Canopy cover affects habitat selection by adult dragonflies
The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish from one another and can produce similar patterns of species distributions. In freshwater systems, the amount of canopy cover from surrounding trees is often associated with transitions in local community structure. These community changes could be driven by habitat selection prior to colonization of the aquatic habitat and/or species-sorting post-colonization. To assess the contributions of pre- versus post-colonization processes in structuring larval dragonfly assemblages, we tested the impact of artificial and natural canopy cover on the selection of experimental aquatic mesocosms by adult dragonflies, and monitored the performance (i.e. growth and survival) of larval dragonflies that were placed in mesocosms under a gradient of natural canopy cover. We found that greater levels of canopy cover resulted in fewer adult visits to mesocosms, and more natural canopy cover decreased the species richness of visitors. There were no effects of canopy cover on the growth and survival of larvae added to the mesocosms. Our results suggest that adult habitat selection plays a dominant role in structuring larval dragonfly assemblages across a canopy cover gradient, and that canopy cover can be an important environmental filter on species distributions.
KeywordsBehaviour Forest cover Performance Aquatic–terrestrial linkages Odonata
We are grateful to S. Catania and D. Frances for their assistance in field sampling, S. Schneider for his help in the construction of field equipment, and Koffler Scientific Reserve for research support. We thank H. Rodd, B. Gilbert, B. Raboy, P. Kotanen, and members of the McCauley lab for their comments during early stages of this manuscript. We also thank E. Werner and colleagues who participated in the ESGR survey for sharing their data with us. Funding was provided by the Departments of Ecology and Evolutionary Biology at the University of Toronto and Biology at University of Toronto Mississauga, the University of Toronto, a Queen Elizabeth II/Pfizer-Graduate Scholarship in Science and Technology to SKF, and a Natural Sciences and Engineering Research Council of Canada Doctoral Postgraduate Scholarship to SKF. Funding to SJM from the Canada Foundation for Innovation, the Ontario Research Fund (31974), and a Natural Sciences and Engineering Research Council of Canada Discovery Grant (RGPIN435614) also supported this research.
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