1. Predator-Prey Cycles Control of Population Size

2. 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

3. Lynx

4.  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

5. Young Lynx

6. 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

7. Lynx cycle lags behind hare by 1-2 yrs. Why?

8. Snowshoe Hare

9. 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)

10. 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).

11. (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 …

12. 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…..

13. Highest peaks always belong to PREY Why?