Ecosystems

EcosystemsChapter 3

ECOLOGY

The study of how organisms interact with one another and their environment

Cells

Prokaryote• One-celled organism• Lacks a nucleus • Lacks internal membrane structures• Example – bacteriaEukaryote• Distinct nucleus• Contain organelles with membranes

Cells

Species

• Definition: set of individuals that produce fertile offspring

• Nomenclature system – Page S46 in text• How many? Best guess is 10 – 14 million• 1.8 x 106 identified

Connections in Nature

Population• Group of individuals of same species living in

same place at same time• There is genetic diversity (variation)• A habitat is a place where an individual or

population lives; a supply of resources


Community• Definition: All the populations of different

species living in a certain place• Interaction occurs! This includes feeding,

competition for other resources


Ecosystem• Definition: A community of different species

interacting with each other and their non-living environment

• Huge range in sizes• Natural or artificial• No clear boundaries (erosion, winds,

migration, etc)


Biospheres• Definition: parts of the earth, air, water and

soil where life is found• A global ecosystem

Fig. 3-3, p. 52

Parts of the earth's air, water, and soil where life is found

Biosphere

Smallest unit of a chemical element that exhibits its chemical properties

Ecosystem

Community

Population

Organism

A community of different species interacting with one another and with theirnonliving environment of matter and energy

Populations of different species living in a particular place, and potentially interacting with each other

A group of individuals of the same species living in a particular place

Cell

An individual living being

The fundamental structural and functional unit of life

Molecule

Atom

Chemical combination of two or more atoms of the same or different elements

KEEPING US ALIVE

Components of Life Support

Atmosphere• Troposphere: closest to surface of the earth

(7-11 km thick); • Majority of air is here (78% N2, 21% O2, 1%

CO2, H2O, CH4 – greenhouse gases!)


Atmosphere• Stratosphere: next closest layer, rides on top

of troposphere• Most of atmospheric O3 is found here• Ozone absorbs most of the sun’s UV radiation


Hydrosphere• Consists of all water on or near the surface of

the earth• May be in liquid form• May be in solid form (ice caps, permafrost,

etc.)• May be in vapor form


GeosphereConsists of the:• Core: liquid and solid; produces magnetic field• Mantle: semi-molten state; largest portion of

the geosphere• Crust: hard, outermost shell; all our resources

are here


Biosphere• Parts of the atmosphere, geosphere, and

hydrosphere where life exists• Extends from about 9 km up to the bottom of

the ocean

Land and Water

Biomes• ‘Biome’ only applies to terrestrial portions of

the biosphere• A biome will have a distinct climate• A biome will have a distinct set of speciesAquatic Life Zones• Includes freshwater and ocean (marine) life

zones

Factors Sustaining Life

One-way flow of high quality energy• Originates from the sun• Travels through organisms• Is dissipated into the environment (low-

quality E)


Cycling of Matter (Nutrients)• There is a fixed supply of nutrients/matter• Round trips must be done• Time involved varies from seconds to

centuries


Gravity• Keeps the atmosphere around!• Enables movement• Enables cycling

THE FLOW OF ENERGY AND NUTRIENTS

What Happens to Solar Energy?

Comes to earth as shortwave radiation• UV and visible light• 30% is reflected back into space (albedo)• 20% is absorbed by the atmosphere• 50% absorbed by the surface

What Happens to Solar Energy?

Absorbed energy:• Land, water heat up• They re-radiate in longer wavelengths (IR)• This IR is absorbed or “trapped” by CO2, H2O,

etc.• Air heats up – Greenhouse effect• <0.1% is used by green plants

Ecosystem Components

Living and Nonliving • Abiotic: the nonliving portion; water, air,

nutrients, rocks, heat, solar energy• Biotic: the living and once-living; plants,

animals, microbes, dead organisms, and waste products

• Range of Tolerance: varies for each population in an ecosystem; optimum levels


Abiotic Factors• Limiting Factors regulate population growth• On land these include precipitation,

temperature, nutrients; too much is just as bad as too little

• Aquatic: temperature, sunlight, nutrients


Producers and Consumers• Trophic Level (feeding level): determined by food

source of the organism; energy & nutrients are transferred through levels

• Autotrophs (Producers): make their own food– Land: plants; – Open water: phytoplankton– Most: photosynthesis; near hydrothermal vents -

chemosynthesis


• (Heterotrophs) Consumers: –Primary: Herbivores– Secondary (carnivores); ex – spiders, frogs,

birds– Tertiary (third) or higher; feed on other

carnivores–Other terms: omnivores, decomposers,

detritivores


• Aerobic Respiration: –Occurs in cells, energy is obtained from glucose

and oxygen–Products are CO2 and H2O

• Anaerobic Respiration (Fermentation)–Done by some decomposers–Breakdown of glucose w/out O2; products are

methane, ethanol, acetic acid, and H2S


Energy Flow and Nutrient Cycling• The importance of decomposers• There would be little, if any, nutrient

cycling without detritus feeders

Energy Flow

Energy Flows Through Trophic Levels• Food Chain: sequence of organisms, each of

which serves as a food or energy source for the next

• Food Web: network of interconnected food chains; most consumers feed on more than one type of organism

Energy Flow

Usable Energy ↓ With Each Link• Biomass: dry wt. of all the organic matter at a trophic

level• Energy transfer is not efficient• Ecological efficiency- The proportion of consumed

energy that can be passed from one trophic level to another –10% is typical– Follows a pyramidal flow

Energy Transfer Efficiency and Trophic Pyramids

• Biomass- The energy in an ecosystem is measured in terms of biomass.

• Standing crop- The amount of biomass present in an ecosystem at a particular time.

• Trophic pyramid- The representation of the distribution of biomass among trophic levels.

Energy Flow

Production Rates• Gross Primary Productivity: rate at which an

ecosystem’s producers convert solar E to chem E as biomass

• Measured in kcal/m3/yr• Net Primary Productivity (NPP): rate of chem E

production minus the rate at which E is used

The Flow of Matter

Water Cycle: collects, purifies, & distributes H2O• Evaporation• Condensation (precipitation)• Transpiration• Surface runoff: feeds lakes, streams, etc.• Stored: glaciers, aquifers, etc• Humans alter in 3 ways: over-withdrawal,

clearing vegetation (erosion), increase flooding ( by draining wetlands)

The Flow of Matter

Carbon Cycle (Predominant form: CO2)• Producers remove CO2 through photosynthesis• Consumers and decomposers return it via

respiration.• Human alter in a big way:• Fossil fuels are the result of millions of years of

compression of organic material; storing CO2. In the past 100 years, we have released all that CO2

The Flow of Matter

Nitrogen Cycle• 78% of the air = N2; cannot be fixed (exceptions)• 2 natural fixers: lightning, bacteria• Fixation: N2 → NH3 → NH4

+ (ammonium ion)

• Nitrification: NH3, NH4+ → NO3

- (used by plants)

• Denitrification: NH3 → N2 (back into air)

The Flow of Matter

Nitrogen Cycle: Human Impact• NO production → acid rain• N2O (livestock waste) → greenhouse gas• Deforestation, etc. → release of N2• Ag runoff → ↑ NO3

-

• Removal of N from topsoil during harvest

The Flow of Matter

Phosphorus Cycle (does not use atmosphere)• Major reservoir: PO4

3- in rocks, ocean sediment• Water erodes P from rock, picked up by plants• Limiting factor in plant growth• Human impact: making fertilizer, runoff

The Flow of Matter

Sulfur Cycle• Major underground reservoirs, ocean sediment• Volcanic eruptions (H2S)• Atmospheric SOx → acid rain• Human impact: burning coal

Ecosystems respond to disturbance

Disturbance- An event caused by physical, chemical or biological agents that results in changes in population size or community composition

Watershed- All of the land in a given landscape that drains into a particular stream, river, lake or wetland.

Resistance versus Resilience• Resistance- A measure of how much a

disturbance can affect its flows of energy and matter.

• Resilience- The rate at which an ecosystem returns to its original state after a disturbance.

• Restoration ecology- A new scientific discipline that is interested in restoring damaged ecosystems.

Instrumental Values of Ecosystems• Provisions- Goods that humans can use directly.• Regulating services- The service provided by natural

systems that helps regulate environmental conditions.• Support systems- The support services that natural

ecosystems provide such as pollination, natural filters and pest control.

• Resilience- Resilience of an ecosystem ensures that it will continue to provide benefits to humans. This greatly depends on species diversity.

• Cultural services- Ecosystems provide cultural or aesthetic benefits to many people.

Documents

Ecosystems