1. Population Biology

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

3. Review
Community: a group of interacting plants and animals forming an identifiable group
Organisms of different species interacting together

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

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

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

7. Population Size Calculations
Growth rate (gr) is involve changes in populations (N) over a time period (t) in a defined space.
gr= N/ t

8. Ex) What is the growth rate?
Initial Population 200
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
Time 1 year
Total
So gr= ( )/1
Annual growth rate increase of +40 birds per year

9. 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
(D= 200bison/100acres)

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

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

12. Factors that cause populations to change
A) Density independent factor: affect a population regardless of size
Ex. Climate, oxygen, natural disasters, etc
b) Density dependent factors: affect a population only if it’s a big population
Ex) food, space, parasitism

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 (per capita growth rate)
A lynx population was 19 per sq. km in In 1993 it was 3 per sq. km. What was the cgr of this population from 1991 to 1993?
Cgr = N/ N
= -16 / 19
= 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 (sigmoid curve) (logistic growth curve)

20. Closed Populations True closed populations are rare
On islands, isolated communities
Often show a J-shaped curve (exponential growth)
Ex. Mesocosm (aquariums terrariums)

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 realistic 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, usually not achieved naturally due to environmental factors (lack of food, space, and mates, predation, climate, etc)
Biotic potential is determined by:
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. (r-selected 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 ResistanceB K

33. Environmental Resistance

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 cant remain in competition for a limited resource (always a winner, and a loser!)
-Interspecific competition: competition between 2 or more different species
-Intraspecific competition: competition between 2 or more of the same species

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 and aging individuals
Low reproduction rate (B)
Low number of offspring
Long wait period before breeding
Parental care of offspring
Tend to be Big organisms
Ex. Bears, humans, elephants

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
Produce a lot of offspring
Short wait period between breeding
Little or no parental care
Ex. Fish, rabbits, frogs

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 and predict the general trends in populations
This theory suggest that small uncertainties in short-term prediction of individual events may be magnified to such an extent that complex systems become quite unpredictable (‘Butterfly Effect’)
Chaos is normal!

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. Symbiotic Relationships
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

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.