Habitat loss is a leading factor causing biodiversity decline worldwide. In endangered ecosystems like tallgrass prairies, habitat restoration is often the only way to recover lost biodiversity. Prairie restoration typically involves sowing seeds of native prairie plants, but seed predators can impede plant establishment through seed consumption, or perhaps influence community structure through differential consumption of seed species. Despite these concerns, the relative importance of different granivores and their feeding behaviors is not well understood. At twelve first-year prairie restoration sites in southwest Michigan, we conducted a removal experiment using seed depot trays to ask three questions: (1a) What is the relative magnitude of seed removal by arthropods and mammals? (1b) Does the rate of seed removal change over the growing season? (2) Which plant species seeds are preferred by mammals and arthropods? Each tray was accessible to either only arthropods or both mammals and arthropods and contained seeds from ten prairie plant species. Trays were deployed in May (early summer) and July (late summer) 2016. After 26 days, tray contents were recounted to determine removal.
Results/Conclusions
We found significant differences in seed consumption depending on consumer type, time of year, and seed species. (1a) Arthropods accounted for the majority of seed removal, a result which contradicts much previous research in similar systems. In early summer, arthropods consumed 1.8 times more seeds than mammals, while in late summer, they consumed 5.1 times more. (1b) There was greater seed removal later in the growing season. During May, 28% of seeds were removed, compared to 54% of seeds removed during July, an increase driven by arthropods. (2) Certain seed species were consumed more than others, demonstrating that preferences for seeds exist. The relatively large-seeded legume Lespedeza capitata was always consumed at high rates, while the smaller-seeded asterid Coreopsis lanceolata and grass Andropogon gerardii were always consumed at low rates. For several species, seed removal varied across trays with different consumer access, suggesting different preferences by mammals and arthropods. This research suggests that insects may be more influential on tallgrass prairie establishment than previously expected and implies that land managers could prevent seed predation by altering the time of sowing or alter seed mixes to compensate for predation.