Abstract
Conspecific individuals inhabiting nearby breeding colonies are expected to compete strongly for food resources owing to the constraints imposed by shared morphology, physiology, and behavior on foraging strategy. Consequently, colony‐specific foraging patterns that effectively partition the available resources may be displayed. This study aimed to determine whether intraspecific resource partitioning occurs in two nearby colonies of Lesser Frigatebirds (Fregata ariel). A combination of stable isotope analysis and GPS tracking was used to assess dietary and spatial partitioning of foraging resources during the 2013 and 2014 breeding seasons. These results were compared to vessel‐derived estimates of prey availability, local primary productivity, and estimates of reproductive output to suggest potential drivers and implications of any observed partitioning. Isotopic data indicated a more neritic source of provisioned resources for near‐fledged chicks at an inshore colony, whereas their offshore counterparts were provisioned with resources with a more pelagic signal. Deep pelagic waters (>200 m) had higher availability of a preferred prey type despite a trend for lower primary productivity. Differences in foraging ecology between the two populations may have contributed to markedly different reproductive outputs. These findings suggest environmental context influences dietary and spatial aspects of foraging ecology. Furthermore, the effect of colony‐specific foraging patterns on population demography warrants further research.
Highlights
Colonial organisms may gain fitness benefits from their group-living lifestyle
Field work was conducted at two locations in the Browse Basin, northwestern Australia (Figure 1)
No significant differences in δ 13C or δ 15N values between years or sexes were found for feather or red blood cell (RBC) samples of adult Lesser Frigatebirds breeding at Ashmore Reef (Feathers PERMANOVA: F3,38 = 0.23, p = .74; RBC PERMANOVA: F3,38 = 0.55, p = .60) (Figure 3a,b)
Summary
Colonial organisms may gain fitness benefits from their group-living lifestyle. These benefits include predator defense (Uetz & Hieber, 1994), transmission of social information (Krebs, 1974; Riley, Greggers, Smith, Reynolds, & Menzel, 2005; Robinson, Richardson, Sendova- Franks, Feinerman, & Franks, 2009), and increased likelihood of finding a mate (Simpson, Smith, & Kelsall, 1987). Does provision of adequate food avoid starvation-mediated mortality, but higher prey delivery correlates with faster growth of the young (Bukaciński, Bukacińska, & Spaans, 1998; Harfenist, 1995), shorter development times (Harfenist, 1995), and higher body mass at independence (Bosch & Vicens, 2006; Harfenist, 1995) These qualities confer advantages on the young that may be maintained long after the young have reached independence (Hamer, Furness, & Caldow, 1991; Schwagmeyer & Mock, 2008). Competition from adjacent colonies within the foraging range of a population of seabirds tends to impose limits on total population size (Furness & Birkhead, 1984) This indicates that depletion of prey resources has occurred as a result of metapopulation-wide foraging activity and that the reduced availability of food for provisioning young sets a limit on the total reproductive output of the metapopulation. Findings were compared to at-sea abundance estimates of their primary prey type, local primary productivity, and estimates of reproductive success to infer putative effects of any observed resource partitioning on populations
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