Ecology Study Guide
Miracle Fish/Easter Island
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Introducing species into a new environment (Nile perch) can have intended and
unintended consequences for an ecosystem.
Introduced (non-native) species are moved outside of the organism’s normal range
(habitat) and placed in a new habitat, often by humans.
If introduced species thrive in their new environment and negatively affect native
species or humans, they are considered invasive. Often this happens because they
lack natural predators in the new space.
The complexity of ecosystems makes it difficult to predict the outcome of
ecological change. Making decisions about complex issues often involves trade-offs
(giving up one thing in favor of another).
Since introducing the Nile Perch to feed people living near the
lake and provide more fishing jobs, Lake Victoria has faced
many challenges. Many species of fish have gone extinct,
including those that ate algae, the perch are running out of
food and have gone cannibalistic, etc…
Easter Island faced similar dilemmas when it’s inhabitants introduced new species
that became invasive, overused their resources and began to fight one another.
Question: What were the trade-offs for Lake Victoria when the Nile perch was added?
Eating for Energy
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 Ecology is the study of relationships between living
organisms (community) and the physical environment.
 Feeding relationships in ecosystems are very
complex and are best represented by webs, not the oldschool “food chain”.
 In food webs, arrows always point from prey to
predator and plant to consumer, which is the direction of
energy flow.
 Energy in an ecosystem is gained from sunlight by
producers (plants and plant-like protists, which includes
phytoplankton) and is later passed to consumers and
decomposers.
Within a food web there are always producers, consumers and decomposers
Ecosystem changes, such as the introduction of a new species (zebra mussels) can
cause both short- and long-term effects on populations
Question: Why are producers, such as plankton, an essential part of an ecosystem? What
happened to the food web in Lake Erie when zebra mussels were introduced?
Carrying Capacity/ Room for One More?
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Organisms have habitat requirements, which include food, air, space, warmth, light (or
darkness) water and sometimes shelter.
The availability of food is one factor that can dramatically affect population size and a
population’s range.
Competition between species occurs when two species compete for limited resources
such as space or food (clams and zebra mussels).
Introduction of a non-native species such as the zebra mussel can compete with a native
species (clam) for resources and cause a change in the population of the native species.
 Carrying capacity is the maximum population of a species that an
ecosystem can support long-term. It is determined by biotic and abiotic
factors, which affect the size of the carrying capacity over time.
Question: Why and how do zebra mussels effect clam populations? What
factors might affect the maximum number of individuals of a species
(carrying capacity) in an ecosystem?
Biodiversity
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Biodiversity can be defined in many different ways. It can
refer to genetic diversity, the number of species in an
ecosystem, or total of species on Earth.
New species evolve and old species go extinct naturally over
time, but many people are concerned with the rate of
extinctions we are currently experiencing. Because of this,
many people think that humans should work to protect
current levels of biodiversity.
Reasons for conservation of biodiversity vary, but here are a few: We use nature for
inspiration in art and technology, many medicines are made from natural sources and the
cure to diseases could lie within a living organism that we haven’t discovered yet, we use
nature for recreation and enjoyment, all species deserve a right to live, removing one
species can upset the balance of an entire ecosystem.
Ecosystem Services are natural processes that humans need for survival. Some examples
are pollination, plants preventing erosion and providing oxygen.
Ups and Downs
A population is group of individuals of one species living within the same area.
Population fluctuation (increase and decrease in population size) is expected when studying
any living organisms.
 Biotic (living) and abiotic (nonliving) factors affect population size.
 Limiting factors (parts of an ecosystem that limit population size) could include
competition for shared resources, pollution, introduction of predator, etc…
Question: How might an ecologist explain a rapid decline in a population? Should it always be
a cause of concern?
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