Natal dispersal in great bustards: the effect of sex, local population size and spatial isolation

1. We investigated the causes of natal dispersal in four Spanish areas where 35 breeding groups of the polygynous great bustard Otis tarda were monitored intensively. A total of 392 juveniles were radio-tracked between 1991 and 2006 by ground and via aeroplane to avoid potential biases derived from the non-detection of long-distance dispersers. 2. We explored 10 explanatory variables that were related to individual phenotypic features, habitat and conspecific traits in terms of group size and breeding performance, and spatial distribution of available breeding groups. Probability of group change and natal dispersal distances were investigated separately through multifactorial analyses. 3. Natal dispersal occurred in 47.8% of the birds and median natal dispersal distance of dispersers was 18.1 km (range 4.97-178.42 km). Sex largely determined the dispersal probability, with 75.6% of males being dispersers and 80.0% of females being philopatric, in contrast to the general pattern of female-biased dispersal found in most avian species. 4. Both the frequency of natal dispersal and dispersal distances were affected by the spatial distribution of breeding groups. More isolated groups showed a higher proportion of philopatric individuals, the effect being more evident in males than in females. This implies a reduction in gene flow in fragmented populations, as most genetic exchange is achieved through male dispersal. Additionally, dispersers hatched in more isolated groups tended to exhibit longer dispersal distances, which increases the associated energetic costs and mortality risks. 5. The dispersal decision was influenced by the number of conspecifics in the natal group. The individual probability of natal dispersal was related inversely to the size of the natal group, which supports the balanced dispersal model and the conspecific attraction hypothesis. 6. Overall, our results provide a good example of phenotypic plasticity and reinforce the current view that dispersal is an evolutionary complex trait conditioned by the interaction of individual, social and environmental causes that vary between individuals and populations.     

Patterns of extrapair mating in relation to male dominance status and female nest placement in black-capped chickadees

In sexually promiscuous animals, females may benefit by nestingclose to the edge of their partner's territory to facilitateextrapair copulations. In the present study, we describe theextrapair mating system of black-capped chickadees, Poecileatricapillus, and test whether nest locations are influencedby conspecific attraction to extrapair partners. We conducteda spatial analysis of female mating strategies by using microsatellitepaternity analysis in conjunction with geographic informationsystem (GIS) analysis of nest and territory locations. Extrapairoffspring comprised 52 of 351 offspring (14.8%) and were presentin 19 of 57 broods (33.3%). Females paired to males with lowdominance status in the previous winter's flock hierarchy weremore likely to engage in a mixed reproductive strategy thanwere females paired to males with high dominance status. Femaleshad extrapair copulations and extrapair fertilizations withhigh-ranking males more often than with low-ranking males. Notall extrapair copulations resulted in extrapair fertilizations.Females constructed their nests within 16.8 ± 1.0 m ofthe edge of their partner's territory, significantly closerto the edge of their nearest neighbor's territory than to thecenter of their own partner's territory. Extrapair males usuallyshared territory boundaries with cuckolded males. Females pairedto low-ranking males constructed nests near the territory edgesof neighboring high-ranking males. However, females did nothave extrapair copulations with the neighbor nearest to theirnest or even with the high-ranking neighbor nearest to theirnest. We conclude that conspecific attraction to neighbors mayinfluence nesting location in black-capped chickadees; however,it does not operate by facilitating extrapair copulations.     

Interspecific Pollen Transfer: Magnitude,Prevalence and Consequences for Plant Fitness

Interspecific pollen transfer (IPT) is one of the mechanisms underlying potential competition among plants for pollinators, and it refers to movement of pollen between different plant species by pollinators that visit their flowers simultaneously. Two components of IPT, related to each other, are distinguished: (a) heterospecific pollen deposition (HPD) on conspecific stigmas, which may interfere with fertilization by conspecific pollen; and (b) conspecific pollen loss (CPL) on heterospecific flowers, which may reduce the amount of pollen transferred between conspecific flowers. Thus, IPT may lead to reciprocal losses for male and female functions of the plant, with potentially important ecological and evolutionary consequences. In this review, we explore the magnitude and prevalence of IPT, examining documented mechanisms and evaluating such potential ecological and evolutionary consequences. We compiled existing evidence of interspecific pollinator sharing and interspecific pollinator switching between flowers of different species in natural communities. We evaluated the relative importance of both HPD and CPL from studies comparing these variables in pure vs. mixed floral neighborhoods, analyzing evidence for the claim that IPT is an evolutionary force promoting character displacement in habitat affinity, flowering times, and floral morphology. We also examined the findings of hand-pollination experiments carried out to reveal different mechanisms by which heterospecific pollen can affect performance of native pollen. Finally, we review evidence for impacts of alien plant species on native species' reproduction, and briefly comment on risks of crop-to-wild gene flow imposed by the release of genetically modified (transgenic) crops through IPT.     

Conspecific nest parasitism is associated with inequality in nest predation risk in the common goldeneye (Bucephala clangula)

Previous studies of the role of nest predation in conspecificnest parasitism have not taken into account the possibilitythat predation risk may not be randomly distributed among nestsites and that breeding individuals may use different cues toassess the risk and adjust their reproductive tactic betweenyears accordingly. Especially in cavity-nesting species, therole of nest predation in conspecific nest parasitism has beendownplayed, while the role of nest site limitation has beenhighlighted. Using both observational and experimental data,I show that in the common goldeneye (Bucephala clangula), acavity-nesting species in which conspecific nest parasitism iscommon, predation risk varies considerably between nest sitesand does not follow a random expectation. The inequality inpredation risk between nest sites also showed up in the occurrenceof parasitized nests in an experimental setup. Nests parasitizedin year t were more frequent in those nest sites that were notdepredated during the previous nesting attempt in year t - nthan in nest sites that were depredated and in control nestsites that had not been used for nesting before. A nest siteaddition experiment revealed that conspecific nest parasitismwas not associated with nest site limitation. My findings givesupport for the hypothesis that nest predation is an importantecological factor explaining conspecific nest parasitism ingoldeneyes.     

Abundance variations within feeding guilds reveal ecological mechanisms behind avian species richness pattern along the elevational gradient of Mount Cameroon

Two distinct diversity patterns are observed along tropical elevations: (a) decreasing number of species toward high elevations and (b) a hump-shaped pattern with the peak at mid-elevations. As diversity is likely supported by ecological capacity of the environment, decomposition of the overall richness into ecological facets and considering number of individuals within them is crucial for the proper understanding of richness patterns. We examined abundances of different avian guilds along the forested part of the elevational gradient on Mt. Cameroon. We (a) compared richness and abundance elevational patterns, (b) assessed the effective contribution of multiple guilds to richness and abundance patterns, and (c) assessed to what extent observed abundances of guilds differed from those expected by chance. We sampled birds in 2011–2015 during the dry season at seven elevations (30 m, 350 m, 650 m, 1100 m, 1500 m, 1850 m, 2200 m a.s.l.). For each assemblage, we estimated proportions of species and individuals that use particular diets, foraging modes, and feeding strata. We found that a rather decreasing pattern of species richness turns into a hump-shaped one if we look at the total abundances, implying different mechanisms behind these patterns. The number of species and individuals thus do not seem to be directly related, contrary to “the more-individuals hypothesis.” Abundances of foliage gleaners at mid-elevations, nectarivores at high elevations, and frugivores at low elevations deviated from random expectations. Our results imply that parts of ecological space are filled separately by bird species and individuals along elevation of Mt. Cameroon.