Population and community responses to anthropogenic environmental changes

Abstract

Humans are dramatically altering the planet. I use classic ecological theory, original conceptual models, and a novel analytical tool (Rank Occupancy-Abundance Profiles; ROAPs) to explore the effects anthropogenic changes have on plant communities and bird populations. Chapter one investigates the influence of nutrient deposition on native prairie grass communities. I show that soil phosphorus levels alter plant diversity by changing the degree to which mycorrhizae benefit plant species. Chapter two investigates plant extinctions in a fragmented landscape. Extinction rates of early-successional plant species on large versus small habitat patches vary according to species' life history traits. In Chapter three I quantify declines in North American bird species over the past 30 years. Nearly 20% of the 209 birds sampled are declining significantly; local densities tend to decline prior to occupancy. Results from this dissertation confirm that humans are dramatically altering the relative abundance of species--at local, landscape, and continental scales.