Classic life-history theory predicts that menopause should not occur because there should be no selection for survival after the cessation of reproduction 1. Yet, human females routinely live 30 ...years after they have stopped reproducing 2. Only two other species-killer whales (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus) 3, 4-have comparable postreproductive lifespans. In theory, menopause can evolve via inclusive fitness benefits 5, 6, but the mechanisms by which postreproductive females help their kin remain enigmatic. One hypothesis is that postreproductive females act as repositories of ecological knowledge and thereby buffer kin against environmental hardships 7, 8. We provide the first test of this hypothesis using a unique long-term dataset on wild resident killer whales. We show three key results. First, postreproductively aged females lead groups during collective movement in salmon foraging grounds. Second, leadership by postreproductively aged females is especially prominent in difficult years when salmon abundance is low. This finding is critical because salmon abundance drives both mortality and reproductive success in resident killer whales 9, 10. Third, females are more likely to lead their sons than they are to lead their daughters, supporting predictions of recent models 5 of the evolution of menopause based on kinship dynamics. Our results show that postreproductive females may boost the fitness of kin through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female resident killer whales and humans continue to live long after they have stopped reproducing.
Many animals preferentially associate with certain other individuals. This social structuring can influence how populations respond to changes to their environment, thus making network analysis a ...promising technique for understanding, predicting, and potentially manipulating population dynamics. Various network statistics can correlate with individual fitness components and key population-level processes, yet the logical role and formal application of animal social network theory for conservation and management have not been well articulated. We outline how understanding of direct and indirect relationships between animals can be profitably applied by wildlife managers and conservationists. By doing so, we aim to stimulate the development and implementation of practical tools for wildlife conservation and management and to inspire novel behavioral research in this field.
Understanding social network structure and position can aid wildlife conservation.
Threatened wildlife populations offer a vital experimental platform for animal SNA.
Linking animal SNA to practice stimulates design of new practical tools and theory.
Hypothesis testing in animal social networks Croft, Darren P.; Madden, Joah R.; Franks, Daniel W. ...
Trends in ecology & evolution (Amsterdam),
10/2011, Letnik:
26, Številka:
10
Journal Article
Recenzirano
Behavioural ecologists are increasingly using social network analysis to describe the social organisation of animal populations and to test hypotheses. However, the statistical analysis of network ...data presents a number of challenges. In particular the non-independent nature of the data violates the assumptions of many common statistical approaches. In our opinion there is currently confusion and uncertainty amongst behavioural ecologists concerning the potential pitfalls when hypotheses testing using social network data. Here we review what we consider to be key considerations associated with the analysis of animal social networks and provide a practical guide to the use of null models based on randomisation to control for structure and non-independence in the data.
•The evolution of prolonged PRLSs is a scientific puzzle.•We discuss evidence for PRLSs in human and nonhuman animals.•We evaluate evidence for classic and modern hypotheses proposed to explain the ...evolution of PRLSs.•We argue that interacting mechanisms are needed to explain the evolution of PRLSs.
Why females of some species cease ovulation before the end of their natural lifespan is a longstanding evolutionary puzzle. For many species in captivity, post-reproductive life is simply an epiphenomenon of lengthened lifespan. Yet in natural populations of humans as well as some cetaceans and insects, reproductive senescence occurs much faster than somatic aging and females exhibit prolonged post-reproductive lifespans (PRLSs). Determining the mechanisms and functions that underpin PRLSs has proved a significant challenge. Here we bring together both classic and modern hypotheses proposed to explain PRLSs and discuss their application to both human and nonhuman animals. By taking an integrative and broad taxonomic approach we highlight the need to consider multiple interacting explanations for the evolution of PRLSs.
The scientific study of networks - computer, social, and biological - has received an enormous amount of interest in recent years. However, the network approach has been applied to the field of ...animal behaviour relatively late compared to many other biological disciplines. Understanding social network structure is of great importance for biologists since the structural characteristics of any network will affect its constituent members and influence a range of diversebehaviours. These include finding and choosing a sexual partner, developing and maintaining cooperative relationships, and engaging in foraging and anti-predator behavior. This novel text provides an overview of the insights that network analysis has provided into major biological processes, and how it has enhanced our understanding of the social organisation of several important taxonomic groups. It brings together researchers from a wide range of disciplines with the aim of providing both an overview of the power of the network approach for understanding patterns and process in animal populations, as well as outlining how current methodological constraints andchallenges can be overcome. Animal Social Networks is principally aimed at graduate level students and researchers in the fields of ecology, zoology, animal behaviour, and evolutionary biology but will also be of interest to social scientists.
The impact of environmental change on the reproduction and survival of wildlife is often behaviourally mediated, placing behavioural ecology in a central position to quantify population- and ...community-level consequences of anthropogenic threats to biodiversity. This theme issue demonstrates how recent conceptual and methodological advances in the discipline are applied to inform conservation. The issue highlights how the focus in behavioural ecology on understanding variation in behaviour between individuals, rather than just measuring the population mean, is critical to explaining demographic stochasticity and thereby reducing fuzziness of population models. The contributions also show the importance of knowing the mechanisms by which behaviour is achieved, i.e. the role of learning, reasoning and instincts, in order to understand how behaviours change in human-modified environments, where their function is less likely to be adaptive. More recent work has thus abandoned the 'adaptationist' paradigm of early behavioural ecology and increasingly measures evolutionary processes directly by quantifying selection gradients and phenotypic plasticity. To support quantitative predictions at the population and community levels, a rich arsenal of modelling techniques has developed, and interdisciplinary approaches show promising prospects for predicting the effectiveness of alternative management options, with the social sciences, movement ecology and epidemiology particularly pertinent. The theme issue furthermore explores the relevance of behaviour for global threat assessment, and practical advice is given as to how behavioural ecologists can augment their conservation impact by carefully selecting and promoting their study systems, and increasing their engagement with local communities, natural resource managers and policy-makers. Its aim to uncover the nuts and bolts of how natural systems work positions behavioural ecology squarely in the heart of conservation biology, where its perspective offers an all-important complement to more descriptive 'big-picture' approaches to priority setting. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
The dynamics of wildlife populations often depend heavily on interspecific interactions and understanding the underlying principles can be an important step in designing conservation strategies. ...Behavioural ecological studies can here provide useful insights into the structure and function of communities and their likely response to environmental changes. In this study of the Masai Mara herbivore community, we use a social network approach to investigate social affinities between species and how these change over the year in response to seasonal changes in ecological conditions. We find that even though social networks were correlated across different ecological conditions, for half the species dyads in the community, the strength of social affinities responded to changes in rainfall and/or the presence of migratory wildebeest. Several species consequentially adopted more or less central positions in the network depending on the ecological conditions. The findings point out interspecific social links that are likely to be attenuated or strengthened as a consequence of human-induced environmental changes and therefore call for particular attention from conservation managers. The eco-evolutionary ramifications of the perturbations of social affinities still require further study. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
Prolonged life after reproduction is difficult to explain evolutionarily unless it arises as a physiological side effect of increased longevity or it benefits related individuals (i.e., increases ...inclusive fitness). There is little evidence that postreproductive life spans are adaptive in nonhuman animals. By using multigenerational records for two killer whale (Orcinus orca) populations in which females can live for decades after their final parturition, we show that postreproductive mothers increase the survival of offspring, particularly their older male offspring. This finding may explain why female killer whales have evolved the longest postreproductive life span of all nonhuman animals.
Understanding how and why menopause has evolved is a long-standing challenge across disciplines. Females can typically maximize their reproductive success by reproducing for the whole of their adult ...life. In humans, however, women cease reproduction several decades before the end of their natural lifespan
. Although progress has been made in understanding the adaptive value of menopause in humans
, the generality of these findings remains unclear. Toothed whales are the only mammal taxon in which menopause has evolved several times
, providing a unique opportunity to test the theories of how and why menopause evolves in a comparative context. Here, we assemble and analyse a comparative database to test competing evolutionary hypotheses. We find that menopause evolved in toothed whales by females extending their lifespan without increasing their reproductive lifespan, as predicted by the 'live-long' hypotheses. We further show that menopause results in females increasing their opportunity for intergenerational help by increasing their lifespan overlap with their grandoffspring and offspring without increasing their reproductive overlap with their daughters. Our results provide an informative comparison for the evolution of human life history and demonstrate that the same pathway that led to menopause in humans can also explain the evolution of menopause in toothed whales.
Abstract
Among mammals, bovids provide some of the most striking examples of sexual dimorphism in colouration and pelage appendages, such as beards and manes. This dimorphism is usually assumed to ...have evolved through sexual selection on males in the context of intra- or intersexual communication. However, the sexes coloration and pelage appendages look similar between the two sexes in several bovid species thought to be characterized by large opportunities for sexual selection, hinting at fitness costs of dimorphic traits due to other selection pressures. This study applies the comparative method with phylogenetic control to identify the factors promoting and constraining the evolution of dimorphism in coloration and pelage appendages across bovids. We found that trait dimorphism correlated positively with large breeding group size, an indicator of the intensity of sexual selection, and negatively with male territoriality, which is also likely to affect the operation of sexual selection. The relative rarity of color and pelage dimorphism in species with territorial mating systems may be explained by weaker sexual selection due to difficulty in monopolizing females and/or sexual selection targeting other traits, such as territorial quality as an extended phenotype. We also found that dimorphism in color and pelage was reduced in species spending more time in mixed-sex groups outside the breeding season, possibly due to increased predation costs from non-uniformity. This suggests that benefits from integration into mixed-sex groups select against the extravagant male morphologies otherwise promoted by sexual selection.
If sexual selection is such a powerful force in nature, why are the sexes strikingly similar in some of the bovid species where the competition for mates is believed to be most intense? This study finds that although sexual dimorphism in coloration and pelage appendages generally characterizes species where the potential for males to monopolize females is high, such dimorphism is less common in species where the sexes tend to form mixed-sex groups outside the breeding season. We propose that a predation cost from divergent appearance of the sexes may be higher in taxa that form mixed-sex groups.
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