Abstract Detail

Reproductive Processes

Martin, Valerie [1], Miller-Struttmann, Nicole [2].

Upslope migration of subalpine bees reinforces alpine visitation network structure but disrupts pollination services.

Climate-induced shifts in species ranges are resulting in novel communities as the ranges of colonizing species overlap with resident taxa. The availability of empty niches or opportunities for resource partitioning could promote coexistence between colonizing and resident taxa. Bumble bee communities in cold, high alpine habitats of the central Rocky Mountains, have become more diverse as the range of subalpine bumble bees has moved upslope and that of resident alpine bees has remained static. The composition of alpine plant taxa, on the other hand, has remained relatively unchanged, because many species can live decades or more. While several studies in mountain ecosystems have documented upslope shifts in pollinator distributions, few have investigated how the characteristics of resulting novel communities may differ from past alpine communities or how changes in those characteristics may affect their pollination services. In this study, we assess the effects of climate change on alpine bumble bee community assembly, plant-pollinator interaction networks, and potential pollination services. Using bumble bee visitation records spanning 50 years, we test whether documented changes in foraging behavior and the upward migration of subalpine bees modify resource partitioning and network structure, robustness, and function. We quantified network structure and dynamics for the “past” (1966-69) and “modern” (2012-2014) networks pooled across locations and years, and calculated z-scores standardized against a null model to control for network size. We then resampled the past and modern visitation networks to estimate confidence limits for each network characteristic (i.e., modularity and robustness to extinction) and tested for a difference between the past and modern network. We tested for changes in (1) bumble bee niche breadth and partitioning and (2) plant partner diversity and reliance (i.e., interaction push-pull).
The number of modules was similar between the past and modern networks, despite a significant increase in bee species diversity. However, the strength of modularity (M) increased. This is consistent with increased niche partitioning among bumble bee species as each species integrated a unique suit of new plant species into their diet. Niche partitioning was higher among bees with similar tongue lengths, indicating that competition has increased for resident species that have similar traits to colonizing species. Colonizing taxa have shorter tongues than alpine resident bumble bees, resulting in a functional shift to the detriment of the long-tongue phenotype and, potentially, their host plants. Plant partner diversity decreased, increasing their reliance on a smaller subset of the pollinator community. However, neither change in partner diversity nor push-pull was predicted by tube depth, indicating that shifts in pollinator behavior are consistent across species with different tube depths. Reliance on fewer, more cosmopolitan pollinator species may reduce pollen purity and make alpine plant species susceptible to future perturbations. Moreover, behavioral shifts resulted in lower predicted network robustness to bumble bee extinction, but increased robustness to plant extinction. Our results suggest that, while adaptive foraging may buffer resident bumble bees from competition with colonizing taxa, shifts in pollinator behavior may have negative fitness consequences for their alpine host plants.

1 - Webster University, Biological Sciences, 470 E. Lockwood Ave. , St. Louis, MO, 63119, USA
2 - Webster University, 470 Lockwood Ave., St. Louis, MO, 63119, United States

climate change
pollination services
visitation network
alpine ecology.

Presentation Type: Oral Paper
Number: RP4001
Abstract ID:625
Candidate for Awards:None

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