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Global change is expected to expand and shrink species' distributions in complex ways beyond just retraction at warm edges and expansion at cool ones. Detecting these changes is complicated by the need for robust baseline data for comparison. For instance, gaps in species' distributions may reflect long‐standing patterns, recent shifts, or merely insufficient sampling effort. We investigated an apparent gap in the distribution of the American pika, Ochotona princeps, along the North American Sierra Nevada. Historical records from this region are sparse, with ~100 km separating previously documented pika‐occupied sites. Surveys during 2014–2023 confirmed that the gap is currently unoccupied by pikas, and evidence of past occurrence indicates that the gap has expanded over time, likely due to contemporary global change. Sites lacking evidence of past pika occurrence were climatically and geographically more distant from sites with signs of recent (former) occurrence and currently occupied sites. Formerly and currently occupied sites were partially climatically distinct, suggesting either metapopulation‐like dynamics or an extinction debt that may eventually result in further population losses at the edge of suitable climate space. The Feather River gap aligns with one of several “low points” in the otherwise continuous boreal‐like conditions spanning the Cascade Range and Sierra Nevada and is coincident with discontinuities in ranges of other mammals. These results highlight the potential for climate‐driven fragmentation and range retraction in regions considered climatically and geographically interior to a species' overall distribution.

The species‐range size distribution is a product of speciation, transformation of range‐sizes, and extinction. Previous empirical studies showed that it has a left‐skewed lognormal‐like distribution. We developed a new mathematical framework to study species‐range‐size distributions, one in which allopatric speciation, transformation of range size, and the extinction process are explicitly integrated. The approach, which we call the gain‐loss‐allopatric speciation model, allows us to explore the effects of various speciation scenarios. Our model captures key dynamics thought to lead to known range‐size distributions. We also fitted the model to empirical range‐size distributions of birds, mammals, and beetles. Since geographic range dynamics are linked to speciation and extinction, our model provides predictions for the dynamics of species richness. When a species‐range‐size distribution initially evolves away from the range sizes at which the likelihood of speciation is low, it tends to cause diversification slowdown even in the absence of (bio)diversity dependence in speciation rate. Using the mathematical model developed here, we give a potential explanation for how observed range‐size distributions emerge from range‐size dynamics. Although the framework presented is minimalistic, it provides a starting point for examining hypotheses based on more complex mechanisms. We developed a new mathematical framework to study species‐range‐size distributions, one in which allopatric speciation, transformation of range size, and the extinction process are explicitly integrated. Our model captures key dynamics thought to lead to known range‐size distributions. We also fitted the model to empirical range‐size distributions of birds, mammals, and beetles.

The systematic revision of the Platyrrhinus helleri clade, which was found to be a species complex, led to the elevation of some subspecies to species level and the description of Platyrrhinus angustirostris Velazco, Gardner & Patterson, 2010. The conservation status and threats to this species are currently poorly understood. We report a new record of this species, extending its distribution into west‑central Colombia. We used WorldClim bioclimatic layers to model its potential distribution; the results indicate that areas with stable temperatures and substantial precipitation during the warmest quarter offer the best environmental suitability for this species. This information is important for the conservation of P. angustirostris and its tropical habitats.

Of the few endemic vertebrates found in Paraguay, Homonota rupicola Cacciali, Ávila & Bauer, 2007 is considered micro-endemic, globally threatened, absent in conservation units, and restricted to rocky outcrops in a small mountain range, a priority hotspot, known as Cordillera de los Altos. Through sampling efforts in areas surrounding the type locality, we recorded H. rupicola at other sites. Together the current geographic range of this species is approximately 13 km along a segment of the Cordillera de los Altos. Nonetheless, H. rupicola is currently unknown from any protected areas, and non-governmental organizations are working towards establishing conservation units within the geographic range of the species.

The geographical structure of resistance to herbicides inhibiting acetyl-coenzyme A carboxylase (ACCase) was investigated in the weed Alopecurus myosuroides (black-grass) across its geographical range to gain insight into the process of plant adaptation in response to anthropogenic selective pressures occurring in agricultural ecosystems. We analysed 297 populations distributed across six countries in A. myosuroides' main area of occupancy. The frequencies of plants resistant to two broadly used ACCase inhibitors and of seven mutant, resistant ACCase alleles were assessed using bioassays and genotyping, respectively. Most of the resistance was not endowed by mutant ACCase alleles. Resistance and ACCase allele distribution patterns were characterized by mosaicism. The prevalence of resistance and of ACCase alleles differed among countries. Resistance clearly evolved by redundant evolution of a set of resistance alleles or genes, most of which remain unidentified. Resistance in A. myosuroides was shaped by variation in the herbicide selective pressure at both the individual field level and the national level.

Understanding the forms that the geographic range limits of species take, their causes and their consequences are key issues in ecology and evolutionary biology. They are also topics on which understanding is advancing rapidly. This themed issue of Proc. R. Soc. B focuses on the wide variety of current research perspectives on the nature and determinants of the limits to geographic ranges. The contributions address important themes, including the roles and influences of dispersal limitation, species interactions and physiological limitation, the broad patterns in the structure of geographic ranges, and the fundamental question of why at some point species no longer evolve the ability to overcome the factors constraining their distributions and thus fail to continue to spread. In this introduction, these contributions are placed in the wider context of these broad themes.

Mountains are key features of the Earth’s surface and host a substantial proportion of the world’s species. However, the links between the evolution and distribution of biodiversity and the formation of mountains remain poorly understood. Here, we integrate multiple datasets to assess the relationships between species richness in mountains, geology and climate at global and regional scales. Specifically, we analyse how erosion, relief, soil and climate relate to the geographical distribution of terrestrial tetrapods, which include amphibians, birds and mammals. We find that centres of species richness correlate with areas of high temperatures, annual rainfall and topographic relief, supporting previous studies. We unveil additional links between mountain-building processes and biodiversity: species richness correlates with erosion rates and heterogeneity of soil types, with a varying response across continents. These additional links are prominent but under-explored, and probably relate to the interplay between surface uplift, climate change and atmospheric circulation through time. They are also influenced by the location and orientation of mountain ranges in relation to air circulation patterns, and how species diversification, dispersal and refugia respond to climate change. A better understanding of biosphere–lithosphere interactions is needed to understand the patterns and evolution of mountain biodiversity across space and time.

Aim To assess evidence for geographical and environmental range expansion through polyploidy in wild potatoes (Solanum sect. Petota). There are diploids, triploids, tetraploids, pentaploids and hexaploids in this group. Location Wild potatoes occur from the south-western USA (Utah and Colorado), throughout the tropical highlands of Mexico, Central America and the Andes, to Argentina, Chile and Uruguay. Methods We compiled 5447 reports of ploidy determination, covering 185 of the 187 species, of which 702 determinations are presented here for the first time. We assessed the frequency of cytotypes within species, and analysed the geographical and climatic distribution of ploidy levels. Results Thirty-six per cent of the species are entirely or partly polyploid. Multiple cytotypes exist in 21 species, mostly as diploid and triploid, but many more may await discovery. We report the first chromosome count (2n = 24) for Solanum hintonii. Diploids occupy a larger area than polyploids, but diploid and tetraploid species have similar range sizes, and the two species with by far the largest range sizes are tetraploids. The fraction of the plants that are polyploids is much higher from Mexico to Ecuador than farther south. Compared with diploids, triploids tend to occur in warmer and drier areas, whereas higher-level polyploids tend to occur in relatively cold areas. Diploids are absent from Costa Rica to southern Colombia, the wettest part of the group's range. Main conclusions These results suggest that polyploidy played an important role in this group's environmental differentiation and range expansion.

Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.

Aim To test if physiological acclimation can buffer species against increasing extreme heat due to climate change. Location Global. Time period 1960 to 2015. Major taxa studied Amphibians, arthropods, brachiopods, cnidarians, echinoderms, fishes, molluscs, reptiles. Methods We draw together new and existing data quantifying the warm acclimation response in 319 species as the acclimation response ratio (ARR): the increase in upper thermal limit per degree increase in experimental temperature. We develop worst‐case scenario climate projections to calculate the number of years and generations gained by ARR until loss of thermal safety. We further compute a vulnerability score that integrates across variables estimating exposure to climate change and species‐specific tolerance through traits, including physiological plasticity, generation time and latitudinal range extent. Results ARR is highly variable, but with marked differences across taxa, habitats and latitude. Polar terrestrial arthropods show high ARRs [95% upper confidence limit (UCL95%) = 0.68], as do some polar aquatic invertebrates that were acclimated for extended durations (ARR > 0.4). While this physiological plasticity buys 100s of years until thermal safety is lost, combination with long generation times leads to decreased potential for evolutionary adaptation. Additionally, 27% of marine polar invertebrates have no capacity for acclimation and reptiles and amphibians have minimal ARR (UCL95% = 0.16). Low physiological plasticity, long generations times and restricted latitudinal ranges combine to distinguish reptiles, amphibians and polar invertebrates as being highly vulnerable amongst ectotherms. Main conclusions In some taxa the combined effects of acclimation capacity and generation time can provide 100s of years and generations before thermal safety is lost. The accuracy of assessments of vulnerability to climate change will be improved by considering multiple aspects of species’ biology that, in combination may increase persistence under extreme heat events, and increase the probability for evolutionary rescue.