Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Committee Chair(s)

S. K. Morgan Ernest

Committee

S. K. Morgan Ernest

Committee

Peter Adler

Committee

Michelle Baker

Committee

Mevin Hooten

Committee

Ethan White

Abstract

Ecological theories often hinge on species interactions, or how the species in an area "see" other species with whom they have to share food and space. Despite the contributions theoretical coexistence models have made to our understanding of species coexistence, it can still be difficult to match these theories with data from real communities. For example, we know of many species that are very rare where they occur. Theory predicts that these species should quickly go extinct, but they do not. I use simulations and real data to show that rare species are rare because they are more self-limiting. Self-limitation occurs when a species is more negatively affected by other members of the same species than it is by members of other species. The stronger this self-limitation is, the more a species is negatively affected when its numbers get too high. While this can prevent these species from becoming abundant, it also means that a species with strong self-limitation is more positively affected when its numbers are very low, ie. it can rebound quickly when its population becomes small. I also show with simulations and data that rare species that are more self-limiting are less abundant, but they are also less likely to go extinct as a result, explaining why we see rare species so often in nature.

Another way to describe how species that co-occur at a site "see" each other, instead of using abundance, is to use energy use. Species that are very different sizes use very different amounts of energy, because their metabolic rates are different. When co-occurring species are very different sizes, it is more likely that those species are more impacted by how much energy they each use, rather than just their abundances. I look at two different community patterns, the self-limitation described above and a measure of community variability called compensatory dynamics, to determine if energy use is a better currency to use when looking at community patterns. Energy use gives very different estimates for the dynamics I looked at, which could lead to different conclusions about what processes are important for a particular species. But energy is not as important when looking at large-scale patterns. The results across all species do not differ very much when using abundance compared to energy use. The conclusion using either abundance or energy use is that strongly self-limiting rare species are common.

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