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AP Environmental Science

Ecology, Ecosystems,�& Food Webs

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Outline

1. Ecology & Life

What is ecology? What is life?

2. Earth's Life–Support Systems

What are the major components? What sustains life?

3. Ecosystem Concepts

abiotic & biotic components, organization

4. Food Webs & Energy Flow

autotrophs, heterotrophs, productivity, efficiency

5. How do Ecologists Learn?

6. Ecosystem Services & Sustainability

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1. Ecology & Life

ecology: study of relationships between organisms & their environment.

scope, in terms of levels of organization:

ecosphere: (=biosphere) all of Earth's ecosystems

ecosystem: community + non–living environment

community: populations of different species in given area

population: a group of interacting individuals of same species

organism: any form of life

realm of ecology

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Fig. 3-2, p. 51

Communities

Subatomic Particles

Atoms

Molecules

Protoplasm

Cells

Tissues

Organs

Organ systems

Organisms

Populations

Communities

Ecosystems

Biosphere

Earth

Planets

Solar systems

Galaxies

Universe

Organisms

Realm of ecology

Ecosystems

Biosphere

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Organisms

Organism: any form of life.

organisms are classified into species.
Species: groups of organisms that resemble each other, and in cases of sexually reproducing organisms, can potentially interbreed.
most are insects & microorganisms; only 1.4 million identified (5-100 million estimated)
Domesticated/introduced species: population introduced by humans (= non–native species).

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Populations

Population: a group of interacting individuals of the same species.

examples: carp fish in a pond, white oak trees in a forest, people in a city;
Habitat: the place where a population usually lives.
Genetic Diversity: in natural populations individuals vary in their genetic makeup.

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Communities

Community: complex interacting network of plants, animals and microorganisms.

example: redwood forest community, consisting of populations of redwoods & other trees, shrubs and herbaceous species, animals and microorganisms.

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Ecosystems & Ecosphere

Ecosystem: a community of different species interacting with one another & with their non–living environment of matter & energy.

examples:

a patch of woods, a lake or pond, a farm field, an entire watershed in a tropical rain forest.

Ecosphere (=biosphere): all of Earth's ecosystems together.

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What is Life?

Characteristics of Life:

composed of cells
contain (DNA)

capture & transform matter & energy from environment for growth, survival, & reproduction;

maintain favorable internal conditions thru homeostasis

reproduction;

evolution.

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Earth's major components

2. Earth's Life–Support System

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1. Energy From Sun

one–way flow of usable energy from sun, through feeding interactions, to low–quality forms (heat);

2. Cycling of Matter

the continual flow of matter between the nonliving environment & living organisms;

3. Gravity

enables Earth to hold its atmosphere; causes downward movement of matter in nutrient cycles.

What Sustains Life?

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Closed System: a system in which energy, but not matter, is exchanged between the system & its environment.

Earth

Open System: a system in which both energy & matter are exchanged between the system & its environment.

Organisms

Open vs. Closed Systems?

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Energy Flow & Nutrient Cycling

Fig. 4–6

Life on Earth depends upon one–way flow of high–quality energy from sun & cycling of crucial elements.

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Fig. 3-8, p. 55

Absorbed

by ozone

Visible

Light

Absorbed

by the earth

Greenhouse

effect

UV radiation

Solar

radiation

Energy in = Energy out

Reflected by

atmosphere (34% )

Radiated by

atmosphere as heat (66%)

Heat radiated

by the earth

Heat

Troposphere

Lower Stratosphere

(ozone layer)

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Nutrient Cycles

nutrient: any atom, ion, or molecule an organism needs to live, grow, or reproduce.

macronutrients needed in relatively large amounts�e.g., C, O, H, N, P, S, K, Ca, Mg, Fe
micronutrients needed in relatively small amounts�e.g., Na, Zn, Cu, Cl, I
nutrient cycles (= biogeochemical cycles) involve continual flow of nutrients from nonliving (air, water, soil, rock) to living organisms (biota) & back again.
nutrient cycles driven directly or indirectly by solar radiation & gravity.
Major cycles: hydrologic (water), carbon, oxygen, nitrogen, phosphorus and sulfur.

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3. Ecosystem Concepts

biome: large regions characterized by a distinct climate & specific life–forms, especially vegetation, adapted to the region.

major biomes:

temperate grassland, temperate deciduous forest, desert, tropical rain forest, tropical deciduous forest, tropical savannah, coniferous forest, tundra

aquatic life zone: major marine or freshwater portion of the ecosphere, containing numerous ecosystems.

major aquatic life zones:

lakes, streams, estuaries, coastlines, coral reefs, & the deep ocean

(see Fig. 4–8)

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Major Components of Ecosystems

abiotic: non–living components

examples: water, air, nutrients, & solar energy

biotic: living components (=biota)

examples: plants, animals, & microorganisms

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Limiting Factors

law of tolerance: the existence, abundance, & distribution of a species in an ecosystem is determined by whether the levels of one or more physical or chemical factors fall within the range tolerated by that species.

limiting factor: an environmental factor that is more important than other factors in regulating survival, growth, or reproduction.

limiting factor principle: too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimum range of tolerance.

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Range of Tolerance

The survival, growth, & reproduction of organisms is determined, in part, by maximum & minimum tolerance limits for physical conditions such as temperature.

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Major Living Components

Two main categories:

1) producers (also called autotrophs = "self–feeders") make own food

2) consumers (also called heterotrophs "other–feeders") get their energy & nutrients by feeding on other organisms or their remains.

Includes herbivores, carnivores, decomposers, etc.

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Major Components of Ecosystems

Major components of aquatic ecosystems.

Fig. 4–10

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Photosynthesis & Respiration

photosynthesis: complex chemical reaction in plants, in which solar radiation is captured by chlorophyll (& other pigments) & used to combine carbon dioxide & water to produce carbohydrates (e.g., glucose), other organic compounds, & oxygen.

carbon dioxide + water + solar energy → glucose + oxygen

6 CO₂ + 6 H₂O + solar energy → C₆H₁₂O₆+ O₂

aerobic respiration: complex process that occurs in the cells of organisms, in which organic molecules (e.g., glucose) are combined with oxygen to produce carbon dioxide, water, & energy.

glucose + oxygen → carbon dioxide + water + energy

C₆H₁₂O₆+ O₂→6 CO₂ + 6 H₂O + energy

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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

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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 .

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Major Components of Ecosystems

Major components of terrestrial ecosystems.

Fig. 4–11

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Consumers

major kinds of consumers (= heterotrophs)

primary consumers: (=herbivores) feed directly on producers;
secondary consumers: (=carnivores) feed on primary consumers;
tertiary consumers: feed only on carnivores;
omnivores: consumers that feed on both plants & animals;
detritivores: feed on detritus (parts of dead organisms & wastes from organisms) (Carpenter ants, termites)
decomposers: bacteria & fungi that breakdown/recycle organic matter & nutrients

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Decomposers

Fig. 4–13

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4. Food Chains & Energy Flow

2 Things Sustain Ecosystems…1-Way flow of Energy & Nutrient Cycling! Know the trophic level – producer/consumer relationships!

Fig. 4–16

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Summary of Ecosystem Structure

Fig. 4–15

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Generalized Energy Pyramid

Fig. 4–19

In nature, ecological efficiency varies from 5% to 20% energy available between successive trophic levels (95% to 80% loss). About 10% efficiency is a general rule.

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Generalized Energy Pyramid

Fig. 4–20

Annual pyramid of energy flow (in kilocalories per square meter per year) for an aquatic ecosystem

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Pyramids of Numbers

Fig. 4–22

Pyramids of numbers depend upon both the size of organisms (e.g., forests have smaller numbers of large producers than do grasslands) & the biomass pyramid.

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Biomass Pyramids

Fig. 4–21

Biomass pyramids, commonly measured as dry weight per square meter for each trophic level, can either mirror the energy pyramid (as for the abandoned field) or be inverted (as for the ocean). Inverted biomass pyramids result because the producers are eaten by consumers.

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Primary Productivity

Gross Primary Productivity (GPP) is the rate at which an ecosystem's producers convert solar energy into chemical energy as biomass (or total photosynthesis per unit area per time) (kcal/m²/yr)

Net Primary Productivity (NPP) is the rate at which producers can provide energy stored in biomass for use by consumers (or plant growth per area per time). (kcal/m²/yr)

NPP = GPP – Respiration

Respiration is the breakdown of glucose by a plant

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Net Primary Productivity

Estimated annual net primary productivity of major biomes & aquatic life zones, expressed as kilocalories per square meter per year.

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Primary Productivity

Estimated annual contribution of the various types of biomes & aquatic life zones to Earth's overall net primary productivity. Note that the previous bar graph gives the average net primary productivity per unit area.

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5. How Do Ecologist Learn?

Ecologists learn about ecosystems through a combination of methods:

field research
systems analysis

system measurement
data analysis
systems modeling
systems simulation
systems optimization

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Methods for Monitoring & Analysis

New technologies are enabling scientists to collect field information more effectively across broad geographic scales.

Fig. 4–26

B) Geographic Information Systems (GIS) provide the computer technology for organizing, storing, and analyzing complex map data.

A) Remote sensing involves use of sensors to collect information about a system from a distance.

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6. Ecosystem Services & Sustainability

ecosystem services: natural benefits that support life on the earth & are essential to the quality of human life & the functioning of the world's economies.

Examples:

control & moderate climate
recycle vital nutrients
provide energy & mineral resources
furnish food, fiber, medicine, timber, & paper
pollinate crops & useful native plants
absorb, dilute, or detoxify pollutants
control populations of pests & disease organisms
slow soil erosion & prevent flooding
provide biodiversity of genes & species

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Ecosystem Services & Sustainability

Why is biodiversity an important ecosystem service?

The rich variety of organisms provides material benefits (food, raw materials, energy, & medicine), ecosystem services (purification of air & water, natural pest control…), & aesthetic benefits.

What are two principles of ecosystem sustainability?

Almost all natural ecosystems achieve sustainability by�1) using renewable solar energy as the energy source; &�2) recycling nutrients needed for survival, growth, & reproduction.

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Ecology & Environmental Science

Why is an understanding of ecology essential for environmental science?

Understanding the scientific basis for interdependence & connectedness is essential for solving environmental problems & ensuring sustainability of a high–quality life for humans & other organisms.

The problems of the human future range far beyond ecology, yet ecology is an essential part of them.

–– Robert H. Whittaker