Search

Resource dynamics influence the contemporary ecology of consumer-resource mutualisms. Suites of resource traits, such as floral nectar components, also evolve in response to different selective pressures, changing the ecological dynamics of the interacting species at the evolutionary equilibrium. Here we explore the evolution of resource-provisioning traits in a biotically pollinated plant that produces nectar as a resource for beneficial consumers. We develop a mathematical model describing natural selection on two quantitative nectar traits: maximum nectar production rate and maximum nectar reservoir volume. We use this model to examine how nectar production dynamics evolve under different ecological conditions that impose varying cost-benefit regimes on resource provisioning. The model results predict that natural selection favors higher nectar production when ecological factors limit the plant or pollinator's abundance (e.g., a lower productivity environment or a higher pollinator conversion efficiency). We also find that nectar traits evolve as a suite in which higher costs of producing one trait select for a compensatory increase in investment in the other trait. This empirically explicit approach to studying the evolution of consumer-resource mutualisms illustrates how natural selection acting via direct and indirect pathways of species interactions generates patterns of resource provisioning seen in natural systems. [ABSTRACT FROM AUTHOR]

Women have long been underrepresented in the natural sciences, and although great progress has been made in recent decades, many subtle and not-so-subtle barriers persist. In this context, it is easy to get the impression that the early history of ecology and evolutionary biology was exclusively the domain of male researchers. In fact, a number of women made very substantial contributions to The American Naturalist in its first decades. In a follow-up to a series of retrospective essays celebrating 150 years of this journal, we highlight the scientific contributions of the women published in it during its first 50 years (1867–1916). We also discuss the diverse paths that their scientific careers took and the barriers they faced along the way. [ABSTRACT FROM AUTHOR]

The life-history theories of aging predict lifetime tradeoffs between early reproductive allocation and late-life survival, reproduction, or both components of fitness. Recent studies in wild populations have found evidence for these early-late life trade-offs, but rarely have they been found across multiple traits while exploring the additional effects of variation in environmental conditions and individual quality. Benefiting from longitudinal data on adult female mountain goats (Oreamnos americanus), we investigated the influence of age at first reproduction (AFR) and early reproductive success (ERS) on longevity, late reproductive success, and senescence rates while accounting for the influence of natal environmental conditions and individual quality. Contrary to predictions, we did not find evidence for early-late life trade-offs. Instead, an earlier AFR and a greater ERS had positive but weak direct effects on late reproductive success. Natal population density, however, was the strongest determinant of all life-history traits, having a direct negative effect on female longevity, late reproductive success, AFR, and ERS. Although natal density reduced the probability of annual reproduction and annual survival during adulthood, higher allocation to reproduction in early life and poorer natal conditions dida not lead to accelerated rates of senescence during adulthood. The results of this investigation provide an integrated picture of early-late life tradeoffs, underscoring the importance of accounting for environmental conditions because of their potentially strong implications for population dynamics. [ABSTRACT FROM AUTHOR]

Both body size and temperature directly influence consumer-resource dynamics. There is also widespread empirical evidence for the temperature-size rule (TSR), which creates a negative relationship between temperature and body size. However, it is not known how the TSR affects community dynamics. Here we integrate temperature- and size-dependent models to include indirect effects of warming, through changes in body size, to answer the question, How does the TSR affect the predicted response of consumer-resource systems to warming? We find that the TSR is expected to maintain consumer-resource biomass ratios and buffer the community from extinctions under warming. While our results are limited to conditions where organisms are below their thermal optimum, they hold under a range of realistic temperature-size responses and are robust to the type of functional response. Our analyses suggest that the widely observed TSR may reduce the impacts of warming on consumer-resource systems. [ABSTRACT FROM AUTHOR]

Models of cooperation among nonkin suggest that social assortment is important for the evolution of cooperation. Theory predicts that interacting phenotypes, whereby an individual's behavior depends on the behavior of its social partners, can drive such social assortment. We measured repeated indirect genetic effects (IGEs) during cooperative predator inspection in eight populations of Trinidadian guppies (Poecilia reticulata) that vary in their evolutionary history of predation. Four broad patterns emerged that were dependent on river, predation history, and sex: (i) current partner behavior had the largest effect on focal behavior, with fish from low-predation habitats responding more to their social partners than fish from high-predation habitats; (ii) different focal/partner behavior combinations can generate cooperation; (iii) some high-predation fish exhibited carryover effects across social partners; and (iv) high-predation fish were more risk averse. These results provide the first large-scale comparison of interacting phenotypes during cooperation across wild animal populations, highlighting the potential importance of IGEs in maintaining cooperation. Intriguingly, while focal fish responded strongly to current social partners, carryover effects between social partners suggest generalized reciprocity (in which one helps anyone if helped by someone) may contribute to the evolution of cooperation in some, but not all, populations of guppies. [ABSTRACT FROM AUTHOR]

Natural selection has both genetic and ecological dynamics. The fitnesses of individuals change with their ecological context, and so the form and strength of selective agents change with abiotic factors and the phenotypes and abundances of interacting species. I use standard models of consumer-resource interactions to explore the ecological dynamics of natural selection and how various trait types influence these dynamics and the resulting structure of a community of coevolving species. Evolutionary optima favored by natural selection depend critically on the abundances of interacting species, and the traits of species can undergo dynamic cycling in limited areas of parameter space. The ecological dynamics of natural selection can also drive shifts from one adaptive peak to another, and these ecologically driven adaptive peak shifts are fundamental to the dynamics of niche differentiation. Moreover, this ecological differentiation is fostered in more productive and more benign environments where species interactions are stronger and where the selection gradients generated by species interactions are stronger. Finally, community structure resulting from coevolution depends fundamentally on the types of traits that underlie species interactions. The ecological dynamics of the process cannot be simplified, neglected, or ignored if we are to build a predictive theory of natural selection. [ABSTRACT FROM AUTHOR]

Predators control prey populations and influence communities and the functioning of ecosystems through a combination of consumptive and nonconsumptive effects. These effects can be locally confined to one ecosystem but can also be extended to neighboring ecosystems. In this study, we investigated the nonconsumptive effects of terrestrial avian predators on the communities of aquatic invertebrates inhabiting bromeliads and on the functioning of these natural ecosystems. Bromeliads with stuffed birds placed nearby showed a decrease in aquatic damselfly larvae abundance and biomass, and we can infer that these changes were caused by antipredator responses. These larvae, which are top predators in bromeliad ecosystems, changed the composition of the entire aquatic invertebrate community. While total species richness, mesopredator richness, and shredder abundance increased in the presence of birds, scraper biomass decreased, possibly as a consequence of the increase in mesopredator richness. High scraper biomass in the absence of birds may have accelerated detrital decomposition, making more nutrients available for bromeliads, which grew more. These results show that nonconsumptive effects triggered by terrestrial predators can cascade down to lower trophic levels and dramatically affect the functioning of aquatic ecosystems, which can in turn alter nutrient provision to terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

The duration of parental care in animals varies widely, from none to lifelong. Such variation is typically thought to represent a trade-off between growth and safety. Seabirds show wide variation in the age at which offspring leave the nest, making them ideal to test the idea that a trade-off between high energy gain at sea and high safety at the nest drives variation in departure age (Ydenberg's model). To directly test the model assumptions, we attached time-depth recorders to murre parents (fathers [which do all parental care at sea] and mothers; N p 14 of each). Except for the initial mortality experienced by chicks departing from the colony, the mortality rate at sea was similar to the mortality rate at the colony. However, energy gained by the chick per day was ~2.1 times as high at sea compared with at the colony because the father spent more time foraging, since he no longer needed to spend time commuting to and from the colony. Compared with the mother, the father spent ~2.6 times as much time diving per day and dived in lower-quality foraging patches. We provide a simple model for optimal departure date based on only (1) the difference in growth rate at sea relative to the colony and (2) the assumption that transition mortality from one life-history stage to the other is size dependent. Apparently, large variation in the duration of parental care can arise simply as a result of variation in energy gain without any trade-off with safety. [ABSTRACT FROM AUTHOR]

How organisms gather and utilize information about their landscapes is central to understanding land-use patterns and population distributions. When such information originates beyond an individual's immediate vicinity, movement decisions require integrating information out to some perceptual range. Such nonlocal information, whether obtained visually, acoustically, or via chemosensation, provides a field of stimuli that guides movement. Classically, however, models have assumed movement based on purely local information (e.g., chemotaxis, step-selection functions). Here we explore how foragers can exploit nonlocal information to improve their success in dynamic landscapes. Using a continuous time/continuous space model in which we vary both random (diffusive) movement and resource following (advective) movement, we characterize the optimal perceptual ranges for foragers in dynamic landscapes. Nonlocal information can be highly beneficial, increasing the spatiotemporal concentration of foragers on their resources up to twofold compared with movement based on purely local information. However, nonlocal information is most useful when foragers possess both high advective movement (allowing them to react to transient resources) and low diffusive movement (preventing them from drifting away from resource peaks). Nonlocal information is particularly beneficial in landscapes with sharp (rather than gradual) patch edges and in landscapes with highly transient resources. [ABSTRACT FROM AUTHOR]

Species co-occurrence in ecological communities is thought to be influenced by multiple ecological and evolutionary processes, especially colonization and competition. However, effects of other interspecific interactions and evolutionary relationships are less explored. We examined evolutionary histories of community members and roles of mutualistic and parasitic interactions (Müllerian and Batesian mimicry, respectively) in the assembly of mimetic butterfly communities called mimicry rings in tropical forests of the Western Ghats, India. We found that Müllerian mimics were phylogenetically clustered, sharing aposematic signals due to common ancestry. On the other hand, Batesian mimics joined mimicry rings through convergent evolution and random phylogenetic assembly. Since the Western Ghats are a habitat island, we compared species diversity and composition in its mimicry rings with those of habitat mainland to test effects of biogeographic connectivity. The Western Ghats consisted of fewer mimicry rings and an overall smaller number of aposematic species and mimics compared to habitat mainland. The depauperate mimicry rings in the Western Ghats could have resulted from stochastic processes, reflecting their long temporal and spatial isolation and trickling colonization by the mimetic butterfly communities. These results highlight how evolutionary history, biogeographic isolation, and stochastic colonization influence the evolutionary assembly and diversity of ecological communities. [ABSTRACT FROM AUTHOR]

Unicellular plankton employ trophic strategies ranging from pure photoautotrophs overmixotrophy to obligate heterotrophs (phagotrophs), with cell sizes from 10-8 to 1 μg C. A full understanding of how trophic strategy and cell size depend on resource environment and predation is lacking. To this end, we develop and calibrate a trait-based model for unicellular planktonic organisms characterized by four traits: cell size and investments in phototrophy, nutrient uptake, and phagotrophy. We use the model to predict how optimal trophic strategies depend on cell size under various environmental conditions, including seasonal succession. We identify two mixotrophic strategies: generalist mixotrophs investing in all three investment traits and obligate mixotrophs investing only in phototrophy and phagotrophy.We formulate two conjectures: (1)most cells are limited by organic carbon; however, small unicellulars are colimited by organic carbon and nutrients, and only large photoautotrophs and smaller mixotrophs are nutrient limited; (2) trophic strategy is bottom-up selected by the environment, while optimal size is top-down selected by predation. The focus on cell size and trophic strategies facilitates general insights into the strategies of a broad class of organisms in the size range from micrometers to millimeters that dominate the primary and secondary production of the world's oceans. [ABSTRACT FROM AUTHOR]

Variation in behavior among individual top predators (i.e., the behavioral type) can strongly shape pest suppression in intraguild predation (IGP). However, the effect of a top predator's behavioral type--namely, foraging aggressiveness (number of killed divided by prey time) and prey choosiness (preference degree for certain prey type)--on the dynamic of IGP may interact with the relative abundances of top predator, mesopredator, and pest.We investigated the influence of the top predator's behavioral type on the dynamic of IGP in a three-species system with a top predator spider, a mesopredator spider, and a psyllid pest using a simulation model. The model parameters were estimated from laboratory experiments and field observations. The top predator's behavioral type altered the food-web dynamics in a context-dependent manner. The system with an aggressive/nonchoosy top predator, without prey preferences between pest and mesopredator, suppressed the pest more when the top predator to mesopredator abundance ratio was high. In contrast, the system with a timid/choosy top predator that preferred the pest to the mesopredator was more effective when the ratio was low. Our results show that the behavioral types and abundances of interacting species need to be considered together when studying food-web dynamics, because they evidently interact. To improve biocontrol efficiency of predators, research on the alteration of their behavioral types is needed. [ABSTRACT FROM AUTHOR]

Many studies of sexual selection assume that individuals have equal mating opportunities and that differences in mating success result from variation in sexual traits. However, the inability of sexual traits to explain variation in male mating success suggests that other factors moderate the strength of sexual selection. Extrapair paternity is common in vertebrates and can contribute to variation in mating success and thus serves as a model for understanding the operation of sexual selection. We developed a spatially explicit, multifactor model of all possible female-male pairings to test the hypothesis that ecological (food availability) and social (breeding density, breeding distance, and the social mate's nest stage) factors influence an individual's opportunity for extrapair paternity in a socially monogamous bird, the black-throated blue warbler, Setophaga caerulescens. A male's probability of siring extrapair young decreased with increasing distance to females, breeding density, and food availability. Males on food-poor territories were more likely to sire extrapair young, and these offspring were produced farther from the male's territory relative to males on food-abundant territories. Moreover, males sired extrapair young mostly during their socialmates' incubation stage, especially males on food-abundant territories. This study demonstrates how ecological and social conditions constrain the spatial and temporal opportunities for extrapair paternity that affect variation inmating success and the strength of sexual selection in socially monogamous species. [ABSTRACT FROM AUTHOR]

Understanding the conditions under which moderately defended prey evolve to resemble better-defended prey and whether this mimicry is parasitic (quasi-Batesian) or mutualistic (Müllerian) is central to our understanding of warning signals. Models of predator learning generally predict quasi-Batesian relationships. However, predators' attack decisions are based not only on learning alone but also on the potential future rewards.We identify the optimal sampling strategy of predators capable of classifying prey into different profitability categories and contrast the implications of these rules formimicry evolution with a classical Pavlovianmodel based on conditioning. In both cases, the presence of moderately unprofitable mimics causes an increase in overall consumption. However, in the case of the optimal sampling strategy, this increase in consumption is typically outweighed by the increase in overall density of prey sharing the model appearance (a dilution effect), causing a decrease in mortality. It suggests that if predators forage efficiently to maximize their long-term payoff, genuine quasi-Batesianmimicry should be rare, whichmay explain the scarcity of evidence for it in nature. Nevertheless, we show that when moderately defended mimics are profitable to attack by hungry predators, then they can be parasitic on their models, just as classical Batesian mimics are. [ABSTRACT FROM AUTHOR]

Empirical studies in select systems suggest that social information--the incidental or deliberate information produced by animals and available to other animals--can fundamentally shape animal grouping behavior. However, to understand the role of social information in animal behavior and fitness, we must establish general theory that quantifies effects of social information across ecological contexts and generates expectations that can be applied across systems. Here we used dynamic state variable modeling to isolate effects of social information about food and predators on grouping behavior and fitness. We characterized optimal behavior from a set of strategies that included grouping with different numbers of conspecifics or heterospecifics and the option to forage or be vigilant over the course of a day. We show that the use of social information alone increases grouping behavior but constrains group size to limit competition, ultimately increasing individual fitness substantially across various ecological contexts. We also found that across various contexts, foraging in mixed-species groups is generally better than foraging in conspecific groups, supporting recent theory on competitioninformation quality trade-offs. Our findings suggest that multiple forms of social information shape animal grouping and fitness, which are sensitive to resource availability and predation pressure that determine information usefulness. [ABSTRACT FROM AUTHOR]

Reinforcement can contribute to speciation by increasing the strength of prezygotic isolating mechanisms. Theoretical analyses over the past two decades have demonstrated that conditions for reinforcement are not unduly restrictive, and empirical investigations have documented over a dozen likely cases, indicating that it may be a reasonably common phenomenon in nature. Largely uncharacterized, however, is the diversity of biological scenarios that can create the reduced hybrid fitness that drives reinforcement. Here I examine one such scenario-the evolution of the "selfing syndrome" (a suite of characters including reductions in flower size and in nectar, pollen, and scent production) in highly selfing plant species. Using a fourlocus model, where the loci are (1) a discrimination locus, (2) a targetof- discimination locus, (3) a pollen-production locus, and (4) a selfing-rate locus, I determine the conditions under which this syndrome can favor reinforcement, an increase in discrimination through change at locus 1, in an outcrossing species that experiences gene flow from a highly selfing species. In the absence of both linkage disequilibrium between loci and pollen discounting, reinforcement can occur, but only in a very small fraction of the parameter combinations examined. Moderate linkage (r = 0:1) between one pair of loci increases this fraction moderately, depending on which two loci are linked. Pollen discounting (a reduction in pollen exported to other plants due to increased selfing), by contrast, can increase the fraction of parameter combinations that result in reinforcement substantially. The evolution of reduced pollen production in highly selfing species thus facilitates reinforcement, especially if substantial pollen discounting is associated with selfing. [ABSTRACT FROM AUTHOR]

Quantifying the relationship between form and function can inform use of morphology as a surrogate for ecology. How the strength of this relationship varies continentally can inform understanding of evolutionary radiations; for example, does the relationship break down when certain lineages invade and diversify in novel habitats? The 75 species of Australian honeyeaters (Meliphagidae) are morphologically and ecologically diverse, with species feeding on nectar, insects, fruit, and other resources. We investigated Meliphagidae ecomorphology and community structure by (1) quantifying the concordance between morphology and ecology (foraging behavior), (2) estimating rates of trait evolution in relation to the packing of ecological space, and (3) comparing phylogenetic and trait community structure across the broad environmental gradients of the continent. We found that morphology explained 37% of the variance in ecology (and 62% vice versa), and we uncovered well-known bivariate relationships among the multivariate ecomorphological data. Ecological trait diversity declined less rapidly than phylogenetic diversity along a gradient of decreasing precipitation. We employ a new method (trait fields) and extend another (phylogenetic fields) to show that while species in phylogenetically clustered, arid-environment assemblages are similar morphologically, they are as varied in foraging behavior as those from more diverse assemblages. Thus, although closely related and similar morphologically, these arid-adapted species have diverged in ecological space to a similar degree as their mesic counterparts. [ABSTRACT FROM AUTHOR]

We study macroevolutionary dynamics by extending microevolutionary competition models to long timescales. It has been shown that for a general class of competition models, gradual evolutionary change in continuous phenotypes (evolutionary dynamics) can be nonstationary and even chaotic when the dimension of the phenotype space in which the evolutionary dynamics unfold is high. It has also been shown that evolutionary diversification can occur along nonequilibrium trajectories in phenotype space. We combine these lines of thinking by studying long-term coevolutionary dynamics of emerging lineages in multidimensional phenotype spaces. We use a statistical approach to investigate the evolutionary dynamics of many different systems. We find (1) that, for a given dimension of phenotype space, the coevolutionary dynamics tend to be fast and nonstationary for an intermediate number of coexisting lineages but tend to stabilize as the evolving communities reach a saturation level of diversity and (2) that the amount of diversity at the saturation level increases rapidly (exponentially) with the dimension of phenotype space. These results have implications for theoretical perspectives on major macroevolutionary patterns such as adaptive radiation, longterm temporal patterns of phenotypic changes, and the evolution of diversity. [ABSTRACT FROM AUTHOR]

The incorporation of ecological processes into models of trait evolution is important for understanding past drivers of evolutionary change. Species interactions have long been thought to be key drivers of trait evolution. However, models for comparative data that account for interactions between species are lacking. One of the challenges is that such models are intractable and difficult to express analytically. Here we present phylogenetic models of trait evolution that include interspecific competition among chosen species. Competition is modeled as a tendency of sympatric species to evolve toward difference from one another, producing trait overdispersion and high phylogenetic signal. Themodel predicts elevated trait variance across species and a slowdown in evolutionary rate both across the clade and within each branch. Themodel also predicts a reduction in correlation between otherwise correlated traits. We use an approximate Bayesian computation approach to estimate model parameters. We find reasonable power to detect competition in sufficiently large (201species) trees compared with Brownian trait evolution and with Ornstein- Uhlenbeck and early burst models. We apply the model to examine the evolution of bill morphology of Darwin's finches and find evidence that competition affects the evolution of bill length. [ABSTRACT FROM AUTHOR]

The evolution of endothermy is a controversial topic in evolutionary biology, although several hypotheses have been proposed to explain it. To a great extent, the debate has centered on the aerobiccapacity model (AC model), an adaptive hypothesis involving maximum and resting rates of metabolism (MMR and RMR, respectively; hereafter "metabolic traits"). The AC model posits that MMR, a proxy of aerobic capacity and sustained activity, is the target of directional selection and that RMR is also influenced as a correlated response. Associated with this reasoning are the assumptions that (1) factorial aerobic scope (FAS; MMR/RMR) and net aerobic scope (NAS; MMR 2 RMR), two commonly used indexes of aerobic capacity, show different evolutionary optima and (2) the functional link between MMR and RMR is a basic design feature of vertebrates. To test these assumptions, we performed a comparative phylogenetic analysis in 176 vertebrate species, ranging from fish and amphibians to birds and mammals. Using disparity-through-time analysis, we also explored trait diversification and fitted different evolutionary models to study the evolution of metabolic traits. As predicted, we found (1) a positive phylogenetic correlation between RMR andMMR, (2) diversification of metabolic traits exceeding that of random-walk expectations, (3) that a model assuming selection fits the data better than alternative models, and (4) that a single evolutionary optimum best fits FAS data, whereas a model involving two optima (one for ectotherms and another for endotherms) is the best explanatory model for NAS. These results support the AC model and give novel information concerning the mode and tempo of physiological evolution of vertebrates. [ABSTRACT FROM AUTHOR]

An impediment to understanding the origin and dynamics of the latitudinal diversity gradient (LDG)--the most pervasive large-scale biotic pattern on Earth--has been the tendency to focus narrowly on a single causal factor when a more synthetic, integrative approach is needed. Using marine bivalves as a model system and drawing on other systems where possible, we review paleobiologic and biogeographic support for two supposedly opposing views, that the LDG is shaped primarily by (a) local environmental factors that determine the number of species and higher taxa at a given latitude (in situ hypotheses) or (b) the entry of lineages arising elsewhere into a focal region (spatial dynamics hypotheses). Support for in situ hypotheses includes the fit of present-day diversity trends in many clades to such environmental factors as temperature and the correlation of extinction intensities in Pliocene bivalve faunas with net regional temperature changes. Support for spatial dynamics hypotheses includes the age-frequency distribution of bivalve genera across latitudes, which is consistent with an out-of-the-tropics dynamic, as are the higher species diversities in temperate southeastern Australia and southeastern Japan than in the tropical Caribbean. Thus, both in situ and spatial dynamics processes must shape the bivalve LDG and are likely to operate in other groups as well. The relative strengths of the two processes may differ among groups showing similar LDGs, but dissecting their effects will require improved methods of integrating fossil data with molecular phylogenies. We highlight several potential research directions and argue that many of the most dramatic biotic patterns, past and present, are likely to have been generated by diverse, mutually reinforcing drivers. [ABSTRACT FROM AUTHOR]

Identifying the selective forces that initiate ecological speciation is a major challenge in evolutionary biology. Sensory drive has been implicated in speciation in various taxa, largely based on phenotype-environment correlations and signatures of selection in sensory genes. Here, we present a reciprocal transplant experiment revealing species differences in performance in alternative visual environments, consistent with speciation by divergent sensory drive. The closely related cichlids Pundamilia pundamilia and Pundamilia nyererei inhabit different visual environments in Lake Victoria and show associated differences in visual system properties. Mimicking the two light environments in the laboratory, we find a substantial reduction in survival of both species when reared in the other species' visual environment. This implies that the observed differences in Pundamilia color vision are indeed adaptive and substantiates the implicit assumption in sensory drive speciation models that divergent environmental selection is strong enough to drive divergence in sensory properties. [ABSTRACT FROM AUTHOR]

The relationship between environmental productivity and species richness often varies among empirical studies, and despite much research, simple explanations for this phenomenon remain elusive. We investigated how phytoplankton and zooplankton coevolution shapes productivity-richness relationships in both phytoplankton and zooplankton, using a simple nutrient-phytoplankton-zooplankton model that incorporates size-dependent metabolic rates summarized from empirical studies. The model allowed comparisons of evolved species richness across productivity levels and at different evolutionary times. Our results show that disruptive selection leads to evolutionary branching of phytoplankton and zooplankton. Both the time required for evolutionary branching and the number of evolved species in phytoplankton and zooplankton tend to increase with productivity, producing a transient unimodal or positive productivity-richness relationship but followed by a positive productivity-richness relationship for both groups over long enough evolutionary time. Our findings suggest that coevolution between phytoplankton and zooplankton can drive the two common forms (unimodal and positive) of productivity-richness relationships in nature. [ABSTRACT FROM AUTHOR]

The effects of regional diversity on diversification remain controversial. The classic hypothesis that diversification decelerates as regional diversity increases has been recently revived. Yet, there is little geographic evidence for slower diversification across regions of high diversity, and diversity is often thought to promote diversification through its effects on ecological divergence and speciation. Here, we use the newest phylogeny for mammals (4,990 species) and two different methods to test the effects of regional diversity on diversification. We find that regions of high diversity are dominated by expanding clades that are far from their estimated carrying capacities. Regions of low diversity host clades that are small and mostly saturated. These results were supported across mammals and their six largest orders. They were corroborated by the two methods when controlling for clade relatedness, clade nestedness, and clade size. Together, these results reject the hypothesis that high geographic concentration of mammals effectively suppresses their further diversification. Instead, highly diverse regions (especially the tropics) seem to act as the engine of mammalian richness. [ABSTRACT FROM AUTHOR]

Increasingly, the species that we discover will be uncommon, area restricted, and vulnerable to extinction. I describe the natural history of a newly discovered seed-eating finch from the Rocky Mountain region, the South Hills crossbill (Loxia curvirostra complex). It relies on seeds in the closed cones of the fire-adapted Rocky Mountain lodgepole pine (Pinus contorta latifolia) and is found only in the higher elevations of two smallmountain ranges in southern Idaho. Here crossbills and pine are engaged in a coevolutionary arms race. Although most of the seeds remain secured within the cones for decades until the heat of a stand-replacing fire causes the cone scales to separate, seeds become accessible to crossbills slowly as cones weather and gaps form between some of the scales. However, hot days (≥32°C), especially four or more hot days, seem to mimic the effect of fire, apparently causing the immediate release of a fraction of the seeds. Such events caused a 20% annual decline in crossbills that lasted up to 4 years and an 80% decline in the population between 2003 and 2011. This is an example of a novel trophic mismatch between a consumer and its resource caused by a shift in the phenology of the resource arising from climate change. Not only do these phenological shifts have the potential to cause seed consumers to decline, these shifts are also likely to cause reduced recruitment of the plants. The South Hills crossbill is especially vulnerable and will likely go extinct this century before lodgepole pine is extirpated from the South Hills. [ABSTRACT FROM AUTHOR]

We present a new phylogenetic comparative method-- phylogenetic analysis of covariance (PANCOVA)--that uses interspecific data and a phylogeny to estimate the effects of major events on both the rate of phenotypic evolution and the association between traits. It could be used, for example, to model the impact of a key innovation, colonization of a new habitat, or environmental change. The approach is optimized with maximum likelihood and is formulated under the familiar phylogenetic generalized least squares framework, which is flexible and easily extended to incorporate other factors and parameters. As an example, we explore the relationship between parental investment and relative telencephalon size in birds and contrast the results of PANCOVA with those from other phylogenetic comparative methods. [ABSTRACT FROM AUTHOR]

Brain size differs substantially among species, and several hypotheses have been proposed to explain the evolution of brain size. Because the brain is among themost energetically expensive organs in the vertebrate body, trade-offs have been hypothesized to exert constraints on brain size evolution. Prominently, the expensive tissue hypothesis (ETH) proposes that reducing the size of another expensive organ, such as the gut, should compensate for the cost of a large brain. But energetic constraintsmay also drive covariation between the brain and other costly traits--such as bodymaintenance, locomotion, or reproduction-- as formulated in the energy trade-off hypothesis. To date, these hypotheses have mainly been tested in homeothermic animals and within the ectothermic animals, primarily in fishes. Here, we undertake a comparative test of the interplay between energetic limitations and brain size evolution within amphibians. After controlling for phylogenetic relationships and body size, we find a negative correlation between brain mass and the length of the digestive tract within 30 species of anurans. We further find that the evolution of large brain size is accompanied by an increase in female reproductive investment into egg size. Our results suggest that the evolution of brain size follows general patterns across vertebrate clades. [ABSTRACT FROM AUTHOR]

Exploitation of sexual signals by predators or parasites increases costs to signalers, creating opportunities for establishment of alternative reproductive tactics (ARTs). In field crickets, males calling may attract acoustically orienting parasitoid flies. Alternatively, males behaving as satellites forgo calling and attempt to intercept females attracted to callers. We modeled the contribution of calling versus satellite behavior to male reproductive success in the larger context of variation in ecology (parasitism rate, background mortality), demography (density, sex ratio), and female behavior (phonotaxis, mating choosiness). Male mating success was most influenced by number of females (standardized effect size 0.42), followed by female choosiness (0.33), background mortality (-0.31), number of males (-0.28), and parasitism rate (-0.21). The smallest effects were phonotaxis (0.10) and satellite behavior (-0.09). Although satellite behavior ameliorated negative effects of parasitism, its comparative effect was slight. ARTs seem most likely to evolve and persist when a single selection pressure on signaling is particularly strong. [ABSTRACT FROM AUTHOR]

The functional response of some predator species changes from a pattern characteristic for a generalist to that for a specialist according to seasonally varying prey availability. Current theory does not address the dynamic consequences of this phenomenon. Since season length correlates strongly with altitude and latitude and is predicted to change under future climate scenarios, including this phenomenon in theoretical models seems essential for correct prediction of future ecosystem dynamics. We develop and analyze a two-season model for the great horned owl (Bubo virginialis) and snowshoe hare (Lepus americanus). These species form a predator-prey system in which the generalist to specialist shift in predation pattern has been documented empirically. We study the qualitative behavior of this predator-prey model community as summer season length changes. We find that relatively small changes in summer season length can have a profound impact on the system. In particular, when the predator has sufficient alternative resources available during the summer season, it can drive the prey to extinction, there can be coexisting stable states, and there can be stable large-amplitude limit cycles coexisting with a stable steady state. Our results illustrate that the impacts of global change on local ecosystems can be driven by internal system dynamics and can potentially have catastrophic consequences. [ABSTRACT FROM AUTHOR]

Generalist parasites can strongly influence interactions between native and invasive species. Host competence can be used to predict how an invasive species will affect community disease dynamics; the addition of a highly competent, invasive host is predicted to increase disease. However, densities of invasive and native species can also influence the impacts of invasive species on community disease dynamics. We examined whether information on host competence alone could be used to accurately predict the effects of an invasive host on disease in native hosts. We first characterized the relative competence of an invasive species and a native host species to a native parasite. Next, we manipulated species composition in mesocosms and found that host competence results did not accurately predict community dynamics. While the invasive host was more competent than the native, the presence of the native (lower competence) host increased disease in the invasive (higher competence) host. To identify potential mechanisms driving these patterns, we analyzed a two-host, one-parasite model parameterized for our system. Our results demonstrate that patterns of disease were primarily driven by relative population densities, mediated by asymmetry in intra- and interspecific competition. Thus, information on host competence alone may not accurately predict how an invasive species will influence disease in native species. [ABSTRACT FROM AUTHOR]

Home range sizes of territorial animals are often observed to vary periodically in response to seasonal changes in foraging opportunities. Here we develop the first mechanistic model focused on the temporal dynamics of home range expansion and contraction in territorial animals. We demonstrate how simple movement principles can lead to a rich suite of range size dynamics, by balancing foraging activity with defensive requirements and incorporating optimal behavioral rules into mechanistic home range analysis. Our heuristic model predicts three general temporal patterns that have been observed in empirical studies across multiple taxa. First, a positive correlation between age and territory quality promotes shrinking home ranges over an individual’s lifetime, with maximal range size variability shortly before the adult stage. Second, poor sensory information, low population density, and large resource heterogeneity may all independently facilitate range size instability. Finally, aggregation behavior toward forage-rich areas helps produce divergent home range responses between individuals from different age classes. This model has broad applications for addressing important unknowns in animal space use, with potential applications also in conservation and health management strategies. [ABSTRACT FROM AUTHOR]

Sex-biased natal dispersal is widespread, and its significance remains a central question in evolutionary biology. However, theory so far fails to predict some of the most common patterns found in nature. To address this, we present novel results from an individual-based model investigating the joint roles of inbreeding load, demographic stochasticity, environmental stochasticity, and dispersal costs for the evolution of sex-biased dispersal. Most strikingly, we found that male-biased natal dispersal evolved in polygynous systems as a result of the interplay between inbreeding avoidance and stochasticity, whereas previous theory, in contrast to empirical observations, predicted male philopatry and female-biased natal dispersal under inbreeding load alone. Furthermore, the direction of the bias varied according to the nature of stochasticity. Our results therefore provide a unification of previous theory, yielding a much better qualitative match with empirical observations of male-biased dispersal in mate defense mating systems. [ABSTRACT FROM AUTHOR]

“Food Web Complexity and Species Diversity” (Paine 1966) is the most-cited empirical article published in the American Naturalist. In short, Paine removed predatory sea stars (Pisaster ochraceus) from the rocky intertidal and watched the key prey species, mussels (Mytilus californianus), crowd out seven subordinate primary space-holding species. However, because these mussels are a foundational species, they provide three-dimensional habitat for over 300 associated species inhabiting the mussel beds; thus, removing sea stars significantly increases community-wide diversity. In any case, most ecologists cite Paine (1966) to support a statement that predators increase diversity by interfering with competition. Although detractors remained skeptical of top-down effects and keystone concepts, the paradigm that predation increases diversity spread. By 1991, “Food Web Complexity and Species Diversity” was considered a classic ecological paper, and after 50 years it continues to influence ecological theory and conservation biology. [ABSTRACT FROM AUTHOR]

Theory suggests that the structure of evolutionary history represented in a species community may affect its functioning, but phylogenetic diversity metrics do not allow for the identification of major differences in this structure. Here we propose a new metric, ELDERness (for Evolutionary Legacy of DivERsity) to estimate evolutionary branching patterns within communities by fitting a polynomial function to lineage-through-time (LTT) plots. We illustrate how real and simulated community branching patterns can be more correctly described by ELDERness and can successfully predict ecosystem functioning. In particular, the evolutionary history of branching patterns can be encapsulated by the parameters of third-order polynomial functions and further measured through only two parameters, the “ELDERness surfaces.” These parameters captured variation in productivity of a grassland community better than existing phylogenetic diversity or diversification metrics and independent of species richness or presence of nitrogen fixers. Specifically, communities with small ELDERness surfaces (constant accumulation of lineages through time in LTT plots) were more productive, consistent with increased productivity resulting from complementary lineages combined with niche filling within lineages. Overall, while existing phylogenetic diversity metrics remain useful in many contexts, we suggest that our ELDERness approach better enables testing hypotheses that relate complex patterns of macroevolutionary history represented in local communities to ecosystem functioning. [ABSTRACT FROM AUTHOR]

Winning or losing a prior contest can influence the outcome of future contests, but it might also alter subsequent reproductive decisions. For example, losers may increase their investment in the current breeding attempt if losing a contest indicates limited prospects for future breeding. Using the burying beetle Nicrophorus vespilloides, we tested whether females adjust their prehatching and posthatching reproductive effort after winning or losing a contest with a same-sex conspecific. Burying beetles breed on carcasses of small vertebrates for which there is fierce intrasexual competition. We found no evidence that winning or losing a contest influenced reproductive investment decisions in this species. Instead, we show that a female's prior contest experience (regardless of its outcome) influenced the amount of posthatching care provided, with downstream consequences for the female's reproductive output; both winners and losers spentmore time provisioning food to their offspring and produced larger broods than females with no contest experience. We discuss the wider implications of our findings and present a conceptual model linking contestmediated adjustments in parental investment to population-level processes. We propose that the frequency of intraspecific contests could both influence and be influenced by population dynamics in species where contest experience influences the size and/or number of offspring produced. [ABSTRACT FROM AUTHOR]

Evolution can alter the stability and dynamics of ecological communities; for example, prey evolution can drive cyclic dynamics in predator-prey systems that are not possible in the absence of evolution. However, it is unclear how the magnitude of additive genetic variation in the evolving species mediates those effects. In this study, I explore how the magnitude of prey additive genetic variation determines what effects prey evolution has on the dynamics and stability of predator-prey systems. I use linear stability analysis to decompose the stability of a general eco-evolutionary predator-prey model into components representing the stabilities of the ecological and evolutionary subsystems as well as the interactions between those subsystems. My results show that with low genetic variation, the cyclic dynamics and stability of the system are determined by the ecological subsystem. With increased genetic variation, disruptive selection always destabilizes stable communities, stabilizing selection can stabilize or destabilize communities, and prey evolution can alter predator-prey phase lags. Stability changes occur approximately when the magnitude of genetic variation balances the (in)stabilities of the ecological and evolutionary subsystems. I discuss the connections between my stability results and prior results from the theory of adaptive dynamics. [ABSTRACT FROM AUTHOR]

Raia et al. propose that the evolution of the shape and complexity of animal ornaments (e.g., deer antlers) can be explained by interspecific variation in body size and is not influenced by sexual selection. They claim to show that ornament complexity is related to body size by an 0.25-power law and argue that this finding precludes a role for sexual selection in the evolution of ornament complexity. However, their study does not test alternative hypotheses and mismeasures antler shape allometry by omitting much of the published data. We show that an index of sexual selection (sexual size dimorphism) is positively correlated with size-corrected antler complexity and that the allometric slope of complexity is substantially greater than 0.25, contra Raia et al. We conclude that sexual selection and physical constraints both affect the evolution of antler shape. [ABSTRACT FROM AUTHOR]

One predicted cost of female infidelity in socially monogamous species is that cuckolded males should provide less parental care. This relationship is robust across species, but evidence is ambiguous within species. We do not know whether individual males reduce their care when paired with cheating females compared with when paired with faithful females (within-male adjustment) or, alternatively, if the males that pair with cheating females are the same males that provide less parental care in general (between-male effect). Our exceptionally extensive long-term data set of repeated observations of a wild passerine allows us to disentangle paternal care adjustment within males-within pairs and between males-while accounting for environmental variables. We found a within-male adjustment of paternal provisioning, but not incubation effort, relative to the cuckoldry in their nest. This effect was mainly driven by females differing consistently in their fidelity. There was no evidence that this within-male adjustment also took place across broods with the same female, and we found no between-male effect. Interestingly, males that gained more extrapair paternity provided less care. Data from a cross-foster experiment suggested that males did not use kin recognition to assess paternity. Our results provide insight into the role of individual variation in parental care and mating systems. [ABSTRACT FROM AUTHOR]

By exploiting unutilized resources, organisms expand into novel niches, which can lead to adaptive radiation. However, some groups fail to diversify despite the apparent opportunity to do so. Although arising multiple times, arboreal folivores are rare and have not radiated, presumably because of energetic constraints. To explore this hypothesis, we quantified the field metabolic rate (FMR), movement, and body temperature for syntopic two- and three-toed sloths, extreme arboreal folivores that differ in their degree of specialization. Both species expended little energy, but three-toed sloths (162 kJ/ day*kg0.734) possessed the lowest FMR recorded for any mammal. Three-toed sloths were more heterothermic and moved less than twotoed sloths.Wethen compared FMRs and basal metabolic rates (BMRs) for 19 species of arboreal folivores along a spectrum of specialization. Overall, arboreal folivores had lower BMRs and FMRs than othermammals, and increasing specialization led to lower FMRs but not BMRs. Thus, reduced energetic expenditure in specialized species was the result of thermoregulatory and behavioral strategies, rather than simply a proportionate reduction in BMR. Altogether, our findings support the concept that arboreal folivores are tightly constrained by nutritional energetics and help to explain the lack of radiation among species exploiting a lifestyle in the trees. [ABSTRACT FROM AUTHOR]

Collective behavior emerges from interactions among group members who often vary in their behavior. The presence of just one or a few keystone individuals, such as leaders or tutors, may have a large effect on collective outcomes. These individuals can catalyze behavioral changes in other group members, thus altering group composition and collective behavior. The influence of keystone individuals on group function may lead to trade-offs between ecological situations, because the behavioral composition they facilitate may be suitable in one situation but not another. We use computer simulations to examine various mechanisms that allow keystone individuals to exert their influence on group members. We further discuss a trade-off between two potentially conflicting collective outcomes, cooperative prey attack and disease dynamics. Our simulations match empirical data from a social spider system and produce testable predictions for the causes and consequences of the influence of keystone individuals on group composition and collective outcomes. We find that a group's behavioral composition can be impacted by the keystone individual through changes to interaction patterns or behavioral persistence over time. Group behavioral composition and the mechanisms that drive the distribution of phenotypes influence collective outcomes and lead to trade-offs between disease dynamics and cooperative prey attack. [ABSTRACT FROM AUTHOR]

Although animals fine-tune their activity to avoid excess heat, we still lack a mechanistic understanding of such behaviors. As the global climate changes, such understanding is particularly important for projecting shifts in the activity patterns of populations and communities. We studied how foraging decisions vary with biotic and abiotic pressures. By tracking the foraging behavior of diurnal desert spiny mice in their natural habitat and estimating the energy and water costs and benefits of foraging, we asked how risk management and thermoregulatory requirements affect foraging decisions. We found that water requirements had the strongest effect on the observed foraging decisions. In their arid environment, mice often lose water while foraging for seeds and cease foraging even at high energetic returns when water loss is high. Mice also foraged more often when energy expenditure was high and for longer times under high seed densities and low predation risks. Gaining insight into both energy and water balance will be crucial to understanding the forces exerted by changing climatic conditions on animal energetics, behavior, and ecology. [ABSTRACT FROM AUTHOR]

We describe a spatially explicit simulation experiment designed to assess relative impacts of macroecological traits on patterns of biological diversification under changing environmental conditions. Using a simulation framework, we assessed impacts of species' niche breadth (i.e., the range of their abiotic tolerances) and dispersal ability on resulting patterns of speciation and extinction and evaluated how these traits, in conjunction with environmental change, shape biological diversification. Simulation results supported both niche breadth and dispersal ability as important drivers of diversification in the face of environmental change, and suggested that the rate of environmental change influences how species interact with the extrinsic environment to generate diversity. Niche breadth had greater effects on speciation and extinction than dispersal ability when climate changed rapidly, whereas dispersal ability effects were elevated when climate changed slowly. Our simulations provide a bottom-up perspective on the generation and maintenance of diversity under climate change, offering a better understanding of potential interactions between species' intrinsic macroecological characteristics and a dynamic extrinsic environment in the process of biological diversification. [ABSTRACT FROM AUTHOR]

The evolutionary stability of quantitative traits depends on whether a population can resist invasion by any mutant. While uninvadability is well understood in well-mixed populations, it is much less so in subdivided populations when multiple traits evolve jointly. Here, we investigate whether a spatially subdivided population at a monomorphic equilibrium for multiple traits can withstand invasion by any mutant or is subject to diversifying selection. Our model also explores the correlations among traits arising from diversifying selection and how they depend on relatedness due to limited dispersal. We find that selection tends to favor a positive (negative) correlation between two traits when the selective effects of one trait on relatedness is positively (negatively) correlated to the indirect fitness effects of the other trait. We study the evolution of traits for which this matters: dispersal that decreases relatedness and helping that has positive indirect fitness effects. We find that when dispersal cost is low and the benefits of helping accelerate faster than its costs, selection leads to the coexistence of mobile defectors and sessile helpers. Otherwise, the population evolves to a monomorphic state with intermediate helping and dispersal. Overall, our results highlight the effects of population subdivision for evolutionary stability and correlations among traits. [ABSTRACT FROM AUTHOR]

Fossils and other paleontological information can improve phylogenetic comparative method estimates of phenotypic evolution and generate hypotheses related to species diversification. Here, we use fossil information to calibrate ancestral reconstructions of suitable climate for Sceloporus lizards in North America. Integrating data from the fossil record, general circulation models of paleoclimate during the Miocene, climate envelope modeling, and phylogenetic comparative methods provides a geographically and temporally explicit species distribution model of Sceloporus-suitable habitat through time. We provide evidence to support the historic biogeographic hypothesis of Sceloporus diversification in warm North American deserts and suggest a relatively recent Sceloporus invasion into Mexico around 6 Ma. We use a physiological model to map extinction risk. We suggest that the number of hours of restriction to a thermal refuge limited Sceloporus from inhabiting Mexico until the climate cooled enough to provide suitable habitat at approximately 6 Ma. If the future climate returns to the hotter climates of the past, Mexico, the place of highest modern Sceloporus richness, will no longer provide suitable habitats for Sceloporus to survive and reproduce. [ABSTRACT FROM AUTHOR]

Range expansions are limited by two key factors. These are (1) dispersal, which includes a species' intrinsic mobility, geographical barriers, and their interaction; and (2) the ability of a species to persist beyond its current range. I evaluate the role of these in affecting bird species distributions across the Himalayas, under a hypothesis that many species have recently expanded their range out of an eastern Pleistocene refuge. I measured wing shape as a proxy for dispersal ability and topographic complexity across the Himalayas as a proxy for dispersal barriers. As a factor affecting the potential for persistence in novel locations, I compared similarity of a species' climatic envelope in the east, the hypothesized historical refuge, and the west, the location of recent colonization. Climatic similarity, wing shape, and the interaction of topographic complexity with wing shape all contribute significantly to the range extent of a given species. The result highlights the important interaction between morphological and landscape factors in affecting successful range expansions. The two dispersal-related parameters together explain two times the variance explained by climate, but I present additional evidence that other factors besides climate-notably biotic interactions-affect the ability of a species to persist beyond its range. [ABSTRACT FROM AUTHOR]

All ecosystems are subjected to chronic disturbances, such as harvest, pollution, and climate change. The capacity to forecast how species respond to such press perturbations is limited by our imprecise knowledge of pairwise species interaction strengths and the many direct and indirect pathways along which perturbations can propagate between species. Network complexity (size and connectance) has thereby been seen to limit the predictability of ecological systems. Here we demonstrate a counteracting mechanism in which the influence of indirect effects declines with increasing network complexity when species interactions are governed by universal allometric constraints. With these constraints, network size and connectance interact to produce a skewed distribution of interaction strengths whose skew becomes more pronounced with increasing complexity. Together, the increased prevalence of weak interactions and the increased relative strength and rarity of strong interactions in complex networks limit disturbance propagation and preserve the qualitative predictability of net effects even when pairwise interaction strengths exhibit substantial variation or uncertainty. [ABSTRACT FROM AUTHOR]

Factors constraining the structure of food webs can be investigated by comparing classes of ecosystems. We find that pelagic ecosystems, those based on one-celled primary producers, have longer food chains than terrestrial ecosystems. Yet pelagic ecosystems have lower primary productivity, contrary to the hypothesis that greater energy flows permit higher trophic levels. We hypothesize that longer food chain length in pelagic ecosystems, compared with terrestrial ecosystems, is associated with smaller pelagic animal body size permitting more rapid trophic energy transfer. Assuming negative allometric dependence of biomass production rate on body mass at each trophic level, the lowest three pelagic animal trophic levels are estimated to add biomass more rapidly than their terrestrial counterparts by factors of 12, 4.8, and 2.6. Pelagic animals consequently transport primary production to a fifth trophic level 50-190 times more rapidly than animals in terrestrial webs. This difference overcomes the approximately fivefold slower pelagic basal productivity, energetically explaining longer pelagic food chains. In addition, ectotherms, dominant at lower pelagic animal trophic levels, have high metabolic efficiency, also favoring higher rates of trophic energy transfer in pelagic ecosystems. These two animal trophic flow mechanisms imply longer pelagic food chains, reestablishing an important role for energetics in food web structure. [ABSTRACT FROM AUTHOR]

Parasites evolve within complex abiotic and biotic environments. Because of this, it is often challenging to ascertain how evolutionary and ecological processes together affect parasite specialization. Here, we use the fungus-growing ant system, which consists of ancient, likely coevolved, complex communities, to explore the ecological and evolutionary forces shaping host-parasite specificity. We use a comparative phylogenetic framework to determine whether patterns of specificity between the fungal parasite Escovopsis and its host fungi at fine phylogenetic scales reflect patterns of specificity at broader phylogenetic levels. In other words, we ask whether parasite specificity across broad host phylogenetic relationships is maintained by specificity toward more closely related hosts. We couple this exploration with manipulations of the community context within which host-parasite interactions are taking place to evaluate how community complexity alters parasite specificity. Regardless of host community complexity, parasites displayed a consistent pattern of specialization on native hosts, that is, those that they are found attacking in nature, with the potential for occasional switching to hosts distantly related to their native hosts. These results suggest that, even within a complex community context, pairwise host and parasite adaptation and coadaptation can be the primary drivers of the evolution and maintenance of parasite specificity. [ABSTRACT FROM AUTHOR]

The prevalence of infection varies dramatically on a fine spatial scale. Many evolutionary hypotheses are founded on the assumption that this variation is due to host genetics, such that sites with a high frequency of alleles conferring susceptibility are associated with higher infection prevalence. This assumption is largely untested and may be compromised at finer spatial scales where gene flow between sites is high. We put this assumption to the test in a natural snail-trematode interaction in which host susceptibility is known to have a strong genetic basis. A decade of field sampling revealed substantial spatial variation in infection prevalence between 13 sites around a small lake. Laboratory assays replicated over 3 years demonstrate striking variation in host susceptibility among sites in spite of high levels of gene flow between sites. We find that mean susceptibility can explain more than one-third of the observed variation in mean infection prevalence among sites. We estimate that variation in susceptibility and exposure together can explain the majority of variation in prevalence. Overall, our findings in this natural host-parasite system argue that spatial variation in infection prevalence covaries strongly with variation in the distribution of genetically based susceptibility, even at a fine spatial scale. [ABSTRACT FROM AUTHOR]

Historically, egg-bound reptile embryos were thought to passively thermoconform to the nest environment. However, recent observations of thermal taxis by embryos of multiple reptile species have led to the widely discussed hypothesis that embryos behaviorally thermoregulate. Because temperature affects development, such thermoregulation could allow embryos to control their fate far more than historically assumed. We assessed the opportunity for embryos to behaviorally thermoregulate in nature by examining thermal gradients within natural nests and eggs of the common snapping turtle (Chelydra serpentina; which displays embryonic thermal taxis) and by simulating thermal gradients within nests across a range of nest depths, egg sizes, and soil types. We observed little spatial thermal variation within nests, and thermal gradients were poorly transferred to eggs. Furthermore, thermal gradients sufficiently large and constant for behavioral thermoregulation were not predicted to occur in our simulations. Gradients of biologically relevant magnitude have limited global occurrence and reverse direction twice daily when they do exist, which is substantially faster than embryos can shift position within the egg. Our results imply that reptile embryos will rarely, if ever, have the opportunity to behaviorally thermoregulate by moving within the egg. We suggest that embryonic thermal taxis instead represents a play behavior, which may be adaptive or selectively neutral, and results from the mechanisms for behavioral thermoregulation in free-living stages coming online prior to hatching. [ABSTRACT FROM AUTHOR]