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The ecological and evolutionary consequences of brood sex ratio variation
No full textEen van de belangrijkste concepten in de evolutionaire biologie is het streven van individuen naar een zo groot mogelijke fitness. Fitness is de relatieve bijdrage van een individu aan de toekomstige genenpool van de soort waartoe het behoord. Naast overleven, waarmee de genen voortbestaan in het individu zelf, is voortplanting de manier om fitness te vergroten. Het streven naar een zo hoog mogelijke fitness resulteert in selectie. Individuen die het best zijn aangepast aan hun omgeving zullen de hoogste fitness behalen en hun genen zullen oververtegenwoordigd zijn in de toekomstige genenpool. Er is dus natuurlijke selectie voor het "type" individu dat het beste aan zijn of haar omgeving is aangepast.
Om een zo hoog mogelijke fitness te bereiken moeten individuen keuzes maken. De hoeveelheid energie en tijd die zij ter beschikking hebben is beperkt en dus moeten de kosten en baten van een keuze afgewogen worden. Individuen moeten bijvoorbeeld afwegen met welke partner te reproduceren en hoeveel nakomelingen zij zouden moeten produceren. Binnen deze keuze is de verhouding tussen het aantal zonen en doch ters ook van belang. Met deze laatste afweging, geslachtsallocatie, houd ik mij in deze dissertatie bezig. Geslachtsallocatie is gedefinieerd als de relatieve investering van ouders in de productie van zonen ten opzichte van hun totale nageslacht. Geslachtsallocatie wordt gestuurd door twee processen. Ten eerste door natuurlijke selectie die de relatieve investering in zonen en dochters evolutionair beïnvloedt. Dit proces duidt men meestal aan met geslachtsallocatie. Bijvoorbeeld: als zonen een lagere overlevingskans hebben dan dochters zouden er in de hele populatie meer zonen geboren moeten worden om er voor te zorgen dat er op het moment van voortplanten evenveel mannen als vrouwen zijn.
Alternative foraging strategies in a wild population of tits (Paridae)
Full text linkHow individual animals divide their time between activities such as feeding, predator vigilance, resting, and interacting with conspecifics reflects trade-offs between different fitness related traits (e.g. starvation avoidance, predator avoidance or reproductive performance). Time allocated for foraging to meet energy requirements forms an essential component of animalsâ daily time budgets. Furthermore, individuals vary in state and the environment they experience, which will influence how they prioritize and organize different behaviours â the dynamics of which may be affected by processes acting at different timescales. Small animals with high metabolic rates must feed frequently each day, enabling fine control of the precise timing of feeding. However, little is known about how fine temporal-scale variation in individual behaviour scales up to shape daily routines, or what the consequences of inter- and intra-individual differences in this process may be. The main objective of this thesis was to investigate the causes and consequences of individual variation in the foraging behaviour of wild great tits (Parus major) and blue tits (Cyanistes caeruleus) visiting artificial feeders during winter, ranging in temporal scale from single feeder visits to seasonal shifts in behaviour.
First, I described a novel axis of individual variation in how individuals distribute their feeder visits across the day. This captured the extent to which single feeding events were clustered into foraging bouts, with âbinge-eatersâ and 'grazers' at either end of a continuous spectrum. This axis (level of binge-eating) described 38% of individual variation in observed feeder behaviour and was repeatable within individuals both within and across seasons. Dominance-related factors (species, age and sex) and territorial location predicted inter-individual differences. Individuals exhibited some flexibility in their foraging strategy in relation to local competition, binge-eating more when feeders were quieter than their average experience. The abiotic environment also influenced feeding patterns; birds clustered their feeding behaviour more tightly within a day as day length decreased in midwinter, while visiting feeders more frequently overall on colder days. I then demonstrated that individuals can vary both in overall foraging behaviour, and in their susceptibility to interference, with subordinate individuals responding more negatively to an increase in competition. An experimental manipulation revealed that interference competition at feeders can reduce foraging efficiency. Next, by incorporating a social network approach, I showed that great tit foraging strategies were related to patterns of social interaction and were non-randomly distributed across the social network. This positive assortment indicated a link between foraging behaviour and social structure, likely due to positive feedback. Finally I found evidence that social bonds influence foraging behaviour: pairs of great tits that subsequently bred together exhibited similar foraging strategies, but only after pair formation, suggesting convergence of foraging behaviour.
This thesis represents the first investigation of individual differences in high temporal-resolution patterns in foraging behaviour in a wild population, carried out across multiple years. The work emphasizes the importance of monitoring individual behaviours at appropriate timescales and relating these measures to relevant processes, e.g. pair formation. The results presented here demonstrate how fine-scale behavioural differences can influence how: individuals cope with a changing environment, interact with other individuals in a group context, and shape social structure which can then feed back to impact on individual behaviour. The interaction of these behavioural processes may have consequences for fitness, population dynamics and community composition.</p
The ecological and evolutionary consequences of brood sex ratio variation
No full textEen van de belangrijkste concepten in de evolutionaire biologie is het streven van individuen naar een zo groot mogelijke fitness. Fitness is de relatieve bijdrage van een individu aan de toekomstige genenpool van de soort waartoe het behoord. Naast overleven, waarmee de genen voortbestaan in het individu zelf, is voortplanting de manier om fitness te vergroten. Het streven naar een zo hoog mogelijke fitness resulteert in selectie. Individuen die het best zijn aangepast aan hun omgeving zullen de hoogste fitness behalen en hun genen zullen oververtegenwoordigd zijn in de toekomstige genenpool. Er is dus natuurlijke selectie voor het "type" individu dat het beste aan zijn of haar omgeving is aangepast. Om een zo hoog mogelijke fitness te bereiken moeten individuen keuzes maken. De hoeveelheid energie en tijd die zij ter beschikking hebben is beperkt en dus moeten de kosten en baten van een keuze afgewogen worden. Individuen moeten bijvoorbeeld afwegen met welke partner te reproduceren en hoeveel nakomelingen zij zouden moeten produceren. Binnen deze keuze is de verhouding tussen het aantal zonen en doch ters ook van belang. Met deze laatste afweging, geslachtsallocatie, houd ik mij in deze dissertatie bezig. Geslachtsallocatie is gedefinieerd als de relatieve investering van ouders in de productie van zonen ten opzichte van hun totale nageslacht. Geslachtsallocatie wordt gestuurd door twee processen. Ten eerste door natuurlijke selectie die de relatieve investering in zonen en dochters evolutionair beïnvloedt. Dit proces duidt men meestal aan met geslachtsallocatie. Bijvoorbeeld: als zonen een lagere overlevingskans hebben dan dochters zouden er in de hele populatie meer zonen geboren moeten worden om er voor te zorgen dat er op het moment van voortplanten evenveel mannen als vrouwen zijn.Sex allocation theory is successful in predicting sex ratio variation in some taxa, but often not in birds and mammals. An important reason may be that most theoretical models do not account for the complexities of avian and mammalian life-history. Radersma investigated the effect of manipulated brood sex ratios on long-term fitness benefits. Since offspring recruitment, parental survival and parental future fecundity were unaffected, there was stabilizing selection for producing brood sex ratios at parity. To gain insight in the underlying mechanism he focused on different aspects of the offspring’s first year. Brood sex ratio did not affect fledging behaviour, but there were some effects on social behaviour in winter, which did not correlate to fitness. As adults, individuals raised as the rare sex in a brood had larger tarsi than individuals of the abundant sex. This relationship was neither present in the nestling phase nor caused by selective disappearance. This suggests a sex-specific directional effect of brood sex ratio on the late development of the offspring, which potentially links brood sex ratio to fecundity. Stabilizing selection for brood sex ratios at parity might provide an explanation why sex allocation in birds and mammals is often subtle. Higher benefits for equal brood sex ratios counteract selection for facultative sex allocation to extreme values
Estimating heritability of social phenotypes from social networks
No full textFor understanding how social behaviour evolves and responds to selection, we need to be able to accurately estimate heritability with quantitative genetic models. More recently, this has moved into using node-specific statistics from social networks as social phenotypes. However, parameter estimation can be problematic because social phenotypes are not independent observations and standard models tend to ignore the uncertainties around their estimates. Here I present a framework using latent variable modelling to account for these dependencies and uncertainties. I use edge weights, rather than node-specific network statistics, as dependent variables. From these edge weights, two types of latent (i.e. unobserved) phenotypes are estimated: the individual tendency to be social (i.e. social tendency) and the relative contribution to associations (i.e. social governance). Effects of the social environment and indirect genetic effects are accounted for in the model and can be estimated post hoc. If edge weights are a proportion (e.g. simple ratio index) their uncertainty can be accounted for by a binomial sampling process. I illustrate this method in Stan, a flexible Bayesian inference library, using a publicly available dataset on bottlenose dolphin networks. This method not only accounts for dependencies and uncertainties, it also illuminates aspects of social evolution which are not observed with standard quantitative genetic models. For instance, indirect genetic effects models predict heritable variation in sociality (21.9%), while latent variable modelling shows heritability of social tendency (28.7%), but not for social governance (0.0%). Covariates at different levels in the model (edge and node level) highlight differences in sociality between different foraging strategies and the sexes. This example shows that not properly accounting for the assumptions underlying the use of social network statistics can have misleading effects on conclusions. Although some model assumption violations are less common, others are inherit to the study of (semi)wild populations. The presented framework offers solutions for some critical assumptions and is a flexible tool to further develop and tailor to the needs of specific studies, to ensure the proper fit to the study system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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