On the Hawaiian island of O'ahu, where native birds have nearly been replaced by invasive ones, local plants depend almost entirely on invasive birds to disperse their seeds, new research shows. The findings are an example of how ecological communities dominated by introduced or invasive non-native species can be as dynamic, complex and stable as native communities, with invaders maintaining crucial ecosystem functions. Previous studies have shown that the network of interactions between plants and animals within an ecological community is particularly sensitive to invasive species or extinctions. Many of these networks, however, have only been investigated in native-dominated communities where invasive species are not present and where complex, coevolved interactions between native plants and animals have formed over long time spans. While human-caused species invasions and extinctions are becoming common across the globe, the novel ecological communities that result from these activities - and the ways in which they compare to native communities - remain virtually unknown. To address this, Jefferson Vizentin-Bugoni and colleagues investigated bird-based seed dispersal networks on O'ahu Hawaii, where native birds have been nearly replaced by invasive bird species. Vizentin-Bugoni et al. identified over 100,000 seeds collected from bird feces across O'ahu and found that native plants are almost entirely dependent on invasive birds for seed dispersal. What's more, the authors find that the novel networks on O'ahu bear a striking resemblance to the structure and stability of native-dominated networks worldwide, suggesting that novel ecological communities can arise over a short period of time and do so independently of the species involved. The results demonstrate that invasive species can quickly become well-integrated into native communities and help to fill critical gaps in ecosystem networks in the absence of native species. However, this role is not fulfilled completely, suggest the authors. While the birds on O'ahu are the only dispersers of native plants, they spread the seeds of non-native plants in much higher proportions.
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Journal
Science