Haynes, K. J., F. Dillemuth, B. Anderson*, A. Hakes, H. B. Jackson, and J. T. Cronin. 2007. Landscape context outweighs local habitat quality in its effects on herbivore dispersal and distribution. Oecologia 151: 431-441.
ABSTRACT
Past studies with fragmented herbivore populations have emphasized the primacy of intrinsic factors (e.g., patch quality), geography (e.g., patch size and isolation), and more recently landscape context (e.g., matrix composition) in affecting local population abundance and dispersal rate. However, few studies have examined the relative importance of each factor, or how they might interact to affect herbivore abundance or dispersal. Here, we performed a factorial field experiment to examine the independent and interactive effects of patch quality (% nitrogen, % phenolics) and matrix composition (mudflat or non-host grass [Bromus inermis])on planthopper (Prokelisia crocea) emigration from host-plant patches (prairie cordgrass, Spartina pectinata). The experiment was followed by a field survey, in which we examined the relative importance of patch quality, geography, and matrix composition on planthopper occupancy and density. In the experiment, we found that rates of emigration from low and intermediate quality patches were, on average, 21% percent higher for patches embedded in brome than mudflat. In contrast, the emigration rate was unaffected by matrix composition in nutrient-rich patches. Within matrix types, plant nutritional quality had little effect on emigration. In the survey, patch occupancy by planthoppers was related to matrix composition and patch size , but not to patch quality (leaf protein or phenolics) or patch isolation . Planthopper density increased with patch size and the proportion of the surrounding matrix composed of mudflat. This study suggests that landscape-level factors, such as the matrix, may be more important than factors intrinsic to the patch. In this case, matrix effects on planthopper dispersal and spatial distribution may be stronger than patch-quality effects because small patch sizes promote frequent encounters with patch edges and high rates of emigration.
Keywords: Prokelisia crocea, Spartina pectinata, metapopulation, source-sink, edge permeability
