Saturday, February 13, 2010

How to Study Invasive Species, a Conservation and Ecological Imperative

The January edition of The American Midland Naturalist includes an essay by Daniel Simberloff (University of Tennessee) that bears the questioning title “Invasions of Plant Communities – More of the Same, Something Very Different, or Both?” As alluded to by the interrogative title, the central theme of the piece is whether or not the ecological characteristics displayed by invasive plant species are similar to those demonstrated by native plants during the natural succession of a vegetative community. In other words, do the strategies and tactics employed by invasives during the conquest of new habitats follow similar patterns of recruitment and regeneration as those exhibited by native plants in moving a community towards maturation? Or, in contrast to natural succession patterns, do invasive species have unique biological or demographic qualities that require a novel or specialized approach to studying their dynamics?

Daniel poses great questions, because, recognizing that we live in a world of mass travel and shifting climates, the study of invasive dynamics is of critical importance to the conservation of biodiversity – protecting natural habitats and native species. In addition to conservation, by researching the interplay of native and non-native species during the establishment of ecosystems we will undoubtedly gain a wealth of knowledge in regards to the feedbacks between evolution and ecology (i.e. how do those species lacking a shared co-evolutionary history come to achieve a stable strategy for survival?).

So, with that in mind, here’s my answer to Daniel’s question: Both!

Cause’ in a nutshell: Although invasive species will exhibit some life-history strategies comparable to those of plants from the newly invaded habitat (growth pattern, time to reproductive maturity, etc…) they will also be subject to environmental factors of a temporal nature that do not influence the natives (at least to the same extent).

Said differently, because the growth, reproductive habits and resource needs of an invasive likely mirror those of at least one native plant, the invasive could theoretically replace the native with little ill effect to the ecosystem; the invasive could fill the niche left void by the out-competed native plant without disrupting the energetics of the plant community as a whole. BUT, at the same time, a newly arrived invasive species may have a distinct advantage over a native transient because it is completely foreign to the ecosystem. For example, being unrecognized by its new environment the invasive may, for a period of time, be buffered against attack by herbivores, parasites and other stressors that may be actively reducing the fitness of the locals.

Similar to the above potential advantages, the invasive could also be subject to the detrimental affects of being an outsider - brought about by a lack of co-evolved pollinators, ect…

I would also argue that the above temporal effects associated with being a novel addition to an ecosystem, though only short-lived, can be magnified greatly by stochastic events. I would suggest this because – generally – variability in initial survival rates contributes greatly to ultimate establishment; often more so than reproductive strategy, which is subject to greater phylogenetic constraint (i.e. initial survival is more important than in choosing to produce many low-quality seeds when young, or to conserve energy and produce fewer higher-quality seeds when older).

Daniel’s essay is a great read and offers plenty of real-world case studies to emphasize his points; definitely check it out!

Simberloff, D. (2010). Invasions of Plant Communities – More of the Same, Something Very Different, or Both? The American Midland Naturalist, 163 (1), 220-233 DOI: 10.1674/0003-0031-163.1.220

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