Chapter 13
Principals of Ecology
Ecology
• Study of interactions between
organisms and their environments
• Reveals relationships between living
and nonliving parts
• “ecology” termed by Ernst Haeckel to
encourage scientists to study these
relationships
Levels of organization
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Organisms
Populations
Communities
Ecosystem
Biosphere
Organisms
• An individual
• Depend on others for food, shelter,
reproduction, protection
• Can interact with others of same
species or different species
• Can interact with abiotic factors
Populations
• Organisms of the same species that
interbreed and live in the same area
• Compete for food, water, mates, etc.
• Sharing resources determines
distances between populations
Communities
• Interacting populations
• Includes different species that live in
the same area
• Change in one population affects the
entire community
Ecosystem
• Interactions of populations and abiotic
factors in a community
• 3 types
– Terrestrial
– Aquatic
– saltwater
Biome
• Major regional or global community of
organisms
• Characterized by climate conditions and
plants
The living environment
• Biosphere – portion of earth that
supports life
– Includes land, air, fresh and salt water
– Extends from highest part of
atmosphere to bottom of ocean
• Biotic factors – all living factors in the
environment
The nonliving environment
• Abiotic factors – nonliving parts of the
environment
– Includes air currents, temperature,
moisture, light, and soil
– Can determine which species survive in
a particular area
Biodiversity
• Variety of living things in an ecosystem
• Amount of biodiversity depends on many
things such as temperature and moisture
• Tropical rain forests account for >50% of
the world’s plants and animals
• Rain forests and barrier reefs are “hot
spots” and are richly diverse
Keystone species
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Have a large effect on its ecosystem
May hold the dynamic ecosystem together
They form a complex web of life
Loss of the keystone species affects all
species in that ecosystem
Feeding relationships
• 4 types
– Autotrophs
– Heterotrophs
– Scavengers
– decomposers
Obtaining energy
• Producers (autotrophs) get their energy
from nonliving sources to make their own
food
– Sunlight or chemicals (chemosynthesis)
• Consumers (heterotrophs) get their energy
by eating other organisms
• Sun is the ultimate source of energy for all
organisms
Food chains
• Links species by their feeding
relationships
• Shows a sample of links that begin with a
single producer
• Model used to show passage of matter
and energy through the ecosystem
• Arrows indicate energy flow
• No more than 5 links
Heterotrophs
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Depend on autotrophs for food
Herbivores eat only plants
Carnivores eat other animals
Omnivores eat plants and animals
Detritivores eat dead organic matter
Decomposers break down organic
matter into simpler substances
Selective eaters
• Specialists – eat primarily one specific
organism or a very small variety of
organisms
• Generalists – have a varying diet
Trophic levels
• Feeding steps in the passage of
energy and materials
• Do not show all relationships
Food webs
• Show complex relationships in an
ecosystem
• Expresses all possible relationships
at each trophic level
Water (hydrologic) cycle
• Water on earth is liquid or solid; in
atmosphere it’s gas
• Steps
– Precipitation falls to the ground
– Water flows into lakes, rivers; can be
absorbed into soil; most will feed the oceans
– Some water evaporates and enters the
atmosphere; released from plants by
transpiration
– Condensation produces precipitation
Water cycle
Oxygen cycle
• Organisms need oxygen for cellular
respiration
• Plants release oxygen during
photosynthesis
• Oxygen is also released by cycling of
other nutrients like carbon, nitrogen, and
phosphorous
Oxygen cycle
Carbon forms
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Carbon dioxide in the atmosphere
Bicarbonate dissolved in water
Fossil fuels
Carbonate rocks (limestone)
Dead organic matter
Carbon cycle
• Steps
– Plants use CO2 to make their food
– Animals eat plants, release CO2 when
they breathe or die
– Decay with NO oxygen makes oil
– Burning oil releases carbon dioxide
Carbon cycle
Nitrogen cycle
• Gaseous nitrogen makes up 78% of air
• Lightning / bacteria convert nitrogen gas to
useable nitrogen for organisms (nitrogen
fixation)
• Steps
– Plants absorb nitrates
– Animals eat plants and make proteins
– Death / decay return nitrogen to soil
– Breakdown of nitrates by bacteria return
nitrogen to the atmosphere
Nitrogen cycle
Phosphorous cycle
• Steps
– Phosphorous released by weathering of rocks
– Plants absorb phosphorous
– Animals eat plants
– Death / decay returns phosphorous to
soil and water
– Phosphates can also be made into
rocks; released by erosion
Phosphorous cycle
Ecological pyramids
• Depict energy conversions in an
ecosystem
• 1st level represents producers
• Higher levels are stacked on lower
levels
• Sun is energy
Energy pyramid