Structural habitat complexity (SHC) and functional habitat connectivity (FHC) are the basic components that make up the physical architecture of an ecosystem, and can have substantial impacts on predator-prey interactions. These structural components influence animal behaviors such as inter-patch movement, foraging, and competition, and can impact community structure/dynamics in terrestrial and aquatic ecosystems. The effects of SHC and FHC on predator-prey dynamics within an ecosystem may also have important cascading effects on neighboring ecosystems by altering the movement of individuals across ecosystem boundaries. A common example in aquatic systems is the emergence of aquatic insects entering the terrestrial ecosystems where they then become an important food resource to terrestrial predators. Using a multiple patch, predator enclosure design in ponds, we tested whether altering intra-patch plant stem densities (SHC) and inter-patch distances (FHC) would influence the impact a predatory fish has on the biomass, quality, and trophic composition of emergent insects.
Results/Conclusions
Fish significantly reduced emergent insect biomass (33%± 7.6, mean ± s.e.). Intra-patch stem densities (SHC) did not significantly alter fish effects. However, inter-patch distance (FHC) did significantly alter the impact of fish on emergent insect biomass, with fish reducing biomass by more in long inter-patch distance treatments (47.3% ± 6.9) compared to in short inter-patch distance treatments (20.5% ± 12.4). Inter-patch distance also altered taxa composition of emergent insects and size of adult damselflies, with proportionally more (49.8% ± 1.2) and larger (4.1 mg/m² ± 0.1) damselflies occurring in treatments with shorter compared to longer inter-patch distances (33.8% ± 1.2, 3.3 mg/m² ± 0.1). Increasing inter-patch distances likely decreases fish movement between patches, decreasing the frequency that each patch is visited by the predator, and shifting prey into more active behaviors based on a lower perceived threat. When fish eventually return, the active prey are more vulnerable, resulting in increased mortality. Our results suggest that structural components of a habitat, such as inter-patch distances, can have important impacts on predator-prey dynamics within habitats. In turn, these altered predator-prey dynamics have cascading effects on adjacent habitats by influencing the abundance, trophic composition, and quality of exported trophic subsidies.