Chapters 55

Concept 5: Ecosystems – Analyzing productivity, energy flow, and chemical cycling.Ecosystems (Ch 55)

How energy flows though the ecosystem by understanding the terms that relate to food chains and food webs

The difference between gross primary productivity and net primary productivity

The carbon and nitrogen biogeochemical cycles

Ecosystemsconsist of all the organisms living in a

community, as well as the abiotic factors with which they interact

Ecosystems range from a microcosm (aquarium) to a large area such as a (forest, lake)

Ecosystem Dynamics involve two main processes: energy flow and chemical cycling

Flow of EnergyThe first law of thermodynamics states that

energy cannot be created or destroyed, only transformedEnergy enters an ecosystem as solar radiation, is

conserved, and is lost from organisms as heat

The second law of thermodynamics states that every exchange of energy increases the entropy of the universeIn an ecosystem, energy conversions are not

completely efficient, and some energy is always lost as heat

Cycling of Chemicals• The law of conservation of mass states that

matter cannot be created or destroyed• Chemical elements are continually recycled

within ecosystems• Ex) In a forest ecosystem, most nutrients enter

as dust or solutes in rain and are carried away in water

Overall: Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

Trophic LevelsAutotrophs - build molecules themselves

using photosynthesis or chemosynthesis as an energy sourceEx) plants and algaeEx) chemosynthetic bacteria

on hydrothermal vents

Heterotrophs - depend on the biosynthetic output of other organisms

Trophic LevelsEnergy and nutrients pass from:

Primary producers (autotrophs) to Primary consumers (herbivores) to Secondary consumers (carnivores) to Tertiary consumers (carnivores that feed

on other carnivores)

Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matterProkaryotes and fungi are important detritivoresDecomposition connects all trophic levels

Try This!Which of the following is absolutely essential

to the functioning of an ecosystem?A) producersB) producers and herbivoresC) producers, herbivores, and carnivoresD) detritivoresE) producers and detritivores

Primary Productivity (Lab 12!)The amount of light energy converted to

chemical energy (organic compounds) by an ecosystem’s autotrophs during a given period of time

Background:Photosynthesis (required light energy)

carbon dioxide + water → glucose + oxygenCellular Respiration (generates ATP – energy

currency) glucose + oxygen → carbon dioxide + water

Primary Productivity• Gross primary production (GPP)

– Total primary production of the ecosystem

• Net primary production (NPP) – GPP minus energy used by primary producers for respiration• Only NPP is available to consumers• Ecosystems vary greatly in NPP and

contribution to the total NPP on Earth

Ecological EfficiencyDescribes the proportion of energy represented at one

trophic level that is transferred to the next trophic level

On average, efficiency is only ~10%10 percent of the productivity of one trophic level is

transferred to the next level. The remaining 90% is consumed by individual metabolic activity or to detritovores

Applications: Farming: Energy required to raise and sustain carnivores is

far greater than that of herbivores… we eat cows, we ride horses

Bioaccumulation as you go up the trophic levels Ex)High mercury in tuna and swordfish Ex) High toxicity levels in orcas

Ecological PyramidsUsed to show relationship between trophic

levels

Horizontal bars or tiers: represent relative size in terms of either: Energy (productivity) Biomass Numbers of organisms

Tiers are stacked in the order in which energy is transferred.

Try ThisWhich of the following is not true of a pyramid of

production?A) Only about 10% of the energy in one trophic level is

passed into the next level.B) Because of the loss of energy at each trophic level,

most food chains are limited to three to five links.C) The pyramid of production of some aquatic

ecosystems is inverted because of the large zooplankton primary consumer level.

D) Eating grain-fed beef is an inefficient means of obtaining the energy trapped by photosynthesis

E) A pyramid of numbers is usually the same shape as a pyramid of production

Biogeochemical CyclesDescribes the flow of essential elements from the

environment to living things and back to the environment.p. 1209-1214 in Campbell

For each of the following essential elements, you

much know:The reservoirs (major storage location)The process of assimilation (incorporation into plants

and animals) The process of release (how it returns to the

environment)

Biogeochemical CyclesHydrolytic Cycle (water cycle)

Carbon Cycle (required for the building of all organic compounds)

Nitrogen Cycle (required for the manufacture the building blocks of proteins and nucleic acids)

Phosphorus Cycle (required for the manufacture of ATP and all nucleic acids. Cycle is similar to other mineral cycles like calcium)

Try ThisThe finding of harmful levels of DDT in

grebes (fish-eating birds) following years of trying to eliminate bothersome gnat populations in a lakeshore town is an example of...

Try ThisThe finding of harmful levels of DDT in

grebes (fish-eating birds) following years of trying to eliminate bothersome gnat populations in a lakeshore town is an example of...

BIOLOGICAL MAGNIFICATION

Concept 5: Ecosystems – Analyzing productivity, energy flow, and chemical cycling.Ecosystems (Ch 55)

How energy flows though the ecosystem by understanding the terms that relate to food chains and food webs

The difference between gross primary productivity and net primary productivity

The carbon and nitrogen biogeochemical cycles