Population and community ecology Population ecology J Gerber and J Goliath 1

Population and community ecology

Population ecology

J Gerber and J Goliath1

Terminology

Species Habitat Population Community Ecosystem Ecology Ecological niche


Size of a population

Definition and impact on population size: Natality Mortality Dispersal (including immigration, emigration and migration)

Aspects of population fluctuation and regulation: Carrying capacity Environmental resistance/limiting factors and its impact on

population growth The effect of annual and seasonal fluctuations on population size


Size of a population

Characteristics of the following growth patterns/forms: Geometric growth form (J-shaped curve) Logistic growth form (S-shaped curve)

Methods to determine population size, demographics

and population movements: Direct technique (census) Indirect technique – simple sampling and mark recapture


Activity 1- Terminology

InstructionsExplanation of activity on terminology.In pairs/groups define the terms on the work

sheet given.After 10 minutes each pair/group give

feedback.


Terminology

Species – Group of organisms with similar characteristics which can interbreed to produce

fertile offspring Habitat – Specific type of environment (area) in

which a plant or animal species normally occur Population – Group of organisms of the same

speciesthat occur in a particular areain a

particular time so that interbreeding occurs


Terminology

Community – Group of populations occurring in a particular area e.g. lion, zebra and giraffe in a National Park.

Ecosystem – Interaction between the biotic factors and abiotic factors in a particular area

Ecology – Study of mutual interaction among living organisms and environment in which they live


Terminology

Ecological niche – Each species has a specific role in a community. Each species needs a particular set of environmental conditions and resources to survive and reproduce in its habitat


Size of a population & population density

Size of a population – the number of individuals in a population

Population density – the number of individuals of the population per unit of area


Population parameters

Natality – birth rate of a population expressed as the number of live births per thousand individuals per year.

Mortality – death rate of a population expressed as the number of deaths per thousand individuals per year.

Immigration – one-way movement of organisms into an area Emigration – one-way movement of organisms out of an area Migration – moves from one place to another and returns to the

original place


Impact of population parameters

Natality and immigration cause an increase in population size.

Mortality and emigration cause a decrease in a population size.

No immigration or emigration in a closed population e.g animals on an island.

Natality and mortality can affect the population size in a closed population.


Impact of population parameters


Population fluctuation and regulation

Carrying capacity – maximum number of individuals of a species that an ecosystem can continually supply resources to.

Certain factors prevent a population from unlimited growth and exceeding its maximum growth rate – limiting factors and together are called environmental resistance.

Seasonal fluctuations – Swallows fly from the cold European winter to Southern Africa where the summer temperature is more favourable.

Annual fluctuation – Migration of millions of wildebeest in East Africa. This phenomen is determined by the availability of grazing which is also dependant on rainfall.


Growth patterns/forms – Geometric or J – shaped curve

Population size increases unrestricted and rapidly with time.

A population can reach its full reproductive potential because of enough food, water and no predators.

Environmental resistance increases when numbers of population increase.

Number of population can decrease rapidly due to limiting factors.


Graph of repeated growth pattern


Logistic growth form (S - shaped)

Lag phase: Population acclimates, individuals

become sexually mature and seek partners for mating.

Accelerating growth phase Population grows rapidly and

reaches its maximum growth rate.Deceleration growth phase Growth rate decreases due to an

increase in environmental resistance.

Equilibrium phase Population numbers reach the

carrying capacity.


Geometric and logistic growth phase


Methods to determine population size - direct technique (census)

Count of all individuals in a population and includes human population census.

Aerial photography may be used in the counting of larger animals in nature reserves.


Indirect technique – simple sampling (quadrated method)

A square frame (quadrat) is used Place it on the ground and count the individuals

inside the quadrat It gives the number of individuals (density) per unit

area Repeat in different places at random and calculate

the average density Method is used for plants and slow moving animals


Mark-recapture technique (Peterson)

Demarcate a specific area. Capture a number of individuals, count and mark them (first

sample). Set the marked individuals free in the area. Allow the marked individuals enough time to mix with unmarked

individuals in the area. Capture a second number of individuals and count them

(second sample). Count the number of previously marked individuals in the

second sample.


Mark-recapture technique

Use this information to calculate the total size of the population by means of the following formula:

P = m x s

t P = estimated population size. m = total number of animals captured and marked in first

sample. s = total number of animals captured in second sample. t = number of marked individuals in second sample.


Mark-recapture technique - validity

Marking methods should not injured the organism. Marks should be clear for the duration of the investigation. Marking methods should not affect the movement of the

animals. Marked organisms should be allowed enough time to mix. Population must be closed. Period between two samplings should be sufficiently brief – no

births or deaths.


Documents

Population and community ecology Population ecology J Gerber and J Goliath 1