Download 2.6 Interactions in Ecosystems

2.6: Interactions in the Ecosystem
pg. 42
Ecological Niche: the function a species serves in its
ecosystem, including where it lives, what it eats, what eats
it, and how it behaves.
Trophic Level: the level of an organism in an ecosystem,
depending on its feeding position along a food chain.
Food Web: a representation of the feeding relationships
within a community.
Ecological Niches
The Ecological niche is the role an organism plays within
its ecosystem. The roles include what it eats, and what may
eat it, where it lives and how it behaves. No two species
have the same niche.
Types of Consumers
What a species eats helps to define its niche. Consumers fit
into the following types based on what they eat and how
they behave.
Herbivore – is a first level consumer that eats only plants
(producers)
Carnivore – are found in the second or higher consumer
that eats only other consumers.
Omnivore - are found throughout the levels of consumers,
they eat both plants (producer) and animals (consumer).
Scavenger and Decomposers – are organisms that feed on
the remains of other, dead or decaying, organisms.
A Community of Eaters
In an ecosystem there are populations of the same species,
these populations make up the community of that
ecosystem.
The organisms of the community depend on each other for
food and survival.
Food Chain
A feeding relationship among species in an ecosystem that
expresses a singular pathway is called a food chain. The
food chain always begins with the producer which is eaten
by the herbivore, followed by the first order consumer. The
carnivores in the food chain represent a predator- prey
relationship.
Energy in the Food Chain
The energy food (chemical potential energy – glucose) in
the producer is passed on directly to the first consumer
(herbivore), the energy food in the herbivore is then passed
onto the first order carnivore. Organisms continuously
consume and release energy to survive.
Figure 2: A food chain shows the feeding relationships in a forest ecosystem.
Feeding Levels
The location where an organism is found within a food
chain or food web, is known as a trophic level.
First Trophic Level – contains producers, such as grass or
algae.
Second Trophic Level – contains herbivores, such as mice,
rabbits and some insects.
Third and Fourth Trophic Levels – contains carnivores
which eat other consumers, such as a snake eating a mouse
and then a hawk eating the snake.
Carnivores that eat other consumers are found in a predator
– prey relationship.
Beyond Food Chains
The food chain is a single pathway indicating a feeding
relationship. These food chains make up a complex system
of relationships among different species.
Food Web
A food web shows many interconnecting food chains,
showing various species feeding on many other organisms.
When consumers feed on many different other species, then
the impact on one specific species is lessened, which in
turn maintains sustainability of the ecosystem.
Figure 5: A food web is still not a complete model of every interaction in an ecosystem.
A complete model would show thousands of species.
Effects of Changes to a Food Web
Any change in an ecosystem can affect a food web. These
changes can be natural increasing competition for food
amongst other organisms.
Human actions are one factor that may disrupt an
ecosystem and its food web. If an organism in a lower
trophic level decreases or is lost, it will affect organism
further up the trophic levels.
Energy Pathways
All living organisms require energy for survival. They use
chemical potential energy (glucose) for cellular respiration.
One form of energy that is released is thermal energy (heat).
When one organism eats another organism it gains its
stored energy (Pyramid of Energy). Only 10% of the
energy is passed on by an organism, from one trophic level
to the next. In each trophic level the amount of energy is
less as you move upward.
Figure 6: A rusty crayfish invades the ecosystem and competes with native crayfish and
minnows for many of the same foods.
Check Your Learning:
Questions 1 – 5, pg. 47
Wrap Up:
- Each species occupies a unique ecological niche.
- Feeding relationships among organisms can be described
by food chains and food webs.
- Ecosystems can be disrupted by natural and human
actions.
- Only about 10 % of the energy available at any trophic
level is transferred to the next higher level.