POPULATION CYCLES

I. WHAT IS A CYCLE? A. The Concept of Cycles u multiannual fluctuations that occur with some regularity (periodicity)

CYCLE CHARACTERISTICS

MORE CHARACTERISTICS OF CYCLES u Regional synchrony in fluctuations of coexisting species, u Summer crashes in abundance u A gradual disappearance of cycles southward

I. WHAT IS A CYCLE? B. Cycles and Body Size u Biological times scale as : u nerve conduction time u cardiac cycle time u respiratory cycle time u generation time u lifespan

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

I. WHAT IS A CYCLE? D. Longer-Period Cycles: Hares u period of 9-10 years u amplitude of fold

I. WHAT IS A CYCLE? D. Longer-Period Cycles: Hares u period of 9-10 years u amplitude of fold

I. WHAT IS A CYCLE? D. Longer-Period Cycles: Hares u Coincident cyclic species animaldiversity.ummz.umich.edu

II. A GENERAL THEORY OF POPULATION CYCLES u Archbishop Olaus Magnus and Lemmings

II. A GENERAL THEORY OF POPULATION CYCLES u Archbishop Olaus Magnus and Lemmings u Intrinsic Versus Extrinsic factors

Some Theories 1) Chitty’s Hypothesis - NS 2) Social Fence Hypothesis - Social behavior

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 yr phase of moon = full moon during spring breeding - 11 yr periodicity on sun spots

Some Theories

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

II. A GENERAL THEORY OF POPULATION CYCLES A. Increase Phase u high fertility rate u low mortality rate u young age structure u large litters u early age at first reproduction u few predators

II. A GENERAL THEORY OF POPULATION CYCLES B. Peak Phase u fertility rate declines u hares: decline in quality and quantity of food

II. A GENERAL THEORY OF POPULATION CYCLES B. Peak Phase u fertility rate declines u voles and lemmings: social factors

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline Phase u low fertility rates u high mortality rates u old age structure

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline Phase  Role of food quality u Proteinase inhibitors u common plant toxin u pancreatic enlargement u build up during peak and year 1 decline phase

II. A GENERAL THEORY OF POPULATION CYCLES u Proteinase inhibitors could cause: u drastic declines in herbivore density u changes in body size and organ mass u the high degree of synchrony in fluctuations

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline Phase u Role of food quality u Reversion to juvenility u woody plants and winter browsing by hares u juvenile defenses u time lags of 2-3 years

Winter Dormant Twigs of Alaska Paper Birch (B. neoalaskana) Mature Stage Juvenile Stage Note Resin Glands Note Catkin And The Lack Of Resin Glands

Resin Gland on Current Year Twig Internode

Results of B. neoalaskana Mature Vs. Juvenile Feeding Trial Mature Stage Twigs Juvenile Stage Twigs Note That These Twigs Do Not Have Catkins At Their Tip.

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline Phase u Role of predators u Direct effects on vital rates

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline Phase: Role of Predators u Direct effects on vital rates u voles and buffer prey u buffer prey promote stability

II. A GENERAL THEORY OF POPULATION CYCLES –Indirect effects of predators –Example: Bank Vole

II. A GENERAL THEORY OF POPULATION CYCLES u Indirect effects of predators

II. A GENERAL THEORY OF POPULATION CYCLES  Indirect effects of predators u diurnal raptors and indoor plumbing by lemmings u birds of prey detect UV light u tundra = vulnerable lemmings u underground latrines in summer European kestrel Collared lemming

II. A GENERAL THEORY OF POPULATION CYCLES C. Decline and Low Phase u Interaction of Food and Predators u >2-3x when food added or predators removed u >11x when food added and predators removed