1. Changes in Populations
Science Foundations

2. Ecological Succession
Populations of species found in certain habitats
change over time. This concept, called
ecological succession or environmental
variation.

3. Primary Succession Primary succession consists of a sequence of
communities developing in a newly exposed
habitat devoid of life.
Examples:
Succession on a bare rock
Newly deposited sand
New land from cooled lava

4. Secondary Succession Secondary succession consists of
communities taking place on sites that have
already supported life.
Examples:
Old field succession
Clear cut forests
Burned areas
Difference between primary and secondary succession is that secondary starts with soil.

5. Pioneer Community The original plant forms that colonize an area
are called the pioneer community. These must
be a strong group, able to withstand the forces
of nature.
Bare rock would be an unwelcome habitat for most plants, but lichens are up to the challenge. Blown there by the wind, lichens attach to the rock and begin the process of breaking it down as it carries on its life functions. As soil accumulates, a bare field forms. This eventually becomes the home of grasses and flowers.

6. The Progression 1. Rock 2. Lichen 3. Soil 4. Grasses
8. Hardwood Forest
5. Flowers
6. Shrubs
7. Pine Forest

7. Climax Community A hardwood forest of trees like oak, beech, and
maple trees, grows in the final stage of
development. This final stage is called the
climax community. The climax community
does not change much, as long as no disasters
strike, like wild fires or tornadoes!

8. Animals The animals that live in the habitat change
as the plants change.
Small animals like mice and rabbits, prefer
the open field.

9. Ponds Pioneer communities may sometimes be ponds
that develop underwater plants, then cattails. As
the pond fills with sediment, grasses may begin
to grow and over many years, the succession
eventually results in a deciduous forest for that
area.

10. Survival of the Fittest
Survival of the fittest is a situation where
organisms compete for the available resources
in their environments: food, shelter, or mates.
Those that are more fit will be able to win this
competition. An animal that outperforms others,
such as running faster, locating food better, or
surviving more fights, will be more likely to
reach maturity and eventually produce
offspring. These traits will then be passed on to
succeeding generations.

11. Geographic Isolation Changes in population can also result from
geographic isolation. Geographic isolation
occurs when a population become separated by
changes in the environment.
For a species to exist in a changing
environment, members must adapt in order to
survive and reproduce. If this does not occur,
the species will become extinct.

12. Responses and Behavior
One very important life function is that of
response. Response characteristics of cells
enable organisms to react to stimuli in their
environment.
A group of complex responses is called a
behavior.
A reflex is an involuntary response to
environmental stimuli.
An instinct is a genetically controlled behavior.

13. Examples Reflexes: A person’s eye blinks as an object flies past it.
A dog sneezes when it inhales pepper.
Instincts:
Birds respond to changes in season by migrating.
A bees developing into drones.

14. Tropism Tropisms are examples of responses to environmental change.
A tropism is an involuntary response of an
organism involving orientation toward or away
from external stimuli.

15. Geotropism Plants respond to gravity by sending roots
“down.” It is called geotropism.

16. Phototropism
Phototropism adjusts plants exposure to light.

17. Thigmotropism
Thigmotropism is a plant’s response to touch.

18. Adaptation Organisms which do not, or cannot respond to
changes in the environment reduce their
chances for surviving. This may mean death for
the individual organism and, in extreme cases,
extinction of the species if too many die before
they are able to reproduce.
Response to the environment is, therefore,
closely related to adaptation.

19. Adaptations Adaptations allow one kind of organism to live
in conditions where other organisms cannot.
Examples:
A cactus has special adaptations which allow it to live in a dry, hot environment.
Polar bears have adaptations which allow them to live in very cold environments.
1. The polar bear could not survive in the desert and the cactus could not live in the Arctic.

20. Homeostasis All organisms must have life functions which
work together to produce and maintain a stable
internal environment. This is the principle of
homeostasis.
Adaptations are made to produce homeostasis.

21. Adaptation Example Certain rabbits turn from brown to white in the
winter so they can be camouflaged with the
snow. Since rabbits with dark coats were more
easily seen, they were more likely eaten.
Gradually, the proportion of winter-white rabbits
to winter-dark rabbits would increase until there
were no dark rabbits left.

22. Human Example In areas where there is a higher incidence of
malaria, there is also a higher incidence of
sickle cell anemia. This is because the sickle
shaped cells cannot be infected with malaria.
Over time, the people in the area with sickle
shaped red blood cells survived because they
were not catching malaria and people with
normally shaped red blood cells were dying.