Ecosystem EnergyCh 5.1 - 5.2, 5.5

Characteristics of Ecosystems

Ch 5.1

Trophic Levels• trophic level: feeding level

• food chains: describe where the energy and nutrients go as they move from one organism to another

• energy moving “up” the food chain

• seldom isolated entities

• food web: interconnected food chains

Trophic Categories

• autotroph: produce their own food

• heterotroph: must consume their food

• consumers: eat living prey

• decomposers: break down dead organic matter

Producers

• primary production: photosynthesis and growth of producers

• most are green plants

• chlorophyll: green pigment involved in photosynthesis

• chemosynthesis: using inorganic chemicals to form organic matter

Consumers• consumers: eat living stuff

• primary consumers: animals that feed directly on producers

• secondary consumers: animals that feed on primary consumers

• carnivores: secondary and higher-order consumers

• omnivores: eat both plants and animals

Decomposers• decomposers: eat dead stuff

• detritus: dead stuff (leaves, grasses, plant material, fecal wastes, dead bodies) eaten by decomposers

• scavengers, detritus feeders, chemical decomposers

• fermentation: modified cell respiration that occurs in the absence of oxygen

• anaerobic: without oxygen

Trophic Levels: Limits

The Flow of Energy in Ecosystems

Ch 5.2

Energy Flow

• photosynthesis captures only 2% of incoming solar energy

• 120 Gigatons = terrestrial net production

• standing-crop biomass: actual biomass of primary producers at any given time

Fate of Food

• 60-90% of food is burned for energy

• remaining 10-40% converted to body tissues

• cellulose: cell wall material that is not digested

Energy Flow• Only a fraction is passed on...

1. much of the preceding trophic level is biomass that is not consumed

2. much of what is consumed is used as energy to fuel the heterotroph’s cells and tissues

3. some of what is consumed is undigested and passes through the organism as waste

Energy Flow• Inefficiency means two things...

1. individuals at higher levels in the biomass pyramid represent a greater amount of the Sun’s energy for the same amount of body tissue

• takes a longer time to produce a top-order consumer

• top-order consumer also requires more water and other resources

Energy Flow

• Inefficiency means two things...

2. Some materials are difficult to get rid of and remain in the bodies of predators at higher rates than in their prey

• biomagnification

• bioaccumilate: build up in the tissues

Aquatic Systems• energy transfer is often more efficient

• takes less energy to support your body weight in water than on land or air

• food chains can be longer

Aquatic Systems

• The biomass pyramid in aquatic systems often does not resemble the biomass pyramid on terrestrial ecosystems

• phytoplankton is often ephemeral

Human Values and Ecosystem Sustainability

Ch 5.5

Human Values: Energy Flow• almost 11% of Earth’s land has

been converted from forest/grassland to agriculture

• Benefits of forests: 3.3 billion cubic meters of wood

• 15% of the world’s energy consumption is derived from plant material

• 40% of primary production on land appropriated for human needs - yet we only represent 5% of the biomass

Human Values: Cycles• burning of fossil fuels has increased CO2 in the atmosphere, where, by

the mid-21st century, it will have doubled since the beginning of the industrial revolution

Value of Ecosystems• incremental value: the economic value placed on changes in the

quantity or quality of various types of services may influence human welfare

• Total value of ecosystems to humans was $41 trillion in 2004....close to the $55 trillion calculated for the gross world economic product in 2004

Value of Ecosystems

• ecosystem capital stock: the ecosystems and the populations in them, including the lakes and wetlands)

• must be given adequate weight in public-policy decisions involving changes to that stock

• annual loss of $250 billion through habitat conversion alone!

Restoration• Potential for restoration rests

on...

1. Abiotic factors must have remained unaltered, or, if not, can at least be returned to their original state

2. viable populations of the species formerly inhabiting the ecosystem must still exist

3. ecosystem must not have been upset by the introduction of one or more nonnative species that cannot be eliminated and that may preclude the survival of reintroduced species

Restoration• Why restore ecosystems?

1. aesthetic reasons

2. for the benefit of human use

3. benefit of the species and ecosystems themselves

The Future

• agriculture will likely require at least 15% more land in the future

• must use these resources sustainably

Managing Ecosystems

• virtually no ecosystem can escape human impact

• objectives can be to maximize profit OR maintain the forest as a sustainable and diverse ecosystem that yields multiple products and services

Managing Ecosystems

• ecosystem management: comprises several main principles

• looks at ecosystems on both small and large scales

• looks at the human element of these ecosystems

US Forest Service

• responsible for managing 192 million acres of national forests

• believes the policy of sustainability should be the guiding star for stewardship of the national forests and grasslands

Human Effects: Summary• everyone in the world depends on

nature

• humans have made unprecedented changes to ecosystems:

• weakened nature’s ability to deliver other key services such as the purification of air/water, protection from disasters, provision of medicines

• edge of a massive wave of species extinctions

• pressures on ecosystems will increase globally