Download Biotic and Abiotic Influences on Ecosystems

Biotic and Abiotic
Influences on Ecosystems
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
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
Limiting Factors – Terrestrial
Ecosystems
Key abiotic
factor
Light
Water
Human action and result
Fire and tree cutting can remove shade
and expose organisms to more light
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
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
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
Biotic Limiting Factors
• Competition – two individuals seek the same
resource (space, food, water, light)
– E.g. Foxes and coyotes both feed on rabbits
Biotic Limiting Factors
• Predation – one individual feeds on another
– E.g. Lynx prey on snowshoe hares
Biotic Limiting Factors
• Mutualism – two individuals benefit each
other
– E.g. Flowers provide nectar for bees; bees
pollinate flowers
Biotic Limiting Factors
• Commensalism – one individual benefits and
the other neither benefits nor is harmed
– E.g. Birds nesting in trees
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
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
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