Biotic and Abiotic Factors
Different Approaches to the Study of Ecology
• Ecology is the study of an
organism or organisms and
their relationship to the
• An organism’s environment
consists of the physical,
chemical and biological
factors with which it interacts.
• The mollusks seen at the right
must deal with changes in
temperature, tides, wave
action, predators and
competition for food. Each
plays its own role or niche.
How can we study Environmental Interactions?
• At the most basic level, an ecologist may be interested
in the interactions of a single organism and its
• Population ecologists focus on factors that affect
populations of organisms that are found in a specific
area. (i.e. What determines the reproductive success
of wood storks in South Florida.)
• At the community level of study one is interested in
understanding the interactions between populations of
different species living in an area. For example, what
determines composition and distribution of trees in a
An Ecosystem Approach
• At a fourth level, studies may examine an ecosystem.
• The ecosystem includes all the organisms in an area
and all of the abiotic factors that affect them.
• In South Florida there are many ongoing studies of the
Everglades ecosystem, as biologists, geologists,
hydrologists and atmospheric scientists work together in
efforts to understand how all the parts of it relate to each
other. Without this knowledge we cannot hope to
preserve, protect or manage the unique natural
environment that is South Florida .
Abiotic factors are the non-living Components
of the Environment
• Abiotic factors include:
– Special events such as:
• Volcanic eruptions
The atmosphere has a tremendous effect on the distribution of plants
and animals. Global patterns of circulations affect rainfall patterns
and the prevailing wind directions. Changes in air circulation over the
Pacific Ocean can lead to events, such as El Nino, which have global
repercussions (i.e. torrential rains in the Andes and severe drought in
Regional climate affects biological communities
• The unequal heating of the earth’s surface leads to the global patterns of
rainfall and winds. At the equator there is maximum heating of the earth’s
surface. This causes hot air to rise, and as it rises it cools, forming clouds
and increasing precipitation. At high altitudes the air cools and moves away
from the equator. At the mid-latitudes this cool air sinks back to the surface.
This results in both the trade winds and relatively dry conditions.
Prevailing wind patterns, set ocean currents in
• The patterns of wind flow can be
seen in the figure at the right.
Land masses can interrupt these
patterns at a local or regional level.
• Ocean currents are created by the
flow of winds, and cause great
patterns of circular flow in the
oceans. The Gulf Stream is one
such current. Without the heat in
this mass of water, the climate of
northern Europe would be much
cooler. This would alter the
biological communities found
Rain shadows greatly affect the availability of
• As previously stated, land masses affect atmospheric movements. Rain
shadow effects are seen when moist oceanic air masses encounter
mountains. The moist air is forced up, cools, and releases its moisture in the
form of rain. On the back side of the mountains, the cooled air decends
towards the surface, but is no quite dry. This may create arid or semi-arid
Other Abiotic Factors
• Temperature also affects the distribution of plants and animals.
• As a rule, temperature are lower as you move towards the poles or
as you climb in elevations. For this reason arctic or sub-arctic
plant communities can be found at high elevations in the tropics.
• In the temperate latitudes living organisms must be able to tolerate
the temperature extremes of summer and winter. This could range
from 90’s in the summer to well below freezing in the winter.
• In the tropics there is very little seasonal change and many
organisms have a narrow range of temperature tolerance. Years
ago an important paper was publish titled ‘ Why mountain passes
are higher in the tropics’. What does that mean??
• It means that in the tropics differences in elevation can be barriers
to the distribution of species. The temperature at which you can
live may prevent your population from moving from one suitable
habitat to another, because of the temperature zones through
which you would need to pass in a vertical migration.
Other Abiotic Factors
• Here are some abiotic factors that you may not have
– Calcium: The lack of availability of calcium will restrict the distribution of
land snails. If there is no calcium a shell can’t be secreted.
– Sand: the size of the sand grains in the soil can impact animal that are
– Nitrogen: Not just nitrogen, but nitrate (NO 3). This is the form of
nitrogen used by plants. When nitrate is not readily available in the soil,
some plants supplement it with a meat diet. (insectivorous plants).
• A living organism is also affected by the living components of its
• Competition exists for available food resources.
• Predators feed on members of the population.
• Microbes can bring diseases. (If time travel were possible, and you
could be transported to the Cretaceous Era to look at dinosaurs,
don’t be afraid of fear Tyrannosaurus, fear the microbes. You
would have no immunity to them!!)
• There may be competition for nesting space.
• Plants may compete for the light needed to carryout
• These are many other biological factors determine the success of
an individual or species.