“Temporal variation in predation risk may explain daily rhythms of foraging behavior in an orb-weaving spider”

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J. Colton Watts, Thomas C. Jones, Ashley Herrig, Madeleine Miller, and Brigitte Tenhumberg

Nocturnal foraging may be an adaptive response to predation risk in an orb-weaving spider

A mature female Cyclosa turbinata resting at the center of her orb-web, camouflaged by carefully arranged prey remains and detritus.
(Photo courtesy of Richard A. Bradley)

Using a combination of mathematical modeling and around-the-clock field observations, researchers from the University of Nebraska-Lincoln and East Tennessee State University lend new insights to a potential ecological explanation for the evolution of daily rhythms of behavior.

For many organisms, the earth’s daily rotation corresponds to some of the most predictable and profound changes in environmental conditions. Unsurprisingly, organisms from across the tree of life express changes in their characteristics at various scales over the daily cycle, ranging from changes in gene expression to rhythms of foraging and sexual behavior. Despite the prevalence of these biological rhythms and extensive research on the mechanisms that produce them, evidence for specific ecological processes that might favor their evolution remains sparse.

Many organisms likely experience daily changes in predation risk that could favor the evolution of daily rhythms. Colton Watts and colleagues created a model of foraging decisions over the course of the day to investigate whether changes in predation risk can explain observed daily rhythms. As a case study, the researchers used data on daily changes in predator and prey abundance experienced by a common orb-weaving spider, Cyclosa turbinata. The researchers found that well-fed individuals should benefit from decreasing their foraging activity during the day, when both their wasp predators and flying insect prey are most abundant. By deploying surveillance cameras to observe C. turbinata spiders around-the-clock under natural conditions, Watts and colleagues found that, as predicted, individuals attacked prey less often during the daytime. In addition to demonstrating a potential role of predation risk in the evolution of daily rhythms, the model generates new predictions that will guide experiments assessing the importance of predation risk for the daily routines of other organisms. Read the Article