2. Population Biology

3. Definition A population is a group of organisms of the same species, interbreeding or closely related through interbreeding and evolving as a unit.

4. Review Community: a group of interacting plants and animals forming an identifiable group

5. Review Biosphere: the entire part of the earth where organisms are found

6. Review Habitat: the place where an organism naturally lives or grows

7. Review Niche: position or function of an organism in its community – its occupation

8. Population Size Calculations Simplest calculations involve changes in populations over a time period in a defined space. gr= N/ t

9. Ex) What is the growth rate? Initial Population200 20 gulls move in (immigration) 20 0 gulls move out (emigration) 0 32 chicks hatch (natality) 32 10 chicks die-10 2 adults die -2 Time1 year Total240 Annual Increase of +40 birds per year

10. Density Formula: D = N/A or N/V Density equals number of organisms divided by area (or volume or space) Eg. 200 bison in a 100 acre pasture is a density of 2 bison per acre

11. Rate of Change Often uses density R = D / t Rate of density change equals change in density over change in time.

12. Example In 1996 there were 10 Grizzly Bears in a 10 000 ha forest. In 2005 there are only 8. What is the rate of density change? R = D / t R = 0.0008 – 0.001 / 2005 – 1996 R= - 0.0000222 bears/ha/y

13. Per Capita Growth Rate Or cgr The amount that a population changes per individual over a set period of time Cgr = N / N Per capita growth rate = change in number divided by initial population size

14. CGR A lynx population was 19 per 10 000 sq. km in 1991. In 1993 it was 3 per 10 000 sq. km. What was the cgr of this population from 1991 to 1993? Cgr = N/ N = -16 / 19 = - 0.84 per lynx

15. Distributions of Populations Can be clumped – more individuals together than apart Often involves cooperation among group members (eg. Herd, pack)

16. Distribution of Populations Can be random – not seen often in nature Organisms have no effect on each other

17. Distribution of Populations Can be uniform: evenly distributed Usually due to competition between individuals Territories, etc.

19. Open Populations Are those where organism can enter or leave Often have S-shaped curves

20. Closed Populations True closed populations are rare On islands, isolated communities

21. Population Growth Graphs typically have numbers on vertical axis and time on horizontal axis

22. Logistic Growth S shaped curves are typical of stable populations.

23. Eg. Wild Horses on reserve land in AB

24. Exponential Growth J shaped curve (initially) occurs with short-lived populations that rapidly deplete their environment

25. Eg. Flies on a carcass

26. Overshoots Result when k is greatly exceeded and the environment deteriorates

27. Carrying Capacity Is the number of organisms a habitat can sustain over the long term “k” Influenced by Biotic Potential and Environmental Resistance

28. Biotic Potential maximum number of offspring produced capacity of offspring to survive to reproduce number of times per year an organism reproduces age at which offspring are reproductively mature

29. Generally speaking, smaller, simpler organisms have a higher biotic potential than larger organisms.

30. Environmental Resistance limiting factors on a population Availability of resources (food, water, space, etc.) Competition for resources with other organisms Intra-specific – within a species Inter-specific – between a species Predators Disease Climate change

31. Environmental Resistance Puts brakes on biotic potential (B) – maximum reproductive rate

32. Environmental Resistance B K

34. Limiting Factors on Populations Law of the Minimum: if any one of many needed nutrients/limiting factors is reduced below the required levels, the population growth rate declines

35. Limiting Factors Can be density independent – those that will affect a population regardless of its size Eg. Cold winter

36. Limiting Factors Can be density dependant – those that increase when the population size increases Eg. Disease Predation Food Supply

37. Gause’s Law Competitive exclusion No two species can remain in competition for a limited resource

38. Other Graphs Survivorship curves

39. Other Graphs Age distribution pyramids

40. Population Histograms are graphs showing the composition by age and gender of a population at a specific time. Population histograms have the following characteristic shapes:

41. R and K Population Strategies This is a continuum Most populations fall between these two extremes

42. K Selection k-selected species is one that typically has: Stable environmental conditions Slow growing individuals Low reproduction rate (B) Parental care of offspring

43. R- Selection An R-selected species is one that typically has: Unpredictable environment Small individuals with short life spans Reproduce at a high rate Little or no parental care

44. Life History Patterns Some organisms undergo regular patterns of growth and decline known as population cycles Small rodents, rabbits, lemmings often cycle every 1 – 4 years

45. Population Cycles Can be due to fluctuations in food supply, predation, or both

46. Predator - Prey Cycles

47. Chaos Theory Used by population biologists to study the general trends in populations Small uncertainties in short-term prediction of individual events may be magnified to such an extent that complex systems become quite unpredictable

48. Chaos The ‘butterfly effect” This is the sensitivity of a system to the initial conditions Change any starting parameter slightly and the resulting changes magnify until the result is very different from the initial prediction

49. Technologies Include: Radio collars

50. Technologies Sampling methods Quadrats – counting organisms in defined areas

51. Transects – counting organisms that touch line

52. Technologies Mark/recapture studies

53. Symbiosis – a relationship between two individuals of different species. Parasitism – one species lives in or on another where it obtains food and resources. The host is usually harmed by the relationship. Ex. Tapeworm Symbiotic Relationships

54. Many parasites are r-selected Eg. Tapeworm

55. Commensalism – one species lives on or near another, but while one species benefits, the other is unaffected.

56. Mutualism – two species that live in close association with one another, where both benefit from the relationship. Ex. honeybee and flower Ex. shark and remora

58. Ecological Succession Ecological succession – is the gradual and orderly change of a community as it is either developed from bare land or replaced by another community.

59. Succession Primary Succession – the gradual colonization of an area that has not supported an ecosystem before. (from bare rock) PrimarySuccession

60. Secondary Succession – the colonization of an area that once supported an ecosystem that was destroyed by fire, flood, etc. Exploring Time Gallery Display

62. Pioneer Community – is the first species to appear during succession. Climax Community – is the final stable community that results at the end of succession.

63. Generalizations about Succession: Species composition changes more quickly at earlier stages. Total number of species increases dramatically at early stages, levels off at intermediate phases and declines at the climax stage. Food webs develop in complexity as succession progresses. Total biomass increases during succession and levels off at the climax stage.