Date of Award:

5-1-1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology Ecology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Committee

Lloyd Bennett

Committee

James Gessaman

Committee

Herman Wiebe

Abstract

Respiration rates, water contents, water loss rates, and abilities to withstand water loss were assessed at 15, 25, and 35 C for adults of three species of crab spiders occuring sympatrically on shrub-steppe vegetation in northern Utah. The three species, Misumenops lepidus (Thorell), Xysticus cunctator (Thorell), and Philodromus histrio (Latreille), differ in their apparent seasonal distributions, with M. lepidus being collected most frequently in spring and fall, X. cunctator appearing most frequently in summer, and P. histrio occuring in all seasons. Rates of oxygen consumption paralleled casual observations of the general rates of activities of these spiders. Hence the generally more active males exhibited higher rates than did females, and P. histrio respired more rapidly than did the relatively inactive M. lepidus and X. cunctator. Xysticus cunctator exhibited the highest body water content among the three species prior to desiccation, but M. lepidus was able to withstand a lower water content before reaching its Critical Activity Point. P. histrio appeared to have the smallest reserve of water, neither having a particularly high initial body water content, nor being able to tolerate a particularly low content. In general, females possessed higher pre-desiccation water contents than did males, but males were able to tolerate lower water contents. Water contents in general were lower at 15 C than at the warmer temperatures. Among the species, X. cunctator exhibited the highest water loss rates, while M. lepidus exhibited the lowest. Males generally lost water more rapidly than did their female counterparts. Water loss rates had a high positive correlation with both respiration rate and body surface area. Overall survival times under desiccating conditions were generally longer for females than for males. Among the species, M. lepidus exhibited the longest survival times, despite its prevalence in field collections only during relatively wet portions of the year. It is suggested that this apparently anomalous pattern may be due to M. lepidus occuring during the hot, dry summer months primarily as early instar spiderlings, exposing this species to greater likelihood of desiccation, while rendering them more difficult to capture in normal field collections.

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