Habitat size is considered one of the primary driving forces for species richness within patches. However, the relationship between species richness and area - as predicted by the species-area relationship (SAR) - are affected by biotic and abiotic factors occurring within patches and in the surrounding matrix. In a naturally fragmented ecosystem with high levels of endemism in southeast Missouri, efforts to conserve this habitat could change the strength of SARs by altering connectivity, patch size and/or species interactions. Across two studies, we investigated the change in SAR of both bees and flowering plants to a) increasing connectivity and b) the presence of a top predator (eastern collared lizard, Crotaphytus collaris). In both studies, bee and plant richness were recorded in habitat patches of varying sizes. To quantify the effects of connectivity in study one, measures of matrix canopy cover for 48 glades was recorded. To measure the effects of presence of a top predator in study two, half of the 24 glades had restored top predators.
Results/Conclusions
In study 1 we found bee richness to be most strongly predicted by interactions between size and connectivity while plant richness responded solely to patch size. This suggests increasing connectivity has differential effects on different trophic levels and management level effects may depend on the group. In study 2, the presence of top predators weakened SARs for plants, but strengthened the SAR for bees. These differential effects are likely due to top predators exhibiting a cascading effect on bees by reducing small predators (e.g. spiders) which then facilitate better pollination and increase flower richness and persistence. The results of these studies illustrate the complex interactions between SARs and biotic and abiotic factors and the importance of connectivity and cascading trophic effects in restoring degraded habitats to achieve management goals.