Search

The New Zealand Greenshell™ mussel (Perna canaliculus) is an endemic bivalve species with cultural importance, that is harvested recreationally and commercially. However, production is currently hampered by increasing incidences of summer mortality in farmed and wild populations. While the causative factors for these mortality events are still unknown, it is believed that increasing seawater temperatures and pathogen loads are potentially at play. To improve our understanding of these processes, challenge experiments were conducted to investigate the combined effects of increased seawater temperature and Vibrio infection on the immune and metabolic responses of adult mussels. Biomarkers that measure the physiological response of mussels to multiple-stressors can be utilised to study resilience in a changing environment, and support efforts to strengthen biosecurity management. Mussels acclimated to two temperatures (16 °C and 24 °C) were injected with either autoclaved, filtered seawater (control) or Vibrio sp. DO1 (infected). Then, haemolymph was sampled 24 h post-injection and analysed to quantify haemocyte immune responses (via flow-cytometry), antioxidant capacity (measured electrochemically) and metabolic responses (via gas chromatography-mass spectrometry) to bacterial infection. Both seawater temperature and injection type significantly influenced the immune and metabolite status of mussels. A lack of interaction effects between temperature and injection type indicated that the effects of Vibrio sp. 24 h post-infection were similar between seawater temperatures. Infected mussels had a higher proportion of dead haemocytes and lower overall haemocyte counts than uninfected controls. The proportion of haemocytes showing evidence of apoptosis was higher in mussels held at 24 °C compared with those held at 16 °C. The proportion of haemocytes producing reactive oxygen species did not differ between temperatures or injection treatments. Mussels held at 24 °C exhibited elevated levels of metabolites linked to the glycolysis pathway to support energy production. The saccharopin-lysine pathway metabolites were also increased in these mussels, indicating the role of lysine metabolism. A decrease in metabolic activity (decreases in BCAAs, GABA, urea cycle metabolites, oxidative stress metabolites) was largely seen in mussels injected with Vibrio sp. Itaconate increased as seen in previous studies, suggesting that antimicrobial activity may have been activated in infected mussels. This study highlights the complex nature of immune and metabolic responses in mussels exposed to multiple stressors and gives an insight into Vibrio sp. infection mechanisms at different seawater temperatures. • 24 h post-infection, Vibrio sp. Proliferated in mussel haemolymph at 16 and 24 °C. • Haemocyte immune responses were altered by infection and temperature. • Acclimating mussels to 24 °C did not exacerbate the impact of Vibrio sp. infection. • Mussels held at 24 °C activated additional energy production pathways. • Mussels injected with Vibrio sp. showed decreased metabolic activity. [ABSTRACT FROM AUTHOR]

A plausible biocontrol strategy for the eradication of invasive species involves augmenting wild populations with genetically modified supermales. Supermales contain double Y Y chromosomes. When they are augmented into a wild population, destabilization and eventual extinction occurs over time due to a strongly skewed gender ratio towards males. Here, we employ a mathematical model that considers an Allee effect, but we have discovered through simulation that the presence of supermales leads to an increase in the minimal number of females needed for survival at a value higher than the mathematically defined Allee effect. Using this effect, we focus our research on exploring the sensitivity of the optimized supply rate of supermale fish to the initial gender ratio and density of the wild populations. We find that the eradication strategy with optimized supply rate of supermales can be determined with knowledge of reproductive rate and survival fitness of supermale fish. [ABSTRACT FROM AUTHOR]

Toxocara prevalence ranges from 0 to >87% and 0 to >60% in dogs and cats, respectively, within the United States, Mexico, Central America and the Caribbean. Higher prevalence occurs in animals less than 1 year of age. Overall, prevalence is higher in cats compared to dogs. The lowest prevalence occurs in the US owned dog population. Specific populations in this industrialized nation, in animal shelters or resource-limited locations, have prevalences similar to those seen in populations from other regions reviewed here. Conversely, subpopulations in Central America and the Caribbean have very low prevalence. Apparent contributors to prevalence, excluding animal age and climate, are socio-economic factors, attitudes towards pet management and animal population density. The lack of data from some regions pose a challenge in assessing trends; however, with the exception of the US owned dog population, there is no strong indication of any decrease in prevalence from historical levels. [ABSTRACT FROM AUTHOR]

To effectively manage species and habitats at multiple scales, population and land managers require rapid information on wildlife use of managed areas and responses to landscape conditions and management actions. GPS tracking studies of wildlife are particularly informative to species ecology, habitat use, and conservation. Combining GPS data with administrative data and a diverse suite of remotely sensed, geo-referenced environmental (e.g., climatic) data, would more comprehensively inform how animals interact with and utilize habitats and ecosystems and our goal was to create a conceptual model for a system that would accomplish this – the 'Automated Interactive Monitoring System (AIMS) for Wildlife'. Our objective for this study was to develop a Customized Wildlife Report (CWR) - the first AIMS for Wildlife deliverable product. CWRs collate and summarize our 8-year GPS tracking dataset of ∼11 million locations from 1338 individual (16 species) avifauna and make actionable, real-time data on animal movements and trends in a specific area of interest available to managers and stakeholders for rapid application in day-to-day management. The CWR exemplar presented in this paper was developed to address needs identified by habitat managers of Sacramento National Wildlife Refuge and illustrates the highly specific, information offered and how it contributes to assessing the efficacy of conservation actions while allowing for near real-time adaptive management. The report can be easily customized for any of the thousands of wildlife refuges or regional areas of interest in the United States, emphasizing the broad application of an animal movement data stream. Utilizing diverse, extensive telemetry data streams through scientific collaboration can aid managers and conservation stakeholders with short and long-term research and conservation planning and help address a cadre of issues from local-scale habitat management to improving the understanding of landscape level impacts like drought, wildfire, and climate change on wildlife populations. [Display omitted] • Our Automated Interactive Monitoring System (AIMS) for Wildlife utilizes animal GPS data. • We developed proof-of-concept Customized Wildlife Reports (CWRs) with 11 million locations. • CWRs inform wildlife managers' decision-making in near real-time. • We conceptualize a multi-tool AIMS for Wildlife incorporating remote-sensing data. • Automated delivery of animal movement data will allow for true adaptive management. [ABSTRACT FROM AUTHOR]

The seasonal breeding patterns of a wide array of marine invertebrates are shaped by strong and deterministic environmental factors over their geographic distribution range, such as temperature or photoperiod. Whether or not such patterns will remain adaptive at more localized scales may depend on how consistent are secondary drivers controlling resource supply to parents and offspring. We address this question by examining the seasonal patterns of both the trophic state of coastal waters, and larval production and quality produced by a filter-feeding invertebrate, the intertidal barnacle Chthamalus bisinuatus , along a 150 km long trophic gradient in Southeastern Brazil. Results are consistent to previous remote sensing work showing strong seasonal variation of chlorophyll- a and particulate organic carbon concentrations, increasing 2 to 2.5 times from summer – early autumn to winter, compatible to enhanced production through vertical mixing caused by passing cold fronts. The spatial gradient was also verified and found to be consistent between seasons, but contrasts were of smaller magnitude (coefficients of variations between 15 and 35%). All reproductive parameters showed important seasonal but no spatial trends. Larval production was much higher in summer-early autumn, agreeing with previous results based on gonad development and early recruitment rate for this same species and published results for other chthamalids. However, per capita parental transfer of neutral fatty acids to larvae and larval survival without exogenous food increased 2 and 1.4 times from the breeding to the non-breeding season, respectively, indicating that coastal oceanographic processes favor larval quality when reproductive activity is lower. Given that food limitation is likely frequent in the study region, shifting from oligotrophic to mesotrophic, and that effects of larval nourishing can be carried over to benthic barnacle stages, results also suggest that the contribution of out-of-season offspring to overall recruitment may be disproportionately higher. [ABSTRACT FROM AUTHOR]

The linkage disequilibrium coefficient r 2 is a measure of statistical dependence of the alleles possessed by an individual at different genetic loci. It is widely used in association studies to search for the locations of disease-causing genes on chromosomes. Most studies to date treat r 2 as a fixed property of two loci in a finite population, and investigate the sampling distribution of estimators due to the statistical sampling of individuals from the population. Here, we instead consider the distribution of r 2 itself under a process of genetic sampling through the generations. Using a classical two-locus model for genetic drift, mutation, and recombination, we investigate the probability density function of r 2 at stationarity. This density function provides a tool for inference on evolutionary parameters such as mutation and recombination rates. We reconstruct the approximate stationary density of r 2 by calculating a finite sequence of the distribution's moments and applying the maximum entropy principle. Our approach is based on the diffusion approximation, under which we demonstrate that for certain models in population genetics, moments of the stationary distribution can be obtained without knowing the probability distribution itself. To illustrate our approach, we show how the stationary probability density of r 2 can be used in a maximum likelihood framework to estimate mutation and recombination rates from sample data of r 2. [ABSTRACT FROM AUTHOR]

Highlights • Individual-based model of density-dependent animal movement is suggested. • The model predicts pattern formation subject to the strength of the density-dependence (autotaxis). • The emerging patterns are shown to be different for the Brownian and Levy walkers. • For Levy walkers, the model predicts formation of dynamical clusters with long term transient behaviour. Abstract Individual animal movement has been a focus of intense research and considerable controversy over the last two decades, however the understanding of wider ecological implications of various movement behaviours is lacking. In this paper, we consider this issue in the context of pattern formation. Using an individual-based modelling approach and computer simulations, we first show that density dependence ("auto-taxis") of the individual movement in a population of random walkers typically results in the formation of a strongly heterogeneous population distribution consisting of clearly defined animal clusters or patches. We then show that, when the movement takes place in a large spatial domain, the properties of the clusters are significantly different in the populations of Brownian and non-Brownian walkers. Whilst clusters tend to be stable in the case of Brownian motion, in the population of Levy walkers clusters are dynamical so that the number of clusters fluctuates in the course of time. We also show that the population dynamics of non-Brownian walkers exhibits two different time scales: a short time scale of the relaxation of the initial condition and a long time scale when one type of dynamics is replaced by another. Finally, we show that the distribution of sample values in the populations of Brownian and non-Brownian walkers is significantly different. [ABSTRACT FROM AUTHOR]

Highlights • The impact of fish predation on golden mussel's density was investigated. • The predatory activity of M. obtusidens significantly reduced the L. fortunei biomass. • M. obtusidens were able to consume a wide mussel's size range in the mesocosms. Abstract Limnoperna fortunei has been dispersing fast across South America by means of anthropic activities, invading aquatic ecosystems and causing substantial ecological and economic changes. Among these changes, L. fortunei has the potential to become an important prey species, and studies have verified their consumption by several fish in the South American continent. However, the impacts of fish predation on mussel densities have not yet been quantified. The present study had as a main objective the experimental evaluation of the potential impact of predation by piapara M. obtusidens on the densities of L. fortunei. Thus, a short-term experiment of predation in a fish farm was conducted in the upper Paraná River basin, Brazil. The exposure to predation by adults of M. obtusidens consistently reduced the biomass of L. fortunei with the level of impact increasing significantly as the density of predators and period of exposure increased. The observation of several substrates with a total removal of mussels indicated that all size classes of shells were preyed. Megaleporinus obtusidens presents various determining characteristics for the predation success on L. fortunei in confined areas, such as resistance to non-natural conditions, and mouth apparatus able to both remove several sizes of mussels on rigid substrates, and break apart the shells. The results of this experiment indicate the important role of predation in reducing the population densities of L. fortunei , as well as the potential use of M. obtusidens as an auxiliary tool for the maintenance of integrated invasive species prevention mechanisms. [ABSTRACT FROM AUTHOR]

Built environment exposure, characterized by ubiquity and changeability, has the potential to be the prospective target of public health policy. However, little research has been conducted to explore its impact on schizophrenia. This study aimed to investigate the association between built environmentand and schizophrenia rehospitalization by simultaneously considering substantial built environmental exposures. We recruited eligible schizophrenia patients from Hefei, Anhui Province, China between 2017 and 2019. The main outcome for this study was the time interval until the first recurrent hospital admission occurred within one year after discharge. For each included subject, we estimated the built environment exposures, including population density, walkability, land use mix, green and blue space, public transportation accessibility and road traffic indicator. Lasso (Least Absolute Shrinkage and Selection Operator) analysis was used to select the key variables. Multivariable Cox regression model was applied to obtain hazard ratio (HR) and its corresponding 95% confidence intervals (CI). Further, we also evaluated the joint effects of built environment characteristics on rehospitalization for schizophrenia by Quantile g-computation model. A total of 1564 hospitalized schizophrenia patients were enrolled, with 347 patients (22.2%) had a rehospitalization within one-year after discharge. Multivariable Cox regression analysis indicated that the re-hospitalization rate for schizophrenia would be higher in areas with a high population density (HR: 1.10, 95%CI: 1.04–1.16). Nonetheless, compared to the reference (Q1), participants who lived in a neighborhood with the highest walkability and NDVI (Normalized Difference Vegetation Index) (Q4) had a 76% and 47% lower risk of re-hospitalization within one year (HR:0.24, 95%CI: 0.13–0.45; and 0.53, 95%CI:0.32–0.85), respectively. Moreover, quantile-based g-computation analyses revealed that increased walkability and green space significantly eliminated the adverse effects of population density increases on schizophrenia patients, with a HR ratio of 0.61 (95%CI:0.48,0.79) per one quartile change at the same time. Our study provides scientific evidence for the significant role of built environment in schizophrenia rehospitalization, suggesting that optimizing the built environment is required in designing and building a healthy city. • The association is assessed by a cohort study design with numerous built environment features included. • Readmission risk for schizophrenia is lower in higher walkability and more greenspace environment. • Improving walkable environment could ameliorate the adverse effects of increasing population density. [ABSTRACT FROM AUTHOR]

While most current predictive models agree that the climate is changing, it is not yet clear what impact these changes will have on animal populations. It is vital to determine the potential consequences in order to develop future management and conservation strategies. Climate change may impact population stability by prompting changes in breeding behaviour. For example, if above-average temperatures negatively affect adult body condition, this will increase the cost of parental care. Theory suggests that under this scenario, individuals may trade off their own body condition and survival against that of their young. Despite convincing evidence that this parental care trade-off exists in nature, the potential impact of climate change on parental investment strategies has rarely been investigated. In cooperatively breeding species, group-living adults can gain group size benefits, such as assistance with raising young. These benefits may mediate the effects of climate change on adult condition and subsequent investment in young. Here, we investigated the extent to which high temperatures and rainfall variation affect (1) adult provisioning rates to dependent nestlings, (2) offspring development and (3) the cost of offspring care in the cooperatively breeding pied babbler, Turdoides bicolor . We found that overall, adults provisioned young significantly less on hot days. However, this pattern was affected by rank: dominant individuals provisioned significantly less while subordinates did not. Offspring development was negatively affected by heatwave events, suggesting that young suffer from reduced investment on hot days. However, there was no evidence that the cost of provisioning young increased during heatwave periods, perhaps owing to the reduction in investment by adults. This study provides some of the first evidence that higher temperatures affect investment decisions in cooperative breeders and that dominant and subordinate individuals respond differently to this stressor. [ABSTRACT FROM AUTHOR]

Plastic behavioural responses by individuals to different conditions and consistent individual differences in mean behaviour across situations both contribute to variation in a population. The relationship between behavioural plasticity and consistent individual differences is not clearly understood but may help predict personality variation in animals. High variation in mean behaviour and low variation in individual plastic responses will tend to maintain the rank order of individuals across situations and so permit consistent individual differences. Conversely, low variation in mean behaviour and high variation in plastic responses, by changing the rank orders of individuals, will erode consistent individual differences. Thus, selection that reduces variation in individual plastic responses should increase the opportunity for consistent individual differences in a population. We tested for relationships between heterogeneous predation regimes, the mean and variance of behavioural plasticity and consistent individual differences among three species groups of larval damselflies. Larvae of Enallagma signatum probably face consistent predation from fish over successive generations, whereas Enallagma ebrium/hageni and Enallagma annexum/boreale face a changing predation regime over generations either from fish or larval dragonflies. The behavioural reaction norms of larvae in repeated exposure trials to cues from a predatory fish, dragonfly larvae or no predator differed between species groups. Enallagma ebrium/hageni expressed the most consistent plastic response to predator cues, less variability in plasticity and greater consistent individual differences across cues compared to more variable plastic responses and low consistent individual differences in E. signatum . Selection on behavioural plasticity may enhance consistent individual differences in E. ebrium/hageni whereas relaxing selection on plasticity may reduce consistent individual differences in E. signatum . More generally, selection on plastic behaviour may enhance behavioural types while selection on mean behaviour may reduce behavioural types in animal populations. [ABSTRACT FROM AUTHOR]

Mobility is a general feature of human and animal populations living in physical space. In particular, it has been observed that often these movements are of the Lévy flight type. In this paper we study the effect of such power-law distributed displacements on the evolution of cooperation in simple games played on diluted two-dimensional grids. Using numerical simulations, our results show that unconditional Lévy flights do not favor the evolution of cooperation. However, when Lévy jumps are performed as a reaction to a growing number of defectors in an individual׳s neighborhood, all games studied here, including the harder Prisoner׳s Dilemma, remarkably benefit from this simple heuristics and cooperation can evolve in the population. [ABSTRACT FROM AUTHOR]

In various animal species individuals differ consistently in their behaviour, often referred to as personality. In several species these personality differences also correlate with differences in social behaviour. This is important as the social environment is a key selection pressure in many animal populations, mediated, for example, via competition or access to social information. Using social network analysis, recent studies have furthered our understanding of the role of personality in the social environment, usually by focusing on swarming or flocking populations. However, social associations in such populations are fundamentally different from those in territorial populations, where individuals meet less frequently and where the costs and benefits of spatial associations differ from those for swarming or flocking species. In this study we therefore tested whether social network position is related to individual differences in exploration behaviour, an established measure of an avian personality trait, using a wild, territorial, personality-typed great tit, Parus major , population. By means of novel, large-scale, automated tracking (Encounternet) we show, while controlling for average territory distance, that slower exploring males had less central social network positions. Yet, slower explorers overall did not travel shorter distances than faster explorers, indicating that a less central social network position was not merely a consequence of lower activity. Finally, males with less central social network positions did not have reduced breeding success compared to males with more central positions. Our results suggest that territorial individuals influence the structuring of their own social environment in relation to their personality. This is relevant, because the establishment of social relations and familiarity with possible competitors is predicted to be important in many territorial populations. [ABSTRACT FROM AUTHOR]

The ecological constraints hypothesis states that as group size increases, groups travel further and occupy larger home ranges in order to meet basic energetic needs for survival and reproduction. In this paper we used 19 years of demographic and ranging data on a study population of golden lion tamarins, Leontopithecus rosalia , to examine this hypothesis. Significant variation in rate of predation on lion tamarins during the study affected group size, membership and population density, which allowed us to test for predicted correlations between these changes and home range size. We found that predation-mediated changes in group composition and population density explained 71% of variation in home range size. Increased predation decreased lion tamarin home ranges because of the effects of decreased group size, fewer adult natal males and fewer reproductive females in the group. The effect of these factors on decreased ranging was offset somewhat by lower population density during high predation, which resulted in range expansion due to reduced pressure from neighbouring groups. We also found that groups with high future reproductive potential (i.e. with multiple breeding females) increased their range size. This effect was independent of group size. We propose a new hypothesis, that taxa with high rates of reproduction, such as lion tamarins, will increase home range size to accommodate future energy needs, rather than current needs, as would be predicted by the ecological constraints hypothesis. No or low production of infants and litters on the smallest lion tamarin ranges in our study supports this new hypothesis. [ABSTRACT FROM AUTHOR]

Highlights: [•] This is the first report of Perkinsus olseni in C. gasar and in Brazil. [•] Molecular analyses showed that both P. marinus and P. olseni infected C. gasar. [•] Perkinsus sp. infection prevalences were higher among the cultured oysters. [•] Perkinsus sp. prevalences varied, being maximum in summer and minimum in winter. [Copyright &y& Elsevier]

Highlights: [•] The deadliest virus in shrimp, WSSV. [•] Seasonal variation in WSSV presence along West coast of India. [•] Absolute quantification of WSSV by Real-time PCR at different seasons. [•] WSSV resistant prevalence among four locations along West coast of India. [Copyright &y& Elsevier]

Abstract: The negative relationship between body mass and population abundance was documented decades ago and forms one of the most fundamental scaling-laws in ecology. However, current theory fails to capture observed variations and the subject continues to raise controversy. Here we unify empirically observed size–abundance relationships with theory, by incorporating allometries in resource encounter rate and metabolic costs of movements. Fractal geometry is used to quantify the underlying resources distributions. Our model predicts that in environments packed with resources, body mass to population abundance relationships is less negative than the commonly assumed −3/4 power law. When resources are more patchily distributed, we predict a more negative exponent. These predictions are consistent with empirical observations. The current research provides an important step towards synthesizing metabolism, resource distribution and the global scaling of animal abundance, explaining why size–abundance relationships vary among feeding guilds and ecosystems. [Copyright &y& Elsevier]

Abstract: Woody encroachment is one of the several factors aggravating rangeland degradation in arid and semiarid areas. The goal of this study is to improve our understanding about the relationship between woody encroachment and its potential drivers by analyzing the temporal and spatial pattern of land-cover changes in the lower Omo region of southern Ethiopia. We used a combination of multi-temporal images, as well as climatic and demographic data for the analysis. Between 1985 and 2010 woody vegetation cover increased by 30.6% in the pastoral landuse type, while declining by 4.4% in the semipastoral areas. The increment was negatively associated with altitude and browser livestock density. However, contrary to the traditional presumption, it was not associated with grazer livestock density. Moreover, woody encroachment was higher in remote sites, farther from rivers and towns, where there is relatively lower human activities and livestock disturbance. The finding suggests the ecological significance of landuse type and livestock browsing to regulate the dynamics of woody vegetation in disturbance-adapted rangelands. Thus, a careful introduction of native larger browsers into woody encroached pastoral areas may help to facilitate rapid ecosystem recovery. [Copyright &y& Elsevier]

How food abundance affects (1) whether or not individuals defend territories and (2) what size of territory is defended are crucial to understanding the role that territoriality plays in regulating the population size of stream-dwelling salmonids. The threshold model of feeding territoriality predicts that territorial defence will be most intense at intermediate levels of food abundance, whereas optimal territory-size models predict that territory size will decrease with increasing food abundance. While the latter prediction has been supported by several studies of stream salmonids, too few levels of food abundance were typically used to describe the exact relationship between territory size and food abundance. Hence, to quantify the relation between the intensity of defence, territory size and food abundance, we manipulated food abundance over a broad range of values (0.62, 1.25, 2.5, 5, 10 and 20% of the fish wet body weight in dry food per day) in artificial stream channels (1.92×0.77m), while monitoring the territorial behaviour of juvenile rainbow trout. As predicted by the threshold model of feeding territoriality, the frequency of territorial aggression was highest at intermediate levels of food abundance, but fish never ceased defending territories entirely, particularly at food densities likely found in the wild. Also as predicted, the aggressive radius of rainbow trout decreased significantly, but only by 30% over a 32-fold increase in food abundance, equivalent to a 51% decrease in territory size. Our results suggest that territory size is relatively insensitive to changes in food abundance and may have a regulatory effect on population density. [Copyright &y& Elsevier]

Interpopulation variation in territorial aggression can reflect differences in life history or competitive environments. Life history theory predicts that males with more opportunities for future reproduction should avoid risk-taking behaviour to minimize the cost of current reproduction, whereas competitive environments should favour higher aggression to defend limited resources. Additionally, male aggression can be modulated by familiarity with competitors to be either lower (dear enemies) or higher (nasty neighbours) towards neighbours. We conducted a territory intrusion experiment using neighbour–stranger songs to examine how territorial aggression differed in two populations of orange-crowned warblers, Oreothlypis celata, breeding in California and Alaska. The California population breeds at very high densities and has a higher annual survival relative to the Alaska population, which breeds at significantly lower densities and has a lower annual survival rate. We found that California males showed higher amounts of territorial aggression in response to simulated territory intrusions than did Alaska males, supporting the hypothesis that competitive environments, as indicated by breeding density, rather than life history, shape geographical variation in levels of aggression. Both populations discriminated between song stimuli of neighbours and strangers, but California males responded more strongly towards neighbours, whereas Alaska males responded more strongly towards strangers. We discuss these results in light of the mechanisms for overall aggression and neighbour–stranger discrimination. [ABSTRACT FROM AUTHOR]

Intraspecific variability in mating systems has been documented previously, but there are few studies where investigators have used intraspecific comparisons to investigate the influence of ecological or demographic factors on social and genetic mating systems. We studied two populations of prairie voles, Microtus ochrogaster, one near Lawrence, Kansas, U.S.A., and the other in Bloomington, Indiana, U.S.A. We examined differences in spatial structuring of vegetation between sites, which might contribute to intraspecific variation in social and genetic mating patterns. Since space use is often related to the mating system, we calculated home range size of a subset of adult males and females in both populations and used live trapping to examine the number of same- or opposite-sex conspecifics sharing capture locations. We applied social network analysis to live-trapping data to quantify the number and strength of social ties with opposite-sex conspecifics. Genetic parentage analysis provided an estimate of the number of mates per individual. We found that space use and overlap with members of the same and opposite sex were best explained by effects of site and sex. The relative strength of social associations with opposite-sex conspecifics was best predicted by site, density and sex. The genetic mating system was best explained by population density. Although we cannot disentangle population density from ecological variables related to site (e.g. distribution of vegetation) that may have affected social monogamy in our study populations, our study shows that extrinsic variables do affect differences in social and genetic mating systems between populations. [ABSTRACT FROM AUTHOR]

Promiscuous and repeated mountings by females are evolutionarily intriguing as females are expected to be choosy and matings are expected to be costly. We evaluate the evolutionary basis of these behaviours in a high-density population of European badgers. We analysed postpartum mounting behaviour, in 3years, at two neighbouring social groups each year. We demonstrate a polygynandrous social mating system, with repeated mounting. Mounting was skewed among females in four social-group-years, but overall did not differ from random, potentially because female reproductive success is context dependent, varying with local food availability and female–female competition. Some males mounted more than others; however, male mounting frequency was not related to dominance rank, self-grooming rate, or body condition index. Mounting frequency did not predict paternity success; furthermore, a 16-year genetic data set showed that paternity success was positively correlated with body condition index. Females may therefore mount with males that do not father their offspring to minimize the risk of infanticide from them. Females may also trade mountings for allogrooming from males, but mounting frequency did not vary with relatedness, aggression received from males or sequential allomarking by males. We conclude that promiscuous and repeated mounting in badgers may have evolved to reduce male–male aggression around mounting and the likelihood of infanticide from males by masking paternity. Promiscuous mounting of female badgers does not devalue the previous male’s sperm, but may promote sperm competition, genetic diversity and genetic compatibility. [ABSTRACT FROM AUTHOR]

Studies on social spacing usually analyse spatial distribution using a single distribution index, and compare this with expected values assuming random spacing. However, different distribution indices give information on different aspects of spatial distribution. Furthermore, when animals use some parts of the study area more often because of environmental factors, assumptions of random spacing do not apply. As a contribution to the development of spatial distribution analysis methodology, we compared three distribution indices: nearest-neighbour distances (NND), coefficient of variation of interindividual distances and coefficient of variation of Dirichlet polygon areas. Distribution was studied at different animal densities, in the presence or absence of a wooden structure. Rabbits, Oryctolagus cuniculus, were chosen as the model species because of their apparent plasticity of spatial behaviour. The observed distribution was compared with a random distribution and with a resource-corrected random distribution that accounted for environmental influences on spacing. Comparisons with these two distributions led to different conclusions. This emphasizes the limited usefulness of comparisons with the random distribution, especially in more heterogeneous environments. However, divergence from random spacing could potentially be used to assess the relative importance of resources. Especially for 6-week-old rabbits, the density at which no evidence of avoidance was found differed between the distribution indices. This underlines the need to use multiple indices when studying social spacing. Nine-week-old rabbits generally avoided each other’s proximity, with NND indicating proximity avoidance even in the largest pens. Contrary to expectations, the wooden structure seemed to decrease social attraction between rabbits. [ABSTRACT FROM AUTHOR]

The formation of kin groups is an important step in the path to evolution of sociality in mammals. We used microsatellite DNA analyses, trapping and radiotelemetry data to investigate spatial and genetic associations of the solitary giant kangaroo rat, Dipodomys ingens. We predicted that, as population densities increase, dispersal distances should decrease to form kin groups. As predicted, females decreased dispersal distances as population densities increased to form female kin clusters of related neighbours. Males also decreased dispersal distances, but only at the highest density, and they did not form kin clusters. Males seemed to adjust their home ranges to overlap unrelated females as a possible strategy to avoid inbreeding. They were not highly related to the majority of females that they overlapped, and the nearest neighbour in most cases was an unrelated female. The significant decrease in distance between female neighbours and the formation of female kin groups at high population density represents a potential increase in social interactions among these solitary rodents. Further research is necessary to determine the extent to which D. ingens is able to discriminate between kin and other familiar animals and whether they interact preferentially to facilitate the success of closely related kin. [Copyright &y& Elsevier]

Models of antipredator vigilance show that animals should be more vigilant when in smaller groups, when neighbours are farther away, and when they occur at the edge rather than at the centre of a group. However, models fail to specify how animals are expected to look out for threats while actually scanning. We suggest that head movements during scanning may represent a way that animals can control the value of scanning while in groups. Head movements can be used to increase visual coverage (visual search) as well as bring features of the environment to more sensitive parts of the eyes (visual fixation). We conducted a seminatural experiment with brown-headed cowbirds, Molothrus ater, in which we manipulated group size and neighbour distance, and recorded vigilance for peripheral and central individuals. During scanning, the rate of head movements by peripheral individuals increased, probably to enhance visual coverage due to their higher perceived risk of predation. However, individuals that were farther apart and in smaller groups used a different scanning strategy by reducing their rate of head movements (e.g. increased the averaged time they spent holding a given head position steady), probably to fixate their gaze longer on neighbours. Visual fixation may be useful for obtaining social information about predation threats from the behaviour of groupmates. We show that (1) a vigilance metric associated with head movement behaviour, which is attuned to the visual system of a species, can provide novel information about vigilance in groups, and that (2) birds have different head movement strategies, probably associated with different visual targets, when the risk of predation is higher. [Copyright &y& Elsevier]

Mate searching often involves chemical cues and is a key process in determining fitness in most sexually reproducing animals. Effective mate-searching strategies are, therefore, essential for individuals to avoid wasting resources as a result of misrecognition of mating partners. Marine snails in the genus Littoraria are among the most successful molluscan groups that live closely associated with mangroves. Their population densities are often low, and finding a mate within the complex three-dimensional habitat of tree leaves, branches and trunks requires an effective searching strategy. We tested whether males of L. ardouiniana and L. melanostoma located females by following their mucus trails. In the laboratory, male tracker snails followed mucus trails laid by conspecific female marker snails at a higher intensity compared with other marker–tracker sex combinations in the mating season, but not in the nonmating season, and this was more pronounced in L. ardouiniana. Male trackers did not move faster when following the trails of conspecific female markers compared with other sex combinations; however, tracker snails moved faster in the mating than in the nonmating season, although this might be related to temperature. In both species, males tracked females regardless of trail complexity, and the majority of male trackers were able to detect the direction (polarity) of the trails of conspecific females. Together with previous studies on rocky shore Littorina species, these findings suggest that sex pheromones are incorporated into mucus trails to facilitate the reproductive success of these snails. Mucus trail following is, therefore, an adaptive mate-searching strategy in intertidal gastropod molluscs, and potentially in other gastropod groups in which trail-following behaviour is prevalent. [Copyright &y& Elsevier]

Abstract: We investigate a spatial lattice model of a population employing dispersal to nearest and second-nearest neighbors, as well as long-distance dispersal across the landscape. The model is studied via stochastic spatial simulations, ordinary pair approximation, and triplet approximation. The latter method, which uses the probabilities of state configurations of contiguous blocks of three sites as its state variables, is demonstrated to be greatly superior to pair approximations for estimating spatial correlation information at various scales. Correlations between pairs of sites separated by arbitrary distances are estimated by constructing spatial Markov processes using the information from both approximations. These correlations demonstrate why pair approximation misses basic qualitative features of the model, such as decreasing population density as a large proportion of offspring are dropped on second-nearest neighbors, and why triplet approximation is able to include them. Analytical and numerical results show that, excluding long-distance dispersal, the initial growth rate of an invading population is maximized and the equilibrium population density is also roughly maximized when the population spreads its offspring evenly over nearest and second-nearest neighboring sites. [Copyright &y& Elsevier]

Dispersal, and especially movement between the natal and the new environment, is a costly process. Costs are incurred not only during the preparation or transfer phase but also on arrival in a new environment. Such costs comprise, for instance, time costs because of the need to search for a suitable microhabitat or integration costs when immigration occurs in already densely populated habitat. The failure to settle or to integrate may consequently inflate the costs already incurred during emigration and transfer. Therefore, we expect emigrating individuals to have evolved enhanced integration capacities. In our laboratory experiments, dispersive phenotypes of the agrobiont spider Erigone atra were characterized by (1) faster settlement in empty habitat and (2) increased willingness to compete for ownership of already occupied sites. These correlated behaviours point to dispersive phenotypes (1) being likely to experience a selective advantage at settlement and (2) not being a random subsample from the population. These correlated behaviours are predicted to have a strong impact on spatial population dynamics and gene flow. [ABSTRACT FROM AUTHOR]

We studied the simultaneous activity patterns of a breeding wolf, Canis lupus, pair and five adult moose, Alces alces, cows from April to November 2004 in a wolf territory in southeastern Norway. All study animals were GPS collared, and we used a total of 8297 fixes to analyse their temporal activity patterns. We examined the daily activity rhythm of the two species and how this varied seasonally through the study period, and investigated the association in activity patterns between the two species. Wolf activity peaked at dawn. The distance moved per time unit and the linearity of the movement were higher in wolves than in moose, but both species showed a decrease in these variables in June, coinciding with the denning and calving seasons. With the exception of the summer months when the activity of wolves and moose was limited by the raising of offspring, we found no correlation between the temporal activities of the two species. Hence, we did not find support for the hypothesis that the wolves and moose in Scandinavia have adjusted to each other’s activity patterns. We discuss the results in light of the relative density of the two species and the intensive human harvest of moose, and hypothesize that synchronicity of predator–prey activity patterns may be ratio dependent. [ABSTRACT FROM AUTHOR]

Abstract: The challenge hypothesis proposes that testosterone (T) elevation above what is needed for breeding is associated with social factors, and males possibly modulate their hormonal response to variations in population density and sex ratio. We investigated the role of social environment in altering testosterone levels and aggression in a tropical, seasonally breeding grassquit (Volatinia jacarina). We exposed males to three social conditions during 1year: all-males treatment (six males), mixed treatment (three males–three females), and paired treatment (one male–one female). We quantified aggressiveness among males and T plasma concentration for each individual in each treatment monthly. We found that more aggressive interactions occurred in the all-males treatment than in the mixed treatment. The data also revealed that, coincident with these behavioral changes, the patterns of T variation through time in each treatment were markedly different. The all-males treatment exhibited an early increase in T concentration, which was sustained for a lengthy period with two distinctive peaks, and subsequently declined sharply. The mixed treatment presented an intermediate pattern, with more gradual increase and decrease in T levels. At the other extreme, the paired treatment presented a later rise in T concentration. We conclude that the more competitive environment, with higher density of males, caused the early and higher elevation in T level, thus the presence of competitors may influence the decision of how much a male should invest in reproduction. We suggest that the male''s perception of his social environment ultimately mediates hormonal production and alters his reproductive strategy. [Copyright &y& Elsevier]

Contact calls function to coordinate movements in a wide variety of social animals. Where population density is high, visibility is low and repeated interactions occur between known social companions, calls are often individually recognizable. Parrots are highly social and make substantial daily movements, which appear to be mediated through contact calling. However, there is little experimental evidence for how free-ranging parrots recognize social companions. We quantified intra- and interindividual variation of contact calls in a banded population of green-rumped parrotlets in Venezuela. Recordings of a sample of males were made on replicate days as they announced their return to incubating mates. Spectrographic structure of these contact calls showed significantly more variation between than within individuals, and calls could be correctly classified to individuals more often than was expected by chance. Males varied across multiple dimensions simultaneously, including duration, frequency and frequency modulation of contact calls. Playback experiments showed that free-ranging female parrotlets responded significantly more often to their mates’ calls than to calls of males of other nests. Mate recognition via contact calls may be selectively advantageous during incubation and brooding if this reduces the potential costs associated with confusing contact calls of mates with those of nonmates, including infanticidal conspecifics. [Copyright &y& Elsevier]

Cooperative-breeding studies tend to focus on a few alloparental behaviours in highly cooperative species exhibiting high reproductive skew and the associated short-term, but less frequently long-term, fitness costs. We analysed a suite of alloparental behaviours (assessed via filming) in a kin-structured, high-density population of plurally breeding European badgers, Meles meles, which are not highly cooperative. Group members, other than mothers, performed alloparental behaviour; however, this was not correlated with their relatedness to within-group young. Furthermore, mothers babysat, allogroomed cubs without reciprocation, and allomarked cubs more than other members of the group (controlling for observation time). For welfare reasons, we could not individually mark cubs; however, the number observed pre-independence never exceeded that trapped. All 24 trapped cubs, in three filmed groups, were assigned both parents using 22 microsatellites. Mothers may breed cooperatively, as the time they babysat their assigned, or a larger, litter size did not differ. Furthermore, two mothers probably allonursed, as they suckled more cubs than their assigned litter size. An 18-year genetic pedigree, however, detected no short-term (litter size; maternal survival to the following year) or long-term (offspring breeding probability; offspring lifetime breeding success) fitness benefits with more within-group mothers or other members of the group. Rather, the number of other members of the group (excluding mothers) correlated negatively with long-term fitness. Mothers may tolerate other members of the group, as nonbreeders undertook more digging. Our study highlights that alloparental care varies on a continuum from that seen in this high-density badger population, where alloparenting behaviour is minimal, through to species where alloparental care is common and provides fitness benefits. [Copyright &y& Elsevier]

Most studies of intrasexual mating competition have focused only on males, and have typically shown an increase in aggression and a decrease in courtship rate with increasing operational sex ratio (OSR), the ratio of ready-to-mate males to females. We manipulated the number of males (1, 2 or 4) and females (2, 4, 8 or 16) in a factorial design to investigate mating competition and courtship rate in Japanese medaka, a species with conventional sex roles, over a broad range of OSRs (0.0625 to 2), and in relation to the density of both sexes. As predicted, the rates of intrasexual interactions by both males and females increased with the number of competitors and decreased with the number of potential mates, whereas the rates of courtship decreased with the number of competitors and increased with the number of mates. At OSRs between 0.35 and 2, males engaged in more intrasexual interactions and courtship behaviour than females. However, females became the more competitive sex at OSRs less than 0.35, and engaged in more courtship than males at OSRs greater than 2, rather than at an OSR of 1, as predicted by conventional mating system theory. Our results indicate that OSR can predict the considerable within-sex variability in reproductive behaviour of both males and females, regardless of which sex is more competitive. [Copyright &y& Elsevier]

Abstract: In this study, an analytical method is introduced for the identification of predator–prey populations time-dependent evolution in a Lotka–Volterra predator–prey model which takes into account the concept of accelerated-predator-satiety. Oppositely to most of the predator–prey problem models, the actual model does not suppose that the predation is strictly proportional to the prey density. In reference to some recent experimental results and particularly to the conclusions of about predators which are ‘never not hungry’, an accelerated satiety function is matched with the initial conventional equations. Solutions are plotted and compared to some relevant ones. The obtained trends are in good agreement with many standard Lotka–Volterra solutions except for the asymptotic behaviour. [Copyright &y& Elsevier]

The benefit of monopolizing a limited resource is influenced by competitor density and by the relative competitive ability of defenders and intruders. Nevertheless, few studies have investigated the effect of density on resource defence in groups with large asymmetries in competitive ability, as a consequence of, for example, age and/or body size. We used two age classes (i.e. size groups) of stream-living brown trout, Salmo trutta, to investigate this issue. While old (and large) trout are assumed to be superior during interference competition, younger individuals may be both numerically dominant and constitute more than half of the total population biomass. In this experiment, the ability of one yearling to monopolize a concentrated food source was observed at four densities of under-yearlings (zero, two, six and 12) in an indoor seminatural stream. We predicted that the success of defence would decrease with increasing under-yearling density and that the frequency of defence (i.e. aggression) would peak at an intermediate density. As predicted, yearlings made significantly more unsuccessful foraging attempts and adopted darker body coloration at high density of under-yearlings, suggesting increased stress levels. However, in contrast to our second prediction, the number of aggressive interactions increased progressively with density. These novel findings suggest that the cost of defence increases with under-yearling density, probably as a consequence of stress from interference with under-yearlings employing alternative competitive strategies. However, the difference in size seems to enable yearlings to defend the food resource at higher density of competitors than predicted from the resource defence theory. [Copyright &y& Elsevier]

The immediate movement and behaviour of individuals arriving in novel environments influence long-term survival and population establishment. Studies have previously investigated exploratory behaviour in novel laboratory environments, but never during colonization of natural systems. Experimentally releasing and monitoring animals would allow testing of laboratory and computer-simulation hypotheses. We sequentially released and tracked three adult male brown rats, Rattus norvegicus, on a rat-free island, monitoring their movements hourly for 3 weeks to test laboratory and simulation-generated hypotheses of how animals explore and move in novel environments. We found that (1) individual movements are apparently random; (2) range size increases most rapidly in the first week after arrival; (3) range size is larger than for individuals at high density; (4) movement is mediated by central place foraging behaviour. These findings contradict laboratory hypotheses of nonrandom exploration but support simulation search strategy hypotheses. Random movement and increased ranges at low density have implications for understanding animal colonization dynamics and intercepting invasive species arriving at new locations. [Copyright &y& Elsevier]

Abstract: Sexual reproduction may be divided into two main categories: hermaphroditism and dioecy (Botany)/gonochorism (Zoology). Simultaneous hermaphrodites can function in both male and female roles whereas a dioecious/gonochorist population consists of distinct male and female individuals. Mean-field calculations, which ignore spatial aspects, suggest that self-incompatible hermaphrodites should have a twofold advantage over dioecious population when reproduction is limited by mating encounters. By use of stochastic spatial simulations we demonstrate that hermaphroditism has an even greater advantage when local interactions are considered. This result provides further support for the observation that hermaphroditism is associated with sedentary species, such as plants and animals with poor mate search efficiency. We also investigate the finite size effects associated with the well-known quadratic contact process. [Copyright &y& Elsevier]

Abstract: How many generations ago did the common ancestor of all present-day individuals live, and how does inbreeding affect this estimate? The number of ancestors within family trees determines the timing of the most recent common ancestor of humanity. However, mating is often non-random and inbreeding is ubiquitous in natural populations. Rates of pedigree growth are found for multiple types of inbreeding. This data is then combined with models of global population structure to estimate biparental coalescence times. When pedigrees for regular systems of mating are constructed, the growth rates of inbred populations contain Fibonacci n-step constants. The timing of the most recent common ancestor depends on global population structure, the mean rate of pedigree growth, mean fitness, and current population size. Inbreeding reduces the number of ancestors in a pedigree, pushing back global common ancestry times. These results are consistent with the remarkable findings of previous studies: all humanity shares common ancestry in the recent past. [Copyright &y& Elsevier]

Males generally compete for females through courtship and aggression (conventional sex roles). However, sex roles are reversed in some species and can even vary between populations or over time within a single species. The operational sex ratio (OSR), the sex ratio of ready-to-mate individuals, is a central factor proposed to explain the strength and direction of mating competition. Density can both act as a cue for OSR and have its own effects on competition. In the two-spotted goby, Gobiusculus flavescens, a seasonal switch in sex roles coincides with a change in OSR from male to female biased and a decrease in male density. This dynamic system provides an ideal opportunity to test the effects of OSR and density on competitive behaviour experimentally. In an aquarium experiment, we created two different sex ratios at two different densities and observed courtship and agonistic behaviour in both sexes. We changed sex ratio to equality after 4 days of treatment, to test for a lag in the behavioural response. Contrary to our predictions, males courted more after prolonged exposure to a female-biased sex ratio, although we also found a tendency for a positive effect of male density on male courtship frequency. We did not find any other effects of treatment on either male or female behaviour. Furthermore, we did not find evidence for a lag in the response to a change in density or sex ratio. We conclude that OSR and density did not affect individual frequencies of behaviour in the expected direction. [Copyright &y& Elsevier]

Abstract: Population structure and distribution of Terebralia palustris were compared with the environmental parameters within microhabitats in a monospecific stand of Avicennia marina in southern Mozambique. Stable carbon and nitrogen isotope analyses of T. palustris and potential food sources (leaves, pneumatophore epiphytes, and surface sediments) were examined to establish the feeding preferences of T. palustris. Stable isotope signatures of individuals of different size classes and from different microhabitats were compared with local food sources. Samples of surface sediments 2.5–10m apart showed some variation (−21.2‰ to −23.0‰) in δ 13C, probably due to different contributions from seagrasses, microalgae and mangrove leaves, while δ 15N values varied between 8.7‰ and 15.8‰, indicating that there is a very high variability within a small-scale microcosm. Stable isotope signatures differed significantly between the T. palustris size classes and between individuals of the same size class, collected in different microhabitats. Results also suggested that smaller individuals feed on sediment, selecting mainly benthic microalgae, while larger individuals feed on sediment, epiphytes and mangrove leaves. Correlations were found between environmental parameters and gastropod population structure and distribution vs. the feeding preferences of individuals of different size classes and in different microhabitats. While organic content and the abundance of leaves were parameters that correlated best with the total density of gastropods (>85%), the abundance of pneumatophores and leaves, as well as grain size, correlated better with the gastropod size distribution (>65%). Young individuals (height<3cm) occur predominantly in microhabitats characterized by a low density of leaf litter and pneumatophores, reduced organic matter and larger grain size, these being characteristic of lower intertidal open areas that favour benthic microalgal growth. With increasing shell height, T. palustris individuals start occupying microhabitats nearer the mangrove trees characterized by large densities of pneumatophores and litter, as well as sediments of smaller grain size, leading to higher organic matter availability in the sediment. [Copyright &y& Elsevier]

Abstract: Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrates. The shore crab Carcinus maenas (Crustacea: Brachyura: Portunidae) inhabits a variety of coastal, estuarine and lagoon habitats. At low tide, habitat structural complexity may be most important for crabs in the intertidal, providing refuge from predation and desiccation. The quality of different vegetated and nonvegetated estuarine and rocky shore habitats in SW Portugal and SW England was evaluated for intertidal C. maenas populations. We estimated population density, size–structure, and potential growth (RNA/DNA ratios) to investigate habitat quality. Vegetated estuarine habitats supported higher crab densities, than nonvegetated estuarine and rocky shore habitats. Investigation of population size–structure revealed that all habitats seem important recruitment and nursery areas although estuarine habitats in SW Portugal appeared to support higher densities of new recruits than equivalent habitats in SW England. Significant variation was found in RNA/DNA ratios among habitats. Ratios were highest in the rocky shore suggesting a high quality habitat where growth potential is high. We speculate that competition from other top-predators (Pachygrapsus spp.) rather than low habitat quality may limit the occurrence of C. maenas in intertidal rocky shore habitats in SW Portugal. In estuarine environments RNA/DNA ratios were significantly higher in the vegetated than in the nonvegetated estuarine habitats in SW Portugal but not in SW England, suggesting geographic differences in the extent to which highly structure habitats represent high quality. Our results challenge the current paradigm that structured habitats are necessarily those of higher quality for C. maenas. [Copyright &y& Elsevier]

Abstract: Invasive smooth cordgrass (Spartina alterniflora, hereafter Spartina) has been expanding rapidly in the estuarine wetlands at Chongming Dongtan (East China) at the expense of native sea-bulrush (Scirpus mariqueter, hereafter Scirpus) and common reed (Phragmites australis, hereafter Phragmites). To examine the potential impacts of the Spartina invasion on bird diversity, we compared the abundance and species richness of birds in habitats created by Spartina, Phragmites, Spartina mixed with Phragmites, Scirpus, and the bare intertidal zone at Chongming Dongtan in spring 2008. Most birds were recorded in the native habitats, with songbirds and breeding birds being most abundant in the Phragmites habitats, and waterbirds and migrants being most abundant in the Scirpus habitats and bare intertidal zone. Both species number and population densities of birds were lower in the exotic Spartina habitats than in the other four habitats. Although some songbirds and breeding birds used the Spartina-invaded habitats, and even preferred Spartina-invaded habitats to Scirpus habitats and bare intertidal zone, their densities were lower in the Spartina-invaded habitats than in the native Phragmites habitats. This might have resulted from the dense Spartina stands restricting bird movement and providing insufficient useable food for most birds. We conclude that the spread of exotic Spartina has negative impacts on local bird communities. Because Chongming Dongtan is an important stopover site for energy replenishment of shorebirds in the East Asian–Australasian Flyway, urgent measures are needed to control further spread of Spartina and to restore the native habitats for birds. [Copyright &y& Elsevier]

Abstract: Estuaries consist of a complex mosaic of many distinctive habitat types. Each one may perform several vital functions in the functioning of the whole system and although its value is often based on species density patterns, functional relationships between them also need to be examined. Spatial patterns of estuarine habitat use by fish assemblages were determined within and among nine estuarine systems along the Portuguese coast. Fish sampling surveys were conducted in May and July 2006, covering the full estuarine gradient. All the different habitat types were sampled in each estuarine system with a beam trawl. Estuarine habitats were mapped with GIS and habitat specific associated fish assemblages were described based on several community descriptors, namely richness (S), evenness (J′), and diversity (H′) and on an ecological and feeding guilds classification. A canonical correspondence analysis was performed to evaluate the relationship between estuarine habitats and fish assemblages in this set of estuaries. The intertidal and subtidal soft substratum habitats corresponded to the largest areas in all the estuaries and presented higher number of species. Nevertheless the highest mean density of fish was registered at the salt marsh habitat, which occupies smaller areas within each estuary. The fact that small vegetated habitats like salt marsh and seagrass supported high densities of fish may be an indication of the important role these habitats play in the whole system functioning. Differences in fish assemblage structure were found with latitude and between habitats amongst and within estuaries. Some of the fish species were found to be particularly associated with certain habitat types, which might indicate that each estuarine habitat may be related with specific fish assemblages regardless the estuary. The present work provides valuable information for management by identifying the most important habitats for species conservation and predicting the possible effects of habitat disturbance or destruction, namely by climate change and anthropogenic pressures. [Copyright &y& Elsevier]

Abstract: We study the effects of a disease affecting a predator on the dynamics of a predator–prey system. We couple an SIRS model applied to the predator population, to a Lotka–Volterra model. The SIRS model describes the spread of the disease in a predator population subdivided into susceptible, infected and removed individuals. The Lotka–Volterra model describes the predator–prey interactions. We consider two time scales, a fast one for the disease and a comparatively slow one for predator–prey interactions and for predator mortality. We use the classical “aggregation method” in order to obtain a reduced equivalent model. We show that there are two possible asymptotic behaviors: either the predator population dies out and the prey tends to its carrying capacity, or the predator and prey coexist. In this latter case, the predator population tends either to a “disease-free” or to a “disease-endemic” state. Moreover, the total predator density in the disease-endemic state is greater than the predator density in the “disease-free” equilibrium (DFE). [Copyright &y& Elsevier]

Abstract: Weakly density-dependent effects, characterized by fractional scaling exponents close to one, are rarely studied in the ecological literature. Here, we consider the effect of an additional weakly density-dependent term on a simple competition model. Our investigation reveals that weak density-dependence opens up an “invisible niche”. This niche does not constitute a new mechanism for coexistence, but is a previously unexplored consequence of known mechanisms. In the invisible niche a weaker competitor can survive at very low density. Coexistence thus requires large habitat size. Such niches, if found in nature, would have a direct impact on species-area laws and species-abundance curves and should therefore receive more attention. [Copyright &y& Elsevier]

Quantitatively characterizing the social structure of a population provides important insight into the forces shaping key population processes. Moreover, long-term social dynamics provide an avenue for understanding population-level responses to changes in socioecological conditions. This is particularly true for species that show natal philopatry and highly stable hierarchically structured social units, such as the piscivorous resident killer whales of the northeast Pacific. The southern resident killer whale population is a small, demographically closed population, comprising three commonly recognized pods (J, K and L pods), that has recently been listed as endangered throughout its range in both Canadian and U.S.A. waters. In this study, we quantitatively assessed social structure in this population from 29 years of photo-identification data to characterize significant temporal changes in sociality. Preferential affiliation among killer whales within both genealogical matrilines and pods was supported by two different analytical methods and, despite interannual variability, these social clusters persisted throughout the study. All three pods experienced fluctuations in social cohesion over time, but the overall rate of intrapod affiliation was consistently lowest within L pod, the largest of the southern resident pods. The most recent increase in fluidity within social units, occurring in the mid to late 1990s, was coincident with a significant decline in population size, suggesting a possible common response to external stressors. Quantifying these trends in social structure is the first step towards understanding the causes and consequences of long-term changes in killer whale social structure. [Copyright &y& Elsevier]

Abstract: Ecological modelers have long puzzled over the spatial distribution of species. The random walk or diffusive approach to dispersal has yielded important results for biology and mathematics, yet it has been inadequate in explaining all phenomenological features. Ranges can terminate non-smoothly absent a complementary shift in the characteristics of the environment. Also unexplained is the absence of a species from nearby areas of adequate, or even abundant, resources. In this paper, I show how local searching behavior–keyed to a density-dependent fitness–can limit the speed and extent of a species’ spread. In contrast to standard diffusive processes, pseudo-rational movement facilitates the clustering of populations. It also can be used to estimate the speed of an expanding population range, explain expansion stall, and provides a mechanism by which a population can colonize seemingly removed regions — biogeographic islands in a continental framework. Finally, I discuss the effect of resource degradation and different resource impact/utilization curves on the model. [Copyright &y& Elsevier]

Abstract: The structure of macrofaunal communities at two similar exposed sandy beaches on the western coast of Portugal was monitored for approximately 18 months by sampling all the beach area, from the shoreline to the base of the dunes. The beaches’ physical environment, as well as community density and composition, seasonal variations and the potential relationships between biological data and environmental parameters were studied. The two beaches had similar exposure to wave action, but differed in terms of sediment grain size, extent of the intertidal area, sediment moisture content and, especially, in the potential food availability in the form of allochthonous debris. Differences were observed with regard to the communities’ structure, namely regarding composition and relative contribution of the dominant species. Seasonality, especially temperature variations, and the interaction between seasons and the beach zones (supralittoral vs. intertidal) also had a strong influence on communities: controlling dominant species’ density and the horizontal distribution of the dominant species, and promoting a differential utilization of the beach by several resident macrofaunal animals. The present study allows the identification of key species in exposed sandy beaches of western Portugal and demonstrates that a steady community structure does not persist in the similarly exposed conditions observed, which may be mainly a response to distinct detritus subsidies, combined with differences in sediment grain size, sediment moisture content and extent of the intertidal area. [Copyright &y& Elsevier]

Abstract: This paper presents a framework in which various single-species discrete-time population models exhibiting the Allee effect are derived from first principles. Here, the Allee effect means a reduction in individual fitness at low population sizes. The derivation is based on the distribution of female and male individuals among discrete resource sites, in addition to competitive and cooperative interaction among individuals. These derivations show how the derived population models depend on the type and the intensity of competition, and the degree of clustering of individuals. Along with these models exhibiting the Allee effect, this paper also presents first-principles derivation of population models without the Allee effect which include a parameter relating to the intensity of competition. [Copyright &y& Elsevier]

Density-dependence is a key concept in population dynamics. Here, we review how body mass and demographic parameters vary with population density in large herbivores. The demographic parameters we consider are age- and sex-specific reproduction, survival and dispersal. As population density increases, the body mass of large herbivores typically declines, affecting individual performance traits such as age of first reproduction and juvenile survival. We documented density-dependent variations in reproductive rates for many species from the Arctic to subtropical zones, both with and without predation. At high density, a trade-off between growth and reproduction delays the age of primiparity and often increases the costs of reproduction, decreasing both survival and future reproductive success of adult females. Density-dependent preweaning juvenile survival occurs more often in polytocous than monotocous species, while the effects of density on post-weaning juvenile survival are independent of litter size. Responses of adult survival to density are much less marked than for juvenile survival, and may be exaggerated by density-dependent changes in age structure. The role of density-dependent dispersal in population dynamics remains uncertain, because very few studies have examined it. For sexually dimorphic species, we found little support for higher sensitivity to increasing density in the life history traits of males compared to females, except for young age classes. It remains unclear whether males of dimorphic species are sensitive to male density, female density or a combination of both. Eberhardt's model predicting a sequential effect of density on demographic parameters (from juvenile survival to adult survival) was supported by 9 of 10 case studies. In addition, population density at birth can also lead to cohort effects, including a direct effect on juvenile survival and longterm effects on average cohort performance as adults. Density effects typically interact with weather, increasing in strength in years of harsh weather. For some species, the synchronization between plant phenology and reproductive cycle is a key process in population dynamics. The timing of late gestation as a function of plant phenology determines whether density-dependence influences juvenile survival or adult female reproduction. The detection of density-dependence can be made difficult by nonlinear relationships with density, high sampling variability, lagged responses to density changes, changes in population age structure, and temporal variation in the main factors limiting population growth. The negative feedbacks of population size on individual performance, and hence on life history traits, are thus only expected in particular ecological contexts and are most often restricted to certain age-specific demographic traits. [ABSTRACT FROM AUTHOR]