Transcript Presentación de una novedad

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?).