Wetland insect communities in an agricultural landscape: Impacts of historical and contemporary nutrient enrichment and vegetation structure

Background/Question/Methods Wetlands comprise a substantial portion of agricultural landscapes in central and south Florida.  Understanding the impact of agricultural management regimes on these wetlands is a crucial step to sustaining biological diversity and ecosystem function while maintaining agricultural productivity.  We explored patterns in aquatic insect communities and plant structure in 40 wetlands in two pasture types (improved and semi-native) at the MacArthur Agro-Ecology Research Center at Buck Island Ranch (MAERC), Florida.  Improved pastures were disked and seeded with exotic bahia grass (Paspalum notatum) over 40 years ago and are regularly fertilized with N and lime.  Semi-native pastures have never been disked or fertilized and are comprised primarily of native grasses.  We hypothesized that intense pasture management affects aquatic insect community structure and diversity by altering plant assemblages. 

Results/Conclusions Wetland plant assemblages in less intensely managed semi-native pastures had significantly higher species richness (p=0.001) and significantly different composition (p=0.001) than intensely managed improved pasture wetlands.  Composition and relative abundance of insect communities were only marginally different between these pasture types. However, multivariate analyses revealed strong correlations between plant assemblage structure and insect community structure when matrices were overlain using canonical correspondence analysis (Axis 1, r²=0.70). Insect species richness increased significantly with vegetation height (r = 0.412), and total insect abundance rose significantly as insect species richness increased (r = 0.43).  These analyses suggest that vegetation height and structure provide habitat complexity that supports insect richness and abundance.  Because vegetation richness and composition is strongly influenced by pasture management, our results suggest that pasture management indirectly affects insect community structure and abundance by directly affecting plant assemblages.  Ongoing experimental work is examining the effects of grazing pressure and fire suppression on these wetlands using cattle exclosures and fire treatments.