Symbiosis – any relationship in which 2 species live ...



Symbiosis – any relationship in which 2 species live closely together

Competition – organisms of the same species or members of different species fighting over resources

▪ Mutualism – (p. 93) both species benefit

o Example: Angiosperms and insects

o Angiosperms need insects for pollination

o Insects need angiosperms for nectar

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▪ Commensalism – one member benefits and the other is neither harmed nor helped

o Example: barnacles and whales

o Barnacles (small marine animals) attach themselves to the whale’s skin

o Barnacles don’t help or hurt the whale

o But the barnacles benefit because as the whale moves through the water, the barnacle gets food particles

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▪ Parasitism – one organism lives on or inside another organism and harms it (doesn’t usually kill the host)

o Examples: fleas, ticks, lice

▪ Fleas, ticks, and lice live on the bodies of mammals feeding on blood and skin

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▪ Plasmodium in mosquitoes (causes malaria)

Predation – attacking and eating another organism

Predator – Prey Relationship (p. 126)

o Populations in nature often controlled by predation

o Cyclic

o Can be both predator and prey

↑ prey = ↑ predator ( predator eats all the prey

↑ ↓

with no predators ← ↓prey = ↓predator

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1. Who is the predator? _____________

2. Who is the prey? _________________

3. What happened to the wolves’ population in 1975 when the moose population had gone up? _________________________

4. What happened as a result of this? _________________________________

5. The moose population stays high when the wolf population is _____________.

Chapter 5 Populations (p. 119)

Population – group of organisms of one type that live in the same area (i.e. bison herd)

Population Density – the number of individuals per unit area

o How many bison are located in a given km2 area?

o Limited by food availability, competition, disease, weather conditions

❖ More animals live in a tropical rain forest than the frozen arctic

How do you determine the number and kind of organisms in a given area?

Sampling and quadrant studies

Sampling – counting a number of organisms from predetermined areas around the habitat instead of trying to count all the organisms

o Done so that statistically your numbers represent what would be found in the entire area

o For example: In the island below, you might randomly select 10 of the 29 quadrants to count instead of trying to count the organisms on the entire island

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Quadrant - a given area within your sample

o Used to determine if the population changes over time and how many different types of species are in one area

Characteristics of a population (used to describe the population in nature):

1. Geographic distribution – range (area where they can be survive)

2. Density – number of individuals in a certain area (too many in a given area can lead to death of some)

3. Growth rate – number of individuals vs. time

a. Bacteria can reproduce every 20 minutes while elephants have a gestation period of 18 to 22 months (p. 121)

4. Population’s age structure – shows the numbers of people in different age groups in the population

Growth rate is effected by:

o Birth rate

o Death rate

o Emigration and Immigration

1. Birth Rate - The ratio of total live births to total population in a specified community or area over a specified period of time.

• Increases to a certain point with available food supply, lack of predators, lack of disease, etc.

2. Death Rate - The ratio of total deaths to total population in a specified community or area over a specified period of time.

• Increases with harsh conditions, lack of food, increase in predators or disease, etc.

3. Emigration – movement of individuals out of an area

• Increases may be due to lack of space, lack of food, too many competitors, etc.

Immigration – movement of individuals into an area

• Increases may be due to lots of space, lots of food, few competitors, few predators, etc.

Types of Growth rates (p. 121 – 122)

Exponential growth – occurs when the individuals in a population reproduce at a constant rate

• Unlimited resources (no limiting factors)

• Absence of predation and disease

• Produces a J-shaped curve when plotted number of individuals vs. time

• Curve starts off slow but reaches a point where the population becomes larger and larger

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Logistic Growth – occurs when a population’s growth slows or stops following a period of exponential growth

• Resources become less available after population “explodes”

• Birth rate may decrease

• Death rate may increase

• Rate of immigration decreases

• Rate of emigration increases

• S-shaped curve when plotted number of individuals vs. time

• Top part of the curve represents the carrying capacity of that environment

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1. Which phases together are seen on an exponential growth curve? ___________ and ___________________

2. What does this steep line tell you about the bacterial growth at this time? _______________________________

3. Are there any limiting factors during the exponential? ________ Are there any limiting factors at the top of the curve? ________

Carrying capacity – the largest number of individuals that a given environment can support

o If the number of individuals exceeds this point, some individuals will die

How do limiting factors influence carrying capacity?

1. Food availability – limited food will result in fewer organisms being able to survive in a given area; will move to more favorable site

2. Competition – more individuals will mean more competition for limited resources

3. Harsh conditions – limit the number of individuals an environment can support (hot, dry summers or cold, harsh winters)

Limiting factors: a factor that causes population growth to decrease

A. Density-dependent factors: factors that depend on the population size (competition, predation, parasitism, and disease)

B. Density-independent factors: affect all populations in similar ways, regardless of the population size (weather, natural disasters, seasonal cycles and certain human activities – i.e. clear cutting the forest)

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