Pollinators in complex landscapes: modelling and mapping the distribution of wild bees and hoverflies in the Netherlands

Doctoral Thesis

This thesis explores how bees and hoverflies are distributed across the Dutch landscape and how ecological and landscape factors shape their occurrence. Because these insects are essential pollinators for wild plants and crops, understanding their spatial distribution is vital for conservation and food security. Using species distribution models (SDMs), the research addresses key challenges such as incorporating landscape complexity, accounting for biotic interactions, and integrating fine-scale habitat features.
First, the thesis compares threatened and non-threatened bee species, revealing that threatened bees have smaller ranges, occupy more extreme climates, rely on fewer natural habitat types, and benefit less from urban green spaces. These patterns underscore their vulnerability under environmental change. Next, the work demonstrates that including biotic interaction, such as plant–pollinator relationships and parasitism, significantly improves SDM performance,...Show moreThis thesis explores how bees and hoverflies are distributed across the Dutch landscape and how ecological and landscape factors shape their occurrence. Because these insects are essential pollinators for wild plants and crops, understanding their spatial distribution is vital for conservation and food security. Using species distribution models (SDMs), the research addresses key challenges such as incorporating landscape complexity, accounting for biotic interactions, and integrating fine-scale habitat features.
First, the thesis compares threatened and non-threatened bee species, revealing that threatened bees have smaller ranges, occupy more extreme climates, rely on fewer natural habitat types, and benefit less from urban green spaces. These patterns underscore their vulnerability under environmental change. Next, the work demonstrates that including biotic interaction, such as plant–pollinator relationships and parasitism, significantly improves SDM performance, especially depending on specialization and data resolution.
The research also incorporates small-scale agricultural landscape features like hedges and ditch banks, showing that these elements increase predicted species richness and serve as biodiversity hotspots along field edges. Field data from three agricultural regions further confirm that landscape elements support higher abundance and diversity of bees and hoverflies, influenced by floral composition, vegetation structure, region, and season.
Overall, the thesis enhances ecological understanding and provides improved tools and insights for conserving pollinators in complex, changing landscapes.
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Spatial ecology

Species distribution models