Habitat fragmentation and habitat loss may affect the dispersal of insects and influence their distribution and abundance in a landscape. These effects may vary in dependence of the biotic and/or abiotic changes of the habitat over time. Here we show evidence of this phenomenon in coccinellids in experimentally fragmented alfalfa landscapes. Four continuous 30 x 30 m patches of alfalfa were fragmented in four units, separated by 2 or 6 m. By varying size of the fragments the resulting landscapes had 55% or 84% habitat loss. The matrix surrounding fragments was mowed alfalfa. A fifth unfragmented patch was kept as a control. In December 2001 and March 2002, we evaluated the spatial distribution of adults coccinellids by sweep netting. We also evaluated the dispersal behavior of adult coccinellids through mark-recapture studies and their mortality in matrix and fragments. In December, the highest abundance of adult coccinellids was in the control and the lowest in the 84%-2m landscape. Adult coccinellids were three times more abundant in fragments than in matrix. In March, the abundance of adults was lower in all landscapes, but the highest abundance was in the 84%-6m landscape. The differences in the abundance of adults between matrix and fragments generally disappeared this time of the year. Dispersal patterns, mortality and the temporal changes in the quality of alfalfa in fragments and in the matrix explain the variable distribution of these insects over time.
Species 1: Coleoptera Coccinellidae Eriopis connexa
Keywords: habitat fragmentation, habitat loss
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