Date of Degree

2-2020

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Lisa Manne

Keywords

species distributions, climate change, birds, North America, community ecology

Abstract

Species distributions are becoming increasingly altered by climate change which has been identified as one of the leading threats to biodiversity through altered community composition. I address changes in species distributions of North American birds and how species responses affect community assemblages, functional traits and temporal trends in biodiversity. Chapter 1 investigates inter-seasonal differences in range shifts for 77 species of North American migratory birds. I quantify how shifts between winter and breeding ranges have potentially impacted migration distances. I found that winter range shifted predominantly northward while shifts in breeding range were more variable. These disproportional shifts have caused decreased migration distances. Species in this study tracked their historic temperatures and precipitation conditions in winter, but only tracked precipitation during the breeding season. Chapter 2 focuses on species-specific responses to climate during the breeding season, and how changes in species distributions can alter community composition. I evaluate the temporal changes of two community indices, the Community Temperature Index (CTI), which measures contributions of “warm” or “cool” dwelling species in a community and then establish a new index, the Community Precipitation Index (CPI), which measures relative influences contributions of “high precipitation” or “low precipitation” affiliated species. CTI and CPI significantly increased over time, though the strength and significance of these relationships varied at difference latitudes. Most changes were characterized by southerly species moving to higher latitudes and concurrent decreases in “cool” and “low precipitation” species affiliated with urban and grassland habitats. Chapter 3 builds on the results from Chapter 2 and investigates if these community indices inform alpha (α) and beta (ß) diversity. Species richness decreased over time at the regional scale, and varied with latitude. CTI varied inversely with richness, while CPI showed a positive relationship. Beta diversity also changed over time, driven by biotic homogenization at higher latitudes, and greater community dissimilarity at the lowest latitudes. Multi-species, inter-seasonal studies are scare in the literature. The complementary analyses presented in this dissertation provide new insights into the macroecological responses of North American birds to changing climate at the population and community levels. Chapter 1 demonstrates that wintering and breeding range shifts have occur independently in North American birds and is the first study to evaluate independent range shifts using multiple species. Chapter 2 addresses changes in community composition in response to temperature and precipitation and show that species contribution to CTI and CPI are different among latitude bands. Chapter 3 expands on Chapter 2 and demonstrates that temporal trends in species turnover and nestedness have resulted in biotic homogenization between the highest latitudes of the study. While communities become increasingly composed of southern dwelling species moving north, we observe decreased species richness. These chapters combined offer perspective on population and community changes that can be used in informing conservation at the macroecology scale.

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