POPULATION POPULATION CYCLESCYCLES

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE?

A. The Concept of Cycles multiannual fluctuations that occur

with some regularity (periodicity)

CYCLE CHARACTERISTICSCYCLE CHARACTERISTICS

Time

Ab

un

dan

ce

IncreasePhase

Peak Phase

Decline Phase

LowPhase

MORE CHARACTERISTICS MORE CHARACTERISTICS OF CYCLESOF CYCLES

Regional synchrony in fluctuations of coexisting species,

Summer crashes in abundance A gradual disappearance of cycles

southward

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE?

B. Cycles and Body Size Biological times scale as :

nerve conduction time cardiac cycle time respiratory cycle time generation time lifespan

1 4W

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE? B. Cycles and Body Size

Mass (kg)

10-2 10-1 100 101 102 103 104

Cyc

le L

eng

th (

yrs)

100

101

102

Cycle = 8.15M0.26

Source: Peterson et al. (1984, Science 224:1350-1352)

n = 40 species

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE?

D. Longer-Period Cycles: Hares period of 9-10 years amplitude of 15-200 fold

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE?D. Longer-Period Cycles: Hares

period of 9-10 years amplitude of 15-200 fold

Year

1865 1875 1885 1895 1905

Nu

mb

er

of

Ha

res

0

25000

50000

75000

100000

125000

150000 period

am

pli

tud

e

I. WHAT IS A CYCLE?I. WHAT IS A CYCLE?

D. Longer-Period Cycles: Hares Coincident

cyclic speciesanimaldiversity.ummz.umich.edu

www.aquatic.uoguelph.ca

www.arttoday.com

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

Archbishop Olaus Magnus and Lemmings

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

Archbishop Olaus Magnus and Lemmings

Intrinsic Versus Extrinsic factors

Some Theories

1) Chitty’s Hypothesis- NS

2) Social Fence Hypothesis - Social behavior

Time

Ab

un

da

nc

e

IncreasePhase

Peak Phase

Decline Phase

LowPhase

Pop Size increases

Competition increases: tolerants stay but low fertility

Pop size decreasing = emmigration & fertility

Animals spaced out & competition reduced

Some Theories

3) Climate- indirect/direct

Some Theories

4) Nodal Lunar Cycles & Sun Spots- 9.3 yr phase of moon = full moon during spring breeding

- 11 yr periodicity on sun spots

Some Theories

Some Theories

5) Trophic-Level Interactions* plant-herbivore* predator-prey* parasite-host* seasonality* predator switching

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

A. Increase Phase high fertility rate low mortality rate young age structure large litters early age at first reproduction few predators

Time

Ab

un

da

nc

e

IncreasePhase

Peak Phase

Decline Phase

LowPhase

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

B. Peak Phase fertility rate declines hares: decline in quality and

quantity of food

Time

Ab

un

dan

ceIncreasePhase

Peak Phase

Decline Phase

LowPhase

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

B. Peak Phase fertility rate declines voles and lemmings: social

factors

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline Phase low fertility rates high mortality rates old age structure

Time

Ab

un

da

nc

e

IncreasePhase

Peak Phase

Decline Phase

LowPhase

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline Phase Role of food quality

Proteinase inhibitors common plant toxin pancreatic enlargement build up during peak and year

1 decline phase

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

Proteinase inhibitors could cause: drastic declines in herbivore density changes in body size and organ

mass the high degree of synchrony in

fluctuations

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline Phase Role of food quality

Reversion to juvenility woody plants and winter

browsing by hares juvenile defenses time lags of 2-3 years

Winter Dormant Twigs of Alaska Paper Birch Winter Dormant Twigs of Alaska Paper Birch

(B. neoalaskana)(B. neoalaskana)Mature Stage

Juvenile Stage

Note Resin Glands

Note Catkin And The Lack Of Resin Glands

Resin Gland on Current Year Twig Resin Gland on Current Year Twig InternodeInternode

Results ofResults of B. neoalaskana B. neoalaskana Mature Vs. Juvenile Feeding Mature Vs. Juvenile Feeding TrialTrial

Mature Stage Twigs

Juvenile Stage Twigs

Note That These Twigs Do Not Have Catkins At Their Tip.

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline Phase Role of predators

Direct effects on vital rates

Pro

po

rtio

n S

urv

ivin

g

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Source: Krebs (1996, J. Mammal. 77:8-24)

June July August

Predator exclosure

Lemmingcontrols

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline Phase: Role of Predators

Direct effects on vital rates

voles and buffer prey buffer prey promote

stability

www.abdn.ac.uk

II. A GENERAL THEORY OF POPULATION CYCLES

– Indirect effects of Indirect effects of predatorspredators

– Example: Bank VoleExample: Bank Vole

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

Indirect effects of predators

% Bank Voles in Diet

0 10 20 30 40 50 60

An

tip

red

ato

r R

es

po

ns

es

0

1

2

3

4

Source: Ylonen (1994, TREE 9:426-430)

Raccoondog

PolecatRed fox

Marten

Stoat

Weasel

www.abdn.ac.uk

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

Indirect effects of predators diurnal raptors and indoor plumbing by

lemmings birds of prey detect UV light tundra = vulnerable lemmings underground latrines in summer

www.goals.com

European kestrel

Collared lemming

II. A GENERAL THEORY OF II. A GENERAL THEORY OF POPULATION CYCLESPOPULATION CYCLES

C. Decline and Low Phase Interaction of Food and Predators

>2-3x when food added or predators removed

>11x when food added and predators removed