Theoretical Framework

Predation on polychaets and Predation on polychaets and crustaceans through ontogeny in a small crustaceans through ontogeny in a small

bentonic shark (bentonic shark (Mustelus schmittiMustelus schmitti))

Theoretical FrameworkTheoretical Framework

• Size of sharks depend on sex and Size of sharks depend on sex and ontogenic stage.ontogenic stage.

• Body Length (Body Length (LtLt) can affect search and ) can affect search and manipulation time of preys.manipulation time of preys.

• Changes in diet and resource Changes in diet and resource partitioning minimize intraspecific partitioning minimize intraspecific competion.competion.

Hypothesis & predictionsHypothesis & predictions• Change of size implies different quantities and Change of size implies different quantities and

species of preys eaten.species of preys eaten.

– The higher the body length, the less polychaets The higher the body length, the less polychaets consumed.consumed.

– Crustaceans are preyed as size and ontogeny Crustaceans are preyed as size and ontogeny advances.advances.

Polychaets < Crustaceans < Fishes

P C F

ObjectivesObjectives

•Study the effect of the ontogeny on Study the effect of the ontogeny on feeding in small bentonic sharks.feeding in small bentonic sharks.

•Describe the relationship between quantities of Describe the relationship between quantities of polychaets and crustaceans eaten and the lenght, polychaets and crustaceans eaten and the lenght, according to stages and sex of according to stages and sex of Mustelus schmittiMustelus schmitti..

Experimental Experimental designdesign /methods/methods

Ontogeny

# of preys eaten

Body lengthImmature, Maturing, Mature, Pregnant

Two habitats: •Coastal

•Depth

Quantities of prey eatenQuantities of prey eatenObserved distribution

Glm, poisson distribution

Glm, neg binomial distribution

mle2 exponential function

mle2, neg binom. Holling ,III, IV

mle2, neg binomRicker

mle2, poissonZero inflated

mle2, neg binom.quadratic

GAM (crustaceans)

Model selectionModel selection

ModelModel AICAIC dfdf weightweight

e.Mod (glm, neg e.Mod (glm, neg binomial (link=log), binomial (link=log), polychaets=Lt+Sex:Estpolychaets=Lt+Sex:Est

1464.01464.0 99 0.47000.4700

Mod2 (glm, Lt, sex)Mod2 (glm, Lt, sex) 1465.81465.8 44 0.19540.1954

Rick (Lt)Rick (Lt) 1466.71466.7 33 0.12750.1275

rick_sex (Lt, sex)rick_sex (Lt, sex) 1466.71466.7 55 0.12730.1273

Mlemod1 (Lt, sex)Mlemod1 (Lt, sex) 1467.61467.6 55 0.07990.0799

nullnull 1495.31495.3 22 <0.001<0.001

PolychaetsPolychaets

Contrasts between sexes within stages Contrasts between sexes within stages

Model selectionModel selection

AICAIC dfdf weightweight

mod3mod3 1150.61150.6 12.1412.14 0.953400.95340

mod1mod1 1157.61157.6 7.817.81 0.029590.02959

mod5mod5 1159.51159.5 8.818.81 0.011060.01106

mod4mod4 1162.31162.3 10.6810.68 0.002820.00282

mod2mod2 1162.31162.3 10.6410.64 0.002720.00272

modcuad2modcuad2 1166.81166.8 44 <0.001<0.001

modcuad2Sexmodcuad2Sex 1168.81168.8 55 <0.001<0.001

modcuadmodcuad 1180.71180.7 66 <0.001<0.001

modRmodR 1189.21189.2 33 <0.001<0.001

modrickmodrick 1237.31237.3 55 <0.001<0.001

CrustaceansCrustaceans

GAM model fitted to GAM model fitted to crustaceans preyedcrustaceans preyed

Quadratic model for crustaceans Quadratic model for crustaceans preyedpreyed

ConclusionsConclusions

• Body length had a signifficant effect on Body length had a signifficant effect on the number of prey consumed of each the number of prey consumed of each class.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?).