American Naturalist最新文献

AbstractBird species with high demand for efficient flight (e.g., migrants) tend to have more pointed wing tips than sedentary birds, and indices describing wing tip pointedness, such as the hand-wing index (HWI), are often used as proxies for dispersal propensity in comparative studies. Wing pointedness also varies among closely related populations of the same species that experience different selection pressures on flight, but we know surprisingly little about how variation in bone versus feather lengths contributes to wing pointedness. Here, we compare wing tip shape (HWI) of migratory versus sedentary populations of a widespread songbird, the Yellow Warbler (Setophaga petechia), to deconstruct variation in the individual skeletal and feather components of the hand-wing. Our results reveal that the relatively pointed wing shape of migrants is a consequence of shorter secondary feathers (i.e., a narrower wing) compared with nonmigrants, rather than longer wings. Indeed, despite having more pointed wings, migratory populations have similar wing length (i.e., wing chord) as sedentary continental populations. These populations show similar trunk size, but migrants have significantly shorter limb bones. Our results reveal the morphological underpinnings of a wing shape metric that has been widely used in macroevolutionary and macroecological studies of avian dispersal.

AbstractThe last 30 years have seen major advances in our understanding of the evolution of cooperation-traits that have evolved because of the benefit they provide other individuals. In contrast, we have been much less successful in determining the consequences of cooperation for long-term ecological and evolutionary change. Studies of birds, insects, and bacteria suggest that cooperation has major consequences for fundamental features of life, such as ecological niche range, genetic variation within species, and rates of species diversification. However, the role of cooperation in driving these changes is largely limited to hypotheses, as we lack both data and a general theoretical framework. We synthesize the progress that has been made and highlight the major gaps in our understanding for future study.

AbstractOptimal egg size is considered a classic and important concept in life history theory. Here, we used comparative analyses to investigate the ecological factors affecting egg size across 87 Lake Tanganyikan cichlid species, which employ either a mouth-brooding or a substrate-brooding strategy to raise their offspring. These two strategies differ substantially in resource availability, potentially leading to different selective regimes on egg size. We observed a strong negative correlation between egg size and egg number (clutch size) in mouth-brooding species but not in substrate-brooding cichlids. Our results suggest that the strength of the relationship between egg size and number differs between the two brooding strategies. Interestingly, in mouth-brooding species, we found that egg size increases when offspring exhibit external feeding behaviors (i.e., grazing behavior). We also demonstrate that substrate-brooding species that have relatively short periods of parental care typically have larger eggs compared with species with longer periods of parental care. Overall, our results demonstrate that behavioral and ecological differences, including parental care strategy and duration, play an important but often overlooked role in the evolution of egg size across species.

AbstractGlobal warming is reducing food availability in many aquatic systems, raising questions about the combined effects of higher temperatures and lower food availability on fish life histories. In ectotherms, higher temperatures accelerate growth and promote an earlier onset of reproduction. However, when fish have less food during development, resource depletion might constrain these temperature-driven processes. We investigated how water temperature (24°C or 28°C) and early-life food availability (control or restricted) affected adult life history traits in female guppies (Poecilia reticulata). There was no significant interaction between temperature and food availability affecting adult traits, nor was there an independent effect of food availability. Instead, higher temperature alone affected female life histories. Females at 28°C were larger in early adulthood but then grew more slowly and produced fewer, smaller offspring than females at 24°C. The effect of temperature on reproduction persisted after controlling for female size, suggesting a shift in the fecundity-female size relationship. Adult mortality was greater at 28°C. Higher temperatures also resulted in a longer gut but did not affect immunity or telomere length of the surviving females. Our results suggest that tropical fish may be vulnerable to increased temperatures but resilient to brief periods of early-life food limitation.

AbstractLife has evolved different strategies to take advantage of seasonal changes in the environment that are emblematic of boreal and arctic biomes. However, ecological theories often ignore seasonal changes for tractability or simplicity. Understanding the effect of seasonality may prove crucial as the changing climate puts more pressure on ecosystems. Hybrid dynamical models are an efficient way to represent seasonal adaptations where switches in food web compositions account for species migrations and predator movements. We use the highly seasonal and cyclic dynamics of an Arctic food web to showcase the utility of hybrid models. The simplified representation of community dynamics provided by the hybrid framework eases the study of conditions leading to lemming cycles and facilitates parameterization with empirical data. We corroborate that seasonal switches, accounting for the onset of reproduction of resident predators and the migration of mobile predators, likely drive cyclic fluctuations in lemming abundance. Our empirical investigation reveals that each predator alone does not reduce lemming growth rate enough to generate population cycles, which reinforces the idea that the predator community as a whole is responsible for the cyclic dynamics. This situation arises because each predator has unique adaptations to seasonality and impacts the dynamics in different but complementary ways. Our results have implications for community ecology, as they show how hybrid models can help understand complex dynamics in highly seasonal ecosystems. This is especially relevant in the Arctic, considering that rapid warming has the potential to disrupt lemming population cycles and negatively affect their predators.

AbstractTipping point theory has garnered substantial attention over recent decades. It predicts abrupt and often irreversible transitions from one ecosystem state to an alternative state. However, ecosystem models that predict tipping typically neglect spatial dynamics. Recent studies reveal that incorporating spatial dynamics may enable ecosystems to evade tipping predicted by nonspatial models. Here, we use a dryland and a savanna-forest model to synthesize mechanisms by which spatial processes can alter the theory of tipping. We further propose that the underlying drivers of positive feedback leading to alternative stable states may provide insight into the tipping evasion mechanisms most relevant to a specific ecosystem. For instance, while positive feedbacks may arise in drylands from direct self-facilitation, such as enhancing the uptake of a limiting resource, at the savanna-forest boundary, it may arise from mutual inhibition between two ecosystem components. In the former case ecosystems can evade tipping by forming self-organized patterns, whereas in the latter the presence of environmental heterogeneity may be required. Our study highlights that deepening our understanding of how ecological feedbacks connect to tipping evasion mechanisms is crucial to formulate better strategies to increase ecosystem resilience.

AbstractAnthropogenic climate change is driving increases in temperature and droughts. Cooperative breeding, common in regions with greater environmental variation, has been proposed to buffer against such conditions, but findings across taxa are mixed. Life history strategies may partly explain these discrepancies, as long-lived species should invest less in reproduction. We examined how climatic, social, and life history factors affect reproduction in the long-lived cooperative southern ground-hornbill (Bucorvus leadbeateri). Using 17 years of data from 23 groups within the Greater Kruger National Park, South Africa, we tested for associations between temperature, rainfall and group composition, and several reproductive parameters. Low winter rainfall decreased breeding probability, while higher temperatures delayed laying and reduced nestling mass, regardless of group composition. Nestlings had longer tarsi in groups with more adults, and groups with more juveniles bred earlier and were more likely to breed, likely reflecting territory quality rather than group composition. In conclusion, hot and dry conditions negatively impacted ground-hornbill breeding, and, as expected given their life history, group composition did not mitigate these effects. We suggest that life history strategies and nonreproductive benefits of collective behavior, such as resource defense and survival, should be considered when assessing cooperative breeders' responses to environmental fluctuations.

AbstractMigration is the synchronized movement of a large part of a population from breeding grounds to nonbreeding grounds driven by seasonal variation of resources and avoidance of harsh winter conditions. Migration is a central component of many species' life histories, including birds, mammals, fishes, and invertebrates. However, the interplay of ecological and evolutionary drivers of migration has long intrigued biologists and remains contentious. Shorebirds represent a valuable group for testing multiple predictors of migration, as they demonstrate a range of morphological and ecological characteristics (e.g., wing shape and habitat breadth) and a large proportion of shorebird species migrate. Here we tested whether breeding site climate, wing shape, body mass, and number of habitats occupied can predict migration across 196 shorebird species using novel Bayesian regression modeling allowing explicit decomposition of trait correlations into both phylogenetic and nonphylogenetic components. Increasing climate seasonality and pointier wing shapes favoring dispersal appeared strongly associated with migration, matching our predictions and potentially reflecting resource availability optimization and the energetic costs of migration. Higher number of habitats occupied also appeared associated with migration, perhaps reflecting selection to decrease the specific habitat requirements of migration transits. The lack of a significant relationship for body mass may reflect conflicting selection pressures, as migration efficiency (energetics) increases with body size but migration duration (and time that can be spent at breeding sites) decreases.

AbstractIn recent decades, numerous observations have been made of evolution induced by anthropogenic change in natural populations. Evolution in response to harvest, climate change, pollution, landscape change, and introduced invasive species are common. Here, we provide evidence for evolution in a new context by documenting a large increase in the frequency of defensive pelvic spines in two unusual threespine stickleback (Gasterosteus aculeatus) populations previously shown to mostly lack such structures. These populations, in Parc national du Lac-Témiscouata, Québec, Canada, were historically free of predatory fish and consisted nearly entirely of pelvic-spineless stickleback. This phenotypic change coincided with the stocking of the lakes with brook trout (Salvelinus fontinalis), a stickleback predator, and the introductions of other species used by anglers as live bait. The rapid evolutionary change toward a more defensive morph in the populations should prompt increased caution regarding the effects of management practices on native species.

AbstractGenomic offset models are increasingly popular tools for identifying populations at risk of maladaptation under climate change. These models estimate the extent of genetic change required for populations to remain adapted under future climate change scenarios but face strong limitations and still lack broad empirical testing. Using 9,817 single-nucleotide polymorphisms (SNPs) genotyped in 454 trees from 34 populations of maritime pine, a species with a marked population genetic structure, we found substantial variability across genomic offset predictions from different methods, SNP sets, and general circulation models. Using five common gardens, we mostly found positive associations between genomic offset predictions and mortality, as expected. However, contrary to our expectations, we observed very few negative monotonic associations between genomic offset predictions and height. Higher mortality rates were also observed in national forest inventory plots with high genomic offset, but only for some methods and SNP sets. The differing genomic offset patterns produced by the best-validated methods across the maritime pine range hindered drawing definitive conclusions for the species. Our study demonstrates the imperative of employing different methods and validating genomic offset predictions with independent data sources before using them as reliable metrics to inform conservation or management.