Download Science 7: Unit A – Interactions and Ecosystems

Science 7: Unit A –
Interactions and Ecosystems
Topic 6: Succession and Change
in Ecosystems
Succession
Succession occurs when changes in an
ecosystem lead to some species replace
other species in the ecosystem.
Eg. A fire burns through a forest,
destroying trees and grass. A few years
later, scrubs and bushes are growing in
the same location.
Primary Succession
Primary Succession is the gradual growth
of organisms in an area where no life
previously existed.
Lichens, moss, and ferns are usually the
first organisms to grow on bare rock.
As these organisms do establish
themselves, the break down rock and
make the ecosystem more suitable for
other, more complex species of life.
Ferns Growing in bare rock
Secondary Succession
Secondary succession is the gradual
growth of organisms in an area that
already hosted life.
The example of the forest fire is an
example of secondary succession.
Some species of bushes grow best in soil
where there is large amounts of ash.
Grasses and Bushes Growing in an area
previously burned.
Human Effects on Succession
 Because humans are having a wide effect on
many ecosystems, we are influencing the
process of succession in these ecosystems.
 Certain species of animals succeed in an
ecosystem because they can adapt to the
changes we cause in an ecosystem. These
species are called generalists because they are
a jack of all trades that scavenge for scraps of
food we leave behind.
Generalists tend to be Scavengers
 Generalists are species that can adapt to wide
range of conditions. They include: rats,
raccoons, cockroaches, seagulls, pigeons. Many
generalists are scavengers.
 These animals are succeeding against native
animals such as owls, wolves, foxes, etc. Many
of the animals suffering are carnivores and
herbivores. These animals cannot adapt as
easily to living with humans.
Pest Control
Using chemicals such as DDT to kill pests
leads to quite a few problems. Pollution,
resistance, bioaccumulation, and damage
to non-pest organisms.
When you use a pesticide it can affect
organisms that you don’t want to harm,
such as your crops.
Also, using pesticides can lead to the pest
species developing resistance to the
chemical.
Biological Control
Another way to eliminate pests is to use
their predators as a natural pesticide.
Beetles and lady-bugs are very effective at
controlling pest plants and animals.
There is still a risk with biological control.
Introducing species into a new area could
have unpredicted effects.
Introduced Species
 An introduced species is one that is brought to a
new ecosystem with humans. Often introduced
species do damage to the ecosystem by
harming the organisms there.
 Eg. Settlers brought rabbits with them to
Australia. The rabbits escaped into the wild, and
without predators in Australia, began to grow
quickly in numbers, feasting on the grasses. This
lead to a drop in the herbivore population in that
part of Australia.
Species in Danger
Threatened Species – a species whose
numbers are dropping.
Endangered Species – a species whose
numbers are so low that they are in
danger of becoming extinct or extirpated in
an area.
Extinct - a species which has been
completely wiped out .
Extirpated – a species which has been
wiped out in an area or ecosystem.
Causes of Extinction
 Humans have had a large impact on recent
extinctions. This happens in a numbers of ways:
 1. Loss of habitat and food sources. If the
organism loses its home, everything else will
suffer.
 2. Over-hunting by humans.
 3. Competition by introduced species. An
introduced species can eat all of the species’
food, or the species itself.
How Can We Help?
By designating certain areas as wildlife
preserves. Wildlife preserves are areas
that we leave completely alone. They are
not parks because people are not even
supposed to go camping there.
Habitats are preserved and introduced
species are kept from spreading into the
preserve.