Spiders’ webs are a major investment of time and resources, and vitally important to catch prey. Webs also have to cope with the environment in which they’re spun — factors including the threat of damage by wind or rain. Such "microhabitat" considerations determine what kinds of webs can be spun in a given location, as a study recently published in the journal Biotropica by CSUN Biology alumna Andrea Haberkern shows.
Haberkern, who earned her MS at CSUN, worked with collaborators at Simon Fraser University and the University of British Columbia, where she is currently earning her PhD, to test the hypothesis that spiders seek more sheltered locations for webs that require more resources. Specifically, they compared the locations in which three-dimensional "sheet-and-tangle" or "tangle" type webs are found to the locations where simpler, flat orb webs are found.
The coauthors conducted field surveys near a biological field station in Ecuador, and rexamined survey results from an earlier study across several different sites with varying rainfall conditions. In the survey, they noted the architecture and microhabitat characteristics of each web they found, and randomly selected web-free sites distributed across the survey site as a standard for comparison to see whether webs were concentrated in a particular subset of available locations.
They found that, indeed, about two-thirds of three-dimensional webs were located under some sort of shelter, like leaves or an overhanging branch. In contrast, less than a quarter of orb webs were located under cover; which was no different than expected based on the randomly chosen control sites. The reanalysis of the prior study’s data replicated this result, and revealed that the difference changed with site climate — in sites with higher rainfall, a higher proportion of three-dimensional webs were located under shelter. In contrast, the proportion of sheltered lower-cost orb webs didn’t change with the rainfall across sites.
The full paper is available on the Biotropica website.
Image: A spiderweb beaded with dew (Flickr: Mario Antonio Para Zapata)