Energy and Matter in Ecosystems

Laws of Energy

• First Law: Energy is neither created nor destroyed, it simply changes form.

• Energy transformations are very important in living systems. • Second Law: Systems naturally move towards more disorder. • It takes a lot of energy to maintain organization (like that found

in a living creature). • All energy ultimately ends up as the very disordered entity we

call heat.• Energy flows through ecosystems because the Earth is an open

system to energy• The Earth constantly receives energy from the sun

Laws of Energy

A. First law: For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (B).

B. Second law: For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism.

Chemicalenergy

Heatco2

H2O+

Energy Flows Through Ecosystems

• Producers absorb sunlight and convert radiant energy into “food”

• Only plants, some algae (protists), and certain bacteria

• All forms of life depend on this process (very few exceptions)

Energy Flows Through Ecosystems

• Consumers (heterotrophs)– Can only acquire energy from other

organisms– Must either ingest or absorb nutrients– Some bacteria, archaebacteria, protists– All animals and fungi

HerbivoresCarnivores Omnivores Detritivores Decomposers

eat only plants eat other animals eat plants and animals eat plant and animal remains break down organic matter

Feeding Relationships

• For consumers, we call the energy that flows through and ecosystem “food”

• Most simple feeding relationship example is a food chain

Trophic Levels

• The word “troph” comes from the Greek and refers to food or feeding

• Refers to each step in a food chain or web

Trophic level 1

Trophic level 2

Trophic level 3

Ecological Pyramids• 1. Pyramid of Biomass• Shows the total amount of living or

organic matter in an ecosystem at any time (biomass).

• The most biomass occurs in producers

• Biomass decreases as you move from lower to higher trophic levels.

Ecological Pyramids

• 2. Pyramid of Numbers

• Shows the relative number of organisms at each trophic level

1 hawk

8 finches

24 snails

or worms

48

green leaves

Ecological Pyramids• 3. Pyramid of Energy• Shows energy as it moves from one feeding level in a

food chain to another.  

Only 10 %of energy available at each level is transferred to next

From the sun to producers, only 1% is transferred

Only 10 %of energy available at each level is transferred to next

From the sun to producers, only 1% is transferred

The Ecology of a Meat-Based Diet vs. a Vegetarian Diet

• What do ecological principles tell us about availability of energy to humans?

Pyramid of Numbers (# organisms): Bluegrass Pasture

Autotroph/Primary Producer 5,542,424

708,624

3

Herbivore/Primary Consumer

Carnivore/Secondary Consumer

Grass/Grain

Grasshopper

Bird

Land can support more producers (plants) than consumers.

Pyramid of Biomass (lb/acre): Bluegrass Pasture

Autotroph/Primary Producer 4,190

54

1Herbivore/

Primary Consumer

Carnivore/Secondary Consumer

Grass/Grain

Grasshopper

Bird

Land can support more plant mass than consumer mass.

Pyramid of Energy (calories): Bluegrass Pasture

Solar Energy

Plant/Autotroph

Insect/Herbivore

Bird/Carnivore1

10

100

10,000 CALORIES

9,900CALORIES

90

9

Energy Lost

Plants provide more energy than consumers.

Effect of Feeding at Lower Trophic Levels

4 million pounds plants (grains, corn, potato, rice, etc)

54 million grasshoppers

180,000 frogs

600 fish

Human Adult

One

Number of adult humans supported for one year

Thirty

Nine Hundred

Two Thousand

Ecological Preference: Eat Plants, Not Animals• Energy is lost in each food

chain transition, so it is more efficient to “eat lower on the food chain”

• “More efficient” means that less land is needed to support survival on plants

• In other words, the same amount of land needed to support 1 person eating a meat-based diet can support 10-20 vegetarians

Energy Cost for Meat Production

• One half of the USA agriculture energy goes into livestock production

• Energy Ratio: kcal of energy to produce one kcal of protein

(kcal of fossil fuel: kcal protein)• Beef 54:1• Lamb 50:1• Pork 17:1• Turkey 13:1• Chicken 4:1• Grain 3.3:1

Conversion of Plant Protein to Animal Protein (USA)

• 41 million tons of plant protein are needed to produce 7 million tons of animal protein– 26 million tons grain

– 15 million tons grass

• Many people in the poor areas of the world cannot afford the “luxury” of converting grain to meat

Percent of Calories From Starch

Law of Conservation of Matter

• In any chemical or physical process, no matter is created or destroyed.

• All matter cycles through an ecosystem

• The Earth is a closed system for matter

• There is no “away”

Video: Unknown World

Law of Conservation of Matter: Trophic Level Effects

• Bioaccumulation– Some substances aren’t easily excreted– Instead build up in fat and other tissues of an organism– Some substances are toxic (e.g., DDT)

• Biomagnification– An increase in the concentration of a substance as it moves through the food

chain from one organism to another– Because some substances accumulate in tissues, when an organism is

consumed, all these accumulated substances are passed on to the next trophic level

– Organisms at the top of the food web may end up with huge amounts of toxic substances stored in their tissues

Matter Cycles in Ecosystems: Biogeochemical Cycles

• Sulfur

• Phosphorous (never stored in the atmosphere)

• Oxygen

• Water/hydrologic (driven by solar energy (evaporation) & gravity (precipitation))

• Nitrogen

• Carbon

The Nitrogen Cycle• The most complex of the cycles• N2 = 78% of the troposphere• However, N2 cannot be used directly by plants or animals • People can give their plants usable nitrogen by applying a

fertilizer or by planting legumes (beans or clover)• Nitrogen cycle steps: nitrogen fixation, nitrification,

assimilation, ammonification and denitrification

The Nitrogen Cycle• 1. Nitrogen Fixation: N2 converted to ammonia (NH3)• By bacteria in soil/water and bacterium Rhizobium in root nodules

of legumes (peas, clover, beans, etc.)

The Nitrogen Cycle

• 2. Nitrification: Ammonia converted to nitrite (NO-2)and then nitrate (NO-3), the most usable forms of nitrogen

• Both reactions carried out by bacteria

The Nitrogen Cycle• 3. Assimilation: These usable forms are taken in by plants and animals. Plant

roots absorb nitrates that are then converted into organic compounds like proteins and DNA. And of course, animals eat plants.

The Nitrogen Cycle• 4. Ammonification: The organic compounds, wastes, caste-off

particles, dead bodies, etc., are converted into simpler compounds (e.g., ammonia NH3)

• By decomposer bacteria

The Nitrogen Cycle• 5. Denitrification: Ammonia (NH3) is converted back to N2• Mostly by anaerobic bacteria in waterlogged soil, bottom sediments of

lakes, swamps, bogs and oceans

Significant Human Interventions• Internal combustion engine exhaust (i.e., fossil fuel

burning) – Results in O2 being added to the atmosphere– Combining O2 with atmospheric nitrogen results in nitric acid,

a significant component of acid rain

• Farming, agriculture and cities– Nitrogen-rich fertilizers from farms and sewage from

municipalities runs off into bodies of water– This stimulates the growth of algae and aquatic plants which

then die and are broken down by aerobic decomposers– This aerobic decomposition reduces the dissolved oxygen (DO)

content in the water, killing fish and other aquatic animals (creates a “dead zone”)

The Carbon Cycle• Carbon cycles closely with oxygen in two reactions• 1. Respiration (all organisms)• Aerobic respiration: C6H12O6 + 6O2 > 6 CO2 + 6H2O + 38 ATP

• 2. Photosynthesis (autotrophs)• Photosynthesis: 6CO2 + 6H2O + light energy > C6H12O6 + 6O2

• CO2 also naturally enters the atmosphere by volcanic activity

• CO2 is a heat-trapping gas, and an important component of the earth’s thermostat

• More CO2 = higher temperatures with the greenhouse effect

Significant Human Interventions• There are two major human actions that lead to increasing levels

of CO2 in the atmosphere• 1. Vegetation removal/deforestation• 2. Fossil fuel burning and wood burning

• Reason for concern: magnified natural greenhouse effect• A. Altered global food production due to shifting climate belts• B. Altered wildlife habitat due to changes in temperature and

precipitation (e.g., loss of Arctic sea ice impacts polar bears)• C. Altered species interactions (e.g., births and food supplies)• D. Rise in sea levels due to melting ice and thermal expansion of

water as troposphere temperature increases (e.g., Tuvalu)• Another reason for concern: increasing CO2 in the oceans

Carbon Dioxide & the Oceans

• The oceans help regulate the CO2 in the atmosphere because CO2 can be dissolved in water

• There is an increasing amount of CO2 in the oceans

• This causes the oceans to become more acidic through the reaction: H20+ CO2 > H2 CO3 (carbonic acid)

• Acidic water negatively impacts corals, mussels, and other marine organisms by slowing the rate of calcification