A Theoretical Investigation of the Effect of Latitude on Avian Life Histories

Department of Mathematics, University of Bristol, University Walk, Bristol BS8 1TW, United Kingdom.
The American Naturalist (Impact Factor: 3.83). 10/2008; 172(3):331-45. DOI: 10.1086/589886
Source: PubMed


Tropical birds lay smaller clutches than birds breeding in temperate regions and care for their young for longer. We develop a model in which birds choose when and how often to breed and their clutch size, depending on their foraging ability and the food availability. The food supply is density dependent. Seasonal environments necessarily have a high food peak in summer; in winter, food levels drop below those characteristic of constant environments. A bird that cannot balance its energy needs during a week dies of starvation. If adult predation is negligible, birds in low seasonal environments are constrained by low food during breeding seasons, whereas birds in high seasonal environments die during the winter. Low food seasonality selects for small clutch sizes, long parental care times, greater age at first breeding, and high juvenile survival. The inclusion of adult predation has no major effect on any life-history variables. However, increased nest predation reduces clutch size. The same trends with seasonality are also found in a version of the model that includes a condition variable. Our results show that seasonal changes in food supply are sufficient to explain the observed trends in clutch size, care times, and age at first breeding.

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    • "In general, populations inhabiting alpine habitats, i.e., high altitudes, have lower fecundity and higher adult survival than populations at lower elevations (Berven 1982; Innes and Millar 1990; Dobson 1992; Sandercock et al. 2005b; but see Krementz and Handford 1984). The opposite pattern is observed for populations at high latitudes, with an increase in fecundity and a decrease in adult survival from the tropics to the pole (Griebeler and Bohning-Gaese, 2004; Sandercock et al. 2005b; McNamara et al. 2008; Griebeler et al. 2010). Optimal management actions differ between populations with different demographic characteristics. "
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    • "during early morning and late afternoon exhibiting a bimodal pattern (Aschoff 1966; Morton 1967a; Daan & Aschoff 1975; Bednekoff & Houston 1994; McNamara et al. 1994) Such patterns could be related to timing and abundance of food availability (Hutto 1981) or avoidance of higher temperatures at midday, especially in warm areas (Morton 1967b; Jacquet & Launay 1997; Molokwu et al. 2007) In temperate regions, highly seasonal environment has more profound effect on daily activity pattern in birds (McNamara et al. 2005; Schoech & Hahn 2008). However, the tropical/ subtropical regions, without seasonal environment, provide a unique opportunity to study the bird's daily behaviors. "
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