Abstract Detail

Ecological Section

Miller-Struttmann, Nicole [1], Franklin, James [2], Galen, Candace [2].

Bumblebee foraging behavior and plant-pollinator network structure across an altitudinal gradient.

Background and methods: Due to reduced time for growth and productivity at high elevations, consumer-producer interactions should vary along altitudinal gradients. These changes can affect producer diversity when keystone consumers are involved. Bumblebees, keystone pollinators in temperate ecosystems, are increasingly limited by a shorter growing season and low colony productivity at high altitudes. High altitude bumblebees should therefore be more generalized in their host plant-use. At a community level, their interaction networks should be strongly nested with few, highly-connected bumblebee species visiting numerous relatively specialized host plant species. At lower-elevations, with increased productivity and higher forager density, bumblebees should exhibit greater resource partitioning and less nested pollination networks. These network properties have implications for species persistence because networks that are highly nested have greater redundancy (i.e., niche overlap) and thus are more robust to the extirpation of any given species. We use regional surveys of bumblebees conducted by L. W. Macior from 1966-1969 at three altitudinal ranges (montane, sublapline, and alpine) in the Colorado Rocky Mountains to test for altitudinal changes in foraging niche overlap and pollination network properties. Such changes could indicate whether altitudinal zones pose unique challenges for bumblebees and their host plants.
Results and conclusions: Historical surveys reveal altitudinal variation in the degree to which bumblebee species partition floral resources. Foraging niche overlap among bumblebees was higher in the alpine than the subalpine, but bumblebee niche overlap did not differ between subalpine and montane communities. These results indicate that low-elevation bumblebees exhibited greater resource partitioning, as predicted if competition for floral resources drives host use in lower, more productive habitats. Additionally, alpine networks tended to be more nested than subalpine and montane networks, suggesting a lower degree of foraging specialization. Analysis of network characteristics also reveals altitudinal variation in community dynamics of pollen foragers. Relative to lower elevations, alpine networks of pollen foraging bumblebees tended to be less specialized and more robust to the extirpation of plant species. Results suggest that alpine networks were historically dependent on few, highly connected bumblebee species, features that could render them highly sensitive to changes in bumblebee diversity. This finding emphasizes the importance addressing how resident alpine bumblebee species are changing with upward mobility of congeners from subalpine and montane habitats.

Broader Impacts:

1 - University of Missouri, Biology, 110 Tucker Hall, St. Louis, MO, 65211, USA
2 - University of Missouri, Biological Sciences, 105 TUCKER HALL, Columbia, MO, 65211, USA

Keywords:
bumblebee host plant-use
Altitudinal gradient
foraging niche partitioning
networks
caste foraging patterns
pollen and nectar foragers.

Presentation Type: Oral Paper:Papers for Sections
Session: 41
Location: Newberry/Riverside Hilton
Date: Wednesday, July 31st, 2013
Time: 10:30 AM
Number: 41006
Abstract ID:531
Candidate for Awards:None