I just took a quick look at the U.S. Fish and Wildlife Service's decision to strip wolves in the northern Rocky Mountains of Endangered Species Act protections. Our fundamental problem with the decision is that there just aren't enough wolves in the region to conclude that they have recovered. So one quote in the delisting rule jumped out at me. According to the Bush Administration:
Commenters provided no convincing scientific evidence that at least 2,000 to 6,000 wolves are required in a wolf population for it to be recovered to meet the Act's purposes.
Really? Here's an excerpt from the comments that NRDC submitted (and ours were only one of many) on this very issue:
It is a well-established principle of conservation biology that populations of organisms need substantial and robust numbers of individuals to maintain viability. An often cited estimate for minimum population viability (MPV) is an effective population size (Ne) of 500 individuals to avoid the effects of genetic loss due to drift (Soule and Wilcox 1980, Frankel and Soule 1981, Soule 1986, Franklin and Frankham 1998). For these reasons, Soule and Simberloff (1986) concluded that "estimates of MVPs for many animal species are rarely lower than an effective size of a few hundred." Since effective population sizes are generally only 10-20% of the census population, this lower limit translates into a total population count of 2,500-5,000 individuals (Frankham 1995, Palstra and Ruzzante 2008).
Other estimates have predicted that viable population numbers should be even higher. For example, Lande (1988) criticized the application of a blanket number like Ne=500 because it fails to consider critical species-specific demographic data. Lande then outlined examples in which demographic parameters, such as an alee effect, stochasticity, edge effects or local extinctions in a patchy habitat, could require populations to have even larger numbers than an effective population of 500. Lande (1995) further explored this topic in the context of genetic variation and mutation and concluded that effective populations should number in the 5,000s. C. D. Thomas (1990) also estimated that MVPs should number in the thousands - ideally, 10,000 individuals for populations that experience fluctuations. Similarly, in 2004, Reed and Hobbs examined the population viability of 2,387 populations of 203 species and found that vertebrates need to number in the thousands for effective conservation.
Recently, a number of studies have been published that examine population viability based on empirical data and gray wolves specifically. Brook et al. (2006) estimated the MVP for 1,198 species including the gray wolf and found that the median overall estimate was 1,377 individuals. Traill et al. (2007) conducted a meta-analysis of MVPs for 212 species including gray wolves and concluded that the MVP for most species will exceed a few thousand individuals. Finally, Reed et al. (2003) estimated the minimum viable population size for over 100 vertebrate organisms, including the gray wolf. The MVP for adult gray wolves was estimated at 1,403. When Reed et al (2003) corrected for 40 generations worth of data, the MVP for gray wolves was estimated to be 6,332. Moreover, genetic data shows that wolves in the United States historically numbered in the several hundreds of thousands (Leonard et al. 2005) and that the genetic diversity of the extirpated North American gray wolves was twice that of the current population. Therefore, the current assemblage of gray wolves in the lower-48 states is a profound under-representation both numerically and genetically of the original gray wolves that once occupied this landscape.
Moreover, genetic data shows that wolves in the United States historically numbered in the several hundreds of thousands (Leonard et al. 2005) and that the genetic diversity of the extirpated North American gray wolves was twice that of the current population. Therefore, the current assemblage of gray wolves in the lower-48 states is a profound under-representation both numerically and genetically of the original gray wolves that once occupied this landscape.