Transcript Ecol_11_Predator

Am. beech
Sugar maple
Axis
Sun to shade
Lion
Blackburnian
G. pyramidum
Tradeoff
Allocation of
Energy: vertical
or horizontal
Cheetah
Prey size/speed
In capture techniques
mass vs speed
Micro-habitats
in spruce trees
Time allocation;
adaptation to parts
of the tree
BTGW
G. allenbyii
Patch quality
Cream-skimmers
must get to patches first,
or monopolize access
HW #3 (25 points): Mechanisms of Coexistence
Due March 20th. See Website
77%
turned in 2 HWs
45%
0 or 1 HW
Next week: Mutualisms; Mark McGinley
March 20-22: Communities and Food Webs; Travis Hinkelman
Exam II: Post-LV competition up to spring break
MARCH 29th
Effect * of species 1 on species 2
Effect of
species 2
on species 1
+
X
COMPETITION
PREDATION
+
PREDATION
MUTUALISM
* On per capita growth rate
Predation – species interaction where one party benefits
(predator) and one is hurt (prey)
- behaviorally: diet choice, patch use
- community level: How does predation contribute to
species diversity ?
- population impacts: how predators control and/or
regulate prey numbers (or vice versa)
Lethal approach – predators kill their prey
Fear approach – predators scare their prey
Predators have two responses to their prey:
(1) Numerical response -  predators with  prey
(2) Functional response – predator consumption changes with prey
density
type II - satiation
type III
# prey
consumed
type I - linear
density of prey (N)
Predator-prey models
1 N = r(K-N) - (N)P
N t
K
mortality
logistic
growth
from
predators
1 P = (N)N - d
mortality
P t
birth via
consumption
of prey
 = conversion of consumed prey
into new predators
d = predator death rate
(N) = predator functional response
rate of prey consumption by an
individual predator as a function of
prey density.
What does it mean for the prey isocline to be humped?
Pred
(+)
Pred
(-)
P
Prey
(+)
N
Prey
(-)
K
What does it mean for the predator isocline to be a vertical line?
What does it mean for the prey isocline to be humped?
safety
in #’s
limits to
growth
P
N
What does it mean for the predator isocline to be a vertical line?
 no interactions among predators
Predator-prey Isoclines: per capita growth rates = 0
Region of pos. DD:
expanding oscillations
(unstable)
Apex of isocline: stable limit cycle
(neither expands nor dampens)
Region of neg. DD:
damped oscillations
(stable)
P
N
Region of pos. DD:
expanding oscillations
(unstable)
P
N
Unstable dynamics leads to population eruptions,
particularly among insects
Eucalyptus
psyllid
Spruce
budworm
Pine beauty
moth
Viburnum
whitefly
How do you stabilize unstable predator-prey interactions?
(Huffaker’s 1958 experiments)
prey
predator
Simple environments lead to simple
outcomes -- EXTINCTION
So, create complex environments including barriers to predator
dispersal and cycles emerge – illustrates the importance of REFUGES
Physical Refugia – Predators
do not have access to prey
*
*
*
*
**
Behavioral Refugia – Predators
and prey not together in time
and space
Refugia work by reducing predator efficiency
& go from unstable to stable
P
N
Low N* =
efficient predator
High N* =
inefficient predator
mountain lion
What NOT to do – the Paradox of Enrichment
 Feed deer
(increases K to K’)
stable EQ
KK
mule
mule
deer
deer
(1) Productivity goes into building
new predators NOT prey
unstable EQ
P*
(2) Instability increases
(3) Populations go extinct
N*
K
K’
Summary:
(1) Predator-prey interactions contain inherent time lags that result in
population cycles
(2) These cycles can be stable, unstable, or neutrally stable
(3) Relatively efficient predators lead to unstable cycles and extinction
(4) Complex environments and refuges can stabilize predator-prey
interactions
(5) Enriching the prey population is not a viable strategy, rather it
destabilizes interactions and leads to population extinction
The Ecology of FEAR
Fear in the South African
Landscape – Augrabies NP
Rock Hyrax
The view away from
the Kopje -
Comparison of the lethal and fear approaches
Lethal
Fear
- predators kill their prey
- predators scare their prey
- Population density driven systems
- Fear driven systems: fierce predators and
fearful prey
- Brownian motion behavior of pred/prey
- Sophisticated game of stealth and fear
L
W
W
L
W
L
W
W
The Catch-22 of the lethal approach
Inefficient predators
lead to extinction
of the predator in variable
environments
Efficient predators
lead to highly
unstable predatorprey interactions
K K
K
The Catch-22 of the lethal approach
Inefficient predators
lead to extinction
of the predator in variable
environments
K K
K
Incorporating the Ecology of Fear (Brown et al. 1999)
Prey are apprehensive – i.e., they engage in vigilance behavior
M
Fear (i.e., predation risk) = ---------------(k + bu*)
Fear:
(prey have perfect info)
-  w/likelihood of encountering a predator, M
-  w/predator’s lethality, 1/k
-  w/effectiveness of vigilance, b
-  w/level of vigilance, u*
# pred, #prey, feeding
opportunities
Tradeoff:
Too much vigilance  miss out on valuable feeding opportunities
Too little vigilance  likely killed by a predator
Shift the hump in
the prey’s isocline.
Still safety in #s, but
reduced vigilance @
high N reduces
its effectiveness
Bend down the predator’s
isocline.
Predator’s have reduced
efficiency because more
predators results in greater
vigilance in the prey making
them harder to catch
 Interference or
Behavioral Resource
Depression
Implications:
(1) Greater stability in predator-prey interactions – no Catch-22,
and reduce the Paradox of Enrichment
(2) Territoriality in fierce predators may function to protect the
catchability of the prey – avoid the “wayward” Mnt. Lion
stumbling into your territory
(3) Behavior (e.g., vigilance) is a leading indicator of ecological
change
Wolves, elk, and bison in Yellowstone: reestablishing the
“Landscape of Fear”
(Laundre et al. 2001 – Can J. Zool. 79:1401)
Wolves reintroduced into the Lamar
Valley of Yellowstone in 1994-1995.
This now becomes a familiar scene – wohoo!!!
Vigilance in female elk
w/calves increases…
...while time spent
foraging declines
Similarly for bison, however, males and females
w/o calves no show behavioral shift
1996
2002
1997
versus
2001
Three kinds of evidence:
- The changes are much faster
than could occur from elk
mortality
- Reduced herbivory is restricted
to risky habitats
- Elk have exhibited behavioral
changes consistent with an
Ecology of Fear Hypothesis:
(1) favor areas with good visibility
& escape structures (scat)
(2) increased vigilance and
less feeding
These changes have left
physiological evidence
Cottonwood trees need wolves in order to
establish their populations....
...as does willow and aspen.
O. Schmitz et al. 1997
Experimental demonstrations
of non-lethal effect of predators
lethal
spiders
Control
no spiders
non-lethal
spiders
if spiders have (-)
on grasshoppers
GH
Plants
Most of the decrease in
grasshoppers is due to
‘non-lethal’ effects
20%
29%
How do grasshoppers die with non-lethal spiders?
w/o
w/spiders
Shift in daily activity to safer (from predators) but high stress
Exposure to Sun & Heat
Do we see an increase in plant biomass?
Its less clear there is an effect on plants
Broad Conclusions:
Predators have at least two general effects on prey: lethal and non-lethal
Predators kill prey and are also involved in a sophisticated
game of stealth and fear
Incorporating behavior (Fear) has important consequences for pred-prey
interactions ….”Ignore Behavior at your peril”
Raptors
Raptors
Lemmings
Moss
Are lemmings and voles
predators or prey ??
Voles
Roots