Windows of opportunity: the timing of dispersal events influences zooplankton community response to environmental change in Subarctic ponds
Symons, Celia Claire
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Theoretical and empirical work has shown that community diversity and composition can be influenced by both local conditions and dispersal from a regional species pool. This may be especially true shortly after environmental disturbances, because perturbations can provide spatial or temporal niche opportunities for dispersers to establish. Theory predicts that after environmental disturbances tolerant functionally-redundant dispersing species can establish in disturbed communities, maintaining local community diversity and ecosystem function; however, this model relies on the successful establishment of dispersers (i.e., the community must be invasible). Invasibility is expected to decline as time-since-disturbance increases because the local community can use freed resources and increases in abundance. Although studies have acknowledged that timing may influence invasibility, very few studies have focused on how dispersal timing influences the role of dispersal in community response to disturbance. My thesis was conducted to test the role of crustacean zooplankton dispersal timing in the establishment success, and subsequent influence on diversity and ecosystem function of dispersers. To assess this, a field mesocosm study was completed in Churchill, Canada to test the effects of disturbance (nutrients and salinity) and immigration timing (from 51 regional ponds/pools) on invasibility, local community structure and ecosystem functioning (i.e., chl-a). Results show that invasibility was initially high following disturbance, but decreased with time- since-disturbance as the resident community exerted priority effects over dispersers. As a result community diversity was most influenced by immigration when dispersers were added shortly after disturbance. Many coarse measures of diversity were resistant to disturbance, but community composition and the relative abundance of functional groups shifted, and likely influence ecosystem function (i.e., chl-a). When dispersers were added to disturbed communities ecosystem function was recovered to undisturbed levels. Overall, my results suggest that dispersal timing can influence the role of dispersal in communities and the ability of species to capitalize on windows of invasion opportunity will influence their ability to establish in favorable local patches.