| 7 | where dB,,i,,/dt represents the growth rate during the time interval dt of group (''i'') in terms of its biomass, B,,i,,, g,,i,, is the net growth efficiency (production/consumption ratio), ''M0'',,''i'',, the non-predation (‘other’) natural mortality rate, F,,i,, is fishing mortality rate, e,,i,, is emigration rate, Ii is immigration rate, (and'' e,,i,,·B,,i,,-I,,i,,'' is the net migration rate). The two summations estimates consumption rates, the first expressing the total consumption by group (i), and the second the predation by all predators on the same group (i). The consumption rates, ''Q,,ji,,'', are calculated based on the ‘foraging arena’ concept, where Bi’s are divided into vulnerable and invulnerable components (Walters et al., 1997 Figure 1), and it is the transfer rate (''v,,ij,,'') between these two components that determines if control is top-down (i.e., Lotka-Volterra), bottom-up (i.e., donor-driven), or of an intermediate type. |