Reading the heading might make you think that what follows will explain how biocentrists want us to behave. I by no means wish to mislead you. The following actually concerns one of James P. Sterba’s arguments, addressing why all living beings have moral worth. If you want to skip directly to the page about what one might be justified in doing with regards to nature and its creatures, you can go to Different treatment.
Constraints
James Sterba argues that a living being must have the potential to be benefited and harmed in order to have moral worth, but he does not want to distinguish those who have moral worth in terms of what characteristics they possess. It is irrelevant whether or not an individual is rational or sentient, or has the capacity for goal oriented actions (Sterba 1998), and this is where constraints and how to behave come in.
What should help define those who have moral worth is whether one can reasonably impose constraints on how humans [moral agents] treat the individuals in question (Ibid.). By this definition, trees, lions, and other living organisms have intrinsic value and moral worth because the good of these individuals ought to constrain the way we use them to pursue our own interests.
Environmental ethics
Sterba explains his move by referring to what he claims environmental ethics is actually about, namely, the human relationship with nature and how to determine the constraints on and the prerogatives of humans in their relationship with other living beings. Sterba hereby uses a narrow definition of environmental ethics (Ibid.).
When philosophers focus on what NOT TO DO, rather than what TO DO, we refer to it as negative rights. Sterba’s take on environmental ethics does not concern itself with positive rights, where the question is what obligations we have towards nature (Ibid.).
Questions such as: Are we obliged to not only refer from harming nature, but also to promote life on earth? If we meet a starving animal, should we give it food? If we see a plant about to wither, should we water it? If whales are stranded should we help them back into the sea?
“Ought” implies “can”
Sterba here bases his position on the “ought” implies “can”’ principle, a principle common to all moral and political perspectives. According to this principle, people are not morally required to do what they lack the power to do, or what would involve such a great sacrifice that it would be unreasonable to ask it of them, and similarly, in cases of severe conflict of interest where it would be unreasonable to abide customary moral requirements (Sterba 2008).
To give up your livelihood for another being, or cure HIV without any scientific research, would basically require you to be a saint rather that a human with common strengths and sensibilities.
Independent individuals
Moreover, when moral agents such as us recognize beings as having intrinsic value, we should also recognize that certain constraints apply when interacting with them. It is worth noting, that it’s herein assumed that the living beings commonly covered by these principles will actually benefit from such noninterference. They are independent individuals, and do not require for their survival any additional support from humans, who have no obligation to provide it (Sterba 1998). 
Sterba concludes that: These living beings whom are considered to have intrinsic value are such living beings whose good ought to constrain the way that moral agents pursue their own interests (Sterba 1998).
References
- Sterba, James P. 1998 ”A Biocentrist Strikes Back” Environmental Ethics 20 (4):361-376 (1998) Philosophy Documentation Center
- Sterba, James P. 2008 “COMPLETING THE KANTIAN PROJECT: FROM RATIONALITY TO EQUALITY” Presidential Address delivered before the One Hundred Fifth Annual Central Division Meeting of The American Philosophical Association in Chicago, Illinois
Pictures
- Lions and humans: Greg Hewgill, (CC BY 2.0)
- Bear: Cecilie Skogheim Amundsen
- Maria: GFreihalter (CC BY-SA 3.0)
- Chimpanzees: Cecilie Skogheim Amundsen
Environmental ethics 