1. AP Environmental Science
Population Dynamics
AP Environmental Science

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

3. Characteristics of a Population
Population - individuals inhabiting the same area at the same time
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

4. 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

5. 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

6. 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

7. 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

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

10. 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)

11. 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

12. Environmental Resistance
Ability of populations of a given species to decrease 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

14. The Rule of 70
To find doubling time when you have the population growth rate:
Take 70 divided by the growth rate = doubling time
70/% = doubling time

15. Example
If the growth rate is 2%, what is the doubling time of the population?
70/2 =

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

17. 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

18. Exponential Population Growth
Exponential growth occurs when resources are not limiting.
during exponential growth population size increases faster and faster with time;
currently the human population is undergoing exponential growth;
exponential growth can not occur forever because eventually some factor limits population growth.
Fig. 10–4a
© Brooks/Cole Publishing Company / ITP

19. Density Dependent Factors
Limiting Factors
Density Dependent Factors
Food
Water
Predators
Disease
Density Independent Factors
Weather

20. 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

21. 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)

23. 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

25. A comparison of the logistic growth model and the exponential growth model
Carrying capacity
Logistic growth
Figure 18.20

26. Exceeding the Carrying Capacity
During the mid–1800s sheep populations exceeded the carrying capacity of the island of Tasmania. This "overshoot" was followed by a "population crash". Numbers then stabilized, with oscillation about the carrying capacity.
Fig. 10–5
© Brooks/Cole Publishing Company / ITP

27. Exceeding the Carrying Capacity
Reindeer introduced to a small island off of Alaska in the early 1900s exceeded the carrying capacity, with an "overshoot" followed by a "population crash" in which the population was totally decimated by the mid–1900s.
Fig. 10–5
© Brooks/Cole Publishing Company / ITP

28. Population Curves in Nature
Population cycles for the snowshoe hare and Canadian lynx are believed to result because the hares periodically deplete their food, leading to first a crash of the hare population and then a crash of the lynx population.
Fig. 10–8
© Brooks/Cole Publishing Company / ITP

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

31. 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

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

33. 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

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

35. 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

36. Survivorship Curves Fig. 10–9 Three kinds of curves:
late loss (usually K–strategists), in which high mortality is late in life;
constant loss (such as songbirds), in which mortality is about the same for any age;
early loss (usually r–strategists), in which high mortality is early in life.
Fig. 10–9
© Brooks/Cole Publishing Company / ITP

38. Population Curves in Nature
Natural populations display a broad diversity of population curves. Stable populations are relatively constant over time. Cyclic curves are often associated with seasons or fluctuating resource availability. Irruptive curves are characteristic of species that only have high numbers for only brief periods of times (e.g., seven–year cicada).
Fig. 10–6
© Brooks/Cole Publishing Company / ITP

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

40. 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

41. 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

43. Habitat fragmentation in northern Alberta
Habitat fragmentation in northern Alberta

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

45. 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

46. Human Impacts on Ecosystems
Some major human impacts on ecosystems:
fragmenting and degrading habitat;
simplifying natural ecosystems;
strengthening some populations of pest species and disease–causing bacteria by speeding natural selection and causing genetic resistance through overuse of pesticides and antibiotics;
eliminating some predators;
deliberately or accidentally introducing new species;
overharvesting potentially renewable resources;
interfering with chemical cycling and energy flows.
© Brooks/Cole Publishing Company / ITP

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

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

49. 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

50. 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

51. 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.