1 July 2009 Spatial Variation in Top-down Direct and Indirect Effects on White Oak (Quercus alba L.)
Nicholas A. Barber, Robert J. Marquis
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Recent attention has been paid to spatial variation in the direct and indirect effects of trophic interactions. Because abundances of predators and prey vary naturally through space, their interactions and the effects of these interactions may vary as well. We conducted a bird exclosure experiment on white oak (Quercus alba L.) using a randomized block design to assess how the direct effects of bird predation on arthropods and indirect effects of birds on plant damage and growth differ between five sites separated by 350–1000 m. Insect herbivore and arthropod predator abundances varied spatially, but were not affected by the exclosure treatment. Bird abundance also varied among sites. Herbivore community structure (herbivore feeding guilds) differed by site as well. Bird predation significantly reduced damage to oak leaves, but this effect did not vary spatially. However, the size of this effect was positively correlated with insectivorous bird abundance. Thus despite herbivore and predator communities that varied among sites, the direct and indirect effects of bird predation appeared to be constant at the local scale at which this experiment was conducted.

Nicholas A. Barber and Robert J. Marquis "Spatial Variation in Top-down Direct and Indirect Effects on White Oak (Quercus alba L.)," The American Midland Naturalist 162(1), 169-179, (1 July 2009). https://doi.org/10.1674/0003-0031-162.1.169
Received: 9 January 2008; Accepted: 1 October 2008; Published: 1 July 2009
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