Aim Compare the performance of continental and regional models in predicting species distributions at range margins. Selection of study area extent, resolution and threshold affects ecological model ...predictions. At range margins of species distribution, local populations may be restricted to suboptimal environments distinct from the species' global range, which may be missed by continental models. Location Africa and West Africa. Methods We analysed differences in predicted distributions at range margins of three widespread African species that in West Africa occur in peripheral populations restricted to particular habitats. We made comparisons between models built with data from the complete and restricted range of species' distributions (Africa and West Africa, respectively), with coarse and fine resolutions (10 × 10 km and 1 × 1 km, respectively), and classified with three thresholds of species presence (minimum training presence, 10th percentile training presence and maximum training sensitivity plus specificity thresholds). We predicted the species' distributions and quantified environmental variable importance and profile using maximum entropy and estimated niche breadth parameters with ecological niche factor analysis. Results We found differences between model types in niche breadth estimates and also in response curves of the most important variables, suggesting that fine resolution models are more accurate at selecting marginal habitats in West Africa than in Africa. The predictions of species distributions differed with model extent, resolution and threshold analysed. Models built with the complete species environmental range and with coarse resolution tended to overestimate species distributions at the edge, but accuracy increased when more restrictive thresholds were used. In West Africa, independently of the resolution, the threshold value was less important for maximizing agreement between predicted probabilities and observed distribution. Main conclusions At range margins of species distributions, regional models with precise data and conservative thresholds should be preferred over continental models with coarser resolution to identify suitable areas for peripheral populations.
Deserts are among the harshest environments on Earth. The multiple ages of different deserts and their global distribution provide a unique opportunity to study repeated adaptation at different ...timescales. Here, we summarize recent genomic research on the genetic mechanisms underlying desert adaptations in mammals. Several studies on different desert mammals show large overlap in functional classes of genes and pathways, consistent with the complexity and variety of phenotypes associated with desert adaptation to water and food scarcity and extreme temperatures. However, studies of desert adaptation are also challenged by a lack of accurate genotype–phenotype–environment maps. We encourage development of systems that facilitate functional analyses, but also acknowledge the need for more studies on a wider variety of desert mammals.
The genomics of adaptation to deserts is a rapidly growing research field that provides examples of adaptation over different timescales and of vastly different organisms facing shared challenges.Mammals inhabiting deserts show remarkable adaptive traits that have evolved repeatedly and independently in different species across the globe and in response to similar selective pressures of extreme temperatures, aridity, and water and food deprivation.Genomic studies have shown that there are shared patterns of adaptation at the genomic level involving fat metabolism and insulin signaling, as well as arachidonic acid metabolism.Understanding the mechanisms by which species have successfully adapted to the physical and climatic challenges of deserts is important for evaluating the possibility of evolutionary rescue of species currently challenged by increased desertification.
AIM: Climate change assessments are largely based on correlative species distribution models (SDMs) that are sensible to spatial biases or incompleteness of input distribution data. We tested whether ...changes on the species' climatic niche resulting from recent human‐induced range contractions have a significant influence on SDM predictions of future species distributions. LOCATION: Africa. METHODS: For this study, we selected two highly detectable species with acknowledged human‐induced range contractions, namely the African savanna elephant (Loxodonta africana) and giraffe (Giraffa camelopardalis). We used presence data until the 1970s to describe each species' historical distribution, while more recent data characterized the contemporary distribution. We compared the temporal variation between these species distributions using multivariate analyses and the combination of four different SDM algorithms to predict historical, contemporary and future distributional ranges under climate change scenarios. RESULTS: We show how range contraction differentially reduces the climatic variability associated with the species niche and has an important influence on the predictions of suitable climatic space and species vulnerability trend under climate change scenarios. Future predictions of the distribution of the elephant were mainly affected by the loss of occupied area at the margins of the historical distributions, resulting in a lesser predicted extent when using the contemporary dataset. As for the giraffe models, there were more dramatic consequences with large areas of West Africa failing to be predicted as suitable in the contemporary models, probably as a result from the loss of climatic information due to the species almost complete disappearance from that region. MAIN CONCLUSIONS: Our findings support the importance of considering historical distributional ranges of species in climate change studies in order to account for their full climatic niche and to derive more reliable predictions of future distribution. This is particularly important in species for which distributional ranges have been strongly affected by human activities.
Current climate change is a major threat to biodiversity. Species unable to adapt or move will face local or global extinction and this is more likely to happen to species with narrow climatic and ...habitat requirements and limited dispersal abilities, such as amphibians and reptiles. Biodiversity losses are likely to be greatest in global biodiversity hotspots where climate change is fast, such as the Iberian Peninsula. Here we assess the impact of climate change on 37 endemic and nearly endemic herptiles of the Iberian Peninsula by predicting species distributions for three different times into the future (2020, 2050 and 2080) using an ensemble of bioclimatic models and different combinations of species dispersal ability, emission levels and global circulation models. Our results show that species with Atlantic affinities that occur mainly in the North‐western Iberian Peninsula have severely reduced future distributions. Up to 13 species may lose their entire potential distribution by 2080. Furthermore, our analysis indicates that the most critical period for the majority of these species will be the next decade. While there is considerable variability between the scenarios, we believe that our results provide a robust relative evaluation of climate change impacts among different species. Future evaluation of the vulnerability of individual species to climate change should account for their adaptive capacity to climate change, including factors such as physiological climate tolerance, geographical range size, local abundance, life cycle, behavioural and phenological adaptability, evolutionary potential and dispersal ability.
► we analyzed how dynamics and uncertainty in species distributions may affect conservation planning decisions. ► A new version of the Marxan software was developed to deal with uncertainty in ...species distributions. ► A set of sites in the Iberian Peninsula were identified, where conservation investment is robust to uncertainty.
Climate warming challenges our approach to building systems of protected areas because it is likely to drive accelerating shifts in species distributions, and the projections of those future species distributions are uncertain. There are several important sources of uncertainty intrinsic to using species occurrence projections for reserve system design including uncertainty in the number of occurrences captured by any reserve selection solution, and uncertainty arising from the different approaches used to fit predictive models. Here we used the present and future predicted distributions of Iberian herptiles to analyze how dynamics and uncertainty in species distributions may affect decisions about resource allocation for conservation in space and time. We identified priority areas maximizing coverage of current and future (2020 and 2080) predicted distributions of 65 species, under “Mild” and “Severe” uncertainty. Next, we applied a return-on-investment analysis to quantify and make explicit trade-offs between investing in areas selected when optimizing for different times and with different uncertainty levels. Areas identified as important for conservation in every time frame and uncertainty level were the ones considered to be robust climate adaptation investments, and included chiefly already protected areas. Areas identified only under “Mild” uncertainty were considered good candidates for investment if extra resources are available and were mainly located in northern Iberia. However, areas selected only in the “Severe” uncertainty case should not be completely disregarded as they may become climatic refugia for some species. Our study provides an objective methodology to deliver “no regrets” conservation investments.
The Sahara desert is the largest warm desert in the world and a poorly explored area. Small water-bodies occur across the desert and are crucial habitats for vertebrate biodiversity. Environmental ...DNA (eDNA) is a powerful tool for species detection and is being increasingly used to conduct biodiversity assessments. However, there are a number of difficulties with sampling eDNA from such turbid water-bodies and it is often not feasible to rely on electrical tools in remote desert environments. We trialled a manually powered filtering method in Mauritania, using pre-filtration to circumvent problems posed by turbid water in remote arid areas. From nine vertebrate species expected in the water-bodies, four were detected visually, two via metabarcoding, and one via both methods. Difficulties filtering turbid water led to severe constraints, limiting the sampling protocol to only one sampling point per study site, which alone may largely explain why many of the expected vertebrate species were not detected. The amplification of human DNA using general vertebrate primers is also likely to have contributed to the low number of taxa identified. Here we highlight a number of challenges that need to be overcome to successfully conduct metabarcoding eDNA studies for vertebrates in desert environments in Africa.
ABSTRACT
Deserts and arid regions are generally perceived as bare and rather homogeneous areas of low diversity. The Sahara is the largest warm desert in the world and together with the arid Sahel ...displays high topographical and climatic heterogeneity, and has experienced recent and strong climatic oscillations that have greatly shifted biodiversity distribution and community composition. The large size, remoteness and long‐term political instability of the Sahara‐Sahel, have limited knowledge on its biodiversity. However, over the last decade, there have been an increasing number of published scientific studies based on modern geomatic and molecular tools, and broad sampling of taxa of these regions. This review tracks trends in knowledge about biodiversity patterns, processes and threats across the Sahara‐Sahel, and anticipates needs for biodiversity research and conservation. Recent studies are changing completely the perception of regional biodiversity patterns. Instead of relatively low species diversity with distribution covering most of the region, studies now suggest a high rate of endemism and larger number of species, with much narrower and fragmented ranges, frequently limited to micro‐hotspots of biodiversity. Molecular‐based studies are also unravelling cryptic diversity associated with mountains, which together with recent distribution atlases, allows identifying integrative biogeographic patterns in biodiversity distribution. Mapping of multivariate environmental variation (at 1 km × 1 km resolution) of the region illustrates main biogeographical features of the Sahara‐Sahel and supports recently hypothesised dispersal corridors and refugia. Micro‐scale water‐features present mostly in mountains have been associated with local biodiversity hotspots. However, the distribution of available data on vertebrates highlights current knowledge gaps that still apply to a large proportion of the Sahara‐Sahel. Current research is providing insights into key evolutionary and ecological processes, including causes and timing of radiation and divergence for multiple taxa, and associating the onset of the Sahara with diversification processes for low‐mobility vertebrates. Examples of phylogeographic patterns are showing the importance of allopatric speciation in the Sahara‐Sahel, and this review presents a synthetic overview of the most commonly hypothesised diversification mechanisms. Studies are also stressing that biodiversity is threatened by increasing human activities in the region, including overhunting and natural resources prospection, and in the future by predicted global warming. A representation of areas of conflict, landmines, and natural resources extraction illustrates how human activities and regional insecurity are hampering biodiversity research and conservation. Although there are still numerous knowledge gaps for the optimised conservation of biodiversity in the region, a set of research priorities is provided to identify the framework data needed to support regional conservation planning.
The formation of stable genetic boundaries between emerging species is often diagnosed by reduced hybrid fitness relative to parental taxa. This reduced fitness can arise from endogenous and/or ...exogenous barriers to gene flow. Although detecting exogenous barriers in nature is difficult, we can estimate the role of ecological divergence in driving species boundaries by integrating molecular and ecological niche modelling tools. Here, we focus on a three‐way secondary contact zone between three viper species (Vipera aspis, V. latastei and V. seoanei) to test for the contribution of ecological divergence to the development of reproductive barriers at several species traits (morphology, nuclear DNA and mitochondrial DNA). Both the nuclear and mitochondrial data show that all taxa are genetically distinct and that the sister species V. aspis and V. latastei hybridize frequently and backcross over several generations. We find that the three taxa have diverged ecologically and meet at a hybrid zone coincident with a steep ecotone between the Atlantic and Mediterranean biogeographical provinces. Integrating landscape and genetic approaches, we show that hybridization is spatially restricted to habitats that are suboptimal for parental taxa. Together, these results suggest that niche separation and adaptation to an ecological gradient confer an important barrier to gene flow among taxa that have not achieved complete reproductive isolation.
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•A geographical comprehensive phylogeny for the Saharo-Arabian Tropiocolotes.•A calibrated timeframe for the diversification of Tropiocolotes.•Putative undescribed biodiversity ...identified in North Africa, Levant and Arabia.•Main role of plate tectonics on the evolutionary history of Tropiocolotes.
Plate tectonics constitute one of the main mechanisms of biological diversification on Earth, often being associated with cladogenetic events at different phylogenetic levels, as well as with exchange of faunas and floras across previously isolated biogeographic regions. North Africa and Arabia share a complex geological history that dates back to the break-up of the Arabian plate from the African plate ~30–25 Mya, followed by various geological events, such as the formation of the Red Sea or the connection between the African, Arabian and Eurasian plates. Species with Saharo-Arabian distributions have shown a close association between their evolutionary history and these geological events. In this study, we investigate the systematics, biogeography and evolution of the genus Tropiocolotes, a group of small ground-dwelling geckos, comprised by 12 species distributed from the Atlantic coast of North Africa to southwestern Iran. Species delimitation analyses uncovered the existence of high levels of undescribed diversity, with forms here considered at the species level including Tropiocolotes tripolitanus (Mauritania and southern Morocco), T. nattereri (southern Israel) and T. scorteccii (Yemen and Oman). Phylogenetic and biogeographic analyses recovered two main clades, an exclusively African clade and a Saharo–Arabian clade, that split ~25 Mya following the vicariant event mediated by the separation of the Arabian and African plates. The complex geological activity around the Red Sea is associated with the diversification within the Saharo-Arabian clade, including the colonization of North Africa from a second Tropiocolotes group. Results also provide new insights into the geographic distribution of Tropiocolotes nubicus, previously considered as exclusively associated to the Nile River valley, extending its known distribution further west, up to the Central Mountains of the Sahara. Accordingly, the Nile River seems to act as a major biogeographic barrier, separating Tropiocolotes nubicus and T. steudneri in their western and eastern margins, respectively.
One of the most celebrated textbook examples of physiological adaptations to desert environments is the unique ability that desert mammals have to produce hyperosmotic urine. Commonly perceived as an ...adaptation mainly observed in small rodents, the extent to which urine‐concentrating ability has evolved independently in distinct mammalian lineages has not previously been assessed using modern phylogenetic approaches.
We review urine‐concentrating ability data from the literature in 121 mammalian species with geographic ranges encompassing varying climatic conditions. We explicitly test the general hypothesis that desert‐dwelling mammals have evolved greater ability to concentrate urine than non‐desert species, controlling for body mass, phylogenetic affinity and other covariates.
Ancestral state reconstruction across our dataset’s phylogeny shows that the ability to produce hyperosmotic urine, measured as maximum urine osmolality, has evolved convergently in mammalian species with geographic ranges characterised by low mean annual aridity index.
Phylogenetic generalised least‐squares (PGLS) models show that the mean annual aridity index of a species’ geographic range largely predicts its urine‐concentrating ability, even when accounting for body mass differences, phylogenetic correlations, the specific condition under which urine osmolality was measured, the method used to measure urine osmolality, and the species’ diet.
In contrast, we find much weaker correlations between mass‐adjusted basal metabolic rate and environmental variables when analysing 84 of the species included in the urine osmolality analysis.
Taken together, our results not only show that desert mammals effectively concentrate more urine than non‐desert mammals, but further suggest that aridity is likely to have been one of the main selective pressures leading to increasing maximum urine‐concentrating ability and driving its repeated evolution in different desert mammalian lineages.
Desert mammals are remarkably adapted in their physiology. Among the many physiological mechanisms allowing desert mammalian species to survive in extreme conditions of water scarcity is their ability to produce hyperosmotic urine. We review urine‐concentrating ability in 121 mammal species, measured as maximum urine osmolality (mOsm/kg), and use a phylogenetic comparative approach to explicitly test the hypothesis that desert‐dwelling species have evolved increased ability to concentrate urine compared to non‐desert species. We also demonstrate that the mean aridity index of a species’ geographic range largely predicts its urine‐concentrating ability. This suggests that, among the many physical and climatic challenges faced by desert species, aridity has been one of the main selective pressures leading to increasing maximum urine‐concentrating ability and driving its repeated evolution in different desert mammalian lineages. Future comprehensive statistical studies, investigating correlations of diverse bioclimatic variables with more desert adaptive phenotypes, will provide further elucidation on the extent to which climate is predictive for mammalian phenotypes.
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