High conservation importance of range-edge populations of Hooded Vultures (Necrosyrtes monachus).

Critically endangered Hooded Vultures (Necrosyrtes monachus Temminck, 1823), like many vulture species globally, are experiencing rapid population declines due to anthropogenic factors such as poisonings, human persecution, trading for belief-based use, and habitat loss/degradation. The Hooded Vulture is widespread across sub-Saharan Africa. Although it is considered one of the most abundant vultures in West Africa, this vulture species is less common in East and southern Africa, with the population at the southern-most edge of the distribution (in South Africa and Eswatini) estimated at only 100-200 mature individuals. The distribution of Hooded Vultures has contracted dramatically in southern Africa, with breeding populations largely confined to protected areas such as the Greater Kruger National Park. This study aimed to investigate the genetic diversity of the southern African range-edge population and assess if the recent contraction in the distribution has resulted in the population experiencing a genetic bottleneck. Sixteen microsatellite loci were amplified for samples collected along the Olifants River in the Greater Kruger National Park (n = 30). The genetic diversity in the South African population was compared to samples (n = 30) collected in Ghana, where Hooded Vultures are more abundant. Contrary to expectations, the South African peripheral Hooded Vulture population showed higher levels of heterozygosity (HO = 0.495) than the Ghanaian population (HO = 0.315). Neither population showed signs of recent bottleneck events when tested using demographic modelling and Approximate Bayesian computation (ABC). However, both populations showed high levels of inbreeding and relatedness. Our results suggest that despite being a small peripheral population, the South African Hooded Vulture population showed a similar level of genetic diversity as individuals sampled from a core population within the species distribution (in Ghana). This study supports the need for Hooded Vulture conservation efforts in the southern African region and highlights the evolutionary importance of range-edge populations.

Isolation by environment and its consequences for range shifts with global change: Landscape genomics of the invasive plant common tansy.

Invasive species are a growing global economic and ecological problem. However, it is not well understood how environmental factors mediate invasive range expansion. In this study, we investigated the recent and rapid range expansion of common tansy across environmental gradients in Minnesota, USA. We densely sampled individuals across the expanding range and performed reduced representation sequencing to generate a dataset of 3071 polymorphic loci for 176 individuals. We used non-spatial and spatially explicit analyses to determine the relative influences of geographic distance and environmental variation on patterns of genomic variation. We found no evidence for isolation by distance but strong evidence for isolation by environment, indicating that environmental factors may have modulated patterns of range expansion. Land use classification and soils were particularly important variables related to population structure although they operated on different spatial scales; land use classification was related to broad-scale patterns and soils were related to fine-scale patterns. All analyses indicated a distinctive genetic cluster in the most recently invaded portion of the range. Individuals from the far northwestern range margin were separated from the remainder of the range by reduced migration, which was associated with environmental resistance. This portion of the range was invaded primarily in the last 15 years. Ecological niche models also indicated that this cluster was associated with the expansion of the niche. While invasion is often assumed to be primarily influenced by dispersal limitation, our results suggest that ongoing invasion and range shifts with climate change may be strongly affected by environmental heterogeneity.

Evolutionary potential under heat and drought stress at the southern range edge of North American Arabidopsis lyrata.

The warm edges of species' distributions are vulnerable to global warming. Evidence is the recent range retraction from there found in many species. It is unclear why populations cannot easily adapt to warmer, drier, or combined hot and dry conditions and locally persist. Here, we assessed the ability to adapt to these stressors in the temperate species Arabidopsis lyrata. We grew plants from replicate seed families of a central population with high genetic diversity under a temperature and precipitation regime typical of the low-latitude margin or under hotter and/or drier conditions within naturally occurring amplitudes. We then estimated genetic variance-covariance (G-) matrices of traits depicting growth and allocation as well as selection vectors to compare the predicted adaptation potential under the different climate-stress regimes. We found that the sum of genetic variances and genetic correlations were not significantly different under stress as compared to benign conditions. However, under drought and heat drought, the predicted ability to adapt was severely constrained due to strong selection and selection pointing in a direction with less multivariate genetic variation. The much-reduced ability to adapt to dry and hot-dry conditions is likely to reduce the persistence of populations at the low-latitude margin of the species' distribution and contribute to the local extinction of the species under further warming.

Projecting kelp (Ecklonia radiata) gametophyte thermal adaptation and persistence under climate change.

BACKGROUND AND AIMS: Kelp forests underpin temperate marine ecosystems but are declining due to ocean warming, causing loss of associated ecosystem services. Projections suggest significant future decline but often only consider the persistence of adult sporophytes. Kelps have a biphasic life cycle, and the haploid gametophyte can be more thermally tolerant than the sporophyte. Therefore, projections may be altered when considering the thermal tolerance of gametophytes. METHODS: We undertook thermal tolerance experiments to quantify the effect of temperature on gametophyte survival, relative growth rate (RGR) and sex ratio for three genetically distinct populations of Ecklonia radiata gametophytes from comparatively high, mid- and low latitudes (43°, 33° and 30°S). We then used these data to project the likely consequences of climate-induced thermal change on gametophyte persistence and performance across its eastern Australian range, using generalized additive and linear models. KEY RESULTS: All populations were adapted to local temperatures and their thermal maximum was 2-3 °C above current maximum in situ temperatures. The lowest latitude population was most thermally tolerant (~70 % survival up to 27 °C), while survival and RGR decreased beyond 25.5 and 20.5 °C for the mid- and low-latitude populations, respectively. Sex ratios were skewed towards females with increased temperature in the low- and high-latitude populations. Spatially explicit model projections under future ocean warming (2050-centred) revealed a minimal decline in survival (0-30 %) across populations, relative to present-day predictions. RGRs were also projected to decline minimally (0-2 % d-1). CONCLUSIONS: Our results contrast with projections for the sporophyte stage of E. radiata, which suggest a 257-km range contraction concurrent with loss of the low-latitude population by 2100. Thermal adaptation in E. radiata gametophytes suggests this life stage is likely resilient to future ocean warming and is unlikely to be a bottleneck for the future persistence of kelp.

Multiscale stability of an intertidal kelp (Postelsia palmaeformis) near its northern range edge through a period of prolonged heatwaves.

BACKGROUND AND AIMS: Climate change, including gradual changes and extreme weather events, is driving widespread species losses and range shifts. These climatic changes are felt acutely in intertidal ecosystems, where many organisms live close to their thermal limits and experience the extremes of both marine and terrestrial environments. A recent series of multiyear heatwaves in the northeast Pacific Ocean might have impacted species even towards their cooler, northern range edges. Among them, the high intertidal kelp Postelsia palmaeformis has traits that could make it particularly vulnerable to climate change, but it is critically understudied. METHODS: In 2021 and 2022, we replicated in situ and aerial P. palmaeformis surveys that were conducted originally in 2006 and 2007, in order to assess the state of northern populations following recent heatwaves. Changes in P. palmaeformis distribution, extent, density and morphometrics were assessed between these two time points over three spatial scales, ranging from 250 m grid cells across the entire 167 km study region, to within grid cells and the individual patch. KEY RESULTS: We found evidence consistent with population stability at all three scales: P. palmaeformis remained present in all 250 m grid cells in the study region where it was previously found, and neither the extent within cells nor the patch density changed significantly between time points. However, there was evidence of slight distributional expansion, increased blade lengths and a shift to earlier reproductive timing. CONCLUSIONS: We suggest that apparent long-term stability of P. palmaeformis might be attributable to thermal buffering near its northern range edge and from the wave-exposed coastlines it inhabits, which may have decreased the impacts of heatwaves. Our results highlight the importance of multiscale assessments when examining changes within species and populations, in addition to the importance of dispersal capability and local conditions in regulating the responses of species to climate change.

Adaptive constraints at the range edge of a widespread and expanding invasive plant.

Identifying the factors that facilitate and limit invasive species' range expansion has both practical and theoretical importance, especially at the range edges. Here, we used reciprocal common garden experiments spanning the North/South and East/West range that include the North American core, intermediate and range edges of the globally invasive plant, Johnsongrass (Sorghum halepense) to investigate the interplay of climate, biotic interactions (i.e. competition) and patterns of adaptation. Our results suggest that the rapid range expansion of Johnsongrass into diverse environments across wide geographies occurred largely without local adaptation, but that further range expansion may be restricted by a fitness trade-off that limits population growth at the range edge. Interestingly, plant competition strongly dampened Johnsongrass growth but did not change the rank order performance of populations within a garden, though this varied among gardens (climates). Our findings highlight the importance of including the range edge when studying the range dynamics of invasive species, especially as we try to understand how invasive species will respond to accelerating global changes.

Demography-driven and adaptive introgression in a hybrid zone of the Armeria syngameon.

Syngameons represent networks of otherwise distinct species connected by limited gene exchange. Although most studies have focused on how species maintain their cohesiveness despite gene flow, there are additional relevant questions regarding the evolutionary dynamics of syngameons and their drivers, as well as the success of their members and the network as a whole. Using a ddRADseq approach, we analysed the genetic structure, genomic clines and demographic history of a coastal hybrid zone involving two species of the Armeria (Plumbaginaceae) syngameon in southern Spain. We inferred that a peripheral population of the sand dune-adapted A. pungens diverged from the rest of the conspecific populations and subsequently hybridized with a locally more abundant pinewood congener, A. macrophylla. Both species display extensive plastid DNA haplotype sharing. Genomic cline analysis identified bidirectional introgression, but more outlier loci with excess A. pungens than A. macrophylla ancestry, suggesting the possibility of selection for A. pungens alleles. This is consistent with the finding that the A. pungens phenotype is selected for in open habitats, and with the strong correlation found between ancestry and phenotype. Taken together, our analyses suggest an intriguing scenario in which bidirectional introgression may, on the one hand, help to avoid reduced levels of genetic diversity due to the small size and isolated location of the A. pungens range-edge population, thereby minimizing demographic risks of stochastic extinction. On the other hand, the data also suggest that introgression into A. macrophylla may allow individuals to grow in open, highly irradiated, deep sandy, salt-exposed habitats.

Phenotypic variation in the molt characteristics of a seasonal coat color-changing species reveals limited resilience to climate change.

The snowshoe hare (Lepus americanus) possesses a broad suite of adaptations to winter, including a seasonal coat color molt. Recently, climate change has been implicated in the range contraction of snowshoe hares along the southern range boundary. With shortening snow season duration, snowshoe hares are experiencing increased camouflage mismatch with their environment reducing survival. Phenological variation of hare molt at regional scales could facilitate local adaptation in the face of climate change, but the level of variation, especially along the southern range boundary, is unknown. Using a network of trail cameras and historical museum specimens, we (1) developed contemporary and historical molt phenology curves in the Upper Great Lakes region, USA, (2) calculated molt rate and variability in and among populations, and (3) quantified the relationship of molt characteristics to environmental conditions for snowshoe hares across North America. We found that snowshoe hares across the region exhibited similar fall and spring molt phenologies, rates and variation. Yet, an insular island population of hares on Isle Royale National Park, MI, completed their molt a week earlier in the fall and initiated molt almost 2 weeks later in the spring as well as exhibited slower rates of molting in the fall season compared to the mainland. Over the last 100 years, snowshoe hares across the region have not shifted in fall molt timing; though contemporary spring molt appears to have advanced by 17 days (~ 4 days per decade) compared to historical molt phenology. Our research indicates that some variation in molt phenology exists for snowshoe hares in the Upper Great Lakes region, but whether this variation is enough to offset the consequences of climate change remains to be seen.

Integrating demographic niches and black spruce range expansion at subarctic treelines.

When investigating relationships between species' niches and distributions, niches can be divided demographically, resulting in unique niches for different life stages. This approach can identify changing substrate requirements throughout a species' life cycle. Using non-metric multidimensional scaling, we quantified microsite conditions associated with successful recruitment in the tundra landscape and successful seed production amongst adult trees of black spruce (Picea mariana) at subarctic treeline in Yukon, Canada to assess how life stage-specific requirements may impact the distribution of this widespread boreal tree species. Treeline ecotones in this region showed high heterogeneity in tundra microsites available for establishment. Black spruce exhibited changing microsite associations from germination to reproductive maturity, which were mainly driven by changes in plant community and soil moisture. These associations limit the microsites where individuals can establish and reproduce to a subset available within the heterogeneous landscape. Overall, we suggest that (1) substrates suitable for early recruitment are limited at the range edge; and (2) reproductive adults have a narrow niche, limiting successful seed production in adults and forming sink populations where suitable conditions are limited. Our multivariate assessment of microsite suitability can provide valuable insights into the spatial distribution of a species throughout its life cycle and identify life stage-specific constraints to range expansion.

Sexual reproduction is light-limited as marsh grasses colonize maritime forest.

Climate change is driving abiotic shifts that can threaten the conservation of foundation species and the habitats they support. Directional range shifting is one mechanism of escape, but requires the successful colonization of habitats where interspecific interactions may differ from those to which a species has adapted. For plants with multiple reproductive strategies, these range-edge interactions may alter the investment or allocation toward a given reproductive strategy. In this study, we quantified sexual reproduction of the clonal marsh grass Spartina patens across an inland colonization front into maritime forest being driven by sea-level rise. We find that flowering is variable across S. patens meadows, but consistently reduced in low light conditions like those of the forest understory. Observational surveys of S. patens flowering at four sites in the Delmarva Peninsula agreed with the results of two experimental manipulations of light availability (shading experiment in S. patens-dominated marsh and a forest dieback manipulation). These three approaches pinpointed light limitation as a principal control on S. patens flowering capacity, suggesting that light competition with taller upland species can suppress S. patens flowering along its upland migration front. Consequently, all propagation in shaded conditions must occur clonally or via seeds from the marsh, a reproductive restriction that could limit the potential for local adaptation and reduce genetic diversity. Future research is needed to determine whether the lack of flowering is the result of a trade-off between sexual and clonal reproduction or results from insufficient photosynthetic products needed to achieve either reproductive method.

Genetic Diversity and Structure of Rear Edge Populations of Sorbus aucuparia (Rosaceae) in the Hyrcanian Forest.

Sorbus aucuparia (Rosaceae) is a small tree species widely distributed in Eurasia. The Hyrcanian forest is the southernmost distribution limit of this species. Severe habitat degradation and inadequate human interventions have endangered the long-term survival of this species in this region, and it is necessary to develop and apply appropriate management methods to prevent the loss of its genetic diversity. In this study, we used 10 SSR markers in order to evaluate the genetic diversity of this taxon. Leaf samples were collected from five known populations of S. aucuparia throughout its distribution area in the Hyrcanian forest. Expected heterozygosity ranged from 0.61 (ASH) to 0.73, and according to the M-ratio, all populations showed a significant reduction in effective population size, indicating a genetic bottleneck. Global FST was not statistically significant and attained the same values with and without excluding null alleles (ENA) correction (FST = 0.12). Bayesian analysis performed with STRUCTURE defined two genetic clusters among the five known populations, while the results of discriminant analysis of principal components (DAPC) identified three distinct groups. The average proportion of migrants was 22. In general, the gene flow was asymmetrical, with the biggest differences between immigration and emigration in Barzekoh and Asbehriseh. The Mantel test showed that there was no significant correlation between genetic distance (FST) and geographic distance in S. aucuparia. The best pathway for theoretical gene flow is located across the coast of the Caspian Sea and significant spatial autocorrelation was observed in only one population. In order to reduce the extinction risk of very small and scattered populations of S. aucuparia in the Hyrcanian forest, it is very important to establish and/or enhance the connectivity through habitat restoration or genetic exchange.

Signature of mid-Pleistocene lineages in the European silver fir (Abies alba Mill.) at its geographic distribution margin.

In a conservation and sustainable management perspective, we identify the ecological, climatic, and demographic factors responsible for the genetic diversity patterns of the European silver fir (Abies alba Mill.) at its southwestern range margin (Pyrenees Mountains, France, Europe). We sampled 45 populations throughout the French Pyrenees and eight neighboring reference populations in the Massif Central, Alps, and Corsica. We genotyped 1,620 individuals at three chloroplast and ten nuclear microsatellite loci. We analyzed within- and among-population genetic diversity using phylogeographic reconstructions, tests of isolation-by-distance, Bayesian population structure inference, modeling of demographic scenarios, and regression analyses of genetic variables with current and past environmental variables. Genetic diversity decreased from east to west suggesting isolation-by-distance from the Alps to the Pyrenees and from the Eastern to the Western Pyrenees. We identified two Pyrenean lineages that diverged from a third Alpine-Corsica-Massif Central lineage 0.8 to 1.1 M years ago and subsequently formed a secondary contact zone in the Central Pyrenees. Population sizes underwent contrasted changes, with a contraction in the west and an expansion in the east. Glacial climate affected the genetic composition of the populations, with the western genetic cluster only observed in locations corresponding to the coldest past climate and highest elevations. The eastern cluster was observed over a larger range of temperatures and elevations. All demographic events shaping the current spatial structure of genetic diversity took place during the Mid-Pleistocene Transition, long before the onset of the Holocene. The Western Pyrenees lineage may require additional conservation efforts, whereas the eastern lineage is well protected in in situ gene conservation units. Due to past climate oscillations and the likely emergence of independent refugia, east-west oriented mountain ranges may be important reservoir of genetic diversity in a context of past and ongoing climate change in Europe.

What shapes the range edge of a dominant African savanna tree, Colophospermum mopane? A demographic approach.

Climate is widely assumed to be the primary process that limits the distribution ranges of plants. Yet, savannas have vegetation not at equilibrium with climate, instead its structure and function are shaped by interactions between fire, herbivory, climate, and vegetation. I use the rich literature of a dominant African savanna woody plant, Colophospermum mopane, to demonstrate that climate and disturbance interact with each demographic stage to shape this species range limits. This synthesis highlights that climate-based predictions for the range of C. mopane inadequately represents the processes that shape its distribution. Instead, seed bank depletion and rainfall limitation create a demographic bottleneck at the early seedling stage. The legacy of top-kill from disturbance changes tree stand architecture causing a critical limitation in seed supply. Exposure to top-kill at all demographic stages causes a vigorous resprouting response and shifts tree architecture from that of 1-2 stemmed tall trees to that of a short multi-stemmed shrub. The shorter, multi-stemmed shrubs are below the height threshold (4 m) at which they can produce seeds, resulting in shrub-dominated landscapes that are effectively sterile. This effect is likely most pronounced at the range edge where top-kill-inducing disturbances increase in frequency. The proposed mechanistic, demographic-based understanding of C. mopane's range limits highlights the complexity of processes that interact to shape its range edges. This insight serves as a conceptual model for understanding the determinants of range limits of other dominant woody savannas species living in disturbance limited ecosystems.

Range expansion, habitat use, and choosiness in a butterfly under climate change: Marginality and tolerance of oviposition site selection.

Poleward range shifts under climate change involve the colonization of new sites and hence the foundation of new populations at the expanding edge. We studied oviposition site selection in a butterfly under range expansion (Lycaena dispar), a key process for the establishment of new populations. We described and compared the microhabitats used by the species for egg laying with those available across the study sites both in edge and in core populations. We carried out an ecological niche factor analysis (ENFA) to estimate (1) the variety of microhabitats used by the butterfly for egg laying (tolerance) and (2) the extent to which these selected microhabitats deviated from those available (marginality). Microhabitat availability was similar in edge and core populations. Ambient temperature recorded at the site level above the vegetation was on average lower at core populations. In contrast with what is often assumed, edge populations did not have narrower microhabitat use compared to core populations. Females in edge populations even showed a higher degree of generalism: They laid eggs under a wider range of microhabitats. We suggest that this pattern could be related to an overrepresentation of fast deciding personalities in edge populations. We also showed that the thermal time window for active female behavior was reduced in edge populations, which could significantly decrease the time budget for oviposition and decrease the threshold of acceptance during microhabitat selection for oviposition in recently established populations.

Hiding from the climate: Characterizing microrefugia for boreal forest understory species.

Climate warming is likely to shift the range margins of species poleward, but fine-scale temperature differences near the ground (microclimates) may modify these range shifts. For example, cold-adapted species may survive in microrefugia when the climate gets warmer. However, it is still largely unknown to what extent cold microclimates govern the local persistence of populations at their warm range margin. We located 99 microrefugia, defined as sites with edge populations of 12 widespread boreal forest understory species (vascular plants, mosses, liverworts and lichens) in an area of ca. 24,000 km2 along the species' southern range margin in central Sweden. Within each population, a logger measured temperature eight times per day during one full year. Using univariate and multivariate analyses, we examined the differences of the populations' microclimates with the mean and range of microclimates in the landscape, and identified the typical climate, vegetation and topographic features of these habitats. Comparison sites were drawn from another logger data set (n = 110), and from high-resolution microclimate maps. The microrefugia were mainly places characterized by lower summer and autumn maximum temperatures, late snow melt dates and high climate stability. Microrefugia also had higher forest basal area and lower solar radiation in spring and autumn than the landscape average. Although there were common trends across northern species in how microrefugia differed from the landscape average, there were also interspecific differences and some species contributed more than others to the overall results. Our findings provide biologically meaningful criteria to locate and spatially predict potential climate microrefugia in the boreal forest. This opens up the opportunity to protect valuable sites, and adapt forest management, for example, by keeping old-growth forests at topographically shaded sites. These measures may help to mitigate the loss of genetic and species diversity caused by rear-edge contractions in a warmer climate.

Genetic drift during the spread phase of a biological invasion.

Recent theoretical and experimental models have revealed the role played by evolution during species spread, and in particular have questioned the influence of genetic drift at range edges. By investigating the spread of an aquatic invader in patchy habitats, we quantified genetic drift and explored its consequences for genetic diversity and fitness. We examined the interplay of gene flow and genetic drift in 36 populations of the red swamp crayfish, Procambarus clarkii, in a relatively recently invaded wetland area (30 years, Brière, northwest France). Despite the small spatial scale of our study (15 km2 ), populations were highly structured according to the strong barrier of land surfaces and revealed a clear pattern of colonization through watercourses. Isolated populations exhibited small effective sizes and low dispersal rates that depended on water connectivity, suggesting that genetic drift dominated in the evolution of allele frequencies in these populations. We also observed a significant decrease in the genetic diversity of isolated populations over only a 2-year period, but failed to demonstrate an associated fitness cost using fluctuating asymmetry. This study documents the possible strong influence of genetic drift during the spread of a species, and such findings provide critical insights into the current context of profound rearrangements in species distributions due to global change.

Species characteristics affect local extinctions.

PREMISE OF THE STUDY: Human activities threaten thousands of species with extinction. However, it remains difficult to predict extinction risk for many vulnerable species. Species traits, species characteristics such as rarity or habitat use, and phylogenetic patterns are associated with responses to anthropogenic environmental change and may help predict likelihood of extinction. METHODS: We used historical botanical data from Kalamazoo County, Michigan, USA, to examine whether species traits (growth form, life history, nitrogen-fixation, photosynthetic pathway), species characteristics (community association, species origin, range edge, habitat specialization, rarity), or phylogenetic relatedness explain local species loss at the county level. KEY RESULTS: Across Kalamazoo County, prairie species, species at the edge of their native range, regionally rare species, and habitat specialists were most likely to become locally extinct. Prairie species experienced the highest local extinction rates of any habitat type, and among prairie species, regionally rare and specialist species were most vulnerable to loss. We found no evidence for a phylogenetic pattern in plant extinctions. CONCLUSIONS: Our study illustrates the value of historical datasets for understanding and potentially predicting biodiversity loss. Not surprisingly, rare, specialist species occupying threatened habitats are most at risk of local extinction. As a result, identifying mechanisms to conserve or restore rare or declining species and preventing further habitat destruction may be the most effective strategies for reducing future extinction.

Seasonal ecology of a migratory nectar-feeding bat at the edge of its range.

Migratory species that cross geopolitical boundaries pose challenges for conservation planning because threats may vary across a species' range and multi-country collaboration is required to implement conservation action plans. The lesser long-nosed bat (Leptonycteris yerbabuenae) is a migratory pollinator bat that was removed from the Endangered Species List in the United States in 2018 and from threatened status in Mexico in 2013. The seasonal ecology and conservation status of the species is well understood in the core part of its range on mainland Mexico and in the southwestern United States, but relatively little is known about the species on the Baja California peninsula in northwestern Mexico, a part of its range range separated by the Gulf of California. We studied the seasonal ecology of lesser long-nosed bats on the Baja peninsula at 8 focal roosts along a 450-km north-to-south transect to test hypotheses about migratory or residential status of the species on the Baja peninsula. We provide evidence of an extensive population of lesser long-nosed bats on the Baja peninsula that is primarily seasonally migratory and includes 2 mating roosts with males on the southern part of the peninsula. Seasonal ecology of lesser long-nosed bats was closely associated with the flowering and fruiting season of the cardón (Pachycereus pringlei), the dominant columnar cactus on the peninsula. However, we discovered that some female lesser long-nosed bats arrive and give birth at southern roosts in mid-February, about 2 months earlier than other migratory populations in more northern Sonoran Desert habitats. We documented the loss of nearly a third of the known maternity roosts during the study, demonstrating that action to protect key roosts remains a high priority. Migratory pollinators are particularly vulnerable to climate and land-use changes and we recommend continued monitoring and research to guide effective range-wide conservation of the species. Las especies migratorias o con rangos de distribución amplios que incluyen fronteras geopolíticas, representan desafíos particulares para la planificación de estrategias de conservación, ya que las amenazas así como las tendencias poblacionales pueden variar a lo largo de su rango geográfico y se requiere la colaboración de múltiples países para implementar planes de acción que permitan su conservación. El murciélago magueyero menor (Leptonycteris yerbabuenae) es un murciélago polinizador migratorio que recientemente fue sacado de la lista de especies en peligro en los Estados Unidos en 2018 y en México en 2013. La ecología estacional y el estatus de conservación de esta especie, ha sido bien estudiado en el centro de su rango de distribución en México continental, pero se sabe muy poco acerca de la especie en la Península de Baja California en el noreste de México, región que está separada del resto del rango por el golfo de California. Nosotros estudiamos la ecología estacional del murciélago magueyero menor, en ocho cuevas a lo largo de un transecto de 450 km norte-sur, en la Península de Baja California y pusimos a prueba la hipótesis del status migratorio o residente de sus poblaciones en esta región. Proporcionamos la primera evidencia de una extensa población de esta especie en la península, a cual es principalmente migratoria estacional e incluye dos cuevas de reproducción ubicadas al sur de esta región. La ecología estacional del murciélago magueyero menor estuvo fuertemente asociada con la estación de floración y fructificación del cardón (Pachycereus pringlei), el cactus columnar dominante en la península. Nosotros también descubrimos que algunas hembras llegan y dan a luz en las cuevas más sureñas, a mediados de febrero, cerca de dos meses antes que otras poblaciones migratorias, en el desierto de Sonora del norte. Durante el tiempo de este estudio, documentamos la destrucción de una de las cuevas de maternidad, lo que demuestra la necesidad de acciones de conservación para proteger estos refugios. Los polinizadores migratorios son particularmente vulnerables a cambios en el uso del suelo y al cambio climático y recomendamos continuar con el monitoreo y la investigación, con el fin de guiar su conservación a lo largo de todo el rango de distribución de la especie.

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems.

We quantify the relative importance of multi-scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo-Pacific biogeographical provinces. Large (>30 cm), functionally-important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km2). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local-scale variables, 'distance from port', a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re-emphasise the importance that historical processes play in structuring contemporary biotic communities.

Common garden test of range limits as predicted by a species distribution model in the annual plant Mimulus bicolor.

PREMISE OF THE STUDY: Direct tests of a species distribution model (SDM) were used to evaluate the hypothesis that the northern and southern edges of Mimulus bicolor's geographical range are limited by temperature and precipitation. METHODS: Climatic suitability was predicted using an SDM informed only by temperature and precipitation variables. These predictions were tested by growing plants in growth chambers with temperature and watering treatments informed by weather stations characteristic of environments at the geographic center, edges, and outside the range. An Aster analysis was used to assess whether treatments significantly affected lifetime flower production and to test for local adaptation. The relationship between climatic suitability and lifetime flower number in the growth chambers was also evaluated. KEY RESULTS: The temperature and watering treatments significantly affected lifetime flower number, although local adaptation was not detected. Flower production was significantly lower under the two edge treatments compared to the central treatment. While no flowers were produced under the beyond-south treatments, flower production was greatest under the beyond-north treatment. These results suggest a hard abiotic limit at the southern edge, and suitable temperature and precipitation conditions beyond the northern edge. While predicted climatic suitability was significantly lower at the range edges, there was no correlation between the climatic suitability of the weather stations' locations and flower production. CONCLUSIONS: These results suggest that temperature and precipitation play a significant role in defining the distribution of M. bicolor, but also indicate that dispersal limitation or metapopulation dynamics are likely important factors restricting access to habitable sites beyond the northern range limit.