Transcript Food Chains and Webs

Food Chains and
Webs
Ecosystem Interactions

Organisms in an ecosystem constantly
interact causing:
1. Stability within ecosystems
2. Growing or declining populations
3. Changes in abiotic and biotic factors
Stable Ecosystem

A stable ecosystem is one where each of the
following occurs:
1.
Population numbers of each organism fluctuates at a
predictable rate.
2.
Supply of resources in the physical environment
fluctuates at a predictable rate.
3.
Energy flows through the ecosystem at a fairly
constant rate over time.
Stable Ecosystems
 Predator-Prey relationships help to
stabilize ecosystems.
 As the prey population increases, so
does the predator population.
 As the prey population decreases, so
does the predator population.
Limited Resources
 When resources are limited, species with
compete for resources.
 Can be among same or different species, but
usually within the same *niche*
 Niche is the role an organism in its
environment (includes type of food it eats, how
it gets food and how it interacts with other
organisms).
Flow of Energy in Ecosystems
1. A food chain is the simplest path that
energy takes through an ecosystem.
2. Energy enters an ecosystem from the
sun.
3. Each level in the transfer of energy in
an ecosystem is called a trophic level.
Flow of Energy in Ecosystems
 Organisms in each trophic level use some of
the energy in the process of cellular
respiration, lose energy from heat loss and
store the rest.
Trophic Levels
 1st Trophic Level: Producers/Autotrophs
 2nd Trophic Level: Primary Consumers (herbivores-eat
plants only) and Heterotrophs
 3rd Trophic Level (or any higher): Secondary/Tertiary
Consumers-can be carnivores (eat only primary
consumers)or omnivores (eat both primary consumers
and producers)
 A heterotroph that breaks down organic material
returns it to the soil is a decomposer.
Food Webs
 Represent many interconnected food
chains describing the various paths that
energy takes through an ecosystem.