Ecology, Ecosystems,
& Food Webs
© Brooks/Cole Publishing Company / ITP
What is Life?
Characteristics of Life:
•
Composed of cells- eukaryotic or
prokaryotic
•
Contain universal genetic code- DNA
Obtain & transform matter & energy- used
for for growth, survival, & reproduction
Maintain homeostasis
Reproduce
Respond to changes (adapt).
Evolve over time
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What is Ecology?
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study of relationships between organisms & their
environment.
Levels of organization:
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biosphere- biotic (living) & abiotic factors (non-living)
ecosystem: community + non–living environment
community: populations of different species in given area
population: a group of interacting individuals of same
species
– organism (individuals): any form of life
Organisms (Individuals)
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organisms are classified into species.
species: groups of organisms that resemble each
other, and in cases of sexually reproducing
organisms, can potentially interbreed.
estimates of 5 to 100 million species, most are
insects & microorganisms; so far only about 1.8
million named; each species is the result of long
evolutionary history.
wild or native species: population that exists in its
natural habitat .
domesticated or introduced species: population
introduced by humans (= non–native species).
Populations
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population: a group of individuals of the
same species.
examples: sunfish 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.
Ex: blue eyes vs. green eyes
Communities
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community: populations of different
species living together in a given area.
– a biological community is a 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.
Ecosystems
ecosystem: communities & the non–
living parts of the environment.
 example:
 Ducks, fish, and insect larvae living
in/on a lake or pond.
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Biosphere
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Largest level consisting of air, water, soil,
minerals, and life.
Layers of the Earth
Atmosphere- thin layer of gases (N, O, CO2,
Ne, Ar, etc) held close to the earth’s surface.
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Troposphere- atmosphere’s inner layer.
- Nitrogen & Oxygen found here.
- All weather occurs here.
- Contains “greenhouse” gases: CO2 & H2O
Stratosphere- layer above troposphere.
- Contains ozone (O3) which filters sun’s harmful UV. Called
Mesophere- above the stratosphere
- area where meteors burn up.
Thermosphere (ionosphere)- thinnest gas layer
-aurora’s take place and space shuttle orbits
Layers of the Earth
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Hydrosphere- water layer. Liquid, Ice,
Vapor.
Lithosphere- Earth’s crust and upper
mantle.
- Fossil fuels, minerals, soil
chemicals.
Biosphere- biotic & abiotic factors.
Earth's Life–Support System
Earth's
major
components
Fig. 4–7
What Sustains Life?
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Energy From Sun
– one–way flow of usable energy from sun 
through feeding interactions heat
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Cycling of Matter
– the continual flow of matter between the
nonliving environment & living organisms
(biogeochemical cycles)
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Gravity
– enables Earth to hold its atmosphere gases;
causes downward movement of matter in
nutrient cycles.
Energy Flow & Nutrient
Cycling
Life on Earth
depends upon
one–way flow
of high–quality
energy from
sun & cycling
of crucial
elements.
Energy Flow
The ultimate source of energy in most ecosystems is
the sun.
Nutrient Cycles
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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,
– 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.
Ecosystem Concepts
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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.
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aquatic life zone: major marine or freshwater
portion of the biosphere
– major aquatic life zones:
– lakes, streams, estuaries, coastlines, coral reefs, & the
deep ocean
Vocabulary for
Ecosystems
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Abiotic: non–living components. Ex:
water, air,sun
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Biotic: living components Ex: plants,
animals, bacteria
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Trophic level- feeding level for an
organism
Major components of aquatic ecosystems.
Fig. 4–11
Major components of terrestrial ecosystems.
Fig. 4–12
Factors Limiting
Populations
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Law of tolerance: the ability of species to tolerate changes
in their environment (physical or chemical factors).
Pollution, global warming, habitat loss are some concerns
associated with this.
Limiting factor: any environmental factor that reduces
survival or reproduction within a population.
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Ex: predation, temperature
Limiting factor principle: too much or too little of any
abiotic factor can limit or prevent growth of a population,
regardless if all other factors are near optimum range of
tolerance.
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Ex: too much fertilizer will kill plants.
Range of Tolerance
The survival, growth, & reproduction of organisms is
determined, in part, by maximum & minimum tolerance
limits for physical conditions such as temperature.
Key Players in
Ecosystems
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Autotrophs/ producers: make their own
food via photosynthesis (plants) or
chemosynthesis (bacteria in thermal vents
use hydrogen sulfide (H2S) & carbon
dioxide)
Heterotrophs/ consumers: can’t make
their own food, feed on other organisms or
their remains.
–
Ex: herbivores, carnivores, decomposers, etc.
Key Energy Processes
Photosynthesis: use of chlorophyll. Energy
storing process.
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6 CO2 + 6 H2O + solar energy  C6H12O6 + 6 O2
Cellular Respiration:
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Aerobic Respiration: energy releasing process.
C6H12O6 + 6 O2  6CO2 + 6 H2O + energy (ATP)
Anaerobic Respiration
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Ex. Fermentation: energy releasing process used by
yeast and bacteria
Categories of
Consumers
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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;
scavengers: feed on dead organisms;
decomposers (saprobes): consumers that
complete the breakdown & recycling of organic
materials from the remains & wastes of other
organisms;
detritivores: feed on detritus (partially decomposed
organic matter, such as leaf litter & animal dung).
The Importance of Decomposers
Fig. 4–16
Summary of Ecosystem Structure
Fig. 4–17
Food Chains
Food chains are a simple food path involving a sequence
of organisms, each of which is the food for the next.
Fig. 4–18
Food Webs
Food webs are multiple food chains that are
interconnected. More complex than food chains.
Ecological Pyramids
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Represent the flow of energy through an
ecosystem.
Typically each trophic level has a certain
amount of BIOMASS (dry weight of organic
matter)
Ecological efficiency- amount of usable
energy transferred as biomass. Usually
10% at each transfer.
Food chains and webs only have 4-5
trophic levels, because too little energy
left to support top consumers.
Energy Pyramid
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.
Fig. 4–19
Another Energy Pyramid
Annual pyramid of energy flow (in kilocalories per
square meter per year) for an aquatic ecosystem in
Silver Springs, FL.
Fig. 4–21
Note: More individuals
can be supported at
lower trophic levels.
Less energy is lost.
Biomass Pyramids
Displays the biomass at each trophic level.
Pyramid of Numbers
Pyramid of numbers displays the number of individuals
at each level.
1 owl
25 voles
2000
grass plants
Primary Productivity of
Ecosytems
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1.Gross primary productivity (GPP) is the
rate at which an ecosystem's producers
convert solar energy into chemical energy
as biomass.
2. Net primary productivity (NPP) is the rate
at which energy for use by consumers is
stored in new biomass.
NPP = GPP – R [rate at which producers
use biomass]
Net Primary Productivity
Estimated annual net primary productivity of major
biomes & aquatic life zones, expressed as kilocalories
per square meter per year.
Fig. 4–24
How Do Ecologists
Learn?
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Ecologists learn about ecosystems
through a combination of methods:
– field research
– systems analysis
 system
measurement
 data analysis
 systems modeling
 systems simulation
 systems optimization
Methods for Monitoring & Analysis
New technologies are enabling scientists to collect field
information more effectively across broad geographic scales.
A) Remote sensing involves use of
sensors to collect information about a
system from a distance.
B) Geographic Information Systems
(GIS) provide the computer
technology for organizing, storing,
and analyzing complex map data.
Ecosystem Services &
Sustainability
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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:
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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
Ecosystem Services &
Sustainability
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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.
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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.
Ecology &
Environmental Science
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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.