population cycles

group selection

adaptations within groups for the group

lemmings winter where

subnivean pukak layer

how long are lemming cycles

3-5 years

features of population cycles

1. periodic

2. regular

3. large amplitude

4. northern distribution

5. synchronous

how long are hare cycles

8-11 yrs

lemming intrinsic

1. density dependent

2. social stress

lemming extrinsic

1. abiotic

2. vegetation herbivore

3. predator-prey

chitty effect

animal largest at peak phase

density dependent

• low density = selection for docile

• high density = selection for aggressive

social stress hypothesis

• behaviour and physiological

• more pop density = chronic stress = more glucocortoid

• reproduction decline

sun spots

• 11 yr

• predictable but cycles go in and out

• snow and snowshoe hare

vegetative- herbivore

a. food abundance

• sedges, grass, moss

• low digestion rate

• high metabolic

b. quality

• more lemming = reduce standing dead

c. grazing

• induced plant chemical defenses

• decrease digestability

• toxic

• not

predation

specialist

generalist

numerical

• how predator population size changes in response to prey density

functional response

predation feeding depending on prey abundance

what drives lynx

both top down and bottom up

trait mediated

pred affect the prey phenotype

• predator induced hypothesis

predator induced hypothesis

climate changed

• only happened for two population cycles

why is the world green

HSS hypothesis - pred and para control herb

herbivory is costly and plants get defenses

constitutive

present in plant no matter what

induced

in response to attack