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University of California Berkeley (2018)

A Century of Avian Community Change in the Desert Southwest

Iknayan, Kelly Jeanette

Titre : A Century of Avian Community Change in the Desert Southwest

Auteur : Iknayan, Kelly Jeanette

Université de soutenance : University of California Berkeley

Grade : Doctor Philosophy (PhD) in Environmental Science, Policy, and Management 2018

Résumé partiel
Species extinctions and population declines have accelerated over recent decades due to habitat destruction, overexploitation, and invasive species, with cascading effects on ecosystem functions and services as well as human well-being. Climate change has emerged as another powerful driver of species decline, one whose effects are beginning to intensify. It should lead to shifts in species distributions and rearranged communities, unless climatic disruption acts as a systemic threat leading to a community collapse. Desert birds comprise a species-rich, easily detectable assemblage, and are closely coupled to their physical environment, which makes them suitable indicators of climatic change. I assessed how desert bird populations have been impacted over the past century by resurveying 106 sites throughout the Mojave and Great Basin deserts that were originally surveyed for avian diversity in the early 20th century by Joseph Grinnell and colleagues from the Museum of Vertebrate Zoology at University of California, Berkeley. Multispecies occupancy models were employed throughout this research to capture the dynamics of the entire avian community. In my first chapter, I review the impacts of imperfect detection on the estimation of community diversity and how the application of multispecies occupancy models to estimate these measures can alleviate this source of error. The hierarchical structure of the model allows data from the entire sample to inform the estimation of occupancy, colonization, survival, and detection probabilities, despite encounter histories being stratified by historic and modern surveys, species, site, and visit. Data from all species’ informs the estimation of community-level values, and the structure of the model itself facilitates the modeling of all species, including rare ones. Correcting for detection is particularly important when using historic data, because differences in methodology and changes in technology that can alter the detectability of species through time can also influence the conclusions drawn from the comparison. Deserts, already defined by climatic extremes, have warmed and dried more than other regions in the contiguous United States due to climate change. In my second chapter, I assessed how climate change and habitat disturbance have impacted bird populations of the Mojave Deserts. The resurveys of sites originally visited in the early 20th century found Mojave Desert birds strongly declined in occupancy and sites lost nearly half of their species. Declines were associated with climate change, particularly decreased precipitation. The magnitude of the decline in the avian community and the absence of species that were local climatological “winners” is exceptional. Our results provide evidence that bird communities in the Mojave Desert have collapsed to a new, lower baseline. Declines could accelerate with future climate change, as this region is predicted to become drier and hotter by the end of the century.

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Page publiée le 19 novembre 2019