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ECOLOGY
TOPIC 4
4.1 Species, communities, and
ecosystems
• Species are groups of organisms that can
potentially interbreed to produce fertile
offspring.
• Species:
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Have a common gene pool
The basic unit for classifying organisms
Have similar physiological and morphological characteristics
Are genetically distinct from other species
Have a common phylogeny (family tree)
Challenges to definition of species
• Similar species can sometimes mate and produce offspring.
• Examples:
• Horse and zebra, donkey and zebra. Don’t have same
number of chromosomes so offspring are usually infertile.
• Populations that can’t breed due to distance
• Populations that don’t interbreed because they reproduce
asexually.
• What about infertile individuals?
Hybrids
• When members of different species mate, their offspring are
infertile and referred to as an interspecific hybrid.
• Examples are mule and liger
• Hybrids don’t continue as a population due to being infertile
Populations can become isolated
• Isolation can cause changes in evolutionary paths creating
new species.
• Causes for isolation:
• Bodies of water
• Mountain ranges
• Deep canyons
• Breeding times
• Breeding habits ( songs, dances etc)
Autotrophs and Heterotrophs
• Autotrophs are capable of making their own
organic molecules as a food source.
• Photosynthesis converts inorganic molecules
into organic molecules.
• Examples of Autotrophs (Producers)
• Algae, cyanobacteria, grass, trees
Autotrophs and Heterotrophs
• Heterotrophs cannot make their own food
from inorganic molecules and must obtain
organic molecules from other organisms.
• They obtain their energy from autotrophs or
other heterotrophs.
Consumers
• Ingest other organisms to get the molecules
needed for survival.
• The only component we can make from
sunlight is vitamin D
Detritivores
• Eat non-living organic matter such as dead
leaves, feces, and carcasses.
• Examples of detritivores are earthworms,
woodlice and dung beetles.
• Many bottom feeding organisms in lakes and
rivers are detritivores.
Saprotrophs
• Live on or in non-living organic matter.
• Secrete digestive enzymes and absorb the
products of digestion.
• Examples are bacteria and fungi.
• Saprotrophs, bacteria and fungi, are also
called decomposers.
Communities
• A group of populations living and interacting
in an area.
• Ways of interacting includes feeding on each
other, protecting each other, providing habitat
for each other.
Ecosystems
• A community of organisms along with their
abiotic environment.
• Examples of abiotic components of an
ecosystem:
• Air, water, soil, light, humidity, pH
Systematic Sampling Techniques
• Random sampling of an area to determine what
is there, how much is there and what abiotic
components are there.
• A quadrat is a 1 square meter box used to take
random samples of an area.
• A transect is a line running across numerous
environments within an given area. It is used
along with a quadrat to show relationships
between organisms and the environment they
live in.
Nutrients
• Autotrophs need nutrients to grow and be
healthy and they can’t get them from their
diets like heterotrophs do.
• Nutrients are available to plants from the soil
and are taken up by their roots.
• The supply of nutrients is maintained by
recycling due to decomposers.
• Carbon and nitrogen are examples
Nutrients
• Returned to the system through the action of
decomposers.
• By returning nutrients to the system,
ecosystems can be sustainable.
• Nitrogen cycle: N2 as a gas in the atmosphere
• Plants and animals can’t use this gas directly
• Some bacteria can – nitrogen fixation- take
nitrogen from air and create nitrogen
compounds that plants and animals can use.
4.2 Energy Flow
• Most ecosystems depend on energy from the
sun
• Photo synthesizers (autotrophs) use light
energy to create organic molecules (sugar)
from inorganic molecules CO2
• They form the basis or first trophic level of the
food or energy chain.
Food chains
• By feeding on autotrophs, heterotrophs can use
the energy of autotrophs to grow and stay
healthy.
• A food chain is the process of passing energy
from organism to organism, trophic level to
trophic level.
• Only about 10% of the energy contained within a
trophic level is used by the next trophic level.
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Energy loss in a food chain
• Not consumed
• Consumed but not used by the consumer
• Lost in the form of heat