Reproductive skew and individual strategies: infanticide or cooperation?

Infanticide in species with shared reproduction may indicate attempts to control the degree of skew within groups. Alternatively, individuals that have done poorly in reproduction could use infanticide for hastening the next breeding attempt. Many factors influence the individual’s decision over whether it is best to cooperate or engage in destruction. We present a qualitative model incorporating kinship among adults and progeny, social status, group size and seasonality to predict behavioural options for individuals of diverse backgrounds. The social system used for the model was that of the guira cuckoo (Guira guira), a Neotropical bird that breeds communally. We suggest communal breeders utilise the best available predictors for enhancing seasonal reproductive success, with favourable consequences for lifetime inclusive fitness. Predictors rely upon parameters that change over time, including the individual’s assessment of present and future possibilities. The model produces predictions that may be tested through field observations and molecular analyses for species with similar social dynamics.     

Population regulation by habitat heterogeneity or individual adjustment?

1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of high-quality territories as preferential conservation targets.     

Psychopathology or adaptation? Genetic and evolutionary perspectives on individual differences and psychopathology

A greater understanding of psychopathology will be found in the integration of genetic and evolutionary perspectives on adaptation and function. Evolutionary theory proposes that adaptive traits are reproduced more successfully than maladaptive ones. However, some traits, while contributing to fitness in the ancestral environment, may contribute to fitness no longer. This is known as mismatch theory. Evolutionarily informed research into various \"pathologies\" has yielded interesting results, some based on this theory. This paper serves to distinguish between genetic and evolutionary perspectives on psychopathology as well as to examine some recent research on the selective forces that may be implicated in psychopathy, anorexic behavior, and ADHD. We suggest that research into psychopathy in general would benefit from an evolutionary perspective and an examination of the assumptions behind past research.     

Sexual differences in habitat use by small mammals: evolutionary strategy or reproductive constraint?

Summary This study examines the hypothesis that intersexual differences in habitat use by small mammals is an adaptive strategy. Specifically, I evaluate the occurrence of sexual differences in habitat by Peromyscus and Microtus, and test possible adaptive mechanisms which may lead to such differences.White-footed mice and meadow voles were live-trapped and microhabitat quantified in four habitats. Sexual differences in microhabitat use were found in three of 12 comparisons. These differences may be related to density dependent resource subdivision and habitat heterogencity, but neither of these can account completely for the observed patterns. Sexual differences in habitat do not appear to be an evolutionary strategy maximizing reproductive effort by females, or reducing predation. These sexual differences may reduce intraspecific resource overlap, or may simply reflect reproductive constraints limiting female habitat use to suitable nesting areas.     

Determinants of helminth aggregation in natural host populations: individual differences or spatial heterogeneity?

We assessed the importance of spatial heterogeneity for the aggregation of helminth populations in the bank vole Clethrionomys glareolus (Arvicolinae) using a previously published method which allows to analyse parasite aggregation at two host population levels, i.e., within and between spatial samples of the host population.
In the main empirical material from Finnish Lapland (Pallasjärvi), all five helminth species were significantly aggregated within study sites, but only three rare species showed significant aggregation among sites. In all helminth species, the total aggregation was primarily (79-98%) determined by aggregation within sites, i.e., between host individuals. Despite the larger spatial scale and more heterogeneous landscape, the comparative material from South Finland (Luhanka) supported the generally high proportion of the total aggregation due to within-site heterogeneity.
Despite the clear interspecific differences in patchiness of helminth populations, the proportion of the total aggregation due to among-site heterogeneity did not vary significantly among helminth species. The results indicate a link between aggregation at two population levels; species that showed strong within-site aggregation were also characterised by pronounced spatial heterogeneity and significant among-site aggregation.     

School Variation in Asthma: Compositional or Contextual?

Background

Childhood asthma prevalence and morbidity have been shown to vary by neighborhood. Less is known about between-school variation in asthma prevalence and whether it exists beyond what one might expect due to students at higher risk of asthma clustering within different schools. Our objective was to determine whether between-school variation in asthma prevalence exists and if so, if it is related to the differential distribution of individual risk factors for and correlates of asthma or to contextual influences of schools.

Methods

Cross-sectional analysis of 16,640 teens in grades 7–12 in Wave 1 (data collected in 1994–5) of the National Longitudinal Study of Adolescent Health. Outcome was current diagnosis of asthma as reported by respondents'' parents. Two-level random effects models were used to assess the contribution of schools to the variance in asthma prevalence before and after controlling for individual attributes.

Results

The highest quartile schools had mean asthma prevalence of 21.9% compared to the lowest quartile schools with mean asthma prevalence of 7.1%. In our null model, the school contributed significantly to the variance in asthma ( = 0.27, CI: 0.20, 0.35). Controlling for individual, school and neighborhood attributes reduced the between-school variance modestly ( = 0.19 CI: 0.13–0.29).

Conclusion

Significant between-school variation in current asthma prevalence exists even after controlling for the individual, school and neighborhood factors. This provides evidence for school level contextual influences on asthma. Further research is needed to determine potential mechanisms through which schools may influence asthma outcomes.     

Cursorial spiders and succession: age or habitat structure?

Summary The structure of cursorial spider assemblages was examined along a gradient of four temperature successional communities. Species diversity (H), richness (S), and evenness (J) exhibited a dichotomy between herbaceous and woody communities rather than a progressive change with community age: all three parameters were higher in the two younger fields than in the two older woodlands, which is contrary to conventional successional theory. Species importance curves were steeper in the two woody communities. The breadth of the distribution of adult body lengths was greater in the two herbaceous communities. Indices of community similarity revealed neither a successional trend nor the vegetative dichotomy. We suggest the hypothesis that habitat structure is a more important determinant of cursorial spider diversity than successional age per se, and that the switch in dominance from herbaceous to woody vegetation is the critical change. We further suggest that competition for prey is more important to cursorial spiders in early successional (herbaceous) communities, because of a switch in the limiting resource from prey in these communities to the amount of accumulating litter (a spatial resource) in older woody stands. This may explain the greater variation in adult body size of these generalist predators in the two younger communities.     

The heterospecific habitat copying hypothesis: can competitors indicate habitat quality?

According to the "habitat copying" hypothesis, animals use thereproductive performance of conspecifics to assess habitat suitabilityand choose their future breeding site. This is because conspecificsshare ecological needs and thus indicate habitat suitability.Here, we propose the "heterospecific habitat copying" hypothesis,which states that animals should use public information (i.e.,information derived from the performance of others) from con-and heterospecifics sharing ecological needs. In a correlationalapproach we test some assumptions and predictions of this hypothesiswith a data set from two sympatric bird populations, rollers(Coracias garrulus) and kestrels (Falco tinnunculus), usingthe same nest-boxes and exploiting similar food resources. Sincekestrels are residents and breed earlier, we assumed that theyare dominant over rollers for nest-box acquisition. The environmentappears to be patchy for both species and temporally predictablefor kestrels only. Two results suggest that the use of heterospecificpublic information in breeding habitat selection may be at work:(1) an increase in the reoccupancy probability by kestrels ofprevious roller nests with increasing nest success, and (2)an increase in roller breeding population with increasing localkestrel success. Most of the other observed patterns could beexplained by alternative mechanisms such as natal philopatry,breeding fidelity, conspecific attraction, intraspecific habitatcopying, and the effect of interspecific competition.     

Omnivory in lacertid lizards: adaptive evolution or constraint?

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.     

Variation in reproductive traits in European passerines in relation to nesting site: allometric scaling to body weight or adaptive variation?

Summary The relationships between different reproductive traits and body weight, in relation to nesting site, were studied in European passerines. Body weight explains a significant proportion of the variance in clutch size, egg weight, clutch mass, and incubation period. Whereas clutch size decreases, the other three traits increase with body weight. Even though both clutch mass and clutch size are related to body size, for a given body weight, concealed nesters lay a larger clutch and a greater clutch mass than open-nesters.     

Clustered or scattered? The impact of habitat quality clustering on establishment and early spread

The match between the environmental conditions of an introduction area and the preferences of an introduced species is the first prerequisite for establishment. Yet, introduction areas are usually landscapes, i.e. heterogeneous sets of habitats that are more or less favourable to the introduced species. Because individuals are able to disperse after their introduction, the quality of the habitat surrounding the introduction site is as critical to the persistence of introduced populations as the quality of the introduction site itself. Moreover, demographic mechanisms such as Allee effects or dispersal mortality can hamper dispersal and affect spread across the landscape, in interaction with the spatial distribution of favourable habitat patches. In this study, we investigate the impact of the spatial distribution of heterogeneous quality habitats on establishment and early spread. First, we simulated introductions in one‐dimensional landscapes for different dispersal rates and either dispersal mortality or Allee effects. The landscapes differed by the distribution of favourable and less favourable habitats, which were either clustered into few large aggregates of the same quality or scattered into multiple smaller ones. Second, we tested the predictions of simulations by performing experimental introductions of hymenopteran parasitoids (Trichogramma chilonis) in ‘clustered’ and ‘scattered’ microcosm landscapes. Results highlighted two impacts of the clustering of favourable habitat: by decreasing the risks of dispersal from the introduction site to unfavourable habitat early during the invasion, it increased establishment success. However, by increasing the distance between favourable habitat patches, it also hindered the subsequent spread of introduced species over larger areas.     

Variation in growth and age at maturity in bluegill sunfish: genetic or environmental effects?

Populations of bluegill sunfish Lepomis macrochirus , experiencing heavy juvenile predation, showed increased growth rates and increased age and size at maturity relative to populations experiencing decreased predation on juveniles but increased predation on adults. This study examined bluegills experimentally from both types of populations and a cross between them in a common environment to determine if variation in growth and age at maturity is genetically or environmentally induced. Two factorial experiments, varying strain of bluegills and resource availability, were used to evaluate differences in growth rate. One experiment, varying strain of bluegills, was used to assess differences in age at maturity. Growth was strongly influenced by resource level, but growth rate did not vary among populations. Nearly all bluegills in each population matured at 1 year of age in a common environment. Thus, variation observed in source populations must be mostly attributable to differences in the environment between populations. At least three factors could potentially cause differences in growth and age at maturity: (1) variation in resource availability; (2) variation in demographic structure; and (3) variation in size-specific mortality rates caused by differences in predator abundance between populations. Observed patterns of variation between populations are best explained by effects of differences in predator populations.     

Parasites and individual major histocompatibility complex diversity--an optimal choice?

Overdominant selection or heterozygote advantage can partly explain the extraordinary polymorphism found at classical major histocompatibility complex (MHC) loci. However, several studies employing only single infectious agents often failed to detect it. Here, we review recent studies suggesting that due to the dominant nature of MHC-mediated resistance, a heterozygote advantage is most likely to be detected in multiple pathogen challenges.