• 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 Ecology

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

Small

Large

• 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

Ecosystem Ecology

Simple Ecosystem

Model

Energy input from sun

NutrientCycling

ProducersAutotrophs (plants and other

self-feeding organisms)

ConsumersHeterotrophs (animals, most fungi,

many protists, many bacteria)

Energy output (mainly metabolic heat)

Ecosystem

Plants Animals

Materials

• 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

Ecosystem Ecology

• 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

Energy and Materials

Ecosystems1. Population Interactions

2. Energy Flow

3. Material Cycles

Ecosystems1. Population Interactions2. 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 ProducersPhotoautotrophs

+ + +C6H12O6

+ O2sugar oxygen

Sunlight + water + CO2 + minerals =

=

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. Herbivore2. Carnivores3. Omnivores4. Parasites5. Decomposers

Role of Organisms• Consumers

1. Herbivore2. Carnivores3. Omnivores4. Parasites5. Decomposers

Role of Organisms• Consumers

1. Herbivore2. Carnivores3. Omnivores4. Parasites5. Decomposers

Role of Organisms• Consumers

1. Herbivore2. Carnivores3. Omnivores4. Parasites5. Decomposers

Role of Organisms• Consumers

1. Herbivore2. Carnivores3. Omnivores4. Parasites5. 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

4th trophic level

3rd trophic level

2nd trophic level

1st trophic level

Food Chain

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

crow

upland sandpiper

garter snake

frog

spider weasel badger coyote

ground squirrelpocket gopherprairie vole

sparrow

earthworms, insects

First Trophic Level

Second Trophic Level

Higher Trophic Levels

Connections in a tallgrass prairie food web

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