Abstract
Change in land cover is thought to be one of the key drivers of pollinator declines, and yet there is a dearth of studies exploring the relationships between historical changes in land cover and shifts in pollinator communities. Here, we explore, for the first time, land cover changes in England over more than 80 years, and relate them to concurrent shifts in bee and wasp species richness and community composition. Using historical data from 14 sites across four counties, we quantify the key land cover changes within and around these sites and estimate the changes in richness and composition of pollinators. Land cover changes within sites, as well as changes within a 1 km radius outside the sites, have significant effects on richness and composition of bee and wasp species, with changes in edge habitats between major land classes also having a key influence. Our results highlight not just the land cover changes that may be detrimental to pollinator communities, but also provide an insight into how increases in habitat diversity may benefit species diversity, and could thus help inform policy and practice for future land management.
Highlights
Shifts in pollinator communities and assemblages are well documented in certain regions of the world [1,2,3,4,5]
While some studies have explored the impact of contemporary changes in landscape and land utilization on pollinator communities [16,17,18,19,20,21,22], long-term historical land cover change and its impacts on pollinators have yet to be quantified—primarily owing to the lack of availability of historical land cover data and/or methods to standardize existing biodiversity data collected by volunteers
To determine whether there was a turnover of species in our study sites and to evaluate changes in patterns of pollinator assemblages, we investigated how species composition across space changed over time using the bsim index described by Lennon et al [36]
Summary
Shifts in pollinator communities and assemblages are well documented in certain regions of the world [1,2,3,4,5]. The earliest known land cover map of Britain [23] has recently been digitized, and this, combined with the availability of novel statistical methods that enable comparison of species richness data with varying sampling effort [5,24,25], allows study of the impacts of historical land cover on pollinator communities. Land cover changes at different spatial scales outside of the site were tested in separate models (examples given in the electronic supplementary material). The change in habitat suitability value, the change in edge habitat and the weighted change in each major land cover type within and around each site at varying spatial scales were used as explanatory variables and model simplified using stepwise AIC method. If accumulation curve estimates did not completely remove the bias owing to sampling effort (i.e. whenever DR had a significant effect on estimated richness change across sites), we calculated the partial residuals after removing the effect of sampling effort for each cell to obtain unbiased estimates of richness change for each grid cell (following Carvalheiro et al [5])
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