Conspecific Food Competition Explains Variability in Colony Size: A Test in Magellanic Penguins

Forero, Manuela G.; Tella, José Luis; Hobson, K. A.; Bertellotti, Marcelo; Blanco, Guillermo

doi:10.2307/3072095

Cited by 42 publications

(51 citation statements)

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“…5). This evidence supporting an effect of the number of competitors per unit of habitat indicates that, as expected according to theory, the size of rook colonies in Spain decreased with a greater number of competitors relative to foraging habitat within 6 km from the colony site, which is in agreement with the findings of Griffin and Thomas (2000) for rooks in England, and is also compatible with that found for Scottish rooks (Gimona and Brewer 2006), and for other colonial species (for competence: Furness and Birkhead 1984;Forero et al 2002;for habitat: Gibbs et al 1987;Gibbs 1991;Ambrosini et al 2002;Barbraud et al 2002;. For the first time a derived variable made up of the combination of both number of competitors and area of foraging habitat is found to be associated with colony size.…”

Section: Food and Competition-related Hypothesessupporting

confidence: 86%

“…If food is a determinant of colony size and foraging ranges overlap between colonies, competition for food by members of the same colony (competition intra-colony; Ashmole 1963) and the neighbouring colonies (competition inter-colony; Furness and Birkhead 1984) may reduce net food availability around colonies and ultimately affect their population sizes. This idea has been mainly supported by negative correlations found between colony size and the number of conspecifics breeding in neighbouring colonies (Furness and Birkhead 1984;Ainley et al 1995;Griffin and Thomas 2000;Forero et al 2002). However, this is not always the case (Gibbs et al 1987;Ainley et al 1995;Griffin and Thomas 2000;, and, therefore, evidence of the effect of neighbours is mixed.…”

Section: Introductionmentioning

confidence: 82%

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Analysing spatial and temporal variation in colony size: an approach using autoregressive mixed models and information theory

Olea

2008

Population Ecology

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The spatial and temporal variation in population sizes of animal colonies are rarely studied simultaneously. I examined factors determining colony size (number of nests) for 23 colonies from the only breeding population of rook Corvus frugilegus in Spain over 7 years. Population sizes within colonies were highly predictable over time, with autocorrelations up to a distance (lag) of 6 years. Autoregressive mixed models were used to explain colony size as a function of environmental factors, while controlling for temporal autocorrelation. These factors included refuse tips, widely used as food resource, and a derived variable that incorporated the two factors most often related to avian colony size (inter-colony competition and foraging habitat around colonies). Autoregressive models provided a better fit to the data than models which did not consider temporal autocorrelation. The information-theoretic (AIC c -based) approach revealed uncertainty in the selection of the best model explaining colony-size, but relatively strong support for certain variables. The highest weights of evidence were for year (x i = 0.90) and the number of competitors per unit of foraging habitat (i.e., derived variable; x i = 0.63), showing that the size of rook colonies in Spain was negatively affected by inter-colony competition relative to the foraging habitat surrounding the colonies. This variable measured within a 6-km radius from the colonies had *30 times higher weight of evidence (more plausible) than the same variable measured within 3 km, indicating that food limitation may occur outside the breeding period. Sizes of colonies tended to decrease when distance between the colony and the nearest refuse tip increased. There was some evidence supporting the idea that the effect of the number of competitors per unit of foraging habitat on colony size varied from year to year, but statistical power was weak. These findings suggest that variation in number of rook nests within colonies reflects spatial and temporal heterogeneity of net food via both inter-colony competition and foraging habitat around the colony.

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Section: Food and Competition-related Hypothesessupporting

confidence: 86%

Section: Introductionmentioning

confidence: 82%

Analysing spatial and temporal variation in colony size: an approach using autoregressive mixed models and information theory

Olea

2008

Population Ecology

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“…For example, Magellanic penguin fledglings (Spheniscus magellanicus) feed mainly on anchovies, and to a lesser extent on squid . Anchovies have higher d 15 N values than squid, and individuals that consume a higher proportion of anchovies have higher body condition (Forero and Tella 2002). This would result in a positive relationship between d 15 N and BCI (the opposite of that found here), but in other circumstances, the relationship between these two variables may be negative.…”

Section: Discussionmentioning

confidence: 38%

“…However, several recent studies have suggested that an individual's physiology may also affect its isotopic signature (Gannes et al 1997;Wolf et al 2009;Ehrich et al 2010), potentially obscuring or biasing differences that are too often assumed to reflect only diet or foraging location. For instance, fractionation of heavy and light isotopes may vary during growth (Trueman et al 2005;Sears et al 2009) and in relation to body condition (Forero and Tella 2002) and nutritional stress (Hobson et al 1993;Cherel et al 2005a;Sears et al 2009). Moreover, physiological condition might also differ between sexes (Owen et al 2005), particularly in species with sexual size dimorphism where the larger sex has higher energy requirements (Magrath et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Stable isotope ratios of a tropical marine predator: confounding effects of nutritional status during growth

et al. 2012

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Stable isotope analysis of carbon and nitrogen is frequently used to study the diets and foraging ecology of marine predators. However, isotopic values may also be affected by an individual's nutritional status and associated physiological processes. Here, we use C and N stable isotopes in blood and feathers of blue-footed booby chicks at the Galápagos Islands to examine how isotopic values are related to body condition and growth rate, and to assess the consistency in the isotope ratios of individuals during growth. Size dimorphism in blue-footed boobies provided an additional opportunity to examine how isotope ratios differ between sexes in relation to body size and growth rate. There was no significant difference between sexes but both C and N stable isotopes were significantly negatively related to the body condition of chicks. These data were consistent with individual variation in physiological processes affecting fractionation, although we cannot rule out the possibility that they were also influenced to some extent by population-level variation in the stable isotope ratios of prey fed to chicks, for instance related to prey size, depth or lipid content. Our results highlight the need for methods that take proper account of confounding physiological factors in isotopic studies of foraging ecology and diet.

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“…Lindström et al 2005). As higher densities are expected on better-quality sites the strength of density dependence may be underestimated, so that this method usually cannot be used to give sensible results (but see, for example, Stokes and Boersma 2000;Forero et al 2002). …”

Section: Introductionmentioning

confidence: 97%

Quantifying density dependence in a bird population using human disturbance

Mallord

Dolman

Brown³

et al. 2007

Oecologia

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Although density dependence has long been recognised as vital to population regulation, there have been relatively few studies demonstrating it spatially in wildlife populations, often due to the confounding effects of variation in habitat quality. We report on a study of woodlarks Lullula arborea, a species of European conservation concern, breeding on lowland heath in Dorset, England. We take the novel approach of utilising the birds' response to human disturbance, which resulted in much of the variation in density but had no direct impact on demographic rates. Within years, in sites with greater density there were smaller mean chick masses, lower post-fledging survival, and higher rates of nestling mortality attributed to starvation. The effects on clutch size and fledging success were confounded by the area of grassland within a site. There was no effect on brood size. Density dependence also operated within sites between years: as density increased there were reductions in mean chick mass and post-fledging survival, while nestling mortality attributed to starvation increased. Density-dependent effects on clutch size were only weakly regulatory, whereas density-dependent starvation and post-fledging mortality rates contributed strongly to differences in overall breeding output. Heavier chicks (when 7 days old) were significantly more likely to fledge and less likely to starve. Broods with heavier chicks were more likely to supply recruits to the breeding population. Nestling mass was not a factor in survival in the immediate post-fledging period, suggesting that density-dependent processes act independently on this stage. We conclude that the number of birds per hectare of suitable habitat is a valid means of expressing density, and that habitat acts as a surrogate for food abundance through which density dependence operates on the woodlark population.

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Conspecific Food Competition Explains Variability in Colony Size: A Test in Magellanic Penguins

Cited by 42 publications

References 0 publications

Analysing spatial and temporal variation in colony size: an approach using autoregressive mixed models and information theory

Analysing spatial and temporal variation in colony size: an approach using autoregressive mixed models and information theory

Stable isotope ratios of a tropical marine predator: confounding effects of nutritional status during growth

Quantifying density dependence in a bird population using human disturbance

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