Award Date

Spring 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Biological Sciences

Department

Life Sciences

Advisor 1

Javier A. Rodriguez, Committee Chair

First Committee Member

Michelle M. Elekonich

Second Committee Member

Daniel B. Thompson

Third Committee Member

Robert N. Reed

Graduate Faculty Representative

Thomas E. Piechota

Number of Pages

142

Abstract

Our understanding of space use variation in response to the temporally varying importance of specific resources is poorly understood in reptiles, because spatial studies are rarely placed into an explicit ecological and behavioral context. I examined how space use differed between the mating and post-mating seasons, and how this variation related to three important resources, mating partners, food, and refuge, in an adult population of the speckled rattlesnake Crotalus mitchellii in the Mojave Desert of southwestern North America. During the mating season (late April to early June), Crotalus mitchellii increased distance traveled per unit time, because wide-ranging behavior likely enhances mating opportunities, and males traveled more than females, because male reproductive success is strongly limited by access to females. At the home range level Crotalus mitchellii did not select specific habitat types (rolling hills, slopes, rock outcrops) during the mating season. At the microhabitat level, snakes did not select specific locations where rodent prey was abundant, possibly because mating activities prevailed over foraging. However, snakes selected microhabitats close to rock refuges, which may partially explain the low predator-induced mortality observed during the mating season. During the post-mating season (early June to mid-October), distance traveled per unit time was reduced, and males moved more than females, suggesting that the sexual difference in movement patterns is not simply a consequence of Crotalus mitchellii's mating system. At the home range level Crotalus mitchellii selected rock outcrops and avoided rolling hills, which positively correlated with the varying abundance of prey and refuges between these macrohabitats. That is, rodents and refuges were more abundant in rock outcrops than in rolling hills. However, at the microhabitat level, Crotalus mitchellii's locations were characterized by low prey availability, because rodents seemingly avoided the areas where snakes occurred. Further, snake locations were also characterized by being close to wood rat Neotoma lepida nests, and when wood rat nests were not available snakes preferred locations close to rock refuges. These refuges likely provide protection from the high summer temperatures of the Mojave Desert during Crotalus mitchellii's post-mating season, as well as from predators. Yet, predator-induced mortality was high during the post-mating season, suggesting that encounters between Crotalus mitchellii and its predators are relatively common at this time of the year. My research indicates that examining patterns of space use in a biologically-relevant temporal framework can reveal significant seasonal variation in the spatial ecology of free-ranging organisms, and effectively demonstrate the behavioral shifts exhibited by organisms in response to seasonally-prevailing activities (e.g., mating and foraging activities).

Keywords

Crotalus mitchellii; Foraging; Habitat selection; Mojave Desert; Movement ecology; Predator-prey relationship; Rattlesnakes; Reptilian spatial studies; Seasonal travel; Sex role

Disciplines

Behavior and Ethology | Desert Ecology | Zoology

Language

English


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