I should hope that the following won't have me designated a stalwart poseur, but I consider it necessary to make a sort of meta-point concerning our relationship to the natural realm, a subject on which - as I believe some of the subtexts of the infamous crunchy-con debates disclosed - some conservatives are woefully confused.
Nature, then, may be considered as an end in itself, an end prior to all human purposes, its value not contingent upon those purposes - this, by virtue of its Creator's original donation of being, and subsequent declaration that this natural reality, having been given being, is good. Good, that is, in itself, and independent of the existence, and therefore, purposes, of man. The natural environment is good because it participates in being, in the Great Chain of Being, if you will; that is, nature is good because it is.
Several consequences follow, the first of which is that the existence of the natural world, or any aspect thereof, requires no justification: its justification is simply that it exists, and by existing, that it manifests the glory and refulgent splendor of its Creator, as an analogy of the intratrinitarian self-giving of Father, Son, and Holy Spirit. (If one is inclined to philosophical and mystical theology, David Hart's The Beauty of the Infinite is a masterful work of Christian thought, notwithstanding the "Greek thought corrupted Christianity" arguments of the first Amazon reviewer.)
A second consequence is that, in our approach to nature, it is incumbent upon us to apprehend, appreciate, and respect the natural teleologies of the created order. There is a certain good which is instantiated when, for example, a cow is a cow - which is to say that a cow flourishes according to its created nature, doing the things that cows naturally do, ie., munching grass and fodder, bearing calves, and so forth, as opposed to being crammed into feedlots, fed things they'd never eat of their own 'volition' (term used analogically!), and pumped full of antibiotics.
A third consequence, following upon the first two, is that human purposes towards nature are derivative of, and contingent upon, the intrinsic goodness of created being and the natural ends of particular created things. These things are given to man insofar as man receives them as gifts and acknowledges that their existence for themselves and for God is prior to their existence for him. The natural realm does not participate in the goodness of being only insofar as it subserves man's utilitarian ends; to posit that it does, or, what is more directly relevant to the way we comport ourselves toward it, to act as though its value is merely instrumental, is to deny in act the original declaration of God that creation is good.
Now, when mankind, by means of millions, even billions, of private utilitarian decisions, drives some part of the created order to extinction, two declarations are made. First, that the created order participates in goodness only insofar as it subserves the utility of man, which is to say, the desires of men; thus, acts of willed extinction declare that the will of man toward the satisfaction of his desires supercedes, and overrides, the nature of the created order: all that exists exists to serve man, whose desires must find no inherent limit. In other words, that the good of man to is satisfy himself, and not to chasten and discipline himself. Second, and more abstractly or ontologically, that it is not God who declares of being that it is good, but man: and what man giveth, man taketh away by the exercise of his voluntarist, self-ascribed divinity.
Hence, in the very broadest philosophical sense, the necessity of such things as protection for endangered species and aspects of the natural world. The technological conditions of modernity, which have greatly enhanced the power of men to dominate and destroy the natural world, only increase the necessity of such collective limitations. Which, as I have already indicated in Lydia's thread, does not entail that each particular regulatory decision is rational, let alone virtuous; the ESA process is replete with absurdities - of which the reintroduction of wolves onto private property is arguably one (they could be restricted to national parks, for example). Another is the occasional identification of a localized population as a distinct species, when it is, objectively, merely a localized population of a wider-ranging species. Yet another would be the conflation of the accidental and thus unintentional reduction of a population - say, of kangaroo rats on some California farm - with intentional destruction. All of these concrete dilemmas can be discussed and debated, but only in a proper framework, which begins with the acknowledgment that nature is not a utilitarian means of preference-satisfaction, but a manifestation of the goodness of being.
So yes, shoot the wolf that stalks your flocks, and by all means, Californians, shoot the cougars that stalk your children; but let us not indulge the lie that it is licit to willfully push species into nonbeing.