Impact Of Habitat Fragmentation Research Articles

Swimming through sand: connectivity of aquatic fauna in deserts.

Freshwater ecosystems in arid regions range from highly fragmented to highly connected, and connectivity has been assumed to be a major factor in the persistence of aquatic biota in arid environments. This review sought to synthesize existing research on genetic estimation of population connectivity in desert freshwaters, identify knowledge gaps, and set priorities for future studies of connectivity in these environments. From an extensive literature search, we synthesized the approaches applied, systems studied, and conclusions about connectivity reached in population genetic research concerning desert freshwater connectivity globally. We restrict our scope to obligate aquatic fauna that disperse largely via freshwaters and exclude those with active aerial dispersal abilities. We examined 92 papers, comprising 133 studies, published from 1987 to 2014. Most described studies of fishes and invertebrates in the deserts of Australia and North America. Connectivity declined with increasing scale, but did not differ significantly among arid regions or taxonomic classes. There were significant differences in connectivity patterns between species with different dispersal abilities, and between spring and riverine habitats at local scales. Population connectivity in desert freshwaters is typically most influenced by the ecology of the species concerned and hydrological connectivity. Most studies did not assess predefined models of connectivity, but described gene flow and/or genetic structure. Climate change and anthropogenic impacts worldwide are likely to increase the incidence and impact of habitat fragmentation in already threatened desert freshwaters. To reduce this risk, biodiversity conservation and environmental management must address connectivity, but often the required information does not exist. Researchers can provide this by explicitly considering the effects of hydrology and species’ ecology on connectivity, and incorporating these into connectivity models, which are vital for understanding connectivity in desert freshwaters.

Impact of habitat fragmentation on tsetse populations and trypanosomosis risk in Eastern Zambia.

BackgroundFragmentation of tsetse habitat in eastern Zambia is largely due to encroachments by subsistence farmers into new areas in search of new agricultural land. The impact of habitat fragmentation on tsetse populations is not clearly understood. This study was aimed at establishing the impact of habitat fragmentation on physiological and demographic parameters of tsetse flies in order to enhance the understanding of the relationship between fragmentation and African animal trypanosomosis (AAT) risk.MethodsA longitudinal study was conducted to establish the age structure, abundance, proportion of females and trypanosome infection rate of Glossina morsitans morsitans Westwood (Diptera: Glossinidae) in areas of varying degrees of habitat fragmentation in Eastern Zambia. Black screen fly rounds were used to sample tsetse populations monthly for 1 year. Logistic regression was used to analyse age, proportion of females and infection rate data.ResultsFlies got significantly older as fragmentation increased (p < 0.004). The proportion of old flies, i.e. above ovarian category four, increased significantly (P < 0.001) from 25.9 % (CI 21.4–31.1) at the least fragmented site (Lusandwa) to 74.2 % (CI 56.8–86.3) at the highly fragmented site (Chisulo). In the most fragmented area (Kasamanda), tsetse flies had almost disappeared. In the highly fragmented area a significantly higher trypanosome infection rate in tsetse (P < 0.001) than in areas with lower fragmentation was observed. Consequently a comparatively high trypanosomosis incidence rate in livestock was observed there despite lower tsetse density (p < 0.001). The overall proportion of captured female flies increased significantly (P < 0.005) as fragmentation reduced. The proportion increased from 0.135 (CI 0.10–0.18) to 0.285 (CI 0.26–0.31) at the highly and least fragmented sites, respectively.ConclusionsHabitat fragmentation creates conditions to which tsetse populations respond physiologically and demographically thereby affecting tsetse-trypanosome interactions and hence influencing trypanosomosis risk. Temperature rise due to fragmentation coupled with dominance of old flies in populations increases infection rate in tsetse and hence creates high risk of trypanosomosis in fragmented areas. Possibilities of how correlations between biological characteristics of populations and the degree of fragmentation can be used to structure populations based on their well-being, using integrated GIS and remote sensing techniques are discussed.

Small Urban Stands of the Mangrove Avicennia marina are Genetically Diverse but Experience Elevated Inbreeding

Anthropogenic impacts contribute to the fragmentation of urban mangrove forests, and in the Sydney region of Australia, Avicennia marina is commonly found in small stands of 1500 trees), intermediate (300–500 trees) and small (<50 trees) stands within each of two urbanized estuaries and estimated mating system parameters using progeny arrays for sets of five adults within the large and small stands. We detected no significant effect of stand size on levels of single-locus genetic diversity. There were low, although significant, levels of allelic differentiation within (F SE = 0.021, P = 0.003) and among (F ET = 0.055, P = 0.005) estuaries but no evidence of isolation by distance. In contrast, our analysis of progeny arrays revealed that, while all stands displayed high levels of biparental inbreeding, an expected consequence of pollination by honeybees, current outcrossing rates (t m ) were significantly lower in small (0.55) as compared to large (0.75) stands. The genetic makeup of the adult populations imply that stands are interconnected and suggest little impact of habitat fragmentation, while the progeny arrays suggest that plants within small stands may display reduced fitness.

Roe deer population structure in a highly fragmented landscape

Northern Belgium (Flanders) is one of the most densely populated and urbanized regions in Europe. Many species are therefore likely to suffer from anthropogenic pressure and habitat destruction and fragmentation. Although many large mammals are recolonizing in parts of Europe, including Belgium, due to adaptation, a relaxation of persecution and habitat restoration, we have little actual data concerning the effects of landscape features on their population structure. We analysed the genetic structure of discrete roe deer (Capreolus capreolus) populations in the Eastern part of Flanders, with special emphasis on the impact of habitat fragmentation and anthropogenic barriers. The sampled populations were clearly genetically differentiated. Genetic structure could be explained by purely distance-based landscape modelling, but a simpler model focusing solely on barrier effects of large transportation infrastructure explained nearly as much genetic variance. In contrast, analyses based on least-cost landscape modelling failed to yield a significant effect. Overall, the results suggest considerable landscape-level effects of transportation infrastructure.

Severe Habitat Fragmentation Leads to Declines in Genetic Variation, Mate Availability, and Reproductive Success in Small Populations of a Once-Common Australian Grassland Daisy

Premise of research. Inference concerning the impact of habitat fragmentation on genetic variation and demography of plant species is a key theme in conservation biology. For once-common Australian temperate grassland species where there has been almost complete habitat loss, generalizations about habitat fragmentation are unclear because most prior study has focused on rare species.Methodology. We examine the relationship between population setting (density, isolation), reproductive population size (n = 26 to >8000 flowering plants), and genetic variation by using allozyme markers, field seed set, and laboratory germination and growth in fragmented populations of the grassland daisy Leucochrysum albicans var. tricolor, a species once common across southeastern Australia.Pivotal results. Allelic richness, observed and expected heterozygosity, percent seed set, and seed germination were all positively and significantly correlated with log population size (). There was no significant association, however, between log population size and the level of polymorphism, the inbreeding coefficient, or plant fitness (measured as biomass at 28 wk). Diallel crossing showed that small populations were mate limited, suggesting that erosion of allelic richness at self-incompatibility loci may be responsible for lower and variable reproductive output.Conclusions. The outcomes of habitat fragmentation on plant population persistence of common species are likely mediated by population size, as this impacts mate availability via loss of genetic diversity. This will likely elevate the extinction risk of small populations in the long term in ecosystems where there has been intensive long-term land use and population losses and may require conservation measures that include genetic rescue to recover small populations.

Mating system and intrapatch mobility delay inbreeding in fragmented populations of a gecko

Habitat fragmentation can cause high levels of inbreeding within populations by creating small isolated populations and therefore can affect population survival. While most genetic studies of fragmented systems focus on the impact of habitat fragmentation on interpatch patterns or processes, here we focus on inbreeding (avoidance) processes within patches. We used both genetic and mark-recapture data to study within-patch processes in fragmented and continuous populations of the gecko Oedura reticulata in the Western Australian Wheatbelt. Our results revealed that O. reticulata in fragments and continuous populations alike share a promiscuous mating system (involving both polygyny and polyandry) and exhibit no detectable difference in mean levels of relatedness. However, we also found that proportions of full- and half-sib matings were higher in the habitat fragments, subadults disperse further, and all demographic classes move further and more frequently. We contend that the net result of this combination of promiscuity and greater movement is that small isolated populations have been able to retain mean levels of relatedness similar to those in nearby continuous habitat despite fragmentation and close to complete isolation over generations. It is likely that these behavioral changes have ameliorated some of the genetic effects caused by habitat fragmentation, potentially delaying reductions in the fitness effects expected from fragmentation into small populations.

Genetic diversity in peripheral and central populations of the Cantabrian endemism &lt;i&gt;Genista legionensis&lt;/i&gt; (Pau) M. Laínz (Fabaceae)

Cires, E., Perez, R., Bueno, A. & Fernandez Prieto, J.A. 2013. Genetic diversity in peripheral and central populations of the Cantabrian endemism Genista legionensis (Pau) M. Lainz (Fabaceae). Anales Jard. Bot. Madrid 70(1): 91-96. The impact of habitat fragmentation and isolation on the genetic diversity of populations has attracted much attention in studies of plant conservation. The central-peripheral population hypothesis predicts that peripheral populations have reduced genetic variability, so it is often assumed that they deserve higher conservation priority over central populations. In this work, using amplified fragment length polymorphism (AFLP), we studied the genetic diversity of central and peripheral populations of the Cantabrian endemism Genista legionensis (Fabaceae). At the species level, percentage of polymorphic bands, Nei heterozygosity and Shannon information index were PPB = 89.21%, HE = 0.246 and I = 0.377, respectively. The study revealed that peripheral populations were smaller in number, with lower levels of genetic diversity compared to the central populations. Furthermore, analysis of molecular variance (AMOVA) indicated that most of the variability was partitioned among populations, also supported by principal coordinates analysis. This study indicates that the decrease in diversity from central to peripheral populations could be explained as a result of edge effect and fragmentation through the enhanced inbreeding and genetic drift, and thus supported the view that habitat fragmentation and related edge effect reduce the population genetic diversity. However, the presence of discriminating fragments in the peripheral populations suggests their conservation in order to preserve the genetic diversity in the Cantabrian endemism G. legionensis.

Evaluating the effect of habitat connectivity on the distribution of lesser horseshoe bat maternity roosts using landscape graphs

The destruction and fragmentation of habitats due to anthropogenic land use changes have led to the decline of numerous species by reducing the size and the connectivity of the remaining local populations and so contributing to their isolation. The impact of habitat fragmentation can be modeled using landscape graphs, which have become a popular tool. Habitat reduction and fragmentation has been suggested as one hypothesis for the decline of the lesser horseshoe bat Rhinolophus hipposideros in most of western and central Europe. Consequently, we expected habitat connectivity to influence the spatial distribution of the species, particularly through the presence of maternity roosts, which are essential for the persistence of the species. We designed this study to evaluate the impact of landscape connectivity on the distribution of the lesser horseshoe bat by comparing the predictive power of landscape composition alone with a model including both landscape composition and connectivity. We assessed the impact of landscape composition on maternity roost presence for different distances covered daily by bats (600, 2500 and 5000m). We then applied a landscape graph-based approach to the roosting habitat of the lesser horseshoe bat to extract several patch-level metrics representing the functional connectivity of the landscape at different spatial scales. The results from those approaches show that the bats’ presence in the Franche-Comté region depends on the availability of wooded elements near small built areas and, at a broader scale, on the spatial integration of maternity roosts into a connected network allowing exchanges of individuals among roosts. This approach is a promising way to establish whether the presence probability of a given species depends on the potential connectivity between habitat patches quantified at different spatial scales. We expect that this method can be applied to taxa for which habitat fragmentation is one of the causes of population decline. We anticipate that using a graph-based species distribution model as a tool to predict species presence may focus conservation efforts on areas where habitat potential connectivity and landscape composition together should be taken into account, e.g. where anthropogenic landscape modifications are the main drivers of habitat connectivity.

The impact of habitat fragmentation on the ecology of xenarthrans (Mammalia) in the Brazilian Cerrado

The impact of deforestation and fragmen- tation upon ecologically important and poorly known groups is currently an important issue for conservation biology. Herein we describe xenathran communities across the Brazilian Cerrado and study the effects of habitat fragmentation on occupancy and activity patterns on these assemblages. Our hypothesis was that larger and specialized species would be more ecologically sensitive, and likely to exhibit shifts in their activity patterns in more deforested areas as a way of dealing with the myriad of effects involved in the fragmentation process. The study was conducted by camera trapping in ten Cerrado sites. Five species were analyzed: Priodontes maximus, Euphractus sexcinctus, Dasypus novemcintus (Order Cingulata), Tamandua tetradactyla and Myrmecophaga tridactyla (Order Pilosa). Fragmentation was quantified by landscape metrics, calculated on scales that matched the species' home ranges. Occupancy and detection probability analyses were conducted to test for shifts in occupancy under different fragmentation condi- tions. A mixed-effects model analysis was conducted to test for shifts in species' frequency of records related to time of day, controlling for spatial autocor- relation by means of eigenvector-based spatial filters for the models' residuals. There were no changes in activity pattern between more and less fragmented areas, so that our behavioural plasticity hypothesis was not corroborated for this group. The lack of changes in the patterns could be explained by a species' time-lag response, or by the lack of a wide enough fragmen- tation gradient in our study.

A panel of microsatellite markers developed for solitary trap-nesting wasp Ancistrocerus trifasciatus (Müller, 1776) by cross-species amplification

Solitary cavity-nesting Hymenoptera constitute a group of important bioindicators of terrestrial habitats. Some of them, like caterpillar-hunting potter wasp Ancistrocerus trifasciatus (Hymenoptera: Vespidae: Eumeninae), are quite abundant in both continuous and fragmented habitats and might be a promising model species for studying the impact of habitat fragmentation and landscape connectivity on genetic diversity of entomophagous insects. Highly polymorphic microsatellites are a powerful molecular tool for intraspecific studies but the development of this marker system de novo is especially laborious and time-consuming. An alternative time- and effort-effective approach to establish the microsatellite markers for the species of interest is the cross-species amplification of loci already isolated in related species. Here we present a panel of five polymorphic microsatellite loci for A. trifasciatus developed by cross-species amplification of twenty-nine microsatellite markers published so far for nearctic potter wasps.

Predicting Landscape-Genetic Consequences of Habitat Loss, Fragmentation and Mobility for Multiple Species of Woodland Birds

Inference concerning the impact of habitat fragmentation on dispersal and gene flow is a key theme in landscape genetics. Recently, the ability of established approaches to identify reliably the differential effects of landscape structure (e.g. land-cover composition, remnant vegetation configuration and extent) on the mobility of organisms has been questioned. More explicit methods of predicting and testing for such effects must move beyond post hoc explanations for single landscapes and species. Here, we document a process for making a priori predictions, using existing spatial and ecological data and expert opinion, of the effects of landscape structure on genetic structure of multiple species across replicated landscape blocks. We compare the results of two common methods for estimating the influence of landscape structure on effective distance: least-cost path analysis and isolation-by-resistance. We present a series of alternative models of genetic connectivity in the study area, represented by different landscape resistance surfaces for calculating effective distance, and identify appropriate null models. The process is applied to ten species of sympatric woodland-dependant birds. For each species, we rank a priori the expectation of fit of genetic response to the models according to the expected response of birds to loss of structural connectivity and landscape-scale tree-cover. These rankings (our hypotheses) are presented for testing with empirical genetic data in a subsequent contribution. We propose that this replicated landscape, multi-species approach offers a robust method for identifying the likely effects of landscape fragmentation on dispersal.

Impact of habitat fragmentation on the genetics of populations in dendritic landscapes

Summary 1. The effect of habitat fragmentation on freshwater species has been addressed using brown trout Salmo trutta L. as a model species with a dendritic population structure. 2. Microsatellite loci were employed as molecular markers. Levels of gene flow and population subdivision were determined in more than 1200 brown trout individuals inhabiting four south European rivers with contrasting patterns of fragmentation, defined by the presence of barriers. 3. The genetic units in the four rivers were restricted by artificial barriers, and gene flow among samples within each river was associated with the level of fragmentation of the river. 4. Loss of genetic diversity and dislocation of the dendritic model have been detected in fragmented rivers. These results emphasise the importance of mitigating the impact of dams by constructing passages to restore gene flow along the river, for fish and other migratory species, as well as the need for caution in relation to stocking in isolated areas to avoid problems of inbreeding.

Impact of Habitat Fragmentation on the Demography of Lion-tailed Macaque (Macaca silenus) Populations in the Rainforests of Anamalai Hills, Western Ghats, India

Habitat fragmentation is considered the most serious threat to primate conservation in the tropics, and understanding it effects on lion-tailed macaque is very important because most of the populations live in fragmented habitats. We examined demographic parameters of 9 lion-tailed macaque groups in 8 rain forest fragments with reference to fragment area, tree density, canopy cover, tree height, and total basal area of food trees. Group size ranged from 7 to 90 individuals but was not related to habitat variables. Birth and growth rates of groups did not differ significantly between small (n = 4) and large (n = 4) fragments. Tree density, canopy cover, and total basal of food trees all show strong positive correlations with fragment area. Growth rate correlates with tree density, but there are no other significant relationships between birth or growth rate and habitat variables. The percentage of immature individuals in the group is significantly positively associated with the total basal area of food trees, but not with any other habitat variable. Comparison of our data from this study with data available for the same population in 1996 indicates a slight decline in birth rate but an increase in total number of individuals, from 154 to 242. Of the 5 small fragment groups, 3 have increased in size since 1996 while the sizes of the other 2 groups have remained the same. Based on this study, we advocate that to manage the fragile lion-tailed macaque groups the following steps need to be taken: 1) create dispersal corridors between the fragments using fruit trees to facilitate male dispersal, 2) construct canopy bridges across the prevailing roads, 3) protect the fragments from further degradation, and 4) periodically monitor these populations for long-term conservation.

Habitat fragmentation and altered fire regime create trade‐offs for an obligate seeding shrub

Habitat loss is widely considered the greatest threat to biodiversity. However, habitat loss brings with it myriad other threats that exacerbate impacts to biodiversity. For instance, altered fire regime is associated with habitat loss and fragmentation with unknown consequences to biodiversity. Plant functional groups that rely on fire to complete their life cycle may be adversely affected by disruptions to the natural fire regime, particularly when coupled with population declines due to habitat loss. We used a spatially explicit stochastic population model linked with fire hazard functions to investigate the cumulative effects of habitat loss, fragmentation, and altered fire regime on the expected minimum abundance of a long-lived obligate-seeding shrub, Ceanothus greggii var. perplexans. This species is endemic to the California Floristic Province, a biodiversity hotspot, and is representative of a functional group of plants found in many fire-prone ecosystems. We tested the impact of a range of different fire frequencies under three different combinations of fuel accumulation and weather. The best average fire return interval for population abundance was consistently in the range of 30-50 years. However, observed average fire return intervals in highly fragmented areas can be approximately 20 years or less, and model results show this to be detrimental to C. greggii populations. Results also show that if fires are uncorrelated across habitat fragments then the impact of altered fire regime on populations is worse than the impact of habitat fragmentation because of spatial and temporal decoupling of fire events across the landscape. However, the negative impacts of altered fire regime are outweighed by habitat loss as fragmentation increases. Our results show that large unplanned fires, operating under an altered fire regime, are ultimately detrimental to perennial obligate-seeding shrubs in fragmented landscapes.

Reproductive plasticity, oviposition site selection, and maternal effects in fragmented landscapes

Traditionally, evolutionary ecology and conservation biology have primarily been concerned with how environmental changes affect population size and genetic diversity. Recently, however, there has been a growing realization that phenotypic plasticity can have important consequences for the probability of population persistence, population growth, and evolution during rapid environmental change. Habitat fragmentation due to human activities is dramatically changing the ecological conditions of life for many organisms. In this review, we use examples from the literature to demonstrate that habitat fragmentation has important consequences on oviposition site selection in insects, with carryover effects on offspring survival and, therefore, population dynamics. We argue that plasticity in oviposition site selection and maternal effects on offspring phenotypes may be an important, yet underexplored, mechanism by which environmental conditions have consequences across generations. Without considering the impact of habitat fragmentation on oviposition site selection, it will be difficult to assess the effect of fragmentation on offspring fitness, and ultimately to understand the impact of anthropogenic-induced environmental change on population viability.

Seed Dispersal Distances and Plant Migration Potential in Tropical East Asia

ABSTRACTMost predictions of vegetation responses to anthropogenic climate change over the next 100 yr are based on plant physiological tolerances and do not account for the ability of plant species to migrate over the distances required in the time available, or the impact of habitat fragmentation on this ability. This review assesses the maximum routine dispersal distances achievable in tropical East Asia and their vulnerability to human impacts. Estimates for various plant–vector combinations range from &lt; 10 m, for species dispersed by ants or mechanical means, to &gt; 10 km for some species dispersed by wind (tiny seeds), water, fruit pigeons, large fruit bats (tiny seeds), elephants, rhinoceroses, and people. Most plant species probably have maximum dispersal distances in the 100–1000 m range, but the widespread, canopy‐dominant Dipterocarpaceae and Fagaceae are normally dispersed &lt; 100 m. Large fruit bats and fruit pigeons are particularly important for long‐distance dispersal in fragmented landscapes and should be protected from hunting. The maximum seed dispersal distances estimated in this study are potentially sufficient for many plant species to track temperature changes in steep topography, but are far too small for a significant role in mitigating climate change impacts in the lowlands, where temperature and rainfall gradients are much more shallow.

Impacts of habitat fragmentation on genetic diversity in a tropical forest butterfly on Borneo

Many areas of rain forest now exist as habitat fragments, and understanding the impacts of fragmentation is important for determining the viability of populations within forest remnants. We investigated impacts of forest fragmentation on genetic diversity in the butterfly Mycalesis orseis (Satyrinae) in Sabah (Malaysian Borneo). We investigated mtDNA diversity in 90 individuals from ten forest sites typical of the sizes of forest remnants that currently exist in the region. Nucleotide diversity declined with increasing isolation of remnants, but there was no effect of remnant size or population size, and haplotype diversity was similar among sites. Thus, approximately 50 y after forest fragmentation, few changes in genetic diversity were apparent and remnants apparently supported genetically viable populations of this butterfly. Many studies have shown that responses of species to habitat fragmentation usually follow a time delay, and so we developed a Monte Carlo simulation model to investigate changes in genetic diversity over time in small remnants. Model output indicated a substantial time delay (&gt; 100 y) between fragmentation and genetic erosion, suggesting that, in the smallest study remnants, an increased risk of extinction from reduced genetic diversity is likely in the longer term.

Fragments as Islands: a Synthesis of Faunal Responses to Habitat Patchiness

Scientific interest in the impact of habitat fragmentation on biodiversity is increasing, but our understanding of fragmentation is clouded by a lack of appreciation for fundamental similarities and differences across studies representing a wide range of taxa and landscape types. In an effort to synthesize data describing ecological responses of animals to fragmentation across two classes of independent variables (taxonomic group and landscape), we sampled 148 studies offive major faunal groups from the primary literature and analyzed data on 13 variables extracted from those studies. We focused our analyses on three classes of dependent variables (effects of area and isolation on species richness, z values, and nestedness and species composition). Area ranged over more orders of magnitude than isolation and tended to explain more variation in species richness than isolation. There were few matrix or taxon effects on the patterns we investigated, although we did find that sky islands tended to manifest isolation effects on both species richness and nestedness more frequently than other patch types. Sky islands may offer insight into the future of habitat patches fragmented by contemporary habitat loss, and because they show a stronger effect of isolation than other patch types, we suggest that isolation will play an increasing role in the biology of habitat fragments. We use multiple lines of evidence to suggest that our understanding of the role of isolation on community assembly in fragmented landscapes is inadequate. Finally, our observation that consistent taxonomic differences in community patterns were minimal suggests that conservation actions intended to mitigate the negative effects of extinction may have far-reaching effects across taxonomic groups.

Impact of habitat fragmentation on allelic diversity at microsatellite loci in Cunningham’s skink (Egernia cunninghami); a preliminary study

Knowledge of processes that lead to genetic erosion for a range of species is important for conservation management. Relatively little work has assessed anthropogenic impacts on genetic variation in lizards. As part of our research program investigating effects of habitat fragmentation on Cunningham’s skink (Egernia cunninghami), allelic diversity at 10 microsatellite loci was assessed in deforested and adjacent naturally vegetated habitats at two locations on the Central tablelands of NSW, Australia. Previously we have shown that deforestation is associated with significantly reduced dispersal, but not increased levels of inbreeding and homozygosity, presumably owing to strong kin avoidance in mate choice. However, in this study, two measures of allelic diversity, allelic richness and the ratio of allele number to size range, indicate that local levels of variability are lower in deforested habitats. Levels of allelic diversity may be expected to decrease more rapidly than levels of heterozygosity, thereby flagging potential longer-term problems, such as inbreeding depression or reduced recruitment because of mate limitation through strong inbreeding avoidance.

Case studies in the conservation of biodiversity: degradation and threats

The rating of biodiversity in arid and semiarid regions on the basis of ecological function and genetic traits of adaptation to severe environmental stresses produces significantly higher values, than that based solely on the commonly applied structural criteria of forms of life and levels of organization. The indirect driving forces of biodiversity impoverishment listed in the Global Biodiversity Strategy that are particularly effective in arid and semi-arid regions are (a) population growth, (b) economic systems and policies that fail to value the environment and its natural resources; (c) inequity in the ownership, management and flow of benefits from both the use and conservation of biological resources; and (d) weakness in legal and institutional systems. The most effective direct human impacts are (a) habitat destruction and fragmentation, (b) overexploitation of biological resources, (c) biological invasion, and (d) agriculture. The problem in arid and semiarid regions, particularly in developing countries, is exacerbated by the lack of knowledge and awareness, the paucity of research, and the diminishing number of competent systematists. This paper discusses the theoretical and practical aspects of each of the indirect driving forces, and the direct human impacts on biodiversity, and reviews case studies related to these impacts, with special reference to those carried out in arid and semiarid regions. These studies include monitoring of the human impact on land cover by remote sensing, effects of landuse on species diversity, impact of habitat fragmentation by summer resorts on coastal dunes, consequences of protection from grazing on biodiversity, comparison of biodiversity in nature reserves and the traditional ema system with that of nearby territories, and the impact of desertification on animal life and endangered species. Case studies also include the tools applied for biodiversity conservation in arid and semiarid lands with special emphasis on endangered species, restoration of degraded habitats and their biodiversity, the significance of nature reserves and captive breeding, the importance of conserving the populations below the species level throughout their geographical range of distribution, and ecotonal biodiversity.