UC San Diego

Energy is a core ecological currency and modeling its fluxes has provided important insights for fundamental questions of both species - environment interactions and ecosystem processes. The energetic need of species has received attention as being a core ecological trait that may reconcile the two perspectives. However, researchers have previously relied on crude measures of energy needs, depending on proxies in lieu of direct measurement. In addition, an integrative energetic framework accounting for species energy needs, energy flow through ecosystems, and energetic interactions between species is lacking. I present such a framework here and consider the energetic position or "metabolic niche" of a species in an assemblage. Primary productivity required (PPR) measures the amount of energy from primary productivity required to sustain the daily energy needs of a species. PPR quantifies the "metabolic niche" of species by accounting not only for basic energetic requirements, but also energy flow (and importantly, energy loss) in animal communities. Thus, PPR extends the species-based approach to consider potential constraints of community assembly at the ecosystem level.

In Chapter 1 I present justification for the use of PPR as a valuable measure of energy needs in ecological studies at both the species and community levels. I quantify PPR for all mammals and birds globally and provide a first exploration of the major patterns. Further, I discuss implications of PPR across the fields of ecology, evolution, and conservation biology.

In Chapter 2 I develop a model using PPRs of species to predict community-level abundance distributions. I show that PPR, by quantifying a single dividable resource axis, places species energy needs in a community context and provides accurate prediction of species abundance distributions.

In Chapter 3 I quantitatively describe the strong relationship between energy needs and population abundance. I explore additional biotic, abiotic, and biogeographic predictors of abundance, highlighting the fundamental importance of energy needs and, after controlling for PPR, the lessened value of some predictors previously thought significant.

In Chapter 4 I explore geographic patterns of community PPR distributions and describe how analyzing the shape of those distributions provides insight into how animal communities are assembled.