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Tuesday, 7 October 2014

Journal of Animal Ecology, October 2014: Accepted articles on Red Knot, Wren, and Blue Tit.

Journal of Animal Ecology 
Cover image for Vol. 83 Issue 5

Accepted manuscripts online, October 2014:

Moving on with foraging theory: incorporating movement decisions into the functional response of a gregarious shorebird.

Jan A. van Gils, Matthijs van der Geest, Brecht De Meulenaer, Hanneke Gillis, Theunis Piersma and Eelke O. Folmer 

Accepted: 5 OCT 2014 | DOI: 10.1111/1365-2656.12301

LINK

Abstract
1.Models relating intake rate to food abundance and competitor densities (generalized functional response models) can predict forager distributions and movements between patches, but we lack understanding of how distributions and small-scale movements by the foragers themselves affect intake rates.

2.Using a state-of-the-art approach based on continuous-time Markov chain dynamics, we add realism to classic functional response models by acknowledging that the chances to encounter food and competitors are influenced by movement decisions, and, vice versa, that movement decisions are influenced by these encounters.

3.We used a multi-state modelling framework to construct a stochastic functional response model in which foragers alternate between three behavioural states: searching, handling and moving.

4.Using behavioural observations on a molluscivore migrant shorebird (red knot, Calidris canutus canutus), at its main wintering area (Banc d'Arguin, Mauritania), we estimated transition rates between foraging states as a function of conspecific densities and densities of the two main bivalve prey.

5.Intake rate decreased with conspecific density. This interference effect was not due to decreased searching efficiency, but resulted from time lost to avoidance movements.

6.Red knots showed a strong functional response to one prey (Dosinia isocardia), but a weak response to the other prey (Loripes lucinalis). This corroborates predictions from a recently developed optimal diet model that accounts for the mildly toxic effects due to consuming Loripes.

7.Using model-averaging across the most plausible multi-state models, the fully parameterized functional response model was then used to predict intake rate for an independent dataset on habitat choice by red knot.

8.Comparison of the sites selected by red knots with random sampling sites showed that the birds fed at sites with higher than average Loripes and Dosinia densities, i.e. sites for which we predicted higher than average intake rates.

9.We discuss the limitations of Holling's classical functional response model that ignores movement and the limitations of contemporary movement ecological theory ignoring consumer-resource interactions. With the rapid advancement of technologies to track movements of individual foragers at fine spatial scales, the time seems ripe to integrate descriptive tracking studies with stochastic movement-based functional response models.


Keywords:

competition;continuous-time Markov chain;cryptic interference;diet;distribution;habitat choice;movement ecology;intake rate;predation;toxic prey



Assembly Patterns Of Mixed-Species Avian Flocks In The Andes.

Gabriel J.Z. Colorado and Amanda D. Rodewald


Accepted: 5 OCT 2014 | DOI: 10.1111/1365-2656.12300

LINK

Abstract
The relative contribution of deterministic and stochastic processes in the assembly of biotic communities is a central issue of controversy in community ecology. However, several studies have shown patterns of species segregation that are consistent with the hypothesis that deterministic factors such as competition and niche-partitioning structure species assemblages in animal communities. Community assembly provides a theoretical framework for understanding these processes, but it has been seldom applied to social aggregations within communities. In this research we assessed patterns of non-randomness in Andean mixed-species flocks using three assembly models: (a) co-occurrence patterns (b) guild proportionality; and (c) constant body-size ratios using data from 221 species of resident and Neotropical migrant birds participating in 311 mixed-species flocks at 13 regions distributed in Venezuela, Colombia, Ecuador, and Peru. Significant assembly patterns for mixed-species flocks based on co-occurrence models and guild proportionality models suggest that competitive interactions play an important role in structuring this social system in the Andes. Distribution of species among foraging guilds (i.e. insectivore, frugivore, omnivore, nectivore) was generally similar among flocks, though with some regional variation. In contrast, we found little evidence that structuring of mixed-species flocks in the Andes was mediated by body size. Rather, we found greater than expected variance of body-size ratios within flocks, indicating that birds did not segregate morphologically. Overall, our findings suggest that deterministic factors associated to competitive interactions are important contributors to mixed-species flock assemblages across the Andes.

Keywords:

birds;competition;co-occurrence;guild proportionality;body-size ratio


Persistent sex-by-environment effects on offspring fitness and sex-ratio adjustment in a wild bird population.

E. Keith Bowers, Charles F. Thompson and Scott K. Sakaluk

Accepted: 29 SEP 2014 | DOI: 10.1111/1365-2656.12294

LINK

Abstract
A major component of sex-allocation theory, the Trivers-Willard Model (TWM), posits that sons and daughters are differentially affected by variation in the rearing environment. In many species, the amount of parental care received is expected to have differing effects on the fitness of males and females. When this occurs, the TWM predicts that selection should favour adjustment of the offspring sex ratio in relation to the expected fitness return from offspring. However, evidence for sex-by-environment effects is mixed and little is known about the adaptive significance of producing either sex.

Here, we test whether offspring sex ratios vary according to predictions of the TWM in the house wren (Troglodytes aedon, Vieillot). We also test the assumption of a sex-by-environment effect on offspring using two experiments, one in which we manipulated age-differences among nestlings within broods, and another in which we held nestling age constant but manipulated brood size.

As predicted, females with high investment ability over-produced sons relative to those with lower ability. Males were also over-produced early within breeding seasons. In our experiments, the body mass of sons was more strongly affected by the sibling-competitive environment and resource availability than that of daughters: males grew heavier than females when reared in good conditions but were lighter than females when in poor conditions.

Parents rearing broods with 1:1 sex ratios were more productive than parents rearing broods biased more strongly towards sons or daughters, suggesting that selection favours the production of mixed-sex broods. However, differences in the condition of offspring as neonates persisted to adulthood, and their reproductive success as adults varied with the body mass of sons, but not daughters, prior to independence from parental care. Thus, selection should favour slight but predictable variations in the sex ratio in relation to the quality of offspring that parents are able to produce.


Offspring sex interacts with the neonatal environment to influence offspring fitness, thus favouring sex-ratio adjustment by parents. However, increased sensitivity of males to environmental conditions, such as sibling rivalry and resource availability, reduces the fitness returns from highly male-biased broods.

Keywords:
family life;life history;sex allocation;sex ratio;sibling rivalry


Spatial patterns of extra-pair paternity: beyond paternity gains and losses.

Lotte Schlicht, Mihai Valcu and Bart Kempenaers

Accepted: 29 SEP 2014 | DOI: 10.1111/1365-2656.12293

LINK

Abstract
1.Most studies on extra-pair paternity (EPP) focus either on a specific male's extra-pair gains or his extra-pair losses. For an individual bird however, mate choice or mate availability may underlie strong spatial restrictions. Disregarding this spatial aspect may underestimate or mask effects of parameters influencing observed EPP patterns.

2.Here, we propose a spatially explicit model for investigating the probability of having extra-pair offspring (EPO) within local networks of breeding pairs. The dataset includes all realized and unrealized potential extra-pair matings. This method is biologically meaningful because it allows (a) considering both members of an extra-pair mating as well as their social mates, and (b) direct modelling of the spatial context in which extra-pair behaviour occurs. The method has the advantage that it can provide inference about the relative contribution of spatial and non-spatial parameters, and about the relative importance of male and female neighbourhoods.

3.We apply this method to parentage data from 1025 broods collected over 12 breeding seasons in two independent study populations of blue tits (Cyanistes caeruleus). We investigate a set of predictions based on the EPP literature, namely that EPP depends on male age and body size, breeding density, and breeding synchrony. In all analyses, we control for breeding distance, a parameter that is expected to influence EPP even under random mating.

4.The results show that older and larger males were more likely to sire EPO, but both effects decreased with increasing breeding distance. Local breeding density but not synchrony predicted whether a particular male-female combination had EPO, at least in one of the study areas. Apart from breeding distance, male age had the strongest effect on EPP, followed by a measure of breeding density. The method thus allows a comprehensive assessment of the relative importance of different types of spatial and non-spatial parameters to explain variation in the occurrence of EPP, while controlling for the fact that individuals that breed further apart are less likely to have EPO.


5.The proposed approach is not limited to investigate EPP, but can be applied to other behavioural interactions between two individuals, such as dominance, competition, and (social) mating.

Keywords:

competition;extra-pair behaviour;female behaviour;promiscuity;male behaviour;mate choice;mating system;neighbourhood;sexual selection;social network

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