Ecology

1. Ecology Population Growth

2. Population Growth • 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

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

4. 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?

5. Carrying Capacity

6. Carrying Capacity The largest # of individuals an environment can support

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

8. 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

9. Logistic Growth Occurs when resources become less available (Slows population growth rate) Slow population growth rate due to • Decrease in birthrate • Increase in deathrate • Immigration decreases • Emigration increases

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

12. Density Dependent Limiting Factors • Predation • Just about every species serves as food for some other species • Predators vs. Prey

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

14. Poison

15. Batesian mimicry • Monarch butterfly or viceroy butterfly?

16. Mertensian mimicry (Warning coloration) • Coral snake or King snake?

18. Camouflage in nature Industrial melanism of the peppered moth

19. Shells as Defense

20. Slime as Defense

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

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

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

25. Density Dependent Limiting Factors • 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 • Make Love Not War

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

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

28. Why Competition? Limited resources • Food • Water • Space • Shelter • Mates • Sunlight

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

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

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

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

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

37. Human Population Growth • 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

42. Demography The scientific study of human populations • Birthrates • Deathrates • Age structure

43. U.S. Age Distribution

44. South Africa Age Distribution

45. South Africa and U.S.