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Total Richness (total + richness)
Selected AbstractsBird densities are associated with household densitiesGLOBAL CHANGE BIOLOGY, Issue 8 2007JAMIE TRATALOS Abstract Increasing housing density is an important component of global land transformation, with major impacts on patterns of biodiversity. However, while there have been many studies of the changes in biodiversity across rural,urban gradients, which are influenced in large part by housing densities, how biodiversity changes across the full range of regional variation in housing density remains poorly understood. Here, we explore these relationships for the richness and abundance of breeding birds across Britain. Total richness, and that of 27 urban indicator species, increased from low to moderate household densities and then declined at greater household densities. The richness of all species increased initially faster with household density than did that of the urban indicator species, but nonurban indicator species richness declined consistently after peaking at a very low housing density. Avian abundance showed a rather different pattern. Total abundance and that summed across all urban indicator species increased over a wide range of household densities, and declined only at the highest household densities. The abundance of individual urban indicator species generally exhibited a hump-shaped relationship with housing density. While there was marked intraspecific variation in the form of such relationships, almost invariably avian abundance declined at housing densities below that at which the UK government requires new developments to be built. Our data highlight the difficulties of maintaining biodiversity while minimising land take for new development. High-density housing developments are associated with declines in many of those species otherwise best able to exploit urban environments, and those components of native biodiversity with which human populations are often most familiar. [source] Effects of forest management on epiphytic lichen diversity in Mediterranean forestsAPPLIED VEGETATION SCIENCE, Issue 2 2010Gregorio Aragón Abstract Question: What are the responses of epiphytic lichens to the intensity of management along a large environmental gradient in Mediterranean Quercus forests? Location: Central Spain. Methods: This study was carried out on 4590 trees located in 306 forest stands dominated by Quercus faginea or Quercus ilex ssp. ballota. The effect of forest management and other predictor variables on several species diversity indicators were studied. Variables modelled were total species richness, cyanolichen richness and community composition. A large number of predictor variables were included: forest fragmentation (patch size, stand variability), climate and topographic (altitude, slope, sun radiation, annual rainfall and mean annual temperature) and intensity of management. General linear models and constrained ordination techniques were used to model community traits and species composition, respectively. Results: Total richness and especially cyanolichens richness were significantly and negatively affected by the intensity of management. Lichen composition was influenced by management intensity, climatic and topographic variables and stand variability. Conclusions: In Mediterranean forests, human activities related to forestry, agricultural and livestock use cause impoverishment of lichen communities, including the local disappearance of the most demanding species. The conservation of unmanaged forests with a dense canopy is crucial for lichen diversity. [source] Biodiversity hotspots, centres of endemicity, and the conservation of coral reefsECOLOGY LETTERS, Issue 6 2002Terry P. Hughes Abstract On land, biodiversity hotspots typically arise from concentrations of small-range endemics. For Indo-Pacific corals and reef fishes, however, centres of high species richness and centres of high endemicity are not concordant. Moreover ranges are not, on average, smaller inside the Central Indo-Pacific (CI-P) biodiversity hotspot. The disparity between richness and endemicity arises because corals and reef fishes have strongly skewed range distributions, with many species being very widespread. Consequently, the largest ranges overlap to generate peaks in species richness near the equator and the CI-P biodiversity hotspot, with only minor contributions from endemics. Furthermore, we find no relationship between the number of coral vs. fish endemics at locations throughout the Indo-Pacific, even though total richness of the two groups is strongly correlated. The spatial separation of centres of endemicity and biodiversity hotspots in these taxa calls for a two-pronged management strategy to address conservation needs. [source] Contribution of native and non-native species to fish communities in French reservoirsFISHERIES MANAGEMENT & ECOLOGY, Issue 3-4 2004P. Irz Abstract Previous studies showed that only 20% of the variability in fish community structure in French reservoirs could be explained by site characteristics. In addition, no relationship was found between the relative abundance of species and stocking effort. Therefore, deliberate or uncontrolled introductions are likely to be the source of a great part of the observed communities. The objective of this study was to assess the importance of species introductions in French reservoirs. Fifty-one reservoirs were sampled to obtain species presence/absence data. Local native (LNaR) and non-native (LNNR) species richness were negatively correlated. LNaR was strongly correlated to the lake surface area, depth and catchment area, whereas LNNR was independent of environmental variables. Furthermore, LNaR was positively correlated to regional native richness. Conversely, local total richness was independent of regional total richness, but was related to the reservoirs' environmental characteristics. It was hypothesised that the native fish communities in French reservoirs are unsaturated and species introductions lead to saturated communities. [source] Are species,area relationships from entire archipelagos congruent with those of their constituent islands?GLOBAL ECOLOGY, Issue 4 2010Ana M. C. Santos ABSTRACT Aim, To establish the extent to which archipelagos follow the same species,area relationship as their constituent islands and to explore the factors that may explain departures from the relationship. Location, Thirty-eight archipelagos distributed worldwide. Methods, We used ninety-seven published datasets to create island species,area relationships (ISARs) using the Arrhenius logarithmic form of the power model. Observed and predicted species richness of an archipelago and of each of its islands were used to calculate two indices that determined whether the archipelago followed the ISAR. Archipelagic residuals (ArcRes) were calculated as the residual of the prediction provided by the ISAR using the total area of the archipelago, standardized by the total richness observed in the archipelago. We also tested whether any characteristic of the archipelago (geological origin and isolation) and/or taxon accounts for whether an archipelago fits into the ISAR or not. Finally, we explored the relationship between ArcRes and two metrics of nestedness. Results, The archipelago was close to the ISAR of its constituent islands in most of the cases analysed. Exceptions arose for archipelagos where (i) the slopes of the ISAR are low, (ii) observed species richness is higher than expected by the ISAR and/or (iii) distance to the mainland is small. The archipelago's geological origin was also important; a higher percentage of oceanic archipelagos fit into their ISAR than continental ones. ArcRes indicated that the ISAR underpredicts archipelagic richness in the least isolated archipelagos. Different types of taxon showed no differences in ArcRes. Nestedness and ArcRes appear to be related, although the form of the relationship varies between metrics. Main conclusions, Archipelagos, as a rule, follow the same ISAR as their constituent islands. Therefore, they can be used as distinct units themselves in large-scale biogeographical and macroecological studies. Departure from the ISAR can be used as a crude indicator of richness-ordered nestedness, responsive to factors such as isolation, environmental heterogeneity, number and age of islands. [source] | |||||||||||||