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Population Sustainability (population + sustainability)
Selected AbstractsEffect of habitat fragmentation on spawning migration of brown trout (Salmo trutta L.)ECOLOGY OF FRESHWATER FISH, Issue 3 2006C. Gosset Abstract , Human-induced habitat alteration is one of the main causes of the decline of freshwater fish populations. The watershed of the River Bidasoa (Spain) is an example of heavily fragmented habitat. The local brown trout (Salmo trutta L.) population is disturbed, with evidence of poor recruitment as well as low adult densities in the main stem. Forty male and female adult migratory trout were tagged with external or internal radio transmitters and released. Fixed stations with data loggers and mobile antennae were used with daily surveys to track fish movements during the migration and spawning period (3 months). Migration distances did not exceed 10 km, and half of the fish never entered a tributary in the study area. Fragmentation because of weirs on the main stem apparently prevented fish from reaching their spawning destination. Fish that entered the tributaries were first confronted with an accessibility problem because of low discharge. However, each fish chose one tributary, without making attempts to run up in other tributaries. Once in the tributary, fish were restrained in their upstream movements by dams. The study area appeared to be isolated from the vast upper part of the watershed. Within the study area, upper parts of tributaries also seemed strongly disconnected from the main stem. This study illustrates the negative impact of river fragmentation on S. trutta migration pattern. Population sustainability can be directly affected through the low availability of spawning grounds for migratory fish. Long-term effects of fragmentation may cause reproductive isolation within watersheds, which in the case of trout also means isolated phenotypic population units. [source] Alternatives for Reintroducing a Rare Ecotone Species: Manually Thinned Forest Edge versus Restored Habitat RemnantRESTORATION ECOLOGY, Issue 5 2009Jennifer Possley Abstract Species native to ecotones are often overlooked in restoration efforts despite the increasing rarity of ecotone habitat. In fragmented, fire-suppressed landscapes, true ecotone may no longer exist. Restoration biologists interested in reintroducing ecotone species must decide whether to plant them in historic ecotones maintained by manual thinning or whether to opt for discrete restoration areas that are easier to maintain. We investigated these two alternatives with Lantana canescens, a rare tropical shrub native to the ecotone between pine and hardwood forests of Miami-Dade County, Florida, U.S.A. Our short-term findings show that after 15 and 18 months, survival of transplants was 69% in a restored site and 65% and 84% in two historic ecotone sites. The restored site had significantly higher photosynthetically active radiation (PAR) (75%) than the historic ecotones (25,39%). Correspondingly, 267 seedlings have recruited at the restored site, whereas only 8 have emerged at both historic ecotone sites. Seedling establishment was associated with higher PAR at the restored site. We found that overall population sustainability was higher at the restored site where there is the additional benefit of less maintenance. Our work suggests that, by reducing succession, a discrete restoration area can approach the historic conditions of hardwood/pine forest ecotone more closely than degraded historic ecotones themselves. We present a viable solution for conserving rare ecotone species when their natural habitat and the processes that maintained it no longer exist. [source] Prescribed fire and conservation of a threatened mountain grassland specialist: a capture,recapture study on the Orsini's viper in the French alpsANIMAL CONSERVATION, Issue 3 2009A. Lyet Abstract Burning has traditionally been used in the southern French Alps to maintain open lands for grazing. In the context of land use abandonment, prescribed burning may be the only realistic practical tool available to oppose encroachment by woody plants in numerous mountainous landscapes. Although only recently developed as a modern tool for wildfire prevention and management of pastoral grasslands, this practice is now becoming widespread, which raises the issue of its impact on the fauna in general, and on endangered species in particular. We studied the impact of a prescribed fire on the survival and small-scale movements of one of the rarest snakes in Europe, the Orsini's viper Vipera ursinii, in order to evaluate its potential threat to population sustainability. We evaluated the body condition of snakes and the quality of their habitat, more precisely the abundance of grasshoppers as the main food resource, and the vegetation cover as shelter. About 3.6 ha of a 8.8 ha study site was burnt in autumn 2003. Snake population parameters were estimated using multi-state capture,mark,recapture methods. We demonstrate that burning reduced the survival of the vipers by more than half during the first year following the fire. Contrary to what was expected, there was no evidence of emigration from the burned to the unburned area immediately after the fire. Despite the decrease in grasshopper density and vegetation cover in the burned area, there was no evidence of mid-term mortality in snakes that could result from an increased predation rate or from the reduced body condition of snakes. As such high mortality, mainly or entirely due to the direct effect of fire, is likely to have large repercussions on population sustainability, we suggest several improvements of prescribed fire protocols to minimize their impact and strongly emphasize the need for a prescribed fire policy that takes into account specific recommendations for threatened species like Orsini's viper. The case of the Orsini's viper is very typical of conservation problems in open mountain lands, and we believe that our research will help determine the most suitable approach for long-term conservation of biodiversity in such semi-natural ecosystems. [source] Conservation of the Montagu's harrier (Circus pygargus) in agricultural areasANIMAL CONSERVATION, Issue 4 2002Beatriz Arroyo The Montagu's harrier (Circus pygargus) is a ground-nesting raptor that breeds mainly in cereal crops in western Europe. We evaluate how the use of agricultural habitats may affect population sustainability in this species, based on simulation analyses, and explore how conservation measures could be optimized. Probability of extinction increased with decreasing harrier productivity, and this trend was accentuated when the carrying capacity (maximum number of breeding pairs) decreased. Harrier productivity in agricultural habitats is strongly affected by harvesting activities. An average of 60% of nestlings in agricultural areas of France and the Iberian Peninsula would perish in the absence of conservation measures. These losses would make populations unsustainable, if no immigration occurred. Simulation analyses showed that connectivity between populations through natal dispersal could allow persistence of threatened populations even in the absence of conservation measures. The probability of extinction of four hypothetical populations connected through natal dispersal would be lowest if one of those populations were fully protected (or fully productive), even if the other ones were unprotected. Montagu's harriers are semi-colonial, and populations could be considered as a compound of subpopulations (the colonies). Additionally, Montagu's harriers bred more frequently in areas where food abundance was high, and where the number of fledglings produced in the previous reproductive attempt was high. These factors could be used to develop sustainable and efficient conservation plans, identifying and protecting the most productive and stable colonies in agricultural areas, and further exploring experimentally factors that are likely to attract and maintain harriers in protected areas. [source] | ||||||||||