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 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

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