Although animals are widely assumed to select habitats in ways that enhance organismal fitness, there are few empirical data to demonstrate this link. We studied flat rock spiders (Hemicloea major, Gnaphosidae) from eastern Australia, where these highly modified (dorsoventrally flattened) spiders live under loose surface rocks on sandstone outcrops. Field surveys showed that the rocks used as diurnal retreat sites by spiders were relatively thin with low canopy cover and a rocky substrate and therefore were likely to experience high temperatures and large thermal fluctuations. Laboratory trials suggest that this nonrandom rock use is a direct response to thermal cues; juvenile spiders selected warmer over cooler retreat sites. To investigate consequences of habitat selection on fitness-related traits, we maintained cohorts of juvenile spiders at cycling-temperature regimes corresponding to those measured in the field under rocks that were fully, partially, or never exposed to direct sunlight (diel thermal ranges of 16.2°-37.8°C, 15.5°-31.2°C, and 15.2°-24.3°C). Survival rates were high for all groups over the eight-week study, but hotter conditions accelerated growth and development. Our data thus confirm that thermal cues are used in retreat-site selection and that selection of warmer retreat sites will confer fitness benefits to flat rock spiders.
Bibliographical noteCopyright by the Ecological Society of America, C.L. Goldsbrough, D.F. Hochuli, R. Shine, Fitness benefits of retreat-site selection: spiders, rocks, and thermal cues, Ecology, 85 (2004), pp. 1635-1641.
- Habitat use
- Hemicloea major
- Rock outcrop