干旱区典型湖泊湿地主要植物生态种组分析

根据2007年7-9月新疆艾比湖湿地25种主要植被在47个调查样地的存在．缺失数据,应用非度量多维标度（NMDS）方法研究了干旱区典型湖泊湿地内植物群落生态种组的划分,并与系统聚类分析结果做了比较分析。研究显示：艾比湖湿地的主要植物种划分为5个生态种组,各生态种组内的植物种之间具有相似的生境和生态位;NMDS是基于高维数据非线性迭代的降维排序方法,与传统的生态种组分析方法相比较,NMDS充分抽取了植被在样地内非线性集聚分布的信息,因而其种组划分结论更符合实际调查结果,也更为可靠、有效。研究结果从生态种组的视角为艾比湖湿地生态恢复和保护植物多样性提供更具有实践价值的参考依据。     

Spatial predictions of phylogenetic diversity in conservation decision making

Considering genetic relatedness among species has long been argued as an important step toward measuring biological diversity more accurately, rather than relying solely on species richness. Some researchers have correlated measures of phylogenetic diversity and species richness across a series of sites and suggest that values of phylogenetic diversity do not differ enough from those of species richness to justify their inclusion in conservation planning. We compared predictions of species richness and 10 measures of phylogenetic diversity by creating distribution models for 168 individual species of a species-rich plant family, the Cape Proteaceae. When we used average amounts of land set aside for conservation to compare areas selected on the basis of species richness with areas selected on the basis of phylogenetic diversity, correlations between species richness and different measures of phylogenetic diversity varied considerably. Correlations between species richness and measures that were based on the length of phylogenetic tree branches and tree shape were weaker than those that were based on tree shape alone. Elevation explained up to 31% of the segregation of species rich versus phylogenetically rich areas. Given these results, the increased availability of molecular data, and the known ecological effect of phylogenetically rich communities, consideration of phylogenetic diversity in conservation decision making may be feasible and informative.     

Nestedness of remnant sonoran desert plant communities in metropolitan Phoenix, Arizona

Urbanization can have profound effects on the plant communities persisting in remnant habitats. That process can be explored by examining patterns of nestedness. Species composition for a set of communities exhibits a nested pattern if species present in progressively richer assemblages form a series of subsets. Nestedness can form as a result of the dynamic processes of extinction or colonization. It can also reflect a nested distribution of habitats among the sites or the differential abundance properties of species through passive sampling. This study investigated whether Sonoran Desert woody vegetation in remnant islands within metropolitan Phoenix is nested and explored which mechanisms are responsible for the pattern. It also examined whether vegetation is nested in similar habitat types across islands, and how species abundance relates to the nested pattern and hypothesized mechanisms. All data sets were significantly nested, indicating a nested pattern at the island and habitat levels. Community-level analyses did not indicate a primary mechanism leading to the nested pattern. Among species with abundances correlated with the nested rank-order of sites, abundance properties were significantly related to different variables. This suggests that individual taxa respond to divergent ecological mechanisms, leading to nestedness. Thus, nestedness in plant communities can result from a complex set of contributors and may not be attributable to a single factor.     

Global Patterns of Mammalian Diversity, Endemism, and Endangerment

To assess the conservation status of the world's land mammals, we compiled data on the number of total species, endemic species, recently extinct species, and currently endangered species for 155 countries. Total species richness was significantly correlated with territorial land area, whereas number of endemic species was only weakly correlated with both area and total number of species. The large amount of variation left unexplained by species-area regressions reflects the influence of other factors, such as latitude, topographic and habitat heterogeneity, and historical biogeography, on species richness and especially on patterns of endemism. Countries of particular conservation concern, because they have rich mammalian faunas containing many endemic species, are the large islands of Australia, Madagascar, Indonesia, and the Philippines, as well as continental Mexico. Patterns of recent extinctions and the current endangered status of species were difficult to interpret, largely because of inadequate and inconsistent data. The majority of officially listed endangered species are large, well known, and popular mammals, such as primates, ungulates, and carnivores, whereas the majority of species known to have gone recently extinct and likely to be currently threatened are small and inconspicuous, such as rodents and bats. Our work not only illustrates the role of ecological, evolutionary, and biogeographic processes in the origin and maintenance of land mammal diversity, it also presents the information at the level of biogeographic regions and political units where management and policy must be applied in order to slow the loss of this diversity.     

Influence of Forest Fragmentation on Community Structure of Frogs and Lizards in Northeastern Costa Rica

Abstract:  To better understand responses of reptiles and amphibians to forest fragmentation in the lowland Neotropics, we examined community and population structure of frogs and lizards in the fragmented landscape surrounding La Selva Biological Station in the Sarapiquí region of northeastern Costa Rica. We used diurnal quadrats and nocturnal transects to sample frogs and lizards in nine forest fragments (1–7 ha each) and La Selva (1100 ha). Species richness in all fragments combined was 85% of that found in La Selva with comparable sampling effort. Richness varied from 10 to 24 species among forest fragments, compared with 36 species at La Selva. Lizard density was higher and frog density was lower in forest fragments than in La Selva. Community composition varied among sites and by fragment size class, and species occurrence was nested with respect to fragment area. Isolation and habitat variables did not significantly affect species richness, composition, or nestedness. We classified 34% of species as fragmentation sensitive because they were absent or occurred at low densities in fragments. Nevertheless, the relatively high diversity observed in the entire set of fragments indicates that preserving a network of small forest patches may be of considerable conservation value to the amphibians and reptiles of this region.     

Species Richness, Endemism, and the Choice of Areas for Conservation

Although large reserve networks will be integral components in successful biodiversity conservation, implementation of such systems is hindered by the confusion over the relative importance of endemism and species richness. There is evidence (  Prendergast et al. 1993) that regions with high richness for a taxon tend to be different from those with high endemism. I tested this finding using distribution and richness data for 368 species from Mammalia, Lasioglossum, Plusiinae, and Papilionidae. The study area, subdivided into 336 quadrats, was the continuous area of North America north of Mexico. I also tested the hypothesis that the study taxa exhibit similar diversity patterns in North America. I found that endemism and richness patterns within taxa were generally similar. Therefore, the controversy over the relative importance of endemism and species richness may not be necessary if an individual taxon were the target of conservation efforts. I also found, however, that richness and endemism patterns were not generally similar between taxa. Therefore, centering nature reserves around areas that are important for mammal diversity (the umbrella species concept) may lead to large gaps in the overall protection of biodiversity because the diversity and endemism of other taxa tend to be concentrated elsewhere. I investigated this further by selecting four regions in North America that might form the basis of a hypothetical reserve system for Carnivora. I analyzed the distribution of the invertebrate taxa relative to these regions and found that this preliminary carnivore reserve system did not provide significantly different protection for these invertebrates than randomly selected quadrats. I conclude that the use of Carnivora as an umbrella taxon is an unreliable method for invertebrate conservation.     

Landscape connectivity strengthens local-regional richness relationships in successional plant communities

Local species diversity is maintained over ecological time by a balance between dispersal and species interactions. Local-regional species richness relationships are often used to investigate the relative importance of these two processes and the scales at which they operate. For communities undergoing succession, theory predicts a temporal progression in local-regional species richness relationships: from no relationship to positive linear to saturating. However, observational tests have been mixed, and experiments have been rare. Using a replicated large-scale experiment, we evaluate the impact of two dispersal-governing processes at the regional scale, connectivity and shape of the region (i.e., patches), on the progression of local-regional species richness relationships for plant communities undergoing succession. Regional connectivity accelerates the transition from no relationship to a positive linear relationship, while the shape of the region has no consistent effect nine years post-disturbance. Our results experimentally demonstrate the importance of dispersal in structuring local-regional species richness relationships over time and suggest that conservation corridors among regions can increase local diversity through regional enrichment of plant communities undergoing reassembly.     

Using Gall Wasps on Oaks to Test Broad Ecological Concepts

Abstract:  Planning conservation of insect herbivores requires knowing what needs to be conserved and developing a set of predictor variables that aid management. We conducted a state-wide survey to examine the species richness of gall wasps (Hymenoptera: Cynipidae) on six oak species dominant in the threatened scrub-oak vegetation in peninsular Florida. Eighty-eight cynipid species were recorded; 23 were new species to Florida (a 35% increase), including 17 species new to science and 6 species newly recorded in the state. The cynipid species represented 68% of cynipids of Florida, on only 24% of oak species sampled. This fauna represents a hotspot of richness, justifying conservation initiatives in scrub-oak habitat and throughout the state. We derived predictor variables from general ecological concepts: (1) the theory of island biogeography that insect species richness increases as host plant geographic area increases and as local abundance increases, (2) the plant-architecture hypothesis that insect species richness increases with increased plant size, and (3) phytochemical patterns in leaves, including nutrients and digestibility reducers predicting suitability for insect herbivores. Concepts 1 and 2, developed for large scales and species numbers, were tested at smaller scales relevant to much conservation research and management. A stepwise multiple regression including all predictor variables accounted for 99% of the variance in cynipid species richness with three variables: foliar hemicellulose concentration (81%), host geographic area (16%), and tree height (2%). The trends were negative, however, and opposite to those predicted by concepts 1 and 2. Ecological theory was not applicable to discovery of predictors of cynipid species richness on six oak species. Thus, we promote caution in applying ecological theory to a narrow set of species without specific testing of how patterns conform to theoretical predictions.     

Conservation of Insect Diversity: a Habitat Approach

Abstract: Neither time nor resources exist to design conservation plans for every species, particularly for little-studied, noncharismatic, but ecologically important taxa that make up most of biodiversity. To explore the feasibility of basing conservation action on community-level biogeography, we sampled a montane insect community. We addressed three issues: (1) the appropriate scale for sampling insect communities; (2) the association of habitat specialization—perhaps a measure of extinction vulnerability—with other ecological or physical traits; and (3) the correlation of diversity across major insect groups. Using malaise traps in Gunnison County, Colorado, we captured 8847 Diptera (identified to family and morphospecies), 1822 Hymenoptera (identified to morphospecies), and 2107 other insects (identified to order). We sampled in three habitat types—meadow, aspen, and conifer—defined on the basis of the dominant vegetation at the scale of hundreds of meters. Dipteran communities were clearly differentiated by habitat type rather than geographic proximity. This result also holds true for hymenopteran communities. Body size and feeding habits were associated with habitat specialization at the family level. In particular, habitat generalists at the family level—taxa perhaps more likely to survive anthropogenic habitat alteration—tended to be trophic generalists. Dipteran species richness was marginally correlated with hymenopteran species richness and was significantly correlated with the total number of insect orders sampled by site. Because these correlations result from differences in richness among habitat types, insect taxa may be reasonable surrogates for one another when sampling is done across habitat types. In sum, community-wide studies appear to offer a practical way to gather information about the diversity and distribution of little-known taxa.     

Relationships between Plant and Animal Species Richness at a Regional Scale in China

Abstract:  Important questions in conservation biology and ecology include whether species diversities of different groups of organisms are correlated and, in particular, whether plant diversity influences animal diversity. I used correlation and partial regression analyses to examine the relationships between species richness of vascular plants and four major groups of terrestrial vertebrates (mammals, amphibians, reptiles, and birds) in 28 provinces in China. Species richness data were obtained from the literature. Environmental variables included normalized difference vegetation index, mean January temperature, mean annual temperature, annual precipitation, May through August precipitation, actual evapotranspiration, potential evapotranspiration, and elevation range. Species richness was strongly and positively correlated among the five groups of organisms. Plant richness was correlated with animal richness more strongly than the richness of different animal groups correlated with each other except for reptile richness, which had a slightly higher correlation with amphibian richness than with plant richness. Plant richness uniquely explained 41 times more variance in the species richness of the four vertebrate groups combined than environmental variables uniquely did, suggesting that plant richness influences terrestrial vertebrate richness at the regional scale examined. Because of strong correlations between the diversity of vascular plants and vertebrates, the diversity of vascular plants may be used as a surrogate for the diversity of terrestrial animals in China. My results have implications for selection of areas to be protected at both regional and local scales.     

Increased primary production shifts the structure and composition of a terrestrial arthropod community

Numerous studies have examined relationships between primary production and biodiversity at higher trophic levels. However, altered production in plant communities is often tightly linked with concomitant shifts in diversity and composition, and most studies have not disentangled the direct effects of production on consumers. Furthermore, when studies do examine the effects of plant production on animals in terrestrial systems, they are primarily confined to a subset of taxonomic or functional groups instead of investigating the responses of the entire community. Using natural monocultures of the salt marsh cordgrass Spartina alterniflora, we were able to examine the impacts of increased plant production, independent of changes in plant composition and/or diversity, on the trophic structure, composition, and diversity of the entire arthropod community. If arthropod species richness increased with greater plant production, we predicted that it would be driven by: (1) an increase in the number of rare species, and/or (2) an increase in arthropod abundance. Our results largely supported our predictions: species richness of herbivores, detritivores, predators, and parasitoids increased monotonically with increasing levels of plant production, and the diversity of rare species also increased with plant production. However, rare species that accounted for this difference were predators, parasitoids, and detritivores, not herbivores. Herbivore species richness could be simply explained by the relationship between abundance and diversity. Using nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM), we also found significant changes in arthropod species composition with increasing levels of production. Our findings have important implications in the intertidal salt marsh, where human activities have increased nitrogen runoff into the marsh, and demonstrate that such nitrogen inputs cascade to affect community structure, diversity, and abundance in higher trophic levels.     

Expanding Kenya's protected areas under the Convention on Biological Diversity to maximize coverage of plant diversity

Biodiversity is highly valuable and critically threatened by anthropogenic degradation of the natural environment. In response, governments have pledged enhanced protected‐area coverage, which requires scarce biological data to identify conservation priorities. To assist this effort, we mapped conservation priorities in Kenya based on maximizing alpha (species richness) and beta diversity (species turnover) of plant communities while minimizing economic costs. We used plant‐cover percentages from vegetation surveys of over 2000 plots to build separate models for each type of diversity. Opportunity and management costs were based on literature data and interviews with conservation organizations. Species richness was predicted to be highest in a belt from Lake Turkana through Mount Kenya and in a belt parallel to the coast, and species turnover was predicted to be highest in western Kenya and along the coast. Our results suggest the expanding reserve network should focus on the coast and northeastern provinces of Kenya, where new biological surveys would also fill biological data gaps. Meeting the Convention on Biological Diversity target of 17% terrestrial coverage by 2020 would increase representation of Kenya's plant communities by 75%. However, this would require about 50 times more funds than Kenya has received thus far from the Global Environment Facility.     

Littoral Fish Communities in Lake Tanganyika: Irreplaceable Diversity Supported by Intricate Interactions among Species

The rocky littoral areas of Lake Tanganyika harbor diverse fish communities, mainly composed of cichlids. Their stability, structure, and organizing mechanism were examined at three locations by census, behavioral observations, and dietary analyses. These fish communities were stable, characterized by their persistence during a 10-year period and resilience after a perturbation. Partitioning of spawning sites among substrate spawners was evident, which might be a factor in their ability to coexist. The fish communities were consistently composed of 12 food-habit groups, but composition of species in each group differed from location to location. Among species of different food-habit groups, facultative commensalisms were prevalent. Although aggressive interactions are common among fishes of the same food-habit group, each predatory fish obtained an advantage in feeding efficiency from the different feeding behaviors of other species of the same group. This mutualism and the facultative commensalism should both increase species richness in different parts of the communities. These intricate interactions among species may be a base of stability of the fish communities. We assert that maintenance of ecological networks among species are most important for conservation of biodiversity in tropical regions.     

Indicator Taxa, Rapid Biodiversity Assessment, and Nestedness in an Endangered Ecosystem

Abstract: To prioritize areas for conservation, biologists and managers need information on species diversity in threatened habitats. The resources available for such inventories remain severely limited, increasing the need to develop speedier ways to estimate the status of target habitats. We present a study of the use of such techniques in the highly fragmented oak savannas of southern Ontario, including selection of indicator taxa, use of rapid biodiversity assessment based on morphospecies, and analysis of community structure. We found that butterflies and skippers can be used to predict richness among Hymenoptera in the study sites, which is consistent with the hypothesis that these easily surveyed Lepidoptera are good candidates for indicator status. Richness values for hymenoptera morphospecies in these savanna remnants were strongly correlated with species richness scores as estimated by systematists, although nonspecialists tended to "split" species into more than one morphospecies. Finally, both the Hymenoptera and Lepidoptera communities in these oak savannas exhibited a high degree of nestedness, suggesting that local extinctions, mostly undocumented, are important determinants of the richness patterns across these widely separated savanna study sites. We found no evidence of significant spatial autocorrelation, probably because of the wide separation of study sites.     

Prioritizing Conservation Effort through the Use of Biological Soil Crusts as Ecosystem Function Indicators in an Arid Region

Abstract: Conservation prioritization usually focuses on conservation of rare species or biodiversity, rather than ecological processes. This is partially due to a lack of informative indicators of ecosystem function. Biological soil crusts (BSCs) trap and retain soil and water resources in arid ecosystems and function as major carbon and nitrogen fixers; thus, they may be informative indicators of ecosystem function. We created spatial models of multiple indicators of the diversity and function of BSCs (species richness, evenness, functional diversity, functional redundancy, number of rare species, number of habitat specialists, nitrogen and carbon fixation indices, soil stabilization, and surface roughening) for the 800,000‐ha Grand Staircase‐Escalante National Monument (Utah, U.S.A.). We then combined the indicators into a single BSC function map and a single BSC biodiversity map (2 alternative types of conservation value) with an unweighted averaging procedure and a weighted procedure derived from validations performance. We also modeled potential degradation with data from a rangeland assessment survey. To determine which areas on the landscape were the highest conservation priorities, we overlaid the function‐ and diversity‐based conservation‐value layers on the potential degradation layer. Different methods for ascribing conservation‐value and conservation‐priority layers all yielded strikingly similar results (r= 0.89–0.99), which suggests that in this case biodiversity and function can be conserved simultaneously. We believe BSCs can be used as indicators of ecosystem function in concert with other indicators (such as plant‐community properties) and that such information can be used to prioritize conservation effort in drylands.     

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

Abstract:  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 of five 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.     

A direct comparison of the consequences of plant genotypic and species diversity on communities and ecosystem function

Biodiversity loss is proceeding at an unprecedented rate, yet we lack a thorough understanding of the consequences of losing diversity at different scales. While species diversity is known to impact community and ecosystem processes, genotypic diversity is assumed to have relatively smaller effects. Nonetheless, a few recent studies suggest that genotypic diversity may have quantitatively similar ecological consequences compared to species diversity. Here we show that increasing either genotypic diversity of common evening primrose (Oenothera biennis) or species diversity of old-field plant species resulted in nearly equivalent increases (approximately 17%) in aboveground primary production. The predominant mechanism explaining this effect, niche complementarity, was similar for each type of diversity. Arthropod species richness also increased with both types of plant diversity, but the mechanisms leading to this effect differed: abundance-driven accumulation of arthropod species was important in plant genotypic polycultures, whereas resource specialization was important in plant species polycultures. Thus, similar increases in primary productivity differentially impacted higher trophic levels in response to each type of plant diversity. These results highlight important ecological similarities and differences between genotypic and species diversity and suggest that genotypic diversity may play a larger role in community and ecosystem processes than previously realized.     

Impact of Grazing Intensity during Drought in an Arizona Grassland

Abstract:  The ecological benefits of changing cattle grazing practices in the western United States remain controversial, due in part to a lack of experimentation. In 1997 we initiated an experimental study of two rangeland alternatives, cattle removal and high-impact grazing, and compared grassland community responses with those with more conventional, moderate grazing practices. The study was conducted in a high-elevation, semiarid grassland near Flagstaff, Arizona (U.S.A.). We conducted annual plant surveys of modified Whittaker plots for 8 years and examined plant composition shifts among treatments and years. High-impact grazing had strong directional effects that led to a decline in perennial forb cover and an increase in annual plants, particularly the exotic cheatgrass ( Bromus tectorum L.). A twofold increase in plant cover by exotic species followed a severe drought in the sixth year of the study, and this increase was greatest in the high-impact grazing plots, where native cover declined by one-half. Cattle removal resulted in little increase in native plant cover and reduced plant species richness relative to the moderate grazing control. Our results suggest that some intermediate level of cattle grazing may maintain greater levels of native plant diversity than the alternatives of cattle removal or high-density, short-duration grazing practices. Furthermore, episodic drought interacts with cattle grazing, leading to infrequent, but biologically important shifts in plant communities. Our results demonstrate the importance of climatic variation in determining ecological effects of grazing practices, and we recommend improving conservation efforts in arid rangelands by developing management plans that anticipate this variation.     

Linkages between measures of biodiversity and community resilience in Pacific Island agroforests

Designing agroecosystems that are compatible with the conservation of biodiversity is a top conservation priority. However, the social variables that drive native biodiversity conservation in these systems are poorly understood. We devised a new approach to identify social–ecological linkages that affect conservation outcomes in agroecosystems and in social‐ecological systems more broadly. We focused on coastal agroforests in Fiji, which, like agroforests across other small Pacific Islands, are critical to food security, contain much of the country's remaining lowland forests, and have rapidly declining levels of native biodiversity. We tested the relationships among social variables and native tree species richness in agroforests with structural equation models. The models were built with data from ecological and social surveys in 100 agroforests and associated households. The agroforests hosted 95 native tree species of which almost one‐third were endemic. Fifty‐eight percent of farms had at least one species considered threatened at the national or international level. The best‐fit structural equation model (R² = 47.8%) showed that social variables important for community resilience—local ecological knowledge, social network connectivity, and livelihood diversity—had direct and indirect positive effects on native tree species richness. Cash‐crop intensification, a driver of biodiversity loss elsewhere, did not negatively affect native tree richness within parcels. Joining efforts to build community resilience, specifically by increasing livelihood diversity, local ecological knowledge, and social network connectivity, may help conservation agencies conserve the rapidly declining biodiversity in the region.     

The Botanist Effect Revisited: Plant Species Richness, County Area, and Human Population Size in the United States

Abstract:  The "botanist effect" is thought to be the reason for higher plant species richness in areas where botanists are disproportionately present as an artefactual consequence of a more thorough sampling. We examined whether this was the case for U.S. counties. We collated the number of species of vascular plants, human population size, and the area of U.S. counties. Controlling for spatial autocorrelation and county area, plant species richness increased with human population size and density in counties with and without universities and/or botanical gardens, with no significant differences in the relation between the two subsets. This is consistent with previous findings and further evidence of a broad-scale positive correlation between species richness and human population presence, which has important consequences for the experience of nature by inhabitants of densely populated regions. Combined with the many reports of a negative correlation between the two variables at a local scale, the positive relation between plant species richness in U.S. counties and human population presence stresses the need for the conservation of seminatural areas in urbanized ecosystems and for the containment of urban and suburban sprawl.