Climate Change and Population Dynamics of Invasive Species

Most invasive species are wimps, but some are Godzilla types.
— Professor David Allan

According to recent studies, poison ivy is one of those Godzilla types when it comes to rising CO2 levels. Two studies, one by Duke University researchers and the other by USDA in Maryland, show that poison ivy flourishes under conditions of higher CO2. The plant grows larger and faster, is more resistant to disturbance, and creates oils that are more irritating to human skin. As climate change increases global CO2 levels, poison ivy is beginning to appear (and take over) regions that were previously unsuitable, such as the arid South and West. Higher average temperatures also increase the growing season for poison ivy in locations that were previously too cold to support it. (http://thelede.blogs.nytimes.com/2007/06/27/poison-ivy-now-with-stronger-poison/ , http://online.wsj.com/article/SB118281532052547766.html?mod=rss_Today%27s_Most_Popular)

So what does this mean in terms of population dynamics? Poison ivy is an early colonizer, an r-selected species, that grows quickly and in harsh conditions or places of recent disturbance. Its rapid growth rate allows it to take over areas previously dominated by native species, particularly when CO2 levels or other conditions favor its growth. Thus, poison ivy spreads rapidly.

Other similarly Godzilla-like species that are poised to take over the world with climate change are:
- Japanese beetles
- Fire ants
- Ticks
- Mosquitoes

Note: Another PNAS paper, entitled "Sharply increased insect herbivory during the Paleocene–Eocene Thermal Maximum" (published February 2008), suggests that "increased insect herbivory is likely to be a net long-term effect of anthropogenic pC02 increase and warming temperatures." The authors examine plant fossils from Wyoming to analyze combined effects of temperature and pC02 on insect herbivory during the Paleocene-Eocene Thermal Maximum, a global warming event "comparable in rate and magnitude to modern anthropogenic climate change." Perhaps not an example of invasive species per say, but a noteworthy change in ecosystem equilibriums. Read more at http://www.pnas.org/content/105/6/1960.abstract.

Each of these species seems to be r-selected, quickly reproducing, early colonizers, while the charismatic megafauna that are losing out to climate change seem to be k-selected (polar bears, penguins, elephants, humans). This trend probably speaks to the adaptability of r-selected species and their ability to survive in harsh environments. So now, politically, we have a new fear tactic in the call for climate change mitigation: if we don't take action now, the next few years will become exceedingly itchy.

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