Chapter 54

Ecosystems

Ecosystems

Ecosystem - consists of all the organisms living in a community as well as all the abiotic factors with which they interact.

Trophic structure - all the feeding relationships within an ecosystem.

Trophic levels - divides the species of an ecosystem by what their main source of nutrition is.

Trophic Relationships in Ecosystems Primary Producers - 1st trophic level

consisting of autotrophs; “the base” (photosynthesize)

Primary Consumers - herbivores Secondary Consumers - carnivores that

eat herbivores Tertiary Consumers - carnivores that eat

other carnivores

Trophic Relationships in Ecosystems (con’t) Quarternary Consumers - high order

carnivores that consume larger carnivores

Detritovores - derive energy by consuming dead organic material such as leaves, feces, and dead organisms from all trophic levels.

Food Chains and Food Webs

Food Chain - pathway by which food energy is passed from trophic level to trophic level– Example

• dandelion - grasshopper - mouse - snake - hawk (terrestrial)

• phytoplankton - zooplankton - small fish - medium sized fish - large fish (marine)

Food Webs - elaborate feeding relationships between all trophic levels

Food Chains and Food Webs (con’t)

Ecosystem Processes

Production - rate of incorporation of energy and materials into bodies of organisms

Consumption - metabolic use for growth and reproduction of assimilated organic materials

Decomposition - breakdown of organic material into inorganic material– bacteria, fungi, and some animals

– links all trophic levels recycling nutrients back into the abiotic environment

Energy Flow in Ecosystems

An ecosystem’s energy budget depends on the amount of primary productivity.– the amount of light energy converted to

chemical energy (organic compounds) Biomass - term used to describe primary

productivity– the amount of new vegetation added to the

ecosystem in terms of dry weight per unit time

Productivity of Different Ecosystems

Energy Flow through Ecosystems

Most of the energy is lost as it flows through each trophic level due to heat.– metabolic rate of the organism

Secondary Productivity - rate at which consumers convert chemical energy into their own new biomass.– Herbivores can only eat a fraction of the plant

biomass produced, and can only digest a fraction of what they eat.

Energy Partitioning in a Caterpillar

lost as heat

converted to biomass

recycled by detritovores

Energy Flow through Ecosystems (con’t) Ecological efficiency - percentage of energy

transferred from one trophic level to the next (~10% is transferred)

Pyramid of Productivity - food chain is diagrammatically represented using blocks where the primary producers form the base

Biomass pyramid - representation of the standing crop biomass in a trophic level

Pyramid of Net Productivity

Primary Producers only convert ~1% of light energy into biomass.

Consumers convert ~10% of chemical energy into biomass.

Biomass Pyramid

Biogeochemical Cycles

Water cycle Carbon cycle Nitrogen cycle Phosphorus cycle

Biological Magnification

Biological magnification - concentration of toxins at successive trophic levels– top-level carnivores tend to be the

organisms most severely affected . These toxins, such as DDT and PCBs,

are pesticides that may accumulate in tissues after ingestion. (fat tissue)

Biological Magnification of DDT in a Food Chain

Food Chain Concentration of DDT in A Long Island Marsh sprayed for Mosquito Control 1967

ppm

Water .00005

Plankton .04

Silverside Minnow .23

Sheephead Minnow .94

Pickerel 1.23

Needlefish 2.07

Heron 3.57

Tern 3.91

Osprey 13.8

Merganser 22.8

Cormorant 26.4

Human Impact-Ozone Depletion Ozone (O3) - bottom layer of the stratosphere that

protects Earth from UV radiation. Depletion since 1975 is due to CFC’s,

chlorflourocarbons, chemicals used in refrigerators, aerosol, and styrofoam.

Chlorine reacts with the O3 molecules reducing them to O2 molecules

Reactions allow the chlorine to dissociate from the O2 molecules allowing the chlorine to react with more ozone.

Human Impact-Ozone Depletion (con’t)

Ozone is constantly produced and destroyed, however, atoms, such as Cl & Br, siphon ozone away faster than

it is being produced.

Ozone Depletion - Antarctica