Are Wolf-Mediated Trophic Cascades Boosting Biodiversity in the Great Lakes Region? (original) (raw)
Related papers
Recolonizing wolves trigger a trophic cascade in Wisconsin (USA)
Journal of Ecology, 2013
We tested the hypothesis that wolves are reducing local browse intensity by white-tailed deer, thus indirectly mitigating the biotic impoverishment of understorey plant communities in northern Wisconsin. 2. To assess the potential for such a top-down trophic cascade response, we developed a spatially and temporally explicit model of wolf territory occupancy based on three decades of wolf monitoring data. Using a nested multiscale vegetation survey protocol, we compared the understorey plant communities of northern white cedar wetlands found in high wolf areas with control sites found in low wolf areas. 3. We fit species-area curves for plant species grouped by vegetation growth form (based on their predicted response to release from herbivory, i.e. tree, seedling, shrub, forb, grass, sedge or fern) and duration of wolf territory occupancy. 4. As predicted for a trophic cascade response, forb species richness at local scales (10 m 2 ) was significantly higher in high wolf areas (high wolf areas: 10.7 AE 0.9, N = 16, low wolf areas: 7.5 AE 0.9, N = 16, P < 0.001), as was shrub species richness (high wolf areas: 4.4 AE 0.4, N = 16, low wolf areas: 3.2 AE 0.5, N = 16, P < 0.001). Also as predicted, percentage cover of ferns was lower in high wolf areas (high wolf areas: 6.2 AE 2.1, N = 16, low wolf areas: 11.6 AE 5.3, N = 16, P < 0.05). 5. Beta richness was similar between high and low wolf areas, supporting earlier assumptions that deer herbivory impacts plant species richness primarily at local scales. Sampling at multiple spatial scales revealed that changes in species richness were not consistent across scales nor among vegetation growth forms: forbs showed a stronger response at finer scales (1-100 m 2 ), while shrubs showed a response across relatively broader scales (10-1000 m 2 ). 6. Synthesis. Our results are consistent with hypothesized trophic effects on understorey plant communities triggered by a keystone predator recovering from regional extinction. In addition, we identified the response variables and spatial scales appropriate for detecting such differences in plant species composition. This study represents the first published evidence of a trophic cascade triggered by wolf recovery in the Great Lakes region.
Wolves, Elk, Bison, and Secondary Trophic Cascades in Yellowstone National Park
The Open Ecology Journal, 2010
Wolves were reintroduced into Yellowstone National Park in 1995/96, likely reestablishing a trophic cascade involving wolves, elk, and woody browse species. The return of wolves may have also triggered a secondary trophic cascade involving bison, which are generally a minor prey species for wolves in northern Yellowstone. We hypothesize a sequence of events in northern Yellowstone where: 1) wolves prey on elk, changing elk behavior and reducing elk numbers, 2) causing reduced elk herbivory and more forage available to bison, and 3) allowing higher bison densities and additional bison effects on the ecosystem. This secondary trophic cascade, whereby wolf predation may have indirectly allowed bison numbers to increase through a reduction in inter-specific competition with elk, may represent an example of an alternative top-down pathway by which predators can influence multiple trophic levels through mediating the competitive interaction between two prey species. Both wolves and bison can have important effects on ecosystems, and there is growing interest in restoring these animals to wider portions of their former range. However, there are many potential routes for interactions between species and it is important to consider the conservation implications of other cascading effects when reintroducing such ecologically influential species into wild landscapes. The potential benefits of bison to their native ecosystems may not be realized in situations with low predation pressure, high bison densities, and constraints on bison movement and migration, thus likely contributing to impairment of resources.
Oecologia, 2015
through direct reduction in deer numbers or indirectly through changing deer behavior. We found that in areas of high wolf use, deer were 62 % less dense, visit duration was reduced by 82 %, and percentage of time spent foraging was reduced by 43 %; in addition, the proportion of saplings browsed was nearly sevenfold less. Average maple (Acer spp.) sapling height and forb species richness increased 137 and 117 % in areas of high versus low wolf use, respectively. The results of the exclosure experiments revealed that the negative impacts of deer on sapling growth and forb species richness became negligible in high wolf use areas. We conclude that wolves are likely generating trophic cascades which benefit maples and rare forbs through trait-mediated effects on deer herbivory, not through direct predation kills.
Trophic cascades and Yellowstone’s aspen: A reply to Fleming (2019)
Forest Ecology and Management, 2019
Recent correspondence by Fleming (2019) identifies a number of concerns regarding the methods and conclusions used in the Beschta et al. (2018) study of wolves, elk, and aspen in Yellowstone National Park. Herein, we respond to those concerns and assertions. We also provide clarifying and supplemental information regarding two hypotheses: (1) trophic cascades and (2) human shielding. We conclude that there is strong support for both hypotheses.
WOLVES INFLUENCE ELK MOVEMENTS: BEHAVIOR SHAPES A TROPHIC CASCADE IN YELLOWSTONE NATIONAL PARK
Ecology, 2005
A trophic cascade recently has been reported among wolves, elk, and aspen on the northern winter range of Yellowstone National Park, Wyoming, USA, but the mechanisms of indirect interactions within this food chain have yet to be established. We investigated whether the observed trophic cascade might have a behavioral basis by exploring environmental factors influencing the movements of 13 female elk equipped with GPS radio collars. We developed a simple statistical approach that can unveil the concurrent influence of several environmental features on animal movements. Paths of elk traveling on their winter range were broken down into steps, which correspond to the straight-line segment between successive locations at 5-hour intervals. Each observed step was paired with 200 random steps having the same starting point, but differing in length and/or direction. Comparisons between the characteristics of observed and random steps using conditional logistic regression were used to model environmental features influencing movement patterns. We found that elk movements were influenced by multiple factors, such as the distance from roads, the presence of a steep slope along the step, and the cover type in which they ended. The influence of cover type on elk movements depended on the spatial distribution of wolves across the northern winter range of the park. In low wolf-use areas, the relative preference for end point locations of steps followed: aspen stands Ͼ open areas Ͼ conifer forests. As the risks of wolf encounter increased, the preference of elk for aspen stands gradually decreased, and selection became strongest for steps ending in conifer forests in high wolf-use areas. Our study clarifies the behavioral mechanisms involved in the trophic cascade of Yellowstone's wolf-elk-aspen system: elk respond to wolves on their winter range by a shift in habitat selection, which leads to local reductions in the use of aspen by elk.
Wolves influence elk movements: behavior shapes a trophic cacade in Yellowstone National Park
1995
A trophic cascade recently has been reported among wolves, elk, and aspen on the northern winter range of Yellowstone National Park, Wyoming, USA, but the mechanisms of indirect interactions within this food chain have yet to be established. We investigated whether the observed trophic cascade might have a behavioral basis by exploring environmental factors influencing the movements of 13 female elk equipped with GPS radio collars. We developed a simple statistical approach that can unveil the concurrent influence of several environmental features on animal movements. Paths of elk traveling on their winter range were broken down into steps, which correspond to the straight-line segment between successive locations at 5-hour intervals. Each observed step was paired with 200 random steps having the same starting point, but differing in length and/or direction. Comparisons between the characteristics of observed and random steps using conditional logistic regression were used to model environmental features influencing movement patterns. We found that elk movements were influenced by multiple factors, such as the distance from roads, the presence of a steep slope along the step, and the cover type in which they ended. The influence of cover type on elk movements depended on the spatial distribution of wolves across the northern winter range of the park. In low wolf-use areas, the relative preference for end point locations of steps followed: aspen stands Ͼ open areas Ͼ conifer forests. As the risks of wolf encounter increased, the preference of elk for aspen stands gradually decreased, and selection became strongest for steps ending in conifer forests in high wolf-use areas. Our study clarifies the behavioral mechanisms involved in the trophic cascade of Yellowstone's wolf-elk-aspen system: elk respond to wolves on their winter range by a shift in habitat selection, which leads to local reductions in the use of aspen by elk.
Trophic cascades from wolves to alders in Yellowstone
Forest Ecology and Management, 2015
We explored possible interactions among gray wolves (Canis lupus), Rocky Mountain 20 elk (Cervus elaphus), and thinleaf alder (Alnus incana spp. tenuifoli) in northern Yellowstone 21 National Park. We developed an alder age structure based on annual growth rings for plants 22 33 34 35
Global Ecology and Biogeography, 2007
Aim Our aim was to investigate how the environment, species characteristics and historical factors at the subcontinental scale affect patterns of diversity. We used the assembly of the Yellowstone biota over the past 10,000 years as a natural experiment for investigating the processes that generate a modern non-volant mammal species pool. Location The data represent species from throughout North America with special attention to the non-volant mammals of Yellowstone National Park, USA. Methods We used digitized range maps to determine biogeographical affinity for all non-volant mammals in the Rocky Mountains, Deserts and Great Plains biogeographical regions of North America. This biogeographical affinity, along with taxonomic order and body size class, was used to test whether non-random patterns exist in the assemblage of Yellowstone non-volant mammals. These characteristics were also used to investigate the strength of non-random processes, such as habitat or taxon filtering, on particular groups of species or individual species. Results Our results indicated that the Yellowstone fauna is composed of a non-random subset of mammals from specific body size classes and with particular biogeographical affinities. Analyses by taxonomic order found significantly more Carnivora from the Rocky Mountains region and significantly fewer Rodentia from the Deserts region than expected from random assembly. Analyses using body size classes revealed deviations from expectations, including several significant differences between the frequency distribution of regional body sizes and the distribution of those species found within Yellowstone. Main conclusions Our novel approach explores processes affecting species pool assembly in the Yellowstone region and elsewhere, and particularly identifies unique properties of species that may contribute to non-random assembly. Focusing on the mechanisms generating diversity, not just current diversity patterns, will assist the design of conservation strategies given future environmental change scenarios.