chapretr 42 - ecosystems and energy

Ecosystem

Consists of all the organisms living in a community , and the abiotic factors with which they interact

• range from microcosm (aquariums) to a large area like a lake or forest

• are open systems, absorbing energy and mass and releasing heat and waste products

2 dynamics of ecosystems

Energy flow and chemical cycling

• energy flows through ecosystems while matter cycles within them

• Plants and other photosynthesis organisms convert solar energy to chemical energy but the total amount of energy doesn’t change (1st law of thermodynamics)

• In an ecosystem , energy conversions arent 100% efficient as some gets lost as heat

Law of conservation of mass

States that matter cant be created or destroyed

• chemical elements are continually recycled within ecosystems

How are forest ecosystems getting nutrients

They enter as dust or solutes in rain and carried away in water

Autotrophs vs heterotrophs

Autotrophs - builds molecules themselves using photosynthesis organisms convert solar chemosynthesis as an energy source

Heterotrophs - depend on the biosynthetic output of other organisms

Flow of energy and nutrients

Primary producers (autotrophs) → primary consumers (herbivores) → secondary consumers (carnivores) → tertiary consumers (carnivore feeding on carnivore)

Detritivores / decomposers

Consumers that derive their energy from detritus (non living organic matter)

• prokaryotes and fungi a re important detritvores

• Decomposition connects all trophic levels

Primary production in ecosystem

Amount of light energy converted to chemical energy by autotrophs during a given time period

• extent of photosynthetic production sets the spending limit for the energy budget of an ecosystem

Global energy budget

Amount of solar radiation reaching the earths surface limits photosynthetic output of ecosystems

• only a small fraction of solar energy actually strikes photosynthetic organisms and even less is of a useable wavelength

Gross primary production (GPP)

Ecosystems Total primary production

Net primary production (NPP)

Is GPP minus energy used by primary producers for their autotrophic respiration (Ra)

• NPP is usually about ½ of GPP

Gross and net primary production

To ecologist, NPP is a key measurement because it represents the storage of chemical energy that will be available to consumers in the ecosystem

• ecosystems greatly vary in NPP and contribution to the total NPP on earth

• NPP is expressed as energy per unit area per unit time or as biomass added per unit per unit time

Standing crop

Total biomass of photosynthetic autotrophs at a given time

Which areas have the highest rates of global net primary production

Tropical areas

Which ecosystems are the most productive per unit area

Tropical rain forests, estuaries and coral reefs

Which ecosystem is the most unproductive per unit area

Marine ecosystems

• but contribute much to global net primary production because of their volumes

Net ecosystem production (NEP)

Measure of the total biomass accumulated during a given period of time

• GPP - total respiration of ALL organisms in a system (Rt)

• Useful to ecologists because its value determines whether an ecosystem is gaining or losing carbon over time

Primary production in aquatic systems

In aquatic ecosystems, both light and nutrients are important in controlling primary production

Importance of light to primary production

Because solar radiation drives photosynthesis, light is a key variable driving primary production in oceans (depth of light penetration affects primary production)

• about half the solar radiation is absorbed in the first 15cm of water (even in clear water, only 5-10% of radiation reaches a depth of 75m)

In marine and freshwater what controls primary production

Both light and nutrients

• nitrogen and phosphorus are usually the nutrient that limits marine production

• Some oceans are limited by iron

Limiting nutrient

Is the element that must be added for production to increase in an area

Affects of nitrogen, ammonium and phosphorus on phytoplankton

Phosphorus - rich in supply , no affect

Ammonium - a nitrogen source, increased growth

Nitrogen - limiting phytoplankton growth off the shore of Long Island New York, where pollution from duck farms added phosphorus and nitrogen

Areas of upwelling

Where deep nutrient rich waters circulate in the ocean, are areas of very high primary production

• nutrients stimulate growth of phytoplankton that form the base of marine food webs and are prime fishing locations

Negative effects of nutrients on lakes

• large amounts of nutrients can cause a sewage runoff to cause eutrophication in lakes ‘

• This leads to a loss of most fish species

What affects primary production in terrestrial ecosystems

• temperature

• Moisture

• Soil nutrients - nitrogen limits plant growth, phosphorus limits older soils where phosphate has been leached away by water

Actual evapotranspiration

Water annually transpired by plants and evaporated from a landscape

• can represent contrast between wet and dry climates

• Related to net primary production

Secondary production of an ecosystem

Amount of chemical energy in food converted to new biomass during a given period of time

Production efficiency of an organsim

Is the fraction of energy stored in food, not used for respiration

• ex. When a caterpillar feeds on a leaf, 1/6 of energy in a lead is used for secondary production

Trophic efficiency

Percentage of production transferred from one trophic level to the next

• usually 5-20%

• Is multiplied over the length of a food chain

What percentage of chemical energy fixed by photosynthesis reaches a tertiary consumer

0.1%

Pyramid of net production

Represents the loss of energy with each transfer in a food chain

• progressive loss of energy along a food chain, limits abundance of top level carnivores that an ecosystem can support

Biomass pyramids

Each tier represents the dry weight of all organisms in one trophic level

• most biomass pyramids show a sharp decrease at successively higher trophic levels but some aquatic ecosystems are different

Biogeochemical cycles

A nutrient circuit in ecosystems involving both biotic and abiotic components

• gaseous carbon, oxygen suffer and nitrogen occur in the atmosphere and cycle globally

• Less mobile elements like phosphorus, potassium and calcium cycle on a more local level

• Model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs

• All elements cycle between organic and inorganic reservoirs

What are the four biogeochemical cycle

1. Water cycle

2. Carbon cycle

3. Nitrogen cycle

4. Phosphorus cycle

Biological importance of water cycle

Water is essential to all organisms

Available forms of water cycle

Alll organisms are capable of exchanging water directly with the environment

Reservoirs of water cycle

Oceans contain 97% of water in the biosphere, 2% is bound in glaciers and ice caps, 1% in lakes, rivers annd groundwater

Key processes of water cycle

Evaporation, precipitation and transpiration by plants moving large volumes into the atmosphere

Biological importance of carbon cycle

Carbon forms framework of organic molecules, essential to all organisms

Available forms of the carbon cycle

Photosynthetic organisms use CO2 and convert carbon to organic forms used by consumers

Reservoirs of carbon cycle

• fossil fuels

• Soils

• Sediments of aquatic ecosystems

• Oceans, plants and animal biomass

• Sedimentary rock - largest reservoir

Key processes of carbon cycle

• photosynthesis by plants

• Phytoplankton counterbalances CO2 by added cellular respiration of producers and consumers

• Burning of fossil fuels and wood

Biological importance of nitrogen cycle

Nitrogen is part of amino acids, proteins, and Nucleic acids, often limiting plant nutrient

Available forms of nitrogen cycle

• plants use inorganic ammonium and nitrate

• Animals only use organic sources of nitrogen

Reservoirs of nitrogen cycle

• atmosphere is 80% nitrogen

• Soils

• Sediments of lakes, rivers and oceans

• Biomass of living organisms

Key processes of nitrogen cycle

• Major pathway for nitrogen to enter ecosystem is nitrogen fixation

• human inputs like fertilization and legume crops

Biological importance of phosphorus cycle

Phosphorus is a major constituent of Nucleic acids, phospholipids and ATP and a mineral component of bone

Available forms of phosphorus cycle

Phosphate which plants absorb and use in synthesis of organic compounds

Reservoirs of phosphorus cycle

• Sedimentary rocks of marine origin

• Soil

• Oceans

• Organisims

Key processes of phosphorus cycle

• weathering of rocks adds phosphate to soil

• Some leaches into ground and surface water

• Phosphate taken up by producers, returned to soil by excretion and decomposition

Restoration ecology

Seeks to speed up recovery of degraded ecosystems. It’s based on the assumption that environmental damage is at least partially reversible

2 key strategies of restoration ecology

1. Bioremediation

2. Biological augmentation

Bioremediation

Use of living organisms to detoxify ecosystems. The organisms most often used are prokaryotes, fungi or plant

• these organisms can take up and sometimes metabolize toxic molecules

• Ex. Types cattails remove nutrients and pollutants from aquatic ecosystems

Biological augmentation

Uses organisms to add essential materials to a degraded ecosystem

• encourages growth of plants that can live in nutrient poor soils which often speeds up succession and ecosystem recovery

• Ex nitrogen fixing plants like legumes can increase the avaible nitrogen in soil, once established, other native species can access the soil nitrogen