Introduction to Ecology:
Factors Sustaining Life
February 20-24, 2015
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3 Factors Sustain Life on Earth
o Gravity
o Flow of Energy
 Physical LAWS
 Producers
 Consumers
 Trophic Levels
o Cycling on Matter and Nutrients
 Carbon, Nitrogen, Water,
Phosphorus, (Sulfur) Cycles
 Gravity-Atmosphere and life STUCK ON EARTH
Remember: 3 Physical Laws
1) Conservation of Mass
Matter can’t be created or destroyed.
Chemical elements are recycled & reused within ecosystems.
CO2 photosynthesized by plant; deer eat plants; PLOP; bacteria eat, breath out CO2
2) 1st Law of Thermodynamics
Energy cannot be created or destroyed; only transformed
Energy enters ecosystem as solar radiation, leaves via:
Photosynthesis
Reflected/absorbed by land structures
Lost from organisms as heat
3) 2nd Law of Thermodynamics
Every exchange of energy increases entropy
Entropy = Amount of disorder in the universe
Energy conversions aren’t efficient (energy gets wasted)----Most lost as heat
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Energy Sources
o All living things obtain and use energy and materials
o Energy source for the natural world = SUN or SOLAR ENERGY
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Energy Needs/Why do living things need energy?
Living Things: Autotrophs vs. Heterotrophs
o Various ways to obtain, acquire energy
o Some organisms can capture energy from sunlight or chemicals and convert it into forms
useable to living cells = AUTOTROPHS
o “Auto” = by itself
“trophikos” = Greek “to feed”
Autotroph = “self feeder”
o Photosynthesis (light) or Chemosynthesis (chemicals)
o Light, Hydrogen Sulfide, Ammonium, Nitrate, Iron, etc.
o Autotrophs also called Primary Producers
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Autotrophs are Primary Producers
o The most common primary producers harness solar energy.
o Process called Photosynthesis
o
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Other Primary Producers
o Deep-sea ecosystems depend on primary producers that harness chemical energy from
inorganic molecules such as hydrogen sulfide.
o Use of chemical energy to produce carbohydrates is called chemosynthesis.
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Living Things: Autotrophs vs. Heterotrophs
o Heterotrophs = Organisms that must acquire energy from other organisms by ingesting in some way
o Cannot make their own food
o Must eat/ingest to get their energy
o Heterotrophs also called CONSUMERS.
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Types of Consumers: Diet
o Consumers are classified by the ways in which they acquire energy and nutrients.
o Carnivores kill and eat other animals, and include snakes, birds of prey, lions, etc.
o Scavengers= animals that consume the carcasses of other animals that have been killed by
predators or have died of other causes.
o Herbivores = obtain energy and nutrients by eating plant leaves, roots, seeds, or fruits.
o Omnivores are animals whose diets naturally include a variety of different foods that usually
include both plants and animals.
 Humans, bears, and pigs are omnivores.
o Decomposers =feed by chemically breaking down organic matter.
 The decay caused by decomposers is part of the process that produces detritus—small
pieces of dead and decaying plant and animal remains.
o Detritivores, feed on detritus particles, often chewing or grinding them into smaller pieces.
 Detritivores commonly digest decomposers that live on, and in, detritus particles.
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Energy Flow
What happens to energy stored in body tissues when one organism eats another?
does energy flow through ecosystems?
Energy moves from the “eaten” to the “eater.”
A food chain = a series of steps in which organisms transfer energy by eating and being eaten.
o Food chains can vary in length.
Food Webs
o Feeding relationships much more complicated than a chain---many animals eat more than one
kind of food.
o This network of feeding interactions = a food web.
o Each path through a food web is a food chain.
o Links all of the food chains in an ecosystem together
Decomposers and Detritivores in Food Webs
o Decomposers convert dead material to detritus, which is eaten by detritivores.
o Ex: crayfish, grass shrimp, worms = detritiovores
o Pig frogs, killifish, and other fishes eat the detritivores.
o Decomposition releases nutrients that can be used by primary producers.
o Break down dead and decaying matter into forms that can be reused by organisms.
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o Without decomposers, nutrients would remain locked in dead organisms.
 Food Chains and Food Webs
How does energy flow through ecosystems?
Energy flows through an ecosystem in a one-way stream, from primary producers to various consumers.
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Trophic Levels and Ecological Pyramids
Each step in a food chain or food web = a trophic level.
o Primary producers always make up the 1st trophic level---Autotrophs
o Primary consumer- eat producers, heterotroph, herbivore
o Secondary consumer- eat #2 and or #1, heterotroph (carni-omnivore)
o Tertiary consumer-eat #3, heterotroph
o ….etc
o Decomposers (Prokaryotes & Fungi)
 Turn inorganic matter into organic matter
 Eat all trophic levels; control rate of nutrient cycling
Trophic Levels and Ecological Pyramids
o Ecological pyramids show the relative amount of energy or matter contained within each trophic
level in a given food chain or food web.
 There are 3 different types of ecological pyramids
 pyramids of energy
 pyramids of biomass
 pyramids of numbers
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Pyramids of Energy
o Only a small portion of the energy that passes through any given trophic level is ultimately
stored in the bodies of organisms at the next level.
o Organisms expend much of the energy they acquire on life processes, such as respiration,
movement, growth, and reproduction.
o Most of the remaining energy is released into the environment as heat—a byproduct of these
activities.
o Pyramids of energy show the relative amount of energy available at each trophic level.
o On average, about 10 percent of the energy available within one trophic level is transferred to
the next trophic level.
o The more levels that exist between a producer and a consumer, the smaller the percentage of
the original energy from producers that is available to that consumer.