1. Population Dynamics Chapter 6 Populations
AP Environmental Science
GNHS

2. 4 types of Population Fluxes
Population flux – changes in pops over
time.
Advantage: Allows vegetation and organism reproduction time to recover
Types: 1) stable 3) irregular
2) irruptive 4) cyclic

3. Stable Pop Flux Pop fluctuates around carrying capacity
either slightly above or below
Typical of species in undisturbed tropical forests…little variation in average temp or rainfall.

4. Stable Pop Flux Example

5. Irruptive Pop Flux
Pop is normally stable but occasionally explodes (erupts) to peak and then crashes to stable lower level.
Ex: Racoon, house mouse

6. Irruptive Pop Flux

7. Irregular Pop Flux Chaotic behavior in population size
No recurring pattern
May be due to: chaos in ecosystem

8. Cyclic Pop Flux
Fluctuations in size that occur over a regular time period. Includes predator-prey (lynx and hare)

10. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

11. Characteristics of a Population
Population - individuals inhabiting the same area at the same time and can interbreed.
Population Dynamics: Population change due to
Population Size - number of individuals
Population Density - population size in a certain space at a given time
Population Dispersion - spatial pattern in habitat
Age Structure - proportion of individuals in each age group in population

12. Population Size Natality Mortality
Number of individuals added through reproduction
Crude Birth Rate - Births per 1000
Total Fertility Rate – Average number of children born alive per woman in her lifetime
Mortality
Number of individuals removed through death
Crude Death Rate Deaths per 1000

13. Population Growth Populations show two types of growth Exponential
J-shaped curve
Growth is independent of population density
Logistic
S-shaped curve
Growth is not independent of population density

14. Population Growth – “Mathway”
Benefits:
Prediction of future generations
Creation of population trends
Assists in determining type of growth:
exponential or logistics

15. Population Growth - Mathway
Basic variables of population growth N=population number r = rate of growth t = Time in days, months, years, generations d = ‘delta” or change in (ex. dN = change in population) K = carrying capacity

16. Zero Population Growth
Population growth depends upon
birth rates
death rates
immigration rates (into area)
emigration rates (exit area)
Pop = Pop0 + (b + i) - (d + e)
Zero Population Growth
(b + i) = (d + e)

17. How is “r” determined? r = births – deaths Total Population (rN)
Does not include immigration or emigration!
Example: 20,000 births – 15,000 deaths
500,000 organisms
Growth Rate (r) = .01 (x 100) = 1.0%

18. Exponential Growth Model (J)

19. Growth Rate Example What type of growth is this?
Time N
Rate (r)
r x N T1 2 10 20 T2
200 T3
2000 T5
20,000

20. J-curve – Exponential Growth

21. Population Growth Rate Practice

22. Exponential Growth Time N r r x N 10 1.5 15 1 23 2 35 3 53 4 80 5 12010
1.5 15 1 23 2 35 3 53 4 80 5
120 6
180

24. Exponential Growth
Rules: If r ˂ 0, then dN is negative and population is declining. If r > 0, then dN is positive and population increases over time If r = 0, then dN is 0 → no change in population

25. Logistics Growth Model (S)

26. Logistics Growth Solve for the right side of the equation.
You must know your carrying capacity (K)
Example;
Look at the N/K part.
If K=100 wolves, the maximum pop
If N =100 wolves, then N/K = 100 = 1
100

27. Logistics (cont) If 1-N/K = 1-1 = 0 and rN (0) = 0 and dN/dt = 0.
This means no change in population because the population = carrying capacity.
6. What if N=50 and K=100, please calculate the outcome using the formula.

28. Logistics (cont) Then N/K = 50/100 = ½. 1-N/K = 1-1/2 = ½
Rate of increase is ½ rN or half of the reproductive rate.
Try it with N=120 and K=100, what is the reproductive rate going to be?

29. Logistics Growth from Model

30. Population Density
Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area
Some species exist in high densities - Mice
Some species exist in low densities - Mountain lions
Density depends upon
social/population structure
mating relationships
time of year

31. Population Doubling
Rule of 70 – used for determining how long it takes for a population to double.
If a population grows at a rate of 7%, how long would it take to double?
70%, 70 / doubling = = 10 =
r (% form) = rr (decimal form) , yrs.
THIS IS THE DOUBLING TIME OF A POPULATION!!! is. It states that to find the doubling time of a quantity growing at a given annual percentage rate, divide the percentage number into 70 to r

32. Population Dispersion
Population dispersion is the spatial pattern of distribution
There are three main classifications
Clumped: individuals are
lumped into groups
ex. Flocking birds or
herbivore herds due to
resources that are clumped
or social interactions
most common

33. Population Dispersion
Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced
tips/2002/clover611.htm
Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

34. Age Structure
The age structure of a population is usually shown graphically
The population is usually divided up into prereproductives, reproductives and postreproductives
The age structure of a population dictates whether is will grow, shrink, or stay the same size

35. Age Structure Diagrams
Positive Growth Zero Growth Negative Growth
(ZPG)
Pyramid Shape Vertical Edges Inverted Pyramid

36. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

38. Environmental Resistance
Biotic Potential
factors allow a population to increase under ideal conditions, potentially leading to exponential growth
Environmental Resistance
affect the young more than the elderly in a population, thereby affecting recruitment (survival to reproductive age)

39. Biotic Potential
Ability of populations of a given species to increase in size
Abiotic Contributing Factors:
Favorable light
Favorable Temperatures
Favorable chemical environment - nutrients
Biotic Contributing Factors:
Reproductive rate
Generalized niche
Ability to migrate or disperse
Adequate defense mechanisms
Ability to cope with adverse conditions

40. Environmental Resistance
Ability of populations of a given species to increase in size
Abiotic Contributing Factors:
Unfavorable light
Unfavorable Temperatures
Unfavorable chemical environment - nutrients
Biotic Contributing Factors:
Low reproductive rate
Specialized niche
Inability to migrate or disperse
Inadequate defense mechanisms
Inability to cope with adverse conditions

42. Exponential Growth
As early as Darwin, scientists have realized that populations have the ability to grow exponentially
All populations have this ability, although not all populations realized this type of growth
Darwin pondered the question of exponential growth. He knew that all species had the potential to grow exponentially
He used elephants as an example because elephants are one of the slowest breeders on the planet

43. Exponential Growth 19,000,000 elephants!!!
One female will produce 6 young over her 100 year life span. In a population, this amounts to a growth rate of 2%
Darwin wondered, how many elephants could result from one male and one female in 750 years?
19,000,000 elephants!!!

44. Exponential Growth Graph

45. Population Dynamics and Carrying Capacity
Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)
There is a dynamic balance between biotic potential and environmental resistance

46. Carrying Capacity (K)
Exponential curve is not realistic due to carrying capacity of area
Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

48. Logistic Growth
Because of Environmental Resistance, population growth decreases as density reaches carrying capacity
Graph of individuals vs. time yields a sigmoid or S-curved growth curve
Reproductive time lag causes population overshoot
Population will not be steady curve due to resources (prey) and predators

51. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

52. Reproductive Strategies
Goal of every species is to produce as many offspring as possible
Each individual has a limited amount of energy to put towards life and reproduction
This leads to a trade-off of long life or high reproductive rate
Natural Selection has lead to two strategies for species: r - strategists and K - strategists

53. r - Strategists Spend most of their time in exponential growth
Maximize reproductive life
Minimum life K

54. R Strategists Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental conditions
High population growth rate – (r)
Population size fluctuates wildly above and below carrying capacity – (K)
Generalist niche
Low ability to compete
Early successional species

55. K - Strategists Maintain population at carrying capacity (K)
Maximize lifespan K

56. K- Strategist Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental conditions
Lower population growth rate (r)
Population size fairly stable and usually close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species

57. Survivorship Curves
Late Loss: K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality
Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes
Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age

59. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

60. Conservation Biology
Careful and sensible use of natural resources by humans
Originated in 1970s to deal with problems in maintaining earth's biodiversity
Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species

61. Conservation Biology Three Principles
Biodiversity and ecological integrity are useful and necessary to all life on earth and should not be reduced by human actions
Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes
Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat

62. Habitat Fragmentation
Process by which human activity breaks natural ecosystems into smaller and smaller pieces of land
Greatest impact on populations of species that require large areas of continuous habitat
Also called habitat islands

64. Habitat fragmentation in northern Alberta
Habitat fragmentation in northern Alberta

65. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

66. Human Impacts Fragmentation and degrading habitat
Simplifying natural ecosystems
Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
Elimination of some predators

67. Human Impacts Deliberately or accidentally introducing new species
Overharvesting potentially renewable resources
Interfering with the normal chemical cycling and energy flows in ecosystem

68. Population Dynamics Outline
Characteristics of a Population
Population Dynamics and Carrying Capacity
Reproductive Strategies
Conservation Biology
Human Impacts
Working with Nature

69. Working with Nature Learn six features of living systems
Interdependence
Diversity
Resilience
Adaptability
Unpredictability
Limits

70. Basic Ecological Lessons
Sunlight is primary source of energy
Nutrients are replenished and wastes are disposed of by recycling materials
Soil, water, air, plants and animals are renewed through natural processes
Energy is always required to produce or maintain an energy flow or to recycle chemicals

71. Basic Ecological Lessons
Biodiversity takes many forms because it has evolved over billions of years under different conditions
Complex networks of + and – feedback loops exist
Population size and growth rate are controlled by interactions with other species and with abiotic
Organisms generally only use what they need

72. Four Principles for Sustainable
We are part of, not apart from, the earth’s dynamic web of life.
Our lives, lifestyles, and economies are totally dependent on the sun and the earth.
We can never do merely one thing (first law of human ecology – Garret Hardin).
Everything is connected to everything else; we are all in it together.