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Ecology 1: Ecosystems
Levels of Organization
• Organism
• Ex. an elephant
• Population
– A group of individuals in the same species, living
and interacting in one area
• Ex. a herd of elephants in the Serengeti
• Community
– Multiple populations interacting in one area
• Ex. grazing antelope, elephants and giraffes in the Serengeti
• Ecosystem
– All populations in one area interacting with each
other and their non-living environment.
• Ex. the Serengeti (all organisms plus climate, nutrients, etc.)
Levels of Organization
• Biosphere
– All areas of the earth from the
ocean depths to the atmosphere
that support life.
Ecological roles
• Autotrophs - Producer
• makes own food (through photosynthesis or
chemosynthesis)
• Heterotrophs - Consumer
• must eat other organisms for food;
• primary (mouse), secondary (fox), tertiary (bobcat)
– Herbivore (eats plants) Carnivore (eats meat)
Omnivore (eats both)
– Detritivore
• Organisms that feed on animals remains and dead
material (crabs, earthworms)
– Decomposer
• An organism (ex. fungi or bacteria) that completes the
final breakdown of materials in an ecosystem
• End of 3.1
How does energy enter the ecosystem?
– Energy hits the earth in
the form of sunlight
– Autotrophs convert
sunlight (or chemical)
energy into organic
molecules
– Less than 1% of the sun’s
energy is converted into
organic material
– Eventually all energy is
lost back to the
atmosphere as heat.
How does energy move through an
ecosystem?
• Energy trapped in
autotrophs (producers) then
gets transferred to
heterotrophs (consumers) as
one organism eats another
• The easiest way to show this
is by using a food chain,
food web, or food
pyramid.
• Food chain – series of
steps in which
organisms transfer
energy by eating and
being eaten.
Food Web
links all ecosystems in a food chain together
Food Pyramids
• A food pyramid is designed
to show the organisms in an
ecosystem, grouped by their
feeding position or trophic
level (1st=prod, 2nd=herbivores, etc)
• Both food chains and food
pyramids show that only
10% of the energy at one
trophic level makes it to
the next trophic level
(from the 2nd law of
thermodynamics).
Primary Productivity
• The rate at which new organic material is created in
an ecosystem by producers is called the Primary
Productivity
• The more energy entering the food chain (from
producers), the more that can pass up through the
levels (only 10% moves up at each level), and as
result, the more levels there can be.
• Therefore, the ecosystems
with the most productive
producers have the most
levels (ex. rain forest)
– In most cases, there are only
3-4 levels.
– End of 3.2
How do nutrients cycle?
• Energy follows a ONE-WAY path
– Sun living organisms heat atmosphere
• Matter CYCLES through living organisms endlessly
• Biogeochemical cycles
– Water
– Carbon and Oxygen
– Nitrogen
Water Cycle
Carbon and Oxygen Cycle
Nitrogen Cycle
Niches
• Niches vs Habitats
– A habitat is the location where a species
lives.
• Ex. tall grassland/prairie
– A niche includes all of the species’
requirements plus its role in the ecosystem.
It is determined by all the the abiotic and
biotic factors relevant to the species.
• Ex. Top predator in prairie areas where
gophers live, and the temperature is never
below freezing.
Niche differences
• Organisms can be identified as either
– Generalists
•
•
•
•
Organisms with a broad niche
Eat lots of types of food
Live in many types of environments
Ex. house mice
– Specialists
•
•
•
•
Organisms with a narrow niche
Eat a narrow range of food items
Live in few, specific types of habitats
Ex. panda bear
Mutualism
• Mutualism occurs when
both species benefit
–
–
–
–
–
Rhinos and oxpeckers
trees and mycorrhizae,
ants and acacia
Termites and protist
Pollination (Yucca and
yucca moth)
Parasitism
– one organism feeds on/lives on another
species
– typically host is bigger than parasite
– parasites usually do not kill host (weaken
them)
– parasites need host for food, shelter, etc.
– ex. fleas on dog, tapeworm in human,
mistletoe, lamprey
Commensalism
• Commensalism occurs
when one species
benefits, and the other
neither benefits, or is
harmed
• examples:
– clownfish and
anemones
– epiphytes and trees
– Cattle egrets and
ungulates
Predation
• Predation - one organism feeds upon
the other
– predator usually bigger than prey
– ex. lion eating zebra
Prey Strategies
Competition
• When two species use the same
resources, they are said to compete and
their interaction = competition.
– ex. lions and hyenas compete for food in
Africa
• Competition does not necessarily
involve contact; interaction may be only
by means of effects on the resources.
• No two organisms can occupy exactly
the same niche at the same time
What determines where species can live?
• All species have requirements for many
factors/conditions.
– Abiotic factors – non-living factors; ex.
temperature, precipitation, pH
– Biotic factors – other species; ex. prey
species, competing species
• For each of these factors, species
exhibit a range of tolerance.
– For example, a fish species may only be
found within a pH range of 4.5 to 6 in
lakes.
Biomes
• A major terrestrial community that is found
in different areas with similar climate is
called a biome. A biome’s structure and
appearance are similar throughout its
distribution.
• The world’s biomes are tropical rain forest,
tropical dry forest, temperate woodland and
shrubland (Chaparral), temperate deciduous
forest, boreal/coniferous forest (taiga),
desert, temperate grassland, tropical
grassland (savanna), and tundra.
Biome distribution
Freshwater Habitats
• These habitats are distinct from both marine
and terrestrial habitats and are very limited in
area.
– make up about 2% of earth’s surface
– can be divided into
• Flowing water (rivers) standing water (ponds and lakes)
and wetlands (seasonal coverage)
Freshwater Habitats
• Estuaries
– These are very important for
• Breeding grounds for fish
• Filtering water
– Very productive ecosystems!
– Disappearing fast (flat land near the ocean)
Ocean
• 75% of earth’s surface
• Continental shelf - shallow ocean waters - smallest area;
large number of species (kelp forests)
– Intertidal zones
• Along our coast
• Species can tolerate being in and out of water
• Sea stars, algae, sea anemones
– Coral Reefs
• The “rain forests” of the ocean
• High diversity
• In tropical waters
Ocean
• open sea surface contains plankton (freefloating microscopic
organisms), bacteria,
algae, fish larvae;
responsible for 40% of
world’s photosynthesis
• Benthic zone - deep sea
waters - below 1000’ feet
animals adapted to dark;
some
blind/bioluminescent
What happens when ecosystems are
disturbed?
• When a disturbance impacts an
ecosystem, it recovers through a
process known as succession.
• Succession on newly formed habitat is
called primary succession.
– No remaining organisms or soil
– Examples, lava flow, sand dune, glacier
retreat
– It can take 1000+ years from sand dune to
forest.