Limitation of complementary resources affects colony growth, foraging behavior, and reproduction in bumble bees

Abstract

Resource availability in agricultural landscapes has been disturbed for many organisms, including pollinator species. Abundance and diversity in flower availability benefit bee populations; however, little is known about which of protein or carbohydrate resources may limit their growth and reproductive performance. Here, we test the hypothesis of complementary resource limitation using a supplemental feeding approach. We applied this assumption with bumble bees (Bombus terrestris), assuming that colony growth and reproductive performance should depend on the continuous supply of carbohydrates and proteins, through the foraging for nectar and pollen, respectively. We placed wild‐caught bumble bee colonies along a landscape gradient of seminatural habitats, and monitored the colonies’ weight, foraging activity, and reproductive performance during the whole colony cycle. We performed supplemental feeding as an indicator of landscape resource limitation, using a factorial design consisting of the addition of sugar water (carbohydrate, supplemented or not) crossed by pollen (protein, supplemented or not). Bumble bee colony dynamics showed a clear seasonal pattern with a period of growth followed by a period of stagnation. Higher abundance of seminatural habitats resulted in reducing the proportion of pollen foragers relative to all foragers in both periods, and in improving the reproductive performance of bumble bees. Interestingly, the supplemental feeding of sugar water positively affected the colony weight during the stagnation period, and the supplemental feeding of pollen mitigated the landscape effect on pollen collection investment. Single and combined supplementation of sugar water and pollen increased the positive effect of seminatural habitats on reproductive performance. This study reveals a potential colimitation in pollen and nectar resources affecting foraging behavior and reproductive performance in bumble bees, and indicates that even in mixed agricultural landscapes with higher proportions of seminatural habitats, bumble bee populations face resource limitations. We conclude that the seasonal management of floral resources must be considered in conservation to support bumble bee populations and pollination services in farmlands.

Joint Impacts of Drought and Habitat Fragmentation on Native Bee Assemblages in a California Biodiversity Hotspot

“…Pollen specialists may withstand drought by associating with drought-hardy plant species, or by evolving more finely-tuned synchronization of phenologies with their host plants, including greater propensity to aestivate through drought years when environmental conditions prohibit their host plants from blooming [19,26] (but see [18]). Lastly, decreases in the relative abundance of non-Dialictus eusocial bees in fragments after the drought event suggest that for the rest of the eusocial taxa, heightened requirements for ample and consistently available food resources [27,28] may have imposed a fitness cost that could not be overcome by a generalist diet. Contrasting responses of different eusocial bee taxa to drought (if indeed no Dialictus species in our system exhibits solitary life history atypical for the subgenus) indicate that a nuanced approach must be taken when attempting to understand and predict the response of bees to environmental perturbations based on examinations of single functional traits.…”

“…While the majority of species in our system are solitary in the broad sense (i.e., non-eusocial), several genera consist at least in part of primitively eusocial species, which form annual colonies founded by a single queen produced by the previous generation. Eusocial species may perform poorly relative to solitary species in years of reduced resource availability because of their higher sensitivity to resource gaps during their long colony lifetime [27,28]. However, all eusocial species in our system exhibit a generalist diet, which, as discussed above, may allow them to profit from those floral resources that are available during the drought.…”

Critical links between biodiversity and health in wild bee conservation

“…The quality of food resources depends on the composition of different flowering plant species because each plant species provides pollen and/or nectar with a specific nutrient profile [31]. In fact, the nutritional profiles of pollen and nectar vary greatly among different plant species [32][33][34][35] and even between plant individuals of the same species growing in different plant communities [36]. Floral communities, which are characterized by a specific composition and diversity of flowering plant species, consequently determine resource availability and diversity, and thus determine the nutritional landscape in which bees are foraging [21].…”

Quantifying habitat and landscape effects on composition and structure of plant-pollinator networks in the US Northern Great Plains

“…For example, proximity to semi-natural habitats increases the abundance of both wild bees and honey bees in crops (Steffan-Dewenter et al 2002;Kremen et al 2004;Heard et al 2007). Likewise, increased availability and diversity of flowering plants in natural areas benefits pollinator populations (Potts et al 2003;Potts et al 2005;Ponisio et al 2019;Requier et al 2020). Recent studies (Nottebrock et al 2017) demonstrate that the level of available sugar resources to pollinators can have considerable effects on the outcome of plantpollinator interactions.…”