1. Biotic and Abiotic Influences on Ecosystems

2. Limiting Factors
Limiting factors determine which types of organisms and how many of each are able to survive in an ecosystem
A limiting factor is any factor that restricts the size of a population or where it can live
These factors can be abiotic or biotic
Human actions can also act as limiting factors

3. Abiotic Limiting Factors
Factors such as temperature and precipitation may influence where a species lives
E.g. Cacti thrive in dry conditions
Each species has a tolerance range: the range of abiotic conditions within which a species can survive
Some species have a wide tolerance range
E.g. Raccoons can live in hot tropical forests or in colder northern forests

4. Limiting Factors – Terrestrial Ecosystems
Key abiotic factor
Human action and result
Light
Fire and tree cutting can remove shade and expose organisms to more light
Water
Damming rivers and draining wetlands reduces water availability; irrigation increases water availability
Nutrients
Farming practices can change nutrient levels in soil
Temperature
Global warming can reduce available habitat for cool-adapted species

5. Limiting Factors – Aquatic Ecosystems
Key abiotic factor
Human action and result
Light
Activities that increase erosion or stir up bottom sediments can reduce light at lower depths
Nutrients
Fertilizer runoff can increase nutrients in water and cause algal blooms
Acidity
Pollution from burning fossil fuels increases acid rain in aquatic ecosystems
Temperature
Industries release heated waste water into lakes and rivers, killing fish and other organisms
Salinity
Salting highways and irrigation can increase the concentration of salt

6. Biotic Limiting Factors
Abiotic factors usually determine where a species is able to live
Biotic factors often determine how easily a species can survive in an ecosystem
Biotic factors include relationships among organisms in an ecosystem

7. Biotic Limiting Factors
Competition – two individuals seek the same resource (space, food, water, light)
E.g. Foxes and coyotes both feed on rabbits

8. Biotic Limiting Factors
Predation – one individual feeds on another
E.g. Lynx prey on snowshoe hares

9. Biotic Limiting Factors
Mutualism – two individuals benefit each other
E.g. Flowers provide nectar for bees; bees pollinate flowers

10. Biotic Limiting Factors
Commensalism – one individual benefits and the other neither benefits nor is harmed
E.g. Birds nesting in trees

11. Biotic Limiting Factors
Parasitism – one individual lives on or in a host organism and feeds on it
E.g. Tapeworms are parasites of lynxes and wolves
National Geographic Videos

12. Carrying Capacity
As a population grows, it requires more food, water, and space
Eventually, it will reach its carrying capacity – the maximum population size of a species that a given ecosystem can sustain
As abiotic and biotic factors change, the carrying capacity also changes
E.g. A forest fire reduces the number of trees but new plants will thrive as they have more space and light

13. Human Actions Affect Carrying Capacity
A decrease in wolf population due to hunting by humans could increase the carrying capacity of moose
Human action to increase productivity of land, such as irrigation, can increase its carrying capacity for different crops