The importance of interactions between deterministic mechanisms that affect species diversity

Background/Question/Methods

For nearly a century, ecologists have attempted to define the most influential mechanisms that drive patterns of species diversity. Yet, there remains plenty of debate over the relative importance deterministic mechanisms such as area, energy, and predators. Although a lot of research has been done on the effects of deterministic factors on species richness, most researchers assume independence between deterministic factors. For example, the Species Area relationship and Species Energy Relationship do not include interactive effects between energy and area, but some researchers have addressed the importance of the species energy-area relationship. The importance of interactions between deterministic mechanisms becomes clearer when reviewing results from studies of species diversity that manipulated a single deterministic factor. For example, some researchers have found that predators positively affect species diversity, but other researchers suggest only keystone predators positively affect diversity, and some researchers have found that predators greatly reduce diversity. These confounding results indicate that interactive effects between deterministic mechanisms are important, and may have great influence on the maintenance of species diversity. To assess the importance of interactions between deterministic factors on diversity, I stocked aquatic mesocosms with a regional species pool of zooplankton (70 species) with three deterministic treatments: area, energy, and predators. The regional species pool was created collecting zooplankton from 15 natural and man-made ponds at Tyson research center, Missouri, USA. I used 16 small and 16 large mesocosms with a fully factorial design to manipulate predators (with and without) and energy (high and low) in the differently sized mesocosms. 

Results/Conclusions

The results from my study indicate that predators, energy, and area affect species richness and species abundances. Importantly, there were strong interactive effects between the treatments, where predators had a greater effect in large, well-connected tanks with high energy, but a stronger effect in poorly connected tanks and low energy. Additionally, when the species accumulation curves were rarefied to account for differences in species abundances among treatments, none of the deterministic factors affected species diversity, therefore I found strong support that a sampling effect greatly impacts the results of studies of species diversity. The strong sampling effect indicates that deterministic mechanism play a complex role in affecting species diversity.