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.
Highlights
Indirect ecological effects due to direct interaction between two species that affect a third species (Wootton, 1994) often arise due to the actions of dominant species, keystone species, or ecosystem engineers (Jones, Lawton & Shachak, 1994; Pringle, 2008). Menge (1995) reported that indirect interactions account for ∼40% of the change in the abundanceHow to cite this article Roberson et al (2016), Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure
The remaining six paired plots were located in the Allegheny Plateau region in north-central Pennsylvania in Elk County (41◦25 N, 78◦50 W)
We examined the effect of deer on habitat suitability for web-building spiders by comparing web scaffold availability index (WSAI) values at 0.5 m and 1.0 m above the forest floor inside and outside of exclosures
Summary
Indirect ecological effects due to direct interaction between two species that affect a third species (Wootton, 1994) often arise due to the actions of dominant species, keystone species, or ecosystem engineers (Jones, Lawton & Shachak, 1994; Pringle, 2008). Menge (1995) reported that indirect interactions account for ∼40% of the change in the abundanceHow to cite this article Roberson et al (2016), Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure. Indirect ecological effects due to direct interaction between two species that affect a third species (Wootton, 1994) often arise due to the actions of dominant species, keystone species, or ecosystem engineers (Jones, Lawton & Shachak, 1994; Pringle, 2008). Menge (1995) reported that indirect interactions account for ∼40% of the change in the abundance. How to cite this article Roberson et al (2016), Deer herbivory reduces web-building spider abundance by simplifying forest vegetation structure. These indirect effects occurred coincident with or shortly after direct effects were observed (Menge, 1997). We examine the indirect effects of a large mammalian generalist herbivore on the structure of a web-building spider guild
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
