The Coexistence and Distribution of Seed-dispersing Animals
AuthorDittel, Jacob William
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This dissertation set out to answer two questions of seed-dispersing animals; what is the distribution of seed-dispersing animals across North America and whether a specific behavior can support the observed diversity in a subset of seed dispersers, scatter-hoarders. I begin with a broad introduction of food-hoarding and the importance of the behavior for both the animals hoarding food, as well as the plants having their seeds hoarded. In Chapter 1, I investigated how one particular behavior, cache-pilfering, may support diversity in species rich rodent communities despite differences in food-hoarding behavior. In Chapter 2, I examined whether rodent community structure influenced the rate of cache-pilfering. Specifically, I was interested in whether community composition or rodent abundance affected the frequency of cache pilfering across western Nevada. Finally, in Chapter 3 I was the first to elucidate the distributional patterns of two seed-dispersing guilds across North America. In addition to describing the distribution of seed dispersers, I also investigated whether or not the distribution of the plants they were dispersing or climatic variables could predict species richness and distribution. In Chapter 1, I was able to determine that cache-pilfering is reciprocal among scatter-hoarding species, but species that larder-hoard are unable to pilfer. This reciprocal pilfering could negate any harvesting advantages one species has over another, allowing for the coexistence and maintenance of species diversity witnessed in many rodent communities. In Chapter 2, I discovered that cache-pilfering is highly correlated with rodent abundance and not rodent richness. These results suggest that individuals of different species pilfer at similar rates, further supporting reciprocal cache-pilfering. Finally, in Chapter 3, I was able to determine the distribution of all North American seed dispersers; richness of these animals is highest in the southwestern portions of North America and decrease with an increase in latitude and in eastern North America. This work was the first to describe the distributional patterns of seed dispersers in North America, and recognize an apparent mismatch in richness between animals and the plants they disperse.