Ecological Recovery for Yellowstone's Grizzly Bears and Wolves
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Biological Conservation 113 (2003) 63–73 www.elsevier.com/locate/biocon Beyond demography and delisting: ecological recovery for Yellowstone’s grizzly bears and wolves Sanjay Pyarea,*, Joel Bergerb aEMRI, PO Box 717, Seeley Lake, MT 59868, USA bWildlife Conservation Society, PO Box 340, Moose, WY 83012, USA Received 6 April 2002; received in revised form 15 September 2002; accepted 25 October 2002 Abstract This paper addresses the question, when are threatened or endangered species really recovered? The US Endangered Species Act enables the de-listing of species once demographic criteria are met. In the Greater Yellowstone ecosystem, two protected apex car- nivores, grizzly bears (Ursus arctos) and wolves (Canis lupus), face removal from federal government protection due to population increases, a point at which they are expected to be integrated components of this ecosystem. We tested the assumption that these two carnivores are playing normative ecological roles in the Yellowstone ecosystem by comparing the extent to which wolves and bears have re-instilled anti-predator responses in a primary prey species, moose (Alces alces), within wolf and bear recovery zones. As a type of control, we contrasted female moose from two areas in Alaska with different predator regimes to those in Wyoming. Populations from mainland Alaska, a region with a relatively intact carnivore assemblage, responded significantly more to odors of both carnivores. In contrast, a basic anti-predator reaction was lacking in Wyoming; and responses to grizzly bear odor only nominally increased after dependent young experienced heightened mortality. Additionally, the level of response among Alaskan moose living under virtual predator-free conditions for 25+ years closely resembled that of conspecifics in Wyoming. That such striking variation in prey responses exists re-enforces critical ecological differences between predator-intact and -defunct systems. Thus, although grizzly bears and wolves in the Yellowstone area will most likely be de-listed within the next few years, whether such action would be ecologically defensible is arguable. At this point in the recovery process, these predators may currently have limited ecological impacts in large portions of this region, at least as gauged by one potentially important prey species, moose. Although our data suggest ecologically incomplete conditions, other indices of carnivore recovery that include responses of other important prey species such as elk (Cervus elaphus), may be more in tune with carnivore activities. We recommend that different types of ecological data available throughout recovery zones be used in consort with demographic criteria to evaluate when endangered carnivores are more fully integrated into their ecosystems. And, in the event of a disparity between these criteria, we also encourage a dialogue focusing on approaches towards bringing ecological conditions in concordance with demographic criteria, irrespective of whether one considers increasing population levels beyond the current target levels required for de-listing,and/or simply, additional time for the recovery process. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Carnivores; De-listing; Endangered Species Act; Recovery plans; Greater Yellowstone ecosystem 1. Introduction horribilis) and gray wolves (Canis lupus) have only been in place for approximately 20 years, and until very Despite the sensational reductions of large carnivores recently the prospects for formal de-listing from the US from terrestrial habitats throughout the twentieth cen- Endangered Species list were low. The recovery of these tury, formal interest in their restitution has only recently types of large carnivores, in particular, represents a new become a focal issue in conservation (Gittleman and chapter in conservation and resource management, and Gomper, 2001). For instance, federal recovery plans for de-listing will continue to generate a host of novel issues two prominent carnivores, grizzly bears (Ursus arctos and challenges for the conservation community, state and federal agencies, local residents, and the public * Corresponding author. Tel.: +1-406-677-0247; fax: +1-406-677- at-large. 0248. What demographic criteria are adequate to ensure the E-mail address: [email protected] (S. Pyare). probability of population persistence remains high? This 0006-3207/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0006-3207(02)00350-6 64 S. Pyare, J. Berger / Biological Conservation 113 (2003) 63–73 question has been asked in one form or another for 1995). Wolves have also had such diverse cascading almost 20 years (Craighead, 1998; Mattson and Craig- effects as altering growth rates of balsam-fir and aspen- head, 1994; Schaffer, 1983). For both grizzly bears and willow communities via impacts on browsing ungulates wolves, whether the existing number of individuals can (McLaren and Peterson, 1994; Messier, 1994; Ripple et be considered sufficient to prevent the species’ extinction al., 2001), as well as affecting mesocarnivore and in the future will undoubtedly remain a contentious scavenging communities in Yellowstone National Park issue in the Rocky Mountains of the United States (Crabtree and Sheldon, 1999a,b; Stahler, 2000). And, (Clark et al., 1999; Keiter, 1998; USFWS, 1993; Wilcox the loss of grizzly bears and wolves has caused a cascade and Ellenberger, 2000). We believe it is prudent to sub- of interactions that ultimately decreased the diversity ject recovery planning for large carnivores to debates and nesting densities of Neotropical avian migrants via about population viability—this will only enhance the herbivory-induced effects in willow (Salix spp.) com- long-term effectiveness of conservation strategies by munities (Berger et al., 2001a). The possibility of such accommodating diverse social, political, and biological ecological effects had not been completely ignored dur- criteria. But, we also think that debates that center on ing recovery planning: Cook (1993) discussed ecological population viability have overshadowed efforts to issues prior to the reintroduction of wolves into Yel- answer a critical underlying question: Will target popu- lowstone National Park. From a heuristic perspective, it lation levels successfully restore the ecological interac- seems appropriate to ask why ecological criteria were tions involving the species in question? Indeed, in the not more explicitly incorporated in recovery plans for haste to support or refute population estimates and these types of important species? prospects for population viability, the ecological rele- One obvious reason is based on the conventional vance of large carnivores has been viewed as less interpretation that the Endangered Species Act solely important to recovery goals. Even when ecological prevents species’ extinctions or declines through popu- issues have been considered during recovery planning, lation-level monitoring (Clark, 1994). Closer exami- as had been done prior to the reintroduction of wolves nation of the Act’s language, however, suggests that (Cook, 1993), anticipated ecological effects ultimately the Act was designed with a broader intent and more have not been incorporated into recovery plans. That is, flexible approach: the degree to which a carnivore is expected to interact with other species and alters its ecosystem at-large has The purposes of this act are to provide a means not been viewed as a measure worthy of a de-listing whereby the ecosystems upon which endangered benchmark. Major recovery criteria for grizzly bears in species depend are conserved; and the Yellowstone area, for instance, are population-level parameters: the number of unduplicated females with The Secretary, in developing and implementing cubs, number of family units, and number of mortalities recovery plans, shall provide objective, measurable among both females and the total population (USFWS criteria which, when met, would result in a deter- 1993). Similarly, for wolves, the number of breeding mination ...that the species be removed from the pairs (i.e. 10 for 3 consecutive years) is the criteria list. (From the Endangered Species Act of 1973) required for ESA reclassification and/or de-listing in the Rocky Mountains (Smith et al., 1999; USFWS, 1987). Thus, the Act is an implicit recognition of the impor- That an ecological perspective should be viewed as tance of restoring species and associated ecological pro- less appropriate than a demographic one in the context cesses to defunct ecosystems. A complementary of large carnivore recovery is surprising. Research con- interpretation of the Act, therefore, appears to support tinues to demonstrate that these terrestrial carnivores, an approach that would include, at least in part, the perhaps more so than most other threatened or endan- monitoring of ecological processes associated with gered species, have far-reaching consequences for their recovering species, so long as these processes are mea- ecosystems. Not only has predation influenced the evo- surable and capable of facilitating recovery objectives. lution and ecology of their prey directly (Caro, 1998; A second reason for the lack of ecological considera- Estes and Duggin, 1995), but it has also had substantive tion may be the expediency with which individuals of a indirect effects on entire ecosystems (Breitenmoser, species can be enumerated and assessed, while ecologi- 1998). Terborgh et al. (1999) summarized anecdotal, cal parameters, such