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American Naturalist

Asta Audzijonyte, Shane A Richards
Trade-offs in energy allocation between growth, reproduction, and survival are at the core of life-history theory. While age-specific mortality is considered to be the main determinant of the optimal allocation, some life-history strategies, such as delayed or skipped reproduction, may be better understood when also accounting for reproduction costs. Here, we present a two-pool indeterminate grower model that includes survival and energetic costs of reproduction. The energetic cost sets a minimum reserve required for reproduction, while the survival cost reflects increased mortality from low postreproductive body condition...
October 2018: American Naturalist
Daniel J Becker, Celine E Snedden, Sonia Altizer, Richard J Hall
Many wildlife species occupy landscapes that vary in the distribution, abundance, and quality of food resources. Increasingly, urbanized and agricultural habitats provide supplemental food resources that can have profound consequences for host distributions, movement patterns, and pathogen exposure. Understanding how host and pathogen dispersal across landscapes is affected by the spatial extent of food-supplemented habitats is therefore important for predicting the consequences for pathogen spread and impacts on host occupancy...
October 2018: American Naturalist
Sonal Singhal, Huateng Huang, Maggie R Grundler, María R Marchán-Rivadeneira, Iris Holmes, Pascal O Title, Stephen C Donnellan, Daniel L Rabosky
Population divergence is the first step in allopatric speciation, as has long been recognized in both theoretical models of speciation and empirical explorations of natural systems. All else being equal, lineages with substantial population differentiation should form new species more quickly than lineages that maintain range-wide genetic cohesion through high levels of gene flow. However, there have been few direct tests of the extent to which population differentiation predicts speciation rates as measured on phylogenetic trees...
October 2018: American Naturalist
Scott L Nuismer, Bob Week, Marcelo A Aizen
Important groups of mutualistic species are threatened worldwide, and identifying factors that make them more or less fragile in the face of disturbance is becoming increasingly critical. Although much research has focused on identifying the ecological factors that favor the stability of communities rich in mutualists, much less has been devoted to understanding the role played by historical and contemporary evolution. Here we develop mathematical models and computer simulations of coevolving mutualistic communities that allow us to explore the importance of coevolution in stabilizing communities against anthropogenic disturbance...
October 2018: American Naturalist
Vérane Berger, Jean-François Lemaître, Dominique Allainé, Jean-Michel Gaillard, Aurélie Cohas
Sociality modulates life-history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided and on the sex of the dominant...
October 2018: American Naturalist
David Wheatcroft, Trevor D Price
Explaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (mobs) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of Phylloscopus warblers. Even when alone, birds are aggressive toward predators of adult birds, both at and away from their nests...
October 2018: American Naturalist
Raul Costa-Pereira, Márcio Silva Araújo, Renan da Silva Olivier, Franco L Souza, Volker H W Rudolf
Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, predator-prey size ratios (PPSRs) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from optimal foraging theory...
October 2018: American Naturalist
Devin Arbuthnott
Why do we observe substantial variation in fitness-related traits under strong natural or sexual selection? While there is support for several selective and neutral mechanisms acting in select systems, we lack a comprehensive analysis of the relative importance of various mechanisms within a single system. Furthermore, while sexually selected male traits have been a central focus of this paradox, female sexual traits have rarely been considered. In this study, I evaluate the contribution of various selective mechanisms to the maintenance of substantial variation in female attractiveness and offspring production observed among Drosophila melanogaster genotypes...
October 2018: American Naturalist
Daniel E Naya, Hugo Naya, Craig R White
One of the most generalized conclusions arising from studies analyzing the ecological variation of energy metabolism in endotherms is the apparent negative correlation between ambient temperature and mass-independent basal metabolic rate (residual BMR). As a consequence, ambient temperature has been considered the most important external factor driving the evolution of residual BMR. It is not clear, however, whether this relationship is size dependent, and artifacts such as the biased sampling of body masses in physiological data sets could cause us to overstate the ubiquity of the relationship...
October 2018: American Naturalist
Julie C Blackwood, Jonathan Machta, Alexander D Meyer, Andrew E Noble, Alan Hastings, Andrew M Liebhold
Periodical cicadas are enigmatic organisms: broods spanning large spatial ranges consist of developmentally synchronized populations of 3-4 sympatric species that emerge as adults every 13 or 17 years. Only one brood typically occupies any single location, with well-defined boundaries separating distinct broods. The cause of such synchronous development remains uncertain, but it is known that synchronous emergence of large numbers of adults in a single year satiates predators, allowing a substantial fraction of emerging adults to survive long enough to reproduce...
October 2018: American Naturalist
John J Schenk, Scott J Steppan
Although the importance of biogeography in the speciation process is well recognized, the fundamental role of geographic diversification during adaptive radiations has not been studied to determine its importance during the adaptive radiation process. We examined the relationship between lineage and regional diversification patterns in the South American rodent subfamily Sigmodontinae, one of the best candidates for an adaptive radiation in mammals, to propose a conceptual framework for geographic transitions during adaptive radiations...
October 2018: American Naturalist
Tabitha S Rudin-Bitterli, Nicola J Mitchell, Jonathan P Evans
When organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog Crinia georgiana, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low water) late in larval development...
October 2018: American Naturalist
Thomas Koffel, Tanguy Daufresne, François Massol, Christopher A Klausmeier
Plants present a variety of defensive strategies against herbivores, broadly classified into tolerance and resistance. Since resource availability can also limit plant growth, we expect plant allocation to resource acquisition and defense to vary along resource gradients. Yet, the conditions under which one defensive strategy is favored over the other are unclear. Here, we use an eco-evolutionary model to investigate plant adaptive allocation to resource acquisition, tolerance, and resistance along a resource gradient in a simple food web module inspired by plankton communities where plants compete for a single resource and are grazed on by a shared herbivore...
September 2018: American Naturalist
O Kennedy Rhoades, Rebecca J Best, John J Stachowicz
Interspecific variation in resource use is critical to understanding species diversity, coexistence, and ecosystem functioning. A growing body of research describes analogous intraspecific variation and its potential importance for population dynamics and community outcomes. However, the magnitude of intraspecific variation relative to interspecific variation in key dimensions of consumer-resource interactions remains unknown, hampering our understanding of the importance of this variation for population and community processes...
September 2018: American Naturalist
Kaitlin M Baudier, Catherine L D'Amelio, Rumaan Malhotra, Michael P O'Connor, Sean O'Donnell
The climatic variability hypothesis (CVH) is a cornerstone of thermal ecology, predicting the evolution of wider organismal thermal tolerance ranges in more thermally variable environments. Thermal tolerance ranges depend on both upper and lower tolerance limits (critical thermal maxima [[Formula: see text]] and critical thermal minima [[Formula: see text]]), which may show different responses to environmental gradients. To delineate the relative effects of mean and extreme temperatures on thermal tolerances, we conducted a within-latitude comparative test of CVH predictions for army ants (Dorylinae) at multiple scales: across elevations, in seasonal versus aseasonal forests, and in subterranean versus surface microhabitats...
September 2018: American Naturalist
Amy Waananen, Gretel Kiefer, Jennifer L Ison, Stuart Wagenius
The timing and synchrony of mating activity in a population may vary both within and among years. With the exception of masting species, in which reproductive activity fluctuates dramatically among years, mating synchrony is typically studied within years. However, opportunities to mate also vary among years in nonmasting iteroparous species. We demonstrate that studying only within-year flowering synchrony fails to accurately quantify variation in mating opportunity in an experimental population ([Formula: see text]) of a nonmasting species, Echinacea angustifolia...
September 2018: American Naturalist
Kayce C Bell, John R Demboski, Joseph A Cook
Parasitism is a common symbiotic interaction across diverse natural systems. Using a comparative evolutionary approach, we investigated the contributions of both host phylogeny and abiotic factors toward diversification of phylogenetically independent endoparasites that inhabit essentially the same physical space. We tested for host-parasite and parasite-parasite phylogenetic concordance in western North American chipmunks (Rodentia: Sciuridae) and two distantly related species of pinworms (Nematoda: Oxyurida)...
September 2018: American Naturalist
Elliot G Aguilar, Erol Akçay
Many physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems and their interaction in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive...
September 2018: American Naturalist
Erik R Hanschen, Matthew D Herron, John J Wiens, Hisayoshi Nozaki, Richard E Michod
From the male peacock's tail plumage to the floral displays of flowering plants, traits related to sexual reproduction are often complex and exaggerated. Why has sexual reproduction become so complicated? Why have such exaggerated sexual traits evolved? Early work posited a connection between multicellularity and sexual traits such as anisogamy (i.e., the evolution of small sperm and large eggs). Anisogamy then drives the evolution of other forms of sexual dimorphism. Yet the relationship between multicellularity and the evolution of sexual traits has not been empirically tested...
September 2018: American Naturalist
James C Mouton, Thomas E Martin
Interspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet tests of such possibilities are lacking. Cavity-nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but across 19 years of study we found that they commonly aggregate by sharing nest trees...
September 2018: American Naturalist
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