Download Predation

High
Low
Intimacy
Parasitoids
Parasite
Predator
Grazer
Low
Lethality
High
There are 4 general categories
• “True” predators
• Herbivores
–
–
–
–
Grazers
Browsers
Granivores
Frugivores
• Parasites
• Parasitoids
“True” predators
• Kill their victims shortly after attack, most
of the time (some get away!)
• Consume many prey items in a lifetime
Herbivores
– Attack many prey
items in a lifetime
– Consume only a bit of
the victim
– Do not usually kill
prey in the short term
(but may do so in the
long term)
• Grazer
– Mainly eats leafy material
• Browser
– Mainly eats woody
material
• Granivore
– Mainly eats seeds
• Frugivore
– Mainly eats fruits
Native vs. Domestic Grazing Systems
• Differences in selection & competition
among species
Grass
Forbs &
Browse
Bison
100%
Horses
100%
Cattle
90%
10%
Sheep
40%
60%
Pronghorn
6%
83%
Cacti
11%
Parasites
• Consume part of their
prey
• Do not usually kill their
prey
• Attack one or very few
prey items in their
lifetime
• Parasitoids
Parasites
• Parasitoids
Predation is important because:
Evolutionary arms race (example of coevolution)
Predation is important because:
1. It may restrict the distribution of, or reduce the
abundance of the prey species.
2. Predation, along with competition, is a major
type of interaction that can influence the
organization of communities.
3. Predation is a major selective force, and many
adaptations of organisms have their explanation
in predator-prey coevolution.
1. Evolutionary arms race
4. Predation drives the movement of energy and
nutrients in ecosystems.
Optimality theory
•
we expect that
natural selection
yields efficient,
economic animals;
maximizing benefits
or minimizing costs,
thus maximizing net
energy/time (e/t)
Predation
• Rate of increase of prey
population
dH/dt = rH
population abundance
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Predation
• Rate of increase of prey
population
– dH/dt = rH
– Predators eat prey
• dH/dt = rH-a'HP
– a' = capture coefficient
– H = Prey pop size
– P = Predator pop size
Predation
• Rate of increase of
predator populations
90
population abundance
dP/dt = -qP
– If only predators exist, no
prey, so predators die
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Predation
• Rate of increase of
predator populations
dP/dt = -qP
– If only predators exist, no
prey, so predators die
• dP/dt = fa’HP-qP
– f = is a predation constant
» Predator’s efficiency
at turning food into
predator offspring.
– a' = capture coefficient
– q = mortality rate
Predation
• Equilibrium population
sizes
– Predator
•
•
•
•
•
dP/dt = fa’HP -qP
0= fa’HP -qP
fa’HP = qP
fa’H= q
H= q/fa’
– Prey
•
•
•
•
•
dH/dt = rH-a’HP
0= rH-a’HP
rH= a’HP
r = a’P
P = r/ a’
Predation
• Graphical Equilibrium
– Prey (H) equilibrium
(dH/dt=0) is determined
by predator population
size.
– If the predator
population size is large
the prey population will
go extinct
– If the predator
population is small the
prey population size
increases
Predator
Pop size
dH/dt =0
r/a’
Prey pop size
Predation
dP/dt =0
• Graphical Equilibrium
Predator
Pop size
q/fa’
Prey pop size
– Predator (P) equilibrium
(dP/dt=0) is determined by
prey population size.
– If the prey population size
is large the predator
population will increase
– If the prey population is
small the predator
population goes extinct
Predation
• Predator-Prey
interaction
– The stable dynamic of
predators and prey is a
cycle
dP/dt =0
Predator
Pop size
r/a’
q/fa’
Prey pop size
Rosenzweig & MacArthur (1963)
• Three possible outcomes of
interactions
i) Prey iscoline
Predator density
N2
Prey increase
ii) Predator iscoline
Prey density
K1
N1
N2
Predator density
K2
Predator decreases Predator increases
Prey density
N1
Predator-Prey Models
– Superimpose prey and predator isoclines
• One stable point emerges: the intersection of the
lines
• Three general cases
Predator
isocline
a)
Population density
Predator Density
– Inefficient predators require high densities of prey
Damped oscillations
Prey
isocline
Prey Density
Time
Predator-Prey Models
• Three general cases (cont.)
Predator Density
b)
Predator
equilibrium
density
Prey Density
Population density
– A moderately efficient predator leads to stable oscillations
of predator and prey populations
Stable oscillations
Time
Predator-Prey Models
• Three general cases (cont.)
Population density
– A highly efficient predator can exploit a prey nearly down
to its limiting rareness
Prey Density
Increasing oscillations
Time
All these models make a series
of simplifying assumptions
• A homogenous world in which there are no
refuges for the prey or different habitats.
• There is one predator species eating one prey
species and there are no other species involved in
the dynamics of these two populations
• Relaxing these assumptions leads to more
complex, but more realistic models.
• All predators respond to prey in the same fashion
regardless of density
– Functional Response
Conclusions form field studies
• There is not a clear relationship between
predator abundance and prey population
size.
– In some, but not all cases, the abundance of
predators does influence the abundance of their
prey in field populations.
What makes predators effective
in controlling their prey?
• Foraging efficieny
– Within a patch, the searching efficiency of a
predator becomes crucial to its success.
– But searching efficiency varies with abiotic
factors and can also decrease at high predator
densities because of interference of other
predators.
What makes predators effective
in controlling their prey?
• Some systems are
Bottom-up regulate.
• Some systems are
Top-down regulated.
Predation
• Response of predator to
prey density
– Numerical
– Aggregative
– Functional
Types of functional responses
•Limited by handling time
•The rate of capture by predator
•Alters Behavior
–Type I
–Type II
–Type III
C. S. Holling
(1930–)
Types of functional responses
Slide 25
Keystone predator
• Bob Paine at
University of
Washington
mussel is a
competitive
dominant in
this system
Other examples of keystone predators
The effects of herbivory
• Individual plants are affected in the
following areas
– plant defenses
– plant compensation
• plant growth
• plant fecundity
Chemicals Defenses
• Quantitative Defenses:
• Qualitative Defenses:
• Prevent digestion as they
accumulate in the gut.
• Usually found in large
quantities in the plant parts that
are eaten.
• Most of these compounds are
“Carbon Rich”
• Common defense of plants
growing in nutrient poor soils
(conifers).
• Usually toxic in small
quantities.
• Found in relatively small
amounts in the portion of plants
that is eaten (leaves).
• These compounds are
“Nitrogen Rich” and therefor
expensive to produce by the
plant.
• More common in plants
growing on nutrient rich soils.