CONSPECIFIC FOOD COMPETITION EXPLAINS VARIABILITY IN COLONY SIZE: A TEST IN MAGELLANIC PENGUINS

By Manuel Guillermo Forero, J. Tella, Keith A. Hobson, M. Bertellotti, G. Blanco. 2002

133 citations recorded by the source corpus.

Food availability has been proposed as one of the main factors regulating population sizes in birds. Seabirds have provided evidence for the hypothesis that food depletion due to intraspecific competition explains variability in colony size. However, the predictions derived from this hypothesis have not been fully tested due mainly to the difficulties in measuring food availability in marine environments. We measured stable isotopes of nitrogen (d 15 N) and carbon (d 13 C) in the blood of Magellanic Penguins (Sphen- iscus magellanicus), which reveal information about their consumed prey and foraging habits. We tested if conspecific competition causes food depletion, affecting penguin breed- ing performance and, ultimately, the size of the colonies. Blood d 15 N values of adults and chicks significantly decreased with increasing size of their colonies and with the number of conspecifics breeding within the parental foraging ranges. This suggests that high breed- ing densities provoke the depletion of high-quality prey (mainly anchovy). We also found positive relationships between d 13 C values and density of conspecifics within the parental foraging ranges, indicating that when competition for food is high, individuals tend to feed closer to the colony on prey of lower quality. Adult d 15 N values were positively correlated with breeding success at the colonies, which was negatively correlated with the density of conspecifics within foraging ranges. Moreover, d 15 N values of fledglings were positively correlated with their body condition but not with their T-cell mediated immune response considered as two measures of their survival prospects. This decreased breeding output was translated to the colony-size structure of the population, since colony size was nega- tively correlated with the number of conspecifics breeding within the parental foraging ranges. Therefore, we provide strong evidence suggesting that density-dependent food de-

Subfields: Ecology

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Citations in the corpus

Stable isotopes reveal trophic segregation by sex and age in the southern giant petrel in two different food webs (2005, background): “…could be influenced by the differential distribution of marine resources, including prey quality and availability (Croxall & Lishman 1987, Velando & Freire 1999), but also by the level of intraspecific competition determined by colony and population size (Ainley et al. 2003, Forero et al. 2003).”
DISPERSAL AND SOCIAL ATTRACTION AFFECT COLONY SELECTION AND DYNAMICS OF LESSER KESTRELS (2004, background): “…et al. 2000), colony populations may be regulated by factors affecting fitness components such as food availability (Furness and Birkhead 1984, Forero et al. 2002, Oro et al. 2003), pre- 3 E-mail: serrano@ebd.csic.es dation pressure (Southern et al. 1985, Kilpi 1995), and parasite loads…”
Components of breeding performance in two competing species: habitat heterogeneity, individual quality and density‐dependence (2006, background): “They have been shown to operate in colonial birds (Ferná ndez et al. 1998, Tella et al. 2001, Forero et al. 2002), but less evidence is available for territorial species.”
An energetic correlate between colony size and foraging effort in seabirds, an example of the Adélie penguinPygoscelis adeliae (2009, background): “An inverse correlation is often evident between colony size and reproductive success, numbers of conspecifics at other colonies with overlapping foraging ranges, and diet quality (Furness and Birkhead 1984, Hunt et al. 1986, Lewis et al. 2001, Forero et al. 2002, Ainley et al. 2003a, 2004, Hipfner”
High trophic overlap within the seabird community of Argentinean Patagonia: a multiscale approach (2004, background): “…alternatives at each trophic level, and in particular where seabird diet is often based on a superabundance of a single prey type such as anchovy (Forero et al. 2002a), Arctic cod (Boreogadus saida, Hobson & Welch 1992) or krill (Euphausia sp.; Croxall & Prince 1987) then trophic overlap has a…”
Using stable isotopes of nitrogen and carbon to study seabird ecology: applications in the Mediterranean seabird community* (2003, background): “…SEABIRD COMMUNITY Most previous studies applying the stable isotope technique to the study of seabird ecology have been carried out in the Northern Hemisphere (but see Bocher et al., 2000; Hodum and Hobson, 2000; Thompson et al., 2000; Forero et al., 2002; Forero et al., 2002b) (Table 1).”
Habitat preference, accessibility, and competition limit the global distribution of breeding Black-browed Albatrosses (2011, background): “This is perhaps unsurprising, as it seems reasonable to assume that on average the fitness of two birds from the same colony diminishes at the same rate with dc (see also Forero et al. 2002).”
Matches and mismatches: ocean climate, prey phenology and breeding success in a zooplanktivorous seabird (2008, background): “Mismatching could have particularly severe consequences for an aggregation of this size because the intensity of intraspecific competition for food can increase with colony size in seabirds (Gaston et al. 1983, Forero et al. 2002).”
Spatial interaction between seabirds and prey: review and synthesis (2009, background): “…range of birds from neighboring colonies overlap less than could be expected from the distance between the colonies alone (Ainley et al. 2003, 2004, Grémillet et al. 2004), and the availability of prey around the colony decrease with increasing colony size (Forero et al. 2002, Ainley et al. 2003).”
Application of central-place foraging theory shows the importance of Mediterranean dehesas for the conservation of the cinereous vulture, Aegypius monachus (2005, background): “(Tella et al., 1998, 2001; Forero et al., 2002 ), even aVecting large-scale population trends (e.g., Tella et al., 1998).”
Stable isotopes indicate sex-specific and long-term individual foraging specialisation in diving seabirds (2006, background): “…(0.4) –18.2 (0.3) –18.3 (0.2) South Georgian shag (feathers) 14.2 (0.4) 13.3 (0.6) –17.4 (0.3) –17.5 (0.2) Bearhop et al.: Foraging specialisations in seabirds shags that the larger bills of males allow them to capture larger prey items (Agnew & Kerry 1995, Kato et al. 2000, Forero et al. 2002).”
GEOGRAPHIC STRUCTURE OF ADÉLIE PENGUIN POPULATIONS: OVERLAP IN COLONY-SPECIFIC FORAGING AREAS (2004, background): “Only the studies by Forero et al. (2002) and Ainley et al. (2003b) attempted to quantify prey availability and depletion simultaneously at more than one colony.”
Central-Place Foraging in an Arctic Seabird Provides Evidence for Storer-Ashmole's Halo (2009, background): “…et al. 2000, Ballance et al. 2009); (3) reduced size of neighboring colonies (Furness and Birkhead 1984; Ainley et al. 1995, 2004; Lewis et al. 2001; Forero et al. 2002; Ford et al. 2007); and (4) increased trip duration (Lewis et al. 2001; Ainley et al. 2003, 2004; Davoren and Montevecchi 2003).”