Abstract
We present novel dynamic mixture models for the monitoring of bumblebee populations on an unprecedented geographical scale, motivated by the UK citizen science scheme BeeWalk. The models allow us for the first time to estimate bumblebee phenology and within-season productivity, defined as the number of individuals in each caste per colony in the population in that year, from citizen science data. All of these parameters are estimated separately for each caste, giving a means of considerable ecological detail in examining temporal changes in the complex life cycle of a social insect in the wild. Due to the dynamic nature of the models, we are able to produce population trends for a number of UK bumblebee species using the available time-series. Via an additional simulation exercise, we show the extent to which useful information will increase if the survey continues, and expands in scale, as expected. Bumblebees are extraordinarily important components of the ecosystem, providing pollination services of vast economic impact and functioning as indicator species for changes in climate or land use. Our results demonstrate the changes in both phenology and productivity between years and provide an invaluable tool for monitoring bumblebee populations, many of which are in decline, in the UK and around the world. Supplementary materials accompanying this paper appear online.
Highlights
Over the past 80 years, two bumblebee species have gone extinct in the UK (Ollerton et al 2014)
To match the species’ ecology, the various parameters are largely required to differ between castes, and for monitoring purposes the model’s appeal lies in the capacity to consider, for example, the extent to which these vary over successive seasons
While issues of representativeness are widely recognised, many such schemes are reported on annually and provide a major component of advice to policymakers as well as the general public
Summary
Over the past 80 years, two bumblebee species have gone extinct in the UK (Ollerton et al 2014). We introduce in this paper an analytical approach motivated by, and designed for, bumblebee count data, accommodating the ecology of the species and thereby producing invaluable information on demographic parameters, such as indices of caste-specific relative abundance, amongst others. An additional advantage of our method is that estimation of the phenology and relative numbers in each caste remains possible from such aggregated data, via the adoption of a mixture model in which the proportions of observations in each caste are additional, estimable parameters This combination of a rigorous statistical method and ongoing, largescale data collection greatly increases the capacity to identify changes experienced by wild bumblebee populations and facilitates the adoption, and assessment, of any agri-environment schemes aimed at the recovery of these species and the pollination services they provide. We note that the total count of group U for the species considered is around 400 for B. hortorum, which corresponds to about 5% of the total count while the corresponding numbers and proportions for the other species are around: B. hypnorum: 700 (11%), B. lapidarius: 800 (3%), B. pascuorum 3600 (9%) and B. pratorum: 400 (4%)
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