Introduction to Ecology
Ecology is the scientific study of interactions among organisms and between organisms and their
environment.
Organisms and their environment are interdependent (depend upon each other).

The area where an organism lives is called it habitat. A habitat includes both biotic and abiotic
factors.
a. Biotic: include all of the organisms that live in the environment.
b. Abiotic: are the nonliving factors in an organism’s environment (sunlight, pH,
temperature, wind, precipitation, humidity, soil type, or salt concentration).

The ability to withstand fluctuations in biotic and abiotic influences (or changes) from the
environment is called tolerance. The more tolerant a species is the great chance it has to
survive.

Together, abiotic and biotic factors determine the survival and growth of an organism and the
productivity of the environment in which the organism lives.
Energy Flow
The sun is the main energy source for life on Earth.
- Some organisms rely on energy stored in inorganic compounds such as
chemicals to make their food.
1. Autotrophs (or producers) capture energy from sunlight or chemicals and use that energy to produce
food.
a. photosynthesis: is the process of using solar energy to produce food (Ex: plants).
b. chemosynthesis: is the process of using inorganic compounds or chemicals to produce food
(Ex: sulfur bacteria near hydrothermal vents).
Autotrophs are the foundation of all ecosystems because they make energy for all the other organisms.
2. Heterotrophs (or consumers) are organisms that get their energy from consuming other organisms.
a. herbivores: eat only plants (cows, deer, rabbits, grasshoppers)
b. carnivores: eat animals (lions, hyenas, wolves).
c. omnivores: eat both plants and animals (humans, bears, crows).
d. detritivores (scavengers): feed on plant and animal remains and other dead matter
(mites, snails, crabs)
e. decomposers: break down organic matter (bacteria and fungi).
Without detritivores and decomposers the entire biosphere (Earth) will be littered with dead organisms
(nature’s garbage men ).
Feeding Relationships
Energy flows through an ecosystem in one direction from the sun or inorganic chemicals to autotrophs
(producers) and then to various heterotrophs consumers).
-
Ecologists use food chains and food webs to model the
energy flow.
-
Food chains show the one way flow of energy in an
ecosystem (the arrow always points in the direction the
energy is going).
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Each step of the food chain/food web is called a
trophic level.
-
As energy flows from one level to the next, a large part
(90%) is lost through heat and work done by
organisms. Only 10 % of the energy flows from one
level to the next level. (The 10% Rule).
-
Food Webs are models representing the
interconnected food chains in which energy flows.
Ecological Pyramids

Ecological Pyramids show the decreasing amounts of energy, living matter or number of
organisms at successive trophic levels.
-
Energy Pyramid: shows the relative amount of energy available at each trophic level.
-
Number Pyramid: shows the relative number
of individual organisms at each trophic level.
-
Biomass Pyramid: represents the amount of
living matter at each trophic level.
Remember:
Food Chains , Food Webs , and Food Pyramids (Ecological Pyramids) are models used to show
how energy moves through ecosystems.