Maybe this article will help you to find the reference that you need.
Regards.
Camilo
Sorensen, T., McLoughlin, P. D., Hervieux, D., Elston, D., Nolan, J., Wynes, B., & Boutin, S. (2008). Determining Sustainable Levels of Cumulative Effects for Boreal Caribou. The Journal of Wildlife Management, 72(4), 900-905. doi: 10.2307/25097630
Murphy, Stephen M., and James A. Curatolo. "Activity budgets and movement rates of caribou encountering pipelines, roads, and traffic in northern Alaska." Canadian Journal of Zoology 65.10 (1987): 2483-2490.
In this paper you will find an interesting approach about the functional habitat. I hope that this paper will help you to find the information that you need.
if you are relating thid term to entomology field then please check this site.
Breeding-season habitat loss drives population declines of monarch butterflies D.T.T.F., D.R.N. and T.G.M. wrote the paper. ... Ecological Entomology, 21, 107–116. .... Functional Ecology, 11, 166–175