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Greatest Threats (greatest + threat)

Distribution by Scientific Domains

Life Sciences	90%

Distribution within Life Sciences

Animal Science & Zoology	30%

Selected Abstracts

Is the matrix a sea?

ECOLOGICAL ENTOMOLOGY, Issue 1 2005
Habitat specificity in a naturally fragmented landscape
Abstract., 1. Metapopulation and island biogeography theory assume that landscapes consist of habitat patches set in a matrix of non-habitat. If only a small proportion of species conform to the patch,matrix assumptions then metapopulation theory may only describe special cases rather than being of more general ecological importance. 2. As an initial step towards understanding the prevalence of metapopulation dynamics in a naturally fragmented landscape, the distribution of beetle species in three replicates of three habitat types was examined, including rainforest and eucalypt forest (the habitat patches), and buttongrass sedgeland (the matrix), in south-west Tasmania, Australia. 3. Ordination methods indicated that the buttongrass fauna was extremely divergent from the fauna of forested habitats. Permutation tests showed that the abundance of 13 of 17 commonly captured species varied significantly among habitats, with eight species confined to eucalypts or rainforest, and three species found only in buttongrass. Approximately 60% of species were confined to forested habitat implying that metapopulation theory has the potential to be very important in the forest,buttongrass landscape. 4. Although floristically the rainforest and eucalypts were extremely distinct, the beetle faunas from eucalypts and rainforests overlapped substantially. Therefore rainforest patches connected by eucalypt forest represent continuous habitat for most species. 5. Other studies report a wide range of values for the proportion of patch-specific species in fragmented landscapes. Understanding the environmental or historical conditions under which a high proportion of species become patch specialists would help to identify where spatial dynamic theory may be especially applicable, and where habitat loss and fragmentation poses the greatest threat to biodiversity. [source]

There and back again: the impact of adult HIV prevalence on national life expectancies

HIV MEDICINE, Issue 2 2005
AL McGuire
Worldwide we have seen dramatic increases in HIV prevalence and decreases in life expectancy over the last decade. The aim of this study was to determine the association between HIV prevalence and life expectancy. A strong negative association between adult HIV prevalence and life expectancy was observed for 137 countries. Because high adult HIV prevalence poses the greatest threat to countries with limited health resources, our study supports increased efforts to provide antiretrovirals in these countries. [source]

Avian productivity in urban landscapes: a review and meta-analysis

IBIS, Issue 1 2009
D. E. CHAMBERLAIN
There is an urgent need to thoroughly review and comprehend the effects of urbanization on wildlife in order to understand both the ecological implications of increasing urbanization and how to mitigate its threat to biodiversity globally. We examined patterns in comparative productivity of urban and non-urban passerine birds, using published estimates from paired comparisons, and by reviewing and developing explanations in terms of resources, competitors, predators and other specifically urban environmental factors. The most consistent patterns were for earlier lay dates, lower clutch size, lower nestling weight and lower productivity per nesting attempt in urban landscapes; these were supported by a formal meta-analysis. Nest failure rates did not show consistent patterns across the species considered. We suggest that food availability is a key driver of differences in passerine demography between landscapes. In urban habitats, human-provided food may improve adult condition over winter, leading to earlier lay dates and, in some species, to higher survival and higher breeding densities, but paucity of natural food may lead to lower productivity per nesting attempt. We demonstrate that additional comparative research is needed on a wider range of species, on the effects of natural and human-provided food availability, and on the differences in survival and dispersal between urban and non-urban populations. Importantly, better-targeted research and monitoring is needed in areas that are at greatest threat from urbanization, especially in the developing world. [source]

The Contribution of Long-Term Research at Gombe National Park to Chimpanzee Conservation

CONSERVATION BIOLOGY, Issue 3 2007
ANNE E. PUSEY
chimpancé; conservación de simios mayores; Parque Nacional Gombe; Tanzania Abstract:,Long-term research projects can provide important conservation benefits, not only through research specifically focused on conservation problems, but also from various incidental benefits, such as increased intensity of monitoring and building support for the protection of an area. At Gombe National Park, Tanzania, long-term research has provided at least four distinct benefits to wildlife conservation. (1) Jane Goodall's groundbreaking discoveries of chimpanzee (Pan troglodytes) tool use, hunting, and complex social relationships in what was then a game reserve drew attention to the area and created support for upgrading Gombe to national park status in 1968. (2) The highly publicized findings have earned Gombe and Tanzania the attention of a worldwide public that includes tourists and donors that provide financial support for Gombe, other parks in Tanzania, and chimpanzee conservation in general. (3) Crucial information on social structure and habitat use has been gathered that is essential for effective conservation of chimpanzees at Gombe and elsewhere. (4) A clear picture of Gombe's chimpanzee population over the past 40 years has been determined, and this has helped identify the greatest threats to the viability of this population, namely disease and habita loss outside the park. These threats are severe and because of the small size of the population it is extremely vulnerable. Research at Gombe has led to the establishment of conservation education and development projects around Gombe, which are needed to build local support for the park and its chimpanzees, but saving these famous chimpanzees will take a larger integrated effort on the part of park managers, researchers, and the local community with financial help from international donors. Resumen:,Los proyectos de investigación de largo plazo pueden proporcionar beneficios importantes a la conservación, no solo a través de investigación enfocada específicamente a problemas de conservación, sino también a través de varios beneficios incidentales, como una mayor intensidad de monitoreo y construcción de soporte para la protección de un área. En el Parque Nacional Gombe, Tanzania, la investigación a largo plazo ha proporcionado por lo menos cuatro beneficios a la conservación de vida silvestre. (1) Los descubrimientos innovadores de Jane Goodall sobre el uso de herramientas, la cacería y las complejas relaciones sociales de chimpancés en lo que entonces era una reserva de caza atrajeron la atención al área y crearon el soporte para cambiar a Gombe a estatus de parque nacional en 1968. (2) Los hallazgos muy publicitados han ganado para Gombe y Tanzania la atención del público en todo el mundo incluyendo turistas y donadores que proporcionan soporte financiero a Gombe, otros parques en Tanzania y a la conservación de chimpancés en general. (3) Se ha reunido información crucial sobre la estructura social y el uso del hábitat que ha sido esencial para la conservación efectiva de chimpancés en Gombe y otros sitios. (4) Se ha determinado un panorama claro de la población de chimpancés en Gombe durante los últimos 40 años, y esto a ayudado a identificar las mayores amenazas a la viabilidad de esta población, a saber enfermedades y pérdida de hábitat fuera del parque. Estas amenazas son severas y la población es extremadamente vulnerable por su tamaño pequeño. La investigación en Gombe ha llevado al establecimiento de proyectos de desarrollo y de educación para la conservación en los alrededores del parque, lo cual es necesario para encontrar soporte local para el parque y sus chimpancés, pero el rescate de estos famosos chimpancés requerirá de un esfuerzo más integrado de parte de los manejadores del parque, investigadores y la comunidad local con la ayuda financiera de donadores internacionales. [source]

Matrix Models as a Tool for Understanding Invasive Plant and Native Plant Interactions

CONSERVATION BIOLOGY, Issue 3 2005
DIANE M. THOMSON
competencia; invasión biológica; plantas invasoras; modelo matricial; perturbación Abstract:,Demographic matrix models are an increasingly standard way to evaluate the effects of different impacts and management approaches on species of concern. Although invasive species are now considered among the greatest threats to biodiversity, matrix methods have been little used to explore and integrate the potentially complicated effects of invasions on native species. I developed stage-structured models to assess the impacts of invasive grasses on population growth and persistence of a federally listed (U.S.A.) endemic plant, the Antioch Dunes evening primrose (Oenothera deltoides subsp. howellii [Munz] W. Klein). I used these models to evaluate two frequently made assumptions: (1) when rare plant populations decline in invaded habitats, invasive species are the cause and (2) invasive plants suppress rare plants primarily through direct resource competition. I compared two control and two removal matrices based on previous experimental work that showed variable effects of invasive grasses on different life-history stages of O. deltoides. Matrix analysis showed that these effects translated into substantial changes in population growth rates and persistence, with control matrices predicting a mean stochastic population growth rate (,) of 0.86 and removal matrices predicting growth rates from 0.92 to 0.93. Yet even the most optimistic invasive removal scenarios predicted rapid decline and a probability of extinction near one in the next 100 years. Competitive suppression of seedlings had much smaller effects on growth rates than did lowered germination, which probably resulted from thatch accumulation and reduced soil disturbance. These results indicate that although invasive grasses have important effects on the population growth of this rare plant, invasion impacts are not solely responsible for observed declines and are likely to be interacting with other factors such as habitat degradation. Further, changes in the disturbance regime may be as important a mechanism creating these impacts as direct resource competition. My results highlight the value of demographic modeling approaches in creating an integrated assessment of the threats posed by invasive species and the need for more mechanistic studies of invasive plant interactions with native plants. Resumen:,Los modelos demográficos matriciales son una forma cada vez más utilizada para evaluar los efectos de diferentes impactos y métodos de gestión sobre las especies en cuestión. Aunque actualmente se considera a las plantas invasoras entre las mayores amenazas a la biodiversidad, los modelos matriciales han sido poco utilizados para explorar e integrar los efectos potencialmente complicados de las invasiones sobre las especies nativas. Desarrollé modelos estructurados por etapas para evaluar los impactos de pastos invasores sobre el crecimiento poblacional y la persistencia de una especie de planta endémica, enlistada federalmente (E.U.A.), Oenothera deltoides ssp. howellii [Munz] W. Klein. Utilicé estos modelos para evaluar dos suposiciones frecuentes: (1) cuando las poblaciones de plantas raras declinan en hábitats invadidos, las especies invasoras son la causa y (2) las plantas invasoras suprimen a las plantas raras principalmente mediante la competencia directa por recursos. Comparé dos matrices de control y dos de remoción con base en trabajo experimental previo que mostró efectos variables de los pastos invasores sobre las diferentes etapas de la historia de vida de O. deltoides. El análisis de la matriz mostró que estos efectos se tradujeron en cambios sustanciales en las tasas de crecimiento y persistencia de la población, las matrices de control predijeron una tasa media de crecimiento poblacional estocástica (,) de 0.86 y las matrices de remoción predijeron tasas de crecimiento de 0.92-0.93. Aun los escenarios más optimistas de remoción de invasores predijeron una rápida declinación y una probabilidad de extinción en 100 años cerca de uno. La supresión competitiva de plántulas tuvo mucho menor efecto sobre las tasas de crecimiento que la disminución en la germinación, que probablemente resultó de la acumulación de paja y reducción en la perturbación del suelo. Estos resultados indican que, aunque los pastos invasores tienen efectos importantes sobre el crecimiento poblacional de esta planta rara, los impactos de la invasión no son los únicos responsables de las declinaciones observadas y probablemente están interactuando con otros factores como la degradación del hábitat. Más aun, los cambios en el régimen de perturbación pueden ser un mecanismo tan importante en la creación de estos impactos como la competencia directa por recursos. Mis resultados resaltan el valor del enfoque de los modelos demográficos para la evaluación integral de las amenazas de especies invasoras y la necesidad de estudios más mecanicistas de las interacciones de plantas invasoras con plantas nativas. [source]

Land use change and the dependence of national priority species on protected areas

GLOBAL CHANGE BIOLOGY, Issue 9 2008
SARAH F. JACKSON
Abstract The establishment and maintenance of a system of protected areas is central to regional and global strategies for the conservation of biodiversity. The current global trend towards human population growth and widespread environmental degradation means that such areas are becoming increasingly isolated, fragmented habitat islands. In regions in which this process is well advanced, a high proportion of species are thus predicted to have become restricted to protected areas. Here, using uniquely detailed datasets for Britain, a region with close to the global level of percentage coverage by statutory protected areas, we determine the extent of restriction of species of conservation concern to these areas. On the basis of currently known distributions, more than a half of such species are highly dependent on protected areas for their continued persistence, occurring either entirely or largely within their bounds. Such coverage is of particular importance for those species with narrower distributions, and therefore, under the greatest threats, underlining the vital importance of adequately resourcing, maintaining, and developing protected areas to prevent these species from being lost. [source]

A brief review of the status, distribution and biology of wild Asian elephants Elephas maximus

INTERNATIONAL ZOO YEARBOOK, Issue 1 2006
R. SUKUMAR
The Asian elephant Elephas maximus is distributed discontinuously across the Asian continent. The total wild population is 38 500-52 500, with a further c. 16 000 in captivity, the majority of which are in range countries. India has 60% of the global population of wild Asian elephants. The species has a multi-tiered social system with ,, living in matriarchal groups of five to 20 individuals that interact with other family units in the area. Adult ,, live alone or in small, temporary groups with weak social bonds. Asian elephants are megaherbivores that spend 12-18 hours per day feeding, and they eat browse and plants depending on availability and season. Home-range size is dependant on the availability of food, water and shelter in the region. Loss and fragmentation of habitat, human-elephant conflicts and poaching are the greatest threats to the species. Asian elephants are managed using traditional and modern methods but progress still needs to be made to improve welfare, training and breeding for these animals. [source]

Approaches for testing herbivore effects on plant population dynamics

JOURNAL OF APPLIED ECOLOGY, Issue 5 2006
STACEY L. HALPERN
Summary 1As plant invasions pose one of the greatest threats to biodiversity, it is critical to improve both our understanding of invasiveness and strategies for control. Much research into plant invasions and their management, including biological control, assumes strong demographic effects by natural enemies, including herbivores. However, the importance of natural enemies in the regulation of plant populations remains controversial: some ecologists contend that they rarely affect plant populations, and others that they can strongly limit plant population sizes. 2We briefly review the conflicting views and suggest that new approaches to gather and analyse data are needed before the effects of natural enemies on plant populations can be fully characterized. 3We outline experimental and analytical approaches that incorporate density dependence into population models and thus provide a more complete test of the long-term effects of natural enemies on plant populations. We also introduce new methods for obtaining stochastic estimates of equilibrium density, which will provide a key test of enemy effects on plant population size. 4Synthesis and applications. Designing effective strategies for invasive plant management requires information about the factors that limit plant population size. Together, the experiments and analyses we describe measure more clearly how natural enemies influence plant population dynamics. They will provide an important tool in evaluating the role of enemy release in plant invasions and for predicting the potential success of biological control. Such information should help to prioritize strategies that are most likely to control invasive plants effectively and will contribute to risk assessment when considering the release of non-native natural enemies as biological control agents. [source]

Vegetation structure and prey abundance requirements of the Iberian lynx: implications for the design of reserves and corridors

JOURNAL OF APPLIED ECOLOGY, Issue 1 2001
F. Palomares
Summary 1,Habitat alteration and fragmentation are two of the greatest threats to biodiversity. The conservation of most species in highly encroached areas requires reserves that are connected by suitable habitat corridors to increase the effectiveness of the area under protection. However, the quality required for such corridors is still debated. This study investigated the habitat characteristics (vegetation structure and prey abundance) of sites used by resident and dispersing Iberian lynx in south-western Spain. 2,Vegetation structure and an index of rabbit abundance (the staple prey of lynx) were measured at sites used by radio-collared lynx in 1996 and 1997. Data from 128 plots used by resident lynx and 310 plots used by dispersing individuals were compared with data from 162 randomly located plots in sites considered to be unused by lynx. 3.,Resident sites had a lower percentage of tree cover, shorter tree height, higher percentage of tall shrub cover, higher percentage of overall understorey and higher number of rabbit pellets than both dispersal and unused sites. The height of the short shrub layer was taller and the rabbit abundance index was higher in dispersing sites than in unused sites. 4,Gender did not affect habitat selection by lynx. During dispersal, lynx frequently (50% of cases) used vegetation patches narrower than 300 m. In these cases, sites used by lynx had higher understorey cover and taller shrub height than adjacent unused sites. The percentage of short shrub cover used by lynx increased with the length of time taken to disperse; this was the only variable that changed over time. 5,Range size of resident individuals declined significantly with the index of rabbit abundance but increased with the percentage of short shrub cover. Both variables were good predictors of range size. 6,The study shows that corridors connecting reserves do not have to be prime habitats; they can even support moderate habitat degradation due to human activity. This result has implications both for the conservation of existing corridors, and for the restoration of the many corridors between reserves that have been lost. [source]

Experimental design and taxonomic scope of fragmentation studies on European mammals: current status and future priorities

MAMMAL REVIEW, Issue 2 2010
Alessio MORTELLITI
ABSTRACT 1Habitat loss, habitat fragmentation and habitat degradation are the greatest threats to mammals in Europe and the rest of the world. Despite the fact that extensive literature exists, no comprehensive review or synthesis is available to date and this may slow down scientific progress and hamper conservation efforts. 2The goal of this study is to understand if and in what direction progress has been made in the study of the effects of habitat loss and fragmentation on the spatial distribution of European terrestrial mammals. Firstly, we carry out a general synthesis which is structured around 11 key points. The aim of this point-by-point analysis is to identify trends, knowledge gaps and any significant bias in the available literature, and to highlight strengths and shortfalls of the different approaches which have to date been applied. Secondly, we follow a species-specific systematic approach: for each species, we synthesise key results. 3Our results show how substantial progress has been hampered for several reasons including: a large predominance of small-scale field studies of short duration, and a generalised lack of control of: (i) confounding variables; (ii) spatial autocorrelation; and (iii) false absences. Also, despite the relatively high number of studies, few were theoretical studies and even fewer were meta-analyses. The lack of meta-analyses is likely to be due to the small amount of crucial details included in the publications, such as model parameters or information on the landscape context (such as the amount of residual forest cover). 4We synthesise the main results for 14 species. The level of progress is highly variable: for some species, such as the red squirrel Sciurus vulgaris, a series of long-term, large-scale process-oriented studies has allowed an in-depth understanding of its ecology in fragmented landscapes. On the other hand, with other species such as the bank vole Myodes glareolus, despite a relatively large number of field studies, little progress has been made. [source]

Evolution of reproductive seasonality in bears

MAMMAL REVIEW, Issue 1 2007
THOMAS J. SPADY
ABSTRACT 1Of the eight species of Ursidae, six are currently at risk of extinction and the remainder face significant risks to their future survival. One of the greatest threats to bears is human-imposed environmental alteration (e.g. global warming, chemical pollutants, deforestation). An examination of the reproductive biology and phylogeny of the Ursidae reveals reproductive seasonality as a probable adaptation to adverse environmental conditions. 2Seven of the eight extant species exhibit distinct mating and birth seasons, with the most ancient species evolving facultative seasonality as an adaptation to the increasingly seasonal climate of the Pliocene. The remainder of the extant species evolved during the Pleistocene glaciations, under conditions of severe seasonal food restriction. Under these conditions, an obligate mode of seasonality emerged and persists to the present. 3Knowledge of the natural history of seasonal reproduction in the ursids and how it evolved in response to global climatic change provides a context for understanding the ramifications of current environmental change on the reproduction of these important species. [source]