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: 4.45). 10/2008; 172(3):331-45. DOI: 10.1086/589886
Source: PubMed

ABSTRACT 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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    01/2010: pages 18-37; Oxford University Press.
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    ABSTRACT: Since their origin about 120 million years ago (Mya), ants have evolved to become the most spe-cies-rich and ecologically diverse group of social insects (Grimaldi and Engel 2005; Hö lldobler and Wilson 1990). Currently there are about 12,500 described species of extant ants (Bolton et al. 2006), but this statistic is undermined by several sources of uncertainty. On the one hand, as taxo-nomic knowledge improves, some of these species names will prove to be redundant (synonyms of older names). On the other hand, it is also evident that there are many ant species remaining to be discovered and/or formally described. In recent taxonomic monographs the number of new syno-nyms is typically less than the number of new species, sometimes by a wide margin (e.g. Bolton 2000, 2007, Wilson 2003), suggesting that the total diversity of ants could well exceed 25,000 species. Ant systematics is concerned with delimiting species and understanding the phylogenetic rela-tionships among them. Demarcation of ant species typically entails detailed morphological scrutiny of the worker caste – supplemented by examination of queens and males, if available – with the aim of discovering phenotypic gaps that indicate the exis-tence of distinct evolutionary lineages (Ward 2001). Phylogenetics involves application of various methods of inference in an attempt to estimate the historical relationships among taxa. In recent years there has been a surge of interest in ant phylogeny, with DNA sequences supplanting morphology as the principal source of evidence. Such molecular studies promise to provide robust phylogenies that will be of great benefit to ant ecologists and behaviourists. This phylogenetic knowledge is also leading to an improved higher classification of ants, one that reflects the main features of evolutionary history. Species-level taxonomy has advanced more fitfully than ant phylogenetics, however, and a great deal remains to be accomplished before most ant species are well characterized (Ward 2007c). This chapter summarizes recent progress in ant phylogeny and provides an outline of the higher classification of ants that is consistent with this new knowledge. The major lineages of ants are identified and features of their biology are dis-cussed. The state of species-level taxonomy is eval-uated, and resources that are available to ecologists for the identification of ant species and genera are documented. The emphasis is on extant taxa, with occasional reference to the fossil record where rele-vant to the discussion. Ant biogeography is consid-ered in Chapter 2 of this volume by Fisher.
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    ABSTRACT: At the onset of winter, warm-blooded animals inhabiting seasonal environments may remain resident and face poorer climatic conditions, or migrate towards more favourable habitats. While the origins and evolution of migratory choices have been extensively studied, their consequences on avian energy balance and winter survival are poorly understood, especially in species difficult to observe such as seabirds. Using miniaturized geolocators, time-depth recorders and a mechanistic model, we investigated the migratory strategies, the activity levels and the energy expenditure of the closely-related, sympatrically breeding Brünnich's guillemots Uria lomvia and common guillemots Uria aalge from Bjørnøya, Svalbard. The two guillemot species from this region present contrasting migratory strategies and wintering quarters: Brünnich's guillemots migrate across the North Atlantic to overwinter off southeast Greenland and Faroe Islands, while common guillemots remain resident in the Barents, the Norwegian and the White Seas. Results show that both species display a marked behavioural plasticity to respond to environmental constraint, notably modulating their foraging effort and diving behaviour. Nevertheless, we provide evidence that the migratory strategy adopted by guillemots can have important consequences for their energy balance. Overall energy expenditure estimated for the non-breeding season is relatively similar between both species, suggesting that both southward migration and high-arctic winter residency are energetically equivalent and suitable strategies. However, we also demonstrate that the migratory strategy adopted by Brünnich's guillemots allows them to have reduced daily energy expenditures during the challenging winter period. We therefore speculate that ‘resident’ common guillemots are more vulnerable than ‘migrating’ Brünnich's guillemots to harsh winter environmental conditions.
    Journal of Avian Biology 05/2013; 44(3). DOI:10.1111/j.1600-048X.2012.00128.x · 2.24 Impact Factor

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