Organisms live as members of populations Population size Population density Population dispersal How do populations grow

1. Organisms live as members of populations Population size Population density Population dispersal How do populations grow?

2. Exponential growth

3. Exponential growth growth without limits at a maximal rate (biotic potential) Actual growth rate: difference between birth and death rates, corrected for migration

4. Effect of death rates on population growth

5. Some species show a very high rate of population growth (exponential) reproduce at early age produce a lot of offspring life span is short “r-selected adaptations” for organisms with that type of life history (and which don’t consume a lot of resources and where resources are not limiting)

6. Populations have innate capacity for exponential growth Usually this is temporary, until carrying capacity is reached. What sorts of things limit population growth?

7. Most populations are affected by limitations in their environment “logistic growth model”: growth is rapid (exponential) for awhile then tapers off

8. Logistic growth model

9. Many species are adapted for life at or near carrying capacity (K-selected) Compete for resources Reproduce late in life Have few offspring-and care for the offspring they have Tend to live long lives and have low mortality rate (low birth rate balanced by low death rate)

10. Life histories

11. At carrying capacity, birth rate is equal to the death rate What sorts of factors affect population growth? Density-dependent factors: increasing density limits availability of resources for all Limited food supply Waste accumulation (toxicity)

12. Density-independent factors independent of population size but do affect its growth Weather (can contribute to population cycles) Natural disasters

13. Reindeer introduced to a small island, 1911

14. “boom and bust” cycles

15. Seen in populations of insects, birds and mammals (e.g., lemmings and other rodents) Predation? Food supply? Overcrowdingstress hormone imbalance and infertility?

16. How predators control prey population As prey population increases, more opportunities for predators. As predators switch to alternatives, original prey can recover. Predators remove weaker prey. Parasites weaken prey

17. Competition within a community Interspecies Intraspecies Competition for what? Food, water, space, breeding sites, shelter, light…

18. Introduced species can upset the whole balance of activity Snails Starlings Kudzu Zebra mussels Prickly pear cacti in Australia- a predatory cactus moth was introduced to control the cacti!

19. Structure of populations Density Dispersion- how organisms are grouped in their geographical range

21. Clumped pattern Most common in nature Unequal distribution of resources Social behavior mating safety in numbers

23. Uniform distribution Often results because of interactions between individuals in the population (to deal with scarce resources) Creosote bushes in the desert- roots compete for water and nutrients Nesting penguin pairs (on islands)

25. Random- no pattern no factors contribute to attraction or repulsion between individuals Rare, but could occur when there are no pressures due to environment Exhibited mainly by plants (why?) What kind of dispersion is shown by humans?

26. Demographics- statistical methods for analyzing populations Cohorts- age groups- birth and death rates populations with many young members tend to grow faster Sex ratio- proportion of males to females effect depends on mating practices

27. Community interactions Community- all the interacting populations within an ecosystem Interactions tend to maintain balance between resources and consumers Populations act as agents of natural selection (e.g. predator-prey) Over time- coevolution

28. Major types of community interactions Competition (harms both) Predation (benefits predator, harms prey) Symbiosis parasitism (helps one, harms the other) mutualism (helps both) commensalism (helps one, no effect on the other)

29. Competition: how much do ecological niches overlap? In plain English: ecological niche is everything an organism needs to survive No two species occupy exactly the same niche, although some aspects of a niche may be shared

30. Competitive exclusion One survives, the other dies

31. Resource partitioning Minimizes niche overlap

32. Remember Darwin’s finches? Finches had evolved different beak shapes and feeding behaviors that minimized competition among them

33. Members of species, or closely related species, compete for limited resources Two species of barnacles that live in intertidal zone One species (A) dominates the upper zone The other (B) predominates in the lower (wetter) zone) When the lower species is removed, the upper species spreads into the area

34. Conclusion: B outcompetes A (A can’t grow in the lower region unless B is removed) However, A has an advantage on the upper shore because it can tolerate low tide (studies of Connell et al.)

35. Predator-prey interactions Prey usually outnumber predators Herbivores “prey” on plants Predators and prey exert a lot of pressure on each other: Prey evolve to become more difficult to catch Predators evolve to become better hunters

36. Behaviors evolved by predators and prey I. Camouflage (by both)

37. Where is the sand dab?

38. Where is the Belize nightjar?

39. Resembling an “uninteresting” object

40. Suited for ambush

41. Warning coloration- approach at your own risk

42. Mimicry Coral snake (poisonous) King snake (harmless)

43. Both of these butterflies taste bad monarch viceroy

44. Startle coloration

46. Snowberry fly mimics the spider

47. Chemical warfare: beetle releases toxin

48. Monarch caterpillar feeding on milkweed

49. Monarch butterfly has adapted to milkweed (a toxic plant) Lays eggs on milkweed Larvae feed on milkweed Caterpillars store toxin in their own tissues as defense against predators!

50. Even grasses and their consumers have coevolved Grasses have tougher consistency Herbivores evolved teeth for grinding