Variation In Mammal Species Richness Research Articles

Agroforestry Systems: A Boon or Bane for Mammal Conservation in Northeastern India?

The degradation, fragmentation and isolation of tropical forests have led to the formation of small patches of human dominated landscapes interspersed with forest fragments. This affects the wildlife habitat and its population negatively. These human landscapes have been observed to have agroforestry systems as a dominant cropping practice in Assam, India. The present study was carried out in agroforestry systems (agri-silviculture systems, home gardens and tea gardens) to understand their role in the conservation of mammal species. Line transects and camera traps were used for recording mammal diversity. Altogether, 17 species of mammals belonging to 16 genera and 14 families were recorded in the selected agroforestry systems. The highest species richness was found in the home gardens (14) and the lowest was found in the agri-silviculture system (10). Home garden had the highest mammal encounter rate and relative abundance. Only five species of mammals were recorded through camera trapping. According to the IUCN Red List, 6% of mammal species recorded in the selected agroforestry systems were endangered or near threatened and 18% were vulnerable. The highest hunting trap encounter rate was found in tea garden (139 traps, 0.181 traps km−1, 24 captures). Distance from forest was inversely proportional whereas hunting threat was directly proportional to mammal species richness. The only and strongest predictor of mammal species richness was hunting threat which accounted for 53.5% of variation in mammal species richness in the study area, implying that the agroforestry systems are capable of conserving species if hunting pressure is reduced. Therefore, promotion of alternative livelihood and formation of community conservation groups are needed to increase and protect the mammalian diversity in these agroforestry systems. Thus, agroforestry systems can act as a suitable habitat next to forests for the dwindling wildlife population.

Variation in mammal species richness and relative abundance in the Karoo

Understanding how climate change and land transformation may impact the distribution and diversity of wildlife species requires landscape-level foundational biodiversity surveys. The Karoo BioGaps Project aims to provide such data and to support the scientific assessment for shale gas development projects in the Karoo basin. In this paper we present the findings of the BioGaps mammal survey, which recorded medium and large mammals across twenty-five 1 km × 1 km sampling sites within the proposed fracking footprint using camera trapping techniques. We use sample rarefaction curves, non-parametric species richness estimators and non-metric multidimensional scaling plots to explore both species richness and community structure. We also used a generalised linear model to investigate how species diversity varies with both site-specific and landscape-level predictors. A total of 38 species were recorded at the majority of sites. Longitude (z = 4.018, p = 0.0005) emerged as the best predictor of species diversity across the study area, which we suggest is linked to the clear east–west aridity gradient. Together these results reveal the cosmopolitan distribution of the mammal taxa in the Karoo and could be used to inform decision-making linked to mining activities in the area.

Untangling human and environmental effects on geographical gradients of mammal species richness: a global and regional evaluation.

Different hypotheses (geographical, ecological, evolutionary or a combination of them) have been suggested to account for the spatial variation in species richness. However, the relative importance of environment and human impacts in explaining these patterns, either globally or at the biogeographical region level, remains largely unexplored. Here, we jointly evaluate how current environmental conditions and human impacts shape global and regional gradients of species richness in terrestrial mammals. We processed IUCN global distributional data for 3939 mammal species and a set of seven environmental and two human impact variables at a spatial resolution of 96.5 × 96.5 km. We used simple, multiple and partial regression techniques to evaluate environmental and human effects on species richness. Actual evapotranspiration (AET) is the main driver of mammal species richness globally. Together with our results at the biogeographical realm level, this lends strong support for the water-energy hypothesis (i.e. global diversity gradients are best explained by the interaction of water and energy, with a latitudinal shift in the relative importance of ambient energy vs. water availability as we move from the poles to the equator). While human effects on species richness are not easily detected at a global scale due to the large proportion of shared variance with the environment, these effects significantly emerge at the regional level. In the Nearctic, Palearctic and Oriental regions, the independent contribution of human impacts is almost as important as current environmental conditions in explaining richness patterns. The intersection of human impacts with climate drives the geographical variation in mammal species richness in the Palearctic, Nearctic and Oriental regions. Using a human accessibility variable, we show, for the first time, that the zones most accessible to humans are often those where we find lower mammal species richness.

Mammal species richness and biogeographic structure at the southern boundaries of the Nearctic region

AbstractWe analyzed whether the spatial variation in mammal species richness reflects the southern boundaries of the Nearctic region as previously established by endemism patterns. Records from 710 mammal species were drawn on a map of North America (from Canada and Alaska to Panama) gridded at 4° latitude-longitude. We evaluated the probable existence of unknown species through three richness estimators (Chao2, ICE, and Jack1), modeled the potential distribution of species, and mapped the predicted pattern of species richness through the number of coexisting potential distributions. The poorest grid cells are in the northern areas, whereas the richest ones are in the southern areas, coinciding with the pattern of collecting points. The average richness of 4° grid cells comprising the Nearctic region was 18 species, and the richest 4° grid cells had 150 species, coinciding with the 26° latitude. From the 406 mammal species of the Nearctic region, 104 are restricted to it, and 305 species situated south of it are not distributed in the region. The map of predicted richness shows the classical latitudinal diversity gradient, with the number of species increasing to the tropics. We conclude that the Nearctic region has a low mammal richness, with a richness pattern corresponding with previously described patterns of endemism, with a boundary situated at 26°–30° latitude.

Environmental correlates of mammal species richness in South America: effects of spatial structure, taxonomy and geographic range

Although some consensus exists regarding the positive synergism between energy and heterogeneity in increasing species diversity, the role of environmental variability remains controversial. We examine how these factors interact to explain spatial variation in mammal species richness in South America. After taking into account the effects of spatial autocorrelation and area, elevation variability and energy mainly drive spatial variation in mammal species richness. The effect of environmental variability is less important. When different taxonomic groups of mammals are analyzed separately, three ways emerge whereby energy and heterogeneity interact to promote species richness. Heterogeneity may have no effect on species richness, habitat heterogeneity and energy availability contribute independently to species richness, or heterogeneity increases in importance with an increase in energy availability. The partition of species into range size quartiles shows that habitat heterogeneity and temporal instability in the resource supply account for the species richness pattern in the narrowest‐ ranging species. Habitat heterogeneity is significant also for intermediate ranging species but not for the widest‐ranging species. Energy alone drives the species richness pattern in the latter species. The interplay between ecology and biogeographic history may ultimately explain these differences given that narrow‐ and wide‐ranging species show distinct biogeographic patterns, and different taxonomic groups also unequally represent them.

Predicting mammal species richness and distributions: testing the effectiveness of satellite-derived land cover data

Mapping species richness and distributions is an important aspect of conservation and land use planning, but the time and cost of producing maps from field surveys is prohibitive. It is useful, therefore, if mappable environmental variables, from a readily accessible source, can be used as surrogates for species attributes. We evaluated the power of satellite-derived land cover information, from the Land Cover Map of Great Britain, to predict species richness and occurrences of terrestrial mammals in one hundred 10×10 km quadrats, from four regions of Britain. The predictive power of the land cover data was relatively poor – with a few exceptions, land cover explained less than half of the variation in mammal species richness and occurrence in regression models. Predictive power was considerably stronger when regions were analyzed separately than when analyzed together, and best fitting models varied between regions and between mammal taxa. Predictive power was also affected (positively or negatively depending on taxon) when PCA-ordinated land cover variables were used as predictors. The predictive strength of the land cover data was probably limited mostly by the high proportion of British mammal species with geographic distributions changing rapidly and independently of land cover (and hence the non-saturation of preferred habitats), and to a lesser extent by shortcomings in the mammal and land cover data, and the influence of landscape factors other than land cover on mammal distributions. The results suggest that regional stratification is essential when attempting to predict species richness and distributions, even across relatively limited areas such as Great Britain. We conclude that caution is necessary in using results from environmental information systems such as this as a basis for conservation and land use planning decisions.

Spatial patterns in the diversity of mammal species: A test of the geographic area hypothesis in South America

The geographic distributions of 577 South American mammalian species are analysed (i) to depict the latitudinal patterns of variation in mammal species richness, and (ii) to test the geographic area hypothesis in the southern hemisphere at two scales of analysis. This hypothesis predicts that variation in the geographic area of biomes (rather than their particular environmental conditions) is the best predictor of mammal species richness. The areal effect is expected to be stronger after tropical species are excluded from the analysis, because the spillover of these species into extra-tropical latitudes can mask the species-area relationship. A latitudinal gradient in mammal species richness is confirmed in South America, although the pattern is stronger in bats than in non-volant quadrupeds. Values of species richness estimated from equal area samples (‘species density’) reveal that species richness of different mammal taxa peaks at different latitudes. The species density pattern in the mammal species assemblage taken as a whole offers support to the geographic area hypothesis after excluding tropical species from the analyses. The number of principally extra-tropical (PE-T) mammal species per unit area depends on the biome area. In contrast, bats and rodents taken separately do not support the geographic area hypothesis at this cell-scaled analysis. At the scale of biomes, the variation in the geographic area of different macrohabitats is the best predictor of mammal species richness. The species richness-area relationship holds even after controlling for the effect of latitude and differences in mean net primary productivity of the different macrohabitats. There is a difference between bats and rodents, to the extent that a strong species richness-area relationship is observed for rodents at the biome-scaled analysis. Excluding tropical species does not enhance the species richness-area relationship at this scale, thus suggesting that the ability to capture the impact of the spillover effect of tropical species into extra-tropical latitudes might depend on the scale of habitat analysis.

The conservation value for mammals of reserves in the western Australian wheatbelt

Abstract Twenty-three reserves in the Western Australian wheatbelt were examined in an attempt to assess their conservation value for native mammals, excluding bats. Multiple regression analysis on log transformed data showed that 72% of the observed variation in mammal species richness between reserves was accounted for by reserve size. The addition of the other reserve variables examined did not increase significantly this explained variation, although significant correlations existed with most variables. Estimates suggest that a minimum reserve area of about 40,000 ha is required to conserve that part of the regional assemblage of mammals in southern and western Australia likely to persist in the face of moderate disturbances by man and his agencies. Reserves should have large areas of major vegetation formations and maximise the number of regional vegetation associations. Nature reserves as small as 30 ha are valuable sanctuaries for certain species of native mammals. Comparison with mammal faunas isolated on islands by Quaternary glacioeustatic sea-level rise shows that in relation to area, wheatbelt reserves are richer in species, but the slopes of the regressions are similar, particularly for those islands that are little disturbed by man and introduced predators. We suggest that most of the species of mammals surviving in the wheatbelt are suited to existing within patches of vegetation, such as nature reserves, because they are adapted to surviving within the natural archipelago of soil and vegetation types which characterise the wheatbelt and southwestern Western Australia. We suggest that the species of mammals that have become extinct in the wheatbelt are those that are unable to cope with alteration in environmental patchiness caused by changes in the pattern of fires resulting from European occupation.