Paradoxical effects and interactions in food webs: a commentary on Nilsson and McCann (2016)

Counter-intuitive responses of population density to changes in parameter values were used by Nilsson and McCann (Theor Ecol 9:59-71, 2016, Theoretical Ecology) to argue for the superiority of a recently proposed measure of interaction strength. They argued that one of these responses (decreasing consumer density in response to increasing per capita resource attack rate) is rarely or never discussed and is distinct from responses to consumer mortality. In fact, there is a long history of work on responses to altered attack rates, and they are linked to responses to mortality because the latter very often produce coupled changes in attack rate. This earlier literature does not support a qualitative difference between the impacts of these two types of parameter change and does not clearly support the desirability of any particular measure of interaction strength.