Biotic and Abiotic Factors
¨ Ecosystems are influenced by a combination of biological and physical
¨ Biotic factors are the biological influences on an organism within an ecosystem.
Ø Included is the entire living cast of characters with which an organism
¨ Abiotic factors are the physical, or nonliving factors that shape ecosystems.
Ø Included are the climate of an area such as temperature, precipitation,
Ø 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.
Ø Includes both biotic and abiotic factors
¨ An organism’s habitat is its address and its niche is its
¨ 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
Ø Includes its place in the food web
Ø The range of temperatures that the organism needs to survive.
Ø The type of food that the organism eats
Ø How an organism obtains food
Ø Which other species use the organism as food
Ø The physical conditions required for survival
Ø 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.
different species of North American warblers live in the same spruce trees but feed at different elevations and in different
parts of those trees.
are similar, yet each warbler has a different niche within the forest.
¨ 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
¨ 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
¨ 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.
¨ 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
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 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 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.