Weighing abiotic and biotic influences on weed seed predation

Weed seed predation is an important ecosystem service supporting weed management in low-external-input agroecosystems. Current knowledge of weed seed predation focuses on biotic mechanisms, with less undersatanding of the relative impact of abiotic variables. In order to quantify relative contributions of abiotic and biotic variables to weed seed predation rates, a field study was made within a maize crop in central Illinois, USA, in 2005 and 2006. From late July through to mid-October, weekly measurements of Abutilon theophrasti, Ambrosia trifida and Setaria faberi seed removal rates by invertebrate and vertebrate granivores, and seed losses because of abiotic processes were recorded. Weed seed rain was measured concurrently in contiguous plots, as were air temperature, precipitation, wind speed, thermal units and invertebrate activity-density. Statistical models supported the possibility that higher-level trophic interactions were contributing to variation in seed predation rates. Approaching granivory in agroecosystems as a food web may help future attempts to regulate this ecosystem service.