Biology
Population Dynamics & Community Ecology
Basic Concepts:
- Everything depends on this.
- Population…
= A group of the same species, in the same place, at the same time, that can be
interbread freely.
- Population size…
= The number of individuals making up a population.
Population Parameters:
1) Population parameters
- This is a factor which affects the size of a population. (increase or decrease)
- Are FOUR population parameters…
1. Natality - birth rate
2. Mortality - death rate
3. Immigration - moving into an area
4. Emigration - moving out of an area
- Natality and immigration are both positive parameters because they make the population
grow.
- Mortality and emigration are both negative factors because the population decrease in
size.
- Migration…
= It is a periodic departure from/return to an area.
= It is seasonal although it has to be factored into our understanding of an area it cannot
be considered to be a parameter.
- If a parameter changes (mortality increases) then the population size will change.
- Population density…
= The number of individuals per unit area.
= A unit area is a measure of area, predetermined by researches, to be representative of
the whole area studied.
- A large population is not necessarily better than a small one since the environment that
they live in can only supply a limited quantity of resources.
= As the resource base declines the population and each individual in the population
comes under increasing and eventually sustained pressure.
= It becomes more difficult to find food, mates, water and shelter.
= This pressure is called ENVIRONMENTAL RESISTANCE.
= This places a ceiling on the growth of a population and unless more resources become
available it will not grow any further.
,- In addition COMPETITION between individuals becomes more of a problem and it is
also possible that the population of one species will be pitted against another population
of species if the resources becomes too limiting.
= This can also lead to the local or total extinction of an unsuccessful species.
= There are lots of adaptions to reduce competition making your chances of avoiding
extinction are higher.
= Avoidance of competition is one of the forces that drives evolutionary chage.
- Population size…
P = (N+I) - (M+E)
P = Population size
N = Natality
I = Immigration
M = Mortality
E = Emigration
, 2) Population Growth
- The population grows when natality mortality or immigration exceeds emigration.
- Population growth rate refers to the speed that a population grows over a unit time.
- Growth rate is influenced by two main factors…
1. Carrying capacity for increase
= Otherwise stated as reproductive potential.
= Rabbits quicker than elephants.
2. Environmental factors
= Are conditions favourable or unfavourable.
= Altered by weather and seasons.
Eg) Rabbit populations grow even quicker when they have no natural predators,
no natural diseas vectors and unlimited food.
Population Growth Forms:
- Different populations have different characteristics patterns of increase or decline.
- Known as population growth forms.
= Illustrated on graphs.
1. Geometric Growth
- J-Shaped
- Initially there is a rapid increase in number then it suddenly stops as environmental
resistance comes into play.
- Rate of growth increases rapidly until the growth rate stops suddenly.
- Growth form has two phases…
= Unrestricted growth phase.
= Sudden halt in growth due to the population runs out of a resource, seasonal factors
intervene, the population pollutes its own environment and this is more of a problem in
closed environment.
- Eg) Bacteria, insects, migratory species.
Population Dynamics & Community Ecology
Basic Concepts:
- Everything depends on this.
- Population…
= A group of the same species, in the same place, at the same time, that can be
interbread freely.
- Population size…
= The number of individuals making up a population.
Population Parameters:
1) Population parameters
- This is a factor which affects the size of a population. (increase or decrease)
- Are FOUR population parameters…
1. Natality - birth rate
2. Mortality - death rate
3. Immigration - moving into an area
4. Emigration - moving out of an area
- Natality and immigration are both positive parameters because they make the population
grow.
- Mortality and emigration are both negative factors because the population decrease in
size.
- Migration…
= It is a periodic departure from/return to an area.
= It is seasonal although it has to be factored into our understanding of an area it cannot
be considered to be a parameter.
- If a parameter changes (mortality increases) then the population size will change.
- Population density…
= The number of individuals per unit area.
= A unit area is a measure of area, predetermined by researches, to be representative of
the whole area studied.
- A large population is not necessarily better than a small one since the environment that
they live in can only supply a limited quantity of resources.
= As the resource base declines the population and each individual in the population
comes under increasing and eventually sustained pressure.
= It becomes more difficult to find food, mates, water and shelter.
= This pressure is called ENVIRONMENTAL RESISTANCE.
= This places a ceiling on the growth of a population and unless more resources become
available it will not grow any further.
,- In addition COMPETITION between individuals becomes more of a problem and it is
also possible that the population of one species will be pitted against another population
of species if the resources becomes too limiting.
= This can also lead to the local or total extinction of an unsuccessful species.
= There are lots of adaptions to reduce competition making your chances of avoiding
extinction are higher.
= Avoidance of competition is one of the forces that drives evolutionary chage.
- Population size…
P = (N+I) - (M+E)
P = Population size
N = Natality
I = Immigration
M = Mortality
E = Emigration
, 2) Population Growth
- The population grows when natality mortality or immigration exceeds emigration.
- Population growth rate refers to the speed that a population grows over a unit time.
- Growth rate is influenced by two main factors…
1. Carrying capacity for increase
= Otherwise stated as reproductive potential.
= Rabbits quicker than elephants.
2. Environmental factors
= Are conditions favourable or unfavourable.
= Altered by weather and seasons.
Eg) Rabbit populations grow even quicker when they have no natural predators,
no natural diseas vectors and unlimited food.
Population Growth Forms:
- Different populations have different characteristics patterns of increase or decline.
- Known as population growth forms.
= Illustrated on graphs.
1. Geometric Growth
- J-Shaped
- Initially there is a rapid increase in number then it suddenly stops as environmental
resistance comes into play.
- Rate of growth increases rapidly until the growth rate stops suddenly.
- Growth form has two phases…
= Unrestricted growth phase.
= Sudden halt in growth due to the population runs out of a resource, seasonal factors
intervene, the population pollutes its own environment and this is more of a problem in
closed environment.
- Eg) Bacteria, insects, migratory species.
