ignorance and blindness to the challenges of caring long-term for enormous predatory reptiles led to the python population in Florida. Ballast water has deposited invertebrates and microorganisms in waters far flung from their original homes. So how do we decide when a particular invasion will be beneficial and in line with what nature might have done on her own anyway? How do we decide when a particular creature has "earned" it's invasive rights?
Not as pretty as a toadstool, but hey - it's a fungus.
I don’t claim to have even the vaguest answers to any of these questions. I welcome any of you true experts in ecology and evolution to point out any problems with these thoughts, or thoughts of your own. These questions seem largely philosophical at their base, but could conceivably have practical consequences in the far-distant to not-so-distant future. And they can ultimately only be answered by you ecologists and evolutionary biologists and the scientific knowledge you produce. The implications of these invasions and our place as both the cause and regulator of their effects simply fascinate me. Will we now become the primary constraint against which all selective pressures rest?
Or will our species die in a few century-long seconds, rendering all of the above completely moot?
Note: It turns out that the snake found this week is a red-tailed boa constrictor and not part of the python population.
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