Phylogenetic correlates of extinction risk in mammals: species in older lineages are not at greater risk

Phylogenetic information is becoming a recognized basis for evaluating conservation priorities, but associations between extinction risk and properties of a phylogeny such as diversification rates and phylogenetic lineage ages remain unclear. Limited taxon-specific analyses suggest that species in older lineages are at greater risk. We calculate quantitative properties of the mammalian phylogeny and model extinction risk as an ordinal index based on International Union for Conservation of Nature Red List categories. We test for associations between lineage age, clade size, evolutionary distinctiveness and extinction risk for 3308 species of terrestrial mammals. We show no significant global or regional associations, and three significant relationships within taxonomic groups. Extinction risk increases for evolutionarily distinctive primates and decreases with lineage age when lemurs are excluded. Lagomorph species (rabbits, hares and pikas) that have more close relatives are less threatened. We examine the relationship between net diversification rates and extinction risk for 173 genera and find no pattern. We conclude that despite being under-represented in the frequency distribution of lineage ages, species in older, slower evolving and distinct lineages are not more threatened or extinction-prone. Their extinction, however, would represent a disproportionate loss of unique evolutionary history.     

Plant diversity in tropical forests: a review of mechanisms of species coexistence

Evidence concerning mechanisms hypothesized to explain species coexistence in hyper-diverse communities is reviewed for tropical forest plants. Three hypotheses receive strong support. Niche differences are evident from non-random spatial distributions along micro-topographic gradients and from a survivorship-growth tradeoff during regeneration. Host-specific pests reduce recruitment near reproductive adults (the Janzen-Connell effect), and, negative density dependence occurs over larger spatial scales among the more abundant species and may regulate their populations. A fourth hypothesis, that suppressed understory plants rarely come into competition with one another, has not been considered before and has profound implications for species coexistence. These hypotheses are mutually compatible. Infrequent competition among suppressed understory plants, niche differences, and Janzen-Connell effects may facilitate the coexistence of the many rare plant species found in tropical forests while negative density dependence regulates the few most successful and abundant species.     

Forecasting insect species richness scores in poorly surveyed territories: the case of the Portuguese dung beetles (Col. Scarabaeinae)

Large-scale biodiversity assessment of faunal distribution is needed in poorly sampled areas. In this paper, Scarabaeinae dung beetle species richness in Portugal is forecasted from a model built with a data set from areas identified as well sampled. Generalized linear models are used to relate the number of Scarabaeinae species in each Portuguese UTM 50 × 50 grid square with a set of 25 predictor variables (geographic, topographic, climatic and land cover) extracted from a geographic information system (GIS). Between-squares sampling effort unevenness, spatial autocorrelation of environmental data, non-linear relationships between variables and an assessment of the models' predictive power, the main shortcomings in geographic species richness modelling, are addressed. This methodological approach has proved to be reliable and accurate enough in estimating species richness distribution, thus providing a tool to identify areas as potential targets for conservation policies in poorly inventoried countries.     

Scale insect host ranges are broader in the tropics

The specificity of the interactions between plants and their consumers varies considerably. The evolutionary and ecological factors underlying this variation are unclear. Several potential explanatory factors vary with latitude, for example plant species richness and the intensity of herbivory. Here, we use comparative phylogenetic methods to test the effect of latitude on host range in scale insects. We find that, on average, scale insects that occur in lower latitudes are more polyphagous. This result is at odds with the general pattern of greater host-plant specificity of insects in the tropics. We propose that this disparity reflects a high cost for host specificity in scale insects, stemming from unusual aspects of scale insect life history, for example, passive wind-driven dispersal. More broadly, the strong evidence for pervasive effects of geography on host range across insect groups stands in stark contrast to the weak evidence for constraints on host range due to genetic trade-offs.     

Species richness of vascular plantsin the subarctic landscape of northern Finland:modelling relationships to the environment

This paper presents models based on empirical data which can be used to predict the patterns of species richness of vascular plants at the poorly explored mesoscale. Using generalized linear modelling, multiple regression models of species richness in the Kevo Nature Reserve, North Finland, are built with a training set of 257 grid squares and 33 environmental variables. We validated the accuracy of the derived models with an independent test set of 100 grid squares. Two different modelling approaches are used: one where species richness is treated straightforwardly as the response variable, and another where it is tentatively stratified into two groups according to taxon types, i.e. alpine taxa versus wide-spread and silvine (forest) taxa. However, the latter approach only marginally improved the accuracy of the predictions of total number of species. Linear altitudinal variables were among the best predictors of vascular plant richness at the mesoscale. As variables involving altitude are crude surrogates for energy-related factors, the results support the available energy hypothesis and advocate its significance in richness-environment relationships. Other important predictors of species richness included length of rivers and brooks, abundance of cliff walls, occurrences of steep-sided gorges and valleys, and relative abundance of gabbro in bedrock. However, the accuracy of the predictions in the derived models is relatively modest. This points towards the necessity of field work as a final guarantee to identify local hotspots of vascular plant species in a subarctic landscape. This revised version was published online in November 2006 with corrections to the Cover Date.     

Using broad-scale, community survey data to compare species conservation strategies across regions: A case study of the Koala in a set of adjacent 'catchments'

Summary   Managers of wildlife populations with a wide geographical range are understandably interested in the question of whether they can manage a broader population with a single conservation strategy (e.g. covering a set of adjacent management regions, referred to as 'catchments' in Australia) or whether separate strategies are required for individual catchments. We addressed this question using data from a statewide, community wildlife survey to quantify Koala ( Phascolarctos cinereus ) habitat relationships in the catchments of four adjacent Catchment Management Authorities or CMA (>10 000 km²) of New South Wales, Australia and then tested whether these habitat relationships were similar across catchments. Although the results were constrained by the coarse resolution of the community survey and environmental data, we were able to model broad-scale patterns of habitat use. Model explanatory power and cross-regional predictability was low, but consistent with Koala ecology. Two environmental variables emerged as having a strong relationship with Koala presence – mean elevation and percentage of fertile soils – the importance of which varied among catchments depending on land-use patterns. The results highlight the need for local wildlife management plans, not a single plan covering multiple catchments.     

Mammals of Australian islands: factors influencing species richness

Distribution patterns of indigenous non-volant terrestrial mammals on 257 Australian islands were examined in relation to environmental parameters and the effects of human-induced disturbance during prehistoric and historic times on island species numbers. Species occurrence for individual species, for taxonomic and trophic groups, and for all species together was related to environmental parameters using regression analysis and the extreme-value function model. Patterns of occurrence were examined separately within three major biogeographic regions derived by pattern analysis. The number of species known to have occurred on these islands during historic times was adequately predicted from area alone. No statistically significant improvement in predicted species number was gained by including island elevation, mean annual rainfall, isolation from the mainland or the number of potentially competing species present on the island. Similarly, no single factor other than area was found to influence consistently the presence of individual species. We conclude that the occurrence of indigenous non-volant terrestrial mammal species on these islands indicates a relictual rather than equilibrial fauna. Visitation by Aboriginal people during prehistoric times did not significantly increase mammal extinctions on islands. Examination of patterns of species richness for a given area on a regional basis showed that islands in and around Bass Strait and Tasmania (Bass Region) were the most species-rich, islands off the northern coasts were slightly less rich, and islands off the south western coasts had fewest species. This is in contrast to the usual latitudinal gradient in species richness patterns. However, islands off the northern and eastern coasts had an overall greater number of different species. When considered in relation to the number of different species of mammals occurring within each region, islands of a given size in Bass Region typically bore a higher proportion of this species pool than other regions. The Bass Region was found to be particularly rich in macropoid herbivores and dasyurid carnivores and insectivores. Analyses indicated that there is a very strong relationship between the presence of exotics as a whole and the local extinction of native mammals. Many mammal species formerly widespread on the Australian mainland are now restricted totally to islands (nine species) or are threatened with extinction on the mainland and have island populations of conservation significance (ten species). In all, thirty-five islands protect eighteen taxa of Australian threatened mammals. The land-use and management of these islands is of considerable importance to nature conservation. The introduction of exotic mammals to these islands should be prevented; any introductions that occur should be eradicated immediately.     

Seasonal variation in the diversity and species richness of phytoplankton in a tropical eutrophic reservoir

The water chemistry, structure of sediment grain size, algal biomass, and patterns of nine bacteria physiological groups were studied monthly from May to October 1991 in an adjacent stream, ecotone, and reservoir zones (southern Poland). The distribution of five particulate organic carbon fractions was significantly different among the zones. Biomass of benthic algae demonstrated a maximum in the ecotone (22.74 g C m^–2). Most of the bacterial groups were more numerous in the stream sediments where aerobic heterotrophs prevailed (1.2–6.5 × 10¹¹ cells m^–2). The significant differences in density were found for anaerobic heterotrophs, anaerobic nitrogen fixing, amylolytic, and cellulolytic bacteria among the zones. The small density of bacteria in the ecotone was probably an effect of the rapid water fluctuations, accompanied by movement of fine sediments or/and an inhibitory effect of compounds secreted by the periphyton. The principal component analysis showed that the ecotone zone was more similar to the reservoir open water than to the stream.     

Cascade effects of crop species richness on the diversity of pest insects and their natural enemies

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology.We explore the effects of crop species richness on the diversity of pest insects and their natural enemies.Using data from a four-year experiment with five levels of crop species richness,we found that crop species richness significantly affected the pest species richness,but there were no significant effects on richness of the pests’natural enemies.In contrast,the species richness of pest insects significantly affected their natural enemies.These findings suggest a cascade effect where trophic interactions are strong between adjacent trophic levels,while the interactions between connected but nonadjacent trophic levels are weakened by the intermediate trophic level.High crop species richness resulted in a more stable arthropod community compared with communities in monoculture crops.Our results highlight the complicated cross-trophic interactions and the crucial role of crop diversity in the food webs of agro-ecosystems.     

Characterization and ranking of biodiversity hotspots: centres of species richness and endemism

On the basis of 121 areas worldwide, the regressions of plantspecies–area relationships and of endemism–area relationships inlog–log space are calculated. These formulae form the basis forcalculating -values. -Valuesdetermine the ranking of biodiversity hotspots. In most cases, areas which havebeen published as biodiversity hotspots are characterized by high values of, i.e. by rich compositions of vascularplant species and high rates of endemism.     

A large-scale inventory of liana diversity in tropical forests of South Eastern Ghats,India

Among the plant life-forms, lianas, the wood climbers still remain less studied than trees. The forests of Eastern Ghats of India are also relatively under studied compared with the Western Ghats biodiversity hotspot. We conducted a large-scale, landscape-level investigation of liana diversity in six hill complexes of the South Eastern Ghats, which covers 4297 km². We divided the study area into 6.25 km × 6.25 km grids and within each grid a 0.5 ha (5 m × 1000 m) transect was established and all lianas ≥1.5 cm diameter at breast height (dbh) were inventoried in 110 transects totalling a 55-ha area. Liana diversity totalled 143 species in 83 genera and 37 families in the 55 ha sampled. Of these 20 species (28.6%) were endemic to peninsular India and 7 (10%) species belonged to the rare and endangered category. Liana species richness ranged from 8–35 species and density 95–544 individuals per transect. A total of 32 033 liana individuals were enumerated in the 55 ha and the mean abundance was 291 individuals per transect. Across sites, liana abundance varied significantly, but not species richness and basal area. Asclepiadaceae (13 species, 9%) and Apocynaceae (11 species, 8%) constituted the most diverse liana families, followed by Papilionaceae, Vitaceae (10 each, 7%), Convolvulaceae, Mimosaceae, Oleaceae (8 each, 6%), Capparaceae, Rhamnaceae (7 each, 5%) and Menispermaceae (5 species, 3%). In liana stem size distribution, the lowest diameter class (1.5–3 cm dbh) accounted for greatest species richness (137 species, 96%), abundance (27 358 individuals, 85%) and basal area (13.5 m², 36%). The stem twiners were the predominant climber type in terms of species richness (61 species, 42.65%), whereas the armed scramblers were abundant due to stem density (21 571 individuals, 67.34%). The dispersal modes of lianas, assessed by fruit types, revealed zoochory as the prevalent mode (85 species, 59%) indicating the faunal dependence of lianas in the Eastern Ghats landscape. Liana diversity of the Eastern Ghats was compared with inventories made across the tropics. With these baseline data generated on lianas, the importance of biodiversity conservation of the already fragmented South Eastern Ghats region is underlined and potential areas of further research on liana ecology are suggested.     

Species richness, rarity and endemicity of European mammals: a biogeographical approach

This paper investigates the distribution of species richness, rarity and endemicity of European land mammals (bats and introduced species excluded). The highest level of species richness was in Central Europe, while Southern areas had the highest rarity and endemicity scores. The distribution of richness was affected by the location of sampling points in islands and peninsulas. After excluding these sampling points, richness continued to decrease Westward suggesting the existence of a large-scale peninsular effect on mammal distribution. These patterns of continental distribution of richness, rarity and endemicity could be the result of the distribution of refuge areas in the southern Mediterranean peninsulas, and the Pleistocene advances and retreats of mammals throughout the Western Palearctic. Thus, European mammal distribution can be interpreted on the basis of two different patterns of abundance distribution in which Palearctic species reduce their abundance from central-Europe outwards, while endemic, rare species show a similar depletion in the North. It should be useful to evaluate the role of the different regions in Europe in conserving the demographic interactions between central and peripheral populations of mammal species. Given the restricted distribution and potential small size of population, these endemic species are most likely to be susceptible to anthropogenic environmental degradation.     

Conservation of vascular plants in single large and several small mires: species richness, rarity and taxonomic diversity

1. This study on vascular plant species of boreal spruce and pine mires concentrated on two geometrical principles: whether single large or several small (SLOSS) reserves contain more species and whether patch shape should be as nearly circular as possible.
2. SLOSS and patch shape have usually been tested by using species richness. Only a few studies have taken the rarity of species into account, and taxonomic diversity has never been used. In our study, all three of these factors were used.
3. Our results showed that the number of species was not related to the spruce mire size, but it increased in relation to the pine mire size. In contrast, the rarity score increased in relation to the area of spruce mires, but it was not related to the area of pine mires. Taxonomic diversity was not related to size in the case of spruce mires, but it increased with pine mires.
4. The SLOSS comparison showed that several small mires contained more vascular plant species than a large one of equal size. Several small mires also had higher rarity scores and taxonomic diversity than a single large mire. The number of species, rarity score and taxonomic diversity increased in relation to the number of small mires in a group. The same results were obtained with both spruce and pine mires.
5. Species richness, rarity score and taxonomic diversity were not related to mire shape. The results did not depend on the mire type.     

Climatic and biophysical controls on conifer species distributions in mountain forests of Washington State, USA

Abstract Aim The purpose of this study was to quantify relationships between conifer species distributions and climatic and biophysical variables, in order to provide better insight into the potential for redistribution of species on the landscape in response to climatic change. Location Data are from 10,653 georeferenced sites in Washington State, USA, along a longitudinal gradient from west of the crest of the Cascade Range to the beginnings of the western slope of the Rocky Mountains, and across two physiographic provinces, the Northern Cascades, characterized by steep, rugged topography, and the Okanogan Highlands, presenting moderate slopes and broad rounded summits. Methods Tree data were drawn from the USDA Forest Service Area Ecology Program database, collected in mature, undisturbed stands. We compared simple climatic variables (annual temperature, growing‐degree days, annual and seasonal precipitation) to biophysical variables (soil, hydrologic, and solar radiation) derived from climatic variables. Climatic and biophysical variables were taken from the output of climatological and hydrological simulation models and estimated for each plot in the tree database. Generalized linear models were used, for each of fourteen tree species, at multiple spatial extents, to estimate the probability of occurrence of that species as a function of climatic and biophysical predictors. Models were validated by a combination of bootstrapping and estimating receiver operating characteristic (ROC) curves. Results For the majority of species, we were able to fit variables representing both moisture and temperature gradients, and in all but a few cases these models identified a unimodal response of species occurrence to these gradients. In some cases the ecological/environmental niche of a species had been clearly captured by the model, whereas in others a longer gradient in the predictor variable(s) would be needed. Responses of most species were consistent across three spatial scales. Main conclusions By identifying the ecological niches of multiple species, we can forecast their redistribution on the landscape in response to climatic change, evaluate the predictions of simulation models, and alert managers to particularly sensitive or vulnerable ecosystems and landscapes.     

Patterns of tree species richness in relation to environment in southeastern New South Wales,Australia

Abstract We present regression models of species richness for total tree species, two growth forms, rainforest trees (broadleaf evergreens) and eucalypts (sclerophylls), and two large subgenera of Eucalyptus. The correlative models are based on a data set of 166 tree species from 7208 plots in an area of southeastern New South Wales, Australia. Eight environmental variables are used to model the patterns of species richness, four continuous variables (mean annual temperature, rainfall, radiation and plot size), plus four categorical factors (topographic position, lithology, soil nutrient level and rainfall seasonality). Generalized linear modelling with curvilinear and interaction terms, is used to derive the models. Each model shows a significant and differing response to the environmental predictors. Maximum species richness of eucalypts occurs at high temperatures, and intermediate rainfall and radiation conditions on ridges with aseasonal rainfall and intermediate nutrient levels. Maximum richness of rainforest species occurs at high temperatures, intermediate rainfall and low radiation in gullies with summer rainfall and high nutrient levels. The eucalypt subgenera models differ in ways consistent with experimental studies of habitat preferences of the subgenera. Curvilinear and interaction terms are necessary for adequate modelling. Patterns of richness vary widely with taxonomic rank and growth form. Any theories of species diversity should be consistent with these correlative models. The models are consistent with an available energy hypothesis based on actual evapotranspiration. We conclude that studies of species richness patterns should include local (e.g. soil nutrients, topographic position) and regional (e.g. mean annual temperature, annual rainfall) environmental variables before invoking concepts such as niche saturation.     

Rainfall,groundwater and refuges: Predicting extinctions of Australian tropical mammal species

Abstract A general decline in populations of some savanna mammal species has occurred since the mid-1980s in a fairly pristine national park environment in the Australian wet-dry tropics. Terrestrial native rodents have exhibited the greatest decline and marsupials the least. During the same period, waterholes have dried up and the previous strong association of mammals with riparian vegetation has diminished. A regional index of the level of groundwater was developed from 16 unexploited bores from across the northern half of the Northern Territory. Predicted mean groundwater values over 28 years showed a strong increase throughout the 1970s and a similar decrease throughout the 1980s. Using data since 1986, strong correlations between mammal numbers and groundwater levels for the preceding two years, and much weaker relationships with rainfall, were obtained. In turn, the groundwater levels were best correlated with an eight-year running mean of rainfall for both Darwin and Alice Springs and an eleven-year running mean for the Southern Oscillation Index. Extrapolating backward in time, cumulative pressure variation at Darwin showed two extended periods of predicted low ground-water values, 1900s–1920s and 1940s. Both periods were preceded by the last records of a number of now-extinct mammals from central Australia. A third trough in the early 1960s suggests another period of extinction in central Australia, previously unappreciated due to the lack of survey work in the 1950s. Further, by this analysis, the past 20 years has been the best period for mammals since weather records commenced. Analysis of continental-scale distributions of mammals showed evidence of fluctuations suggesting rocky areas are important refuges for some species during periods of low groundwater levels. In contrast to those in savanna habitats, the mammals of the extensive wetland areas fluctuated in harmony with rainfall on a short-term basis except where habitat is flooded. It is the species which occur only in savanna but not also in rocky or wetland habitats which are most at risk. A number of other species-vulnerability characteristics were identified: riparian vegetation specificity; the degree to which they fall within the critical size range (35 g-5. 5 kg); degree of semelparity; smallness of population size; and smallness of geographic range. Those savanna species with annual life histories strongly associated with riparian areas are likely to be in greatest jeopardy. The species which appear to be most vulnerable in northwestern Australia are Conilurus penicillatus, Mesembriomys gouldii, Mesembriomys macrurus, Antechinus bellus, Phascogale tapoatafa and Rattus tunneyi. Our recent benign climatic history has coincided with the great public environmental awakening and upsurge in environmental research and management efforts. This historical accident has probably led us to overstate the negative effects of human impact and also our ability to change the course of biological history by ameliorating human impact. Our distorted view of these factors has further led us to over-emphasize research of a spatial nature to the detriment of temporal studies. We must redress this balance.