Am. beech
Lion
Blackburnian
Sugar maple
Axis
Sun to shade
Cheetah
Tradeoff
Allocation of
Energy: vertical or horizontal
Prey size/speed
In capture techniques mass vs speed
BTGW
G. pyramidum G. allenbyii
Micro-habitats in spruce trees
Time allocation; adaptation to parts of the tree
Patch quality
Cream-skimmers must get to patches first, or monopolize access

HW #3 (25 points): Mechanisms of Coexistence
Due March 20 th . 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
-
+
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 from logistic growth predators
1

P =

(N)N

- d
P
 t birth via consumption of prey mortality

= 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
(+)
Prey
(-)
K
N
What does it mean for the predator isocline to be a vertical line?

What does it mean for the prey isocline to be humped?
P safety in #’s limits to growth
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)
P
Region of neg. DD: damped oscillations
( stable )
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
Low N* = efficient predator
N
High N* = inefficient predator

What NOT to do – the Paradox of Enrichment stable EQ

Feed deer
(increases K to K’) unstable EQ
(1) Productivity goes into building new predators NOT prey
(2) Instability increases
(3) Populations go extinct
P*
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

Fear in the South African
Landscape – Augrabies NP
Rock Hyrax

The view away from the Kopje -

Comparison of the lethal and fear approaches
Lethal
- predators kill their prey
- Population density driven systems
- Brownian motion behavior of pred/prey
Fear
- predators scare their prey
- Fear driven systems: fierce predators and fearful prey
- Sophisticated game of stealth and fear
L
W
W
L W
W
L
W

Efficient predators lead to highly unstable predatorprey interactions
The Catch-22 of the lethal approach
Inefficient predators lead to extinction of the predator in variable environments
K

The Catch-22 of the lethal approach
Inefficient predators lead to extinction of the predator in variable environments
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) = ----------------
(prey have perfect info)
(k + bu*)
Fear:
-
 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.

Experimental demonstrations of non-lethal effect of predators lethal spiders non-lethal spiders
Control no spiders
O. Schmitz et al. 1997 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
Lemmings
Moss
prey
Raptors
Voles
Roots