Chapter 3

Ecosystems: What Are They and How Do They

Work?

Core Case Study: Have You Thanked the Insects

Today? Many plant species depend on insects for

pollination. Insect can control other pest insects by

eating them

Figure 3-1

Core Case Study: Have You Thanked the Insects

Today? …if all insects disappeared, humanity

probably could not last more than a few months [E.O. Wilson, Biodiversity expert]. Insect’s role in nature is part of the larger

biological community in which they live.

THE NATURE OF ECOLOGY

Ecology is a study of connections in nature. How organisms

interact with one another and with their nonliving environment.

Figure 3-2

Ecology‣ Ecology: the study of the relationships between

organisms & the abiotic (nonliving) and biotic (living) environment.

The physical conditions influence the habitat in which an organism lives. These include:

substrate

humidity

sunlight

temperature

salinity

pH (acidity)

exposure

altitude

depth

Each abiotic (or physical) factor may be well suited to the organism or it may present it with problems to overcome.

O2

Nutrients

CO2

Fig. 3-2, p. 51

Communities

Subatomic Particles

Atoms

Molecules

Protoplasm

Cells

Tissues

Organs

Organ systems

Organisms

Populations

Populations

Communities

Ecosystems

Biosphere

Earth

Planets

Solar systems

Galaxies

Universe

Organisms

Realm of ecology

Ecosystems

Biosphere

‣Living organisms can be studied at different levels of complexity.

‣From least to most complex, these levels are (in an ecological context):

Individual

Population

Community

Ecosystem

Biome

Biosphere

Biological Complexity

Biosphere

Biome

Ecosystem

Community

Population

Individual

Organisms and Species Organisms, the different forms of life on

earth, can be classified into different species based on certain characteristics.

Figure 3-3

Fig. 3-3, p. 52

Insects751,000

Other animals281,000

Fungi69,000

Prokaryotes4,800

Plants248,400

Protists57,700

Known species1,412,000

Case Study: Which Species Run the World?

Multitudes of tiny microbes such as bacteria, protozoa, fungi, and yeast help keep us alive. Harmful microbes are the minority. Soil bacteria convert nitrogen gas to a usable

form for plants. They help produce foods (bread, cheese, yogurt,

beer, wine). 90% of all living mass. Helps purify water, provide oxygen, breakdown

waste. Lives beneficially in your body (intestines, nose).

Populations, Communities, and Ecosystems

Members of a species interact in groups called populations.

Populations of different species living and interacting in an area form a community.

A community interacting with its physical environment of matter and energy is an ecosystem.

Populations

A population is a group of interacting individuals of the same species occupying a specific area. The space an

individual or population normally occupies is its habitat.

Figure 3-4

Populations

Genetic diversity In most natural

populations individuals vary slightly in their genetic makeup.

Figure 3-5

Community

The population of all species living & interacting in an area.

                                                

Ecosystems Ecosystems consist of nonliving (abiotic) and

living (biotic) components.

Figure 3-10

The biosphere is the region within which all living things are found on Earth, extending from the bottom of the oceans to the upper atmosphere.

The biosphere is but one of the four separate components of the geochemical model along with the lithosphere, hydrosphere, and atmosphere.

The Gaia Hypothesis maintains that the Earth is a single self-regulating complex evolving system. An example being the exchange of elements between oceans and land.

The Biosphere

THE EARTH’S LIFE SUPPORT SYSTEMS

The biosphere consists of several physical layers that contain: Air Water Soil Minerals Life

Figure 3-6

Biosphere

Atmosphere Membrane of air around the planet.

Stratosphere Lower portion contains ozone to filter out most of

the sun’s harmful UV radiation. Hydrosphere

All the earth’s water: liquid, ice, water vapor Lithosphere

The earth’s crust and upper mantle.

Fig. 3-6, p. 54

Lithosphere (crust, top of upper mantle)

RockSoil

Vegetation and animals

Atmosphere

OceanicCrust

Continental Crust

LithosphereUpper mantle

AsthenosphereLower mantle

Mantle

Core

Biosphere

Crust

Crust (soil and rock)

Biosphere (living and dead

organisms)

Hydrosphere (water)

Atmosphere (air)

An organism’s habitat is the physical place or environment in which it lives.

Organisms show a preference for a particular habitat type, but some are more specific in their requirements than others.

Habitat

Lichens, fungi & algae or bacteria, are found on rocks, trees, and bare ground.

Most frogs, like this leopard frog, live in or near fresh water, but a few can survive in

arid habitats.

Habitat NeedsCover – shelter; trees, shrubs,

etc.WaterNutrients

Macronutrients

Chemicals organisms need in large numbers to live, grow, and reproduce.

Ex. carbon, oxygen, hydrogen, nitrogen, calcium, and iron.

Micronutrients

These are needed in small or even trace amounts.

Ex. sodium, zinc copper, chlorine, and iodine.

Habitat The ecological niche

describes the functional position of an organismin its environment.

A niche comprises:the habitat in which the organism lives.

the organism’s activity pattern: the periods of time during which it is active.

the resources it obtainsfrom the habitat.

Ecological Niche

Adaptations

Activitypatterns

Presence of other organisms

Physicalconditions

The fundamental niche of an organism is described by the full range of environmental conditions (biological and physical) under which the organism can exist.

The realized niche of the organism is the niche that is actually occupied. It is narrower than the fundamental niche.

This contraction of the realized niche is a result of pressure from, and interactions with, other organisms.

The Fundamental Niche

Factors That Limit Population Growth Availability of matter and energy resources

can limit the number of organisms in a population.

Figure 3-11

The law of tolerance states that “For each abiotic factor, an organism has a range of tolerances within which it can survive.”

Law of Tolerance

Tolerance range

Optimum range

Unavailable niche

Marginal niche

Nu

mb

er

of

org

an

ism

s

Preferred niche

Marginal niche

Unavailable niche

Examples of abiotic factors that influence size of the realized niche

Too

acidicpH Too

alkaline

Too cold Temperature Too hot

Factors That Limit Population Growth

The physical conditions of the environment can limit the distribution of a species.

Figure 3-12

Limited ResourcesA population can grow until competition

for limited resources increases & the carrying capacity (C.C.) is reached.

Population Growth Cycle

Typical Phases1. The population overshoots the C.C.2. This is because of a reproductive

time lag (the period required for the birth rate to fall & the death rate to rise).

3. The population has a dieback or crashes.

4. The carrying capacity is reached.

What Happens to Solar Energy Reaching the Earth?

Solar energy flowing through the biosphere warms the atmosphere, evaporates and recycles water, generates winds and supports plant growth.

Figure 3-8

Producers: Basic Source of All Food

Most producers capture sunlight to produce carbohydrates by photosynthesis:

Producers: Basic Source of All Food

Chemosynthesis: Some organisms such as deep ocean bacteria

draw energy from hydrothermal vents and produce carbohydrates from hydrogen sulfide (H2S) gas .

Photosynthesis: A Closer Look

Chlorophyll molecules in the chloroplasts of plant cells absorb solar energy.

This initiates a complex series of chemical reactions in which carbon dioxide and water are converted to sugars and oxygen.

Figure 3-A

Fig. 3-A, p. 59

Sun

Chloroplastin leaf cell

Light-dependentReaction

Light-independent

reaction

Chlorophyll

Energy storage and release

(ATP/ADP)

Glucose

H2O

Sunlight

O2

CO2

6CO2 + 6 H2O C6H12O6 + 6 O2

Consumers: Eating and Recycling to Survive

Consumers (heterotrophs) get their food by eating or breaking down all or parts of other organisms or their remains. Herbivores

• Primary consumers that eat producers Carnivores

• Primary consumers eat primary consumers• Third and higher level consumers: carnivores that eat

carnivores. Omnivores

• Feed on both plant and animals.

Decomposers and Detrivores

Decomposers: Recycle nutrients in ecosystems. Detrivores: Insects or other scavengers that feed

on wastes or dead bodies.Figure 3-13

Fig. 3-13, p. 61

Scavengers

Powder broken down by decomposers into plant nutrients in soil

Bark beetle engraving

Decomposers

Long-horned beetle holes

Carpenter ant

galleries

Termite and

carpenter ant work Dry rot

fungus

Wood reduced to powder

Mushroom

Time progression

Aerobic and Anaerobic Respiration: Getting Energy for Survival

Organisms break down carbohydrates and other organic compounds in their cells to obtain the energy they need.

This is usually done through aerobic respiration. The opposite of photosynthesis

Aerobic and Anaerobic Respiration: Getting Energy for Survival

Anaerobic respiration or fermentation: Some decomposers get energy by breaking

down glucose (or other organic compounds) in the absence of oxygen.

The end products vary based on the chemical reaction:• Methane gas• Ethyl alcohol• Acetic acid• Hydrogen sulfide

Two Secrets of Survival: Energy Flow and Matter Recycle

An ecosystem survives by a combination of energy flow and matter recycling.

Figure 3-14

Decomposition

As plant or animal matter dies it will break down and return the chemicals back to the soil.

This happens very quickly in tropical rainforest which results in low-nutrient soils.

Grasslands have the deepest and most nutrient rich of all soils

BIODIVERSITY

Figure 3-15

Biodiversity Loss and Species Extinction: Remember HIPPO

H for habitat destruction and degradation I for invasive species P for pollution P for human population growth O for overexploitation

Biodiversity Loss and Species Extinction: Remember HIPPCO

H for habitat destruction and degradation I for invasive species P for pollution P for human population growth C for Climate Change O for overexploitation

Why Should We Care About Biodiversity?

Biodiversity provides us with: Natural Resources (food water, wood, energy,

and medicines) Natural Services (air and water purification, soil

fertility, waste disposal, pest control) Aesthetic pleasure

Solutions

Goals, strategies and tactics for protecting biodiversity.

Figure 3-16

ENERGY FLOW IN ECOSYSTEMS

Food chains and webs show how eaters, the eaten, and the decomposed are connected to one another in an ecosystem.

Figure 3-17

Food Webs

Trophic levels are interconnected within a more complicated food web.

Figure 3-18

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs

In accordance with the 2nd law of thermodynamics, there is a decrease in the amount of energy available to each succeeding organism in a food chain or web.

Energy Flow in an Ecosystem: Losing Energy in Food Chains and Webs

Ecological efficiency: percentage of useable energy transferred as biomass from one trophic level to the next.

Figure 3-19

10% Rule

We assume that 90% of the energy at each energy level is lost because the organism uses the energy. (heat)

It is more efficient to eat lower on the energy pyramid. You get more out of it!

This is why top predators are few in number & vulnerable to extinction.

Productivity of Producers: The Rate Is Crucial

Gross primary production (GPP) Rate at which an

ecosystem’s producers convert solar energy into chemical energy as biomass.

Figure 3-20

Net Primary Production (NPP)

NPP = GPP – R Rate at which

producers use photosynthesis to store energy minus the rate at which they use some of this energy through respiration (R).

Figure 3-21

What are nature’s three most productive and three least productive systems?

Figure 3-22

What Sustains Life on Earth? Solar energy, the cycling of matter, and gravity

sustain the earth’s life.

Figure 3-7

MATTER CYCLING IN ECOSYSTEMS

Nutrient Cycles: Global Recycling Global Cycles recycle nutrients through the

earth’s air, land, water, and living organisms. Nutrients are the elements and compounds that

organisms need to live, grow, and reproduce. Biogeochemical cycles move these substances

through air, water, soil, rock and living organisms.

The Water Cycle

Figure 3-26

Water’ Unique Properties There are strong forces of attraction between

molecules of water. Water exists as a liquid over a wide

temperature range. Liquid water changes temperature slowly. It takes a large amount of energy for water to

evaporate. Liquid water can dissolve a variety of

compounds. Water expands when it freezes.

Effects of Human Activities on Water Cycle

We alter the water cycle by: Withdrawing large amounts of freshwater. Clearing vegetation and eroding soils. Polluting surface and underground water. Contributing to climate change.

The Carbon Cycle:Part of Nature’s Thermostat

Figure 3-27

The Carbon Cycle

Effects of Human Activities on Carbon Cycle

We alter the carbon cycle by adding excess CO2 to the atmosphere through: Burning fossil fuels. Clearing vegetation

faster than it is replaced.

Figure 3-28

‣ Carbon cycles as gaseous carbon is fixed in the process of photosynthesis and returned to the atmosphere in respiration.

‣ Carbon may remain locked up in sinks or reservoirs that are biotic or abiotic for long periods of time, e.g. in the wood of trees, oceans or in fossil fuels such as coal or oil.

‣ ‣ Indirectly carbon forms carbonate deposits

as carbon is removed from the atmosphere. (The carbonate is stored mostly in the marine ecosystem.)

Humans have disturbed the balance of the carbon cycle through activities such as combustion and deforestation.

Carbon Cycling

Burning fossil fuels

Petroleum & Coal

The Nitrogen Cycle: Bacteria in Action

Nitrogen Cycle

Process Product Formulas

Nitrogen Fixation Ammonia N2 → NH4

Nitrification Nitrite then nitrate NH4 → NO2 →NO3

Assimilation Proteins: amino acids, DNA

NO3 (some NH4) → uptake by plant

Ammonification (Decay & waste products)

Ammonia Plant & animal decay & excretions → NH4

Denitrification Nitrogen gas NO3 → N2

Most of the work done by bacteria & decomposers

Nitrogen in the Environment‣ Nitrogen cycles between the biotic and

abiotic environments. The largest reservoir for nitrogen is the atmosphere and thus it is difficult to fix, bacteria play an important role in this transfer.

Nitrogen-fixing bacteria are able to fix atmospheric nitrogen.

Nitrifying bacteria convert ammonia to nitrite, and nitrite to nitrate.

Denitrifying bacteria return fixed nitrogen to the atmosphere.

Atmospheric fixation also occurs as a result of lightning discharges.

‣ Humans intervene in the nitrogen cycle by producing and applying nitrogen (nitrates) fertilizers which is the main cause of eutrophication.

Lightning can fix atmospheric nitrogen

Bacteria on the roots of legumes can fix nitrogen

Effects of Human Activities on the Nitrogen Cycle

We alter the nitrogen cycle by: Adding gases that contribute to acid rain. Adding nitrous oxide to the atmosphere through

farming practices which can warm the atmosphere and deplete ozone.

Contaminating ground water from nitrate ions in inorganic fertilizers.

Releasing nitrogen into the troposphere through deforestation.

Effects of Human Activities on the Nitrogen Cycle

Human activities such as production of fertilizers now fix more nitrogen than all natural sources combined.

Figure 3-30

Fig. 3-31, p. 77

Dissolvedin Ocean

Water

Marine Sediments Rocks

uplifting overgeologic time

settling out weatheringsedimentation

LandFoodWebs

Dissolvedin Soil Water,Lakes, Rivers

death,decomposition

uptake byautotrophs

agriculture

leaching, runoff

uptake byautotrophs

excretion

death,decomposition

mining Fertilizer

weathering

Guano

MarineFoodWebs

The Phosphorous Cycle

Phosphorus Cycling Phosphorus cycling is very slow and

tends to be local and stable; in aquatic and terrestrial ecosystems, phosphorous is a sedimentary cycle.

Phosphorous is lost from ecosystems through run-off, precipitation, and sedimentation.

A very small amount of phosphorus returns to the land as guano (manure of fish-eating birds). Weathering and phosphatizing bacteria return phosphorus to the soil.

Often the Limiting factor in the ecosystem

The phosphorous cycle has no real significant gas phase and under many conditions will form stable insoluble compounds

Deposition as guano…

Loss via sedimentation…

Fertilizer production

Effects of Human Activities on the Phosphorous Cycle

We remove large amounts of phosphate from the earth to make fertilizer.

We reduce phosphorous in tropical soils by clearing forests.

We add excess phosphates to aquatic systems from runoff of animal wastes and fertilizers contributing to eutrophication

The Sulfur Cycle

Figure 3-32

Fig. 3-32, p. 78

Hydrogen sulfide

Sulfur

Sulfate salts

Decaying matter

Animals

Plants

Ocean

IndustriesVolcano

Hydrogen sulfideOxygen

Dimethyl sulfide

Ammoniumsulfate

Ammonia

Acidic fog and precipitationSulfuric acid

WaterSulfurtrioxide

Sulfur dioxide

Metallicsulfidedeposits

Sulfur Cycling Sulfur is naturally occurring in rock or

mineral forms and is a sedimentary cycle.

Sulfur is an essential component of proteins and is important in determining the acidity of precipitation, surface water, and soil.

Sulfur circulates through the biosphere as:

hydrogen sulfide (H2S), sulfur dioxide (SO2), sulfate (SO4

2-), and elemental sulfur (S)

Sulfur in petrol

Molecular bridges in proteins

Elemental sulfur

Effects of Human Activities on the Sulfur Cycle

We add sulfur dioxide to the atmosphere by: Burning coal and oil Refining sulfur containing petroleum. Convert sulfur-containing metallic ores into free

metals such as copper, lead, and zinc releasing sulfur dioxide into the environment.

HOW DO ECOLOGISTS LEARN ABOUT ECOSYSTEMS?

Ecologist go into ecosystems to observe, but also use remote sensors on aircraft and satellites to collect data and analyze geographic data in large databases. Geographic Information Systems Remote Sensing

Ecologists also use controlled indoor and outdoor chambers to study ecosystems

Geographic Information Systems (GIS)

A GIS organizes, stores, and analyzes complex data collected over broad geographic areas.

Allows the simultaneous overlay of many layers of data.

Figure 3-33

Fig. 3-33, p. 79

Critical nesting sitelocations

USDA Forest ServiceUSDA

Forest ServicePrivateowner 1 Private owner 2

Topography

Habitat type

LakeWetlandForest

Grassland

Real world

Systems Analysis

Ecologists develop mathematical and other models to simulate the behavior of ecosystems.

Figure 3-34

Fig. 3-34, p. 80

SystemsMeasurement

Define objectivesIdentify and inventory variablesObtain baseline data on variables

Make statistical analysis of relationships among variables

Determine significant interactions

Objectives Construct mathematical model describing interactions among variables

Run the model on a computer, with values entered for differentVariables

Evaluate best ways to achieve objectives

DataAnalysis

SystemModeling

SystemSimulation

SystemOptimization

Importance of Baseline Ecological Data

We need baseline data on the world’s ecosystems so we can see how they are changing and develop effective strategies for preventing or slowing their degradation. Scientists have less than half of the basic

ecological data needed to evaluate the status of ecosystems in the United Sates (Heinz Foundation 2002; Millennium Assessment 2005).