Emergence of Holling type III zooplankton functional response: Bringing together field evidence and mathematical modelling

Andrew Yu. Morozov (1, 2)

1 Department of Mathematics [Leicester]
2 Shirshov Institute of Oceanology

Food-web population models are rather sensitive to parameterization of functional response in predation terms. Theoretical studies would predict enhancing of ecosystems' stability for a functional response of sigmoid type (Holling type III). The choice of a correct type of response is especially important for modelling outcome of grazing control of algal blooms by zooplankton in nutrient-rich ecosystems. Extensive experiments on zooplankton feeding in laboratories show non-sigmoid nature of response for most herbivorous zooplankton species. As a consequence, there is a strong opinion in the literature that the implementation of Holling III type grazing in plankton models is biologically meaningless. I argue, however, that such an 'evident' claim might be wrong and sigmoid functional responses in real plankton communities would emerge more often than it was suggested earlier. Especially, this concerns plankton models without vertical resolution, which ignore heterogeneity in species vertical distribution. By having conducted extensive literature search of data on zooplankton feeding , I show that vertical heterogeneity in food distribution as well as active food searching behaviour of zooplankton can modify the type of functional response. In particular, the rate of food intake by the whole zooplankton population in the column, as a function of total amount of food, often exhibits a sigmoid behaviour, instead of a non-sigmoid one postulated previously based upon laboratory experiments. This conceptual discrepancy is due to the ability of zooplankton to feed mostly in layers with high algal density. I propose a generic model explaining the observed alteration of type between the overall and the local functional responses. I show that emergence of Holling type III in plankton systems is due to mechanisms different from those well known in the ecological literature (e.g. food search learning, existence of alternative food, refuge for prey).

Mots clés: Zooplankton functional response; Holling type III; Vertical plankton distribution; Grazing control

Andrew Yu. Morozov. Emergence of Holling type III zooplankton functional response: Bringing together field evidence and mathematical modelling. Journal of Theoretical Biology, 2010, 265 (1), pp.45. ⟨10.1016/j.jtbi.2010.04.016⟩. ⟨hal-00598095⟩