Predator-Prey Cycles

Control of Population Size

Charles Elton

(on the right)

Studied living organisms in relation to their natural environment, or ECOLOGY

He began his studies in Oxford in the 1920s and died in 1991

Lynx

In Canada in the early 1900s, Lynx and hares were both killed for their pelts

Elton saw graphs of the annual fur returns of the Hudson’s Bay Fur Trading Company

He noticed regular 10 year cycles of lynx and hare skins being collected

Young Lynx

Elton was made Biological Consultant to the Hudson’s Bay Fur Company

There he examined records of Canada Lynx (numbers caught) back to 1736 (300 years)

His results were published in 1942

Lynx cycle lags behind hare by 1-2 yrs.

Why?

Snowshoe Hare

What is the cause of these population changes?

When hare numbers increase, 2 things happen:

1. Shortage of food for hares 2. Increase in Lynx number (predation)

Lynx numbers increase when Hare numbers high, but if food for hares is low and predation is high……………………..

…………soon the Hare population will crash (drop).

(1) Some Lynxes leave (emigrate) to where food is more plentiful.

(2) Lynxes eat other prey when hare numbers low.

(3) More competition between Lynxes.

A CRASH in the Lynx population

This drop in Hare numbers leads to 3 things …

Lower Hare numbers – vegetation starts to grow again

+ Hares have fewer Lynx to watch out for

+ There is more vegetation to eat

SO, the number of Hares begins to increase

The PREDATOR PREY cycle begins again

MEANWHILE…..

Highest peaks always belong to PREY

Why?