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Biology 2014-2015

What Shapes an Ecosystem?

SWS Biology
SWS Life Science

Section 4-2

Biotic and Abiotic Factors

       Ecosystems are influenced by a combination of biological and physical factors.

       Biotic factors are the biological influences on an organism within an ecosystem.

       Included is the entire living cast of characters with which an organism might interact.

       Abiotic factors are the physical, or nonliving factors that shape ecosystems.

       Included are the climate of an area such as temperature, precipitation, and humidity.

       Wind, nutrient availability, soil type, and sunlight

       Together, biotic and abiotic factors determine the survival and growth of an organism and the productivity of the ecosystem in which the organism lives.

       Habitat is the area where an organism lives.

       Includes both biotic and abiotic factors


The Niche

       An organism’s habitat is its address and its niche is its occupation.

       A niche is the full range of physical and biological conditions in which an organism lives and the way in which the organism uses those conditions.

       Includes its place in the food web

       The range of temperatures that the organism needs to survive.

       The type of food that the organism eats

       How an organism obtains food

       Which other species use the organism as food

       The physical conditions required for survival

       When and how an organism reproduces

       No two species can share the same niche in the same habitat.

       Different species can occupy niches that are very similar.

Ex) Three different species of North American warblers live in the same spruce trees but feed at different elevations and in different parts of those trees.

The species are similar, yet each warbler has a different niche within the forest.


Community Interaction

       Community interactions, such as competition, predation, and various forms of symbiosis can powerfully affect an ecosystem.



       Competition occurs when organisms of the same or different species attempt to use an ecological resource in the same place at the same time.

       A resource refers to any necessity of life, such as water, nutrients, light, food, or space.

v      Broad-leaved trees such as oak or hickory may compete for sunlight by growing tall, spreading their leaves, and blocking the sunlight for shorter trees.

v      Two species of lizards in a desert might compete by attempting to eat the same type of insect.

       Direct competition often results in a winner and a loser-with the losing organism failing to survive.

       The competitive exclusion principle states that no two species can occupy the same niche in the same habitat at the same time.



       Predation is an interaction in which one organism captures and feeds on another organism.

       The organism that does the killing is called the predator.

       The food organism is the prey.



       Symbiosis is any relationship in which two species live closely together.

       There are three main classes of symbiotic relationships in nature:




       In mutualism, both species benefit from the relationship.

v      Many flowers depend on insects to pollinate them.  The flowers provide the insects with food in the form of nectar or pollen and the insects help the flowers reproduce.

       In commensalism, one member of the association benefits and the other is neither helped nor harmed.

v      Barnacles, small marine animals, attach themselves to a whale’s skin.  The barnacles perform no known service to the whale but they benefit from the constant movement of water that carries food particles.

       In parasitism, one organism lives on or inside another organism and harms it.

       The parasite obtains all or part of its nutritional needs from the other organism, called the host.

       Parasites weaken but do not kill their host, which is usually larger than the parasite.

v      Tapeworms are parasites that live in the intestines of mammals.

v      Fleas, ticks, and lice live on the bodies of mammals, feeding on the blood and skin of the host.


Ecological Succession

       Ecosystems and communities are always changing in response to natural and human disturbances.

       As an ecosystem changes, older organisms die out and new organisms move in further changing the community.

       Ecological succession is a series of predictable changes that occurs in a community over time.

v      Sometimes succession results from slow changes in the physical environment.

v      A sudden natural disturbance

v      Human activities such as clearing a forest



Primary Succession

       Primary succession is succession that occurs on surfaces where no soil exists.

v      Bare rock exposed when glaciers melt

v      Volcanic eruptions build new islands or cover land with lava rock or volcanic ash

       Pioneer species are the first species to populate an area.

v      On volcanic rocks are often lichens that are made up of a fungus and an alga that can grow on bare rock.

v      As lichens grow, they break up the rocks.

v      When they die, their organic material helps to form soil in which plants can grow.



Secondary Succession

       Secondary succession occurs when land cleared and plowed for farming is abandoned or when wildfires burn woodlands.

       The process of succession in a given area is always proceeded in certain specific and predictable stages and ended with a mature, stable community that did not undergo further succession, a “climax community”.

v      Certain plants have adapted to a regular cycle of fire and regrowth.  Their seeds will not sprout unless exposed to fire.


Succession in a Marine Ecosystem

       Due to recent technology, ecologists have found that succession can also occur in the dark, deep ocean.

       Three stages in the succession of a whale-fall community:

1.         Begins when a large whale dies and sinks to the normally barren ocean floor.  The whale carcass attracts scavengers and decomposers that feast on the decaying meat.

2.         Within a year, most of the tissue has been eaten and the carcass supports a smaller number of fish, crabs, marine snails and other organisms.  The decomposition enriches the sediment with nutrients where many marine worms reside.

3.         When only the whale skeleton remains, heterotrophic bacteria begin to decompose oils inside the whale bones.  Chemical compounds that serve as an energy source for other bacteria that are chemosynthetic autotrophs who support a diverse community of mussels, snails, worms, and crabs that live on the bones.