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1 July 2009 Abundance of an Herbivorous Beetle: Factors Affecting Dispersal and Local Reproduction
Stephen F. Matter
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A current challenge for ecologists is identifying the relative effect of factors affecting abundance in spatially segregated populations. I investigated the effects of variables affecting dispersal (current patch size, interpatch distance and patch quality) and reproduction (previous female abundance, previous patch size and their interaction) on the local abundance of an herbivorous beetle, Tetraopes tetrophthalmus. Mark-release-recapture methods were used to monitor beetle populations in a 40 ha landscape containing numerous patches of the beetles' host plant, Asclepias syriaca. Factors affecting dispersal and reproduction were compared using statistical models, and the relative effects of each factor were evaluated by examining the joint and unique deviance explained. Over 3 y, 3952 individuals were captured 10,715 times. The models explained over 80% of the deviance in beetle abundance with significant contributions from factors affecting both dispersal and reproduction. Current patch size and number of females in a patch the previous generation had the largest effects on abundance. Immigration exceeds emigration in larger patches resulting in higher abundance in larger patches, but a large effect of current patch size was also due to confounding with factors affecting reproduction. Abundance also increased with habitat quality and connectivity through their effects on dispersal. The abundance of females in the previous generation affected current abundance directly and via interactions with resources. In a low density year (1995) there was a positive interaction between female abundance and patch size (resources) such that large patches with an abundance of females had high abundances the next generation (1996). In a higher density year (1996) abundance the next generation increased with female abundance, but showed either a negative interaction with patch size (male beetle abundance) or a negative effect of patch size in 1996 (female). For patchy populations a combination of landscape and population factors are needed to understand local abundance.

Stephen F. Matter "Abundance of an Herbivorous Beetle: Factors Affecting Dispersal and Local Reproduction," The American Midland Naturalist 162(1), 19-28, (1 July 2009).
Received: 9 January 2008; Accepted: 1 May 2008; Published: 1 July 2009
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