Theoretical Framework
description
Transcript of 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?).