Invaders all around us

Many of us are horrified by stories of invasive species wreaking havoc on ecosystems, upsetting the natural balance, and even impacting humans directly.

The example of Chikungunya that I mentioned in my last post ( demonstrates two important aspects of the situation. First, humans actually very often transport the invaders to their new habitat, either unintentionally or on purpose. And second, humans are often affected directly by what the invasive species do. Chikungunya shows these two aspects perfectly. It is a tropical disease that has spread rapidly through the Caribbean Islands in the past few years. Many patients diagnosed in the US contracted the disease, which is transmitted by mosquitoes, during travels in that area. Even landlocked Oklahoma is affected (,_Prevention,_Preparedness/Acute_Disease_Service/Disease_Information/Chikungunya_.html).

Several examples of invasive species make it into the news, mainly because they involve spectacular species, like the Burmese Python, currently impacting Florida. This beautiful snake species from Southeast Asia, was brought to Florida as pet and made it from captivity into nature, where the snakes are doing so well that they are held responsible for severe declines in several species of mammals ( One ironic wrinkle of this is, that Burmese Pythons are considered to be vulnerable to extinction in their natural range. Interestingly, South Florida is such a hotbed for invasive species from the tropics, that the Burmese Python shines a spotlight on the situation, even though it may not be the biggest problem for the ecosystems in South Florida.

In the bigger picture Biologists are trying to grapple with invasive species on a more than just the practical level. On that level, all hope is lost already: invasive species are already part of a wildly unnatural situation surrounding us. But what do invasive species represent? In a way, we are making judgment calls based on our values: many people, and not just biologists, place a high premium on ecosystems that are as unperturbed as possible. These places are becoming increasingly rare and more and more difficult to protect. These ecosystems represent the outcome of eons of evolution and allow us to study both its outcome and process undisturbed by human activity. Often invasive species ruin the existing ecosystem, and our chance to study unique situations is lost forever. Under this view, for example, the introduction of placental mammals to Australia was an unmitigated disaster leading to the demise of the resident marsupials.

Another view is to see opportunity for studying both the ecology and evolution of new, albeit unnatural assemblages that are essentially created by humans and attach value to those. Why can’t a new, invasive plant have the same value as the indigenous plant it replaces? This is a view partly proposed by Emma Marris in her publications ( How do we treat our crop plants in this context? Almost all of them are invaders, right? Looking at the beautiful oak tree in my backyard makes me wonder: Does a non-native tree in the mixed grass prairie of Oklahoma not give me the same esthetic pleasure as the same tree in a natural forest?

These are questions both debated by biologists and the general public, often with deeply personal answers. And, as we inhabit the Anthropocene longer and longer, these questions will present themselves with increasing urgency and have important impacts on conservation policies.


Biology in a changing world.

Our world is undergoing a massive change, induced by humans. There is no debate about this among scientists. There is debate, however, about the consequences of this change.
Like many other organisms we actively alter our environment and become ecosystem engineers ( A classical example for this process is beavers that build dams and create lakes they can use as habitat. Of course this comes at the expense of the existing habitat. The plants in the now flooded area are obviously going to drown. Termites build massive structures that house their colonies. Another example is the evolution of photosynthetic algae that led to the release of large amounts of oxygen, causing the extinction of unique biota that were intolerant of oxygen. Our elixir is another organisms toxicant.
Most importantly, the activities of ecosystem engineers create new habitats not just for themselves, but for many other species that can use them, but at a cost.
Clearly, major changes to the environment by organisms are neither uniquely anthropogenic nor new.
While ecosystem engineering always has an impact on the environment, sometimes even at a large scale, I would argue that the human impact on the planet in the Anthropocene is unique in tempo (see also the post by Lynn Soreghan: I have seen unique elements of the natural world that my grandchildren will not be able to see because they have been altered.
Biologists debate what the consequences of our actions are. Models of what may happen to species and ecosystems as climate change progresses are abundant and often offer a bleak outlook: species that are already vulnerable are likely to disappear forever. Some scientists argue that we are in the middle of what they call “Anthropocene defaunation” (Dirzo et al. or the Sixth Extinction (see e.g. the book by Elizabeth Kolbert, The Sixth Extinction). Dirzo et al. are especially alarmed by the loss of range for many species and the resulting reduction in abundance of species. This trend is found across all taxa studied, but the exact mechanisms need further investigation.
Now, why should the extinction of a nocturnal mammal or a shift in the range of an obscure insect interest us? Apart from an ongoing, and loud, debate about the value of nature, ecosystems, and species, all of these changes we induce are also impacting us humans in countless ways. The prospect of a future ecological disaster is haunting and nightmarish, and indeed the changes also impact us directly. For example, many human diseases are transmitted by insects, and humans often help insects colonize new habitats—as with the fast sweep of Chikungunya, which is transmitted by mosquitoes. Chikungunya, is a debilitating disease, which causes high fevers and strong joint pain ( This import from Africa has recently swept through the Caribbean, and has now reached the US in Florida. Travelers help this disease to spread, but areas of the continental USA made habitable to the mosquitoes by climate change give it a permanent foothold the continental USA.
It seems that altering your own habitat can also backfire, clearly this is the case in humans.

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