Graduation Semester and Year

2011

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Quantitative Biology

Department

Biology

First Advisor

Daniel Formanowicz

Abstract

Temperature affects all levels of biological organization and ultimately affects multiple aspects of ecological performance and fitness. Generalist arthropod predators are ectothermic and are strongly affected by temperature in ways that are not fully understood. Descriptions of thermal ecology of important generalist arthropod predators are, therefore, essential pieces of information for studying ecology in changing thermal environments. Rabidosa rabida is a wolf spider that inhabits much of the eastern United States and plays an important role as a generalist predator of large herbivorous arthropods. This study makes the first description of the thermal ecology of R. rabida. A description of intra-specific variation in this spider and applications of this data to habitat selection for this generalist arthropod predator are also made. Descriptions of thermal preference, critical thermal maxima, and locomotor performance were made for spiders collected at four locations in the mountains of Arkansas which differed by less than three degrees. Comparisons of thermal ecology and other ecologically significant thermal performance measures, such as predation and immunity, were made between these populations to determine if intra-specific variation could be described and if small temperature differences would result in measureable differences in thermal response. Estimates of heritability were also made for size, sprint speed, and immunity measures to determine if variation found could be attributed to genetic factors or if environmental factors such as temperature could explain any variation observed. Carapace length differed between spiders from different mountains with spiders from Mt. Magazine having a greater CL. Body mass also differed between sexes and between spiders from different elevations with females and spiders from low elevation showing the greater body mass. Rabidosa rabida was found to have an acute thermal preference of 32.0 ± 0.011◦C. Thermal preference differed between spiders from different mountains. The critical thermal maximum was estimated to be 43.52 ± 0.105◦C. Thermal limits did not differ between mountain or elevation groups. Sprint speed was significantly affected by temperature and differed between spiders from different elevations with spiders from higher elevations showing a greater mean sprint speed. Comparisons with characteristics of insects using various thermal strategies showed that R. rabida is a thermal conformer and thermal generalist with moderate thermal sensitivity. Thermal sensitivity, which did not significantly differ between 5◦ intervals, was greatest at the thermal extremes and between 25◦ and 30◦C for all but male spiders. Measures of prey capture showed an apparent increase in prey capture as temperature increased but the ability for statistical interpretation was limited. Immunity showed limited variation between spiders and no significant differences between spiders from different elevations or mountains. Heritability estimates for size, sprint speed, and immunity measures were low and not significantly different from zero. This first description of the thermal ecology and thermal performance in this large non web building spider gives insights into the thermal habitat selection of this animal. This spider showed a thermal preference suggesting that it can detect temperature differences and actively chooses to occupy one temperature over another. Thermal performance tests show that as temperature increases performance also increases. Survival may be negatively influenced by warmer temperatures especially during early instars and molting. The thermal sensitivity of this spider showed an apparent increase in the temperatures between 25◦ and 30◦C which would suggest that if all other factors were the same then this spider should choose to inhabit temperatures in the low thirties similar to its thermal preference. In the field these spiders are found actively hunting in the low vegetation at night when temperatures are dropping from the 30◦'s into the 20◦'s and in an area where wind would have negative effects on body temperature and hydration. This suggests that other factors such as inter-specific interactions influence habitat choice in this spider.

Disciplines

Biology | Life Sciences

Comments

Degree granted by The University of Texas at Arlington

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