The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: We investigate the effects of disturbance on species coexistence using a general mathematical model. The model can be applied to a variety of communities, and we show how it applies in particular to communities of shrubs in Mediterranean heathlands. Our analysis demonstrates that when species have distinct fire response strategies, disturbance allows for stable species coexistence. Furthermore, we show how the size of the coexistence region depends on fire frequency and dispersal ability. The stabilizing mechanism is classified as the spatial storage effect, which is identified by the covariance between environmental and competitive responses. This is the first time that disturbance, defined as a fluctuating mortality factor, has been definitively shown to promote coexistence via the storage effect. Moreover, we show that the biological driver is a trade‐off between resistance and resilience to disturbance. The resistance‐resilience trade‐off is a biological mechanism of coexistence under patchy disturbance. However, the resistance‐resilience trade‐off has not previously featured in mathematical models of species coexistence. Although the storage effect depends on fluctuations in life‐history parameters presumed to result from environmental variation, rarely are life‐history parameters explicitly linked to environmental phenomena. Here the link is clear and concrete, allowing better definition of the intended application.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Coevolution—reciprocal evolutionary change in interacting species—is one of the central biological processes organizing the web of life, and most species are involved in one or more coevolved interactions. We have learned in recent years that coevolution is a highly dynamic process that continually reshapes interactions among species across ecosystems, creating geographic mosaics over timescales sometimes as short as thousands or even hundreds of years. If we take that as our starting point, what should we now be asking about the coevolutionary process? Here I suggest five major questions that we need to answer if we are to understand how coevolution shapes the web of life. How evolutionarily dynamic is specialization to other species, and what is the role of coevolutionary alternation in driving those dynamics? Does the geographic mosaic of coevolution shape adaptation in fundamentally different ways in different forms of interaction? How does the geographic mosaic of coevolution shape speciation? How does the structure of reciprocal selection change during the assembly of large webs of interacting species? How important are genomic events such as whole‐genome duplication (i.e., polyploidy) and whole‐genome capture (i.e., hybridization) in generating novel webs of interacting species? I end by suggesting four points about coevolution that we should tell every new student or researcher in biology.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Dispersal has long been recognized as a crucial factor affecting population dynamics. Several studies on long‐distance dispersal revealed a peculiarity now widely known as a problem of “fat tail”: instead of the rate of decay in the population density over large distances being described by a normal distribution, which is apparently predicted by the standard diffusion approach, field data often show much lower rates such as exponential or power law. The question as to what are the processes and mechanisms resulting in the fat tail is still largely open. In this note, by introducing the concept of a statistically structured population, we show that a fat‐tailed long‐distance dispersal is a consequence of the fundamental observation that individuals of the same species are not identical. Fat‐tailed dispersal thus appears to be an inherent property of any real population. We show that our theoretical predictions are in good agreement with available data.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: The theory of mate choice posits that intensified competition for mates can generate variation in either the strength or the direction of mate preferences within the competing sex. Here, we show that intensified male competition, manipulated through the operational sex ratio, induced differential mate choosiness among threespine stickleback males Gasterosteus aculeatus. In the absence of male competition, males were choosy independent of their condition when presented sequentially with a large and a small female. However, in a male‐biased social setting, males in poor condition became indiscriminate, whereas good‐condition males continued to be selective. Hence, competition induced condition‐dependent mate choosiness. This was probably due to mating opportunities decreasing more for poor‐condition than for good‐condition males when competition intensified, resulting in condition‐dependent cost of choice. Variation in condition and cost of choice could thus allow the persistence of male mate choosiness in populations experiencing intense male competition.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: An ever larger proportion of Earth’s biota is affected by the current accelerating environmental change. The mismatches between organisms and their environments are now increasing in both magnitude and frequency, resulting in lowered fitness and hence the decline of populations. Under this scenario, species with behavioral and/or physiological traits that provide them shelter from the environment are predicted to be less vulnerable to population declines than species that are always exposed to the elements. Here, we coded 4,536 living mammal species for sleep‐or‐hide (SLOH) behavior, including hibernation, torpor, and the use of burrows, among other related traits. We demonstrate that species that exhibit SLOH behavior are underrepresented in high‐risk International Union for Conservation of Nature Red List categories. We found that SLOH behavior contributes to lowering extinction risk even after we accounted for other factors that directly or indirectly buffer species against extinction, such as larger geographic ranges and smaller body sizes. This result is robust to analyses using phylogenetically independent contrasts. Sleep‐or‐hide behavior, made possible by a related suite of physiological adaptations, allows mammals to function at lower metabolic rates and/or buffer them from changing physical elements. Mammals with SLOH behavior have a greater propensity to survive in the current extinction crisis and probably also in past crises because of reduced exposure to environmental stress.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: When individuals store resources acquired while moving through a spatially variable habitat, a form of population structure arises. The theoretical consequences of this process for resource competition are studied for phytoplankton species consuming a single nutrient resource, using a Lagrangian modeling approach. Each competitor population is divided into many subpopulations that move through two model habitats with gradients in nutrient availability: an unstirred chemostat and a partially mixed water column. The results provide little indication that resource storage contributes to competitive fitness in the scenarios analyzed. Superior competitors usually reduce the limiting nutrient to low concentrations at steady state or sometimes have high maximal growth rates. Resource storage enhances competitive fitness in temporally variable habitats where encounters with rich nutrient pulses are strongly periodic. However, in purely spatially variable habitats where encounters with rich nutrient patches are random, resource storage does not appear to provide much benefit, at least for passively moving organisms that cannot control their location.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Empirical studies have shown that temporally fluctuating inputs of resource subsidies can indirectly increase or decrease the abundance of in situ resources by affecting generalist consumers that feed on both subsidies and in situ resources. By mathematical modeling, we develop a theoretical framework that can explain these variable consumer‐mediated indirect effects. We show that the hierarchy of timescales among fluctuations in the subsidy input rate and consumers’ reproductive and aggregative numerical responses predict the signs of the indirect effects. These predictions are consistent with field observations from a variety of natural systems. Our results suggest that the timescale hierarchy of ecological processes is fundamentally important for understanding and predicting indirect effects in nonequilibrium food web dynamics.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Despite much theoretical discussion on the evolutionary significance of intraclonal genetic variation, particularly for modular organisms whose lack of germ‐soma segregation allows for variants arising in clonal growth to contribute to evolutionary change, the potential of this variation to fuel adaptation remains surprisingly untested. Given intraclonal variation, mitotic cell lineages, rather than sexual offspring, may frequently act as units of selection. Here, we applied artificial selection to such lineages in the branching red seaweed Asparagopsis armata, targeting aspects of clonal growth form and growth‐form plasticity that enhance light acquisition on patchy subtidal reefs and predicting that a genetic basis to intraclonal variation may promote significant responses that cannot accompany phenotypic variation alone. Cell‐lineage selection increased variation in branch proliferation among A. armata genets and successfully altered its plasticity to light. Correlated responses in the plasticity of branch elongation, moreover, showed that cell‐lineage selection may be transmitted among the plasticities of growth‐form traits in A. armata via pleiotropy. By demonstrating significant responses to cell‐lineage selection on growth‐form plasticity in this seaweed, our study lends support to the notion that intraclonal genetic variation may potentially help clonal organisms to evolve adaptively in the absence of sex and thereby prove surprisingly resilient to environmental change.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Females and males of many animals exhibit a striking array of sexual dimorphisms, ranging from the primary differences of the gametes and gonads to the somatic differences often seen in behavior, morphology, and physiology. These differences raise many questions regarding how such divergent phenotypes can arise from a genome that is largely shared between the sexes. Recent progress in genomics has revealed some of the actual genetic mechanisms that create separate sex‐specific phenotypes, and the evidence indicates that thousands of genes across all portions of the genome contribute to male and female forms through sex‐biased gene expression. Related work has begun to define the strength and influence of sex‐specific evolutionary forces that shape these phenotypic dimorphisms and how they in turn affect the genome. Additionally, theory has long suggested that the evolution of sexual dimorphism is facilitated by sex chromosomes, as these are the only portions of the genome that differ between males and females. Genomic analysis indicates that there is indeed a relationship between sexual dimorphism and the sex chromosomes. However, the connection is far more complicated than current theory allows, and this may ultimately require a reexamination of the assumptions so that predictions match the accumulating empirical data.

The American Naturalist, Volume 0, Issue 0, Page 000, Latest Articles.
Abstract: Within large taxonomic assemblages, the number of species with adult body mass M is characterized by a broad but asymmetric distribution, with the largest mass being orders of magnitude larger than the typical mass. This canonical shape can be explained by cladogenetic diffusion that is bounded below by a hard limit on viable species mass and above by extinction risks that increase weakly with mass. Here we introduce and analytically solve a simplified cladogenetic diffusion model. When appropriately parameterized, the diffusion‐reaction equation predicts mass distributions that are in good agreement with data on 4,002 terrestrial mammals from the late Quaternary and 8,617 extant bird species. Under this model, we show that a specific trade‐off between the strength of within‐lineage drift toward larger masses (Cope’s rule) and the increased risk of extinction from increased mass is necessary to produce realistic mass distributions for both taxa. We then make several predictions about the evolution of avian species masses.

The American Naturalist, Volume 173, Issue 1, Page vi, January 2009.

The American Naturalist, Volume 173, Issue 1, Page iv-v, January 2009.

The American Naturalist, Volume 173, Issue 1, Page iv-v, January 2009.

The American Naturalist, Volume 173, Issue 1, Page iii-iv, January 2009.

The American Naturalist, Volume 173, Issue 1, Page 89-104, January 2009.
Abstract: In seasonal environments, timing of reproduction is an important fitness component. However, in ungulates, our understanding of this biological process is limited. Here we analyze how age and body mass affect spatiotemporal variation in timing of ovulation of 6,178 Norwegian moose. We introduced a parametric statistical model to obtain inferences about the seasonal timing of ovulation peak, the degree of synchrony among individuals, and the proportion of individuals that ovulate. These components showed much more spatiotemporal variation than previously reported. Young (primiparous) and old (≥11.5 years of age) females ovulated later than prime‐aged (2.5–10.5 years of age) females. In all age classes, ovulation was delayed with decreasing body mass. Ovulation rates were lower and more variable among primiparous females than among older females. Young females required higher body mass than older females did to ovulate. The body‐mass‐to‐ovulation relationship varied with age, showed large regional variation, and differed among years within region. These results suggest that (1) environmental and population characteristics contribute to shape seasonal variation in the breeding pattern and (2) large regional variation exists in the size‐dependent age at maturity in moose. Hence, the life‐history trade‐off between reproduction and body growth should differ regionally in moose.

The American Naturalist, Volume 173, Issue 1, Page E1-E14, January 2009.
Abstract: Genomic imprinting allows maternally and paternally derived alleles to have different patterns of expression (one allele is often silent). Kin selection provides an explanation of genomic imprinting because conflicts of interest can arise between paternally and maternally inherited alleles when they have different probabilities of being present in other individuals. Our aim here is to examine the extent to which conflicts between paternally and maternally inherited alleles could arise over the allocation of resources to male and female reproduction (sex allocation), for example, conflict over the offspring sex ratio. We examine the situations in which sex allocation is influenced by competitive or cooperative interactions between relatives: local resource competition, local mate competition, and local resource enhancement. We determine solutions for diploids and haplodiploids when either the mother or the offspring controls sex allocation. Our results suggest that the greatest conflict between paternally and maternally inherited alleles and therefore the strongest selection for genomic imprinting will occur in haplodiploid species where the offspring can control sex allocation, such as the social hymenoptera and the polyembryonic parasitoid wasps. Within the social hymenoptera, we expect especially strong selection for genomic imprinting in species subject to local resource competition, such as honeybees and army ants.

The American Naturalist, Volume 173, Issue 1, Page 12-25, January 2009.
Abstract: Male mate selection during polygyny traditionally has been eclipsed in the literature by its female counterpart. Existing models that have studied male mate choice have concluded that males with genetically inherited preferences for females exhibiting particular traits are often less fit than males without such a preference, leading to preference loss. In this article, we explore the consequences of a fundamental difference between male and female mate choice, the way in which the opposite sex acts as a resource during mating. By incorporating a strategic process at the ecological level, we show that if males are allowed to actively adjust the distribution of their courtship efforts over the available classes of females, male preference can be maintained as a polymorphism. Further, the resulting coexistence induces a reproductive segregation within the population that, when coupled with genetic control of female traits, can lead to strong linkage disequilibrium between the alleles for trait and preference. These processes can cause complete assortative mating to emerge in the model.

The American Naturalist, Volume 173, Issue 1, Page 60-71, January 2009.
Abstract: Understanding individual space use remains a major issue in ecology, and it is complicated by definitions of spatial scale and the interplay of multiple factors. We quantified the effect of habitat and biotic and individual factors on space use by amphibians (Bufo bufo spinosus [BB] and Bufo viridis [BV]) that were radio‐tracked in their terrestrial summer habitat. We analyzed two spatial scales, 50% core areas and 95% home ranges (excluding 50% core areas), thought to represent resting and foraging areas, respectively. The 50% core area of BB was best explained by habitat structure and prey density, whereas the 50% core area of BV was determined solely by habitat structure. This suggests that the resting and foraging areas of BB are not spatially separated. The 95% home range of BB was determined by prey density, while for BV both habitat structure and prey density determined home range size. We conclude that the terrestrial area requirements of amphibians depend on the productivity and spatiotemporal complexity of landscapes and that differential space use may facilitate their co‐occurrence. Behavior‐based a priori hypotheses, in combination with an information‐theoretic approach and path analyses, provide a promising framework to disentangle factors that govern individual space use, thereby advancing home range studies.

The American Naturalist, Volume 173, Issue 1, Page 72-88, January 2009.
Abstract: Infectious diseases that affect their host on a long timescale can regulate the host population dynamics. Here we show that a strong Allee effect can lead to complex dynamics in simple epidemic models. Generally, the Allee effect renders a population bistable, but we also identify conditions for tri‐ or monostability. Moreover, the disease can destabilize endemic equilibria and induce sustained oscillations. These disappear again for high transmissibilities, with eventually vanishing host population. Disease‐induced extinction is thus possible for density‐dependent transmission and without any alternative reservoirs. The overall complexity suggests that the system is very sensitive to perturbations and control methods, even in parameter regions with a basic reproductive ratio far beyond $R_{0}=1$. This may have profound implications for biological conservation as well as pest management. We identify important threshold quantities and attribute the dynamical behavior to the joint interplay of a strong Allee effect and infection.

The American Naturalist, Volume 173, Issue 1, Page 47-59, January 2009.
Abstract: Prey living in groups often partly rely on companions to detect predators. Accordingly, individuals having vigilant neighbors could decrease their own vigilance, engendering a certain level of vigilance coordination in the group. However, when a predator attacks, individuals that spot it react quicker than individuals that follow them and have less chance of being targeted. Individuals with vigilant neighbors may then be particularly exposed, since they risk lagging behind their companions in an attack. Here, we incorporate this effect in a spatially explicit model of vigilance. A first version of the model derives the evolutionarily stable proportion of time allocated to vigilance for each position in the group. A second version considers the real alternation of feeding and vigilance and allows individuals to respond immediately when their neighbors raise their head or resume feeding. The model confirms then that the collective detection effect tends to coordinate vigilance. However, when predators display marked preferences for stragglers, adaptive response by prey generates waves of collective vigilance that may spread and circulate over the group. The overall level of vigilance in the group strongly oscillates, sometimes far away from the evolutionarily stable values, and the stabilizing effect of vigilance coordination is thwarted. These results illustrate real patterns of vigilance, in particular, the fact that group members often synchronize their vigilance.