Population Ecology Summary

POPULATION ECOLOGY
Population Ecology Factors
influencing population size, rate / forms and distributions of individuals
:
growth .




Terminology
forms part of
Individual A
single organism that population
° :
a .




•
species Group
: of closely related
organisms ( fertile offspring i. can interbreed )
°
Population Group:
of
organisms of the same species found in a particular area and can crossbreed .




°
Community Groups :
of different species in a particular area .




0
Ecosystem : Unit of plant / animal communities that interact with each other and abiotic factors .




0
Environment :
External factors , biotic and abiotic , surrounding an
organism and influencing it 's development
and survival .




0
Habitat :
A specific environment in which a species normally occurs .




POPULATION SIZE

Population size : total number of individuals



Population density : number of individuals of a population per unit area .




Population Parameters


>
>
Nativity :




Immigration Organisms
birth rate

: move into an area and stay
} T population numbers


Mortality death rate
} d population
> :


>
Emigration organisms : leave a area and stay where they arrived .
numbers


closed system =
no
immigration / emigration
Determining population sizes


Direct techniques :
-

Count all individuals of a
population
=
census
> -
direct contact counting ( smaller organisms)
Helicopter/ vehicle / plane ( larger organisms)
}
-




Aerial photos
'

, Indirect techniques : count
only part of population → SAMPLE

'
Mark recapture
-



technique Peterson method
Total number of 1st sample
^ "
>
total number of 2 sample
Specific demarcated
-



area
P = M ✗5
Individuals caught Sample
1st
-
=


-


Released i. mix with population estimated size
'
t >
marked individuals in 2
"
sample
"
Individuals
caught 2 sample
-
=




More accurate (get average population size)
→
=
repeated more of


VALID IF :



°

Marking methods don't injure / damage organism
°
Marks clearly visible

Marking method doesn't affect
organism's movement / behaviour
°




time for marked
Enough organisms to mix with rest of population
°
.




°
Closed population
°
Brief period between samplings
=
no births / deaths .




2
Quadrats

'
→
Square frame =
1m


-

Area demarcated
Frame placed there number of individuals per unit area
-




-



Repeated in different areas of demarcated area .




Average calculated
-




Population size =

average no of
. individuals ✗
Surface area of area
surface area of
per quadrant quadrant

Reliability depends :




Exact number of
organisms in quad rat is known
°




°
Surface area of quadrant is known
°
Surface area of demarcated area is known
°
Quadrant placed randomly .




* Quad rat =

any shape
d
Size depends on
organism