Landscape-scale habitat requirements of flower-visiting insects in the Nene Valley Nature Improvement Area

Recorded population declines of flower visiting insects are a cause for concern. The presence of an abundant and diverse community of insects is essential for ecosystem stability and continued agricultural prosperity. As human populations continue to increase so do the pressures on the natural environment, therefore it is important to ensure pollinator services for the future. Landscape structure may influence the resilience of pollinators in the face of environmental change. In 2012 a pilot scheme of twelve Nature Improvement Areas (NIA) in England (UK), was created seeking to improve ecological networks through increased landscape connectivity. The Nene Valley NIA follows the course of the River Nene from its source in west Northamptonshire through to Peterborough and covers an area of 41,350 hectares. This thesis evaluates the effects of landscape context on pollinator communities in grasslands within the Nene Valley NIA. Furthermore, the influence of local variables such as floral cover, management and site maturity on insect pollinator abundance and species richness are analysed. At present landscape-scale studies on insect pollinators, whilst limited, generally fall into two categories: those analysing drivers of distribution in landscape or entirely theoretical models with little overlap of the two. This thesis aimed to address this gap, using statistical analysis of field data to produce spatially explicit models of pollinator distribution. A modelling framework is outlined, applying the Generalised Linear Model (GLM) to abundance and species richness data collected in grasslands within the Nene Valley NIA, ultimately producing habitat suitability maps within a Geographical Information System (GIS). This study examines data collected from 34 grassland sites between 2013 and 2015 in the Nene Valley NIA. Overall 1692 individuals were recorded, and 103 species observed, analysis revealed a nested community structure. Abundance and species richness of flower visiting insects was significantly correlated with floral cover. Analysis of local scale habitat factors indicated that day-flying Lepidoptera are sensitive to agri-environment schemes, indicating a need to review the current recommendations and systems. This thesis presents a methodology for producing spatially explicit habitat suitability models for flower visiting insects. This research provides a timely contribution to current methodology, particularly in the context of the emerging ecosystem services framework. The results of the landscape modelling highlight the difficulty in encapsulating resource utilisation and distribution in landscapes and a need for a standardised recording network and open access to data, both ecological and environmental.