Climatic niche conservatism and the evolutionary dynamics in species range boundaries: global congruence across mammals and amphibians

Aim Comparative evidence for phylogenetic niche conservatism – the tendency for lineages to retain their ancestral niches over long time scales – has so far been mixed, depending on spatial and taxonomic scale. We quantify and compare conservatism in the climatic factors defining range boundaries in extant continental mammals and amphibians in order to identify those factors that are most evolutionarily conserved, and thus hypothesized to have played a major role in determining the geographic distributions of many species. We also test whether amphibians show stronger signals of climatic niche conservatism, as expected from their greater physiological sensitivity and lower dispersal abilities. Location Global; continental land masses excluding Antarctica. Methods We used nearly complete global distributional databases to estimate the climatic niche conservatism in extant continental mammals and amphibians. We characterized the climatic niche of each species by using a suite of variables and separately investigate conservatism in each variable using both taxonomic and phylogenetic approaches. Finally, we explored the spatial, taxonomic and phylogenetic patterns in recent climatic niche evolution. Results Amphibians and mammals showed congruent patterns of conservatism in cold tolerance, with assemblages of escapee species (i.e. those escaping most from the climatic constraints of their ancestors) aggregated in the North Temperate Zone. Main conclusions The relative strength of climatic niche conservatism varies across the variables tested, but is strongest for cold tolerance in both mammals and amphibians. Despite the apparent conservatism in this variable, there is also a strong signal of recent evolutionary shifts in cold tolerance in assemblages inhabiting the North Temperate Zone. Our results thus indicate that distribution patterns of both taxa are influenced by both niche conservatism and niche evolution.     

Northwestward range expansion of the bumblebee Bombus haematurus into Central Europe is associated with warmer winters and niche conservatism

Species range expansions are crucial for understanding niche formation and the interaction with the environment. Here, we studied the bumblebee Bombus haematurus Kriechbaumer, 1870, a species historically distributed from northern Serbia through northern Iran which has very recently started expanding northwestward into Central Europe without human-mediated dispersal (i.e., it is a natural spread). After updating the global distribution of this species, we investigated if niche shifts took place during this range expansion between newly colonized and historical areas. In addition, we have explored which climatic factors may have favored the natural range expansion of the species. Our results indicated that Bombus haematurus has colonized large territories in 7 European countries outside the historical area in the period from the 1980s to 2018, a natural expansion over an area that equals 20% of the historical distribution. In addition, this bumblebee performs generalism in flower visitation and it occurs in different habitats, although a preference for forested areas clearly emerges. The land-use associated with the species in the colonized areas is similar to the historical distribution, indicating that no major niche shifts occurred during the spread. Furthermore, in recently colonized localities, the range expansion was associated with warming temperatures during the winter and also during both queen overwintering and emergence phases. These findings document a case of natural range expansion due to environmental change rather than due to niche shifts, and specifically they suggest that warmer winters could be linked to the process of natural colonization of new areas.     

Geographic patterns and environmental correlates of phylogenetic relatedness and diversity for freshwater fish assemblages in North America

The tropical niche conservatism hypothesis suggests that most groups should be most phylogenetically clustered in cold, dry environments. This idea has been well-tested in plants and some animal groups, but not for fishes. We assess the geographic patterns of freshwater fish phylogenetic structure and investigate the relationships between these patterns and environmental variables across North America and within two biogeographic realms. Phylogenetic relatedness and diversity of 360 freshwater fish assemblages across North America were quantified with three metrics based on a well-dated phylogeny, and were related to 15 environmental variables using correlation and regression analyses. Geographically, the data were analyzed for North America as well as for separate biogeographic realms. We found that cold temperatures are the strongest determinant of phylogenetic clustering overall. However, in the arid west, clustering is most pronounced in the driest regions. In eastern North America, phylogenetic clustering increases at higher latitudes, while the reverse is true in western North America. The strongest phylogenetic clustering for freshwater fish assemblages on the continent is found in the most arid, rather than the coldest, climate in North America. Our results highlight that patterns of phylogenetic structure of freshwater fishes in North America are driven by both ecological and evolutionary processes that differ regionally.     

Hidden patterns of phylogenetic non‐stationarity overwhelm comparative analyses of niche conservatism and divergence

Aim Despite the importance of the niche concept in ecological and evolutionary theory, there are still many discussions about its definition and operational evaluation, especially when dealing with niche divergence and conservatism in an explicit phylogenetic context. Here we evaluate patterns of niche evolution in 67 New World Carnivora species, measured using Hellinger distances based on MAXENT models of species distribution. We show how inferences on niche conservatism or divergence depend on the way phylogenetic patterns are analysed using matrix comparison techniques. Innovation Initially we used the simplest approach of Mantel tests to compare Hellinger distances ( N ) derived from MAXENT and phylogenetic distances ( P ) among species. Then we extended the Mantel test to generate a multivariate correlogram, in which phylogenetic patterns are analysed at multiple levels in the phylogeny and can reveal nonlinearity in the relationship between divergence and time. Finally, we proposed a new approach to generate ‘local’ (or ‘specific’) leverages of components for Mantel correlation, evaluating the non‐stationarity in the relationship between N and P for each species. This new approach was used to show if some lineages are more prone to niche shift or conservatism than others. Main conclusions Standard Mantel tests indicated a poor correspondence between N and P matrices, discarding the idea of niche conservatism for Carnivora, but the correlogram supports that closely related species tend to be more similar than expected by chance. Moreover, the variance among Hellinger distances between pairs of closely phylogenetically related species is much larger than for the entire clade. Phylogenetic non‐stationarity analysis shows that in some Carnivora families the niche tends to divergence (Mustelidae and Canidae), whereas in others it tends to conservatism (Procyonidae and Mustelidae) at short phylogenetic distances. Our analyses clearly show that misleading results may appear if niche divergence is analysed only by simple matrix correlations not taking into account complex patterns of phylogenetic nonlinearity and non‐stationarity.     

Relative effects of time for speciation and tropical niche conservatism on the latitudinal diversity gradient of phyllostomid bats

Determinants of contemporary patterns of diversity, particularly those spanning extensive latitudinal gradients, are some of the most intensely debated issues in ecology. Recently, focus has shifted from a contemporary environmental perspective to a historical one in an attempt to better understand the construction of latitudinal gradients. Although the vast majority of research on historical mechanisms has focused on tropical niche conservatism (TNC), other historical scenarios could produce similar latitudinal gradients. Herein, I formalize predictions to distinguish between two such historical processes--namely time for speciation (TFS) and TNC--and test relative support based on diversity gradients of New World bats. TFS and TNC are distinctly spatial and environmental mechanisms, respectively. Nonetheless, because of the way that environmental characteristics vary spatially, these two mechanisms are hard to distinguish. Evidence provided herein suggests that TNC has had a more important effect than TFS in determining diversity gradients of New World bats. Indeed, relative effects of different historical mechanisms, as well as relative effects of historical and contemporary environmental determinants, are probably context-dependent. Future research should move away from attempting to identify the mechanism with primacy and instead attempt to understand the particular contexts in which different mechanisms have greater influence on diversity gradients.     

The geography and ecology of plant speciation: range overlap and niche divergence in sister species

A goal of evolutionary biology is to understand the roles of geography and ecology in speciation. The recent shared ancestry of sister species can leave a major imprint on their geographical and ecological attributes, possibly revealing processes involved in speciation. We examined how ecological similarity, range overlap and range asymmetry are related to time since divergence of 71 sister species pairs in the California Floristic Province (CFP). We found that plants exhibit strikingly different age-range correlation patterns from those found for animals; the latter broadly support allopatric speciation as the primary mode of speciation. By contrast, plant sisters in the CFP were sympatric in 80% of cases and range sizes of sisters differed by a mean of 10-fold. Range overlap and range asymmetry were greatest in younger sisters. These results suggest that speciation mechanisms broadly grouped under ‘budding’ speciation, in which a larger ranged progenitor gives rise to a smaller ranged derivative species, are probably common. The ecological and reproductive similarity of sisters was significantly greater than that of sister–non-sister congeners for every trait assessed. However, shifts in at least one trait were present in 93% of the sister pairs; habitat and soil shifts were especially common. Ecological divergence did not increase with range overlap contrary to expectations under character displacement in sympatry. Our results suggest that vicariant speciation is more ubiquitous in animals than plants, perhaps owing to the sensitivity of plants to fine-scale environmental heterogeneity. Despite high levels of range overlap, ecological shifts in the process of budding speciation may result in low rates of fine-scale spatial co-occurrence. These results have implications for ecological studies of trait evolution and community assembly; despite high levels of sympatry, sister taxa and potentially other close relatives, may be missing from local communities.     

The roles of landscape context, niche breadth, and range boundaries in predicting species responses to habitat alteration

Extant species in human‐dominated landscapes differ in their sensitivity to habitat loss and fragmentation, although extinctions induced by environmental alteration reduce variation and result in a surviving subset of species with some degree of ‘resistance’. Here, we test the degree to which variable responses to habitat alteration are (1) essentially an inherent property of a taxon subject to constraints imposed by its geographical range, as suggested by Swihart et al. (2003), (2) a function of the landscape in which a species occurs, or (3) a function of spatial trends occurring on large scales. We used data collected on 33 vertebrate species during 2001–04 across the upper Wabash River basin, Indiana, in 35 square ‘landscapes’, each 23 km² in size. Six species of forest rodent, six species of grassland rodents, seven species of bats, eight species of aquatic turtles, and six species of amphibians were sampled at 504, 212, 590, 228, and 625 patches, respectively. The fraction of patches of primary habitat (e.g. forests for tree squirrels, wetlands for aquatic turtles) occupied by a target species was used as a response variable. On a basin‐wide scale, 47% of variation in proportional occupancy among species could be explained by taxon‐specific variables; occupancy rates were related positively to niche breadth and negatively to the proximity of a geographical range boundary. After controlling for species effects, landscape‐level occupancy rates varied significantly for 16 of 33 species, with variation partitioned among landscape variables alone (mean = 11% of variation), spatial trend variables alone (26%), and both variable sets jointly (8%). Among landscape variables, percentage forest cover positively affected occupancy rates of three bat species and a tree squirrel. Variation in occupancy rates among landscapes was consistent with large‐scale spatial trends for 13 species. Our findings demonstrate the general importance of niche breadth as a predictor of species responses to habitat alteration and highlight the importance of viewing the effects of habitat loss and fragmentation at multiple spatial scales.     

The spatial frequency of climatic conditions affects niche composition and functional diversity of species assemblages: the case of Angiosperms

Climatic conditions vary in spatial frequency globally. Spatially rare climatic conditions provide fewer suitable environments than common ones and should impose constraints on the types of species present locally and regionally. We used data on 467 North American angiosperms to test the effects of the spatial frequency of climatic conditions on ecological niche specialisation and functional diversity. We predicted that rare climates should favour generalist species that are able to inhabit a broader range of climatic conditions. Our results show that climate frequency filters species that differ in niche breadths and rare environments host species combinations with greater functional diversity. The proposed analytical approaches and hypotheses can be adapted to investigate different aspects of ecological assemblies and their biodiversity. We discuss different mechanisms regarding how spatial frequency of environments can affect niche composition and functional diversity. These should be useful while developing theoretical frameworks for generating a deeper understanding of its underpinnings.     

Global patterns of species richness of the holarctic alpine herb Saxifraga: the role of temperature and habitat heterogeneity

北半球高山和极地虎耳草属物种丰富度的地理格局：温度和生境异质性的作用 现代气候、生境异质性和长期气候变化对森林生态系统中分布的木本植物的物种丰富度格局的影响在以往研究中受到广泛关注,但对高寒-极地生态系统中的草本植物物种丰富度格局及其影响因素的研究仍较少。本研究旨在检验以往研究中基于物种丰富度和环境因子关系提出的假说是否能够解释高寒-极地地区典型草本植物-虎耳草属(Saxifraga)的物种丰富度格局。本研究利用全球437种虎耳草属物种分布数据,探讨了全部物种、广域和狭域物种丰富度格局的影响因素。采用广义线性模型和空间自回归模型,评估了现代气候、生境异质性和历史气候对虎耳草属物种丰富度格局的影响。采用偏回归分析了不同变量对物种丰富度的独立解释率和共同解释率,并检验了4种广泛使用的物种丰富度与环境关系模型对物种丰富度格局的解释能力。研究结果表明,温度与虎耳草属所有物种和广域物种的物种丰富度格局呈显著负相关关系,是影响物种丰富度格局最重要的环境因子,这可能反映了虎耳草属对其祖先温带生态位的保守性。生境异质性和末次冰期以来的气候变化是虎耳草属狭域物种丰富度空间变异的最佳预测因子。总体而言,包含5个预测变量的组合模型可以解释大约40%–50%的虎耳草属物种丰富度的空间变异。此外,进化和生物地理过程在虎耳草属物种丰富度格局形成方面可能发挥了重要作用,这有待进一步研究。     

Responses of 'resistant' vertebrates to habitat loss and fragmentation: the importance of niche breadth and range boundaries

Abstract. An ability to predict species' sensitivities to habitat loss and fragmentation has important conservation implications, and numerous hypotheses have been proposed to explain interspecific differences observed in human-dominated landscapes. We used occupancy data collected on 32 species of vertebrates (16 mammals and 16 amphibians) in an agricultural landscape of Indiana, USA, to compare hypotheses that focus on different causal mechanisms underlying interspecific variation in responses to habitat alteration: (1) body size; (2) morphology and development; (3) behaviour; (4) niche breadth; (5) proximity to range boundary; and multiple-process models combining main effects and interactions of hypotheses (1)–(2) and (4)–(5). The majority of habitat alteration occurred over a century ago and coincided with extinction of several species; thus, our study dealt only with variation in responses of extant species that often are considered 'resistant' to human modifications of native habitat. Corrected Akaike scores and Akaike weights provided strongest support for models incorporating niche breadth and proximity to range boundary. Measures of dietary and habitat breadth obtained from the literature were negatively correlated with sensitivity to habitat alteration. Additionally, greater sensitivity was observed for species occurring at the periphery of their geographical ranges, especially at northern or western margins. Body size, morphological, developmental and behavioural traits were inferior predictors of tolerance to fragmentation for the species and landscape we examined. Our findings reinforce the importance of niche breadth as a predictor of species' responses to habitat alteration. They also highlight the importance of viewing the effects of habitat loss and fragmentation in a landscape within a biogeographical context that considers a species' level of adaptation to local environmental conditions.     

The relationship between range size and niche breadth: a test using five species of Gammarus (Amphipoda)

Data for five closely related species of gammarid crustaceans are used to examine interspecific relationships between the breadth of fundamental tolerance or capacity and geographical range size. Gammarus duebeni is, almost without exception, the most tolerant species and that with the best physiological performance. Although there is some limited variation, the remaining species can be ranked broadly in the sequence G. zaddachi  > G. salinus  >  G. oceanicus > G. locusta . The wide tolerance and high performance of G. duebeni is associated with the occupation of a wider range of environmental 'types' than any other of the species. In terms of geographical range size, the species can be ranked from most to least widespread in the sequence G. oceanicus  > G. duebeni  >  G. zaddachi  >  G. salinus  >  G. locusta . This provides little support for Brown's hypothesis, or the argument that the more widely distributed species within a taxonomic assemblage also tend to have the widest fundamental niches. However, if marine ( G. oceanicus and G. locusta ) and estuarine ( G. duebeni , G. zaddachi , G. salinus) species are considered separately, then in each case the species with the largest geographical range is also the most tolerant/best performer. In this sense, the jack-of-all-trades is the master-of-all, rather than the master-of-none.     

Global patterns of Rhododendron diversity: The role of evolutionary time and diversification rates

Aim

Understanding the evolution of the latitudinal diversity gradient (i.e. increase in species diversity towards the tropics) is a prominent issue in ecology and biogeography. Disentangling the relative contributions of environment and evolutionary history in shaping this gradient remains a major challenge because their relative importance has been found to vary across regions and taxa. Here, using the global distributions and a molecular phylogeny of Rhododendron, one of the largest genera of flowering plants, we aim to compare the relative contributions of contemporary environment, evolutionary time and diversification rates in generating extant species diversity patterns.

Location

Global.

Time period

Undefined.

Major taxa studied

Rhododendron.

Methods

We compiled the global distributions of all Rhododendron species, and constructed a dated molecular phylogeny using nine chloroplast genes and seven nuclear regions. By integrating these two datasets, we estimated the temporal trends of Rhododendron diversification, and explored the global patterns of its species diversity, net diversification rates, and species ages. Next, we reconstructed the geographical ancestral area of the clade. Finally, we compared the relative contribution of contemporary environment, time‐for‐speciation, and diversification rates on the species diversity pattern of Rhododendron.

Results

In contrast to the predictions of the time‐for‐speciation hypothesis, we found that although Rhododendron originated at a temperate latitude, its contemporary species diversity is highest in the tropics/subtropics, suggesting an into‐the‐tropics colonization for this genus. We found that the elevated diversification induced by heterogeneous environmental conditions in the tropics/subtropics shapes the global pattern of Rhododendron diversity.

Main conclusions

Our findings support tropical and subtropical mountains as not only biodiversity and endemism hotspots, but also as cradles for the diversification of Rhododendron. Our study emphasizes the need of unifying ecological and evolutionary approaches in order to gain comprehensive understanding of the mechanisms underlying the global patterns of plant diversity.     

Plant species richness of nature reserves: the interplay of area, climate and habitat in a central European landscape

Aim To detect regional patterns of plant species richness in temperate nature reserves and determine the unbiased effects of environmental variables by mutual correlation with operating factors. Location The Czech Republic. Methods Plant species richness in 302 nature reserves was studied by using 14 explanatory variables reflecting the reserve area, altitude, climate, habitat diversity and prevailing vegetation type. Backward elimination of explanatory variables was used to analyse the data, taking into account their interactive nature, until the model contained only significant terms. Results A minimal adequate model with reserve area, mean altitude, prevailing vegetation type and habitat diversity (expressed as the number of major habitat types in the reserve) accounted for 53.9% of the variance in species number. After removing the area effect, habitat diversity explained 15.6% of variance, while prevailing vegetation type explained 29.6%. After removing the effect of both area and vegetation type, the resulting model explained 10.3% of the variance, indicating that species richness further increased with habitat diversity, and most obviously towards warm districts. After removing the effects of area, habitat diversity and climatic district, the model still explained 9.4% of the variance, and showed that species richness (i) significantly decreased with increasing mean altitude and annual precipitation, and with decreasing January temperature in the region of the mountain flora, and (ii) increased with altitudinal range in regions of temperate and thermophilous flora. Main conclusions We described, in quantitative terms, the effects of the main factors that might be considered to be determining plant species richness in temperate nature reserves, and evaluated their relative importance. The direct habitat effect on species richness was roughly equal to the direct area effect, but the total direct and indirect effects of area slightly exceeded that of habitat. It was shown that the overall effect of composite variables such as altitude or climatic district can be separated into particular climatic variables, which influence the richness of flora in a context‐specific manner. The statistical explanation of richness variation at the level of families yielded similar results to that for species, indicating that the system of nature conservation provides similar degrees of protection at different taxonomic levels.     

Habitat heterogeneity as a driver of ungulate diversity and distribution patterns: interaction of body mass and digestive strategy

Aim Classic island biogeographical theory predicts that reserves have to be large to conserve high biodiversity. Recent literature, however, suggests that habitat heterogeneity can counterbalance the effect of small reserve size. For savanna ungulates, body mass is said to drive habitat selection and facilitate species coexistence, where large species use a higher proportion of the landscape than smaller species, because a wider food quality tolerance allows them to use a higher diversity of habitat types. In this case, high habitat heterogeneity would facilitate diverse assemblages of different‐sized ungulates. Digestive physiology should further modify this relationship, because non‐ruminants have a wider diet tolerance than ruminants. We tested this hypothesis with an empirical dataset on distribution and habitat preference of different‐sized African grazers. Location Hluhluwe‐iMfolozi Park, Republic of South Africa. Methods We recorded herbivore dung and habitat type on 24 line transects varying between 4 and 11 km with a total length of 190 km to determine habitat selection and landscape distribution of six grazer species, three ruminants and three non‐ruminants. Results Larger ruminant grazers were more evenly distributed than smaller ruminants, had a more diverse use of habitats and used more low quality habitat. In contrast, non‐ruminant grazers were more evenly distributed than similar‐sized ruminants and body mass did not clearly influence diversity of habitat use and use of low quality habitat. Main conclusions We confirm that body mass influences diversity of habitat use of large herbivores but digestive strategy potentially modifies this relationship. Hence, habitat heterogeneity might facilitate herbivore diversity in savanna ecosystems and high heterogeneity might counterbalance the effects of fragmentation and declining reserve size. Concluding, processes that homogenize the landscape, such as fire (mis)management and artificial waterholes, might be as threatening to biodiversity as landscape fragmentation, especially for smaller ruminant herbivores.