Spatio-temporal dynamics of landscape use by the bumblebee Bombus pauloensis (Hymenoptera: Apidae) and its relationship with pollen provisioning

Tracking large bees in open landscapes with active radio tags-Advantages and challenges using stationary receivers

Recent technological advancements have allowed ecologists to study the movement of smaller animals, including insects, using remote tracking methods, such as very-high-frequency (VHF) technology. VHF tracking technology enables us to study migration patterns, spatial behaviour and distribution in ecologically relevant species, thereby supporting the development of effective conservation strategies. We applied VHF transmitters on two European carpenter bee species, Xylocopa valga and Xylocopa violacea, and established a remote tracking approach for insects <1 g. We studied the effect of the tags on the species' flight behaviour and their movement patterns within an open grassland landscape in Central Europe. We provided a detailed description of the application of miniaturised transmitters on the dorsal body of the bees and a step-by-step guide from purchasing the material to constructing stationary receivers. We discussed potential pitfalls of the applied technologies and how to overcome them in the field. Further, we provided a dataset and script to process the information collected by the receivers with open-source software. Our study shows that miniaturised VHF transmitters, in combination with stationary receivers, are a powerful tool for insect movement research. However, ecologists must take great care in selecting the study area and target animals and in analysing the data.

Bumble bee movement ecology: foraging and dispersal across castes and life stages

Movement is a dynamic process that changes with ontogeny, physiological state, and ecological context. The results of organismal movement impact multiple dimensions of fitness, population dynamics, and functional interactions. As such, the study of movement is critical for understanding and conserving species. Bumble bees (Apidae: Bombus spp.) offer a powerful system to study multiple complexities of movement within a functionally important clade. Their life history includes distinct social and solitary phases, substantial intraspecific variation in body size, and multiple modes of movement behavior. These traits allow investigations of diverse concepts at multiple scales and during contrasting behavioral and motivational states-from individuals, to colonies, to populations, and among species. Despite extensive study as model organisms of fine-scale movements and optimal foraging theory, understanding of landscape-scale movements is more limited. This knowledge gap is especially troubling given global pollinator declines because such dispersive movements fundamentally affect how populations respond to landscape transformation, climate change, and restoration efforts. To build toward a refined understanding of the bumble bee movement, inform research, and assist conservation programs, we review foraging and dispersal movement across life stages and castes. Using an ontogenetic approach, we compare the movement motivation and capacity of individuals throughout colony development. Despite the growth in recent literature, much remains to be learned about the bumble bee movement, especially dispersive life stages. Focused effort on how movement varies with individual state such as nutrition and age, and comparative studies of species would all fill knowledge gaps with high potential to improve bee conservation and research.

Caterpillar movement mediates spatially local interactions and determines the relationship between population density and contact

BACKGROUND

While interactions in nature are inherently local, ecological models often assume homogeneity across space, allowing for generalization across systems and greater mathematical tractability. Density-dependent disease models are a prominent example of models that assume homogeneous interactions, leading to the prediction that disease transmission will scale linearly with population density. In this study, we examined how the scale of larval butterfly movement interacts with the resource landscape to influence the relationship between larval contact and population density in the Baltimore checkerspot (Euphydryas phaeton). Our study was inspired by the recent discovery of a viral pathogen that is transmitted horizontally among Baltimore checkerspot larvae.

METHODS

We used multi-year larvae location data across six Baltimore checkerspot populations in the eastern U.S. to test whether larval nests are spatially clustered. We then integrated these spatial data with larval movement data in different resource contexts to investigate whether heterogeneity in spatially local interactions alters the assumed linear relationship between larval nest density and contact. We used Correlated Random Walk (CRW) models and field observations of larval movement behavior to construct Probability Distribution Functions (PDFs) of larval dispersal, and calculated the overlap in these PDFs to estimate conspecific contact within each population.

RESULTS

We found that all populations exhibited significant spatial clustering in their habitat use. Subsequent larval movement rates were influenced by encounters with host plants and larval age, and under many movement scenarios, the scale of predicted larval movement was not sufficient to allow for the "homogeneous mixing" assumed in density dependent disease models. Therefore, relationships between population density and larval contact were typically non-linear. We also found that observed use of available habitat patches led to significantly greater contact than would occur if habitat use were spatially random.

CONCLUSIONS

These findings strongly suggest that incorporating larval movement and spatial variation in larval interactions is critical to modeling disease outcomes in E. phaeton. Epidemiological models that assume a linear relationship between population density and larval contact have the potential to underestimate transmission rates, especially in small populations that are already vulnerable to extinction.

Utility of carbon and nitrogen stable isotopes for inferring wild bee (Hymenoptera: Apoidea) use of adjacent foraging habitats

Isotope analysis has proven useful for understanding diets of animals that are difficult to track for extended periods. Bees are small yet highly mobile and often forage from multiple habitats. However, current methods of assessing diet are limited in scope. Efficient methods of tracking bee diets that integrate across life stages, distinguish habitat use, and are sensitive to taxonomic differences will inform conservation strategies. We evaluated the utility of stable isotope analysis for estimating contributions of adjacent habitats to bees’ diets. We also investigated taxonomic variation in bee and flower isotope composition. We measured natural abundance of carbon and nitrogen stable isotopes in two body regions from three wild bee genera, as well as in 25 species of flowers that likely comprised their diets. Bee ∂13C and ∂15N varied with habitat and taxonomic groups (conflated with month), but did not match spatial or seasonal trends in their food plants. Flower ∂13C was lowest in the forest and in April–June, as expected if driven by water availability. However, bee ∂13C was elevated in the spring, likely from overwintering nutritional stress or unpredictable food availability. Bumble bees (Bombus) were enriched in ∂15N compared to others, possibly reflecting differences in larval feeding. Bee diet mixing models had high variation and should be interpreted with caution. Models estimated similar habitat contributions to diets of spring Andrena and overwintered Bombus queens. Summer Bombus queens and workers were indistinguishable. Sweat bees (Halictus) were estimated to use comparatively more field flowers than others. Overall, taxon more strongly influenced isotope composition than either foraging habitat or month, likely because of associated differences in sociality and timing of annual activity. Future studies seeking to reveal bee diets by isotope analysis may gain better resolution in more isotopically distinct habitats, in conjunction with controlled feeding or isotope labeling experiments.