# BIOB50H3 Lecture Notes - Lecture 11: Brachionus, Rotifer, Ecological Society Of America

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16 Mar 2012
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Lecture 11
Chapter 12
Predation
Introduction
RECALL: over half the species on earth obtain energy by feeding on other organisms, in a
variety of types of interactions
All are EXPLOITATION a relationship in which one organism benefits by feeding on, and thus
directly harming, another.
Prey Switching
Classic model
E1/E2 is the ratio of prey 1 eaten relative to prey 2
N1/N2 is the ratio of prey 1 in habitst, relative to prey 2
C is preference for prey 1
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Guppies focused their foraging efforts on whichever prey species was most common in their
habitat: tubificids or fruit flies. The solid green line indicates the results that would have been
expected if the guppies had captured tubificids according to their availability instead of
switching to whichever prey species was most abundant.
(purple line second top dot) when they were 60% of the prey, tubificids constituted nearly
80% of the guppies diet
(purple line botton dot) when they were 20% of the prey, tubificids constituted just 10% of
the guppies diet
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Population Cycles
POPULATION CYCLES CAN BE CAUSED BY FEEING RELATIONS, SUCH AS THREE-WAY
INTERACTION BETWEEN PREDATORS, HERBIVORES, AND PLANTS.
A specific effect of exploitation can be population cycles
Lotka and volterra evaluated these effects mathematically in the 1920s
THE LOTKA-VOLTERRA PREDATORPREY MODEL:
Rn is prey exponential growth
aNP is removal of prey by predators
baNP predator is exponential growth depends on predators ability to turn prey into births
mP is the death rate
N = number of prey
P = number of predators
R = population growth rate
A = capture efficiency
When P = 0 they prey population grows exponentially
With predators present (P does not equal 0) the rate of prey capture depends on how
frequently they encounter each other (NP), and efficiency of prey capture (a)
The overall rate of prey removal is aNP
N = number of prey
P = number of predators
m = mortality rate
a = capture efficiency
b = efficiency with which prey are converted to predator offspring
if N=0, predator population decreases exponentially at death rate m.
When prey are present (N does not equal 0), individuals are added to the predator population
according to the number of prey killed (aNP), and the feeding efficiency with which prey are
converted to predator offspring (b)
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