Grade 12 Environmental Studies - Part 1 POPULATION ECOLOGY

Question 1

Define Natality

Answer 1

Birth rate in animals or the production of seeds in plants

Question 2

Define Mortality

Answer 2

Death rate

Question 3

Define Immigration

Answer 3

Individuals move into a population and stay

Question 4

Define Emigration

Answer 4

Individuals leave a population and do not return

Question 5

Define Stable Population

Answer 5

One that fluctuates around the carrying capacity

Question 6

What are the consequences of an Unstable Population?

Answer 6

Habitat deteriorates rapidly (Lowers carrying capacity)

Habitat eventually unable to support population, which may go extinct

Question 7

Define Predation

Answer 7

Biological interaction in which one species, the Predator, kills and eats another species, the Prey.

Question 8

Define population ecology

Answer 8

Study concerned with the fluctuation in the size of a population and the factors, physical and social, that regulates these fluctuations.

Question 9

All the ecosystems on earth make up the ____________

Answer 9

biosphere

Question 10

Define biosphere

Answer 10

the part of earth where living organisms are found

Question 11

Define ecosystem

Answer 11

Made up of groups of different species of organisms that interact with each other and with the environment.

Question 12

Define organism.

Answer 12

An individual form of life, such as bacterium, protest, fugus, plant or animal, composed of a single cell or a complex of cells that are capable of growing and reproducing.

Question 13

Define community

Answer 13

A group of different species that inhabit and interact in a particular area

Question 14

Define species

Answer 14

A group of closely related organism that are very similar to each other and are usually capable of independent existence.

Question 15

Define individual.

Answer 15

A single organism capable of independent existence.

Question 16

Define population.

Answer 16

A group of organisms of the same species that occupy the same area and can breed freely with each other.

Question 17

Define demographics

Answer 17

The statistics such as the size, age distribution, growth rate, and density of a population.

Question 18

What is the birth rate for humans?

Answer 18

The number of births per 1000 people in a year.

Question 19

What is the death rate for humans?

Answer 19

The number of deaths per 1000 people per year.

Question 20

What is a closed population?

Answer 20

Population with no immigration or emigration - the only parameters affecting any change in population numbers will be births, or deaths e.g. fish in fish pond.

Question 21

List the dynamic parameters that affect the growth of a population:

Answer 21

1. Natality
2. Immigration
3. Mortality
4. Emmigration

Question 22

How is the growth of a population regulated?

Answer 22

• Exponential = increasing more and more rapidly (populations will increase in unoccupied area where there is no shortage of food or other resources and no predators)
• As the number increases, demands are made on available resources
• This builds environmental resistance - which causes birth rate / immigration rate to decrease and death rate / emigration rate to increase.
• Environmental resistance = The total number of factors that stop a population from reproducing at its maximum rate.
• Eventually a balance is achieved - population stabilises at particular size or number.
• This is the carrying capacity of the ecostystem.
• Carrying capacity is the population density that the environment can support.

Question 23

Define environmental resistance:

Answer 23

The total number of factors that stop a population from reproducing at its maximum rate.

Question 24

Define carrying capacity.

Answer 24

Carrying capacity is the population density that the environment can support.

Question 25

Population size is self-regulating. What does this mean?

Answer 25

Fluctuates seasonally and anually, depending on available resources. All negative feedback mechanisms are examples of this self-regulation.

Question 26

# Di Discuss the limiting factors that **help to regulate population growth** - buiding up environmental resistance:

Answer 26

**Density independent factors** - as a result of natural factors e.g physical factors (rainfall, tempererature, humidity, acidity, salinity) & catastrophic events (e.g. floods, fire, droughts, volcanic eruptions, tsunamis, earthquakes) **Density dependent factors **- that have a greater effect when population is high - a) organisms compete for resources such as food, light, oxygen, water, space, shelter b) are more easily found by predators c) spread disease and parasites more readily.

Question 27

Explain stable population:

Answer 27

One in which numbers decrease when its size exceeds the carrying capacity but increase again when numbers fall below the carrying capacity i.e. o**ne that fluctuates around the carrying capacity.**

Question 28

Explain an unstable population:

Answer 28

* Develops if the population far **exceeds the carrying capacity**. * This results in the h**abitat deteriorating rapidly**, which leads to **lower caraying capacity** AND eventually **not being able to support the population**, which will decrease rapidly and possibly become extinct.

Question 29

How is population size estimated?

Answer 29

1. Direct method 1. Mark-recapture method

Question 30

Explain the direct method in estimating population size:

Answer 30

* Counting every single individual in a population = censure *** Can** only be used for** populations of organisms that are large enough to be seen, where the area in which the animals are being counted is not too large. **Can be used when:** * animals are slow moving e.g. snails, tortoises etc. * stationary e.g. plants * usually stay fixed e.g. barnacles, mussels

Question 31

How can direct method of estimating population be used for large areas?

Answer 31

* **aerial photographs** e.g. penguins, seals, species of large trees etc. * **helicopters **- for counting large animals e.g. elephant, buffalo in ga**me reserves

Question 32

How can the direct method for estimating population be used for humans?

Answer 32

Every **5 years in SA** a population census - census forms can be filled in, accounting for everyone in a household.

Question 33

How can population size be estimated by using the indirect method?

Answer 33

* Counting a sample number of the population * then using the sample calculations to estimate the total size of the population

Question 34

Explain the **quadrat metho**d of estimating population:

Answer 34

Involves counting the number of individuals in small measured areas (quadrats) and then using the nubmers to calculate the population size of the total area with the aid of the following formula: Total population = (N) N = n**umbers in sample x size of whoel habitat** over the **size of quadrat ** The purpose is to enable comparable samples to be obtained from areas of consistent size and shape.

Question 35

Discuss the** quadrat method** step by step:

Answer 35

1. Measure the size of the total area 1. use a wooden frame of known diamters as a quadrat - refer to same in each sample 1. quadrats should be distributed at random 1. count the individuals in each quadrat - take several samples 1. - using formula, calculate the size of the population

Question 36

Why is random sampling NB?

Answer 36

* Distribution of individuals may not be uniform throughout the area * NB to sample as quadrats the total area - true reflection

Question 37

Explain the mark-recapture method of estimating a population size:

Answer 37

1. A known number of individuals is caught and marked and then released. 1. After a suitable time period another sample is captured and the nubmer of marked individuals are counted. 1. A formula is used to calculate population size - based on principle that the RATIO OF THE UNMARKED TO MARKED INDIVIDUALS in a sample will be the same as the RATIO IN THE POPULATION as a WHOLE.

Question 38

When is it suitable to use the MARK-RECAPTURE method to estimate population size?

Answer 38

* Mobile animals e.g. butterflies * Not easily visble e.g. fish in a dam

Question 39

Explain the Mark-recapture method of population estimation:

Answer 39

1. Mark a well-defined area 1. Capture as many individuals as possible and mark them e.g. metal tag, spot on plant 1. Release the marked individuals - back into environment 1. Allow them to mix with unmarked 1. Recapture as many individuals as possible 1. Count the total nubmer and count the marked ones amongst them. 1. Calculate the total population size by using PETERSEN INDEX 1. **P = M x C over R** (C = total number of animals caught in second sample, R = total number of marked animals in second sample i.e. recaptured) See page 5 of your textbook.

Question 40

What precautions must be taken for a reliable result when using the MARK-RECAPTURE method?

Answer 40

* Short time should pass between first and second sampling - no births and deaths in meantime * Sampling should be repeated several times * Marking must not damage the individual or affect environment * marked animals must mix freely with rest of population * No immigration or emigration is allowed NB: Study page 6 - 7 of your textbook for a DEMONSTRATION of this method!!!