Ch. 8 Understanding populations

1. Ch. 8 Understanding populations

2. Which of the following is a population? • Green sea turtles nesting on a beach • A flock of cardinals, geese, flamingos, and sparrows • Aquatic insects in the Coosa River • A population is all the members of a species living in the same place at the same time.

3. Properties of populations • Size = # of individuals • Density = # of individuals/area • Dispersion - How members of a population are spread in space Regular Random Clumped

7. How does a population grow? • What adds to a population? • Births • Immigration • What subtracts from a population? • Deaths • Emigration • Change in population size = (B+I)-(D+E)

8. EXAMPLES/PRACTICE • All numbers are per 1,000 people: • e.g. 6 births per 1,000 people would give a birth rate = 6/1,000 • Why report births per thousand?

9. How fast can a population grow? • Fastest rate possible = biotic potential • Which has greatest biotic potential? • Humans or fruit flies? • Fruit flies • Humans or sparrows? • sparrows • Humans or sea turtles? • Sea turtles • In general, the more offspring an organism can have at one time, the greater its biotic potential.

10. How fast can a population grow? • Organisms with high biotic potential: • Tend to: • Be small • Produce lots of offspring at one time • Have short generation times • Become sexually mature early

11. Populations sometimes grow exponentially • Simply put: a population that grows at a fixed percentage each year. • = constant rate

12. Example of exponential growth • Money in an account earning a fixed rate of interest. e.g. $100 invested at 5% interest: • Year balance change (from previous year) 1 100 -- 2 105 5 3 110.25 5.25 4 115.76 5.51 5 121.55 5.79 6 127.63 6.08 7 134.01 6.38 8 140.71 6.70 9 147.75 7.04 10 155.13 7.38 15 197.99 20 252.70 21 265.33 12.63

13. Human population growth year =1 billion

14. What limits population growth? • Populations don’t grow exponentially forever. • Why not? LIMITING FACTORS • = Limiting resources: one or more natural resources that are not abundant enough to support continued growth.

15. Populations have a carrying capacity • Carrying capacity is the size of a population that can be sustained over time.

16. Populations are regulated in 2 ways • Density dependent: when deaths of population members are more common in a crowded population than in a sparse population. • Density independent: when deaths are equally likely in a crowded or sparse population.

17. How species interaction with each other • 5 main kinds • Competition -/- • Predation +/- • Parasitism +/- • Mutualism +/+ • Commensalism +/0

18. Competition • What is it? • Different individuals attempt to use the same limiting resource(s) • Such as: • Food • Water • Shelter • Mates • Nesting sites

19. Competition • KEY POINT: Both individuals harmed in competition, because both have reduced access to a limiting resource, even if one individual ultimately gets the resource. • 2nd key point: Competition can be both within and between species • When members of different species compete, we say that their niches overlap.

20. Competition • Competition can be indirect • Two individuals might never come in contact with each other and still compete • Examples?

21. Competition • KEY POINT: The more similar species are in their niches, the greater the competition between them. • To avoid competition, species sometimes shift their niche

22. Predation • One organism feeds upon another, and kills it. • Specialists vs generalists • Specialist examples? Lynx eats mostly snowshoe hares • Generalist examples? Praying mantises and spiders both eat any vulnerable insect

23. Predation • Specialists

24. PredationGeneralists Above: praying mantis Right: crab spider Both: sit-and-wait predators. Eat whatever comes along that they can catch.

25. Predation • Prey may adapt to better avoid predation. • Predators may adapt to better catch prey.

26. Predation • Prey adaptations • Camouflage • Thorns (physical defense) • Speed • Bad taste/poison (chemical defense)

27. Predation

28. Parasitism • Like predation, is +/- • BUT, unlike predation, parasite doesn’t kill host. • Why not?

29. Parasitism • Parasites may be • Internal: e.g., round worms, bacteria,, protozoan insect larvae • External: e.g., ticks

30. Parasitism • Schistosomiasis is disease caused by parasitic blood flukes

31. Parasitism • Special case: parasitoid • Usually a wasp or fly that lays an egg in an insect host, which eventually kills the host

33. Mutualism When two species benefit each other • +/+ interaction • Sometimes, the two species (or one of them, at least) can’t live without the other. • One example: bacteria in our guts (they can’t live without us; we might get ill or lose weight without them)

34. Mutualism • Ant-acacia in Central America • Many acacias have chemical defenses • Some don’t, and these have evolved a mutualistic relationship with stinging ants, which live inside the thorns • Ants defend the tree against herbivores; tree provides food

35. Commensalism • One species benefits • NO EFFECT on the other species

36. Commensalism • Examples • Cows and Cattle egrets • Sharks and remoras

37. Symbiosis and Coevolution • A relationship in which two organisms live in close association is called symbiosis. • Examples: Honey bees and flowering plants • Over time, these two organisms may evolve adaptations that reduce the harm or improve the benefit of the relationship.