I am new to population ecology, but think that it definitely has some implications that are highly relevant to program sustainability and thereby evaluation. One challenge you might be running into–traditionally, I have seen population ecology as focused on a population of organizations, not just an individual organization. Given that, sustainability-related questions would tend to examine characteristics at the population level at one time point and then again later, to see how characteristics of the population changed as individual organizations survived or did not survive. Which types of programs are more or less common after time has passed? (It always helps me to go back to biological evolution metaphors— over time, the population of primates had larger brains, because individuals with larger brains were more likely to survive and reproduce). Sometimes I find untangling levels of analysis issues helps me. Hope this helps you.
Megan Greeson greesonm@msu.edu
Evaluation Uncertainty 
Hi Megan. You have identified the precise reason why I PE may not be useful as a framework for understanding program sustainability. Namely, population ecology cares not a whit about whether any particular organism survives or not.PE is concerned with populations and species as the level of analysis. It may care about death rates, but not about the death of any particular member of the group. So what’s in it for us evaluators?