The shifting importance of abiotic and biotic factors across the life cycles of wild pollinators

Abstract

Organisms living in seasonal environments are exposed to different environmental conditions as they transition from one life stage to the next across their life cycle. How different life stages respond to these varying conditions, and the extent to which different life stages are linked, are fundamental components of the ecology of an organism. Nevertheless, the influence of abiotic and biotic factors on different parts of an organism's life cycle is often not accounted for, which limits our understanding of the ecological consequences of environmental change. We investigated the relative importance of climate conditions, food availability, and previous life‐stage abundance in an assemblage of seven wild bumble bee species, asking: how do these three factors directly influence bee abundance at each life stage? To do so, we used a 7‐year dataset where we monitored climate conditions, floral resources, and abundances of bees in each life stage across the active colony life cycle in a highly seasonal subalpine ecosystem in the Colorado Rocky Mountains, USA. Bee abundance at different life stages responded to abiotic and biotic conditions in a broadly consistent manner across the seven species: the survival and recruitment stage of the life cycle (overwintered queens) responded negatively to longer winters; the growth stage (workers) responded positively to floral resource availability; and the reproductive stage (males) was positively related to the abundance of the previous life stage (workers). Most species also exhibited some idiosyncratic responses. Our long‐term examination of annual bumble bees reveals a general set of responses in the abundance of each life stage to climate conditions, floral resource availability, and previous life stage. Across species, these three factors each directly influenced a distinct life stage, illustrating how their relative importance can shift throughout the life cycle. The life‐cycle approach that we have taken highlights that important details about demography can be overlooked without considering life‐stage‐specific responses. Ultimately, it is these life‐stage‐specific responses that shape population outcomes, not only for animal pollinators but also for many organisms living in seasonal environments.

The importance of a holistic approach to the factors determining population abundances

“…This is precisely what Ogilvie & CaraDonna (2022) have attempted to do in this study. The authors used a 7 years dataset where they studied climate conditions, floral resources and abundance of bumblebees in each life stage of the colony life in a highly seasonal mountain system, the subalpine habitats near the Rocky Mountain Biological Laboratory in Colorado—USA.…”

“…These periods are determined by snowmelt, which is highly dependent on temperature, and which determines the abundance of flowers in the area (CaraDonna et al, 2014). Ogilvie & CaraDonna (Ogilvie & CaraDonna, 2022) focus on understanding the drivers of pollinator abundance across the different life stages of seven bumblebee species, specifically focusing on abiotic (climatic) and biotic conditions (floral resources and the abundance of previous life stages). In the case of pollinators, their different life stages include periods of hibernation, active food search, nest foundation or mating, each of which presumably requires different conditions.…”

“…In the case of pollinators, their different life stages include periods of hibernation, active food search, nest foundation or mating, each of which presumably requires different conditions. In their research, Ogilvie & CaraDonna (2022) focus on three life stages: overwintered queens, workers and males which reflect periods of survival and new colony establishment, active foraging and growth, and mating respectively. They find that there is some covariation in the abundance of some of the life stages, particularly those related to growth and reproduction, while others were rather independent.…”

“…Another interesting finding of this research is the contrasting effect that climate change and particularly warming could have on different life‐stages. While warming could accelerate snowmelt leading to shorter winters and greater queen abundances, the lack of snowmelt water input could lead to reduced floral resources during the growing season, thus affecting worker and consequently male stages of the bumblebee life cycles (Ogilvie & CaraDonna, 2022). Such contrasting effects of climate change on different life‐stages of species have been shown for other taxonomic groups ranging from trees (Ibáñez et al, 2014), to mammals (Cordes et al, 2020), or seabirds (Fay et al, 2017).…”

“…In this long‐term study, Ogilvie and CaraDonna (2022) demonstrate that the conservation of these bumblebee species will require a detailed knowledge of their ecology, their seasonal demographic responses and the different responses to the biotic and abiotic environment throughout their life cycle. Knowledge of the life‐stages specific responses to multiple factors that impact population abundances such as that provided by Ogilvie and CaraDonna (2022) is critical to understand the environmental changes most likely to influence wild pollinator populations.…”