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 ??