Assistant Professor Biological Sciences, Ecology & Evolutionary Biology, University of Toronto
Background/Question/Methods
The management of pollination services and insect diversity require a deep understanding of the relationship between urbanization and community structure. In agricultural habitats, loss of available semi-natural habitat (i.e., loss of compositional heterogeneity) and intensive habitat fragmentation (i.e., configurational heterogeneity) have been negatively correlated with pollination service. Although at moderate levels, configurational heterogeneity has been positively correlated with pollination service. In this study we aim to disentangle the effect of compositional and configurational heterogeneity on pollination service in urban environments. In the Summer and early Fall of 2019, we examined pollination service provided by insects to native wildflowers at community gardens located across an urbanization gradient in Toronto, ON, Canada. Community gardens were selected along uncorrelated gradients of compositional and configurational heterogeneity which were measured as the proportion of urban area and edge-density of green space, respectively. We selected 5 native wildflower species that varied in floral morphology and phenology as phytometers that were deployed at each garden. At each deployed phytometer, we measured pre-pollination factors including pollinator visitation rate to phytometers, and reproductive outcome which was measured as mean seed mass per flower.
Results/Conclusions
It was found that the edge-density of green space was positively correlated with visitation rate. In contrast, the amount of urban area was uncorrelated with visitation rate, and visitation rate was uncorrelated with mean seed mass per flower. The relationship between configurational heterogeneity and visitation rate suggests a spillover effect in which pollinators move from high quality green spaces (e.g., remnant semi-natural habitat) to community gardens. Although the lack of a statistically significant relationship between visitation rate and reproductive outcome implies that the correlation between configurational heterogeneity and pre-pollination factors did not impact the pollination service provisioned by insects to native wildflowers. This study highlights that urbanization is a nebulous concept which encompasses many ecological pressures that impact ecosystem services in varying ways. It is therefore important to identify metrics that moderate the relationship between these pressures to understand impacts on diversity, and ecosystem functioning and services.
