Ecological Effectiveness: Conservation Goals for Interactive Species
Soule, M.E.; Estes, J.A.; Berger, J.; Del Rio, C.M., Conservation Biology, 17/5 (October 2003), 1238 (13pp)
The rarity or absence of highly interactive species leaves a functional void that can trigger linked changes leading to degraded or simplified ecosystems. A preliminary analysis indicates a relatively high frequency of such interactive species among endangered mammals. Rapid environmental change is likely to increase the interactivity of some species and reduce that of others over relatively short intervals. The current implementation of environmental policies and laws, such as the U.S. Endangered Species Act, generally ignores interspecific effects; recovery goals are autecological, short term, and numerically and spatially minimalistic. Moreover, by failing to account for interspecific interactions, recovery objectives are becoming indefensible in light of increasing knowledge from community ecology. Using the sea otter (Enhydra lutris) and wolf (Canis lupus) as examples, we argue that conservation plans should call for recovery or repatriation of such interactive species at ecologically effective densities in as many places as are currently realistic. It will be prudent and beneficial to estimate ecologically effective densities where there is disagreement among experts and interested parties about the desirability of restoring an interactive species to a particular region and to a particular density.
The Effect of Prey and Predator Densities on Wolf Predation
Vucetich, J.A.; Peterson, R.O.; Schaefer, C.L., Ecology, 83/11(November 2002)
Predator kills rate (i.e., kills per predator per time) is routinely presupposed to depend exclusively on prey density. However, per capita rates of killing may typically depend on the density of both prey and predator. Unfortunately, our perception of many ecological phenomena may be limited by the inappropriate assumption that kill rates do not depend on predator density. One of many ways to represent the influence of predator density is ratio-dependent predation, where kill rate depends on the ratio of prey to predator rather than the actual numbers of prey and predator. Determining the role of ratio dependency in predation theory has been contentious. Assessments of the influence of predator density on kill rate have been primarily limited to theoretical considerations, indirect evidence, and simplified laboratory demonstrations. We directly observed the influence of both prey and predator density on kill rates in an unmanipulated terrestrial system of large mammals--wolves (Canis lupus) and moose (Alces alces). Predator density explained more variation in kill rate than did prey density (R2 = 0.36 vs. R2 = 0.17, respectively). Moreover, the ratio-dependent model greatly outperformed the prey-dependent model. Nevertheless, the ratio-dependent model failed to explain most of the variation in kill rate (i.e., R2 = 0.34). The ratio-dependent--prey-dependent controversy may dissipate with greater appreciation and acknowledgment that both models may be overly simplistic, both have value, and neither deserves primacy.
The Effect of the Last Glacial Age on Speciation and Population Genetic Structure of the Endangered Ethiopian Wolf (Canis simensis)
Gottelli, D.; Marino, J.; Sillero-Zubiri, C.; Funk, S.M., Molecular Ecology, 13/8 (August 2004), 2275 (12 pp)
During the last glacial age, Afro-alpine habitats were widespread across the highlands of Ethiopia. A wolf-like canid ancestor is thought to have colonized this expanding habitat and given rise to a new species that was remarkably well adapted to the high altitude environment: the Ethiopian wolf, Canis simensis. Here, we address the timing of genetic divergence and examine population genetic history and structure by investigating the distribution of mitochondrial DNA (mtDNA) sequence variation. The pattern of mtDNA variation and geographical distribution indicate an initial population expansion, probably immediately after divergence from the wolf-like ancestor, around 100,000 years ago. The partition of mtDNA haplotypes that followed was most likely the result of habitat reduction and fragmentation at the onset of deglaciation -- 15,000 years ago. Phylogenetic and geographical associations suggest that the most likely genetic partitioning corresponds to the three mountain areas, Arsi/Bale, Wollo/Shoa and Simien/Mt. Guna. Although there is a degree of clustering of haplotypes from both sides of the Rift Valley, the lack of reciprocal monophyly does not support the taxonomic classification of two subspecies. This study highlights the importance of populations north of the Rift Valley for the maintenance of genetic variability within the species and has consequent implications for conservation.
Effects of Elk Group Size on Predation by Wolves
Hebblewhite, M. & D. Pletscher, Canadian Journal of Zoology, 80 (May 2002): 800-809 (10 pp)
Wolf-prey research has focused on single-prey systems in North America dominated by moose (Alces alces) or white-tailed deer (Odocoileus virginianus). Elk (Cervus elaphus) are social ungulates and the main prey item of wolves (Canis lupus) in Banff National Park (BNP), Alberta. Grouping behaviour may affect the functional response of predators by changing how predators encounter and kill prey. We studied wolf predation on elk in BNP during the winters of 1997–1998 and 1998–1999 and tested how elk group size affected the availability of and encounter rates with elk groups and attack success of wolves. Wolves encountered larger elk groups than expected based on availability, and killed more elk from large groups than expected based on numbers of encounters. Elk group size increased with elk density in BNP. Increased rates of encounter with and success of attacking large elk groups, and the positive group size – density relationship may be a mechanism for density-dependent predation. We developed a predation-risk model to test the prediction that grouping will benefit individual elk, given this predation regime. Elk appeared to adopt two different strategies to minimize predation risk: living in small herds that were rarely encountered by wolves or living in large herds that reduced their predation risk through dilution.
Effects of Social Structure and Prey Dynamics on Extinction Risk in Gray Wolves
Vucetich, John A.; Peterson, Rolf O.; Waite, Thomas A., Conservation Biology, 11/4 (August 1997): 957-965
Extinction models based on diffusion theory generally fail to incorporate two important aspects of population biology -- social structure and prey dynamics. We include these aspects in an individual-based extinction model for small, isolated populations of the gray wolf (Canis lupus). Our model predicts mean times to extinction significantly longer than those predicted by more general (diffusion) models. According to our model, an isolated population of 50 wolves has a 95% chance of surviving just 9 years and only a 30% chance of surviving beyond 100 years. Reflecting the influence of social structure, a wolf population initially comprising 50 individuals is expected to persist only a few years yonger, on averahe (71 years), than a population initially comprosing just a single reproductive pair (62 years). In contrast, substantially greater average prey abundance leads to dramatically longer expected persistence times. Autocorrelated prey dynamics result in a more complex distribution of extinction times than predicted by many extinction models. We contend that demographic stochasticity may pose the greatest threat to small, isolated wolf populations, although environmental stochasticity and genetic effects may compound this threat. Our work highlights the importance of considering social structure and resource dynamics in the development of population viability analyses.
Effects of Wolf Removal on Livestock Depredation in Montana, Idaho, and Wyoming
Bradley, E.H.; Pletscher, D.H.; Bangs, E.E.; Kunkel, K.E.; Smith, D.W.; Mack, C.M.; Fontaine, J.A.; Niemeyer, C.C.; Meier, T.J.; Jimenez, M.D., Rocky Mountain Wolf Recovery 2003 Annual Report
Methods used to mitigate wolf predation on livestock in Montana, Idaho, and Wyoming have largely consisted of removing individuals from depredating packs, either by lethal or non-lethal (translocation) means. We examined the effects of partial and complete removal of wolf packs on the persistence of livestock depredations. From 1987-2002, an average of 30% of all packs with livestock in their territory (22% of all packs with or without livestock) were confirmed to have depredated per year; of these, 63% underwent removal of [one or more] individual[s]. Most packs (68%) depredated again within a year of undergoing partial pack removal, though intervals between livestock depredations increased by an average of 270 days after removal actions. Removing alpha individuals appeared no more effective than removing non-alphas in reducing depredations within the year. Packs that underwent partial removal contributed similar numbers of breeding pairs (defined as an adult male and female raiding [two or more] pups through 31 December) toward recovery goals as depredating packs that did not undergo removal, but fewer breeding pairs than non-depredating packs. Rate of recolonization of territories where entire packs were removed was high (70%) and most recolonizations (86%) occurred within a year of the previous pack's removal. Most recolonized packs depredated (86%); intervals between the last depredation of the removed pack and the first depredation of the recolonized pack averaged 276 days. All depredations involved [one or more] previously affected livestock producer. We suggest that chronic depredations result more from factors inherent in locality than from individual pack behavior. Our findings may be useful for managers seeking to balance objectives of wolf recovery and depredation mitigation.
Effects of Wolves on Livestock Calf Survival and Movements in Central Idaho
Oakleaf, J.K.; Mack, C.; Murray, D.L., Journal of Wildlife Management, 67/2 (April 2003), 299-306
We examined interactions between wolves (Canis lupus) and domestic calves (Bos taurus) within a grazing allotment in central Idaho, USA, to evaluate the role of wolves on calf survival and movements. During the 1999 and 2000 grazing seasons, we radiomarked 231 calves/year-representing 33% of the calf population-OD the Diamond Moose Association (DMA) grazing allotment and monitored their survival and movements relative to wolf distribution. Overall, calf survival was high ( greater than or equal to 95%), with relatively few mortalities (n = 13) among the marked population. Of the 13 calf mortalities, 8 were unrelated to predation (pneumonia, unknown natural causes, fire), 4 were wolf predation, and 1 was coyote predation. Calves selected by wolves were younger than the surviving cohort by an average of 24 days (wolf-killed +/- 31 Mar 13 days [mean birthdate +/- SE], n = 4; live population: 7 Mar +/- 1.6 days, n = 207; P < 0.05). Calf movement patterns and group size did not vary relative to the level of spatial overlap with wolves. However, vulnerability to predation appeared to be correlated with spatial proximity of calves to wolf home ranges and rendezvous sites. These results suggest that in our study area, the overall impact of wolves was not significant on either calf survival or behavior.
Elk Population Dynamics in Areas With and Without Predation by Recolonizing Wolves in Banff National Park, Alberta
Hebblewhite, Mark; Pletscher, Daniel; Paquet, Paul, Canadian Journal of Zoology, 80 (May 2002), 789-799
Gray wolves (Canis lupus) recolonized the Bow Valley of Banff National Park in the mid-1980s after a 30-year absence. Wolves recolonized one zone of the Bow Valley in 1985 and another in 1991, but human activity excluded wolves from a third zone throughout the study. Elk (Cervus elaphus) are the primary prey of wolves in Banff National Park. We studied the effects of wolf predation, snow depth, elk density, and human-caused mortality on the elk population growth rate in the three different wolf recolonization treatments from 1985 to 2000. We constructed a set of generalized linear models of factors affecting population growth, and used Akaike Information Criteria to guide model selection and inference. In the low wolf predation zone, elk population growth was density-dependent and limited by human-caused mortality. In the zone that wolves recolonized in 1991, elk population growth was limited by the combined effects of snow depth and wolf predation after wolf recolonization, in addition to preexisting mortality caused by humans and other predators. Our correlative approach failed to yield insights into population dynamics in the zone where wolves were present throughout the study. However, by comparing zones we demonstrate important differences in ungulate population dynamics in the presence and absence of wolf predation.
Evaluating Wolf Control in Response to Livestock Depredation in the Northwestern U.S.
Bradley, E.H.; Pletscher, D.H.; Bangs, E.E.; Kunkel, K.E.; Smith, D.W.; Mack, C.M.; Niemeyer, C.C.; Fontaine, J.A.; Meier, T.J.; Jimenez, M.D., World Wolf Congress 2003
Wolf depredation of livestock in the recovery areas of Montana, Idaho, and Wyoming has been a challenging management issue. Effectively mitigating livestock damage without impeding wolf population growth has been important in attempts to improve local tolerance while working towards recovery goals. The U.S. Fish and Wildlife Service, with the assistance of Wildlife Services, translocated 107 wolves and lethally controlled 141 wolves in response to livestock conflicts from 1987-2002. We evaluated these two wolf control methods to determine their effectiveness in reducing livestock conflicts. First, we looked at all cases of removal from established packs, either from lethal control or translocation, where only part of the pack was removed. To determine whether livestock killing behaviour decreased in the remaining pack, we compared depredation intervals pre- and post-removal. We considered control actions successful if packs were not implicated in any confirmed depredations for > 1 year. We looked at effects of remaining pack size and alpha removal in this regard. Wolf removal helped to decrease the rate of livestock depredations, but 2/3 of packs depredated again within 1 year. Second, we assessed the fate of translocated wolves to determine whether they survived, established or joined reproductive packs, and/or resumed livestock depredations. We looked at effects of age, social status, and cohesiveness of relocated wolves, as well as release method (hard or soft), release location, and distance of translocation. For both control methods, we assessed whether wolves reproduced and contributed to recovery goals. Our findings may be useful for future management decisions.
Evaluating Wolf Translocation as a Non-Lethal Method to Reduce Livestock Conflicts in the Northwestern United States
Bradley, E.H.; Pletscher, D.H.; Bangs, E.E.; Kunkel, K.E.; Smith, D.W.; Mack, C.M.; Meier, T.J.; Fontaine, J.A.; Niemeyer, C.C.; Jimenez, M.D., Rocky Mountain Wolf Recovery 2003 Annual Report
In the northwestern United States, wolves have sometimes been translocated with the objective of non-lethally reducing livestock conflicts while promoting wolf recovery. We assessed survival, depredation behavior, establishment and movements of wolves post-translocation to determine the effectiveness of translocation in our region and to consider how it may be improved. We found that translocated wolves had lower annual survival (0.6) than other radio-collared wolves (0.73) with government control composing the largest source of mortality. Survival of translocated wolves was lowest in northwest Montana (0.41), where most of the wolf population has settled outside of protected areas. Over one-quarter of translocated individuals and cohesive groups depredated again after release and few established or joined a non-depredating pack....Translocated wolves showed a strong homing trend; those that failed to home still showed directional movement back toward capture sites. Wolves that successfully homed were more likely to be adults, hard-released rather than soft-released, and moved shorter distances than other wolves. We conclude that translocation was ineffective at meeting management objectives in that few relocated wolves significantly contributed to recovery and failed to depredate again. We suggest managers choosing to translocate wolves or other applicable carnivores consider soft-releasing individuals (preferably in family groups, if social) when feasible as this may decrease wide post-release movements and homing behavior. When selecting release sites, we recommend that the adequacy of habitat between the capture and release sites be considered.
Evaluation of Tranquilizer Trap Devices (TTDs) for Foothold Traps Used to Capture Gray Wolves
Sahr, D.P.; Knowlton, F.F., Wildlife Society Bulletin, 28/3 (Fall 2000)
Humaneness is an important issue associated with using foothold traps. Gray wolves (Canis lupus) captured with foothold traps frequently incur injuries to their feet, legs, and teeth during struggles to escape. We collected data from 112 wolves (91 adults and 21 pups) killed in depredation control efforts in Minnesota during 1996 to determine whether TTDs would improve humaneness by reducing severity of injuries incurred by wolves.
Experimental Reduction of Wolves in the Yukon: Ungulate Responses and Management Implications
Hayes, R.D.; Farnell, R.; Ward, R.M.P.; Carey, J.; Dehn, M.; Kuzyk, G.W.; Baer, A.M.; Gardner, C.L.; O'Donoghue, M., Wildlife Monographs, 152 (July 2003), 1-35
We conducted a large-scale, controlled experiment to study the responses of declining woodland caribou (Rangifer tarandus), moose (Alces alces), and Dall sheep (Ovis dalli) to a 5-year reduction in wolf (Canis lupus) numbers in the Aishihik area in the southwestern Yukon. We monitored 10 contemporary controls including 3 caribou herds and 3 moose, 1 Dall sheep, and 3 wolf populations. We tested the hypothesis that wolf predation was the main factor limiting recruitment, adult survival, and population size for the 3 ungulates. Caribou productivity, winter forage quality, disease prevalence, snow depth, snowmelt phenology, harvest, and migration were also assessed. For moose, we also examined harvest, snow depth, and spring and summer growing seasons. Treated moose and caribou populations showed the greatest differences in changes in rates of increase during wolf treatment compared to controls, supporting the wolf predation hypothesis. We found evidence that wolf predation strongly limited recruitment of caribou and moose, and survival of adult moose. We found no evidence that adult survival of caribou improved when wolf numbers were reduced, nor did we find evidence that Dall sheep recruitment or adult numbers responded to lower wolf numbers. Wolf predation and human hunting were probably the main causes of caribou and moose declines before our study. The combination of reduced hunting and lowered predation by wolves was the primary factor causing the increase in the treated Aishihik caribou herd. Lowered predation by wolves, especially upon adult moose, was more important than harvest reduction to the moose increase in the Aishihik area. We hypothesize that woodland caribou herds are linked to the population dynamics of low-density moose in the Yukon. We conclude that natural predation is the main force maintaining low abundance of moose, and that maximum harvest rates should be set conservatively at 2% for caribou and 5% for moose. We recommend that managers use habitat enhancement and public wolf trapping to sustain higher ungulate densities and avoid the need for reactive broad-scale wolf control. We found that wolf fertility control was effective in reducing the rate of increase of wolves and that it was more publicly acceptable than lethal control....