Abstract
Understanding how landscape heterogeneity promotes biodiversity remains a significant challenge because the drivers of community assembly co-vary across space and time. Contrasting ecological conditions between habitat types strengthen filters that can select for complementary communities at local scales, but it remains unclear how the seasonal variation of species assemblage within a habitat type influences overall diversity. To elucidate how the interaction between space and time structures biodiversity, we sampled bee and flower communities across the growing season in habitat types with contrasting ecological conditions in northeastern Oregon, USA. We found complementary bee communities in riparian and forest habitat types, likely because contrasting ecological conditions alter habitat suitability for different subsets of species. Within each habitat type, bee and flower communities varied seasonally. While alpha and gamma diversity were consistent across months and habitat types, bee spatial beta diversity in the riparian habitat type increased from May to June, suggesting that site-to-site variation of riparian-associated bee communities increases across the growing season. This increased spatial diversity among riparian bee communities in June was associated with a greater proportion of species that were restricted to local communities. We also found no association between bee and flower communities across alpha, beta, or gamma scales. Collectively, these results suggest that ecological filters between different habitat types select for an assemblage of species that have different temporal dynamics across the growing season. Patterns of biodiversity across a heterogenous landscape are a result of the interaction between seasonality and habitat type on community diversity across scales.