Re: Nützlichkeit des Wolfs
Verfasst: 16. Mär 2019, 00:16
Beschta et al. (2009): Large predators and trophic cascades in terrestrial ecosystems of the western United States. DOI: 10.1016/j.biocon.2009.06.015.
Abstract
Ripple et al. (2012a): Trophic cascades in Yellowstone: The first 15years after wolf reintroduction. DOI: 10.1016/j.biocon.2011.11.005.
Abstract
Ripple et al. (2012b): Large predators limit herbivore densities in northern forest ecosystems. DOI: 10.1007/s10344-012-0623-5.
Abstract
Ripple et al. (2011): Can restoring wolves aid in lynx recovery?. DOI: 10.1002/wsb.59.
Abstract
Sergio et al. (2014): Towards a cohesive, holistic view of top predation: a definition, synthesis and perspective. DOI: 10.1111/oik.01468.
Excerpt
-> Sergio et al. (2014): Towards a cohesive, holistic view of top predation: a definition, synthesis and perspective. DOI: 10.1111/oik.01468.
Excerpt
Abstract
Large predators potentially can help shape the structure and functioning of terrestrial ecosystems, yet strong evidence of top-down herbivore limitation has not been widely reported in the scientific literature. Herein we synthesize outcomes of recent tri-trophic cascades studies involving the presence and absence of large predators for five national parks in the western United States, including Olympic, Yosemite, Yellowstone, Zion, and Wind Cave. Historical observations by park biologists regarding woody browse species and recently compiled age structure data for deciduous trees indicate major impacts to woody plant communities by ungulates following the extirpation or displacement of large predators. Declines in long-term tree recruitment indexed additional effects to plant communities and ecological processes, as well as shifts towards alternative ecosystem states. The magnitude and consistency of vegetation impacts found within these five parks, in conjunction with other recent North American studies, indicate that broad changes to ecosystem processes and the lower trophic level may have occurred in other parts of the western United States where large predators have been extirpated or displaced. Thus, where ungulates have significantly altered native plant communities in the absence of large predators, restoration of native flora is urgently needed to recover former ecosystem services. Following the reintroduction of previously extirpated gray wolves Canis lupus into Yellowstone National Park, a spatially patchy recovery of woody browse species (e.g., aspen Populus tremuloides, willow Salix spp., cottonwood Populus spp.) has begun, indicating that large predator recovery may represent an important restoration strategy for ecosystems degraded by wild ungulates.
Ripple et al. (2012a): Trophic cascades in Yellowstone: The first 15years after wolf reintroduction. DOI: 10.1016/j.biocon.2011.11.005.
Abstract
The 1995/1996 reintroduction of gray wolves (Canis lupus) into Yellowstone National Park after a 70 year absence has allowed for studies of tri-trophic cascades involving wolves, elk (Cervus elaphus), and plant species such as aspen (Populus tremuloides), cottonwoods (Populus spp.), and willows (Salix spp.). To investigate the status of this cascade, in September of 2010 we repeated an earlier survey of aspen and measured browsing and heights of young aspen in 97 stands along four streams in the Lamar River catchment of the park’s northern winter range. We found that browsing on the five tallest young aspen in each stand decreased from 100% of all measured leaders in 1998 to means of <25% in the uplands and <20% in riparian areas by 2010. Correspondingly, aspen recruitment (i.e., growth of seedlings/sprouts above the browse level of ungulates) increased as browsing decreased over time in these same stands. We repeated earlier inventories of cottonwoods and found that recruitment had also increased in recent years. We also synthesized studies on trophic cascades published during the first 15 years after wolf reintroduction. Synthesis results generally indicate that the reintroduction of wolves restored a trophic cascade with woody browse species growing taller and canopy cover increasing in some, but not all places. After wolf reintroduction, elk populations decreased, but both beaver (Caster canadensis) and bison (Bison bison) numbers increased, possibly due to the increase in available woody plants and herbaceous forage resulting from less competition with elk. Trophic cascades research during the first 15 years after wolf reintroduction indicated substantial initial effects on both plants and animals, but northern Yellowstone still appears to be in the early stages of ecosystem recovery. In ecosystems where wolves have been displaced or locally extirpated, their reintroduction may represent a particularly effective approach for passive restoration.
Ripple et al. (2012b): Large predators limit herbivore densities in northern forest ecosystems. DOI: 10.1007/s10344-012-0623-5.
Abstract
There is a lack of scientific consensus about how top-down and bottom-up forces interact to structure terrestrial ecosystems. This is especially true for systems with large carnivore and herbivore species where the effects of predation versus food limitation on herbivores are controversial. Uncertainty exists whether top-down forces driven by large carnivores are common, and if so, how their influences vary with predator guild composition and primary productivity. Based on data and information in 42 published studies from over a 50-year time span, we analyzed the composition of large predator guilds and prey densities across a productivity gradient in boreal and temperate forests of North America and Eurasia. We found that predation by large mammalian carnivores, especially sympatric gray wolves (Canis lupus) and bears (Ursus spp.), apparently limits densities of large mammalian herbivores. We found that cervid densities, measured in deer equivalents, averaged nearly six times greater in areas without wolves compared to areas with wolves. In areas with wolves, herbivore density increased only slightly with increasing productivity. These predator effects are consistent with the exploitation ecosystems hypothesis and appear to occur across a broad range of net primary productivities. Results are also consistent with theory on trophic cascades, suggesting widespread and top-down forcing by large carnivores on large herbivores in forest biomes across the northern hemisphere. These findings have important conservation implications involving not only the management of large carnivores but also that of large herbivores and plant communities.
Ripple et al. (2011): Can restoring wolves aid in lynx recovery?. DOI: 10.1002/wsb.59.
Abstract
Herein, we examine the hypothesis that relatively low densities of snowshoe hares (Lepus americanus) and the imperiled status of lynx (Lynx canadensis) may be partially due to an ecological cascade caused by the extirpation of gray wolves (Canis lupus) in most of the conterminous United States decades ago. This hypothesis focuses on 2 plausible mechanisms, one involving “mesopredator release” of the coyote (C. latrans), which expanded its distribution and abundance continentally following the ecological extinction of wolves over the temperate portion of their geographic range. In the absence of wolves, coyotes may have affected lynx via increased predation on snowshoe hares, on which the lynx specializes, and/or by direct killing of lynx. The second mechanism involves increased browsing pressure by native and domestic ungulates following the declines in wolves. A recovery of long‐absent wolf populations could potentially set off a chain of events triggering a long‐term decrease in coyotes and ungulates, improved plant communities, and eventually an increase in hares and lynx. This prediction, and others that we make, are testable. Ecological implications for the lynx may be dependent upon whether wolves are allowed to achieve ecologically effective populations where they recolonize or are reintroduced in lynx habitat. We emphasize the importance of little‐considered trophic and competitive interactions when attempting to recover an endangered carnivore such as the lynx. © 2011 The Wildlife Society.
Sergio et al. (2014): Towards a cohesive, holistic view of top predation: a definition, synthesis and perspective. DOI: 10.1111/oik.01468.
Excerpt
Einige von -zig Autoren, die noch mal festmachen, dass die Erde rund und die Sonne heiß ist. Leider auch, warum Erklärbären weiter herumtrollen.Research on top predation has been strongly intertwined with the development of two broad areas of theoretical ecology: predator–prey theory and spatial ecology. Predator–prey theory is one of the most traditional branches of theoretical ecology and includes themes as diverse as predator–prey population dynamics, optimal foraging theory, food-web structure, top–down forcing, and trophic cascades. Studies and debates in this field have spanned several decades and produced a wide array of results. Among the most notable contributions, theory has shown the potential of top predation to: 1) generate coupled oscillations between predator and prey (Rosenzweig and MacArthur 1963, Jansen 2002); 2) improve the stability of trophic interactions, for example through cross-ecosystem subsidies mediated by the mobility and behavioural flexibility typical of large predators (May 1973, McCoy et al. 2009, McCann 2012); 3) impose shifts between alternative stable states (May 1977, Holt 2002); and 4) structure whole communities and ecosystems through top–down forcing and trophic cascades (Hairston et al. 1960, Holt 2000).
-> Sergio et al. (2014): Towards a cohesive, holistic view of top predation: a definition, synthesis and perspective. DOI: 10.1111/oik.01468.
Excerpt
There is still lively debate about even basic aspects of predator–prey theory (Arditi and Ginzburg 2012).
In turn, this large body of literature has prompted a large number of empirical tests of the predictions generated by theoreticians (Boutin 1995, Soulé et al. 2003). The complexity, ramifications, broadness of interest and disputes that distinguish many of these research themes are epitomized by the protracted debate about the capability of predators to impart cycles to their prey. Already conceptualized through a verbal model 130 years ago (Forbes 1880), cycles of small mammals and grouse have been considered as the ecological signature of boreal ecosystems and are exemplified by the oscillations of snowshoe hares Lepus americanus in North America and voles in northern Europe (Krebs et al. 2001, Korpimäki et al. 2004). In both cases, decades of study have demonstrated the complexity of assessing causation in predator–prey systems and the importance of a pluralistic approach integrating theoretical predictions, long-term observation and large-scale experimentation (Krebs et al. 2001, Korpimäki et al. 2002, 2004).