To select candidate populations of wild species to be given priority for conservation, genetic criteria gained from the study of molecular markers may be useful. Traditionally, diversity measures such as expected heterozygosity or percentage of polymorphic loci have been considered. For conservation we propose instead that priority should be given to measures of allelic richness. To standardize the results of allelic richnexx across populations, we used the technique of rarefaction. This technique allows evaluation of the expected number of different alleles among equal-sized samples drawn from several different populations. We also show how the contribution of each population to total diversity can be partitioned into two components. The first is related to the level of diversity of the population and the second to its divergence from the other populations. For conservation purposes the uniqueness of a population-in terms of its allelic composition-may be at least as important as its diveristy level. These new descriptors are illustrated by means of isozyme and chloroplast DNA data obtained for an endangered tree species, the argan tree of Morocco (Argania spinosa (L.) Skeels). With these analysis the conservation value of the argan tree populations, especially those of two isolated present in the broth of the country, can be better appreciated. The methods proposed to identify priority areas for conservation of the genetic resources of the argan tree are compared to those sometimes advocated in the case of reserve design, where one of the goals is to maximize-species richness.
Single‐tree harvesting with on‐site lumber production produces gaps in Amazonian forest canopy that are structurally different from natural treefall gaps. Harvest gaps are much more open, and there is neither leaf litter nor partial shading as in natural treefalls, so these anthropogenic gaps receive more intense sunlight. We used HOBO XT temperature and light data loggers to measure thermal environments in forest patches. These data were combined with data on lizard activity, activity temperatures, and habitat use to determine whether human‐made gaps influence the structure of Amazon forest lizard assemblages. Human‐made treefalls are not only more extreme thermally than surrounding forest habitat patches and natural treefalls, but they are warmer than expected based on increased light alone. Large‐bodied teiid lizards, which are typically uncommon or rare within forest, bask in sun in treefalls to gain heat. The body temperatures of these heliotherms average 36.1° C. Nonheliothermic species avoid treefalls and remain in shade within the forest. Their body temperatures average 27.7° C. Heliothermic lizards using treefall gaps are large‐bodied predaceous species that feed on vertebrates as well as invertebrates. Increasing the number of anthropogenic treefall gaps in a forest may increase the immigration and population growth of heliothermic lizards, thereby increasing their population density. Predation by these lizards and dominance over smaller lizards in interference competition (for food) may have a cascading effect on forest species, changing community structure. Impacto de la Cosecha Individual de Arboles en Ambientes Termales de Lagartijas de Bosques Tropicales Lluviosos del Amazonas La cosecha de árboles individuales con producción de madera en el sitio crea espacios en el dosel del bosque amazónico que son estructuralmente diferentes a los espacios creados por la caída natural de árboles. Espacios por cosecha son mucho mas abiertos y no dejan ni hojarasca, ni sombreado parcial como sucede en la caída natural de árboles, esto ocasiona que estas áreas abiertas por actividades antropogénicas reciban relativamente mayor iluminación solar. Utilizamos colectores de datos de temperatura HOBO XT y de intensidad luminosa para medir ambientes termales en parches del bosque. Estos datos se combinaron con datos de actividad de lagartijas, temperaturas de actividad y uso del hábitat para determinar si los espacios abiertos por humanos influencían la estructura de los ensamblajes de lagartijas del Amazonas. La caída de árboles provocada por humanos no son únicamente mas exstremos térmicamente que los parches de hábitat boscoso circundantes y los espacios abiertos provocados por la caída natural de arboles, sino que fueron mas calientes de lo esperado debido al incremento de la intensidad luminosa. Lagartijas de cuerpo grande poco comunes o raras dentro del bosque se asolean en áreas abiertas para incrementar el calor. Las temperaturas corporales de estas lagartijas heliotérmicas promedian 36.1° C. La mayoría de las especies de lagartijas no heliotérmicas evitan las áreas abiertas y permanecen en la sombra dentro del bosque. Las temperatures corporales de éstas últimas promedia 27.7° C. Las lagartijas heliotérmicas que utilizan los espacios abiertos presentan cuerpos grandes y son especies depredadoras que se alimentan tanto de vertebrados como de invertebrados. El incremento de espacios abiertos ocasionados por actividades antropogénicas en un bosque puede incrementar la inmigración y crecimiento poblacional de lagartijas heliotérmicas, incrementando en consecuencia la densidad poblacional. La depredación de estas lagartijas y su dominio sobre otras lagartijas pequeñas en competencia por interferencia (por alimento) puede tener un efecto de cascada sobre especies del bosque, cambiando la estructura de la comunidad.
The concept of species redundancy in ecosystem processes is troublesome because it appears to contradict the traditional emphasis in ecology on species singularity. When species richness is high, however, ecosystem processes seem clearly insensitive to considerable variation in biodiversity. Some elementary principles from reliability engineering, where engineered redundancy is a valued part of systems design, suggest that we should rethink our stance on species redundancy. For example, a central tenet of reliability engineering is that reliability always increases as redundant components are added to a system, a principle that directly supports redundant species as guarantors of reliable ecosystem functioning. I argue that we should embrace species redundancy and perceive redundancy as a critical feature of ecosystems which must be preserved if ecosystems are to function reliably and provide us with goods and services. My argument is derived from basic principles of reliability engineering which demonstrate that the probability of reliable system performance is closely tied to the level of engineered redundancy in its design. Empirical demonstrations of the value of species redundancy in ecosystem reliability would provide new insights into the ecology of communities and the value of species conservation. Redundancia de Especies y Confiabilidad del Ecosistema El concepto de redundancia de especies en procesos ecológicos es problemático puesto que aparentemente contradice el énfasis tradicional en ecologia sobre la singularidad de las especies. Sin embargo, cuando la riqueza de especies es alta, los procesos del ecosistema parecen claramente insensibles a variaciones considerables de la biodiversidad. Principios elementales de confiabilidad en ingenieria, donde la redundancia es evaluada como parte del diseño de sistemas, sugiere que deberíamos repensar nuestra postura sobre la redundancia de especies. Por ejemplo, un principio central de confiabilidad ingenieril es que la confiabilidad siempre incrementa cuando componentes redundantes son agregados al sistema, un sistema que directamente soporta especies redundantes como garante del funcionamiento del ecosistema. Yo argumento que deberíamos abarcar la redundancia de especies y percibir redundancia como una característica crítica del ecosistema que debe ser conservada si los ecosistemas funcionaran confiablemente y nos provean de bienes y servicios. Demostraciones empíricas de el valor de la redundancia de especies en confiabilidad de ecosistemas provee nuevas intuiciones dentro de la ecología de comunidades y el valor de la conservación de las especies.
Skeptics have questioned the empirical evidence that corridors provide landscape connectivity. Some also have suggested dangers of corridors. We reviewed published studies that empirically addressed whether corridors enhance or diminish the population viability of species in habitat patches connected by corridors. A randomized and replicated experimental design has not been used—and we argue is not required—to make inferences about the conservation value of corridors. Rather, studies can use observational or experimental analyses of parameters of target populations or movements of individual animals. Two of these approaches hold the greatest promise for progress, especially if the shortcomings of previous studies are remedied. First, experiments using demographic parameters as dependent variables—even if unreplicated—can demonstrate the demographic effects of particular corridors in particular landscapes. Such studies should measure demographic traits before and after treatment in both the treated area (corridor created or destroyed) and an untreated area (habitat patches isolated from one another). This approach is superior to observing the demographic conditions in various landscapes because of the tendency for corridor presence to be correlated with other variables, such as patch size, that can confound the analysis. Second, observations of movements by naturally dispersing animals in fragmented landscapes can demonstrate the conservation value of corridors more convincingly than can controlled experiments on animal movement. Such field observations relate directly to the type of animals (e.g., dispersing juveniles of target species) and the real landscapes that are the subject of decisions about corridor preservation. Future observational studies of animal movements should attempt to detect extra‐corridor movements and focus on fragmentation‐sensitive species for which corridors are likely to be proposed. Fewer than half of the 32 studies we reviewed provided persuasive data regarding the utility of corridors; other studies were inconclusive, largely due to design flaws. The evidence from well‐designed studies suggests that corridors are valuable conservation tools. Those who would destroy the last remnants of natural connectivity should bear the burden of proving that corridor destruction will not harm target populations. Proveen Conectividad los Corredores de Hábitat? Algunos escépticos han cuestionado la evidencia empírica de que los corredores proveen conectividad al paisaje. Otros han sugerido los peligros de los corredores. Revisamos estudios publicados que abordaron empíricamente si los corredores fomentan o disminuyen la viabilidad de poblaciones de especies en parches de hábitat conectados por corredores. A la fecha no se ha llevado a cabo un diseño experimental randomizado y con réplicas para realizar inferencias sobre el valor de los corresdores en la conservación—y nosotros argüímos que no es necesario. En cambio, los estudios pueden emplear análisis observacional o experimental de parámetros de poblaciones de interés o movimientos individuales de animales. Dos de estas aproximaciones son muy prometedoras y pueden progresar, especialmente si las limitantes de los estudios previos son remediadas. Primero, los experimentos que usan parámetros demográficos como variables dependientes—aún si no son replicados—pueden demostrar efectos demográficos de corredores en paisajes particulares. Estos estudios deberán medir características demográficas antes y después del tratamiento, tanto en el área tratada (corredor creado o destruído) como en un área no tratada (parches de hábitat aislados unos de otros). Esta aproximación es superior a observar las condiciones demográficas en varios paisajes puesto que la presencia de un corredor tiende a estar correlacionada con otras variables, como lo es el tamaño del parche lo que puede confundir el análisis. Segundo, las observaciones de movimientos de animales que se desplazan normalmente en paisajes fragmentados puede demostrar el valor de los corredores en la conservación de manera mas convincente que los experimentos controlados sobre animales en movimiento. Este tipo de observaciones de campo están directamente relacionades con el tipo de animal (e.g., juveniles de la especie de interés dispersándose) y con el tipo de paisajes que están sujetos a las decisiones de preservación de corredores. Los estudios observacionales de movimientos de animales a futuro deberán tratar de detectar movimientos extra‐corredores y enfocarse a especies sensitivas a la fragmentación y para las cuales los corredores son factibles a ser propuestos. Menos de la mitad de los 32 estudios revisados provee datos persuasivos referentes a la utilidad de los corredores; otros estudios fueron inconclusos, mayormente debido a diseños defectuosos. Las evidencias de estudios bien diseñados sugieren que los corredores son herramientas valiosas de conservación. Aquellos que intentan destruir los últimos remanentes de conectividad natural deberían sustentarse demostrando que la destrucción de los corredores no afectará a poblaciones de interés.
Skeptics have questioned the empirical evidence that corridors provide landscape connectivity. Some also have suggested dangers of corridors. We reviewed published studies that empirically addressed whether corridors enhance or diminish the population viability of species in habitat patches connected by corridors. A randomized and replicated experimental design has not been usedand we argue is not requiredto make inferences about the conservation value of corridors. Rather, studies can use observational or experimental analyses of parameters of target populations or movements of individual animals. Two of these approaches hold the greatest promise for progress, especially if the shortcomings of previous studies are remedied. First, experiments using demographic parameters as dependent variableseven if unreplicatedcan demonstrate the demographic effects of particular corridors in particular landscapes. Such studies should measure demographic traits before and after treatment in both the treated area (corridor created or destroyed) and an untreated area (habitat patches isolated from one another). This approach is superior to observing the demographic conditions in various landscapes because of the tendency for corridor presence to be correlated with other variables, such as patch size, that can confound the analysis. Second, observations of movements by naturally dispersing animals in fragmented landscapes can demonstrate the conservation value of corridors more convincingly than can controlled experiments on animal movement. Such field observations relate directly to the type of animals (e.g., dispersing juveniles of target species) and the real landscapes that are the subject of decisions about corridor preservation. Future observational studies of animal movements should attempt to detect extra-corridor movements and focus on fragmentation-sensitive species for which corridors are likely to be proposed. Fewer than half of the 32 studies we reviewed provided persuasive data regarding the utility of corridors; other studies were inconclusive, largely due to design flaws. The evidence from well-designed studies suggests that corridors are valuable conservation tools. Those who would destroy the last remnants of natural connectivity should bear the burden of proving that corridor destruction will not harm target populations.
Bottom trawling and use of other mobile fishing gear have effects on the seabed that resemble forest clearcutting, a terrestrial disturbance recognized as a major threat to biological diversity and economic sustainability. Structures in marine benthic communities are generally much smaller than those in forests, but structural complexity is no less important to their biodiversity. Use of mobile fishing gear crushes, buries, and exposes marine animals and structures on and in the substratum, sharply reducing structural diversity. Its severity is roughly comparable to other natural and anthropogenic marine disturbances. It also alters biogeochemical cycles, perhaps even globally. Recovery after disturbance is often slow because recruitment is patchy and growth to maturity takes years, decades, or more for some structure-forming species. Trawling and dredging are especially problematic where the return intervalthe time from one dredging or trawling event to the nextis shorter than the time it takes for the ecosystem to recover; extensive areas can be trawled 100-700% per year or more. The effects of mobile fishing gear on biodiversity are most severe where natural disturbance is least prevalent, particularly on the outer continental shelf and slope, where storm-wave damage is negligible and biological processes, including growth, tend to be slow. Recent advances in fishing technology (e.g., rockhopper gear, global positioning systems, fish finders) have all but eliminated what were de facto refuges from trawling. The frequency of trawling (in percentage of the continental shelf trawled per year) is orders of magnitude higher than other severe seabed disturbances, annually covering an area equivalent to perhaps half of the world's continental shelf, or 150 times the land area that is clearcut yearly. Mobile fishing gear can have large and long-lasting effects on benthic communities, including young stages of commercially important fishes, although some species benefit when structural complexity is reduced. These findings are crucial for implementation of "Essential Fish Habitat" provisions of the U.S. Magnuson-Stevens Fishery Conservation and Management Act which aim to protect nursery and feeding habitat for commercial fishes. Using a precautionary approach to management, modifying fishing methods, and creating refuges free of mobile fishing gear are ways to reduce effects on biological diversity and commercial fish habitat.
The concept of species redundancy in ecosystem processes is troublesome because it appears to contradict the traditional emphasis in ecology on species singularity. When species richness is high, however, ecosystem processes seem clearly insensitive to considerable variation in biodiversity. Some elementary principles from reliability engineering, where engineered redundancy is a valued part of systems design, suggest that we should rethink our stance on species redundancy. For example, a central tenet of reliability engineering is that reliability always increases as redundant components are added to a system, a principle that directly supports redundant species as guarantors of reliable ecosystem functioning. I argue that we should embrace species redundancy and perceive redundancy as a critical feature of ecosystems which must be preserved if ecosystems are to function reliably and provide us with goods and services. My argument is derived from basic principles of reliability engineering which demonstrate that the probability of reliable system performance is closely tied to the level of engineered redundancy in its design. Empirical demonstrations of the value of species redundancy in ecosystem reliability would provide new insights into the ecology of communities and the value of species conservation.
Following reports of dramatic declines in managed and feral honey bees from nearly every region of North America, scientists and resource managers from the U.S., Mexico, and Canada came together to review the quality of the evidence that honey bees as well as other pollinators are in long-term decline and to consider the potential consequences of these losses on the conservation of biodiversity and the stability of the yield of food crops. These experts in pollination ecology confirmed that the last 5 years of losses of honeybee colonies in North America leave us with fewer managed pollinators than at any time in the last 50 years and that the management and protection of wild pollinators is an issue of paramount importance to our food supply system. Although there are conclusive data that indicate 1200 wild vertebrate pollinators may be at risk, data on the status of most invertebrate species that act as pollination agents is lacking. The recommendations from a working group of over 20 field scientists, presented here, have been endorsed by 14 conservation and sustainable agriculture organizations, research institutes, and professional societies, including the Society for Conservation Biology. Among the most critical priorities for future research and conservation of pollinator species are (1) increased attention to invertebrate systematics, monitoring, and reintroduction as part of critical habitat management and restoration plans; (2) multi-year assessments of the lethal and sublethal effects of pesticides, herbicides, and habitat fragmentation on wild pollinator populations in and near croplands; (3) inclusion of the monitoring of seed and fruit set and floral visitation rates in endangered plant management and recovery plans; (4) inclusion of habitat needs for critically-important pollinators in the critical habitat designations for endangered plants; (5) identification and protection of floral reserves near roost sites along the "nectar corridors" of threatened migratory pollinators; and (6) investment in the restoration and management of a diversity of pollinators and their habitats adjacent to croplands in order to stabilize or improve crop yields. The work group encourages increased education and training to ensure that both the lay public and resource managers understand that pollination is one of the most important ecological services provided to agriculture through the responsible management and protection of wildland habitats and their populations of pollen-vectoring animals and nectar-producing plants.
Island populations are more prone to extinction than mainland populations, with island endemic species having higher extinction rates than nonendemic species. Inbreeding depression is one possible explanation for this. Insular populations are expected to suffer increased inbreeding relative to mainland populations due to bottlenecks at foundation and to lower subsequent population sizes. Inbreeding coefficients for 182 nonendemic and 28 endemic island populations were estimated from allozyme and microsatellite heterozygosities in island and related mainland populations. Island populations were significantly inbred, with inbreeding coefficients significantly higher in endemic than nonendemic island populations. Many island populations showed levels of inbreeding associated with elevated extinction rates in domestic and laboratory species. Inbreeding depression cannot be excluded as a factor in the extinction proneness of island populations.
What is most evident in the recent debate concerning new wetland regulations drafted by the U.S. Army Corps of Engineers is that small, isolated wetlands will likely continue to be lost. The critical biological question is whether small wetlands are expendable, and the fundamental issue is the lack of biologically relevant data on the value of wetlands, especially so-called "isolated" wetlands of small size. We used data from a geographic information system for natural-depression wetlands on the southeastern Atlantic coastal plain (U.S.A.) to examine the frequency distribution of wetland sizes and their nearest-wetland distances. Our results indicate that the majority of natural wetlands are small and that these small wetlands are rich in amphibian species and serve as an important source of juvenile recruits. Analyses simulating the loss of small wetlands indicate a large increase in the nearest-wetland distance that could impede "rescue" effects at the metapopulation level. We argue that small wetlands are extremely valuable for maintaining biodiversity, that the loss of small wetlands will cause a direct reduction in the connectance among remaining species populations, and that both existing and recently proposed legislation are inadequate for maintaining the biodiversity of wetland flora and fauna. Small wetlands are not expendable if our goal is to maintain present levels of species biodiversity. At the very least, based on these data, regulations should protect wetlands as small as 0.2 ha until additional data are available to compare diversity directly across a range of wetland sizes. Furthermore, we strongly advocate that wetland legislation focus not only on size but also on local and regional wetland distribution in order to protect ecological connectance and the source-sink dynamics of species populations.
Some alien tree species used in commercial forestry and agroforestry cause major problems as invaders of natural and seminatural ecosystems. The magnitude of the problem has increased significantly over the past few decades, with a rapid increase in afforestation and changes in land use. Trends can be explained by analyzing natural experiments created by the widespread planting of a small number of species in different parts of the world. The species that cause the greatest problems are generally those that have been planted most widely and for the longest time. The most affected areas have the longest histories of intensive planting. Pinus spp. are especially problematic, and at least 19 species are invasive over large areas in the southern hemisphere, where some species cause major problems. The most invasive Pinus species have a predictable set of life-history attributes, including low seed mass, short juvenile period, and short interval between large seed crops. Pine invasions have severely impacted large areas of grassland and scrub-brushland in the southern hemisphere by causing shifts in life-form dominance, reduced structural diversity, increased biomass, disruption of prevailing vegetation dynamics, and changing nutrient cycling patterns. The (unavoidable) negative impacts of forestry with alien species are thus spilling over into areas set aside for conservation or water production. There is an urgent need to integrate the various means available for reducing the negative impacts of current invaders and to implement protocols to regulate the translocation of species that are known to be invasive.
Many semi-aquatic organisms, such as salamanders, depend on both aquatic and terrestrial habitats to complete their life cycle and maintain viable populations. But current U.S. federal and state regulations protect only the wetland itself or arbitrarily defined portions of terrestrial habitat, if any. Part of the reason terrestrial habitats adjacent to wetlands are not protected is the lack of a clear understanding of the distances from shorelines that are biologically relevant to wetland fauna. Such information is critical for delineation of terrestrial "buffer zones" for wetlands, and thus for the conservation of semi-aquatic organisms. I summarized data from the literature on terrestrial habitat use by one group of pond-breeding salamanders, especially distances individuals traveled away from ponds. The results provide a basis for setting terrestrial buffer zones determined from actual habitat use by adult and juvenile salamanders. The mean distance salamanders were found from the edge of aquatic habitats was 125.3 m for adults of six species and 69.6 m for juveniles of two of these species. Assuming that the mean distance encompasses 50% of the population, a buffer zone encompassing 95% of the population would extend 164.3 m (534 ft) from a wetland's edge into the terrestrial habitat. Data from other amphibians suggest that this buffer zone is applicable to a range of species, but caution should be taken for taxa suspected to be more vagile. Wetland managers and policymakers must recognize the special needs of semi-aquatic organisms during their entire life cycle, not just during the breeding season. To maintain viable populations and communities of salamanders, attention must be directed to the terrestrial areas peripheral to all wetlands. Data on habitat use from salamanders and other semi-aquatic species make it increasingly apparent that maintaining the connection between wetlands and terrestrial habitats will be necessary to preserve the remaining biodiversity of our vanishing wetlands.
On the basis of surveys conducted between 1991 and 1996, I report a decline of the amphibian fauna at Las Tablas, Puntarenas Province, Costa Rica. I propose that the reduction in the abundance of Atelopus chiriquiensis and Hyla calypsa, the presence of dead and dying individuals of six species of frogs and salamanders, and changes in population sex ratios of A. chiriquiensis and H. calypsa are evidence for "atypical" population fluctuations. Species with both aquatic eggs and aquatic larvae were most affected (e.g., Rana vibicaria, Hyla rivularis), whereas species with direct development or those that lack tadpoles, such as rainfrogs (Eleutherodactylus spp.) and some salamanders (e.g., Bolitoglossa minutula), do not seem to have declined in numbers. In light of this evidence and in comparison with other declines in tropical upland Australia, Brazil, and Costa Rica, I conclude that environmental contamination (biotic pathogens or chemicals) or a combination of factors (environmental contamination plus climate change) may be responsible for declines in the amphibian populations at this protected site.