Distribution Of Widespread Species Research Articles

Two dominant forms of multisite similarity decline - Their origins and interpretation.

The number of species shared by two or more sites is a fundamental measure of spatial variation in species composition. As more sites are included in the comparison of species composition, the average number of species shared across them declines, with a rate increasingly dependent on only the most widespread species. In over 80% of empirical communities, models of decline in shared species across multiple sites (multisite similarity decline) follow one of two distinct forms. An exponential form is assumed to reflect stochastic assembly and a power law form niche-based sorting, yet these explanations are largely untested, and little is known of how the two forms arise in nature. Using simulations, we first show that the distribution of the most widespread species largely differentiates the two forms, with the power law increasingly favored where such species occupy more than ~75% of sites. We reasoned the less cosmopolitan distribution of widespread species within exponential communities would manifest as differences in community biodiversity properties, specifically more aggregated within-species distributions, less even relative abundance distributions, and weaker between-species spatial associations. We tested and largely confirmed these relationships using 80 empirical datasets, suggesting that the form of multisite similarity decline offers a basis to predict how landscape-scale loss or gain of widespread species is reflected in different local-scale community structures. Such understanding could, for example, be used to predict changes in local-scale competitive interactions following shifts in widespread species' distributions. We propose multiple explanations for the origin of exponential decline, including high among-site abiotic variation, sampling of highly specialized (narrow niche width) taxa, and strong dispersal limitation. We recommend these are evaluated as alternative hypotheses to stochastic assembly.

Low-head dams induce biotic homogenization/differentiation of fish assemblages in subtropical streams.

Extensive distribution of widespread species and the loss of native species driven by anthropogenic disturbances modify community similarity, resulting in a decrease or increase in community distinctiveness. Data from four basins in the Wannan Mountains, China, were used to evaluate the effects of low‐head dams on patterns of fish faunal homogenization and differentiation based on abundance data. We aimed to examine the spatial changes in taxonomic and functional similarities of fish assemblages driven by low‐head dams and to examine whether the changes in the similarity of fish assemblages differed between taxonomic and functional components. We found that low‐head dams significantly decreased the mean taxonomic similarity but increased the mean functional similarity of fish assemblages in impoundments using abundance‐based approaches, suggesting that taxonomic differentiation accompanied functional homogenization in stream fish assemblages. These results show the importance of population abundance in structuring fish faunal homogenization and differentiation at small scales, especially when the major differences among assemblages are in species abundance ranks rather than species identities. Additionally, we also found only a weak positive correlation between changes in mean taxonomic and functional similarities, and partial pairs exhibited considerable variation in patterns of fish faunal homogenization and differentiation for taxonomic and functional components. In conclusion, this study highlighted that the observed taxonomic differentiation of current fish assemblages (short‐term phenomenon) is probably an early warning sign of further homogenization in regions where native species are completely predominated and that changes in taxonomic similarity cannot be used to predict changes in functional similarity.

Beyond tracking climate: Niche shifts during native range expansion and their implications for novel invasions

AbstractAimAlthough ecological niche models have been instrumental in understanding the widespread species distribution shifts under global change, rapid niche shifts limit model transferability to novel locations or time periods. Niche shifts during range expansion have been studied extensively in invasive species, but may also occur in native populations tracking climate change. We compared niche shifts during both types of range expansion in a Mediterranean annual plant to ask (i) whether the species' native range expansion tracked climate change, (ii) whether further range expansion was promoted by niche expansion, and (iii) how these results changed forecasts of two ongoing invasions in Australia and California.LocationEurasian Holarctic, California and Australia.TaxonDittrichia graveolens (L.) Greuter (Asteraceae).MethodsNiche shifts were quantified in both environmental and geographic space, using the framework of niche centroid shift, overlap, unfilling and expansion (COUE) as well as maximum entropy modelling. We used the historic native distribution and climate data (1901–1930) to project the expected distribution in the present climate (1990–2019) and compared it to the observed current distribution of D. graveolens. Finally, we compared invasion forecasts based on the historic and present native niches.ResultsDittrichia graveolens expanded its native range well beyond expectations based on the observed climate change, associated with a 5.5% niche expansion towards more temperate climates. In contrast, both invasions showed niche conservatism and were (still) constrained to climatic areas matching the historic native niche.Main conclusionsContrary to hypotheses in the literature, niche shifts are not necessarily more rapid in invasions than in native range expansions. We conclude that niche expansion during the process of climate tracking may cause further range expansion than expected based on climate change alone.

Genetic evidence for allopatric speciation of the Siberian ibex Capra sibirica in India

Montane systems, formed by a series of climatic oscillations and temporal topographic metamorphoses, have broken up the contiguous distribution of widespread species and accelerated allopatric speciation. We used a partial fragment of the mitochondrial cytochrome b (cytb) gene to address speciation across the entire range of the Siberian ibex Capra sibirica. We demonstrated that the Siberian ibex is a polytypic species, plausibly formed by a combination of at least 2 species and/or 3 to 4 sub-species. Bayesian phylogeny showed that the Indian-Tajikistan (I-T) clade is adequately diverged from the other clades based on the mean intra-specific distance criterion, and warrants recognition as a distinct species. We provide pragmatic evidence for the endorsement of the I-T clade as a distinct species of Siberian ibex and urge prioritization of the conservation of this species at global and regional scales.

Globally common, locally rare: revisiting disregarded genetic diversity for conservation planning of widespread species

Species endangerment, as determined by the national and international authorities, are crucial in conservation decisions at local and regional scales. While species are the priority unit of conservation, the subspecies of widespread species are often neglected in conservation planning and research, irrespective of their unique genetic identity. Peripheral populations of widespread species are often isolated and endangered while their status on the IUCN Red List is considered as ‘Least Concern’. We advocate for the evaluation of widespread polytypic species, and to recognize the importance of assessing intraspecific populations that are distinct from the distribution of widespread species.

Seasonal variations in leaf δ13C values: implications for different water-use strategies among species growing on continuous dolomite outcrops in subtropical China

Plant species growing in shallow-soil habitat are likely to experience water deficit especially in seasonally dry or arid regions. However, only scarce studies focused on their water-use strategies. The current study aimed to reveal water-use strategies of different species growing on continuous dolomite outcrops (a typical shallow-soil habitat) in subtropical China that relied on different water sources, and to investigate the differences between narrow endemic and widespread species, based on season variations in leaf δ13C values. Leaf samples of six plant species (Radermachera sinica, Sapium rotundifolium, Sterculia euosma, Schefflera octophylla, Alchornea trewioides, and Vitex negundo, in different life-forms and leaf phenologies) were collected for carbon isotope measurements in the wet and dry seasons, respectively. Contrary to the expectation, the evergreen big shrub species, S. octophylla, which always relied on deep water sources, exhibited the most positive δ13C values (high water-use efficiency, WUE), indicating more conservative water-use strategies. While the two deciduous small shrubs, A. trewioides and V. negundo, which always relied on shallow water sources, exhibited the most negative δ13C values (low WUE). This result was associated with their short life spans, indicating an opportunistic water-use strategy. Leaf δ13C values of almost all (except for S. octophylla) the selected species were significantly (P < 0.05) higher in the dry season than in the wet season. This indicated that it was a common strategy for species in rocky karst habitat to improve their WUE in dry season. Despite the similar water sources utilized by the selected three tree species, the widespread one (R. sinica) exhibited greater improvement in leaf δ13C values than the narrow endemic ones (S. rotundifolium and S. euosma). This suggested that the widespread tree species had more flexible water-use strategies. It was further speculated that broad spatial distribution of widespread species may contribute to their highly plastic responses to changes in environmental conditions rather than always maintaining high WUE.

Stochastic faunal exchanges drive diversification in widespread Wallacean and Pacific island lizards (Squamata: Scincidae: Lamprolepis smaragdina)

AbstractAimWidespread species found in disturbed habitats are often expected to be human commensals. In island systems, this association predicts that dispersal will be mediated by humans. We investigated the biogeographical relationships among populations of a widespread tree skink that inhabits coastal forest and human‐cultivated plantations in Southeast Asia. We sought to determine whether populations of the emerald tree skink, Lamprolepis smaragdina, dispersed via mechanisms that were not human‐mediated (‘natural’ dispersal) or whether dispersal was mediated by humans. The latter scenario predicts low levels of genetic differentiation across a species' range, coupled with a genetic signature of recent range expansion.LocationSoutheast Asia, the Philippines, Wallacea and the south‐western Pacific.MethodsWe analysed sequences of mitochondrial DNA from 204 samples collected throughout the range of this species. We use phylogenetic and population genetic methods to distinguish between predicted geographical patterns of genetic variation that might indicate natural or human‐mediated dispersal.ResultsIn contrast to predictions derived from similar studies of taxonomy and natural history, we found L. smaragdina to be characterized by highly structured and seemingly geographically stable mitochondrial gene lineages.Main conclusionsOur results demonstrate a novel pattern of widespread species distribution, never before observed in vertebrates of the Indo‐Australian Archipelago. Although this widespread and highly dispersive species is capable of long‐distance dispersal, and has a clear history of over‐water dispersal, it exhibits sharp genetic differentiation across its range. Our results suggest that random waif dispersal has been a pervasive ongoing phenomenon throughout the evolutionary history of this species.

Book review: Tackling thorny issues in seasonally dry tropical forests

news and update ISSN 1948‐6596 book review Tackling thorny issues in seasonally dry tropical forests The ecology and conservation of seasonally dry forests in Asia, by William J. McShea, Stuart J. Davies and Naris Bhumpakphan (editors) 2011, Smithsonian Institution Scholarly Press, 418 pp. ISBN: 978‐1‐935623‐02‐1 Price: $69.95 / £44.95 (Hardback); http://www.scholarlypress.si.edu/ Seasonally dry tropical forests: ecology and conservation, by Rodolfo Dirzo, Hillary S. Young, Harold A. Mooney and Gerardo Ceballos (editors) 2011, Island Press, 391 pp.ISBN: 978‐1‐59726‐703‐8/978‐1‐59726‐704‐5 Price: $95.00 (Hardback)/$50.00 (Paperback); http://islandpress.org/ The first difficulty in reviewing (and I presume writing) any book on seasonally dry tropical for‐ ests (SDTF) is to come to some understanding as to what SDTF actually are. I hazard a guess that what is a seasonally dry tropical forest to one per‐ son is a seasonal rain forest to another. I myself have recently treated ‘seasonally dry tropical for‐ est’ formations as various types of ‘seasonal rain forest’ (Ghazoul & Sheil, 2010). What is clear is that aseasonal tropical wet forests grade almost imperceptibly into seasonally dry evergreen for‐ est, variably deciduous forest and, ultimately, xe‐ rophytic woodland at the other extreme. Imposing clear‐cut system definitions is always going to be problematic, but it is the nature (and necessity) of human enquiry to impose some sort of classifica‐ tion system on hopelessly complex realities. In this vein two recent edited books on Neotropical (Dirzo et al.) and Asian (McShea et al.) forests de‐ fine SDTF as tropical forests with predictable, regular dry seasons lasting 4‐6 (Neotropics) or 2‐6 months (Asia), while also recognising variations on this theme. It is not so much the duration or inten‐ sity of the dry season that matters, but rather the seasonal water stress that plants are subjected to, and this is as much a function of local topography, soil and disturbance history as it is of climate. Thus in Asia SDTF can occur alongside wet ever‐ green formations in a mosaic of different vegeta‐ tion types, adding to the complexities of distin‐ guishing and mapping SDTF. Both these books begin similarly, with a couple of chapters on floristic composition and biogeography of seasonally dry tropical forests in each respective region. In the Neotropics Linares‐ Palomino et al. identify close floristic affinities among isolated SDTF regions that are distributed across a formerly hypothesised ‘Pleistocene Arc’ of SDTF that extends from Argentina in the south through Paraguay and across Brazil in the north. The Andean dry forests might represent an exten‐ sion of this arc, although the data on this point are ambiguous. Yet these authors argue that there is little evidence for a wide‐ranging Pleistocene SDTF formation, citing long‐distance dispersal events to explain the distribution of widespread species. The floristic ordination of continental Southeast Asian SDTF conducted by Bunyavejchewin et al. separates formations by elevation, topography, soil chemistry and soil physical features, all of which are related to soil water‐holding capacity, as well as the length of the dry season. A striking feature of SDTF and other tropical forests in Asia is their abundance of trees belonging to the Dip‐ terocarpaceae, yet some formations (e.g. mixed deciduous forests and lower montane forests) are notable by the near absence of dipterocarps. A biogeographic approach might provide some in‐ sights into such patterns because the Asian mixed deciduous and lower montane forests are domi‐ nated largely by families that are thought to have warm‐temperate Eurasian origins (e.g. Fagaceae, Lythraceae), while the dipterocarps originated in the southern hemisphere (Gondwana) and colo‐ nised the Asian tropics via India’s collision with Asia around 50 Mya. A fascinating chapter on the evolution of dry forest gingers by John Kress is unfortunately not placed in the context of the dis‐ tribution of forest formations outlined in the ear‐ lier chapters. The central defining feature – a predictable dry season – shapes phenological, behavioural, © 2012 the authors; journal compilation © 2012 The International Biogeography Society — frontiers of biogeography 3.4, 2012

Population distribution models: species distributions are better modeled using biologically relevant data partitions.

BackgroundPredicting the geographic distribution of widespread species through modeling is problematic for several reasons including high rates of omission errors. One potential source of error for modeling widespread species is that subspecies and/or races of species are frequently pooled for analyses, which may mask biologically relevant spatial variation within the distribution of a single widespread species. We contrast a presence-only maximum entropy model for the widely distributed oldfield mouse (Peromyscus polionotus) that includes all available presence locations for this species, with two composite maximum entropy models. The composite models either subdivided the total species distribution into four geographic quadrants or by fifteen subspecies to capture spatially relevant variation in P. polionotus distributions.ResultsDespite high Area Under the ROC Curve (AUC) values for all models, the composite species distribution model of P. polionotus generated from individual subspecies models represented the known distribution of the species much better than did the models produced by partitioning data into geographic quadrants or modeling the whole species as a single unit.ConclusionsBecause the AUC values failed to describe the differences in the predictability of the three modeling strategies, we suggest using omission curves in addition to AUC values to assess model performance. Dividing the data of a widespread species into biologically relevant partitions greatly increased the performance of our distribution model; therefore, this approach may prove to be quite practical and informative for a wide range of modeling applications.

Modelling Species' Climatic Distributions Under Habitat Constraints: A Case Study withCoturnix coturnix

Coturnix coturnix is a climatically widespread farmland specialist bird with a well-known distribution in the Iberian Peninsula. Therefore, its current real distribution can be finely mapped. We used recent atlas data and high-resolution climate layers to model the climatic distribution of this species. Next, we compared the obtained predictive maps with the real distribution of the species. Precise information about underestimation and overestimation of model predictions at different sample sizes was obtained. An increase in sample size allowed the predicted distribution to approach the current real distribution, but unbalanced the climatic prediction. This is because the distribution of occurrences is mostly determined by habitat, which depends more on agricultural factors and less on climate. Modelling the climatic distribution of widespread species while ignoring habitat constraints could lead to a non-equilibrium scenario where obtained predictions may not be reliable.

Modelling the impacts of flow regulation on fish distributions in naturally intermittent lowland streams: an approach for predicting restoration responses

Summary1. Understanding the relationships between flow regime and the distribution of biota is critical for managing flows in regulated rivers. In northern Victoria, Australia, efforts are presently underway to restore a natural, intermittent flow regime to several streams which, for over 100 years, have received perennial diversions as part of a stock, irrigation and domestic water supply.2. Bayesian, model‐averaged, binomial regression was used to predict probabilities of occurrence for 13 fish species, including five non‐native species, based on hydrologic variables characterising both the current and modelled future flow regimes at 10 sites representing a range of hydrologic regimes (categorised here as heavily regulated, moderately regulated and unregulated).3. Regression models accurately predicted present probabilities of occurrence for most species across all sites. The models predicted a reduced likelihood of large, native, flow‐dependent species occurring at regulated sites following flow restoration. Predictions regarding the future distribution of widespread species including two small‐bodied native and four exotic species were less certain as current distributions of these widespread species were unrelated to hydrologic variables we examined and thus unlikely to be significantly affected by flow restoration. The distributions of two small native species currently restricted to unregulated sites are predicted to increase throughout the system.4. This study illustrates the effects of artificially induced perennial flow on lowland fish distributions. Furthermore, the combination of pre‐restoration data together with predictive modelling provides valuable insights into the likely outcomes of flow regime shifts.5. This study clearly demonstrates the value of combining empirical research and modelling in guiding environmental flow and ecosystem restoration decisions. Knowledge from the study is now helping guide management decisions and the development of mitigation strategies to protect highly valued species in the system from potential future threats.