Chapter 42 - Ecosystems and Energy

Ecosystem

consists of all the organisms living in a community, as well as the abiotic factors that they interact with

• can range from a microcosm like an aquarium to a large area like a lake or forest

• ecosystems are open systems

  • absorb energy and mass and release heat and waste products

2 main processes of ecosystems

energy flow and chemical cycling

energy flow and chemical cycling in ecosystems

energy flows through ecosystems while matter cycles within them

• plant and other photosynthetic organisms covert solar energy to chemical energy but the total amount of energy does not change (1st law of thermodynamics)

  • not all energy conversions are 100% efficient and some is lost as heat

Law of conservation of mass

states that matter cannot be created nor destroyed

• chemical elements are continually recycled within ecosystems

Flow of energy and nutrients in an ecosystem

primary producers (autotrophs) → primary consumers (herbivores) → secondary consumers (carnivores) → tertiary consumers (carnivores that feed on other carnivores)

detritivores (decomposers)

consumers that get their energy from detritus (nonliving oganic matter)

• prokaryotes and fungi are important detritivores

• decomposition connects all trophic levels

Primary production

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

solar radiation and photosynthetic output

limits photosynthetic output of ecosystems

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

Gross Primary Production (GPP)

total primary production of an ecosystem

Net Primary Production (NPP)

NPP = GPP - Ra

• Ra - energy used by primary producers for their autotrophic respiration (Ra)

• on average, NPP is about ½ GPP

• NPP represents the storage of chemical energy that will be available to consumers in the ecosystem

  • ecosystems vary greatly on NPP and contribution to the total NPP on Earth

• expressed as energy per unit area per unit time (J/m²/year)

  • or biomass added per unit area per unit time (g/m²/year)

standing crop

total biomass of photosynthetic autotrophs at a given time

Which are the most productive ecosystems per unit area

tropical rain forests, estuaries, and coral reefs

• marine ecosystems are relatively unproductive, but contribute to global net primary production because of their volume

Net Ecosystem Production (NEP)

measure of the total biomass accumulated over time

NEP = GPP - Rt

• Rt - total respiration of all organisms in the system

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

WHat is important in controlling primary production in aquatic systems

both light and nutrients

Limitation of light

solar radiation drives photosynthesis, so 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 1st 15m of water

• but aquatic productivity is more than just light

Limiting nutrient

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

• Nitrogen and phosphorus are usually the nutrients that most often limit marine production

  • some areas of the ocean are limited by micronutrient iron

Long island and limiting nutrient

• adding phosphorus (which was already at a high level) did not increase phytoplankton growth, but adding ammonium (nitrogen source) did

• nitrogen was limiting phytoplankton growth

Areas of upwelling and production

• areas of upwelling where deep nutrient-rich waters circulate in the ocean have high productivity

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

Nutrient limitation and ecological impacts

wide range of ecological impacts when large amounts of nutrients are added to lakes

• sewage runoff has caused eutrophication of lakes which can lead to loss of most fish species

factors that affect primary production in terrestrial ecosystems

• temp.

• moisture

• soil nutrients

actual evoapotranspiration

water annually transpired by plants and evaporated from a landscape

• represents contrast between wet and dry climates

• related to NPP

what limits most plant growth globally

nitrogen

• phosphorus limitations are common in older soils where phosphate has been leached away by water

secondary production

amount of chemical energy in food converted to new biomass during a given period of time in an ecosystem

production efficiency

fraction of energy stored in food not used for respiration in an organism

Caterpillar and production efficiency

when eating a leaf, only 1/6 (less than 17%) of the energy is used for secondary production

Trophic efficiency

percentage of production transferred from one trophic level to the next

• usually ranges from 5% - 20%

• multiplied over the length of a food chain

trophic efficiency and ecological pyramids

• approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer

• pyramid of net production represents 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 pyramid

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

nutrient circuits in ecosystems that involve biotic components

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

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

The water cycle biological importance

biological importance

• water is essential to all organisms

water cycle reservoirs

• oceans contain 97% of water in the biosphere, 2% is bound in glaciers and ice caps, 1% in lakes, fivers, and groundwater

water cycle available forms

• all organisms are capable of exchanging water directly with the environment

water cycle key processes

• evaporation and precipitation

• transpiration by plants moves large volumes into the atmosphere

the carbon cycle biological importance

biological importance

• carbon forms the framework of organic molecules essential to all organisms

Carbon cycle available forms

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

carbon cycle reservoirs

• fossil fuels, soils, sediments of aquatic ecosystems, the oceans, plant and animal biomass

• largest reservoir is sedimentary rock

• organisms return CO2 to the atmosphere through respiration

carbon cycle key processes

• photosynthesis by plants and phytoplankton counterbalances CO2 added by cellular respiration of producers and consumers

• burning of fossil fuels and wood

nitrogen cycle biological importance

part of amino acids, proteins, and nucleic acids

• often limiting plant nutrient

nitrogen cycle available forms

plants use inorganic ammonium and nitrate

• animals can only use organic sources of nitrogen

nitrogen cycle reservoirs

• atmosphere is 80% nitrogen

• soils, sediments of lakes, rivers, oceans, biomass of living organisms

nitrogen cycle key processes

nitrogen fixation is the major pathway for nitrogen to enter ecosystem

• human inputs include fertilizers and legume crops

phosphorus cycle biological importance

• phosphorus is a major constituent of nucleic acids, phospholipids, and ATP

• mineral component of bonr

phosphorus cycle available forms

• phosphate that plants absorb and use in synthesis of organic compounds

phosphorus cycle reservoirs

• sedimentary rocks of marine origin

• soil

• oceans (dissolved)

• organisms

phosphorus cycle key processes

• 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 (and 2 key strategies)

seek to speed up the recovery of degraded ecosystems

• based on the assumption that environmental damage is at least partially reversible

• two key strategies

  • bioremediation

  • biological augmentation

bioremediation

use of living organisms to detoxify ecosystems

• most used organisms are prokaryotes, fungi, or plants

  • can take up and sometimes metabolize toxic molecules

• ex. using Typha cattails to remove nutrients and pollutants from aquatic ecosystems

biological augmentation

uses organisms to add essential materials to a degraded ecosystem

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

• ex. nitrogen-fixing plants like legumes can increase the available nitrogen in soil

  • once established, other native species can access the soil nitrogen