Food Niche Analyses of Bumblebees: A Comparison of Three Data Collecting Methods

We compared three methods for field data collecting in the niche analyses of nine subarctic bumblebee species. The basic information consisted of (a) direct observations of flower visits, (b) analyses of pollen contents in pollen loads and (c) in nectar loads of bumblebees. The number of flower species utilized by each bumblebee species turned out to be the same by all the three methods. The methods also agreed with the obtained niche width results (after square root transformation for the data on (b) and (c)). However, the method (c) scored the lowest niche evenness figures. Niche overlap values of the methods (b) and (c) were the same, while the smallest overlap values were obtained by the method (a). Reasons for the differences are discussed. Method (a) is considered to be the easiest to conduct, but methods (b) and (c) are required for certain types of studies (e.g., flower constancy). In studies where the interest is focussed on the number of flower species in the diet of bumblebee species, the result is independent of the method used, while the outcome of frequency dependent niche analyses is, to some extent, affected by the chosen method.