Phylogenetic restriction of plant invasion in drought-stressed environments: Implications for insect-pollinated plant communities in water-limited ecosystems.

Background Plant-pollinator community diversity has been found to decrease under conditions of drought stress; however, research into the temporal dimensions of this phenomenon remains limited. In this study, we investigated the effect of seasonal drought on the temporal niche dynamics of entomophilous flowering plants in a water-limited ecosystem. We hypothesized that closely related native and exotic plants would tend to share similar life history and that peak flowering events would therefore coincide with phylogenetic clustering in plant communities based on expected phenological responses of plant functional types to limitations in soil moisture availability. Location Galiano Island, British Columbia, Canada. Methods Combining methods from pollinator research and phylogenetic community ecology, we tested the influence of environmental filtering over plant community phenology across gradients of landscape disturbance and soil moisture. Floral resource availability and community structure were quantified by counts of flowering shoots. We constructed a robust phylogeny to analyze spatial and temporal variation in phylogenetic patterns across the landscape, testing the significance of the observed patterns against a randomly generated community phylogeny. Phylogenetic metrics were then regressed against factors of disturbance and soil moisture availability. Results Critical seasonal fluctuations in floral resources coincided with significant phylogenetic clustering in plant communities, with decreasing plant diversity observed under conditions of increasing drought stress. Exotic plant species in the Asteraceae became increasingly pervasive across the landscape, occupying a late season temporal niche in drought-stressed environments. Main conclusion Results suggest that environmental filtering is the dominant assembly process structuring the temporal niche of plant communities in this water-limited ecosystem. Based on these results, and trends seen elsewhere, the overall diversity of plant-pollinator communities may be expected to decline with the increasing drought stress predicted under future climate scenarios.