Bumblebees are a charismatic group of insects as they are recognised for their important ecological role in pollination of both wild and agricultural plants. Unfortunately, after the Second World War, their numbers and geographic range declined. Whilst this is likely due to a combination of possible explanations, the leading cause is currently thought to be the intensification of farming (2–4). However, 7 of the 25 bumblebee species in the UK have shown to be more resilient against these changes and remain abundant (4,5).
The reasons behind these different rates of decline are not currently fully understood, but one possible explanation is the ‘plant-food specialisation hypothesis’ which suggests that bumblebee species that forage in a narrower range of flowers (i.e. have a more specialised diet) may be rarer than those that have a more generalist diet (6). Previous studies within relatively small areas provide mixed evidence for this hypothesis (7–9), so my study explores the relationship between British bumblebee species using multiple UK-wide datasets.
I found that the relationship between abundance/distribution and diet breadth varied depending on the method used to quantify diet breadth. The first method I used to measure diet breadth (Chao1 estimator) found that rarer species had narrower diets than more common species. However, the second method I used (Simpson’s index) disagreed and did not find the same relationship! However, rarer species are still more vulnerable to decline and extinction: especially those in isolated areas that may be prone to inbreeding (10). Rarer species may also be less likely to settle in newer habitats which could mean that isolated wildflower patches alone may be less helpful to them. Therefore, there should be a focus on creating more continuous and connected habitats if we are to also conserve the rarer bumblebee species (11).
• Data on abundance were taken from the latest BeeWalk report (12).
• Data on distribution were taken from the National Biodiversity Network Atlas (13).
• Data on bumblebee-plant interactions were taken from the Database of Pollinator Interactions (DoPI). The diet breadth (i.e. diversity of flowers visited) for each species were measured by calculating both a Simpson’s index and Chao1 estimator for each species (14).
• All data analysis was carried out using R version 3.6.2 (15).
This article is based on my MSc Global Biodiversity Conservation dissertation research completed over autumn 2020.
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