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(Sec 3.2 pg 61-66)
When the environment of an organism changes
(biotic or abiotic factors) it must either adapt or it
will not survive.
Adaptation is any genetic trait that improves an
organism’s chance of surviving or reproducing
Natural selection is a process where organisms that
are best suited for their environment will survive,
and those that are not well-suited will die out.
Natural selection is the driving force of evolution.
Organisms best suited to their environment will be
best-able to breed and pass on their genes on to their
Natural selection occurs at the
individual level, but affects
populations. Beneficial traits
(from individuals) will be passed
on and become more common in
the population.
Natural selection occurs because
of abiotic and biotic factors.
Habitat features, predator-prey
interactions, and food
availability are all examples of
selective pressures.
Some common examples of natural selection are:
Camouflage = when a species is able to blend into its
background – the organism will save energy as its predator
cannot see it (or vice versa if the predator’s camouflaged)
see Fig.3&4 p.62
Some common examples of natural selection are:
Mimicry = when one species looks like another more
dangerous, poisonous or distasteful species (see Fig 6 p.63).
Some common examples of natural selection are:
Co-evolution = when two species have adapted in response
to each other. For example, herbivores may respond to
available food sources with specialized beaks, teeth or
digestive systems capable of digesting plant toxins; plants
may respond to herbivore pressures by developing thorns,
spines or tough leaves.
Biodiversity refers to the variety and variation of
organisms in an ecosystem, biome, or the entire
It is closely linked to primary productivity, which is
the amount of energy provided by the producers in
an ecosystem.
A greater number of producers can support a more
complex and diverse community of consumers. The
greatest biodiversity on Earth occurs in tropical
rainforests, where primary productivity is highest.
Extinction occurs when a species is completely gone
from Earth, or when so few individuals remain that
reproduction is not possible.
Extirpation refers to a phenomenon of local
extinction; the species no longer exists in one specific
area, but still occurs in other parts of the world.
Keystone species are species whose presence plays a
crucial role in an ecosystem.
If these species are eliminated from an ecosystem,
there are serious and dramatic effects.
Sea otters are an example of a keystone species in
Pacific marine ecosystems.
They keep bottom-feeding sea invertebrate
populations (e.g. sea urchins) in check, which
ensures that kelp forests remain healthy.
If sea otters didn’t keep sea urchin populations in
check, they would eat too much of the kelp forest.
Sea kelp forests are incredibly important habitats for
juvenile fish, and many other organisms (they
provide nursing grounds, shelter, and food).