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Predation on polychaets and crustaceans through ontogeny in a small bentonic shark (Mustelus schmitti) Theoretical Framework • Size of sharks depend on sex and ontogenic stage. • Body Length (Lt) can affect search and manipulation time of preys. • Changes in diet and resource partitioning minimize intraspecific competion. Hypothesis & predictions • Change of size implies different quantities and species of preys eaten. – The higher the body length, the less polychaets consumed. – Crustaceans are preyed as size and ontogeny advances. Polychaets < Crustaceans < Fishes P C F Objectives •Study the effect of the ontogeny on feeding in small bentonic sharks. •Describe the relationship between quantities of polychaets and crustaceans eaten and the lenght, according to stages and sex of Mustelus schmitti. Experimental design /methods # of preys eaten Two habitats: •Coastal •Depth Ontogeny Body length Immature, Maturing, Mature, Pregnant Quantities of prey eaten Observed distribution Glm, neg binomial distribution Glm, poisson distribution mle2 exponential function mle2, neg binom. Holling ,III, IV mle2, neg binom Ricker mle2, poisson Zero inflated mle2, neg binom. quadratic GAM (crustaceans) Model selection Polychaets Model AIC df weight e.Mod (glm, neg 1464.0 binomial (link=log), polychaets=Lt+Sex:Est 9 0.4700 Mod2 (glm, Lt, sex) 1465.8 4 0.1954 Rick (Lt) 1466.7 3 0.1275 rick_sex (Lt, sex) 1466.7 5 0.1273 Mlemod1 (Lt, sex) 1467.6 5 0.0799 null 1495.3 2 <0.001 Contrasts between sexes within stages Model selection Crustaceans AIC df weight mod3 1150.6 12.14 0.95340 mod1 1157.6 7.81 0.02959 mod5 1159.5 8.81 0.01106 mod4 1162.3 10.68 0.00282 mod2 1162.3 10.64 0.00272 modcuad2 1166.8 4 <0.001 modcuad2Sex 1168.8 5 <0.001 modcuad 1180.7 6 <0.001 modR 1189.2 3 <0.001 modrick 1237.3 5 <0.001 GAM model fitted to crustaceans preyed Quadratic model for crustaceans preyed Conclusions • Body length had a signifficant effect on the • • • number of prey consumed of each class. Female sharks eat signifficantly less polychaets than males. Crustaceans become more important in diet at intermediate body sizes. Decrease of consumption of crustaceans suggests the intake of a bigger and more active prey (fishes?).