1. Biotic and Abiotic Influences on Ecosystems
Section 2.7

2. Limiting Factor The factor that restricts the size of a population
Can be biotic – availability of food
Can be abiotic – access to water
Humans are often the limiting factor in ecosystems

3. Key Limiting Abiotic Factors – Page 53
Human Action & Result
Light Availability
clear-cut forests and expose organisms to too much light, erosion reduces the light in water ecosystems
Water availability
built dams, irrigation – reduces water for organisms
Temperature
Global warming is decreasing suitable habitats, industries release heated water into lakes causing an increase in the water temp.
Nutrient availability
Farming increases or decreases soil/water nutrients which can affect plant growth
Water acidity
Acid rain has increased the acidity of bodies of water – killing marine life
Water salinity
Run off from roads that have been treated with salt increases the salt content of water – killing marine life

4. Key Limiting Biotic Factors
Can be between individuals of the same species or between species
Competition – two individuals fight for the same resource
Predation – one feeds off another
Mutualism – two individuals benefit from each other (nitrogen bacteria that grow on plant roots)
Parasitism – one individual lives in or on another (tapeworms)
Commensalism – one benefits and the other one neither benefits nor is harmed (moss on trees)

5. Tolerance Range
The abiotic conditions within which a species can survive
Some have a wide range others do not
Optimal range is where the organism grows best.

6. Carrying Capacity
The maximum population size of a particular species that a given ecosystem can sustain.
Can be altered through natural or human activity

7. Today’s Task
Pg. 55# 2, 3, 4