1. Populations & Communities

2. Ecology living-living and living-nonliving. Food pyramid
Food chain-shows what eats what
Food web-many food chains together

3. Organization of Life
Populations-grps of the same species, living in a shared space at a specific point of time
Communities-grps of populations
Ecosystem-communities + nonliving environment

4. Population Population size-# of individuals in a population
Factors affecting population: Births, deaths, immigration and emigration

5. I. Population Size
The size of a population is simply the number of individuals it contains.
Over time the size of a population may increase, decrease or remain stable. It is important for ecologist to study population size in order to know if certain species are at risk.
Losing one species or a decline in that species will affect all other species (plant and animal) in the ecosystem.

6. What Factors Affect Population Size?
1) Births- Births of individuals within a population (increases population size)
2) Death- Members of the populations dying. (decrease)
3) Immigration- Arrival of new members of the same species from another population. ( increase)
4) Emigration- Departure of individuals to another region. (decrease)

7. Factors affection population sizeIf
BIRTH + IMMIGRATION > DEATH + EMIGRATION
Then the population increases.
BIRTH + IMMIGRATION = DEATH + EMIGRATION
Then the population stays the same.
BIRTH + IMMIGRATION < DEATH + EMIGRATION
Then the population decreases.

8. Measuring population size
Counting Individuals, Random sampling and Mark and recapture
Counting individuals: counting all the individuals within an area with that population Ex. -Count water lilies in pond
- Aerial photography to
count # of bison in field

11. Random sampling: from humans ( worms, ants etc.)
Counting individuals in randomly selected sections of the study area.
Quadrant sampling: useful for plant populations,
slow moving animals, or animals that don’t run away
from humans ( worms, ants etc.)
Then estimating using the following calculations:
Avg. # individuals per section = Population size
Area of section Total study area

12. Pop. = Avg. # of individuals per section X Total study area
Size Area of the section
Ex. 15 daisies are counted in a quadrant that measures 1 m2
If the field has an area of m2 , what is the population size of daisies in the field?

13. Population size = 15 X m2
1 m2
= daisies

14. Mark and Recapture To estimate pop. of very mobile animals
(birds, fish), widely scattered (hares etc.),
or marine mammals (seals etc.)
1. Install cages or nets
2. Count captured animals & mark
(rings, tags, paint etc.)
3. Release to mix with unmarked individuals

15. 4. Reinstall cages or nets
5. Count captured individuals (2nd time),
with a separate count for marked
6. Estimate size of population using the
equation:

16. Pop.= # Marked animals X Total # of animals captured 2nd time
Size # of Marked animals recaptured
Ex. 50 Lynx have been captured, marked, and released. The second capture results in only 40 out of 120 captured Lynx having tags.
What is the Lynx population?
Pop. Size = X = 150 Lynx 40

17. II. Population Density
Population density-# of individuals per unit area
Ex. There are 126 earthworms in Mary’s garden. If the volume of soil in the garden is 6 m3 , what is the population density?
Pop. density = # individuals
Space (area or volume)
= 126
6 m3
= 21 earthworms per m3 of soil

18. III. Distribution
Population distribution-how individuals are spread out.
1. Clumped: - individuals form groups
Ex. Fish in schools

19. 2. Uniform: - dispersed equally throughout
habitat. Ex. Birds space nests
3. Random: - rare in nature, random &
unpredictable. Ex. Bushes in field

20. Ecological Factors
Refers to aspects of a habitat that effects organisms living there
2 types:
Biotic: actions of living organisms
(birth rate, disease, amount of food, predation, competition, human activity)
Abiotic: Non-living, physical or chemical
( amount of light, soil Ph, terrain, temperature, amounts of precipitation)

21. ABIOTIC BIOTIC
Amount of light Birth rate
Soil or water pH Disease
Terrain Amount of food
Depth of snow Predation
Temperature Competition
Air humidity Human activity

22. Limiting factor
Ecological factor that causes the density of a population to decrease.
ex. Exposure to sunlight limits photosynthesis
Excess water (limiting factor) causes root rot
Question: Frogs die after toxic spill, so number of snakes decline. What is the limiting factor?
Answer: Size of frog population

23. Biological cycles
Alternating periods of rise and fall in population size
Fixed duration, and repeated continually
-e.g. lynx and hare

24. See bullets page 302

25. Community & Biodiversity
Community-a set of populations of different species sharing the same habitat
ex. Grass, butterflies, Robins, bushes in garden
Biodiversity-the variety of species living in a community (must consider 2 things)
1. species richness (# of species)
2. relative abundance of each species
(study diag. 9.16, p.304)

26. Interactions between individuals in a community
Competition
Predation & Parasitism
Mutualism
Commensalism

27. Competition
Interaction between living organisms that seek access to the same resources in their habitat
1. Intraspecific (same species)
ex. Two Maple trees seek water
2. Interspecific (different species)
ex. An Oak trees competes with Maples

28. Predation
Interaction between two living organisms in which one feeds off the other
Predator (feeds) vs prey (being eaten)
Ex. Lynx vs Hare
Parasitism- parasite (food from host by
living inside or on host) and
host is harmed in some way
Ex. Flea and dog

29. Mutualism
Interaction between two living organisms that benefits both organisms
Ex. Clown fish (Attracts prey for anemone)
& Sea anemone (shelter for fish)
Bees(pollinator) & Flowers (food-nectar)

30. Commensalism
Interaction between two living organisms in which one organism benefits from the relationship while the other remains unaffected
Ex. Black bird nest in tree

44. Ecosystems
A community of living organisms interacting with each other and with the non-living aspects of the environment
Trophic relationships-the feeding connections among the living organisms of the ecosystem
Food Chain-each member eats the preceding one
- position corresponds to Trophic level
producers, consumers, decomposers

50. Producer (autotrophs)
Autotrophic organisms with the ability to create organic matter from inorganic matter in an ecosystem (Photosynthesis!)
Bottom of food chain, because they introduce energy into the food chain
Terrestrial: Plants
Aquatic: Algae, phytoplankton
Principle mechanism: Photosynthesis

52. Consumers Heterotrophic organisms that feed on other living organisms
Primary: Feed on producers, or seeds or fruits Ex. Woodland vole
Second, third, fourth eat consumers of the preceding order.
Ex. Owl (tertiary) eats Milk snake (secondary) which eats the Woodland Vole (Consumer) which eats the grass (producer)
Omnivores- consumers of several orders at once
Ex. Bears, Humans

53. Primary

56. Decomposers
Organisms that feed on waste and remains of other living organisms
“Detritivores”
ex. Certain worms, fungi, insects
Note: they are heterotrophs (can be eaten by consumers)

59. Food web More than one food chain is possible in an ecosytem
Ecosystem can contain many trophic levels
A Food web is many food chains together!

65. Secondary, etc.

67. Ecosystem Dynamics
Material and Energy Flow is the exchange of matter and energy between the living organisms in an ecosystem and between those organisms and their environment.

68. “Law of Conservation of Mass”
Remember:
“nothing is lost, nothing created, matter transformed” Lavoisier
applies to matter in an ecosystem

70. Chemical Recycling
is a natural phenomenon by which decomposers make inorganic matter
available in an ecosystem by breaking down matter
Ex. Organic matter to clover to Hare to Lynx to decomposers to inorganic matter
and back to Clover

71. Matter passes from one state to another
(stays in circulation in ecosystem)

72. Energy Flow
Sunlight: usually the primary source of energy in an ecosystem.
Autotrophs (producers) turn radiation energy into chemical energy
Consumers use the chemical energy in food when they are eaten.
Trophic Levels: organisms obtain energy from food, & store it in their tissues.

73. Energy lost at each level
only 10% of energy passed on to the next level
Energy lost:
Ex. waste, activities (moving, growing),
heat etc.
- Unlike MATTER, the energy in the ecosystem is NEVER recycled

74. Primary Productivity in Ecosystems
BIOMAS is the total mass of organic matter in an ecosystem at a given time
Measuring amount of new biomass reveals primary productivity

75. Primary Productivity
Of an ecosystem is the amount of new biomass generated by its producers
- More NEW organic matter created,
the GREATER the capacity of the ecosystem to supply energy to its organisms

76. Producers must be supported
(plants, phytoplankton etc.)
Factors: amount of light, amount of water,
access to essential nutrients
(C, N, P, K), & temperature

77. Disturbances An event that damages the ecosystem.
It can lead to the elimination of organisms & alter availability of resources
Depends on:
1. Type: Snowstorms, sandstorms,
hurricanes, volcanic eruptions

78. 2. Vary in frequency Ex. Spring flooding (annually) Torrential rain 3
2. Vary in frequency Ex. Spring flooding (annually) Torrential rain 3. More or les serious ex. Ice storm could last hours or days

79. Natural Disturbances
Many and varied, causes are environmental rather than human
Impact on ecosystem
Volcanic disruptions, forest fires,
droughts, floods, heat waves etc.

80. Human Disturbances
Principle source of environmental disturbances on Earth
Ex. Small –littering
large – logging, oil spills,

81. Ecological Succession
A series of changes that occur in an ecosystem after a disturbance and that continue until the balance of the ecosystem is restored
Ex. Disease causes trees to die, then birds leave, then Field mice move into area,
then Foxes move into area to eat mice