Global patterns in the shape of species geographical ranges reveal range determinants

Aim Do species range shapes follow general patterns? If so, what mechanisms underlie those patterns? We show for 11,582 species from a variety of taxa across the world that most species have similar latitudinal and longitudinal ranges. We then seek to disentangle the roles of climate, extrinsic dispersal limitation (e.g. barriers) and intrinsic dispersal limitation (reflecting a species’ ability to disperse) as constraints of species range shape. We also assess the relationship between range size and shape. Location Global. Methods Range shape patterns were measured as the slope of the regression of latitudinal species ranges against longitudinal ranges for each taxon and continent, and as the coefficient of determination measuring the degree of scattering of species ranges from the 1:1 line (i.e. latitudinal range = longitudinal range). Two major competing hypotheses explaining species distributions (i.e. dispersal or climatic determinism) were explored. To this end, we compared the observed slopes and coefficients of determination with those predicted by a climatic null model that estimates the potential range shapes in the absence of dispersal limitation. The predictions compared were that species distribution shapes are determined purely by (1) intrinsic dispersal limitation, (2) extrinsic dispersal limitations such as topographic barriers, and (3) climate. Results  Using this methodology, we show for a wide variety of taxa across the globe that species generally have very similar latitudinal and longitudinal ranges. However, neither neutral models assuming random but spatially constrained dispersal, nor models assuming climatic control of species distributions describe range shapes adequately. The empirical relationship between the latitudinal and longitudinal ranges of species falls between the predictions of these competing models. Main conclusions We propose that this pattern arises from the combined effect of macroclimate and intrinsic dispersal limitation, the latter being the major determinant among restricted‐range species. Hence, accurately projecting the impact of climate change onto species ranges will require a solid understanding of how climate and dispersal jointly control species ranges.     

Seeds tend to disperse further in the tropics

Despite the importance of seed dispersal in a plant's life cycle, global patterns in seed dispersal distance have seldom been studied. This paper presents the first geographically and taxonomically broad quantification of the latitudinal gradient in seed dispersal distance. Although there is substantial variation in the seed dispersal distances of different species at a given latitude, seeds disperse on average more than an order of magnitude further at the equator than towards the poles. This pattern is partially explained by plant life‐history traits that simultaneously associate with seed dispersal distance and latitude, including dispersal mode and plant height. The extended seed shadow of tropical plants could increase the distance between conspecific individuals. This could facilitate species coexistence and contribute to the maintenance of high plant diversity in tropical communities. The latitudinal gradient in dispersal distance also has implications for species’ persistence in the face of habitat fragmentation and climate change.     

Latitudinal variation in soil nematode communities under climate warming‐related range‐expanding and native plants

Current climate change has led to latitudinal and altitudinal range expansions of numerous species. During such range expansions, plant species are expected to experience changes in interactions with other organisms, especially with belowground biota that have a limited dispersal capacity. Nematodes form a key component of the belowground food web as they include bacterivores, fungivores, omnivores and root herbivores. However, their community composition under climate change‐driven intracontinental range‐expanding plants has been studied almost exclusively under controlled conditions, whereas little is known about actual patterns in the field. Here, we use novel molecular sequencing techniques combined with morphological quantification in order to examine nematode communities in the rhizospheres of four range‐expanding and four congeneric native species along a 2,000 km latitudinal transect from South‐Eastern to North‐Western Europe. We tested the hypotheses that latitudinal shifts in nematode community composition are stronger in range‐expanding plant species than in congeneric natives and that in their new range, range‐expanding plant species accumulate fewest root‐feeding nematodes. Our results show latitudinal variation in nematode community composition of both range expanders and native plant species, while operational taxonomic unit richness remained the same across ranges. Therefore, range‐expanding plant species face different nematode communities at higher latitudes, but this is also the case for widespread native plant species. Only one of the four range‐expanding plant species showed a stronger shift in nematode community composition than its congeneric native and accumulated fewer root‐feeding nematodes in its new range. We conclude that variation in nematode community composition with increasing latitude occurs for both range‐expanding and native plant species and that some range‐expanding plant species may become released from root‐feeding nematodes in the new range.     

Phytogeography of Italian deciduous oak woods based on numerical classification of plant distribution ranges

Abstract. 358 vascular plant species occurring in the deciduous oak woods of Italy were subdivided into 18 phytogeographical groups (chorotypes) through a numerical classification of their total ranges. The distribution patterns of the chorotypes are illustrated by chorograms, i.e. isopleth maps showing the joint distribution of species in Europe and surroundings regions. Except for Mediterranean species, which occur only occasionally in deciduous forests, the oak-wood flora of Italy consists of four main phytogeographical elements, which have a similar incidence (ca. 25 % each): (a) narrow-ranging, southern European species, (b) southeastern European species of submediterranean woodlands, (c) central-European species, (d) widely distributed European species. The oak woods of Italy differ from their central-European counterparts as to the relatively high floristic diversity, and in the presence of several narrow-ranging taxa, centred in different refugial areas for forest vegetation during the glacial period. There is a relation between the distribution patterns of the chorotypes and their relative frequencies in different communities; the latitudinal and longitudinal extensions of the ranges reflect the thermic and hygric conditions of the communities. The oak woods of northern and southern Italy are phytogeographically well-characterized; the former have a maximum of wide-ranging, central European species, the latter host several narrow-ranging taxa. The woodlands of central Italy have intermediate phytogeographical features, which is one of the main reasons for the difficulties in their syntaxonomical arrangement.     

Occupancy‐derived thermal affinities reflect known physiological thermal limits of marine species

Predicting how species will respond to increased environmental temperatures is key to understanding the ecological consequences of global change. The physiological tolerances of a species define its thermal limits, while its thermal affinity is a summary of the environmental temperatures at the localities at which it actually occurs. Experimentally derived thermal limits are known to be related to observed latitudinal ranges in marine species, but accurate range maps from which to derive latitudinal ranges are lacking for many marine species. An alternative approach is to combine widely available data on global occurrences with gridded global temperature datasets to derive measures of species‐level “thermal affinity”—that is, measures of the central tendency, variation, and upper and lower bounds of the environmental temperatures at the locations at which a species has been recorded to occur. Here, we test the extent to which such occupancy‐derived measures of thermal affinity are related to the known thermal limits of marine species using data on 533 marine species from 24 taxonomic classes and with experimentally derived critical upper temperatures spanning 2–44.5°C. We show that thermal affinity estimates are consistently and positively related to the physiological tolerances of marine species, despite gaps and biases in the source data. Our method allows thermal affinity measures to be rapidly and repeatably estimated for many thousands more marine species, substantially expanding the potential to assess vulnerability of marine communities to warming seas.     

Seed dispersal spectra: a comparison of temperate plant communities

Abstract. We compare the dispersal spectra of diaspores from varied plant communities in Australia, New Zealand, and North America, assigning dispersal mode to each diaspore type on the basis of apparent morphological adaptations. Species with ballistic and external dispersal modes were uncommon in most communities we surveyed. Ant dispersal was also rather uncommon, except in some Australian sclerophyll vegetation types. The frequency of vertebrate dispersal ranged up to 60% of the flora, the highest frequencies occurring in New Zealand forests. Wind dispersal ranged as high as 70% of the flora, with the highest values in Alaska, but usually comprised 10–30% of the flora. Many species in most communities had diaspores with no special morphological device for dispersal. Physiognomically similar vegetation types indifferentbiogeographic regions usually had somewhat dissimilar dispersal spectra. The frequency of dispersal by vertebrates often increased and the frequency of species with no special dispersal device decreased along gradients of increasing vertical diversity of vegetation structure. Elevation and moisture gradients also exhibited shifts in dispersal spectra. Within Australia, vertebrate- and wind-dispersal increased in frequency along a soil-fertility gradient, and dispersal by ants and by no special device decreased. Habitat breadths (across plant communities) and microhabitat breadths (within communities) for species of each major dispersal type did not show consistent differences, in general. Ant-dispersed species often had lower cover-values than other species in several Australian vegetation types. We discuss the ecological bases of these differences in dispersal spectra in terms of the availability of dispersal agents, seed size, and other ecological constraints. Seed size is suggested to be one ecological factor that is probably of general relevance to the evolution of dispersal syndromes.     

Latitudinal and longitudinal barriers in global biogeography

Due to changes in climate and continental arrangement, plant and animal assemblages faced different dispersal barriers at different moments in Earth's history. It is generally accepted that groups which diversified during times of Gondwanan-Laurasian separation show different distribution patterns from those of more recent origin. Here I present principal component-derived maps for two globally distributed groups, with ca 1000 species each. Gymnosperm assemblages perfectly illustrate the existence of southern and northern components, corresponding to the Gondwanan and Laurasian temperate floras at the time when angiosperms started becoming dominant in the tropics, thus imposing a latitudinal barrier. Bat (chiropteran) assemblages indicate that the major biogeographical barrier in their Cenozoic dispersal was the longitudinal separation between the Old and New World.     

Floristic patterns and plant traits of Mediterranean communities in fragmented habitats

Aim To contrast floristic spatial patterns and the importance of habitat fragmentation in two plant communities (grassland and scrubland) in the context of ecological succession. We ask whether plant assemblages are affected by habitat fragmentation and, if so, at what spatial scale? Does the relative importance of the niche differentiation and dispersal‐limitation mechanisms change throughout secondary succession? Is the dispersal‐limitation mechanism related to plant functional traits? Location A Mediterranean region, the massif of Albera (Spain). Methods Using a SPOT satellite image to describe the landscape, we tested the effect of habitat fragmentation on species composition, determining the spatial scale of the assemblage response. We then assessed the relative importance of dispersal‐related factors (habitat fragmentation and geographical distance) and environmental constraints (climate‐related variables) influencing species similarity. We tested the association between dispersal‐related factors and plant traits (dispersal mode and life form). Results In both community types, plant composition was partially affected by the surrounding vegetation. In scrublands, animal‐dispersed and woody plants were abundant in landscapes dominated by closed forests, whereas wind‐dispersed annual herbs were poorly represented in those landscapes. Scrubby assemblages were more dependent on geographical distance, habitat fragmentation and climate conditions (temperature, rainfall and solar radiation); grasslands were described only by habitat fragmentation and rainfall. Plant traits did not explain variation in spatial structuring of assemblages. Main conclusions Plant establishment in early Mediterranean communities may be driven primarily by migration from neighbouring established communities, whereas the importance of habitat specialization and community drift increases over time. Plant life forms and dispersal modes did not explain the spatial variation of species distribution, but species richness within the community with differing plant traits was affected by habitat patchiness.     

Vegetation discontinuities and altitudinal indicator species in mountains of West Greenland: finding the best positions and traits to observe the impact of climate warming in the Arctic

Aims

To delineate boundaries of vegetation belts, characterize these belts by indicator species, plant functional types and plant distribution types, and explore options for climate change monitoring.

Location

Three research sites in the continental inland of West Greenland.

Methods

Based on spatially constrained clustering of 147 vegetation relevés and 145 transect plots of plant communities, boundaries of altitudinal vegetation belts were assessed. Indicators for altitudinal sections were identified from 664 vegetation relevés among vascular plants, bryophytes, lichens and plant functional types using indicator species analysis. The performance of different plant groups along the altitudinal gradient was visualized with response curves.

Results

Boundaries of altitudinal vegetation belts were detected at 400, 800 and 1175 m a.s.l. on north‐facing slopes and at 450, 900 and 1250 m a.s.l. on south‐facing slopes. The resulting four vegetation belts were well defined by 99 indicator species and nine indicator plant functional types. Species, plant functional types and vascular plant distribution types showed clear sequences along the altitudinal gradient, which partly resemble their distribution along the latitudinal gradient.

Conclusions

As an easily observable expansion of shrubs and a decline of mosses and lichens is expected, the boundary at 400/450 m a.s.l. is particularly promising for climate change monitoring. The anticipated replacement of numerous cryophilous by thermophilous indicator species, as well as an obvious shift of plant functional types suggest several monitoring options at 800/900 m a.s.l. The summit areas above 1175/1250 m a.s.l., having a discontinuous plant cover, are considered to be especially vulnerable to fast invasion by species of lower altitudes such as woody plants and sedges. Due to steep gradients and short migration distances in mountains, it can be assumed that these anticipated changes in the study area will be stronger and faster than the already observed changes along the latitudinal gradient in lowland areas of the Arctic.

     

Limited filling of the potential range in European tree species

The relative roles of environment and history in controlling large‐scale species distributions are important not only theoretically, but also for forecasting range responses to climatic change. Here, we use atlas data to examine the extent to which 55 tree species fill their climatically determined potential ranges in Europe. Quantifying range filling (R/P) as realized/potential range size ratios using bioclimatic envelope modelling we find mean R/P = 38.3% (±30.3% SD). Many European tree species naturalize extensively outside their native ranges, providing support for interpreting the many low R/Ps as primarily reflecting dispersal limitation. R/P increases strongly with latitudinal range centroid and secondarily with hardiness and decreases weakly with longitudinal range centroid. Hence, European tree species ranges appear strongly controlled by geographical dispersal constraints on post‐glacial expansion as well as climate. Consequently, we expect European tree species to show only limited tracking of near‐future climate changes.     

Life-history traits are correlated with geographical distribution patterns of western European forest herb species

Aim To investigate whether six plant life‐history traits that have been related to colonization ability at local scales are also related to the geographical range characteristics of 273 forest plant species. Location Continental western Europe, five countries in particular: France, Luxemburg, Belgium, the Netherlands and Germany. The region is situated between 42° and 55°N and 5°W and 15°E and has a summed total area of 971,404 km². Methods Distribution data were compiled from five national data bases and converted to a 10′ grid. Life‐history traits were taken from existing compilations of autecological information of European species. The spatial arrangement of occupied grid cells was investigated using Ripley's K. Cross‐species correlations and phylogenetically independent contrasts were used to investigate the relationships between plant life‐history traits and three range characteristics: area of occupancy, latitudinal extent and centroid latitude. Results For herbaceous species, seed dispersal mode, seed production and seed bank longevity exhibited significant associations with geographical range characteristics, including area of occupancy. Woody plant species exhibited fewer significant associations, although maximum height was positively associated with range centroid latitude within the study area. Furthermore, the ranges of species with limited dispersal ability were found to be more clustered than the ranges of species with morphological adaptations for long‐distance seed dispersal. Main conclusions For western European forest plant species, life‐history traits that are related to colonization ability at local scales are associated with variation in large‐scale geographical range characteristics. This finding implies that the distributions of some forest plant species in the study area may be limited by seed dispersal and colonization capacity rather than climate or other environmental factors.     

黑河下游额济纳绿洲植物群落特征与物种多样性研究

根据53个20 m×20 m样方调查资料,对黑河下游额济纳绿洲植物群落特征及物种多样性进行研究.结果表明:(1)调查样方的植物种类组成成分简单,科属组成较为分散.共有12科26属28种,以藜科、菊科为主,分别占21.43%和14.29%.种类优势现象明显,重要值>10的物种主要有胡杨、梭梭、柽柳、白刺、沙拐枣、苦豆子等;(2)不同植物群落类型的物种多样性指数均较低,且存在较大差异.以重要值计算的Margalef丰富度指数(Rm)介于0.027 3~0.567 7,Simpson多样性指数(Ds)介于0.677 8~0.999 3,Shannon-Weiner多样性指数(H′)介于0.098 2~0.367 3,Pielou均匀度指数(J′)在0.078~0.383之间,表明荒漠绿洲植物群落的结构简单、组织水平低;(3)样方统计的物种多样性指数纬向变化没有经向变化趋势明显,Ds和H′的纬向变化在42.02°N附近存在一个明显的高值区,经向变化呈先增后减的趋势,J′纬向变化与Ds和H′变化趋势较为一致,经向变化趋势不明显,呈连续波动的复杂变化特征.     

Wing morphology and migration status,but not body size,habitat or Rapoport's rule predict range size in North‐American dragonflies (Odonata: Libellulidae)

Understanding why species range sizes vary is important for predicting the impact of environmental change on biodiversity. Here we use a multi‐variable approach in a phylogenetic comparative context to understand how four morphological, two ecological, and two eco‐geographical variables are associated with range size, latitudinal range and longitudinal range in 81 species of North‐American libellulid dragonflies. Our results show that: 1) migratory species and species with a more expanded basal hindwing lobe have a larger range size; 2) opposite to Rapoport's rule, latitudinal range is negatively correlated with mid‐range latitude; 3) longitudinal range is predicted by wing morphology and migration; 4) body size and larval habitat are not correlated with range size, latitudinal range or longitudinal range. These results suggest that dispersal‐related traits, such as wing shape and migratory status, are important factors in predicting the range size of libellulid dragonflies. In addition, the reverse Rapoport's rule suggests that more northern‐centred species might be more specialized than more southern‐centred species. We suggest that the variables predicting range size are likely imposed by taxon‐specific morphological, ecological, physiological and behavioural traits. Taxon‐specific knowledge is thus necessary to understand the dynamics of range sizes and is important to implement successful restoration and conservation plans of threatened species.     

Are Plant Species Able to Keep Pace with the Rapidly Changing Climate?

Future climate change is predicted to advance faster than the postglacial warming. Migration may therefore become a key driver for future development of biodiversity and ecosystem functioning. For 140 European plant species we computed past range shifts since the last glacial maximum and future range shifts for a variety of Intergovernmental Panel on Climate Change (IPCC) scenarios and global circulation models (GCMs). Range shift rates were estimated by means of species distribution modelling (SDM). With process-based seed dispersal models we estimated species-specific migration rates for 27 dispersal modes addressing dispersal by wind (anemochory) for different wind conditions, as well as dispersal by mammals (dispersal on animal''s coat – epizoochory and dispersal by animals after feeding and digestion – endozoochory) considering different animal species. Our process-based modelled migration rates generally exceeded the postglacial range shift rates indicating that the process-based models we used are capable of predicting migration rates that are in accordance with realized past migration. For most of the considered species, the modelled migration rates were considerably lower than the expected future climate change induced range shift rates. This implies that most plant species will not entirely be able to follow future climate-change-induced range shifts due to dispersal limitation. Animals with large day- and home-ranges are highly important for achieving high migration rates for many plant species, whereas anemochory is relevant for only few species.     

Effects of seasonal migration on the latitudinal distribution of west Palaearctic bird species

This paper examines seasonal changes in the latitudinal distribution of birds (excluding seabirds) that breed in the western Palaearctic. Some resident species occupy ranges that span less than 5° of latitude year-round, while some migrant species range over more than 120° of latitude during the course of a year. Among migrant species of land and freshwater habitats, the latitudinal spans of breeding and wintering ranges are correlated. In general, species that breed over a narrow span of latitude also winter over a narrow span of latitude, and vice versa. Among both groups, for any given span of breeding range, species that winter partly in Eurasia and partly in Africa winter over a wider latitudinal span than those that winter entirely within Eurasia or entirely within Africa. Among coastal birds, there is no correlation between the latitudinal spans of breeding and winter areas; most shorebird species breed over a narrow span of (northern) latitude and winter over a wide span distributed linearly along coastlines. Several migration patterns can be distinguished, from complete overlap of breeding and wintering ranges in year-round residents, through partial separation of summer and winter ranges, to complete separation of summer and winter ranges in different geographical regions. In some such species, the gap between breeding and wintering ranges spans up to 55° of latitude (6000 km).     

Consequences of varying regional heterogeneity in source–sink metacommunities

Although the influence of dispersal on coexistence mechanisms in metacommunities has received great emphasis, few studies have addressed how such influence is affected varying regional heterogeneity. We present a mechanistic model of resource competition in a metacommunity based on classical models of plant competition for limiting resources. We defined regional heterogeneity as the differences in resource supply rates (or resource availabilities) across local communities. As suggested by previous work, the highest diversify occurred at intermediate levels of dispersal among local communities. However our model shows how the effects of dispersal depend on the amount of heterogeneity among local communities and vice versa. Both regional and local species richness were the highest when heterogeneity was intermediate. We suggest that empirical studies that found no evidence for source–sink or mass effects at the community level may have examined communities with limited ranges of dispersal and regional heterogeneity. This model of species coexistence contributes to a broader understanding of patterns in real communities.     

Community compensatory trend prevails from tropical to temperate forest

Community compensatory trend (CCT) is thought to facilitate persistence of rare species and thus stabilize species composition in tropical forests. However, whether CCT acts over broad geographical ranges is still in question. In this study, we tested for the presence of negative density dependence (NDD) and CCT in three forests along a tropical-temperate gradient. Inventory data were collected from forest communities located in three different latitudinal zones in China. Two widely used methods were used to test for NDD at the community level. The first method considered relationships between the relative abundance ratio and adult abundance. The second method emphasized the effect of adult abundance on abundance of established younger trees. Evidence for NDD acting on different growth forms was tested by using the first method, and the presence of CCT was tested by checking whether adult abundance of rare species affected that of established younger trees less than did abundance of common species. Both analyses indicated that NDD existed in seedling, sapling and pole stages in all three plant communities and that this effect increased with latitude. However, the extent of NDD varied among understory, midstory and canopy trees in the three communities along the gradient. Additionally, despite evidence of NDD for almost all common species, only a portion of rare species showed NDD, supporting the action of CCT in all three communities. So, we conclude that NDD and CCT prevail in the three recruitment stages of the tree communities studied; rare species achieve relative advantage through CCT and thus persist in these communities; CCT clearly facilitates newly established species and maintains tree diversity within communities across our latitudinal gradient.     

Emus as non-standard seed dispersers and their potential for long-distance dispersal

Long-distance seed dispersal may have important consequences for species range, migration rates, metapopulation dynamics, and gene flow. Plants have evolved various adaptations for seed dispersal by standard agents, with typical dispersal distances associated with them. Seeds may also be dispersed by non-standard agents for which they do not show any apparent adaptation and may reach long distances. By sampling the droppings of emus Dromaius novaehollandiae at three localities in Western Australia, we investigated their potential to act as long-distance dispersers of seeds with adaptations for dispersal modes other than endozoochory, such as unassisted, ant, wind and exozoochory, for which they act as non-standard agents. Seventy-seven plant species with five types of dispersal syndromes were found in the 112 droppings analysed, with at least 68 having viable seeds. Although endozoochory was the most frequent syndrome, the presence of other syndromes was important in terms of number of species (61%) and seeds (50%). Estimates of species richness indicated that an increase in sampling effort would increase the number of species observed, especially among non-endozoochores. As a consequence of their long gut retention times and high mobility, emus can provide long-distance dispersal opportunities that may be especially relevant for species with dispersal modes of typically short distances (unassisted, ant).
Our results suggest that the role of emus as non-standard agents for long-distance dispersal should be taken into account for understanding current geographic ranges, gene flow and metapopulation dynamics of some plant species, as well as for predicting their future responses to climate change and fragmentation.     

Latitudinal pattern in plant composition along the Peruvian and Chilean fog oases

Fog oases in western South America (locally named lomas) are distributed in a kind of fragmented or patchy way into the coastal desert. Their origin, as well as their current ecological connections in terms of species' dispersal capability, remains an open question. We analyzed the latitudinal pattern in plant species and phylogenetic similarities of 13 lomas, which cover the latitudinal extent of these habitats, from 7°58′ to 26°15′ S. A data-set of 1004 species from available checklists was considered. Plant species composition and phylogenetic relationships among lomas were analyzed by non-metric multidimensional scaling. Our results show three main groups of lomas (northern Peruvian, southern Peruvian, and North-Central Chilean lomas) that are aligned along a complex, nonlinear north–south gradient in ordination space. The weak species overlap between Peruvian and Chilean lomas, together with the higher content in endemic species of the Chilean communities, supports the hypothesis that, at least recently, species composition of the three main groups of lomas has been shaped by desert barriers limiting plant dispersal.     

Postglacial migration supplements climate in determining plant species ranges in Europe

The influence of dispersal limitation on species ranges remains controversial. Considering the dramatic impacts of the last glaciation in Europe, species might not have tracked climate changes through time and, as a consequence, their present-day ranges might be in disequilibrium with current climate. For 1016 European plant species, we assessed the relative importance of current climate and limited postglacial migration in determining species ranges using regression modelling and explanatory variables representing climate, and a novel species-specific hind-casting-based measure of accessibility to postglacial colonization. Climate was important for all species, while postglacial colonization also constrained the ranges of more than 50 per cent of the species. On average, climate explained five times more variation in species ranges than accessibility, but accessibility was the strongest determinant for one-sixth of the species. Accessibility was particularly important for species with limited long-distance dispersal ability, with southern glacial ranges, seed plants compared with ferns, and small-range species in southern Europe. In addition, accessibility explained one-third of the variation in species' disequilibrium with climate as measured by the realized/potential range size ratio computed with niche modelling. In conclusion, we show that although climate is the dominant broad-scale determinant of European plant species ranges, constrained dispersal plays an important supplementary role.