Effects of group size and group density on tradeā€offs in resource selection by a groupā€territorial centralā€place foraging woodpecker

  • Authors: Garabedian, James E.; Moorman, Christopher E.; Peterson, M. Nils; Kilgo, John C.
  • Publication Year: 2019
  • Publication Series: Scientific Journal (JRNL)
  • Source: Ibis
  • DOI: 10.1111/ibi.12733

Abstract

Tradeā€offs in resource selection by centralā€place foragers are driven by the need to balance the benefits of selecting resources against the costs of travel from the central place. For groupā€territorial centralā€place foraging birds, tradeā€offs in resource selection are likely to be complicated by a competitive advantage for larger groups at high group density that may limit accessibility of highā€quality distant resources to small groups. We used the groupā€territorial, centralā€place foraging Redā€cockaded Woodpecker Leuconotopicus borealis (RCW) as a case study to test predictions that increases in group density lead to differences in foraging distances and resource selection for groups of different sizes. We used GPS tracking and LiDARā€derived habitat data to model effects of group size on foraging distances and selection for highā€quality pines (≥ 35.6 cm diameter at breast height (dbh)) and lower quality pines (25.4–35.6 cm dbh) by RCW groups across low (n = 14), moderate (n = 10) and high group density (n = 10) conditions. At low and moderate group density, all RCW groups selected distant highā€quality pines in addition to those near the central place because competition for resources was low. In contrast, at high group density, larger groups travelled further to select highā€quality pines, whereas smaller groups selected highā€quality pines only when they were close to the central place and, conversely, were more likely to select lower quality pines at greater distances from the central place. Selection for highā€quality pines only when close to the cavity tree cluster at high group density is important to longā€term fitness of small RCW groups because it allows them to maximize benefits from both territorial defence and selecting highā€quality resources while minimizing costs of competition. These relationships suggest that intraspecific competition at high group density entails substantive costs to smaller groups of territorial centralā€place foragers by limiting accessibility of distant highā€quality foraging resources.

  • Citation: Garabedian, James E.; Moorman, Christopher E.; Peterson, M. Nils; Kilgo, John C. 2019. Effects of group size and group density on tradeā€offs in resource selection by a groupā€territorial centralā€place foraging woodpecker. Ibis. 21: 155-. https://doi.org/10.1111/ibi.12733.
  • Keywords: competition, density dependence, endangered species, forest structure, functional response, LiDAR, Red-cockaded Woodpecker, space use
  • Posted Date: August 12, 2019
  • Modified Date: August 14, 2019
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