The contribution of prey spatial distribution to baleen whale functional responses
W. K. de la Mare
International Whaling Commission
The functional response of a predator to its prey can be constructed as two processes, the first is the relationship between the local density of prey and the amount ingested by the predator, the second is the relationship between the large-scale prey density to the probability of a predator finding prey at a given local density. Here, local density of prey is that in the immediate vicinity of the predator, which determines how much prey can be ingested by a given feeding behaviour at that location. The large-scale prey density is the average density of prey in an area sufficiently large that locating prey of a suitable density for feeding requires searching by the predator. In the context of whales feeding on patchy prey such as krill, local is on the scale of a prey patch, typically tens to hundreds of metres. Large-scale density is from an area that will contain multiple prey patches, and hence is on the scale of tens to hundreds of kilometres. A method for constructing functional response of lunge-feeding rorquals on a local scales is developed in de la Mare, Friedlaender and Goldbogen (2018) by using an individually based energetics model (IBM) of lunge feeding during dives. The model in this paper develops a method for constructing the part of the functional response due to the probability of encountering a prey patch (hereafter referred to as a swarm; the common terminology for a patch of krill).