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Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure
PeerJ (2016)
  • Thomas P. Rooney
Abstract
Indirect ecological effects are a common feature of ecological systems, arising when
one species affects interactions among two or more other species. We examined
how browsing by white-tailed deer (Odocoileus virginianus) indirectly affected the
abundance and composition of a web-building spider guild through their effects
on the structure of the ground and shrub layers of northern hardwood forests. We
examined paired plots consisting of deer-free and control plots in the Allegheny Plateau
region Pennsylvania and Northern Highlands region of Wisconsin. We recorded the
abundance of seven types of webs, each corresponding to a family of web-building
spiders. We quantified vegetation structure and habitat suitability for the spiders by
computing a web scaffold availability index (WSAI) at 0.5 m and 1.0 m above the
ground. At Northern Highlands sites, we recorded prey availability. Spider webs were
twice as abundant in deer-free plots compared to control plots, while WSAI was 7
12 times greater in deerfree plots. Prey availability was lower in deer-free plots. With
the exception of funnel web-builders, all spider web types were significantly more
abundant in deer-free plots. Both deer exclusion and the geographic region of plots
were significant predictors of spider community structure. In closed canopy forests
with high browsing pressure, the low density of tree saplings and shrubs provides few
locations for web-building spiders to anchor webs. Recruitment of these spiders may
become coupled with forest disturbance events that increase tree and shrub recruitment.
By modifying habitat structure, deer appear to indirectly modify arthropod food web
interactions. As deer populations have increased in eastern North America over the past
several decades, the effects of deer on web-building spiders may be widespread.
Publication Date
September 29, 2016
DOI
10.7717/peerj.2538
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Citation Information
Roberson et al. (2016), Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure. PeerJ 4:e2538;
Creative Commons license
Creative Commons License
This work is licensed under a Creative Commons CC_BY International License.