AMS2005-21: Top-down and bottom-up control of life history strategies in coho salmon

M.L. Snover, G.M. Watters and M. Mangel
12/31/2005 09:00 AM
Applied Mathematics & Statistics
Sexual maturation profoundly affects population dynamics, but the degrees to which genetic, top-down, and bottom-up controls affect age at maturity are unclear. 26 Salmonid fishes have plastic age at maturity, and we consider genetic and environmental 27 effects on this trait by developing fitness functions for coho salmon (Oncorhynchus 28 kisutch). The functions are based on size-specific survival and reproductive success, 29 where reproductive success is the product of fecundity and ability to defend nests 30 (females) or the product of sperm volume and ability to mate (males). We model genetic 31 and bottom-up controls (i.e. food availability) with an environmentally explicit growth 32 function and top-down control (predation mortality) with survival functions that consider 33 both size-dependent and size-independent mortality. For females, we predict that early 34 maturation rarely maximizes fitness but males can maximize fitness by maturing early if 35 they grow well in fresh water. We predict that early maturation is most affected by the 36 bottom-up effects of resource distribution at sea, followed by bottom-up and genotypic 37 effects in fresh water. Top-down processes are predicted to have strong effects on the 38 likelihood of delayed maturation. Our work complements the application of game 39 theory; we predict the distribution of phenotypes in a population while the latter can 40 predict the distribution of genotypes. 41