Variety Of Ecological Factors Research Articles

Effect of body size, age and timing of breeding on clutch and egg size of female Eastern Gray Treefrogs, Hyla versicolor

Abstract Information on how organisms allocate resources to reproduction is critical for understanding population dynamics. We collected clutch size (fecundity) and egg size data of female Eastern Gray Treefrogs, Hyla versicolor, and examined whether observed patterns of resource allocation are best explained by expectations arising from life history theory or by expected survival and growth benefits of breeding earlier. Female Hyla versicolor showed high between-individual variation in clutch and egg size. We did not observe maternal allocation trade-offs (size vs number; growth vs reproduction) predicted from life history theory, which we attribute to the large between-female variation in resource availability, and the low survival and post-maturity growth rate observed in the study population. Rather, clutches are larger at the beginning of the breeding season, and this variation in reproductive investment aligns with seasonal variation in ecological factors affecting offspring growth and survival.

Dynamics of local adaptation in a stable environmental gradient

Microbial populations in nature generally inhabit extended environments with substantial spatial variation in ecological factors: light intensity in the ocean, temperature in geothermal hot springs, or a variety of chemical concentrations including salt and pH. In such continuously varying environments, it remains unclear why a finite number of subpopulations form and how this number is set. Here we show that a model of asexual evolution in a gradient maps onto a no-gradient neutral model, and by mapping this model to a gas of kinks and antikinks, we derive the full distribution of the number of coexisting lineages, and their correlation functions. Testing these predictions in controlled laboratory experiments would provide valuable insights into many real-world microbial communities.Received 28 March 2021Revised 13 September 2021Accepted 12 October 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L042026Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBiological complexityEcological population dynamicsEvolutionary dynamicsBiological Physics

A Test of Foraging Models Using Dietary Diversity Indices for the Lomako Forest Bonobos

Optimal diet and functional response models are used to understand the evolution of primate foraging strategies. The predictions of these models can be tested by examining the geographic and seasonal variation in dietary diversity. Dietary diversity is a useful tool that allows dietary comparisons across differing sampling locations and time periods. Bonobos (Pan paniscus) are considered primarily frugivorous and consume fruits, leaves, insects, vertebrates, terrestrial herbaceous vegetation, and flowers. Frugivores, like bonobos, are valuable for examining dietary diversity and testing foraging models because they eat a variety of species and are subject to seasonal shifts in fruit availability. Frugivorous primate species thus allow for tests of how variation in dietary diversity is correlated with variation in ecological factors. We investigated measures of dietary diversity in bonobos at two research camps across field seasons within the same protected area (N’dele and Iyema) in Lomako Forest, Democratic Republic of the Congo. We compared the results of behavioral observation (1984/1985, 1991, 1995, 2014, and 2017) and fecal washing analysis (2007 and 2009) between seasons and study period using three diversity indices (Shannon’s, Simpson’s, and SW evenness). The average yearly dietary diversity indices at N’dele were Shannon’s Hʹ = 2.04, Simpson’s D = 0.82, and SW evenness = 0.88 while at Iyema, the indices were Shannon’s Hʹ = 2.02, Simpson’s D = 0.82, and SW evenness = 0.88. Behavioral observation data sets yielded significantly higher dietary diversity indices than fecal washing data sets. We found that food item (fruit, leaf, and flower) consumption was not associated with seasonal food availability for the 2017 behavioral observation data set. Shannon’s index was lower during periods when fewer bonobo dietary items were available to consume and higher when fruit was abundant. Finally, we found that optimal diet models best-explained patterns of seasonal food availability and dietary diversity. Dietary diversity is an essential factor to consider when understanding primate diets and can be a tool in understanding variation in primate diets, particularly among frugivores. Dietary diversity varies across populations of the same species and across time, and it is critical in establishing a complete understanding of how primate diets change over time.

Fecal Glucocorticoid Metabolites as Biomarkers in Equids: Assay Choice Matters

ABSTRACTFree ranging animals are exposed to environmental, demographic, and ecological challenges over time, which can affect their health and fitness. Non‐invasive biomarkers can provide insight into how animals cope with these challenges and assess the effectiveness of conservation management strategies. We evaluated how free ranging ponies (Equus ferus caballus) on the Carneddau Mountain range, North Wales respond to 2 stimuli: an acute stressor of an annual roundup event in November 2014, and spatial and temporal variation in ecological factors in 2018. We evaluated fecal glucocorticoid metabolites using 2 enzyme immunoassays (EIAs): an 11‐oxoetiocholanolone EIA (measuring 11,17‐dioxoandrostanes [11,17‐DOAs]) and a corticosterone EIA. The former assay has been validated in equids, whereas there is limited evidence for the suitability of the latter. We used an additional parent testosterone EIA to measure fecal androgen metabolites in response to the ecological challenges. Following the roundup, the metabolite concentrations measured by the 2 glucocorticoid EIAs were not correlated. The 11,17‐DOAs were elevated from the second day following the roundup and then slowly returned to pre‐round levels over the next 2 weeks. In contrast, the metabolites measured by the corticosterone assay showed no response to the roundup. For the ecological data, all 3 assays detected a positive correlation between metabolites and social group size in males but not in females. The metabolite concentrations measured by the testosterone and corticosterone assays were highly correlated and were temporally associated with the onset of the breeding season, whereas the 11,17‐DOAs were not. The co‐variance of metabolites measured by the corticosterone and testosterone assays, and the lack of an acute response in the corticosterone assay to the roundup, suggests that metabolites detected by the corticosterone assay were not primarily associated with increased glucocorticoid production. We recommend using well‐validated fecal biomarker assays of hypothalamus‐pituitary‐adrenal axis activity to evaluate and compare the effect of different management interventions and environmental change. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

How Mycorrhizal Associations Influence Orchid Distribution and Population Dynamics.

Orchid distribution and population dynamics are influenced by a variety of ecological factors and the formation of holobionts, which play key roles in colonization and ecological community construction. Seed germination, seedling establishment, reproduction, and survival of orchid species are strongly dependent on orchid mycorrhizal fungi (OMF), with mycorrhizal cheating increasingly observed in photosynthetic orchids. Therefore, changes in the composition and abundance of OMF can have profound effects on orchid distribution and fitness. Network analysis is an important tool for the study of interactions between plants, microbes, and the environment, because of the insights that it can provide into the interactions and coexistence patterns among species. Here, we provide a comprehensive overview, systematically describing the current research status of the effects of OMF on orchid distribution and dynamics, phylogenetic signals in orchid–OMF interactions, and OMF networks. We argue that orchid–OMF associations exhibit complementary and specific effects that are highly adapted to their environment. Such specificity of associations may affect the niche breadth of orchid species and act as a stabilizing force in plant–microbe coevolution. We postulate that network analysis is required to elucidate the functions of fungal partners beyond their effects on germination and growth. Such studies may lend insight into the microbial ecology of orchids and provide a scientific basis for the protection of orchids under natural conditions in an efficient and cost-effective manner.

Seasonal Variation in Activity Budget of Assamese Macaques in Limestone Forest of Southwest Guangxi, China

The activity budget is important for understanding behavioural variability and adaptation in primates. Assamese macaques (Macaca assamensis) found in the limestone forest of Guangxi Nonggang National Nature Reserve, Southwest China, primarily feed on young leaves of Bonia saxatilis (a shrubby, karst-endemic bamboo). To understand how a specific bamboo leaf-based diet and ecological factors affect activity budget, one group of Assamese macaques was studied using instantaneous scan sampling for 1 year. The macaques spent most of their time feeding (32.7 ± 5.4%), followed by resting (28.6 ± 6.3%), moving (28.6 ± 5.3%), grooming (8.0 ± 3.0%), playing (1.7 ± 1.6%) and other activities (0.4 ± 0.2%). Their activity budget was similar to that of typical frugivorous primates and bamboo-dominated primates, which spent more time on active behaviours (feeding and moving, 61.3 ± 6.0%) than on inactive behaviours (resting and grooming, 36.6 ± 6.4%). The macaques spent significantly more time resting during the fruit-lean season and more time moving during the fruit-rich season. Their activity budget was significantly affected by diet. Resting time increased with decreased fruit consumption, whereas moving time decreased with the increasing mature leaf consumption. Playing time decreased when the macaques consumed more young bamboo leaves. The activity budget was also influenced by food availability and climatic factors. Resting time increased with decreasing temperature, whereas moving time increased with increasing day length and young leaf availability. Grooming time increased with decreasing day length and increasing temperature, and playing time increased with increasing day length. Our findings provide evidence of the importance of diet, food availability, temperature and day length in coping with seasonal variation in ecological factors, highlighting the need to increase knowledge of the behavioural ecology of the Assamese macaques living in the unique limestone forest and to understand the influence of a bamboo-dominated diet and ecological factors on their survival.

Revealing the colourful side of birds: spatial distribution of conspicuous plumage colours on the body of Australian birds

In many species of birds, different body parts often display very different colours. This spatial distribution of coloured plumage patches may be determined, among other factors, by the balance between being cryptic to predators, and conspicuous to intended receivers. If this is the case, ventral and anterior body parts in birds – which are less visible to predators but more prominent to conspecifics – should present more conspicuous and sexually dichromatic plumage colours. Here, I test these predictions using reflectance spectrometric measurements of standardised plumage patches across males and females for nearly an entire avifauna (Australian landbirds, n = 538 species). My data show that, as predicted, conspicuous and sexually dichromatic colours are mainly located near the head, while the plumage of the back is the most cryptic. One clear exception to this pattern is the conspicuous rump coloration. In many species, this patch can be concealed by wings, and therefore exposed only when necessary. In addition, conspicuous rump coloration could deflect or confuse predators in case of attack. However, there is considerable variation across species, and this makes position on the body a very poor predictor of plumage elaboration (R2 < 0.02). Future studies should try to determine whether differences between species in the distribution of colours across the plumage are due to variation in ecological factors (predation risk, habitat, etc.).

Ecological factors and morphological traits are associated with repeated genomic differentiation between lake and stream stickleback.

The repeated evolution of similar phenotypes in independent populations (i.e. parallel or convergent evolution) provides an opportunity to identify genetic and ecological factors that influence the process of adaptation. Threespine stickleback fish (Gasterosteus aculeatus) are an excellent model for such studies, as they have repeatedly adapted to divergent habitats across the Northern hemisphere. Here, we use genomic, ecological and morphological data from 16 independent pairs of stickleback populations adapted to divergent lake and stream habitats. We combine a population genomic approach to identify regions of the genome that are likely under selection in these divergent habitats with an association mapping approach to identify regions of the genome that underlie variation in ecological factors and morphological traits. Over 37% of genomic windows are repeatedly differentiated across lake–stream pairs. Similarly, many genomic windows are associated with variation in abiotic factors, diet items and morphological phenotypes. Both the highly differentiated windows and candidate trait windows are non-randomly distributed across the genome and show some overlap. However, the overlap is not significant on a genome-wide scale. Together, our data suggest that adaptation to divergent food resources and predation regimes are drivers of differentiation in lake–stream stickleback, but that additional ecological factors are also important.This article is part of the theme issue ‘Convergent evolution in the genomics era: new insights and directions’.

ROLE OF VIKARVIGHATBHAVA AND VIKARVIGHATABHAVA IN MANIFESTATION OF DIABETES

Abstract: Background: The consequence of variation in ecological factors, intensity of the morbid humors and susceptibility of the body elements influences suppression or incidence of the disease by Vikar vighat bhava and Vikar vighat abhava respectively. Owing to the occurrence of pathological changes, along with vitiation of morbific factor like, increased kleda (excessive fluidity) and shithilata (diminished viscous essential) and due to frequent indulgent etiological factors, the body fluid, combined with humors and adipose tissue, acquires the pathological character of Prameha(diabetes). Objective: The present study was done to conceptualize the role of Vikar vighat bhava and Vikar vighat abhava in resistance and development respectively, of Prameha with all its symptoms. Methods: Conceptual literary search done by referring literature on exercise, Ayurveda texts, and research papers from peer-reviewed journals to explore the role of Vikar vighat bhava and Vikar vighat abhava in manifestation and therapy of Prameha. Result: The vikar vighat abhava like avoidance of exercise, swapnasukha (sleeping for long hours), asyasukha (sedentary life style) and kaphakar aahar (diet increasing and vitiating kapha) leads Aghnimandya (decreased digestive power and metabolism) which is the reason for obesity, hyperlipidemia and development of insulin resistance. Whereas Vikar vighat bhava like losing weight, optimal diet and exercise regime, helps to reduce insulin resistance and prediabetes, thus preventing or delaying type 2 diabetes. Conclusion: The Vikar vighat bhava like strict diet i.e Ystvaharam sharirasyadhatusamyakarm and daily exercise i.e sevate vividhanschy anyacheshtah can keep check on the diabetes. The dietary and exercise regime along with increase in immunity will help more in pre diabetic conditions. Key words: Vikar vighat bhava, vikar vighat abhava, prameha.

生态承载力研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 生态承载力研究进展 DOI: 10.5846/stxb201712292350 作者: 作者单位: 中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划项目（2017YFA0604803）；中国科学院地理科学与资源研究所特色所培育项目——"一带一路"建设决策支持研究 Review of ecological carrying capacity Author: Affiliation: Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:基于生态承载力的概念发展，介绍了常用的生态承载力研究方法，包括生态足迹法、人类净初级生产力占用法、状态空间法、综合评价法、系统模型法和生态系统服务消耗评价法，并客观评述了这些方法的优缺点，指出了目前生态承载力研究中存在的薄弱环节。未来生态承载力研究需要完善理论体系，深入研究承载力过程机理与承载机制，将生态系统服务的空间流动因素纳入评估体系，构建完善的评价指标体系，加强生态承载力时空动态评估。最终将生态承载力作为解决生态脆弱区资源环境问题的抓手，建立区域资源环境监测预警机制，并落实到主体功能规划和生态安全建设上，为生态文明建设提供有力的科学依据。 Abstract:Based on the development of the concept of ecological carrying capacity (ECC), this study summarized the methods in ECC, including ecological footprint, human appropriation of net primary production, state-space techniques, comprehensive evaluation schemes, systematic models, and the ecosystem services consumption method, which has often been used in previous studies. The advantages and disadvantages of these methods have been analyzed objectively and the weakness pointed out. This study suggested that the theory of ECC needs to be enriched, and the interaction mechanism between variation in ecological factors and its influence on the ECC should be examined. Future research should couple the ecosystem services flow factors into the evaluation system, improve the evaluation index system, and strengthen the temporal and spatial dynamics assessment of ECC. By enhancing the study of ECC feedback in ecologically vulnerable regions scientifically, ECC will be the key to solving the resource and environmental problems of the ecologically vulnerable region, which could support regional resources, environment monitoring, early-warning system establishment, and the main function plan implementation and construction of ecological security. This study introduces several ECC methods that are in widespread use, such as human appropriation of net primary production and the ecosystem services consumption method, which combine land use with the social and economic metabolism mechanism to analyze the temporal-spatial evolution of the ecosystem and demonstrates the changes in the ecosystem function. These comprehensive methods also avoid the error caused by subjective decisions based on a single evaluation index, representing the quantitative limits of the regional ecosystem function. 参考文献 相似文献 引证文献

Barn swallows long-distance migration occurs between significantly temperature-correlated areas

Organisms are routinely confronted with crucial decisions on the best time and place to perform fundamental activities. However, unpredictable spatio-temporal variation in ecological factors makes life-history optimization difficult particularly for long-distance migrants, which are putatively blind of conditions thousands of kilometers and weeks ahead along their journey. Here we challenge, on a hierarchy of geographical scales, the common wisdom that migratory birds have no clue to ecological conditions at destination. Using ringing data of the inter-continental migrating barn swallow (Hirundo rustica), we show that temperatures at breeding sites and at times of arrival from migration are more correlated with those at actual wintering sites and at times of departure than with those at other sites and at periods before/after departure. Hence, individual swallows have clues to adjust timing of spring migration based on expected conditions at destination, and they apparently choose wintering sites to increase availability of such information.

Ecological controls of mammalian diversification vary with phylogenetic scale

AbstractAimDiversity dynamics remain controversial. Here, we examine these dynamics, together with the ecological factors governing them, across mammalian clades of different ages and sizes, representing different phylogenetic scales. Specifically, we investigate whether the dynamics are bounded or unbounded, biotically or abiotically regulated, stochastic or ecologically deterministic.LocationWorldwide.Time period150 Myr.Major taxa studiedMammals.MethodsIntegrating the newest phylogenetic and distributional data by means of several distinct methods, we study the ecology of mammalian diversification within a predictive framework, inspired by classic theory. Specifically, we evaluate the effects of several classes of factors, including climate, topography, geographical area, rates of climatic‐niche evolution, and regional coexistence between related and unrelated species. Next, we determine whether the relative effects of these factors change systematically across clades representing different phylogenetic scales.ResultsWe find that young clades diversify at approximately constant rates, medium‐sized clades show diversification slowdowns, and large clades are mostly saturated, suggesting that diversification dynamics change as clades grow and accumulate species. We further find that diversification slowdowns intensify with the degree of regional coexistence between related species, presumably because increased competition for regional resources suppresses the diversification process. The richness at which clades eventually saturate depends on climate; clades residing in tropical climates saturate at low richness, implying that niches become progressively densely packed towards the tropics.Main conclusionsThe diversification process is influenced by a variety of ecological factors, whose relative effects change across phylogenetic scales, producing scale‐dependent dynamics. Different segments of the same phylogeny might therefore support seemingly conflicting results (bounded or unbounded, biotically or abiotically regulated, stochastic or ecologically deterministic diversification), which might have contributed to several outstanding controversies in the field. These conflicts can be reconciled, however, when accounting for phylogenetic scale, which might, in turn, produce a more integrated understanding of global diversity dynamics.

Highly variable lifespan in an annual reptile, Labord\u2019s chameleon (Furcifer labordi)

Among tetrapods, the current record holder for shortest lifespan is Labord’s chameleon, Furcifer labordi. These reptiles from the arid southwest of Madagascar have a reported lifespan of 4–5 months during the annual rainy season and spend the majority of their life (8–9 months) as a developing embryo. This semelparous, annual life history is unique among tetrapods, but only one population (Ranobe) in the southernmost distribution range has been studied. We therefore investigated the potential for environmentally-dependent variability in lifespan in a population in Kirindy Forest, which has a much longer warm rainy season. While no adults were found after March in Ranobe, the disappearance of adults was delayed by several months in Kirindy. Our data also revealed sex-biased mortality, suggesting that females have a longevity advantage. Furthermore, we found that, after an unusually long previous rainy season, one female was capable of surviving until a second breeding season. Keeping F. labordi in cages under ambient conditions demonstrated that also males can also survive until the next season of activity under these conditions. Our study therefore revealed considerable variability in the extreme life history of this tetrapod that is linked to variation in ecological factors.

Activity space and movement patterns of Octopus bimaculatus (Verrill, 1883) around Santa Catalina Island, California

The spatial movement and ecology of highly mobile marine predators can strongly influence, and be influenced by, a variety of ecological factors. Octopuses are voracious predators, and their predatory behavior can have significant impacts on the abundance and diversity of their prey communities. Nine Octopus bimaculatus (Verrill, 1883) were tagged and tracked during August 2014 using active tracking techniques. Octopus GPS position was recorded daily over the course of 12.9±5.6days (mean±SD) and continuous movement was tracked for 20.8±5.0h (mean±SD) for each animal. O. bimaculatus occupied an activity space of approximately 6000±3000km2 (mean±SD). Larger animals moved over larger areas, but activity space size was not correlated with octopus sex, habitat location, or time of day. Movement distances and diurnal movement patterns were highly variable for this species, both within and between individual octopuses. O. bimaculatus were highly mobile compared to other octopuses of similar size tracked in a similar way. These results are contradictory to previous estimates of movement and den fidelity for this species in this area, suggesting either a previous underestimate of O. bimaculatus movement, or a change in the way this species moves through its environment. This study pioneered the application of acoustic telemetry to octopuses in California ecosystems, and provides insight into the heterogeneity of octopus behavior and the potential impacts this heterogeneity may have on octopus prey and predator communities.

Variable Efficacy of the Purple Loosestrife (Lythrum salicaria) Biological Control Program in Ontario: Recommendations for Future Monitoring

Invasive species represent a major threat to global biodiversity and have multi‐million dollar impacts onagricultural productivity as well as the functioning of natural ecosystems. Biological control, theintroduction of the natural enemies of invading species, is a potentially cost‐effective and powerfulmanagement tool for controlling the spread and impact of exotic organisms. However, the monitoringcomponent of biocontrol initiatives is rarely adequate to determine their success, impeding theimprovement of biocontrol techniques. In order to determine the efficacy of the biocontrol beetlesintroduced to control purple loosestrife (Lythrum salicaria), an invasive wetland plant in Ontario, 52 L.salicaria populations were surveyed in eastern and central Ontario in August and September 2009. Threepopulation types were surveyed, those in which the release of Galerucella species biocontrol beetles hadanecdotally been effective, anecdotally ineffective, and those in which beetles had never beenpurposefully released. The level of herbivory damage inflicted by the biocontrol beetles was recorded, aswell as plant height, flower number, and measures of stand density. It was determined that thebiocontrol beetles have spread throughout Ontario, and are inflicting a moderate level of damage onpurple loosestrife populations. However, significant variation exists among populations in thesemeasures, and levels of damage were not significantly different between the three site types. Thisindicates that a variety of ecological factors influence the efficacy of biocontrol, and it is recommendedthat the purple loosestrife biocontrol program be more intensively monitored in future so that it mayinform subsequent initiatives in Canada.

Evolution of anuran brains: disentangling ecological and phylogenetic sources of variation.

Variation in ecological selection pressures has been implicated to explain variation in brain size and architecture in fishes, birds and mammals, but little is known in this respect about amphibians. Likewise, the relative importance of constraint vs. mosaic hypotheses of brain evolution in explaining variation in brain size and architecture remains contentious. Using phylogenetic comparative methods, we studied interspecific variation in brain size and size of different brain parts among 43 Chinese anuran frogs and explored how much of this variation was explainable by variation in ecological factors (viz. habitat type, diet and predation risk). We also evaluated which of the two above-mentioned hypotheses best explains the observed patterns. Although variation in brain size explained on average 80.5% of the variation in size of different brain parts (supporting the constraint hypothesis), none of the three ecological factors were found to explain variation in overall brain size. However, habitat and diet type explained a significant amount of variation in telencephalon size, as well in three composite measures of brain architecture. Likewise, predation risk explained a significant amount of variation in bulbus olfactorius and optic tecta size. Our results show that evolution of anuran brain accommodates features compatible with both constraint (viz. strong allometry among brain parts) and mosaic (viz. independent size changes in response to ecological factors in certain brain parts) models of brain size evolution.

Relative reproductive success of co-infecting parasite genotypes under intensified within-host competition

In nature, host individuals are commonly simultaneously infected with more than one genotype of the same parasite species. These co-infecting parasites often interact, which can affect their fitness and shape host–parasite ecology and evolution. Many of such interactions take place through competition for limited host resources. Therefore, variation in ecological factors modifying the host resource level could be important in determining the intensity of competition and the outcome of co-infections. We tested this hypothesis by measuring the relative reproductive success of co-infecting genotypes of the trematode parasite Diplostomum pseudospathaceum in its snail host Lymnaea stagnalis while experimentally manipulating snail resource level using contrasting feeding treatments (ad libitum food supply, no food). We found that food deprivation constrained the overall parasite within-host reproduction as the release of parasite transmission stages (cercariae) was reduced. This indicates intensified competition among the parasite genotypes. The genotypic composition of the released cercariae, however, was not affected by the feeding treatments. This suggests that in this system, the relative reproductive success of co-infecting parasite genotypes, which is an important component determining their fitness, is robust to variation in ecological factors modifying the strength of resource competition.

Dispatches

Dispatches

Interactive effects of competition and social environment on the expression of sexual dimorphism.

The expression of sexual dimorphism is expected to be influenced by the acquisition of resources available to allocate to trait growth, combined with sex-specific patterns of resource allocation. Resource acquisition in the wild may be mediated by a variety of ecological factors, such as the density of interspecific competitors. Allocation may in turn depend on social contexts, such as sex ratio, that alter the pay-off for investment in sexual traits. How these factors interact to promote or constrain the expression and evolution of sexual dimorphism is poorly understood. We manipulated sex ratio and interspecific resource competition over the growing season of red-spotted newts (Notophthalmus viridescens) in artificial ponds. Fish competitors had a stronger effect on female than male growth, which effectively eliminated the expression of sexual size dimorphism. In addition, newt sex ratio influenced fish growth, leading to reduction in fish mass with an increase in female newt frequency. Fish also reduced the expression of male tail height, a sexually selected trait, but only in tanks with a female-biased sex ratio. This suggests males alter their resource allocation pattern in response to the strength of sexual selection. Our results demonstrate that ecologically and socially mediated interactions between sex-specific resource acquisition and allocation can contribute to variation in the expression of sexual dimorphism.

The contribution of abiotic and biotic factors to spatial and temporal variation in population density of the least killifish, Heterandria formosa

We report the results of a long-term examination of variation in adult density in the least killifish, Heterandria formosa, and the associations among adult density and a variety of ecological factors. We used data from 11 populations of H. formosa in Northwest Florida, collected between 2000 and 2010, to examine the relationships among temporal and spatial variation in adult density and (1) the composition of the aquatic fauna community among habitats (springs, ponds, and tidal marshes) where H. formosa are found, (2) an index of predation pressure and (3) the sampling season, distance from shore (cm), water depth (cm), and aquatic vegetation cover (%) in throw traps at each sampling event. We found clear evidence that adult densities of H. formosa vary widely but consistently among populations, with greater spatial variation than temporal variation in density estimates. Site identity explained most of the variation in density among populations, and there was no long-term consistent association of variation in density with different habitats; sites of the same habitat type were as likely to have characteristically different densities as were sites of different habitat types. Average adult densities of H. formosa increased as aquatic vegetation cover increased and as the index of predation pressure decreased, however assemblage structure was not a strong predictor of density. These results show that despite marked community, abiotic and biotic distinctions between habitat types, location-specific variation was the predominant signal in these data.