Spillover is the movement of desirable species from a source to a receiving habitat, and is driven by high abundance or species richness of these species in source habitats. However, it is unknown whether the established species richness within a receiving habitat alters spillover. Here, we investigate whether spillover occurs from remnant to restored grasslands of varying species richness. Our goal was to assess whether remnants can act as a sufficient seed source for restored grasslands, which lack the high biodiversity and rare species that are characteristic of their remnant counterparts, and to determine whether the established diversity within restorations affected spillover. To do so, we identified restorations adjacent to one of two potential source habitats, remnant prairies and agricultural fields. We obtained seed mix information for all restorations in order to identify which species were intentionally planted and to quantify their seeded species richness. We then surveyed the vegetation at these restorations along transects perpendicular to the source-restoration boundary to see if and how far species from sources moved into restorations.
Results/Conclusions
We found that spillover of desirable grassland species occurred from remnant prairies to lower diversity restorations up to 50 meters from the remnant-restoration border, and that wind dispersed species contributed to spillover more often than species with animal or unassisted dispersal. Our results demonstrate the context-dependent nature of spillover, as changes in both the source and receiving habitat can attenuate the processes of dispersal and establishment. In source habitats, the higher contribution of wind dispersed species to spillover suggests that source community composition can affect spillover. In receiving habitats, higher species richness of established communities mitigates spillover, likely because increased functional redundancy with higher species richness limits the establishment of arriving species. In marine systems, spillover is a way to utilize natural dispersal to extend the benefits of reserves to surrounding communities. Our results show that while spillover can indeed benefit surrounding areas in terrestrial systems, the context of both source and receiving habitats should be considered in order to make informed decisions about how to best utilize spillover and capitalize on its benefits.