Showing papers by "Andrew P. Dobson published in 1997"

Hopes for the Future: Restoration Ecology and Conservation Biology

Abstract: Conversion of natural habitats into agricultural and industrial landscapes, and ultimately into degraded land, is the major impact of humans on the natural environment, posing a great threat to biodiversity. The emerging discipline of restoration ecology provides a powerful suite of tools for speeding the recovery of degraded lands. In doing so, restoration ecology provides a crucial complement to the establishment of nature reserves as a way of increasing land for the preservation of biodiversity. An integrated understanding of how human population growth and changes in agricultural practice interact with natural recovery processes and restoration ecology provides some hope for the future of the environment.

Geographic Distribution of Endangered Species in the United States

Abstract: Geographic distribution data for endangered species in the United States were used to locate "hot spots" of threatened biodiversity. The hot spots for different species groups rarely overlap, except where anthropogenic activities reduce natural habitat in centers of endemism. Conserving endangered plant species maximizes the incidental protection of all other species groups. The presence of endangered birds and herptiles, however, provides a more sensitive indication of overall endangered biodiversity within any region. The amount of land that needs to be managed to protect currently endangered and threatened species in the United States is a relatively small proportion of the land mass.

Transmission dynamics and host-parasite interactions of Trichostrongylus tenuis in red grouse (Lagopus lagopus scoticus)

Abstract: Two components of the transmission dynamics of Trichostrongylus tenuis in red grouse are examined and quantified, namely parasite transmission rate and density-dependent reductions in egg production. Age-intensity data for birds of known age suggest that the rate of parasite uptake increases during the first 6 mo of a bird's life and this increase reflects an increase in feeding rate with age and exhibits no signs of self-cure. Analysis of these age-intensity curves permits us to estimate the transmission rate of the free-living infective stages. Reinfection rates of adults treated to reduce parasite intensities were not significantly different from infection rates of naive immature grouse. Secondary infections continued to rise over a period of 18 mo and this suggests that there is no strong host-mediated response against the parasite. Any density-dependent reduction in parasite fecundity is probably very weak and would act through interspecific competition between parasites. Initial analysis of worm egg production in relation to the intensity of worm infection found weak evidence of density-dependent suppression of egg production at high worm intensities. However, a more rigorous analysis found that such a relationship suffered from Type I errors and was a consequence of the aggregated distribution of the parasites. Any density-dependent suppression of parasite egg production is too weak to be detected and would only occur at high worm intensities. The potential density-dependent reductions in fecundity on the population dynamics of T. tenuis and red grouse are examined using a mathematical model. The model suggests that the presence of density-dependent reductions in worm fecundity could produce significant reductions in the propensity of the grouse-nematode system to exhibit population cycles. The sustained cycles observed in the long-term dynamics of the grouse populations in the study area suggest that density-dependent reductions in worm fecundity and establishment are either absent or only operating at levels that are not detectable in field studies.