Does urbanization favour exotic bee species? Implications for the conservation of native bees in cities.

A growing body of research indicates that cities can support diverse bee communities. However, urbanization may disproportionately benefit exotic bees, potentially to the detriment of native species. We examined the influence of urbanization on exotic and native bees using two datasets from Michigan, USA. We found that urbanization positively influenced exotic-but not native-bee abundance and richness, and that this association could not be explained by proximity to international ports of entry, prevalence of exotic flora or urban warming. We found a negative relationship between native and exotic bee abundance at sites with high total bee abundance, suggesting that exotic bees may negatively affect native bee populations. These effects were not driven by the numerically dominant exotic honeybee, but rather by other exotic bees. Our findings complicate the emerging paradigm of cities as key sites for pollinator conservation.

Response of Coffee Farms to Hurricane Maria: Resistance and Resilience from an Extreme Climatic Event.

Resistance and resilience have become important concepts in the evaluation of disturbance events, providing a framework that is useful in light of the expected increase in frequency and occurrences of hurricanes as a consequence of climate change. Hurricane Maria landed on Puerto Rico as a category 4 storm in September of 2017. Among the affected elements were agricultural systems, including coffee agroecosystems. Historically, coffee has been a major backbone of the island's agricultural sector. Grown with a range of management styles, the coffee agroecosystem provides an excellent model system to study the resistance/resilience of agroecosystems faced with hurricane disturbance. Sampling 28 farms and comparing pre-hurricane data (2013) with post hurricane data we find that management style had only a small effect on either resistance or resilience, likely due to the especially strong nature of the storm. Rather, the socio-political context of individual farms seems to be a more useful predictor of resilience.

Changes in adult sex ratio in wild bee communities are linked to urbanization.

Wild bees are indispensable pollinators, supporting global agricultural yield and angiosperm biodiversity. They are experiencing widespread declines, resulting from multiple interacting factors. The effects of urbanization, a major driver of ecological change, on bee populations are not well understood. Studies examining the aggregate response of wild bee abundance and diversity to urbanization tend to document minor changes. However, the use of aggregate metrics may mask trends in particular functional groups. We surveyed bee communities along an urban-to-rural gradient in SE Michigan, USA, and document a large change in observed sex ratio (OSR) along this gradient. OSR became more male biased as urbanization increased, mainly driven by a decline in medium and large bodied ground-nesting female bees. Nest site preference and body size mediated the effects of urbanization on OSR. Our results suggest that previously documented negative effects of urbanization on ground-nesting bees may underestimate the full impact of urbanization, and highlight the need for improved understanding of sex-based differences in the provision of pollination services by wild bees.

Big city Bombus: using natural history and land-use history to find significant environmental drivers in bumble-bee declines in urban development.

Native bee populations are critical sources of pollination. Unfortunately, native bees are declining in abundance and diversity. Much of this decline comes from human land-use change. While the effects of large-scale agriculture on native bees are relatively well understood, the effects of urban development are less clear. Understanding urbanity's effect on native bees requires consideration of specific characteristics of both particular bee species and their urban landscape. We surveyed bumble-bee (Bombus spp.) abundance and diversity in gardens across multiple urban centres in southeastern Michigan. There are significant declines in Bombus abundance and diversity associated with urban development when measured on scales in-line with Bombus flight ability. These declines are entirely driven by declines in females; males showed no response to urbanization. We hypothesize that this is owing to differing foraging strategies between the sexes, and it suggests reduced Bombus colony density in more urban areas. While urbanity reduced Bombus prevalence, results in Detroit imply that 'shrinking cities' potentially offer unique urban paradigms that must be considered when studying wild bee ecology. Results show previously unidentified differences in the effects of urbanity on female and male bumble-bee populations and suggest that urban landscapes can be managed to support native bee conservation.

Local and Landscape Constraints on Coffee Leafhopper (Hemiptera: Cicadellidae) Diversity.

The intensification of agriculture drives many ecological and environmental consequences including impacts on crop pest populations and communities. These changes are manifested at multiple scales including small-scale management practices and changes to the composition of land-use types in the surrounding landscape. In this study, we sought to examine the influence of local and landscape-scale agricultural factors on a leafhopper herbivore community in Mexican coffee plantations. We sampled leafhopper (Hemiptera: Cicadellidae) diversity in 38 sites from 9 coffee plantations of the Soconusco region of Chiapas, Mexico. While local management factors such as coffee density, branches per coffee bush, tree species, and density were not important in explaining leafhopper abundance and richness, shade management at the landscape level and elevation significantly affected leafhoppers. Specifically, the percentage of low-shade coffee in the landscape (1,000-m radius surrounding sites) increased total leafhopper abundance. In addition, Shannon's diversity of leafhoppers was increased with coffee density. Our results show that abundance and diversity of leafhoppers are greater in simplified landscapes, thereby suggesting that these landscapes will have higher pest pressure and may be more at-risk for diseases vectored by these species in an economically important crop.