In the optimal foraging graph, what do T and T′ represent?
In marginal value models of patch use, travel time T is the interval spent moving between resource patches, whereas patch residence time T′ is the period devoted to exploiting the current patch. A forager should leave when its instantaneous gain rate falls to the average rate available in the habitat, including travel costs. Longer travel generally favors remaining longer in each patch because departure would impose a larger unproductive interval. Search and handling times are components used in prey-choice models and may occur within a patch, but they are not the paired quantities identified
Ref: Ecology: From Individuals to Ecosystems, Begon et al., 5th Ed., Ch. 10