2. Ecology Population Growth

3. –Any organism provided ideal growing conditions will experience rapid population growth –Larger it gets, faster it grows – exponential growth curve –Darwin calculated if all the offspring of 1 pair of elephants were to survive and reproduce, after 750 yrs there would be 19 million elephants

4. Why doesn’t exponential growth happen for long? n Sooner or later, you will run out of resources. n Competition for resources –deer population for example

5. Logistic Growth –Lets introduce a few animals to a new environment –at first the population begins to grow slowly –Soon the population grows rapidly –few die, many produced –Population growth begins to slow – growing still, but slower – why is this happening?

6. Carrying Capacity

7. The largest # of individuals an environment can support

8. Logistic Growth –When birthrate and deathrate are equal, population growth stops –Steady state – population size stays the same (averages out)

9. Logistic Growth –Draw a line through the middle of steady state – carrying capacity –Carrying capacity is the average of the steady state –Factors at this point keep the population from getting any bigger – food, overcrowding, competition

10. Logistic Growth Occurs when resources become less available (Slows population growth rate) Slow population growth rate due to 1. Decrease in birthrate 2. Increase in deathrate 3. Immigration decreases 4. Emigration increases

12. Density Dependent Limiting Factors –factors that control population size operate more strongly on large populations than small ones –Competition, predation, parasitism, and crowding n Competition –struggle for food, water, & space

13. Density Dependent Limiting Factors n Predation –Just about every species serves as food for some other species –Predators vs. Prey

14. Density Dependent Limiting Factors n Prey – defenses –Poison chemicals –Shells –Poison skins –Camouflage –Behaviors such as mimicry

15. Poison n

16. Batesian mimicry n Monarch butterfly or viceroy butterfly?

17. Mertensian mimicry (Warning coloration) n Coral snake or King snake?

19. Camouflage in nature Industrial melanism of the peppered moth

20. Shells as Defense

21. Slime as Defense

22. Limiting Factors n Growth of many species is controlled by density dependent and density independent limiting factors.

23. Density Dependent Limiting Factors n Counterdefenses –Monarch butterfly caterpillars have evolved the ability to avoid certain plant poisons –Predator population varies with prey population n Large # of prey = large # predators = small # prey

24. Density Dependent Limiting Factors n Symbiosis means living together –Parasitism – one benefits, one is hurt  –Commensalism – one benefits, one not affected  –Mutualism - both benefit –Mutualism - both benefit

26. Density Dependent Limiting Factors n Crowding and Stress –crowding helps parasites travel from host to host –Most animals have built in need for certain amount of space – hunting, nesting, territory (fish for example) –Increase fighting = decrease breeding n Make Love Not War

27. Limits to population growth Limiting Factor – causes population growth to decrease Limiting Factor – causes population growth to decrease Density Dependent Limiting Factors Density Dependent Limiting Factors Factors which work best with a large dense population Factors which work best with a large dense population n Interspecific competition n Intraspecific competition n Predation n Disease n Parasitism Density Independent Limiting Factors Density Independent Limiting Factors n Tornado, hurricane, drought, temperature n Human disturbance (Clear-cutting forests or damming rivers)

28. Competition Competitive exclusion principle Competitive exclusion principle n No two species can occupy the same niche in the same habitat at the same time n Interspecific competition occurs between two species for similar resources n Intraspecific competition occurs within a species for similar resources

29. Why Competition? Limited resources Limited resources n Food n Water n Space n Shelter n Mates n Sunlight

31. Predation Prey have evolved defense mechanisms to prevent predation n Poison (Monarch butterflies & Dart frogs) n Mimicry n Camouflage n Shells n Slime

32. Density Independent Limiting Factors n Because population size does not matter in these instances, these natural occurances are called density- independent limiting factors.

33. Density Independent Limiting Factors n Long hot dry weather n Frosts n Happen regardless of how large the population is

34. Density Independent Limiting Factors n Boom and Bust Growth Curves –Populations grow exponentially then crash, then back again n Aphids feed on plant buds that can be washed away in a rain storm

37. Human Population Growth Exponential growth due to: Exponential growth due to: n Agriculture n Industry n Better healthcare / medicine n Reduced death rate n High birth rate

38. Human Population Growth n Human populations tend to increase over time –About 500 years ago, human population began growing exponentially. –Today, it has slowed in the US and parts of Europe, but not in most of the rest of the world –China, India, Africa, and Latin America

43. Demography The scientific study of human populations n Birthrates n Deathrates n Age structure

44. U.S. Age Distribution

45. South Africa Age Distribution

46. South Africa and U.S.