Abstract
Understanding the effects of landscape structure on the distribution of or- ganisms in subdivided habitat is central to spatial ecology and conservation biology. We investigated how suitable habitat patches and the intervening matrix influenced the incidence and abundance of cactus bugs (Chelinidea vittiger) on their naturally patchy host plant, plains prickly pear (Opuntia polyacantha). We compared responses of three life stages of C. vittiger on two landscapes with different matrix properties in Colorado, USA. Patch area and abundances of C. vittiger exhibited a limiting-factor relationship that we estimated with quantile regression. Chelinidea vittiger density in patches was negatively related to patch area for all life stages and landscapes. Our results supported predictions from the under- matching hypothesis, which suggests that limited knowledge of resource patches is one determinant of abundance patterns. Multiple regression models of occupancy and abundance indicated that (1) the amount of explained variance depended greatly on the measured response variable and on the life stage of the insect, (2) metrics of patch connectivity had more support in models of abundance than of presence-absence in patches, (3) patch area had an interactive effect with patch connectivity in most abundance models, and (4) a matrix-matters measure of connectivity received only mixed support when included in abundance models for a landscape with a heterogeneous matrix. A model that included only the two priority variables in basic metapopulation models (patch area and patch con- nectivity) was insufficient for understanding distribution patterns of C. vittiger in patchy landscapes.
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