PARENT SESSION
Oral Session #55: Predator - Prey Interactions.
Presiding: R. Dueser
Wednesday, August 7. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.
Donor-control, Lotka-Volterra, and the functional response of baltic sea cod.
Essington, Timothy*,1, Hansson, Sture2, 1 Marine Sciences Research Center, Stony Brook, NY2 Department of Systems Ecology, Stockholm, Sweden
ABSTRACT- A major limitation in our understanding about the appropriate forms and consequences of the functional response is that it is rarely evaluated in natural settings. The objectives of this study were to use a flexible functional response model that can parameterized as predator-dependent or predator-independent model, and estimate the shape of this model from data collected on cod (Gadus morhua) feeding on two clupeid species, herring (Clupea harengus) and sprat (Sprattus sprattus) in the Baltic Sea. We used extensive data available on abundance, diet composition and consumption rates and used bayesian parameter estimation to calculate probability distributions for the shape parameter of the functional response model, V. Low values of V (<0.3) indicate that the functional response resembles a ratio-dependent (donor-controlled) model, while high values of V(>0.7) indicate that the functional response resembles the Lotka-Volterra model. Age-1 and Age-2 sprat predation mortality was linearly predator-dependent (V=1) and cod mortality accounted for a high proportion of total mortality for these age classes. In contrast, predation mortality was only moderately predator-dependent for age-1 herring (V=0.4), the only age class for which cod predation represented a significant portion of total mortality. These contrasts in the functional response were consistent with the species' numerical responses: sprat biomass increased nearly 3 fold following the crash of the cod population in the late 1980's, while herring biomass showed little trend during this period. These analyses therefore support the hypothesis that food web linkages are comprised of both predator-dependent (donor-controlled) and predator-independent (Lotka-Volterra) linkages.
KEY WORDS: functional response, top-down control, food webs, predation