Mechanisms Structuring Dragonfly Communities across Canopy and Forest Cover Gradients

Forest regrowth, which is occurring across North America, may have large impacts on the structure of larval dragonfly assemblages. My thesis examined how habitat selection, movement behaviour, and species-sorting shape aquatic larval dragonfly assemblages in response to landscape heterogeneity, including forest cover in the landscape and canopy cover over ponds. The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish, so I used multiple approaches to assess the contributions of different mechanisms to these observed patterns. Firstly, I tested the role of adult habitat selection versus larval species-sorting in structuring larval dragonfly assemblages across a canopy gradient using artificial aquatic habitats (i.e. mesocosms) placed across gradients of artificial shading and of natural canopy cover. Adult dragonflies preferentially visited aquatic mesocosms situated under open canopy. I tested for species-sorting effects by placing larvae in mesocosms across a natural canopy cover gradient, but found no evidence of differential mortality or growth. Secondly, I examined the effects of forest cover in the terrestrial landscape on adult dragonfly movement. Adults showed preferences for open field environments rather than closed forest environments, moving marginally more often in fields, more often towards fields, and flying longer in fields. However, adults’ direction of movement also depended on what environments they were released in, and their flight times were species-specific. Lastly, I investigated how forest cover in the landscape and pond canopy cover affected the distribution of larval dragonflies, as well as their reassembly in ponds following a drying event. Both local (pond canopy cover, permanence, and area) and landscape (pond connectivity based on distance and amount of forest cover between ponds) heterogeneity affected species diversity and recovery following a drying event. My thesis work provides new insights into how aquatic communities are structured by forest and canopy cover, and how they might respond to forest regrowth.Ph.D.2020-11-16 00:00:0