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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