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Chapter 18 -- Ecology
What is Ecology?
 Ecology: the scientific study of interactions between organisms and their
environments, focusing on energy transfer
 Known as the science of relationships
What makes up the environment?
 The environment is made up of two factors:
o Biotic factors
 All living organisms inhabiting the Earth
o Abiotic factors
 Non-living parts of the environment
 Ex: temperature, soil, sunlight, moisture
*This is totally NOT photoshopped.
Organism
 Any unicellular or multicellular form exhibiting all of the
characteristics of life
 The lowest level of organization
Population
 Group of organisms of one species living in the same place at the same
time that interbreed
 Produce fertile offspring
 Compete with each other for resources
o Ex: food, mates, shelter
Community
 Several interacting populations that inhabit a common environment and
are interdependent
Ecosystem
 Populations in a community and the abiotic factors with which they
interact
o Ex: marine, terrestrial
Biosphere
 All life supporting portions of Earth composed of air, land, fresh water,
and salt water
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 The highest level of organization
Habitat vs. Niche
 Habitat
o Place in which an organism lives out its life
 Niche
o Role a species plays in a community
o Determined by the tolerance limitations of an organism or
limiting factor
 Limiting factor
o Any biotic or abiotic factor that restricts the existence of
organisms in a specific environment
o Ex: amount of water, food, temperature, space, and mates
Feeding Relationships
 There are three main types of feeding relationships
o Producer – Consumer
 Ex: grass  cow
o Predator – Prey
 Ex: mouse  snake
o Parasite – Host
 Ex: tick  deer
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Producer
 All autotrophs (plants) that trap energy from the sun
 Bottom of the food chain
Consumer
 All heterotrophs
 Organisms that ingest food containing the sun’s energy
o Herbivores
o Carnivores
o Omnivores
o Decomposers
 Primary consumers
 Eat plants (herbivores)
 Secondary, tertiary … consumers
 Prey on animals (carnivores)
 Predators
o Hunt prey for food
 Scavengers
o Feed on carrion, dead animals
 Omnivores
o Eat both plants and animals
 Decomposers
o Breakdown the complex compounds of dead and decaying plants
and animals into simpler molecules that can be absorbed
Symbiotic Relationships
 Symbiosis
o Commensalism
o Parasitism
o Mutualism
 Commensalism
o One species benefits and the other is neither harmed not helped
o Ex: polar bears and cyanobacteria
 Parasitism
o One species benefits (parasite) and the other is harmed (host)
o Parasite – host relationship
 Ex: tick on an animal
 Mutualism
o Beneficial to both species
 Ex: cleaning birds and cleaner shrimp
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Trophic Levels
 Each link in a food chain is known as a trophic level
 Represent a feeding step in the transfer of energy and matter in an
ecosystem
Food web
 Shows all possible feeding relationships in a community at each trophic
level
 Represents a network of interconnected food chains
Food chain
One pathway of energy
paths
Food Web
All possible energy
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Nutrient Cycles
 Cycling maintains homeostasis in the environment
 Three cycles
o Water cycle
o Carbon cycle
o Nitrogen cycle
Water Cycle
 Evaporation, transpiration, condensation, precipitation
Carbon Cycle
 Photosynthesis and respiration cycle carbon and oxygen through the
environment
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Nitrogen Cycle
 Atmospheric nitrogen (N2) makes up nearly 78-80% of air
 Organisms cannot use it in that form
 Lightning and bacteria convert nitrogen in usable forms
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