These data are from Crutsinger et al. (2008) from the journal Ecology Letters. In this study the researchers asked the question, does higher INTRAspecific diversity deter biological invasions. Many studies prior to this have demonstrated that communities with more species can slow rates of invasion more so than species deficient communities. Few studies however have look at intraspecific diversity or genetic diversity (# of different genotypes present). By manipulating the number of tall goldenrod (Solidago altissima) the researchers were able to assess the relationship between genetic diversity and the success of new colonizers or invaders. The top graph (a) has the number of genotypes, the metric of diversity, on the x-axis and total colonizer biomass on the y-axis. This correlation is significant and shows that with increasing genetic diversity the biomass of colonizers decreases. This graph suggests that communities with higher genetic diversity can resist invasion by other organisms (e.g. invasive species) better than communities with less genetic diversity. The researchers also hypothesized a mechanism to explain the observed patterns in the top graph. The bottom graph (b) has the same x-axis but the y-axis is now goldenrod stem density. Plots with greater genetic diversity have on average higher stem densities possibly reducing the available area for colonizing invaders to take root.
1. What is the difference in the patterns observed in graph (a) and graph (b), They are both hypothesis-based but in what ways do they explain different phenomenon (i.e. overall pattern vs. mechanism)?
2. What is an invasive species? Why might invasive species be of concern?
3. What are some examples of invasive species in your environment? How do they affect the environment?
4. How should we manage invasive species? Should we always remove them? How should we remove them (e.g. physical removal, poison, fire)?
5. How could you design an experiment to test the proposed mechanism of stem density?
6. What would you do if an invasive species became home to an endangered species? For example, in the Southwest United States nonnative tamarix (salt cedar) has been introduced into many riparian environments outcompeting native cottonwoods. Tamarix requires more water than cottonwoods and soils are becoming more saline; however, the Federally Endangered Willow Fly-catcher is able to make healthy and successful nests in the tamarix. How does this complicate restoration projects in the Southwestern United States? How might you managed this situation?