Note: this post will work well with Crutsinger et al. 2008 and the post, “Genetic Diversity and Invasion.”
This graph is taken from Stachowicz et al. 1999 from the journal Nature. In this study the researchers asked the question, what is the effect of species diversity on the success of an invasive species? In this particular experiment the researchers used marine invertebrates communities to test the hypothesis that increased native species richness decreases the abundance of an invasive. Experimental communities were composed of 0-4 native species cultured on tiles. The invasive tunicate (Botrylloides diegensis) was then introduced into each of the experimental communities and its success was measured. The top graph (a) has community species richness (# of species) on the x-axis as the independent variable. The y-axis is invaders surviving as a percent as the dependent variable. The negative correlation shows that as species richness increases the percent of surviving tunicates decreases. This relationship suggests that communities that have greater species richness can slow or deter rates of invasion by exotic species more so than communities that are devoid of diversity. Graph (b) offers a hypothesized mechanisms for the observed pattern in graph (a). Graph (b) has the same independent variable, by the dependent variable in this case shows the amount of unoccupied space. The pattern in graph (b) shows that as richness increases that amount of available space (i.e. for invaders) decreases.
1. Why might biologists, managers, politicians, and citizens be worried about invasive species?
2. What are some local invasive species in your environment? What efforts are happening locally to manage these invasive species?
3. These patterns have been observed now in multiple systems (e.g. marine, plant, terrestrial.) How does observing similar patterns across systems and taxa support the general conclusion that higher levels of diversity can protect a community from invasion? Why is it good for science to test theories across multiple systems?
4. What are other examples of invasive species in marine or estuarine systems? What are some of the mechanisms by which these invasive species enter these new systems?