Characteristics such as high dispersal ability, persistence following low original abundances and competitive ability are thought to help a species become established into a novel community. However, most natural communities are so complex that it is extremely challenging to simultaneously address multiple factors affecting invasion success, leaving the predictive power for invasion success ambiguous. Due to this complexity, it has also been challenging to examine more than one trophic level, much less an entire community, making it extremely difficult to assess how factors involved in community assembly affect invasion of a new species and how, if successful, an invader affects community dynamics. I used the microscopic food web found inside pitcher plant (Sarracenia purpurea) leaves as a surrogate for larger scale systems to test which characteristic (competitive ability or propagule pressure or a combination of the two) was a better predictor for invasion success of the intermediate (protozoan) trophic level. The importance of these characteristics for invasion success was tested with and without the presence of a top predator, at high and low resource availability, and at increased resident protozoan diversity.
Results/Conclusions
I found that the competitively dominant intermediate trophic level invader was much more successful at invading and establishing in all communities at all initial densities than the less competitive protozoan invader. The competitive dominant invader was unaffected by resource availability and predation, and even successful at invading a more diverse community. In order to test the effect these invaders had not only on resident protozoan diversity but also the bacterial prey of the bottom trophic level, I incorporated 16s rRNA clone library techniques. These techniques allowed for a much more in-depth examination of the bacterial diversity in the resident community and how that diversity was affected by its consumers. By using these techniques, it was found that when resources are not limiting, the type of invader (competitive or less competitive) shapes the presence, abundance and diversity of the resident prey community.
