Dr. Justin Yeakel, UC Merced
Title: On the dynamics of mortality and the ephemeral nature of mammalian megafauna
Abstract: The vital rates constraining energy flow through consumer-resource interactions largely vary as a function of body size. These allometric relationships govern the dynamics of populations, and the energetic constraints induced by different sources of mortality influence small- to large-bodied species in different ways. Here we derive the timescales associated with four alternative sources of mortality for terrestrial mammals: starvation from resource limitation, mortality associated with aging, consumption by specialist to generalist predators, and mortality introduced by subsidized harvest. The incorporation of these allometric relationships into a minimal consumer-resource dynamic system illuminates central constraints that may contribute to the structure of mammalian communities. Our framework reveals that while starvation largely impacts smaller-bodied species, the allometry of senescence is expected to be more difficult to observe. In contrast, external predation and subsidized harvest primarily influence larger-bodied species. The inclusion of predation mortality reveals mass thresholds of mammalian herbivores at which dynamic instabilities limit the feasibility of megaherbivore populations. Moreover, we show how these thresholds vary with predator-prey mass ratios, a relationship that is little understood within terrestrial systems. Finally, we predict the harvest pressure required to induce mass-specific extinction, and compare these values to estimates from episodes of both paleontological and historical megafaunal exploitation. With co-authors: Taran Rallings and Chris Kempes.
Tuesday 3 October 2023