TMPRSS2-mediated SARS-CoV-2 uptake boosts innate immune activation, enhances cytopathology, and drives convergent virus evolution.

The accessory protease transmembrane protease serine 2 (TMPRSS2) enhances severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uptake into ACE2-expressing cells, although how increased entry impacts downstream viral and host processes remains unclear. To investigate this in more detail, we performed infection assays in engineered cells promoting ACE2-mediated entry with and without TMPRSS2 coexpression. Electron microscopy and inhibitor experiments indicated TMPRSS2-mediated cell entry was associated with increased virion internalization into endosomes, and partially dependent upon clathrin-mediated endocytosis. TMPRSS2 increased panvariant uptake efficiency and enhanced early rates of virus replication, transcription, and secretion, with variant-specific profiles observed. On the host side, transcriptional profiling confirmed the magnitude of infection-induced antiviral and proinflammatory responses were linked to uptake efficiency, with TMPRSS2-assisted entry boosting early antiviral responses. In addition, TMPRSS2-enhanced infections increased rates of cytopathology, apoptosis, and necrosis and modulated virus secretion kinetics in a variant-specific manner. On the virus side, convergent signatures of cell-uptake-dependent innate immune induction were recorded in viral genomes, manifesting as switches in dominant coupled Nsp3 residues whose frequencies were correlated to the magnitude of the cellular response to infection. Experimentally, we demonstrated that selected Nsp3 mutations conferred enhanced interferon antagonism. More broadly, we show that TMPRSS2 orthologues from evolutionarily diverse mammals facilitate panvariant enhancement of cell uptake. In summary, our study uncovers previously unreported associations, linking cell entry efficiency to innate immune activation kinetics, cell death rates, virus secretion dynamics, and convergent selection of viral mutations. These data expand our understanding of TMPRSS2's role in the SARS-CoV-2 life cycle and confirm its broader significance in zoonotic reservoirs and animal models.

The role of tropical rainfall in driving range dynamics for a long-distance migratory bird.

Predicting how the range dynamics of migratory species will respond to climate change requires a mechanistic understanding of the factors that operate across the annual cycle to control the distribution and abundance of a species. Here, we use multiple lines of evidence to reveal that environmental conditions during the nonbreeding season influence range dynamics across the life cycle of a migratory songbird, the American redstart (Setophaga ruticilla). Using long-term data from the nonbreeding grounds and breeding origins estimated from stable hydrogen isotopes in tail feathers, we found that the relationship between annual survival and migration distance is mediated by precipitation, but only during dry years. A long-term drying trend throughout the Caribbean is associated with higher mortality for individuals from the northern portion of the species' breeding range, resulting in an approximate 500 km southward shift in breeding origins of this Jamaican population over the past 30 y. This shift in connectivity is mirrored by changes in the redstart's breeding distribution and abundance. These results demonstrate that the climatic effects on demographic processes originating during the tropical nonbreeding season are actively shaping range dynamics in a migratory bird.

Density-dependent species interactions modulate alpine treeline shifts.

Species interactions such as facilitation and competition play a crucial role in driving species range shifts. However, density dependence as a key feature of these processes has received little attention in both empirical and modelling studies. Herein, we used a novel, individual-based treeline model informed by rich in situ observations to quantify the contribution of density-dependent species interactions to alpine treeline dynamics, an iconic biome boundary recognized as an indicator of global warming. We found that competition and facilitation dominate in dense versus sparse vegetation scenarios respectively. The optimal balance between these two effects was identified at an intermediate vegetation thickness where the treeline elevation was the highest. Furthermore, treeline shift rates decreased sharply with vegetation thickness and the associated transition from positive to negative species interactions. We thus postulate that vegetation density must be considered when modelling species range dynamics to avoid inadequate predictions of its responses to climate warming.

Bringing traits back into the equation: A roadmap to understand species redistribution.

Ecological and evolutionary theories have proposed that species traits should be important in mediating species responses to contemporary climate change; yet, empirical evidence has so far provided mixed evidence for the role of behavioral, life history, or ecological characteristics in facilitating or hindering species range shifts. As such, the utility of trait-based approaches to predict species redistribution under climate change has been called into question. We develop the perspective, supported by evidence, that trait variation, if used carefully can have high potential utility, but that past analyses have in many cases failed to identify an explanatory value for traits by not fully embracing the complexity of species range shifts. First, we discuss the relevant theory linking species traits to range shift processes at the leading (expansion) and trailing (contraction) edges of species distributions and highlight the need to clarify the mechanistic basis of trait-based approaches. Second, we provide a brief overview of range shift-trait studies and identify new opportunities for trait integration that consider range-specific processes and intraspecific variability. Third, we explore the circumstances under which environmental and biotic context dependencies are likely to affect our ability to identify the contribution of species traits to range shift processes. Finally, we propose that revealing the role of traits in shaping species redistribution may likely require accounting for methodological variation arising from the range shift estimation process as well as addressing existing functional, geographical, and phylogenetic biases. We provide a series of considerations for more effectively integrating traits as well as extrinsic and methodological factors into species redistribution research. Together, these analytical approaches promise stronger mechanistic and predictive understanding that can help society mitigate and adapt to the effects of climate change on biodiversity.

Limits to species' range: the tension between local and global adaptation.

We know that heritable variation is abundant, and that selection causes all but the smallest populations to rapidly shift beyond their original trait distribution. So then, what limits the range of a species? There are physical constraints and also population genetic limits to the effectiveness of selection, ultimately set by population size. Global adaptation, where the same genotype is favoured over the whole range, is most efficient when based on a multitude of weakly selected alleles and is effective even when local demes are small, provided that there is some gene flow. In contrast, local adaptation is sensitive to gene flow and may require alleles with substantial effect. How can populations combine the advantages of large effective size with the ability to specialise into local niches? To what extent does reproductive isolation help resolve this tension? I address these questions using eco-evolutionary models of polygenic adaptation, contrasting discrete demes with continuousspace.

Population decline of the saguaro cactus throughout its distribution is associated with climate change.

BACKGROUND AND AIMS: Climate change is a global phenomenon species are experiencing, which in arid regions will translate into more frequent and intense drought. The Sonoran Desert is becoming hotter and drier, and many organisms are rapidly changing in abundance and distribution. These population attributes directly depend on the dynamics of the population, which in turn depends on the vital rates of its individuals; yet few studies have documented the effects of climate change on the population dynamics of keystone species such as the saguaro cactus (Carnegiea gigantea). Although saguaros have traits that enable them to withstand present environmental conditions, climate change could make them vulnerable if forced beyond their tolerance limits. METHODS: We evaluated the effect of climate change on 13 saguaro populations spanning most of the species' distribution range. Using field data from 2014 to 2016, we built an integral projection model (IPM) describing the environmentally-explicit dynamics of the populations. We used this IPM, along with projections of two climate change and one no-change scenarios, to predict population sizes (N) and growth rates (λ) from 2017 to 2099 and compared these scenarios to demonstrate the effect of climate change on saguaro's future. KEY RESULTS: We found that all populations will decline, mainly due to future increases in drought, mostly hindering recruitment. However, the decline will be differential across populations, since those located near the coast will be affected by harsher drought events than those located further inland. CONCLUSIONS: Our study demonstrates that climate change and its associated increase in drought pose a significant threat to the saguaro cactus populations in the Sonoran Desert. Our findings indicate that the recruitment of saguaros, vital for establishing new individuals, is particularly vulnerable to intensifying drought conditions. Importantly, regional climate trends will have different impacts on saguaro populations across their distribution range.

Dependence of Europe's most threatened mammals on movement to adapt to climate change.

Current rates of climate change and gloomy climate projections confront managers and conservation planners with the need to integrate climate change into already complex decision-making processes. Predicting and prioritizing climatically stable areas and the areas likely to facilitate adaptive species' range adjustments are important stages in maximizing conservation outcomes and rationalizing future land management. I determined, for the most threatened European terrestrial mammal species, the spatial adaptive trajectories (SATs) of highest expected persistence up to 2080. I devised simple spatial network indices for evaluation of species in those SATs: total persistence; proportion of SATs that offer in situ adaptation (i.e., stable refugia); number of SATs converging in a site; and relationship between SAT convergence and persistence and protected areas, the Natura 2000 and Emerald networks, and areas of low human disturbance. I compared the performance of high-persistence SATs with a scenario in which each species remained in the areas with the best climatic conditions in the baseline period. The 1000 most persistence SATs for each of the 39 species covered one fifth of Europe. The areas with the largest adaptive potential (i.e., high persistence, stability, and SAT convergence) did not always overlap for all the species. Predominantly, these regions were located in southwestern Europe, Central Europe, and Scandinavia, with some occurrences in Eastern Europe. For most species, persistence in the most climatically suitable areas during the baseline period was lower than within SATs, underscoring their reliance on adaptive movements. Importantly, conservation areas (particularly protected areas) covered only minor fractions of species persistence among SATs, and hubs of spatial climate adaptation (i.e., areas of high SAT convergence) were seriously underrepresented in most conservation areas. These results highlight the need to perform analyses on spatial species' dynamics under climate change.

Los mamíferos más amenazados de Europa y su dependencia del movimiento para adaptarse al cambio climático Resumen La tasa actual del cambio climático y las proyecciones climáticas pesimistas confrontan a los gestores y a los planeadores de la conservación con la necesidad de integrar este cambio a la ya de por sí compleja toma de decisiones. La predicción y priorización de áreas con estabilidad climática y áreas con probabilidad de facilitarles ajustes adaptativos de distribución a las especies son etapas importantes para maximizar los resultados de conservación y racionalizar la gestión futura de las tierras. Determiné las trayectorias espaciales adaptativas (TEA) para la mayoría de los mamíferos terrestres más amenazados de Europa con la persistencia esperada más alta hasta el 2080. Diseñé los siguientes índices de redes espaciales simples para la evaluación de especies en aquellas TEA: persistencia total, proporción de TEA que brindan adaptación in situ (refugios estables), número de TEA que convergen en un sitio y relación entre la convergencia de TEA y la persistencia con las áreas protegidas, las redes Natura 2000 y Emerald y las áreas de poca perturbación humana. Comparé el desempeño de las TEA de gran persistencia con un escenario en el que las especies permanecían dentro de las áreas con las mejores condiciones climáticas en el periodo de línea base. Las mil TEA más persistentes para cada una de las 39 especies cubrieron la quinta parte de Europa. Las áreas con el mayor potencial adaptativo (es decir, gran persistencia, estabilidad y convergencia de TEA) no siempre se traslaparon para todas las especies. Estas regiones predominaron en el suroeste de Europa, Europa Central y Escandinavia, con algunas ocurrencias en el este de Europa. Para la mayoría de las especies, la persistencia de las áreas con el mejor clima posible durante el periodo de línea base fue menor que dentro de las TEA, lo que resalta su dependencia por los movimientos adaptativos. Destaca que las áreas de conservación (en particular las áreas protegidas) cubrieron sólo pequeñas fracciones de la persistencia de las especies entre las TEA y los núcleos de adaptación climática (es decir, las áreas de gran convergencia de TEA) contaban con muy poca representación dentro de la mayoría de las áreas de conservación. Estos resultados enfatizan la necesidad de realizar análisis de las dinámicas espaciales de las especies bajo el cambio climático.

Speciation of rock-dwelling snail species: Disjunct ranges and mosaic patterns reveal the importance of long-distance dispersal in Chilostoma (Cingulifera) in the European Southern Alps.

To better understand the origin of the high diversity and endemism in the Southern Alps of Europe, we investigated the phylogeny and population structure of the rock-dwelling snail group Chilostoma (Cingulifera) in the Southern Alps. We generated genomic ddRAD data and mitochondrial sequences of 104 Cingulifera specimens from 28 populations and 14 other Ariantinae. Until recently, about 30 Cingulifera taxa were classified as subspecies of a single polytypic species. The phylogenetic and population genetic analyses of the ddRAD data and mitochondrial sequences revealed that Cingulifera in the Southern Alps is differentiated into three species. Each of the three Chilostoma (Cingulifera) species occupies disjunct sub-areas, which are separated by areas occupied by other Chilostoma taxa. Neighbouring populations of different species show little or no admixture. Tests indicating that the genetic differentiation of the three Cingulifera taxa cannot be explained by isolation by distance confirmed their species status. The disjunct range patterns demonstrate the importance of stochastic events such as passive long-distance dispersal for the evolution of population structure and speciation in these snails, and of priority effects and ecological competition as important factors influencing species distributions.

Protected areas not likely to serve as steppingstones for species undergoing climate-induced range shifts.

Species across the planet are shifting their ranges to track suitable climate conditions in response to climate change. Given that protected areas have higher quality habitat and often harbor higher levels of biodiversity compared to unprotected lands, it is often assumed that protected areas can serve as steppingstones for species undergoing climate-induced range shifts. However, there are several factors that may impede successful range shifts among protected areas, including the distance that must be traveled, unfavorable human land uses and climate conditions along potential movement routes, and lack of analogous climates. Through a species-agnostic lens, we evaluate these factors across the global terrestrial protected area network as measures of climate connectivity, which is defined as the ability of a landscape to facilitate or impede climate-induced movement. We found that over half of protected land area and two-thirds of the number of protected units across the globe are at risk of climate connectivity failure, casting doubt on whether many species can successfully undergo climate-induced range shifts among protected areas. Consequently, protected areas are unlikely to serve as steppingstones for a large number of species under a warming climate. As species disappear from protected areas without commensurate immigration of species suited to the emerging climate (due to climate connectivity failure), many protected areas may be left with a depauperate suite of species under climate change. Our findings are highly relevant given recent pledges to conserve 30% of the planet by 2030 (30 × 30), underscore the need for innovative land management strategies that allow for species range shifts, and suggest that assisted colonization may be necessary to promote species that are adapted to the emerging climate.

Range expansions of sexual versus asexual organisms: Effects of reproductive assurance and migration load.

It is generally considered that sexual organisms show faster evolutionary adaptation than asexual organisms because sexuals can accumulate adaptive mutations through recombination. Yet, empirical evidence often shows that the geographic range size of sexual species is narrower than that of closely related asexual species, which may seem as if asexuals can adapt to more varied environments. Two potential explanations for this apparent contradiction considered by the existing theory are reproduction assurance and migration load. Here, we consider both reproductive assurance and migration load within a single model to comparatively examine their effects on range expansions of sexuals and asexuals across an environmental gradient. The model shows that higher dispersal propensity decreases sexuals' disadvantage in reproductive assurance while increasing their disadvantage in migration load. Moreover, lower mutation rate constrains adaptation more strongly in asexuals than in sexuals. Thus, high dispersal propensity and high mutation rates promote that asexuals have wider range sizes than sexuals. Intriguingly, our model reveals that sexuals can have wider geographic range sizes than asexuals under low dispersal propensity and low mutation rates, a pattern consistent with a few exceptional empirical cases. Combining reproductive assurance and migration load provides a useful perspective to better understand the relationships between species' mating systems and their geographic ranges.

Region-wide retreats from lower elevations of range-restricted birds across the Northern Andes.

Local studies show upslope shifts in the distribution of tropical birds in response to warming temperatures. Unanswered is whether these upward shifts occur regionally across many species. We considered a nearly 2000-km length of the Northern Andes, where deforestation, temperature, and extreme weather events have increased during the past decades. Range-restricted bird species are particularly vulnerable to such events and occur in exceptionally high numbers in this region. Using abundant crowd-sourced data from the Cornell Lab of Ornithology database, eBird, and the Global Biodiversity Information Facility, we documented distributions of nearly 200 such species. We examined whether species shifted their elevational ranges over time by comparing observed versus expected occurrences below a low elevational threshold and above a high elevational threshold for 2 periods: before and after 2005. We predicted fewer observations at lower elevations (those below the threshold) and more at upper elevations (those above the threshold) after 2005. We also tested for deforestation effects at lower elevations within each species' distribution ranges. We compared relative forest loss with the differences between observed and expected occurrences across the elevational range. Species' retreats from lower elevations were ubiquitous and involved a 23-40% decline in prevalence at the lowest elevations. Increases at higher elevations were not consistent. The retreats occurred across a broad spectrum of species, from predominantly lowland to predominantly highland. Because deforestation showed no relationship with species retreats, we contend that a warming climate is the most parsimonious explanation for such shifts.

Repliegues regionales desde elevaciones más bajas de aves de distribución restringida en los Andes septentrionales Resumen Los estudios locales muestran cambios en la distribución altitudinal de las aves tropicales como respuesta al aumento de la temperatura. No sabemos si estos cambios suceden en muchas especies a nivel regional. Consideramos casi 2000 km de los Andes septentrionales, en donde la deforestación y los eventos climáticos extremos han incrementado en las últimas décadas. Las aves con distribución restringida son particularmente vulnerables a dichos eventos y su presencia es numerosa en esta región. Usamos datos abundantes de origen colectivo tomados de la base de datos del Laboratorio de Ornitología de Cornell, eBird y el Sistema Global de Información sobre Biodiversidad para documentar la distribución de aproximadamente 200 de estas especies. Analizamos si las especies cambiaron su distribución altitudinal con el tiempo al comparar entre la presencia observada y la esperada bajo un umbral de elevación reducida y por encima de un umbral de elevación alta durante dos periodos: antes y después de 2005. Pronosticamos una cantidad menor de observaciones por debajo del umbral y una mayor cantidad por encima del umbral para después de 2005. También analizamos los efectos de la deforestación en elevaciones más bajas dentro de los rangos de distribución de las especies y comparamos la pérdida relativa del bosque con las diferencias entre la presencia observada y la esperada en todo el rango altitudinal. El repliegue de las especies a partir de las elevaciones más bajas fue ubicuo e involucró una declinación del 23-40% de la prevalencia en las elevaciones más bajas. Los incrementos en las elevaciones más altas no fueron uniformes. Los repliegues ocurrieron a lo largo de un espectro amplio de especies, desde las que predominan en las tierras bajas hasta las que predominan en las tierras altas. Ya que la deforestación no se relacionó con el repliegue, sostenemos que un clima más cálido es la explicación más parsimoniosa para estos cambios.

Projected climate change impacts on the phylogenetic diversity of the world's terrestrial birds: more than species numbers.

Ongoing climate change is a major threat to biodiversity. As abiotic tolerances and dispersal abilities vary, species-specific responses have the potential to further amplify or ameliorate the ensuing impacts on species assemblages. Here, we investigate the effects of climate change on species distributions across non-marine birds, quantifying its projected impact on species richness (SR) as well as on different aspects of phylogenetic diversity globally. Going beyond previous work, we disentangle the potential impacts of species gains versus losses on assemblage-level phylogenetic diversity under climate change and compare the projected impacts to randomized assemblage changes. We show that beyond its effects on SR, climate change could have profound impacts on assemblage-level phylogenetic diversity and composition, which differ significantly from random changes and among regions. Though marked species losses are most frequent in tropical and subtropical areas in our projections, phylogenetic restructuring of species communities is likely to occur all across the globe. Furthermore, our results indicate that the most severe changes to the phylogenetic diversity of local assemblages are likely to be caused by species range shifts and local species gains rather than range reductions and extinctions. Our findings highlight the importance of considering diverse measures in climate impact assessments.

Increasing temporal variance leads to stable species range limits.

What prevents populations of a species from adapting to the novel environments outside the species' geographic distribution? Previous models highlighted how gene flow across spatial environmental gradients determines species expansion versus extinction and the location of species range limits. However, space is only one of two axes of environmental variation-environments also vary in time, and we know temporal environmental variation has important consequences for population demography and evolution. We used analytical and individual-based evolutionary models to explore how temporal variation in environmental conditions influences the spread of populations across a spatial environmental gradient. We find that temporal variation greatly alters our predictions for range dynamics compared to temporally static environments. When temporal variance is equal across the landscape, the fate of species (expansion versus extinction) is determined by the interaction between the degree of temporal autocorrelation in environmental fluctuations and the steepness of the spatial environmental gradient. When the magnitude of temporal variance changes across the landscape, stable range limits form where this variance increases maladaptation sufficiently to prevent local persistence. These results illustrate the pivotal influence of temporal variation on the likelihood of populations colonizing novel habitats and the location of species range limits.

Hybrid breakdown is elevated near the historical cores of a species' range.

New species form when they become reproductively isolated. A classic model of speciation posits that derived mutations appear in isolated populations and reduce fitness when combined in hybrids. While these Bateson-Dobzhansky-Muller incompatibilities are known to accumulate as populations diverge over time, they may also reflect the amount of standing genetic variation within populations. We analysed the fitness of F2 hybrids in crosses between 24 populations of a plant species (Campanula americana) with broad variation in standing genetic variation and genetic differentiation driven by post-glacial range expansions. Hybrid breakdown varied substantially and was strongest between populations near the historical cores of the species range where within-population genetic diversity was high. Nearly half of the variation in hybrid breakdown was predicted by the combined effects of standing genetic variation within populations, their pairwise genetic differentiation and differences in the climates they inhabit. Hybrid breakdown was enhanced between populations inhabiting distinct climates, likely reflecting local adaptation. Results support that the mutations causing hybrid breakdown, the raw material for speciation, are more common in long-inhabited areas of the species range. Genetic diversity harboured in refugial areas is thus an important source of incompatibilities critical to the speciation process.

Not all species will migrate poleward as the climate warms: The case of the seven baobab species in Madagascar.

It is commonly accepted that species should move toward higher elevations and latitudes to track shifting isotherms as climate warms. However, temperature might not be the only limiting factor determining species distribution. Species might move to opposite directions to track changes in other climatic variables. Here, we used an extensive occurrence data set and an ensemble modelling approach to model the climatic niche and to predict the distribution of the seven baobab species (genus Adansonia) present in Madagascar. Using climatic projections from three global circulation models, we predicted species' future distribution and extinction risk for 2055 and 2085 under two representative concentration pathways (RCPs) and two dispersal scenarios. We disentangled the role of each climatic variable in explaining species range shift looking at relative variable importance and future climatic anomalies. Four baobab species (Adansonia rubrostipa, Adansonia madagascariensis, Adansonia perrieri¸ and Adansonia suarezensis) could experience a severe range contraction in the future (>70% for year 2085 under RCP 8.5, assuming a zero-dispersal hypothesis). For three out of the four threatened species, range contraction was mainly explained by an increase in temperature seasonality, especially in the North of Madagascar, where they are currently distributed. In tropical regions, where species are commonly adapted to low seasonality, we found that temperature seasonality will generally increase. It is, thus, very likely that many species in the tropics will be forced to move equatorward to avoid an increase in temperature seasonality. Yet, several ecological (e.g., equatorial limit, or unsuitable deforested habitat) or geographical barriers (absence of lands) could prevent species to move equatorward, thus increasing the extinction risk of many tropical species, like endemic baobab species in Madagascar.

Discriminating climate, land-cover and random effects on species range dynamics.

Species are reportedly shifting their distributions poleward and upward in several parts of the world in response to climate change. The extent to which other factors might play a role driving these changes is still unclear. Land-cover change is a major cause of distributional changes, but it cannot be discarded that distributional dynamics might be at times caused by other mechanisms (e.g. dispersal, ecological drift). Using observed changes in the distribution of 82 breeding birds in Great Britain between three time periods 1968-72 (t1 ), 1988-91 (t2 ) and 2007-2011 (t3 ), we examine whether observed bird range shifts between t1 -t2 and t1 -t3 are best explained by climate change or land-cover change, or whether they are not distinguishable from what would be expected by chance. We found that range shifts across the rear edge of northerly distributed species in Great Britain are best explained by climate change, while shifts across the leading edge of southerly distributed species are best explained by changes in land-cover. In contrast, at the northern and southern edges of Great Britain, range dynamics could not be distinguished from that expected by chance. The latter observation could be a consequence of boundary effects limiting the direction and magnitude of range changes, stochastic demographic mechanisms neither associated with climate nor land-cover change or with complex interactions among factors. Our results reinforce the view that comprehensive assessments of climate change effects on species range shifts need to examine alternative drivers of change on equal footing and that null models can help assess whether observed patterns could have arisen by chance alone.

Drivers of distributions and niches of North American cold-adapted amphibians: evaluating both climate and land use.

Species distribution estimates are often used to understand the niche of a species; however, these are often based solely on climatic predictors. When the influences of biotic factors are ignored, erroneous inferences about range and niche may be made. We aimed to integrate climate data with a unique set of available land cover and land use data for the six cold-adapted amphibians of North America (Ambystoma macrodactylum, Anaxyrus hemiophrys, Anaxyrus boreas, Pseudacris maculata, Rana sylvatica, Rana luteiventris) to determine the relative importance of climate and non-climate drivers through the use of ecological niche models for present-day range estimates. We compared climate-only, land use-only, and combination models of climate and land use, derived from two different model selection techniques, to determine which was most likely to drive current distributions of cold-adapted amphibian species. Land use layers included land cover type, human population, vegetation type, ecoregion, and the overall human footprint. The most supported models included both climate and land use, with climate and human footprint variables having the highest permutation importance and percent contribution. Models that incorporated climate and land use data performed best as measured with AIC and AUC, although qualitatively most underestimated the northern range edge, implying potential sampling bias or locations of reduced habitat quality for these species in the northern area of the ranges. There were small differences in overall combination models dependent on the method of model selection. The overall effect sizes of landscape factors within the combination models were small except for one landscape feature: human footprint, which incorporated multiple aspects of anthropogenic change on the landscape, including human population density, travel access, and agricultural impact. This aspect of the landscape was just as important as climate, and counter to what we expected, the association was mostly positive, with a negative response only occurring at very high levels. This highlights the importance of moving beyond climate only species range estimates as land cover, specifically human impact, may be driving the patterns of species' ranges.

Life in the margins: host-parasite relationships in ecological edges.

Transitional zones, such as edge habitat, are key landscapes for investigating biodiversity. "Soft edges" are permeable corridors that hosts can cross, while "hard edges" are impermeable borders that hosts cannot pass. Although pathogen transmission in the context of edges is vital to species conservation, drivers of host-parasite relationships in ecological edges remain poorly understood. Thus, we defined a framework for testing hypotheses of host-parasite interactions in hard and soft edges by (1) characterizing hard and soft edges from both the host and parasite perspectives, (2) predicting the types of parasites that would be successful in each type of edge, and (3) applying our framework to species invasion fronts as an example of host-parasite relationships in a soft edge. Generally, we posited that parasites in soft edges are more likely to be negatively affected by habitat fragmentation than their hosts because they occupy higher trophic levels but parasite transmission would benefit from increased host connectivity. Parasites along hard edges, however, are at higher risk of local extinction due to host population perturbations with limited opportunity for parasite recolonization. We then used these characteristics to predict functional traits that would lead to parasite success along soft and hard edges. Finally, we applied our framework to invasive species fronts to highlight predictions regarding host connectivity and parasite traits in soft edges. We anticipate that our work will promote a more complete discussion of habitat connectivity using a common framework and stimulate empirical research into host-parasite relationships within ecological edges and transitional zones.

Intra-Annual Variability in Responses of a Canopy Forming Kelp to Cumulative Low Tide Heat Stress: Implications for Populations at the Trailing Range Edge.

Anthropogenic climate change is driving the redistribution of species at a global scale. For marine species, populations at trailing edges often live very close to their upper thermal limits and, as such, poleward range contractions are one of the most pervasive effects of ongoing and predicted warming. However, the mechanics of processes driving such contractions are poorly understood. Here, we examined the response of the habitat forming kelp, Laminaria digitata, to realistic terrestrial heatwave simulations akin to those experienced by intertidal populations persisting at the trailing range edge in the northeast Atlantic (SW England). We conducted experiments in both spring and autumn to determine temporal variability in the effects of heatwaves. In spring, heatwave scenarios caused minimal stress to L. digitata but in autumn all scenarios tested resulted in tissue being nonviable by the end of each assay. The effects of heatwave scenarios were only apparent after consecutive exposures, indicating erosion of resilience over time. Monthly field surveys corroborated experimental evidence as the prevalence of bleaching (an indication of physiological stress and tissue damage) in natural populations was greatest in autumn and early winter. Overall, our data showed that L. digitata populations in SW England persist close to their upper physiological limits for emersion stress in autumn. As the intensity of extreme warming events is likely to increase with anthropogenic climate change, thermal conditions experienced during periods of emersion will soon exceed physiological thresholds and will likely induce widespread mortality and consequent changes at the population level.

Climate change impacts on mismatches between phytoplankton blooms and fish spawning phenology.

Substantial interannual variability in marine fish recruitment (i.e., the number of young fish entering a fishery each year) has been hypothesized to be related to whether the timing of fish spawning matches that of seasonal plankton blooms. Environmental processes that control the phenology of blooms, such as stratification, may differ from those that influence fish spawning, such as temperature-linked reproductive maturation. These different controlling mechanisms could cause the timing of these events to diverge under climate change with negative consequences for fisheries. We use an earth system model to examine the impact of a high-emissions, climate-warming scenario (RCP8.5) on the future spawning time of two classes of temperate, epipelagic fishes: "geographic spawners" whose spawning grounds are defined by fixed geographic features (e.g., rivers, estuaries, reefs) and "environmental spawners" whose spawning grounds move responding to variations in environmental properties, such as temperature. By the century's end, our results indicate that projections of increased stratification cause spring and summer phytoplankton blooms to start 16 days earlier on average (±0.05 days SE) at latitudes >40°N. The temperature-linked phenology of geographic spawners changes at a rate twice as fast as phytoplankton, causing these fishes to spawn before the bloom starts across >85% of this region. "Extreme events," defined here as seasonal mismatches >30 days that could lead to fish recruitment failure, increase 10-fold for geographic spawners in many areas under the RCP8.5 scenario. Mismatches between environmental spawners and phytoplankton were smaller and less widespread, although sizable mismatches still emerged in some regions. This indicates that range shifts undertaken by environmental spawners may increase the resiliency of fishes to climate change impacts associated with phenological mismatches, potentially buffering against declines in larval fish survival, recruitment, and fisheries. Our model results are supported by empirical evidence from ecosystems with multidecadal observations of both fish and phytoplankton phenology.