Bee community response to local and landscape factors along an urban-rural gradient

Kristen R. Birdshire,Adrian L. Carper,Christy E. Briles

doi:10.1007/s11252-020-00956-w

Kristen R. Birdshire, Adrian L. Carper + Show 1 more

Open Access

https://doi.org/10.1007/s11252-020-00956-w

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Abstract

Over a third of the world’s crops require insect pollination, and reliance on pollination services for food continues to rise as human populations increase. Furthermore, as interest in urban agriculture has grown, so has a need for studies of urban pollinator ecology and pollination. Analyzing pollinator assemblages along a rural-urban gradient provides powerful mechanistic insight into how urbanization impacts pollinators. Yet, studies examining pollinators along urban-rural gradients are limited and results vary. Since pollinators vary tremendously in life history characteristics and respond to urbanization differently, studies from different regions would improve our understanding of pollinator response to urbanization. This study documents different bee assemblages along a high-plains semi-arid urban-rural gradient in Denver, Colorado, USA. Percent impervious surface was used to define the extent of urbanization at 12 sites and local and landscape characteristics were estimated using field assessments and geospatial analysis. Wild bees were collected and the relationships between urbanization and bee communities were explored using linear modeling. Overall, bee abundance and diversity decreased with increasing urbanization, suggesting that urban areas negatively impact bee communities. However, all bee guilds responded positively to local floral richness and negatively to the degree of landscape urbanization, suggesting that different types of bees responded similarly to urbanization. These findings suggest that providing a greater diversity of floral resources is key to mitigating the negative impacts of urbanization on pollinator communities.

Highlights

Pollination services provided by bees and other insects is fundamental to the production and regeneration of wild plants and agricultural crops
These results demonstrate that while the Denver metro area has a diverse bee community, both bee abundance and diversity decrease with increasing urbanization along the rural to urban gradient
Floral richness had positive effects on bee communities, and both metrics likely drive variation in communities across the Denver rural-urban gradient. While these results suggest that urbanization in Denver does have negative effects on bee communities, it suggests that increasing floral richness could help mitigate the impacts of urbanization on bees in general, and that the benefits of increased floral richness may not necessarily be guild specific

Summary

Introduction

Pollination services provided by bees and other insects is fundamental to the production and regeneration of wild plants and agricultural crops. Over a third of the world’s crops– including fruits, vegetables, nuts, spices, and oilseed–require insect pollination (Klein et al 2007), and our reliance on pollination services to promote these crops continues to rise due to increasing demands from growing human populations. Demand for pollinatordependent crops has tripled during the last half century and pollinator losses could have serious implications for plant reproduction, animal populations that depend on those plants, and world food security (Majewski 2016; Novais et al 2016; Aizen and Harder 2009). Understanding the biogeography of insect pollinators in a variety of environments (e.g., urban, rural, and agricultural) will become increasingly important as pollination needs increase

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