1. Community Ecology
Chapter 3

2. Review
A community is a group of interacting populations that occupy the same place at the same time.

3. Reproductive strategies
r – strategists
Rate
Small organisms
Produce a lot of offspring
Little parenting effort
k – strategists
Carrying capacity
Large organisms
Produce few offspring
A lot of parenting effort

4. Limiting factors
any abiotic factor or biotic factor that restricts the numbers, reproduction, or distribution of organisms
temperature, nutrients,
predators, fire etc.
What are some
limiting factors in
this desert?

5. Range of tolerance
The ability of any organism to survive when subjected to abiotic factors or biotic factors is called tolerance.
Lower Limit
Upper Limit
Zone of physiological stress
Greatest # of Species
Zone of Intolerance

7. Species richness The number of species in the community
Varies by latitude
Closer to the equator = greater species richness

8. Disturbance
Disturbances are events that change communities (the organisms or the resources available)
Examples: fires, droughts, volcanic eruptions, storms

9. Long leaf pine forest

10. How does a community respond when there is a disturbance?
The community experiences succession, a gradual, sequential regrowth of the species in the community.

11. Primary succession
Occurs where life has never before existed or where life was completely wiped out.
ex. On an island formed from a volcanic eruption or on bare rock
NO TOPSOIL.
Only biological organisms are bacteria, fungal spores, pollen strains, etc.

12. Primary succession

13. Secondary succession
Occurs following the disruption of an existing community (ex. Fire, tornado, farming, etc.)
Pioneer species (mainly plants) are the first species to start re-growing.

14. Secondary succession

15. Is there an endpoint to succession?
A climax community is the stable mature community that results when there is little change in the composition of species
cannot be predicted
slow complex process that involves many factors.
Ex. Weather patterns, different rates of growth of species, human activities

16. Succession Stages
The first species to dominate is called the pioneer species
Primary example: On bare rock, lichens (mutualistic relationship between fungi and algae) live and form soil.
With soil available, plants can move in.
With plants available, animals can move in

17. Succession Stages Grasses and weeds begin the process
Perennial grasses and shrubs take over
Softwood trees (pines) compete with shrubs for sunlight and nutrients, dominate
Ends with deciduous forest community (hardwoods)

18. Quick Quiz
Limiting Factor
A ____________ restricts numbers and distributions of organisms.
The range in which a organism ca survive is called ________________
_____________ are events that change communities.
The first species to dominate during succession is the ________________
Range of tolerance
Disturbances
Pioneer species

19. Population Dynamics
Chapter 4

20. Review
A population is a group of organisms, all of the same species, that live in a specific area.

21. Population size Mark-recapture method
Individuals are captured, marked, and released
Researchers obtain another sample later and keep track of those already marked
A formula is used to estimate the population size.
Random Sampling
Apply # of individuals in sample to whole area

22. Population Density It’s the # of individuals per unit area or volume.
If pop. density is too high, it can have serious consequences for the population.

23. Population Density Comparison
China
Japan
1.3 billion people
9.6 million km2
Pop. density: 135 people/km2
126 million people
377,835 km2
Pop. Density: 325 people/km2

24. Dispersion Patterns
Dispersion- the pattern of spacing of a population within an area due to many factors both biotic and abiotic.
1) Uniform
Organisms keep their space

25. Dispersion patterns 2) Clumped
Occurs where food or space is clumped or due to social nature of organisms
3) Random
Most populations show some degree of uniformity or clumping

26. Population Growth Rate
Birth rate – death rate = growth rate
Immigration – Movement of individuals into a population
Emigration – Movement out of a population
When birthrate > death rate, the pop.
When immigration > emigration, pop.

27. Exponential Growth Model (J Curve)
Populations of organisms grow slowly at first and as the population grows and has more reproducing individuals, it grows faster.
This is exponential growth.
It is shown by a J-shaped curve.

28. Logistic Growth Model (S Curve)
the pop. growth curve levels off and becomes an S-shaped curve.
This is the
Carrying
Capacity

29. Can a population grow indefinitely?
a population is limited by limiting factors, such as temperature, nutrients, predators, fire, etc.
Populations with plenty of resources have more births than deaths, so they grow until the environment is “maxed out.”
the population is at carrying capacity, it contains all the individuals that the environment can support.

30. Limiting Factors
Density-dependent factors have an increasing effect as the population increases.
Ex. Disease, predators, food supply, competition, crowding, parasites
Density-independent factors can affect populations, regardless of their density.
Ex. Volcanic eruptions, floods, pesticides

31. Human Population Terminology
Demography is the study of human population size, distribution, birth/death rates
Birthrate – the # of live births / 1000 individuals in a year
Death rate - the # of deaths / 1000 individuals in a year

32. Human Population on Earth
Pretty stable until recently…
-In 1999 population was over 6 billion people
-Current growth rate over 80 million per year
-Expected population by 2050 is 9 billion

33. Percent Increase in Human Population
Even though human population is
The rate at which it grows has
Due to diseases and voluntary population control

34. Decreasing growth rate
Although the total human population is steadily increasing, the rate of increase itself is slowing (the peak was in the 1960s).
The overall slowing is a result of several factors—increased use of birth control, better education of women in developing countries, and rising standards of living

35. Trends in Human Population Growth
1) Demographic Transitions
The change in a population from high birth rate and death rates to low birth rates and death rates.

36. Trends in Human Population Growth
2) Zero Population Growth (ZPG)-occurs when births plus immigration equals deaths plus emigration.
Immigration – Movement of individuals into a population
Emigration – Movement out of a population
Birth + immigration = Death + Emigration

37. Trends in Human Population Growth
3) Age Structure -the proportions of the population that are in different age levels.
Wide base = rapidly growing (many young people)
Fairly
even
Between
ages =
stable

38. Trends in Human Population Growth
4) Human Carrying Capacity
All populations have a carrying capacity
Family planning is a way to control our population
Technology has enabled us to increase our carrying capacity, although disease and overcrowding is still a concern.