Download Predation (Chapter 15)

Predation
(Chapter 15)
1.
2.
3.
4.
5.
Predator-prey cycles
Physical Characteristics
Adaptations
Functional vs. numeric responses
Models of predation
What is Predation?
– one species feeds on another  enhances fitness
of predator but reduces fitness of prey
(+/– interaction)
Two big themes:
1. Predators can limit prey populations.
*This keeps populations below K.
2. Predator and prey populations increase
and decrease in regular cycles.
A verbal model of predator-prey cycles:
1. Predators eat prey and reduce their
numbers
2. Predators go hungry and decline in
number
3. With fewer predators, prey survive better
and increase
4. Increasing prey populations allow
predators to increase
And repeat…
Why don’t predators increase at the same
time as the prey?
Factors promoting stability in predator-prey
relationships
1. Inefficient predators (prey escaping)
–
–
less efficient predators allow more prey to
survive
more living prey support more predators
2. Outside factors limit populations
–
–
higher death rate (d) for predators
lower growth rate (r) for prey
3. Alternative food sources for the predator
–
less pressure on prey populations
4. Refuges from predation at low prey
densities
–
prevents prey populations from falling too
low
5. Rapid numeric response of predators to
changes in prey population
6. Intimidation by predators!
• Is an important factor influencing the
spatial distribution and behavior of prey
organisms.
• Prey may be forced to seek shelter, switch
microhabitats, or restrict activity, all of
which can reduce foraging rates and
growth .
• Different predators-may interact in their
effects on prey organisms……..
• For example – the activities of one predator
may increase prey encounter rates for
other predators.
• If a small mammal hides in the trees and
shrubs it will then be more prey for avian
species.
Huffaker’s Experiment on Predator-Prey Coexistence
• 2 mite species (1 predator and 1 prey)
• Initial experiments – predators drove prey extinct
then went extinct themselves
• Adding barriers to dispersal allowed predators and
prey to coexist.
Refuges from predation allow predator and
prey to coexist.
Predator-prey cycles can be unstable
– efficient predators can drive prey to extinction
– if the population moves away from the
equilibrium, there is no force pulling the
populations back to equilibrium
– eventually random oscillations will drive one
or both species to extinction
Characteristics of Predators
1. Eye Position: Predators’ eyes face forward to
give them a clear view of their prey
Predators’ Eye Position
Predators’ eyes face forward so they can see the animals
they are chasing. This allows them to focus their vision
on just the prey. They have great depth perception, so
they can see how close or far away the prey is.
Predators have their best vision in their
binocular area because they are seeing the prey
with both eyes. They don’t see the prey as well
in their monocular areas because they can only
see with the eye on that particular side.
Characteristics of Predators
2. Feet: Have sharp claws that the predators use
to hold onto the prey while they are killing
it
Characteristics of Predators
3. Teeth: Sharp, pointed teeth for grabbing and
cutting their food. Predators don’t usually chew
the meat completely. It is swallowed whole or
in chunks
Characteristics of Prey
1.
Eyes: Located on the side of the head so they
can see if predators are approaching
Preys’ Eyes
Preys’ eyes are located at the sides of the head, so they
have good side and rear vision. Since prey spend most
of their time eating grass and leaves, it is important for
them to see to the side and rear without moving their
heads to allow them to look out for predators and to eat at
the same time. Prey have almost
360-degree vision.
Prey have monocular vision, meaning they use each
eye separately. This allows them to see two different
objects on opposite sides of their bodies at the same
time.
Characteristics of Prey
2. Feet: Made for running
Characteristics of Prey
3. Teeth: Flat teeth used to grind tough plant
material
Deer basically have two types of teeth. The front teeth, or
incisors, are used for cutting the food. The back teeth, or
premolars and molars - are used for chewing and grinding
the food. Between the incisors and molars is an open space
along the jaw that has no teeth.
Predator or Prey?
By looking at an animal’s feet, eye position, and teeth a person can
usually tell if an animal is a predator or prey. See if you can
determine which of these animals are predators and which are
prey. Remember to look at their feet and eye positions.
The Predator Becomes the Prey
Some animals can be both predators and prey. For example, a
Texas horned lizard is a predator when it eats ants, termites,
beetles, and grasshoppers. It is also a prey when it is eaten by
snakes, bobcats, roadrunners and other birds such as hawks
and loggerhead shrikes.
The horned lizard is a
predator when it eat ants
and other insects.
A horned lizard is a prey when it
is eaten by birds, snakes, wolves,
bobcats, and coyotes.
How has predation influenced evolution?
Adaptations to avoid being eaten:
spines (cactii, porcupines)
hard shells (clams, turtles)
toxins (milkweeds, some newts)
bad taste (monarch butterflies)
camouflage
aposematic colors
mimicry
Camouflage – blending in
Aposematic colors – warning
Red on Yellow kills a fellow!
Red on Black – your safe Jack!
Is he crazy???
Mimicry – look like something that is dangerous
or tastes bad
Mimicry – look like something that is dangerous
or tastes bad
Mullerian mimicry – convergence of several unpalatable
species
Mimicry – look like something that is dangerous
or tastes bad
Batesian mimicry – palatable species mimics an unpalatable
species
model
mimics
mimic
model
Why are ecological interactions important?
Interactions can affect distribution and abundance.
Changing the number of prey can
cause 2 types of responses:
Functional response – relationship between an
individual predator’s food consumption and
the density of prey
Numeric response – change in the population of
predators in response to prey availability
Type I functional response:
– predators never satiate! ( never get full)
– no limit on the growth rate of predators!
Type II functional response:
– consumption rate increases at first, but
eventually predators satiate (upper limit on
consumption rate)
Type III functional response : consumption
rate is low at low prey densities, increases,
and then reaches an upper limit
Why type III functional response?
– at low densities, prey may be able to
hide, but at higher densities hiding
spaces fill up
– predators may be more efficient at
capturing more common prey
– predators may switch prey species as
they become more/less abundant
Number of Prey Consumed
Functional Responses of Predation
Density of Prey Population
Lotka-Volterra mathematical model describes predator
and prey population cycling.
Real world predator and prey populations can cycle
in size.
The Lotka-Volterra Model:
*Predicts oscillations in the abundances
of predator and prey populations
*Predator numbers lag behind those of
their prey
*Separate calculations for predators
and prey
The Lotka-Volterra Model:
Assumptions
1. Prey grow exponentially in the absence
of predators.
2. Predation is directly proportional to the
product of prey and predator
abundances (random encounters).
3. Predator populations grow based on the
number of prey. Death rates are
independent of prey abundance.
The Lotka-Volterra Model
Variables:
= change
t = time
V = # of prey individuals (“victims”)
P = # of predator individuals
r = exponential growth rate of prey
c = capture efficiency of the predators
The Lotka-Volterra Model
For the Prey:
V
 rV  cVP
t
rate of change in
the prey population
intrinsic growth
rate of the prey
removal of prey
by predators
The Lotka-Volterra Model
For the predators:
P
 acVP  dP
t
death rate of
predators
rate of change in the
predator population
conversion of prey
into new predators
a = efficiency with which prey consumption results
in baby predators
d = death rate of predators
• Equilibrium- state of balance
between opposing forces
–populations at equilibrium do not
change
• Isocline- a line on a graph along
which populations will not change
over time
Equilibrium Isocline
Number of
Predators (P)
• Prey population reaches equilibrium when ΔV/Δt = 0
– Prey population stabilizes based on the size of the
predator population
Prey
Isocline
r/c
d/ac
Number of prey (R)
Equilibrium Isocline
• Predator population reaches equilibrium when ΔP/Δt = 0
– Predator population stabilizes based on the size of the
prey population
Number of
Predators (P)
Predator
isocline
d/ac
Number of prey (R)
Predator-prey systems can have multiple stable
states
• Reducing the number of predators can lead to an
outbreak of prey
Keystone species affect community structure
Predators can allow coexistence of competing prey
Starfish
Pisaster
predator
competitors
Barnacles
Balanus
Mussels
Mytilus
(Paine 1966)
How can we test the effect of a predator on
community structure?
Experiment - Remove the predator
Starfish
Pisaster
Barnacles
Balanus
Mussels
Mytilus
Removal experiment
- mussels are the dominant competitor
- competitive exclusion of barnacles
starfish
removed
%
of
intertidal
zone
mussels
barnacles
time
What is the effect of the predator
on the structure of this community?
- starfish allow coexistence of competitors
starfish
removed
%
of
intertidal
zone
mussels
barnacles
time
How do starfish promote coexistence?
Starfish
Pisaster
Barnacles
Balanus
Mussels
Mytilus
Starfish are picky – they prefer mussels (dominant competitor),
which allows barnacles (weaker competitor) to coexist.
Keystone species affect community structure
disproportionately to their abundance.
Picky predators can promote coexistence among
competing prey species.
Competitive exclusion is prevented when the
dominant competitor is the preferred prey.
COMMUNITY ECOLOGY
Community ecology is concerned with the interaction of
populations.
 One form of interaction is
interspecific competition:
competition between different
species.
 Another form of interaction is
intraspecific competition:
competition between individuals
of the same species
 the strength of competition is
greatest when individuals share
all of the same limited resources.
 Populations tend to shrink when resources become limited
Knowing the environmental niche of an organism
will help determine where it can live.
Fundamental Niche
• The range of conditions
under which the species
can survive and
reproduce
Realized Niche
• Where the species
actually lives within a set
of environmental
conditions.
The difference between the two is a result of biotic interactions
Like predation, facilitation, and competition!
1. The competitive exclusion principle (Gause's principle).
When two species compete for exactly the same
resources (or occupy the same niche), one is likely to
be more successful.
As a result, one species outcompetes the other, and
eventually, the second species
is eliminated.
 This principle states that no two
species can coexist in exactly the
same ecological niche
 One of them is expected to win the
Competition and drive the other to
Extinction.
2. Resource partitioning. Some species coexist in spite
of apparent competition for the same resources.
• Close study, however, reveals that they occupy
slightly different niches. By pursuing slightly
different resources or securing
their resources in slightly
different ways, individuals
minimize competition and
maximize success.
• Dividing up the resources in
this manner is called resource
partitioning.
3. Character displacement (niche shift). As a result of
resource partitioning, certain characteristics may
enable individuals to obtain resources in their
partitions more successfully. Selection of these
characteristics (or characters) reduces competition
with individuals in other partitions and leads to a
divergence of features, or character displacement.
http://www.youtube.com/watch?v=IUIRG6aWtXs
The wolves in this clip are
showing obvious agonistic
behavior, in a ritual display that
has probably evolved to decide
which males gain access to a
resource such as a mate or
food. This generally symbolic
activity that does not result in
actual injury. The wolves show
aggression by baring their
teeth; erecting their ears, tail,
and fur; standing upright; and
looking directly at their
opponent.
http://youtu.be/SciC1PjlVrI
Resource Competition: occurs most frequently
when one individual deprives another of a resource
through consumption of that resource.
This chimp is engaged in agonistic behavior in the form of
an aggressive threat display. Behavior such as this is
ritualized and is performed in order to gain the animal
access to greater resources, such as food, a mate, or
higher standing in this group.
http://www.youtube.com/watch?v=a7XuXi3mqYM
Many males being macho!!!
http://www.youtube.com/watch?feature=endscreen&NR=1
&v=nPS3uxMKaHg
Competition Active Read
• You will be learning the following terms
involving competition
• Interference competition
Allopathy
Territoriality
Preemption
Prepare and Study for Test!