2. ECOSYSTEMS vary in size. They can be as small as a puddle or as large as the
Earth itself. Any group of living and nonliving things interacting with each
other can be considered as an ecosystem.
Within each ecosystem there
are habitats which may also
vary in size. A habitat is the
place where population lives.
A population is a group of
living organisms living in the
same place at the same time.
All of the populations interact
and form a community. The
community of living things
interacts with the nonliving
world around it to form the
ecosystem.

3. 1. Energy Flow – passage of energy through the components of the
ecosystem
> Autotrophs – convert light energy into chemical energy
> Heterotrophs – obtain chemical energy from food
> Decomposers - feed on all levels
2. Chemical Cycling – circular movements of materials within the
ecosystem
> ecosystems are more or less self-contained in terms of materials
> chemical components are cycled between abiotic components
(air, water, soil) and biotic components of the ecosystem.

4. This figure with
plants, zebra, lion
and so forth
illustrates the 2
main ideas on how
ecosystem function:
ecosystems have
energy flows and
ecosystem cycles
materials. These 2
processes are linked
but they are not
quite the same.

5. > The transformation of
energy in an ecosystem
begin first with the input of
energy from the sun. Energy
from the sun is captures by
the process of
Photosynthesis. Carbon
Photosynthesis
Dioxide is combined with
Hydrogen to produce
carbohydrates. Energy is
stored in the high energy
bonds of adenosine
triphosphate or ATP.

6. Diversity
>the varierty of different organisms in a community is its biodiversity. Two components:
species richness (how many ?)
relative abundance of species
>ecologists consider both richness and relative abundance in measuring biodiversity.
Prevalent form of vegetation
>applies mainly to terrestrial situations
>determine to a large part what other organisms will live there
Response to disturbance
>some communities are stable (e.g. cedar and hemlock forests may last 1000’s years);
when disturbed, such communities rebound to original state very slowly.
>other communities are constantly changing and unless disturbed by fire, for example,
succession would lead to different species composition (e.g. grasslands require periodic
fires to remove competitors and allow grasses to dominate). Therefore disturbance plays a
vital role in determining community structure and composition.
Trophic structure
>feeding relationships among various species making up a community.
>determines pasage of energy and nutrients from plants and other primary producers to
herbivores to carnivores.

7.  Competition may occur when a shared resource is
limited
 Predation leads to diverse adaptations in predators
and prey
 Predation can maintain stability in a community
 Symbiotic relationships help structure communities.
 Disturbance is a dominant feature of most
communities