1. Population Growth Curves and Mechanisms

3. Species and Population
Organism
Species: genetically similar organisms that reproduce
Population: all members of a species in an area

4. Characteristics of populations:
Same species living in same area

5. Age structure:
Prereproductive
Reproductive
Postreproductive

6. What limits population growth?

7. Biotic Potential
vs.
Environmental Resistance

8. Biotic Potential an organism’s maximum reproductive rate, provided:
unlimited resources are available (food, water, shelter, etc.)
freedom from inhibiting factors (no predators or disease, etc.)
Cunningham, Cunningham and Saigo, “Environmental Science, 8th ed.” McGraw Hill, Table 6.2

9. Biotic potential – capacity for growth
Intrinsic rate of increase (r)

11. Environmental Resistance –
Biotic and Abiotic factors limiting population size

14. Recruitment - ability to survive environmental resistance and become part of the breeding population

15. Reproductive strategies
High biotic potential and low recruitment
Low biotic potential and high recruitment

16. r - strategists
K – strategists

17. Transparency

18. R strategists:
Many small offspring
Little /no parental care
Early reproductive age
Most offspring die
Small adults
High growth rate (r)
Population fluctuates wildly above and below carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species

20. K strategists:
Fewer, larger offspring
High parental care
Later reproductive age
Larger adults
Lower population growth rate (r)
Population size fairly stable and close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species

21. Growth Curve - Result of biotic potential and environmental resistance.

22. Exponential growth -
(J-curve) before environmental resistance factors kick in to reduce population size

23. Population explosion

26. Logistic growth -
(S - curve) Balance between environmental resistance and biotic potential

29. Carrying Capacity -
The maximum population a habitat can support without being degraded over the long term.

30. Carrying Capacity Population Size maximum # individuals
Time
maximum # individuals
of a given species that the
environment can support
Cunningham, Cunningham and Saigo, “Environmental Science, 8th ed.” McGraw Hill, Fig. 6.4

31. Carrying Capacity maximum # individuals of a given species that the
environment can support
J-curve
Cunningham, Cunningham and Saigo, “Environmental Science, 8th ed.” McGraw Hill, Fig. 6.4

32. Critical number – minimum population required to provide protection and support for members of population

34. Calculating Fertility Rates and Doubling Times
(CBR - CDR)/10 = Rate of Increase in percentage
To get r (intrinsic growth rate), divide by 100
70/ Rate of Increase = Doubling Time

35. A population had a growth rate of 1. 7 in 2000
A population had a growth rate of 1.7 in In what year would the population be double its current population?

36. 70 / 1.7 = 41 years
= 2041

37. Calculating Fertility Rates and Doubling Times: Practice

38. Threatened – species whose populations are declining rapidly
Endangered – population is near the critical number

39. Mechanisms of population equilibrium:

40. Predator – prey dynamics

41. Snowshoe hare
Cunningham, Cunningham and Saigo, “Environmental Science, 8th ed.” McGraw Hill, Fig. 6.9

44. Predator-prey Balance:Wolves and Moose

45. Isle Royale

46. Isle Royale As Wolves decreased Moose increased.
As Wolves increased the Moose decreased.
Wolves kept the Moose population stabilized until canine parvovirus probably killed off large #’s of Wolves.
Moose prospered until overgrazing of Ash and Aspen caused mass death.

47. Plant Herbivore dynamics:
Herbivores are the natural enemies of plants
Overgrazing

48. Mechanisms of Population Equilibrium: Plant-Herbivore

49. Introduced Species: Rabbits in Australia
Introduced into Australia from England in 1859
No natural enemies – rabbit population exploded
Overabundant herbivore population devastated natural vegetation (see Fig in text).
Using disease as control measure – why will this procedure fail in the long term?

50. Eliminating predators upsets basic plant – herbivore relationships.

51. Competition
Interspecific
Intraspecific

52. Density dependent factors affecting population growth:
Increasing effect as population increases
Examples
Competition
Disease
Parasites
Stress due to crowding

53. Density independent factors controlling population:
affect all populations, regardless of density
Most are abiotic
Forest fires
Floods