Land cover conditions between habitat patches (i.e., matrix habitat) can affect connectivity by restricting or promoting organismal movement. Dispersers may preferentially use matrix habitats that provide resources or refuges, or that facilitate movement. In dragonflies, the distribution of the aquatic larval stage across habitats is determined by adult movements and so may depend on the permeability of the matrix that aquatic habitats are nested in. Forested conditions appear to limit adult dragonfly dispersal. However adults may use forest edges for roosting (i.e., resting overnight or in between daytime forages) or as refuge from predators, thereby complicating our understanding of the effects of forests on dispersing dragonflies. We tested dragonfly responses to different terrestrial matrix conditions using experimental releases. Captured adults were released either interior or exterior to the forest, or at the forest edge. Their direction of flight after release (towards forest or field, or along forest edge) was observed. Nearby ponds were monitored for marked individuals, to assess the impact of release matrix type on ability to reach a reproductive habitat. We predicted that dragonflies would orient themselves towards fields rather than forests, and that release in a forest would impede their arrival at nearby ponds.
Results/Conclusions
Adult dragonflies preferentially moved into fields in comparison to forests but being released into forests did not impede their return to breeding sites. More individuals flew towards fields (52%) versus towards forests (25%) or along forest edges (23%; p < 0.001, V = 0.32), independent of release site. When released at forest edges, only 5% of individuals flew into the forest. When released in forests, similar numbers of individuals remained in the forest as flew towards the field. Dragonflies did not, however, completely avoid forest edges as among dragonflies released in fields, 30% flew in the direction of the forest. Despite a behavioral preference for moving into fields, matrix conditions did not strongly affect an individual’s probability of reaching reproductive habitat, with similar re-sight rates for adults released in fields, forests, and along forest edges (p = 0.8, V = 0.06). Adult dragonflies therefore seemed to prefer field matrix habitats, but also readily used forest edges and were capable of navigating through forest environments to return to their breeding ponds. Our results suggest that a mosaic of habitats (forest and field) may enhance landscape connectivity for dragonflies.