Space use patterns and the extent of complementarity across scales in introduced seed dispersers

Abstract

Community-level evaluations of space use patterns are critical to understand how species separate themselves across habitats and the extent of overlap (complementarity vs. redundancy) between species. Differential space use patterns have cascading effects on community assembly and ecosystem function and can alter the robustness of communities to perturbations. This is particularly true in seed dispersers because of their impacts on plant communities. To adequately examine variation in space use, habitat features should be evaluated at multiple scales owing to different processes that occur at each scale. Here we assess if four introduced birds responsible for the majority of seed dispersal on Oʻahu, Hawaiʻi (almost 98% of plant-bird interactions), show variation in space use patterns in response to landscape scale (canopy cover, topography, vegetation type) and understory scale (light availability, habitat complexity, plant community composition) habitat features and if species show complementary or redundant patterns in their use of native and alien vegetation at both scales. We found that landscape scale habitat features explained more variation in space use than understory features. Overall, we found redundancy in space use across spatial scales, indicating a robust dispersal community in most habitats. Nevertheless, some habitats only had 1–2 disperser species, suggesting that these habitats may be more vulnerable to the loss of single disperser species. Based on the variation observed here, we argue that studying community-level space use patterns is critical to understanding how introduced species settle within novel ecosystems and ultimately impact the persistence of critical ecosystem processes, such as seed dispersal.