Testing a highly replicable and standardized method to rapidly assess seed removal probabilities

Abstract

Seed removal can result in either seed predation or dispersal and is therefore an indicator of important ecosystem functions. To better understand how these variable processes are affected by environmental changes, rapid and reliable assessments with high temporal and spatial replication are needed. We address this need by testing the application of a rapid ecosystem function assessment (REFA) method to investigate seed removal in habitats with differing land use intensity. We recorded seed removal hourly over eight hours at 301 sites in five habitat types in three urban regions in Germany. We calculated seed removal rates per sampling period, traditionally used in seed removal studies, as well as instantaneous seed removal probabilities based on hourly sampling. Across regions, seed removal probabilities and rates were lowest in arable fields, a habitat type with high land-use intensity. Except in urban sealed areas, temperature had a negative effect on seed removal. Additional Cox hazard regressions suggest invertebrates as the main seed removing animals in arable fields, whereas vertebrates were likely removers in other habitat types. We confirm that seed removal is strongly negatively affected by human disturbance, indicating that the tested method is appropriate in different settings. We were able to recognize patterns in highly variable data and the method also has the advantages of low cost, high replication and high temporal resolution. However, there is a trade-off between the high temporal-resolution of instantaneous seed removal probabilities and the sampling effort, but adjustments in the standardized setup can be made depending on the study. To further utilize the extensive data collection in the REFA method, we propose to combine instantaneous seed removal probabilities, seed removal rates and Cox hazard regressions of seed removal to provide complementary information on the extent and temporal patterns of seed removal and indications about potential seed removing guilds. Keywords: Seed predation, seed dispersal, seed removal, granivore, REFA