Showing papers on "Biodiversity published in 2001"

Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges

Abstract: The ecological consequences of biodiversity loss have aroused considerable interest and controversy during the past decade. Major advances have been made in describing the relationship between species diversity and ecosystem processes, in identifying functionally important species, and in revealing underlying mechanisms. There is, however, uncertainty as to how results obtained in recent experiments scale up to landscape and regional levels and generalize across ecosystem types and processes. Larger numbers of species are probably needed to reduce temporal variability in ecosystem processes in changing environments. A major future challenge is to determine how biodiversity dynamics, ecosystem processes, and abiotic factors interact.

Forecasting agriculturally driven global environmental change

Abstract: During the next 50 years, which is likely to be the final period of rapid agricultural expansion, demand for food by a wealthier and 50% larger global population will be a major driver of global environmental change. Should past dependences of the global environmental impacts of agriculture on human population and consumption continue, 10(9) hectares of natural ecosystems would be converted to agriculture by 2050. This would be accompanied by 2.4- to 2.7-fold increases in nitrogen- and phosphorus-driven eutrophication of terrestrial, freshwater, and near-shore marine ecosystems, and comparable increases in pesticide use. This eutrophication and habitat destruction would cause unprecedented ecosystem simplification, loss of ecosystem services, and species extinctions. Significant scientific advances and regulatory, technological, and policy changes are needed to control the environmental impacts of agricultural expansion.

Partitioning selection and complementarity in biodiversity experiments

Abstract: The impact of biodiversity loss on the functioning of ecosystems and their ability to provide ecological services has become a central issue in ecology. Several experiments have provided evidence that reduced species diversity may impair ecosystem processes such as plant biomass production. The interpretation of these experiments, however, has been controversial because two types of mechanism may operate in combination. In the 'selection effect', dominance by species with particular traits affects ecosystem processes. In the 'complementarity effect', resource partitioning or positive interactions lead to increased total resource use. Here we present a new approach to separate the two effects on the basis of an additive partitioning analogous to the Price equation in evolutionary genetics. Applying this method to data from the pan-European BIODEPTH experiment reveals that the selection effect is zero on average and varies from negative to positive in different localities, depending on whether species with lower- or higher-than-average biomass dominate communities. In contrast, the complementarity effect is positive overall, supporting the hypothesis that plant diversity influences primary production in European grasslands through niche differentiation or facilitation.

Diversity and productivity in a long-term grassland experiment

Abstract: Plant diversity and niche complementarity had progressively stronger effects on ecosystem functioning during a 7-year experiment, with 16-species plots attaining 2.7 times greater biomass than monocultures. Diversity effects were neither transients nor explained solely by a few productive or unviable species. Rather, many higher-diversity plots outperformed the best monoculture. These results help resolve debate over biodiversity and ecosystem functioning, show effects at higher than expected diversity levels, and demonstrate, for these ecosystems, that even the best-chosen monocultures cannot achieve greater productivity or carbon stores than higher-diversity sites.

Biology of mangroves and mangrove Ecosystems

Abstract: Mangroves are woody plants that grow at the interface between land and sea in tropical and sub-tropical latitudes where they exist in conditions of high salinity, extreme tides, strong winds, high temperatures and muddy, anaerobic soils. There may be no other group of plants with such highly developed morphological and physiological adaptations to extreme conditions. Because of their environment, mangroves are necessarily tolerant of high salt levels and have mechanisms to take up water despite strong osmotic potentials. Some also take up salts, but excrete them through specialized glands in the leaves. Others transfer salts into senescent leaves or store them in the bark or the wood. Still others simply become increasingly conservative in their water use as water salinity increases Morphological specializations include profuse lateral roots that anchor the trees in the loose sediments, exposed aerial roots for gas exchange and viviparous waterdispersed propagules. Mangroves create unique ecological environments that host rich assemblages of species. The muddy or sandy sediments of the mangal are home to a variety of epibenthic, infaunal, and meiofaunal invertebrates Channels within the mangal support communities of phytoplankton, zooplankton and fish. The mangal may play a special role as nursery habitat for juveniles of fish whose adults occupy other habitats (e.g. coral reefs and seagrass beds). Because they are surrounded by loose sediments, the submerged mangroves' roots, trunks and branches are islands of habitat that may attract rich epifaunal communities including bacteria, fungi, macroalgae and invertebrates. The aerial roots, trunks, leaves and branches host other groups of organisms. A number of crab species live among the roots, on the trunks or even forage in the canopy. Insects, reptiles, amphibians, birds and mammals thrive in the habitat and contribute to its unique character. Living at the interface between land and sea, mangroves are well adapted to deal with natural stressors (e.g. temperature, salinity, anoxia, UV). However, because they live close to their tolerance limits, they may be particularly sensitive to disturbances like those created by human activities. Because of their proximity to population centers, mangals have historically been favored sites for sewage disposal. Industrial effluents have contributed to heavy metal contamination in the sediments. Oil from spills and from petroleum production has flowed into many mangals. These insults have had significant negative effects on the mangroves. Habitat destruction through human encroachment has been the primary cause of mangrove loss. Diversion of freshwater for irrigation and land reclamation has destroyed extensive mangrove forests. In the past several decades, numerous tracts of mangrove have been converted for aquaculture, fundamentally altering the nature of the habitat. Measurements reveal alarming levels of mangrove destruction. Some estimates put global loss rates at one million ha y−1, with mangroves in some regions in danger of complete collapse. Heavy historical exploitation of mangroves has left many remaining habitats severely damaged. These impacts are likely to continue, and worsen, as human populations expand further into the mangals. In regions where mangrove removal has produced significant environmental problems, efforts are underway to launch mangrove agroforestry and agriculture projects. Mangrove systems require intensive care to save threatened areas. So far, conservation and management efforts lag behind the destruction; there is still much to learn about proper management and sustainable harvesting of mangrove forests. Mangroves have enormous ecological value. They protect and stabilize coastlines, enrich coastal waters, yield commercial forest products and support coastal fisheries. Mangrove forests are among the world's most productive ecosystems, producing organic carbon well in excess of the ecosystem requirements and contributing significantly to the global carbon cycle. Extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens. Mangroves may be further developed as sources of high-value commercial products and fishery resources and as sites for a burgeoning ecotourism industry. Their unique features also make them ideal sites for experimental studies of biodiversity and ecosystem function. Where degraded areas are being revegetated, continued monitoring and thorough assessment must be done to help understand the recovery process. This knowledge will help develop strategies to promote better rehabilitation of degraded mangrove habitats the world over and ensure that these unique ecosystems survive and flourish.

Elevation gradients of species-density: historical and prospective views

Abstract: Studies of elevation clines in diversity and composition of ecological communities date back to the origins of biogeography. A modern resurgence of interests in these elevational clines is likely to contribute important insights for developing a more general theory of species diversity. In order to gain a more comprehensive understanding of geographical clines in diversity, the research programme for montane biogeography should include statistically rigorous tests of apparent patterns, comparisons of patterns among regions and taxonomic or ecological groups of species, and analyses of clines in environmental variables concurrent with biogeographical surveys. The conceptual framework for this research programme should be based on the assumption that elevational gradients in species diversity result from a combination of ecological and evolutionary processes, rather than the presumed independent effects of one overriding force. Given that montane ecosystems are hot spots of biological diversity, an expanded and integrated programme for biogeographic surveys in montane regions should provide valuable insights for conservation biologists.

Restoring Heterogeneity on Rangelands: Ecosystem Management Based on Evolutionary Grazing Patterns

Abstract: R are the most common form of terrain in both the United States (where it accounts for 61% of all land surface) and the world (70% of all land surface). Rangelands consist primarily of native plant communities managed, typically, for livestock production (Holechek et al. 1998). Because they can embrace extensive native plant communities, rangelands can serve as biodiversity repositories. However, in the Great Plains of the United States, where decisions about land use are made largely at the discretion of the private landowner, many plant and animal species dependent on rangelands are imperiled. For example, according to data from the North American Breeding Bird Survey, 70% of the 29 bird species characteristic of North American prairies experienced a decline in population between 1966 and 1993. Indeed, these grassland species are declining at a faster rate than any other guild of terrestrial birds in North America (Knopf 1994). Excessive herbivory by domestic livestock may have contributed to the decline in some of these species, but many species endemic to North American prairies evolved with large grazing animals. The Mountain Plover (Charadrius montanus), Baird’s Sparrow (Ammodramus bairdii), and Chestnut-collared Longspur (Calcarius ornatus) are examples of birds that occur in highest densities in grazed landscapes (Kantrud 1981, Renken and Dinsmore 1987, Knopf 1996). There are many potential causes for this decline in grassland bird populations, but the fact that it occurred when the condition of rangelands had improved, according to traditional means of evaluation (Holechek et al.1998), suggests that techniques currently used to manage rangelands may be insufficient to maintain biological diversity. Most techniques of rangeland management were developed under the paradigm of increasing and sustaining livestock production by decreasing the inherent variability associated with rangelands and grazing. This rangeland management approach is incapable of providing an ecological framework for alternative management objectives that have become more important over the past quarter-century. For example, the maintenance of biodiversity, as well as the preservation of habitat for many individual species, depends on the interspersion of diverse habitat types throughout a heterogeneous landscape. We contend that traditional rangeland management techniques reduce rangeland heterogeneity by favoring the most productive, most palatable forage species for domestic cattle. In this article, we propose a paradigm that promotes the potential heterogeneity of landscapes through an alternative approach to managing those rangelands with a long evolutionary history of large-ungulate grazing (Milchunas et al. 1988). Hence, for these rangelands we attempt to link the goals

The management of lowland neutral grasslands in Britain: effects of agricultural practices on birds and their food resources

Abstract: Summary 1The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound. 2In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species-rich swards have been largely replaced by relatively dense, fast-growing and structurally uniform swards, dominated by competitive species. 3Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds. 4The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed-eating birds. 5The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity. 6Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi-natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity. 7There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management-related changes in habitat; and (iii) the impact of alternative anti-helminithic treatments for livestock on invertebrates and birds.

Agri-environment schemes do not effectively protect biodiversity in Dutch agricultural landscapes

Abstract: Roughly 20% of the European Union's farmland is under some form of agri-environment scheme to counteract the negative impacts of modern agriculture on the environment. The associated costs represent about 4% (1.7 billion euros) of the European Union's total expenditure on the Common Agricultural Policy and are expected to rise to 10% in the near future. Although agri-environment schemes have been implemented in various countries for well over a decade, to date no reliable, sufficiently replicated studies have been performed to test whether such measures have the presumed positive effects on biodiversity. Here we present the results of a study evaluating the contribution of agri-environment schemes to the protection of biodiversity in intensively used Dutch agricultural landscapes. We surveyed plants, birds, hover flies and bees on 78 paired fields that either had agri-environment schemes in the form of management agreements or were managed conventionally. Management agreements were not effective in protecting the species richness of the investigated species groups: no positive effects on plant and bird species diversity were found. The four most common wader species were observed even less frequently on fields with management agreements. By contrast, hover flies and bees showed modest increases in species richness on fields with management agreements. Our results indicate that there is a pressing need for a scientifically sound evaluation of agri-environment schemes.

Environmental influences on regional deep-sea species diversity

Abstract: Most of our knowledge of biodiversity and its causes in the deep-sea benthos derives from regional-scale sampling studies of the macrofauna. Improved sampling methods and the expansion of investigations into a wide variety of habitats have revolutionized our understanding of the deep sea. Local species diversity shows clear geographic variation on spatial scales of 100-1000 km. Recent sampling programs have revealed unexpected complexity in community structure at the landscape level that is associated with large-scale oceanographic processes and their environmental consequences. We review the relationships between variation in local species diversity and the regional-scale phenomena of boundary constraints, gradients of productivity, sediment heterogeneity, oxygen availability, hydrodynamic regimes, and catastrophic physical disturbance. We present a conceptual model of how these interdependent environmental factors shape regional-scale variation in local diversity. Local communities in the deep sea may be composed of species that exist as metapopulations whose regional distribution depends on a balance among global-scale, landscape-scale, and small-scale dynamics. Environmental gradients may form geographic patterns of diversity by influencing local processes such as predation, resource partitioning, competitive exclusion, and facilitation that determine species coexistence. The measurement of deep-sea species diversity remains a vital issue in comparing geographic patterns and evaluating their potential causes. Recent assessments of diversity using species accumulation curves with randomly pooled samples confirm the often-disputed claim that the deep sea supports higher diversity than the continental shelf. However, more intensive quantitative sampling is required to fully characterize the diversity of deep-sea sediments, the most extensive habitat on Earth. Once considered to be constant, spatially uniform, and isolated, deep-sea sediments are now recognized as a dynamic, richly textured environment that is inextricably linked to the global biosphere. Regional studies of the last two decades provide the empirical background necessary to formulate and test specific hypotheses of causality by controlled sampling designs and experimental approaches.

Métodos para medir la biodiversidad

Abstract: All biological systems are diverse. This means that the parts that compose them vary in their number and quantity. Biological diversity or biodiversity refers to this variety of life, at different levels of organization. Thus, individuals of a particular species show differences in the structure of their deoxyribonucleic acid (DNA), the molecule that codifies genetic information. This variability is known as genetic diversity. At other level of organization, ecological communities are composed by a certain number of species, and each one of these species has a particular importance within the community. Such importance is determined by their number of individuals, biomass, cover, etc. This type of variability is recognized as species diversity. Finally, those geographic areas identified as "landscapes" because of their particular history and environmental conditions, are composed by different habitats that exchange biotic and abiotic materials. The number and cover of these habitats are known as the ecosystem diversity of the landscape. Over the last decades a number of methods for measuring the different aspects of biodiversity have been proposed. But, although the importance of biodiversity is evident from different points of view, we still lack of standard protocols for measuring it. Most of the proposed methods have been published in English in specialized journals of ecology, so they are not usually available in Spanish-spoken countries. This work gathers and exemplifies the most common methods to measure biodiversity. Emphasis is given on species diversity because this is the better-known level of organization to date, although a general description and literature references about genetic and ecosystem diversity are presented. To make easier the selection of the most appropriate method for each particular case, methods are classified in relation to the biological aspect that they assess. Thus, to measure within community or habitat diversity (alpha diversity), the reader can select among the methods that consider only the number of species, or among the methods that highlight the structure of the community considering both the number of species and their relative importance. Such methods that are based upon the structure of the community may underline the dominance of a few species (as in the case of Simpson's index), or else the degree of evenness among the whole set of species (as in the case of Shannon-Wiener's index). Also, to compare two or more communities according to changes in their species composition (beta diversity), different methods are suggested. These methods can be based only on the presence or absence of species in the communities, or on the relative importance of each species. Finally, some methods to measure the diversity of the arrangement of communities within a landscape (gamma diversity) are presented. These methods are derived from the contribution of alpha and beta diversities within the landscape. This way, this anthology of methods is a simple guide for those interested on studies of community ecology or environmental assessment of biodiversity. It can be especially useful to quantify changes on species diversity as a consequence of ecosystem perturbations or modifications, or to follow such changes through time (monitoring).

Plant diversity enhances ecosystem responses to elevated CO2 and nitrogen deposition

Abstract: Human actions are causing declines in plant biodiversity, increases in atmospheric CO2 concentrations and increases in nitrogen deposition; however, the interactive effects of these factors on ecosystem processes are unknown. Reduced biodiversity has raised numerous concerns, including the possibility that ecosystem functioning may be affected negatively, which might be particularly important in the face of other global changes. Here we present results of a grassland field experiment in Minnesota, USA, that tests the hypothesis that plant diversity and composition influence the enhancement of biomass and carbon acquisition in ecosystems subjected to elevated atmospheric CO2 concentrations and nitrogen deposition. The study experimentally controlled plant diversity (1, 4, 9 or 16 species), soil nitrogen (unamended versus deposition of 4 g of nitrogen per m2 per yr) and atmospheric CO2 concentrations using free-air CO2 enrichment (ambient, 368 micromol mol-1, versus elevated, 560 micromol mol-1). We found that the enhanced biomass accumulation in response to elevated levels of CO2 or nitrogen, or their combination, is less in species-poor than in species-rich assemblages.

Regional-scale assembly rules and biodiversity of coral reefs.

Abstract: Tropical reef fishes and corals exhibit highly predictable patterns of taxonomic composition across the Indian and Pacific Oceans. Despite steep longitudinal and latitudinal gradients in total species richness, the composition of these key taxa is constrained within a remarkably narrow range of values. Regional-scale variation in reef biodiversity is best explained by large-scale patterns in the availability of shallow-water habitat. Once habitat area is accounted for, there is surprisingly little residual effect of latitude or longitude. Low-diversity regions are most vulnerable to human impacts such as global warming, underscoring the urgent need for integrated management at multinational scales.

The Function of Marine Critical Transition Zones and the Importance of Sediment Biodiversity

Abstract: Estuaries and coastal wetlands are critical transition zones (CTZs) that link land, freshwater habitats, and the sea. CTZs provide essential ecological functions, including decomposition, nutrient cycling, and nutrient production, as well as regulation of fluxes of nutrients, water, particles, and organisms to and from land, rivers, and the ocean. Sediment-associated biota are integral to these functions. Functional groups considered essential to CTZ processes include heterotrophic bacteria and fungi, as well as many benthic invertebrates. Key invertebrate functions include shredding, which breaks down and recycles organic matter; suspension feeding, which collects and transports sediments across the sediment–water interface; and bioturbating, which moves sediment into or out of the seabed. In addition, macrophytes regulate many aspects of nutrient, particle, and organism dynamics above- and belowground. Animals moving within or through CTZs are vectors that transport nutrients and organic matter across terrestrial, freshwater, and marine interfaces. Significant threats to biodiversity within CTZs are posed by anthropogenic influences; eutrophication, nonnutrient pollutants, species invasions, overfishing, habitat alteration, and climate change affect species richness or composition in many coastal environments. Because biotic diversity in marine CTZ sediments is inherently low whereas their functional significance is great, shifts in diversity are likely to be particularly important. Species introductions (from invasion) or loss (from overfishing or habitat alteration) provide evidence that single-species changes can have overt, sweeping effects on CTZ structure and function. Certain species may be critically important to the maintenance of ecosystem functions in CTZs even though at present there is limited empirical evidence that the number of species in CTZ sediments is critical. We hypothesized that diversity is indeed important to ecosystem function in marine CTZs because high diversity maintains positive interactions among species (facilitation and mutualism), promoting stability and resistance to invasion or other forms of disturbance. The complexity of interactions among species and feedbacks with ecosystem functions suggests that comparative (mensurative) and manipulative approaches will be required to elucidate the role of diversity in sustaining CTZ functions.

New Ages for the Last Australian Megafauna: Continent-Wide Extinction About 46,000 Years Ago

Abstract: All Australian land mammals, reptiles, and birds weighing more than 100 kilograms, and six of the seven genera with a body mass of 45 to 100 kilograms, perished in the late Quaternary. The timing and causes of these extinctions remain uncertain. We report burial ages for megafauna from 28 sites and infer extinction across the continent around 46,400 years ago (95% confidence interval, 51,200 to 39,800 years ago). Our results rule out extreme aridity at the Last Glacial Maximum as the cause of extinction, but not other climatic impacts; a "blitzkrieg" model of human-induced extinction; or an extended period of anthropogenic ecosystem disruption.

Biodiversity: towards a unifying theme for river ecology

Abstract: 1. A broadened concept of biodiversity, encompassing spatio-temporal heterogeneity, functional processes and species diversity, could provide a unifying theme for river ecology. 2. The theoretical foundations of stream ecology often do not reflect fully the crucial roles of spatial complexity and fluvial dynamics in natural river ecosystems, which has hindered conceptual advances and the effectiveness of efforts at conservation and restoration. 3. Inclusion of surface waters (lotic and lentic), subsurface waters (hyporheic and phreatic), riparian systems (in both constrained and floodplain reaches), and the ecotones between them (e.g. springs) as interacting components contributing to total biodiversity, is crucial for developing a holistic framework of rivers as ecosystems. 4. Measures of species diversity, including alpha, beta and gamma diversity, are a result of disturbance history, resource partitioning, habitat fragmentation and successional phenomena across the riverine landscape. A hierarchical approach to diversity in natural and altered river-floodplain ecosystems will enhance understanding of ecological phenomena operating at different scales along multidimensional environmental gradients. 5. Re-establishing functional diversity (e.g. hydrologic and successional processes) across the active corridor could serve as the focus of river conservation initiatives. Once functional processes have been reconstituted, habitat heterogeneity will increase, followed by corresponding increases in species diversity of aquatic and riparian biota.

Beyond Kyoto: Forest Management in a Time of Rapid Climate Change

Abstract: Policies to reduce global warming by offering credits for carbon sequestration have neglected the effects of forest management on biodiversity. I review properties of forest ecosystems and management op- tions for enhancing the resistance and resilience of forests to climate change. Although forests, as a class, have proved resilient to past changes in climate, today's fragmented and degraded forests are more vulnerable. Ad- aptation of species to climate change can occur through phenotypic plasticity, evolution, or migration to suit- able sites, with the latter probably the most common response in the past. Among the land-use and manage- ment practices likely to maintain forest biodiversity and ecological functions during climate change are (1) representing forest types across environmental gradients in reserves; (2) protecting climatic refugia at multi- ple scales; (3) protecting primary forests; (4) avoiding fragmentation and providing connectivity, especially parallel to climatic gradients; (5) providing buffer zones for adjustment of reserve boundaries; (6) practicing low-intensity forestry and preventing conversion of natural forests to plantations; (7) maintaining natural fire regimes; (8) maintaining diverse gene pools; and (9) identifying and protecting functional groups and keystone species. Good forest management in a time of rapidly changing climate differs little from good forest management under more static conditions, but there is increased emphasis on protecting climatic refugia and providing connectivity.

El Niño effects on the dynamics of terrestrial ecosystems.

Abstract: New studies are showing that the El Nino Southern Oscillation (ENSO) has major implications for the functioning of different ecosystems, ranging from deserts to tropical rain forests. ENSO-induced pulses of enhanced plant productivity can cascade upward through the food web invoking unforeseen feedbacks, and can cause open dryland ecosystems to shift to permanent woodlands. These insights suggest that the predicted change in extreme climatic events resulting from global warming could profoundly alter biodiversity and ecosystem functioning in many regions of the world. Our increasing ability to predict El Nino effects can be used to enhance management strategies for the restoration of degraded ecosystems.

Human-caused environmental change: Impacts on plant diversity and evolution

Abstract: Human-caused environmental changes are creating regional combinations of environmental conditions that, within the next 50 to 100 years, may fall outside the envelope within which many of the terrestrial plants of a region evolved. These environmental modifications might become a greater cause of global species extinction than direct habitat destruction. The environmental constraints undergoing human modification include levels of soil nitrogen, phosphorus, calcium and pH, atmospheric CO2, herbivore, pathogen, and predator densities, disturbance regimes, and climate. Extinction would occur because the physiologies, morphologies, and life histories of plants limit each species to being a superior competitor for a particular combination of environmental constraints. Changes in these constraints would favor a few species that would competitively displace many other species from a region. In the long-term, the “weedy” taxa that became the dominants of the novel conditions imposed by global change should become the progenitors of a series of new species that are progressively less weedy and better adapted to the new conditions. The relative importance of evolutionary versus community ecology responses to global environmental change would depend on the extent of regional and local recruitment limitation, and on whether the suite of human-imposed constraints were novel just regionally or on continental or global scales.

Countryside biogeography: use of human-dominated habitats by the avifauna of southern costa rica

Abstract: Understanding the multifaceted relationship between biodiversity and land- use intensity is key to conservation policy. To begin to characterize this relationship in a tropical region, we investigated the bird fauna in an agricultural landscape in southern Costa Rica. Landsat Thematic Mapper (TM) data show that about 27% of the land remains forested in the 15 km radius study region encompassing our sites. The rest was cleared about 40 yr ago for relatively small-scale coffee and cattle production, intermixed with other crops. Our goals were to: (1) compare the composition of the avifauna found in forest- fragment and open habitats of the countryside; (2) assess the faunal change that has occurred since deforestation; and (3) provide a baseline for future comparisons. We surveyed the avifauna of eight forest fragments (0.3-25 ha) and 13 open-habitat sites (1.0 ha each) in the agricultural landscape. The pre-deforestation avifauna was ap- proximated by the long-term bird list for the largest forest fragment (Las Cruces, LC; 227 ha) in the study region. We assumed conservatively that a species recorded in LC but not detected elsewhere occurred only in LC. Of the 272 locally extant bird species considered in this study, 149 (55%) occurred in forest habitats only. There was a significant positive correlation between forest fragment size and species richness for these forest birds. Of the remaining 123 species, 60 (22% of the total) occurred both in forest and open habitats. Sixty-three species (23%) occurred in open habitats only; the three nonnative species (1%) are in this group. Based on comparisons with larger forest tracts outside of the study region, it appeared that between 4 and 28 species (1-9% of the possible original totals) have gone locally extinct since deforestation began. The avifauna of open habitats was similar through- out the study region and did not vary with proximity to extensive forest. A substantial proportion of the native bird fauna occurs in a densely (human) populated, agricultural landscape almost a half-century after extensive clearance. There are, however, cautionary messages: (1) the common occurrence of forest birds in human-dominated coun- tryside (including both forest-fragment and open habitats) does not necessarily imply that these species maintain sustainable populations there; (2) about half of the species have little prospect of surviving outside of the forest; and (3) ongoing intensification of land use may greatly reduce avian diversity in countryside habitats. Nonetheless, countryside habitats may buy time for the conservation of some species; at best, they may even sustain a moderate fraction of the native biota.

A literature review of insect responses to fire, compared to other conservation managements of open habitat

Abstract: This literature review concerns insect responses to fire, compared to other feasible and appropriate conservation managements of open habitats. Many insect groups decline markedly immediately after fire, with the magnitude of reduction related to the degree of exposure to the flames and mobility of the insect. Niche diversity is lower in recently burned habitat, and the rate of insect increase following fire also relates to the species' ability to gain access to the regrowing vegetation. Postburn flora can be quite attractive to some recolonizing insects, possibly to some degree a result of fire-caused insect mortality which provides plants with short-term release from insect herbivory. Insect declines may follow immediately after mowing, but usually of lesser degree and shorter duration than after a fire of comparable timing and size. Season and scale of cutting may affect how much and which species showed positive or negative responses. Cut areas offer the vegetational structure and composition preferred by some insects, but cutting – or cutting at certain scales, seasons, or frequencies – may also be unfavorable for some species. Heavy grazing results in niche and assemblage simplification. Nonetheless, some invertebrates prefer the short turfs and bare ground resulting from heavier grazing. Other species vary in whether they peak in abundance and diversity in intermediate, light, or no grazing. In comparisons of mowing/haying and grazing regimes of similar compatibility with maintenance of the same habitat types, responses of particular species and species groups varied as to whether they had a preference for one or the other. Characteristics associated with insect responses to fire related to the degree of exposure to lethal temperature and stress experienced in the post-fire environment, suitability of post-treatment vegetation as habitat, and ability to rebuild numbers in the site (from survivors and/or colonizers). These factors appear equally useful for explicating insect responses to other managements such as haying, mowing, and grazing. By contrast, the assumption that the most habitat-restricted species will be most adapted to ecological forces believed to be prevalent in that ecosystem appears less efficacious for predicting insect management preferences.

Effects of macrophyte species richness on wetland ecosystem functioning and services

Abstract: Wetlands provide many important ecosystem services to human society1,2,3,4,5, which may depend on how plant diversity influences biomass production and nutrient retention4,6,7,8. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species4,9. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species—in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water2,10,11. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.

Evolution of genome–phenome diversity under environmental stress

Abstract: The genomic era revolutionized evolutionary biology. The enigma of genotypic-phenotypic diversity and biodiversity evolution of genes, genomes, phenomes, and biomes, reviewed here, was central in the research program of the Institute of Evolution, University of Haifa, since 1975. We explored the following questions. ( i ) How much of the genomic and phenomic diversity in nature is adaptive and processed by natural selection? ( ii ) What is the origin and evolution of adaptation and speciation processes under spatiotemporal variables and stressful macrogeographic and microgeographic environments? We advanced ecological genetics into ecological genomics and analyzed globally ecological, demographic, and life history variables in 1,200 diverse species across life, thousands of populations, and tens of thousands of individuals tested mostly for allozyme and partly for DNA diversity. Likewise, we tested thermal, chemical, climatic, and biotic stresses in several model organisms. Recently, we introduced genetic maps and quantitative trait loci to elucidate the genetic basis of adaptation and speciation. The genome–phenome holistic model was deciphered by the global regressive, progressive, and convergent evolution of subterranean mammals. Our results indicate abundant genotypic and phenotypic diversity in nature. The organization and evolution of molecular and organismal diversity in nature at global, regional, and local scales are nonrandom and structured; display regularities across life; and are positively correlated with, and partly predictable by, abiotic and biotic environmental heterogeneity and stress. Biodiversity evolution, even in small isolated populations, is primarily driven by natural selection, including diversifying, balancing, cyclical, and purifying selective regimes, interacting with, but ultimately overriding, the effects of mutation, migration, and stochasticity.

The role of landscape structure in species richness distribution of birds, amphibians, reptiles and lepidopterans in Mediterranean landscapes

Abstract: The parameters referring to landscape structure are essential in any evaluation for conservation because of the relationship that exists between the landscape structure and the ecological processes. This paper presents a study of the relationships between landscape structure and species diversity distribution (estimated in terms of richness of birds, amphibians, reptiles and butterflies) in the region of Madrid, Spain. The results show that the response of species richness to landscape heterogeneity varies depending on the group of species considered. For birds and lepidopterans, the most important factor affecting the distribution of richness of species is landscape heterogeneity, while other factors, such as the specific composition of land use, play a secondary role at this scale. On the other hand, richness of amphibians and reptiles is more closely related to the abundance of certain land-use types. The study highlights the importance of heterogeneity in Mediterranean landscapes as a criterion for landscape planning and for definition of management directives in order to maintain biodiversity.

A habitat island approach to conserving birds in urban landscapes: case studies from southern and northern Europe

Abstract: Wildlife conservation in urban habitats is increasingly important due to current urbanization trends. We review the different approaches to studying birds in urban landscapes, and point out the impor- tance of the habitat island ecological theory as a research framework for the management and conservation of urban birds. Based on two comprehensive research projects conducted at urban parks in Spain (Ma- drid) and Finland (Oulu and Rovaniemi), several different issues related to bird conservation in cities are discussed, main findings of these projects are presented, and future research needs are suggested. Urban parks are important biodiversity hotspots in cities. Fragmentation conditions have the same deleterious effects to urban birds as in other fragmented landscapes. Park size accounts for species accumulation in urban parks; this pattern being highly nested. Urban parks of 10-35 ha would contain most of the species recorded in cities, but other indicators related to the probabilities of persistence of the target species should be obtained. Wooded streets can increase urban landscape connectivity by providing alternative habitat for feeding and nesting during the breeding season. Because increasing the size of parks is difficult in cities, enhancement of habitat diversity and resource availability for birds within parks (e.g. nest boxes, winter feeding tables, etc.) appears to be a straightforward way of increasing urban bird diversity. However, human disturbance (pedestrians) should be controlled since it can negatively influence many urban birds. We present a conceptual model for urban bird conservation, which includes three aspects (management, environmental education and research) and new alternatives to promote the involvement of different sectors of the society.

Fisheries managed to rebuild ecosystems? reconstructing the past to salvage the future

Abstract: This paper presents the case for adopting ecosystem rebuilding as the goal of fisheries management. Movement toward this goal may represent the only hope for fisheries, as we know them, to exist 50 years in the future alongside essential services provided by marine ecosystems. First, I review archaeological, historical, and recent evidence that bears witness to a long, dismal record of overexploitation. Second, I examine the ecological effects of overfishing on aquatic ecosystems. Fish with life histories and spatial behavior inimical to harvesting are selectively removed, both within and among species. The loss of keystone species and the replacement of high-value, demersal resources with pelagic, rapid-turnover, low-value species shifts the nature of ecosystems, evidenced by accelerating local extinctions and a worldwide decline in trophic level. Disconcertingly, harvest limits that appear safe by single species evaluation can engender ecosystem changes that are hard to reverse. Driven by a progression ...