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Am. beech Sugar maple Axis
Sun to shade
Tradeoff
Allocation of Energy: vertical
or horizontal
Prey size/speedIn capture techniques
mass vs speed
Micro-habitats in spruce trees
Time allocation;adaptation to parts
of the tree
Patch qualityCream-skimmers
must get to patches first,or monopolize access
Lion Cheetah
G. pyramidum G. allenbyii
Blackburnian BTGW
HW #3 (25 points): Mechanisms of Coexistence Due March 20th. See Website
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
77% turned in 2 HWs
45% 0 or 1 HW
Effect * of species 1 on species 2
-
+
+
-Effect ofspecies 2
on species 1
COMPETITION
MUTUALISM
PREDATION
PREDATION
* On per capita growth rate
X
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 preyFear approach – predators scare their prey
type I - linear
type II - satiation
# preyconsumed
density of prey (N)
Predators have two responses to their prey:
(1) Numerical response - predators with prey
(2) Functional response – predator consumption changes with prey density
type III
Predator-prey models
1 N = r(K-N) - (N)P N t K
1 P = (N)N - dP t
= 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.
logisticgrowth
mortalityfrom
predators
mortalitybirth via
consumption of prey
What does it mean for the prey isocline to be humped?
What does it mean for the predator isocline to be a vertical line?
P
N
Pred(-)
Pred(+)
Prey(+)
Prey(-)
K
What does it mean for the prey isocline to be humped?
safetyin #’s
limits to growth
What does it mean for the predator isocline to be a vertical line?
P
N
no interactions among predators
Predator-prey Isoclines: per capita growth rates = 0
P
N
Region of neg. DD:damped oscillations (stable)
Region of pos. DD:expanding oscillations (unstable)
Apex of isocline: stable limit cycle (neither expands nor dampens)
P
N
Region of pos. DD:expanding oscillations (unstable)
Unstable dynamics leads to population eruptions, particularly among insects
Eucalyptus psyllid
Spruce budworm
Pine beauty moth
Viburnumwhitefly
How do you stabilize unstable predator-prey interactions?(Huffaker’s 1958 experiments)
prey predator
Simple environments lead to simpleoutcomes -- 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
***
**
*
P
N
Refugia work by reducing predator efficiency& go from unstable to stable
Low N* =efficient predator
High N* =inefficient predator
What NOT to do – the Paradox of Enrichment
Kmule deer
mou
ntai
n lio
n
mule deerK
K K’
stable EQ
unstable EQ
(1) Productivity goes into building new predators NOT prey
(2) Instability increases
(3) Populations go extinct
Feed deer (increases K to K’)
N*
P*
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
- 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
LW
L
W
W
W
WL
K
The Catch-22 of the lethal approach
Efficient predatorslead to highlyunstable predator-prey interactions
Inefficient predatorslead to extinctionof the predator in variable environments
KK
K
The Catch-22 of the lethal approach
Inefficient predatorslead to extinctionof the predator in variable environments
KK
Incorporating the Ecology of Fear (Brown et al. 1999)
Prey are apprehensive – i.e., they engage in vigilance behavior
MFear (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, butreduced vigilance @ high N reduces its effectiveness
Bend down the predator’sisocline.
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 LamarValley of Yellowstone in 1994-1995.
This now becomes a familiar scene – wohoo!!!
...while time spentforaging declines
Vigilance in female elkw/calves increases…
Similarly for bison, however, males and femalesw/o calves no show behavioral shift
1996 2002
1997 versus2001
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
Control no spiders
GH
Plants
lethal spiders
non-lethal spiders
if spiders have (-)on grasshoppers
Experimental demonstrationsof non-lethal effect of predators
20%
29%
Most of the decrease in grasshoppers is due to ‘non-lethal’ effects
How do grasshoppers die with non-lethal spiders?
Shift in daily activity to safer (from predators) but high stressExposure to Sun & Heat
w/spidersw/o
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
Raptors
Voles
Roots
Are lemmings and volespredators or prey ??