Ecosystem Ecology
• The biological and physical components of
the environment are a single interactive
system in the concept of the ecosystem
– A.G. Tansley coined “ecosystem” in 1935
Ecosystem =
Ecosystem =
A group of interacting populations and their
physical environment.
All interacting by a flow of energy and
with their physical and chemical
environments.
Ecosystems can be
Large
Small
Ecosystem Ecology
• An ecosystem is a spatial concept. It has
boundaries and can be viewed in the
context of its surrounding environment
– It is sometimes difficult to clearly separate
ecosystems
Simple
Ecosystem
Model
Energy
input from
sun
Producers
Autotrophs (plants and other
self-feeding organisms)
Nutrient
Cycling
Consumers
Heterotrophs (animals, most fungi,
many protists, many bacteria)
Energy output (mainly metabolic heat)
Ecosystem
Materials
Plants
Animals
Ecosystem Ecology
• Community structure varies in response to
environmental conditions
• Organisms, in part, define the abiotic
environment through succession
– Tress affect temperature in a forest
– Phytoplankton can affect water temperature
Energy and Materials
• Inputs are exchanges from the
surrounding environment into the
ecosystem
• Outputs are exchanges from inside the
ecosystem to the surrounding environment
• A closed ecosystem is one with no
inputs; an open ecosystem receives
inputs form the surrounding environment
Ecosystems
1. Population Interactions
2. Energy Flow
3. Material Cycles
Ecosystems
1. Population Interactions
2. Energy Flow
3. Material Cycles
Modes of Nutrition
• Autotrophs
– Capture sunlight or chemical energy
– Primary producers
• Heterotrophs
– Extract energy from other organisms or
organic wastes
– Consumers, decomposers, detritivores
Role of Organisms
• Producers
(photoautotrophs)
Primary Producers
Photoautotrophs
=
+
+
+
Sunlight + water + CO2 + minerals = C6H12O6 + O2
sugar oxygen
Energy
Materials
Concept 21.1
Feeding Relationships
• Each feeding category, or trophic
level, is based on the number of
feeding steps by which it is separated
from autotrophs.
Role of Organisms
•
Consumers
1.
2.
3.
4.
5.
Herbivore
Carnivores
Omnivores
Parasites
Decomposers
Role of Organisms
•
Consumers
1. Herbivore
2. Carnivores
3. Omnivores
4. Parasites
5. Decomposers
Role of Organisms
•
Consumers
1.
2.
3.
4.
5.
Herbivore
Carnivores
Omnivores
Parasites
Decomposers
Role of Organisms
•
Consumers
1.
2.
3.
4.
5.
Herbivore
Carnivores
Omnivores
Parasites
Decomposers
Role of Organisms
•
Consumers
1.
2.
3.
4.
5.
Herbivore
Carnivores
Omnivores
Parasites
Decomposers
Concept 21.1
Feeding Relationships
• The 1st trophic level consists of
autotrophs or primary producers.
• Autotrophs generate chemical energy
from sunlight or inorganic chemical
compounds.
• This level also generates most of the
dead organic matter in an ecosystem.
Concept 21.1
Feeding Relationships
• 2nd trophic level:
•
Herbivores that consume
autotrophs; also includes detritivores
that consume dead organic matter.
• 3rd (and higher) trophic levels:
•
Carnivores that consume animals
from the level below.
Feeding Relationships
• Dead organisms and feces are
consumed by organisms called
detritivores (primarily bacteria and
fungi), in a process called
decomposition.
• Detritus is considered part of the 1st
trophic level, and detritivores are part of
the 2nd level.
Concept 21.1
Feeding Relationships
• Some organisms do not conveniently fit
into trophic levels.
• Omnivores feed at multiple trophic
levels.
• Example: Coyotes are opportunistic
feeders, consuming vegetation, mice,
other carnivores, and old leather boots.
Concept 21.1
Feeding Relationships
• All organisms are either consumed by
other organisms or enter the pool of
dead organic matter (detritus).
• In terrestrial ecosystems, only a small
portion of the biomass is consumed,
and most of the energy flow passes
through the detritus.
Energy Flow through Detritus
Feeding Relationships
• Much of the detritus in streams, lakes,
and estuaries is derived from terrestrial
organic matter.
• These external energy inputs are called
allochthonous inputs.
• Energy produced by autotrophs within
the system is autochthonous energy.
Food Chain
• A straight-line
sequence of who
eats whom
• Simple food
chains are rare in
nature
marsh hawk
upland sandpiper
garter snake
cutworm
plants
Trophic Levels
• Feeding relationships
– All organisms at a trophic level are the same
number of steps away from the energy input
into the system
• Autotrophs are producers
– closest to energy input
– first trophic level
Food Chain
4th trophic level
3rd trophic level
2nd trophic level
1st trophic level
Trophic Levels in a Desert Ecosystem
Food Webs
• A food web is a diagram showing the
connections between organisms and
the food they consume.
• It shows qualitatively how energy flows
from one component of this ecosystem
to another.
Food Webs
• As more organisms are added to a food
web, complexity increases to reflect the
complexity of real ecosystems.
• Feeding relationships can span multiple
trophic levels (omnivory) and may even
include cannibalism (circular arrows).
Food Web
marsh hawk
Higher
Trophic
Levels
Connections in a
tallgrass prairie food web
crow
upland
sandpiper
garter snake
frog
weasel
spider
Second
Trophic
Level
sparrow
earthworms, insects
First
Trophic
Level
badger coyote
prairie vole
pocket gopher
ground squirrel
grasses, composites
Fig. 30-4, p.529
Food Webs Are Complex
Trophic Cascades
• Trophic cascade: Series of trophic
interactions that result in changes in
biomass and species composition.
• Predation by a top carnivore (4th level)
decreases abundance of 3rd level
carnivores, which leads to an increase
in herbivores (2nd level), and then a
decrease in primary producers.
Trophic Cascades
• What controls energy flow through
ecosystems?
• The “bottom-up” view:
– Resources that limit producers determine
energy flow through an ecosystem.
Trophic Cascades
• The “top-down” view:
– Energy flow is governed by predator
consumption rates at the highest trophic
level, which influences multiple trophic
levels below them.
Trophic Cascades
• In reality, both controls are operating
simultaneously in ecosystems.
• Top-down control has implications for
the effects of trophic interactions on
energy flow.
Biological Magnification
Non-degradable or slowly degradable
substances become more and more
concentrated in tissues of organisms at
higher trophic levels of a food web
DDT in Food Webs
• Synthetic pesticide banned
in United States since
1970s
• Carnivorous birds
accumulate DDT in their
tissues, produce brittle egg
shells