Effects of habitat loss and fragmentation on the abundance and species richness of aphidophagous beetles and aphids in experimental alfalfa landscapes

摘要: In agro-ecosystems, habitat loss and fragmentation may alter the assemblage of aphidophagous insects, such as foliar- foraging (coccinellids) ground-foraging predators (carabids), potentially affecting intraguild interactions. We evaluated how (0, 55 84%), (1, 4 16 fragments) their combination affected abundance species rich- ness coccinellids carabids, aphid abundance, both in short-term (summer: December to February) over a longer time span (autumn: March May), when different demographic mechanisms participate. created four types 30 × m patches (landscapes) which alfalfa was grown: Control (1F - 0%, patch with no or loss), 4F 55% (4 fragments, total 84% 16F (16 loss). Each landscape type replicated five times. Insects were sampled by sweep-netting pitfall traps, from (summer) May (autumn). Total richness short-term, highest landscapes. adult similar among landscapes, but at level Hyperaspis sphaeridioides, Adalia bipunctata, long-term, had densities fragments within landscapes high (84%), independently fragmentation. Species long-term higher loss. Among aphids, long term Aphis craccivora less abundant land- scapes (16-84%), while Therioaphis trifolii showed opposite trend. These results sug- gest that increase density diversity effects on aphids are more variable.