I'd just like to throw up some specific points and underlying premises here so that the parameters of the topic might be clearer, as well as try to summarise the current front of debate in the realms of animal and environmental philosophy. That said, the following is probably overly simplistic and incorrect in places:
1. The debate of animal rights seems tied to the notion of animal rights relative to our granted premises of human rights.
2. Thus, the common perception of the debate hinges on the moral considerations that accompany the property of moral agency (or more specifically, the capacity for moral agency). In particular moral agency involves capacity to react to situations, and for decision making. This implies an inherent degree of autonomy.
3. It should be noted at this point that the egalitarian part of our liberal axiology (right to life and liberty of ALL people) is pervasive insofar as we consider a species as a whole. I suppose this is primarily because existence of an individual depends on existence of a species (I'll take a basic understanding of evolution as a given without going into the details).
4. Animals as a general rule are sentient in that they also possess a consciousness and display emotional and cognitive behavioral responses which are not entirely dependent on some biologically hard-wired function. They should thus be considered as being moral agents.
5. This is essentially aimed at previously prevalent cultural practices which held that animals do not have rights as humans are 'a race apart'. Sentience was taken to be a defining factor and therefore the license to our right to subjugate and treat other animals as we pleased. This stems from a certain specisism, or perhaps anthropocentrism, that grants humans some kind of "intrinsic value" or in other words, a pedestal. Not only was this a mistaken belief, I'm arguing that regardless of how it is defined, this is an irrelevant consideration. Other animals would have rights in so far as they apply to we (human) animals.
6. It must be asked at this point what a right entails. I suggest it is not a concrete term apart from having a moral connotation which may be manifest in some legal terms. Commonly referred concrete moral principles here are that of murder and control (denial of life and liberty), and here the treatment gets very tricky.
7. Moral vegetarianism! I'm hoping to steer clear of this particular debate because...it tends to spawn a bunch of biological arguments ("you're meant to eat meat" "if you eat meat you will get bowel cancer") which are all WRONG insofar as they purport to convey a definitive moral judgment but invariably will fall short, relying on semantics and rhetoric to tide them over. But that's where we seem to be at, especially since Singer.
I'd like therefore to extrapolate on something Sarah said:
Because we are the dominant species we have a responsibility to care for and protect the species we coexist with on this planet
If I may, I'd suggest that by "dominant" we mean the one who exert the most destabilising influence on the ecosystem as a whole, due to our method of manipulation of it. That I guess means conversion of the most resources, or in terms of physics, we fight entropy the most. I agree with the general sentiment of that statement, especially because it concurs with my general outlook on morality- a consequentialist one that always considers context, as opposed to a prescriptive list of behaviors and judgments of various properties.
Why do I say this? Because one also must be aware (as implied by my reference to entropy) that survival and co-existence entails a necessary tension. Our own living comes at the expense of other resources and our responsibility I believe (for the sake of the earth and everything on it, including us!) is at the very least the management of the interaction between ourselves and the environment. However, this doesn't necessarily mean we can't kill animals for our own purposes, as strange as it may sound, this is not quite synonymous with respect. Nor does it make hard and fast conclusions on farming and agriculture. Discussion of these topics should take much more detail into consideration.
That's all I will write for starters. If it's valid, then hopefully people will keep this in mind if the thread were to continue. If it's not, hopefully somebody will tell me why.