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  1. Patchily distributed resources require individuals to balance risks and rewards associated with foraging sites that vary widely in quality, as determined by factors such as food availability, disturbance rates and predation risk. These trade‐offs may be especially acute for migratory species during the non‐breeding season when they must access high‐quality resources to recover from and prepare for migration. We assessed how density and body condition of non‐breeding Hudsonian GodwitsLimosa haemastica, acting as proxies for foraging site quality, were related to foraging success, availability of intertidal foraging habitat, landscape and bay characteristics, human disturbances and predation risk at 42 intertidal mudflats in southern Chile. Godwit density and body condition increased with availability of foraging habitat and foraging success, except on mudflats where individuals were more alert and agitated (i.e. higher scanning rates and more displacement flights). In contrast, body condition and density of foraging Godwits were lower at sites with high levels of perceived disturbance. Our findings suggest that the non‐lethal effects of disturbances (i.e. perceived risks) may affect behaviour (e.g. scanning rates and displacement flights) in ways that can compromise refuelling rates, body condition and performance across seasons. Thus, efforts to reduce disturbances to individuals foraging on tidal mudflats may be important to conserve migratory shorebirds, a guild undergoing severe population declines.

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  2. Sork, Victoria (Ed.)
    Abstract When species are continuously distributed across environmental gradients, the relative strength of selection and gene flow shape spatial patterns of genetic variation, potentially leading to variable levels of differentiation across loci. Determining whether adaptive genetic variation tends to be structured differently than neutral variation along environmental gradients is an open and important question in evolutionary genetics. We performed exome-wide population genomic analysis on deer mice sampled along an elevational gradient of nearly 4000 m of vertical relief. Using a combination of selection scans, genotype-environment associations, and geographic cline analyses, we found that a large proportion of the exome has experienced a history of altitude-related selection. Elevational clines for nearly 30% of these putatively adaptive loci were shifted significantly up- or down-slope of clines for loci that did not bear similar signatures of selection. Many of these selection targets can be plausibly linked to known phenotypic differences between highland and lowland deer mice, although the vast majority of these candidates have not been reported in other studies of highland taxa. Together, these results suggest new hypotheses about the genetic basis of physiological adaptation to high-altitude, and the spatial distribution of adaptive genetic variation along environmental gradients. 
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  3. Abstract

    Climate change has caused shifts in seasonally recurring biological events leading to the temporal decoupling of consumer–resource pairs, that is, phenological mismatching. Although mismatches often affect individual fitness, they do not invariably scale up to affect populations, making it difficult to assess the risk they pose. Individual variation may contribute to this inconsistency, with changes in resource availability and consumer needs leading mismatches to have different outcomes over time. Nevertheless, most models estimate a consumer's match from a single time point, potentially obscuring when mismatches matter to populations. We analyzed how the effects of mismatches varied over time by studying precocial Hudsonian godwit (Limosa haemastica) chicks and their invertebrate prey from 2009 to 2019. We developed individual‐ and population‐level models to determine how age‐specific variation affects the relationship between godwits and resource availability. We found that periods with abundant resources led to higher growth and survival of godwit chicks, but also that chick survival was increasingly related to the availability of larger prey as chicks aged. At the population level, estimates of mismatches using age‐structured consumer demand explained more variation in annual godwit fledging rates than more commonly used alternatives. Our study suggests that modeling the effects of mismatches as the disrupted interaction between dynamic consumer needs and resource availability clarifies when mismatches matter to both individuals and populations.

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  4. Abstract

    Events during one stage of the annual cycle can reversibly affect an individual's condition and performance not only within that stage, but also in subsequent stages (i.e. reversible state effects). Despite strong conceptual links, however, few studies have been able to empirically link individual‐level reversible state effects with larger‐scale demographic processes.

    We studied both survival and potential reversible state effects in a long‐distance migratory shorebird, the Hudsonian GodwitLimosa haemastica. Specifically, we estimated period‐specific survival probabilities across the annual cycle and examined the extent to which an individual's body condition, foraging success and habitat quality during the nonbreeding season affected its subsequent survival and reproductive performance.

    Godwit survival rates were high throughout the annual cycle, but lowest during the breeding season, only slightly higher during southbound migration and highest during the stationary nonbreeding season. Our results indicate that overwintering godwits foraging in high‐quality habitats had comparably better nutritional status and pre‐migratory body condition, which in turn improved their return rates and the likelihood that their nests and chicks survived during the subsequent breeding season.

    Reversible state effects thus appeared to link events between nonbreeding and breeding seasons via an individual's condition, in turn affecting their survival and subsequent reproductive performance. Our study thus provides one of the few empirical demonstrations of theoretical predictions that reversible state effects have the potential to influence population dynamics.

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  5. Abstract

    Elevations >2,000 m represent consistently harsh environments for small endotherms because of abiotic stressors such as cold temperatures and hypoxia.

    These environmental stressors may limit the ability of populations living at these elevations to respond to biotic selection pressures—such as parasites or pathogens—that in other environmental contexts would impose only minimal energetic‐ and fitness‐related costs.

    We studied deer mice (Peromyscus maniculatus rufinus) living along two elevational transects (2,300–4,400 m) in the Colorado Rockies and found that infection prevalence by botfly larvae (Cuterebridae) declined at higher elevations. We found no evidence of infections at elevations >2,400 m, but that 33.6% of all deer mice, and 52.2% of adults, were infected at elevations <2,400 m.

    Botfly infections were associated with reductions in haematocrit levels of 23%, haemoglobin concentrations of 27% and cold‐induced VO2maxmeasures of 19% compared to uninfected individuals. In turn, these reductions in aerobic performance appeared to influence fitness, as infected individuals exhibited 19‐34% lower daily survival rates.

    In contrast to studies at lower elevations, we found evidence indicating that botfly infections influence the aerobic capabilities and fitness of deer mice living at elevations between 2,000 and 2,400 m. Our results therefore suggest that the interaction between botflies and small rodents is likely highly context‐dependent and that, more generally, high‐elevation populations may be susceptible to additional biotic selection pressures.

    Aplain language summaryis available for this article.

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