Download Populations And Communities

Populations And Communities
Populations
• Definition: A group of individuals of the same
species, living in a shared space at a specific
point in time.
The Gaspésie Caribou Herd
EXAMPLE - 2
Population Size
• Definition: It refers to the number of individuals
in a population.
FACTORS
1. Births
2. Deaths
3. Immigration (arrivals)
4. Emigrations (departures)
How does the populations size change?
And what if we get rid of predators?
Methods for measuring population size
1) It is sometimes possible to simply count all
individuals in a populations. DIFFICULT!!!!
Methods for measuring population size
2) Counting by sample area
- Counting individuals in randomly selected
areas and using the following proportion.
Average number of individuals per section = Population size
Area of a section
Total study area
quadrats
Methods for measuring population size
3) Mark and Recapture
-good to study species that
are very mobile and widely
scattered within their habitat
# of marked individuals recaptured = Number of marked individuals
Total number of individuals captured
Population size
the 2nd time
5 = 10
10 x
Population Density
Definition: The number of individuals per unit
area or volume
Population Density
EXAMPLE
Population Density = Number of individuals
Space occupied
Since you were in grade 1, you have fish at home! In an
aquarium, you have 5 goldfish in a 100L of water
Pop density = 5 individuals = 0.05 fish per liter of water
100 L of water
Population Distribution
Definition: the way in which individuals are
dispersed within their habitat.
Population Distribution
Individuals form
groups, where
conditions
are better.
Individuals are
dispersed equally
throughout the
habitat because of
competition.
Rarely found in
nature.
Individuals are
randomly
dispersed.
ECOLOGICAL FACTORS
Definition: An aspect of a habitat that can affect the
organisms living there.
ABIOTIC (non-living) –
Physical or chemical factors affecting organisms, such as
pH, or terrain.
BIOTIC (living) – Biological factors affecting organisms,
such as the presence of predators or disease.
LIMITING FACTORS
• Definition: an ecological factor that causes the
density of a population to decrease.
EXAMPLE: If there is too
much water in the ground,
cactus roots rot and the cactus
populations decreases. The
limiting factor is the
amount of water.
BIOLOGICAL CYCLES IN POPULATIONS
• It is composed of alternating periods of rise
and fall in population size. These periods are
of fixed duration and are repeated continually.
For example:
Lynx and hare
populations
cycle over 10
year periods.
BIODIVERSITY
Definition: It describes the variety of species
living in a community. Ex: Sri Lanka: hot spot!
How do we measure biodiversity?
2 FACTORS
1) The number of species
2) Relative abundance: the number of
individuals of a particular species in relation
to the total number of individuals in the
community.
Let’s compare both of these forests!
1) Both forest have 4
species of trees. Species
richness is the same!
BUT!
2) In community 2, most
trees are the same (tree
A). In community 1, the
relative abundance of
each species is the same,
25% .
WHEN IS BIODIVERSITY HIGH?
1) The number of species is high
2) The relative abundance of each species is similar
Interactions Between Individuals in a
Community
• Individuals establish relationships.
For example: Lions eat antelopes!
COMPETITION
Definition: An interaction between living
organisms that seek access to the same resource
in their habitat. (such as food)
Intraspecific
(same species)
Interspecific
(different species)
Example – Intraspecific Competition
• What are cactus species competing for?
PREDATION
Definition: Interaction between two living
organisms in which one feeds on the other.
GREAT
GREY OWL
MOUSE
MUTUALISM
Definition: An interaction between two living
organisms that benefits both organisms.
The clown fish is protected by the anemone, but also
serve as bait for the anemone! (anemones eat fish)
EXAMPLE OF MUTUALISM: HONEY
BEES
• How do these two species benefit from one
another?
COMMENSALISM
Definition: The interaction between two living
organisms in which one organism benefits
from the relationship, while the other remains
unaffected.
This warbler’s nest
does not harm the pine
tree. The birds benefit
from the tree, but the
tree gains nothing.
EXAMPLE of COMMENSALISM
• Barnacles grow on whales, but whale don’t gain
anything from these small molluscs.