Dynamics of the interactions between big sagebrush (Artemisia tridentata L.) and its associated arthropods in southeastern Idaho: food webs and effects of herbivory in a changing climate [dissertation]

Call Number:

URL:

Keywords:

Abstract:

Species interactions are complex, can 'cascade' through trophic levels, and have been recognized as important ecological processes. Trophic cascades have been documented primarily in aquatic ecosystems and in terrestrial systems that are often simplified. In desert ecosystems, the length of trophic chains has been predicted to be very short (primary consumer only or primary consumer-herbivore only), because scarce water can limit the productivity of primary producers and so limit length and complexity of consumer food chains. Therefore, understanding the roles of trophic cascades in terrestrial ecosystems remains challenging. Big sagebrush is the dominant perennial shrub species structuring the Sagebrush Steppe, one of the largest ecosystems in North America. Big sagebrush also hosts a wide array of arthropods (insects and spiders). However, whether and how this arthropod fauna, which forms a complex food web of primary consumers, omnivores, predators, parasitoids, and hyper-parasitoids, has significant effects on big sagebrush is unknown. For this dissertation, the author tested the effects of the arthropod food webs on the growth and reproduction of big sagebrush under both naturally varying and experimentally increased precipitation to better understand the dependence of herbivory and its effects on changing climate. I further explored the arthropod species composition, abundance, and seasonal dynamics. Additionally, the author tested the effects of mammal and insect herbivores on the survivorship of sagebrush seedlings to investigate their roles on recruitment. Insect herbivores significantly reduced the growth and seed production of sagebrush in all four years of the study. However, the magnitude of the effects of insect herbivores on growth, reproduction, water use efficiency, and carbon and nitrogen economy of sagebrush also depended on precipitation. Cooler conditions in wet years lowered arthropod abundance and occurrence, and this likely delayed the phenology of species interactions and minimized the herbivory impact. Unique interactions were observed between thatching ants and mutualistic homopterans, complex feeding linkages between gall-flies and parasitoids, and high abundances and species richness of predator, parasitoid, and herbivore guilds of sagebrush. These arthropod interactions were potentially important for generating trophic cascades. This study contributed to understanding of the roles and dynamics of arthropod guilds that were associated with big sagebrush.

Notes:

ELECTRONIC FILE - Zoology: Invertebrates

Citation (CSE style): Takahashi M. 2012. Dynamics of the interactions between big sagebrush (Artemisia tridentata L.) and its associated arthropods in southeastern Idaho: food webs and effects of herbivory in a changing climate [dissertation]. Pocatello (ID): Idaho State University. 170 p. Available at: http://gradworks.umi.com/35/36/3536204.html.