Publicação
Juvenile settlement and recruitment as drivers of population responses to environmental change in a migratory shorebird
| Resumo: | Human activity is altering environments globally, including destruction and deterioration of habitats and global climatic warming. Population-level responses to these changes include shifts in space, for example range shifts towards higher latitudes, or in time, for example advances in breeding phenology. Understanding the demographic mechanisms involved in driving such responses is essential for predicting future rates and directions of shifts, and their consequences. However, studying these issues is challenging, especially in migratory systems, due to the need to track large numbers of individuals throughout their lives and over vast distances. In this thesis, I focus on the Icelandic population of Black-tailed Godwit (Limosa limosa islandica), a long-distance migratory shorebird with an expanding distribution in both its breeding and wintering ranges. As is typical of most migratory species, individuals in this population show extremely high site-fidelity and consistent individual timings of events such as spring migration. Therefore, populationlevel responses such as changes in distribution or phenology must arise through generational changes in the relative frequencies of site-use and timings amongst new recruits to the population. Consequently, understanding environmental influences on the development of juvenile behaviour, and their consequences for settlement, recruitment and survival, is crucial for predicting population responses to change. This thesis contains five empirical chapters. Its overall aim was to (i) understand how variation in juvenile behaviour originates and (ii) what the consequences of that variation are, both for individuals and for the dynamics of the Icelandic godwit population across its distribution range. In particular, I was interested in the role of information and its social transmission in driving large-scale processes. In Chapter 2, I explore the mechanisms generating variation in juvenile hatch dates, which could have consequences for the time and information available to juveniles during the post-fledging period. In the next two chapters, I explore how timing of hatching can influence the development of key aspects of juvenile behaviour, namely their acquisition of foraging skills (Chapter 3) and winter settlement (Chapter 4). In Chapter 5, I then explore the individual and population-level consequences of juvenile settlement across the range. Finally, in Chapter 6 I present an applied analysis of estuary-scale connectivity, as revealed by godwit movements, to assess the impact of a major proposed development on a local population in a key wintering site. Through these studies, I show how largescale, long-term patterns can emerge from the behavioural traits of individuals. The flow of social information can result in behaviour that is correlated between individuals, including the selection of foraging sites (Chapter 3) and winter site settlement (Chapters 4-5). The social information available to juveniles appears to strongly influence their settlement patterns: juveniles tend to recruit into sites with high numbers of older conspecifics, and juveniles that fledge late are less likely to settle in traditionally-used sites, possibly because they have fewer opportunities to join flocks with experienced adults on southward migration from Iceland. The Icelandic godwit range shift may therefore have arisen due to increasing numbers of later-fledging juveniles, and/or decreasing mortality amongst those that settle in northerly winter sites (e.g. due to climatic amelioration). The behaviour displayed by new recruits, and the social information to which they have access, may therefore be crucial drivers of population responses to environmental change in systems where such responses are generational, and understanding and predicting these responses will require us to understand the factors that influence development of the adult phenotype. This thesis therefore aims to contribute to our understanding of how juveniles settle and recruit into migratory populations, giving rise to populationlevel shifts in response to environmental change. |
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| Autores principais: | Nightingale, Joshua |
| Assunto: | Black-tailed godwit Limosa limosa Breeding Conservation Demography Foraging Migration Ontogeny Phenology Range shift Social learning Survival |
| Ano: | 2023 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Human activity is altering environments globally, including destruction and deterioration of habitats and global climatic warming. Population-level responses to these changes include shifts in space, for example range shifts towards higher latitudes, or in time, for example advances in breeding phenology. Understanding the demographic mechanisms involved in driving such responses is essential for predicting future rates and directions of shifts, and their consequences. However, studying these issues is challenging, especially in migratory systems, due to the need to track large numbers of individuals throughout their lives and over vast distances. In this thesis, I focus on the Icelandic population of Black-tailed Godwit (Limosa limosa islandica), a long-distance migratory shorebird with an expanding distribution in both its breeding and wintering ranges. As is typical of most migratory species, individuals in this population show extremely high site-fidelity and consistent individual timings of events such as spring migration. Therefore, populationlevel responses such as changes in distribution or phenology must arise through generational changes in the relative frequencies of site-use and timings amongst new recruits to the population. Consequently, understanding environmental influences on the development of juvenile behaviour, and their consequences for settlement, recruitment and survival, is crucial for predicting population responses to change. This thesis contains five empirical chapters. Its overall aim was to (i) understand how variation in juvenile behaviour originates and (ii) what the consequences of that variation are, both for individuals and for the dynamics of the Icelandic godwit population across its distribution range. In particular, I was interested in the role of information and its social transmission in driving large-scale processes. In Chapter 2, I explore the mechanisms generating variation in juvenile hatch dates, which could have consequences for the time and information available to juveniles during the post-fledging period. In the next two chapters, I explore how timing of hatching can influence the development of key aspects of juvenile behaviour, namely their acquisition of foraging skills (Chapter 3) and winter settlement (Chapter 4). In Chapter 5, I then explore the individual and population-level consequences of juvenile settlement across the range. Finally, in Chapter 6 I present an applied analysis of estuary-scale connectivity, as revealed by godwit movements, to assess the impact of a major proposed development on a local population in a key wintering site. Through these studies, I show how largescale, long-term patterns can emerge from the behavioural traits of individuals. The flow of social information can result in behaviour that is correlated between individuals, including the selection of foraging sites (Chapter 3) and winter site settlement (Chapters 4-5). The social information available to juveniles appears to strongly influence their settlement patterns: juveniles tend to recruit into sites with high numbers of older conspecifics, and juveniles that fledge late are less likely to settle in traditionally-used sites, possibly because they have fewer opportunities to join flocks with experienced adults on southward migration from Iceland. The Icelandic godwit range shift may therefore have arisen due to increasing numbers of later-fledging juveniles, and/or decreasing mortality amongst those that settle in northerly winter sites (e.g. due to climatic amelioration). The behaviour displayed by new recruits, and the social information to which they have access, may therefore be crucial drivers of population responses to environmental change in systems where such responses are generational, and understanding and predicting these responses will require us to understand the factors that influence development of the adult phenotype. This thesis therefore aims to contribute to our understanding of how juveniles settle and recruit into migratory populations, giving rise to populationlevel shifts in response to environmental change. |
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