ENVIRONMENTAL STUDIES (60 marks)

• POPULATION ECOLOGY (30 – 35 marks)• Terminology – Section A• Graphs – Phases of J- and S-curves• Pyramids – deductions from developing and developed countries • Determining population size • Trends in human populations – forecasts• Implications – ecology footprint,• Human demands vs. conservation – LO3• Social organisations – examples, packs, division of labour, flocks

Terminology:Population and Community structure• Species: a group of organisms which share the same

characteristics and are capable of interbreeding• Population: a group of organisms of the same species which live

in the same habitat so that random interbreeding takes place• Community: all the plants and animals living in a defined area• Ecosystem: the study of living things and their relationship to

each other and to the environment• Ecology: the study of living things and their relationship to each

other and to the environment

l

The relationship between species, populations community and the ecosystem

• Habitat:• Ecological niche: the functional position of an

organism in its environment

Terminology c:Population and Community structure

1.Use the following diagram to list:1.1 A few species 1.2 A population 1.3 A community

2. What kind of ecosystem is illustrated here?

Factors affecting population size

Migration of zebra and wildebeest in the Serengeti

Yearly migration of wildebeest in the Serengeti. Migration is most common amongst birds, mammals

and some insects (monarch butterflies)

Factors that affect population size• Natality: the birth rate. It’s the production of new

individuals by birth, hatching, germination or division.

• Mortality: the death rate. Dispersal through:• Immigration: the process that occurs when an

organism enters a new place to settle permanently• Emigration: the process that occurs when an

organism leaves one place to go and live in another place

• Migration: a group of birds, or other animals that are moving together from one region or country to another to avoid harsh environmental conditions

.

Wildebeest migration: migration is a response to seasonal change. The function of migration is to keep

animals in a suitable environment throughout the year.

Migration of birds: If habitat quality declines, animals improve their chances of survival and reproduction by going elsewhere

Migrating swallows: Animals appear to anticipate the changes in season.

Aspects of population fluctuation and regulation• Carrying capacity is the maximum population size a

certain environment can support for a population of a particular species over an extended period of time

• Environmental resistance: the combined effect of all the limiting factors that limit the growth of a population

• Limiting factor: factors (density dependent or density independent) that limit the rate of population growth

• Identify the effect of annual and seasonal fluctuations on population size

Under ideal conditions, a population naturally increases until it overshoots the carrying capacity. At this point, the environment can no longer provide for the species, due to a number of different environmental resistances, including food, crowding, competition, etc. The population, due to lack of resources, will begin to die out, allowing the environment to recover. As the environment recovers, the species population is able to flourish once more. This leads to a fluctuation between the number of organisms of the species and the health of the environment (hence the fluctuations in the graph).

Aspects of population fluctuation and regulation

Carrying capacity

Time

If a population reaches carrying capacity it can remain stable or move up and down (fluctuate). If there is more rainfall and more food available the carrying capacity increases and the population will increase until it reaches the new carrying capacity before it levels off again. If there is habitat destruction or a draught the carrying capacity decreases and the population will decrease until it reaches the new carrying capacity and levels off again.

Carrying capacity of rabbits in a specific area1. What does the blue line represent? What does the purple line represent? What does it mean when the purple line rises above the blue line? 2. Which of the following situations might cause the purple line to decrease below the blue line: abundant food sources, lack of competition, a young population, or plentiful roaming space?

1.1 Suggest THREE reasons why the growth form between the period 1920 and 1935 is as it is.1.2 What is the growth phase called between 1910 and 1920? (1)1.3 During which year did the jackal enter the fenced area? Give a reason for your answer from

the information supplied. (3)1.4 Between 1940 and 1950 the springbok population increased again. Mention a possible reason

for this increase. (2)1.5 Mention FOUR other factors, besides the jackals, which could have caused the decline in the

springbok population between 1935 and 1940? (4)1.6 What method was most probably used to determine the size of the springbok population? (1)1.7 Do you think the line representing the carrying capacity is accurate?

Give a reason for your answer. (3)1.8 The population between 1965 and 1975 appears to have stabilised. Suggest how the farmer

might be controlling the population. (2)1.9 What do you notice about the growth from 1915 – 1925 and 1940 – 1950? (1)

(20)

Question: Carrying capacity

Density dependent and factors

Density dependent Density independent

a density-dependent factor affects a greater percentage of individuals in a population as the number of individuals increases; it will also affect each individual more strongly. Population growth declines because death rate increases, birth rate decreases or both. Resource limitation is one such density dependent factor. A reduction in available food often limits reproductive output as each individual produces fewer eggs or seeds. Health and survivorship also decrease as crowding results in smaller, less robust individuals. Many predators concentrate on a particular prey when its population density is high, taking a greater percentage than usual.

Density-independent factors affect the same percentage of individuals regardless of population size. Weather, climate and natural disasters such as freezes, seasonal changes, hurricanes and fires are examples; the severity and time of occurrence being the determining factor on what number of organisms is affected. In some natural populations, these effects routinely control population size before density-dependent factors become important

Growth patterns/forms:

Geometric growth form (J- curve)

Time

Growth patterns/forms:

Logistic growth form (S-shaped curve)

Question : growth patterns4. A certain fast growing unicellular micro-organism is cultivated in a sugar solution in a closed test tube at 250 C. At regular intervals, samples were taken in order to calculate the population size. The graph below was drawn from the data obtained. Study the graph and answer the questions that follow.

4.1 Which specific organism was most probably cultivated in the test tube? (1) 4.2 Name the growth phases indicated by A, B and C respectively. (3) 4.3 Give an explanation for the specific growth pattern of each of the phases A, B and C. (6) 4.4 What is phase Y called and what is the possible cause, thereof, for this specific population in particular? (3) [ 13 ]

Comparison between geometric (J-curve) and Logistic (S-curve)

Methods to determine population size1. Direct method: census

A pitfall sampling method can also be used

Methods to determine population size2. Indirect method: simple sampling

Simple sampling can be used to determine the number of plants in an area

Quadrat sampling method for plants

In simple sampling a physical count of all the animals/plants under investigation in a small sample are of the habitat is done. The total population in the big area is calculated as follows: Estimate number of = number of individuals in sample x habitat sizeindividuals in the __________________________population sample size

Activity 1: simple samplingMethod

Mix an unknown number of tiny beads with sea sand thoroughly to fill a 500 ml jar.

Remove a level teaspoon (5 ml) of the mixture from the jar.

Spread the mixture on a saucer and count the number of beads.

Use the formula below to estimate the total number of beads in the bottle :

 Total no of beads = no of beads in sample x total volume of mixture (500 ml)

____________________________

volume of teaspoon (5ml)

Place the bead and sea sand mixture back into the jar.

Mix thoroughly and repeat the exercise a few more times.

Obtain an average estimate of the number of beads in the jar

 Results

Complete the table :-

 

Questions

1.Why is it necessary to repeat the

investigation a number of times?

2. How is this investigation limited?

Investigation Total population

1

2

3

4

5

Ave estimate of beads/jar

Simple sampling can be used to determine the number of micro organisms on a slide

A leading Kwa-Zulu entomologist ( a person that studies insects ) decided to work out the number of worms that occurred in Kwa-Mashu. The total area in Kwa Mashu where the worms occurred was 2000 m2. He chose five 10 m2 plots and found 120, 100, 150, 130 and 100 worms in each plot respectively. (i) Estimate the total number of worms in the Kwa-Mashu area. (Show ALL calculations). (5) (ii) Describe two ways how the entomologist could improve the reliability of these results. (2)

(7)

Question : Simple sampling

Ave. number of worms in a plot = 120+100+150+130+100 =

= 120 worms/plot

Estimate number of = number of individuals in sample x habitat sizeindividuals in the __________________________population sample size

=

plots5

600

m

mx

10

2000120

= 24 000 worms

Answer : Simple sampling

Methods to determine population size2. Indirect method: mark recapture

A number of animals are caught and marked

• Mark / recapture techniques involve sampling a population of animals and then marking all of the individuals captured in a recognizable way.

• The marked animals are then released back into the population and left to mingle for a suitable period of time.

• Once they have become thoroughly mixed into the population again, the population is re-sampled.

• Enough time must be allowed to elapse for complete mixing to have occurred.

• The assumption is then made that the proportion of marked animals in the second sample is the same as the proportion of marked animals to non-marked within the whole population.

Mark recapture

The same method are used with fish

The fish are marked – but don’t take them out of water for too long!

The following should be taken into account when animals are caught and marked

1. The animal usually needs to be captured to be marked, the animal should not be injured and its behaviour pattern should not be altered.

2. The mark used should not harm the animal - for example a dot of a particular paint may turn out to be toxic to the animal. Trials therefore need to be done to ensure that the animal is not harmed in any way.

3. Take random samples from the population. If you take samples from only one place each time, they you are likely to catch the same animals that you released.

4. Once you have released the first sample, give the animals enough time to mix randomly with the rest of the population before you take the second sample.

5. Ensure that animals do not become 'trap-shy' and avoid the traps after the first capture. This can be reduced as far as possible by choosing a method which will not distress the animal unduly. Some animals may become 'trap-happy', particularly if the traps are baited. This can be overcome by setting out the baited traps, without actually trapping, for some time before the first sample is taken. This allows all animals in the population to become equally trap-happy before you start.

Trap-shyness results in population overestimates, while trap-happiness results in population underestimation

They are released back into the water and some are caught again after a period of time

The mark-recapture method can also be used on frogs

The mark-recapture method can also be used on crabs

Activity 2: Mark -recaptureMethod:

1.Get into groups of 4.

2.Tear old papers (newspaper/unused notes) into small pieces and throw into a container. The container will represent a dam and the paper pieces fish. You should have ± 100 - 200 fish in your dam.

3.Mark 30 of your fish with a pen. Discuss how you should mark real fish.

4.Put the marked fish back into your dam and mix them up with the rest of the fish.

5.Take a handful of the mixed fish out of the dam. Count the marked and the unmarked fish.

6.Estimate the size of your fish population by using the formula:

7.Repeat your estimate at least 5 times and calculate the estimated average fish in your dam. Tabulate your results.

8.List possible shortcomings of your investigation

sampleondtheinsindividualmarkedofnumber

sampleondtheinnumberxsamplefirsttheinnumbersizePopulation

sec

sec

It is evident from the graph that :-1. the human population is increasing rapidly and shows a geometric (J-shaped) growth form2. the population is doubling in shorter periods3. the next doubling period (8 000 million) has been calculated to be in the year 2010 – a doubling period of 35 years4. this increase in population CANNOT go on indefinitely – as environmental resistance (shortage of food, O2 and living space) increases – something has to give – unless we are able to stabilise the population at the carrying capacity of the world

Trend in the human population growth up to 1650 and from 1650 to the present moment

Worldwide human

population growth

from 1750 to 2000

Human population growth in SA from 1947 to 2011

Human population age and gender distribution in:1. an increasing population

A population pyramid with a small number of old people indicates a population with a high birth rate, a high death rate and a short life expectancy. This pattern is typical of less economically developed countries (LDC) like South Africa, South America and Asia (excluding Japan)

2. a stable populationThere is approximately the same number of young people and old people. About the same number of children is born each year compared to the number of people who die each year. Economical developed countries like Ireland have this kind of pyramid

3. a decreasing populationThere are more old people than young people. Each year more people die than are born. Developed countries like Germany have this kind of pyramid. Some southern African countries, like Botswana (experiencing the effects of HIV/AIDS) are also starting to show this kind of age-gender pyramid.

Population sizes in different parts of the world

The graph is divided into 2 groups:1. The less developed countries (LDC) like Latin America, Africa and Asia (excluding Japan). Population growth is expanding rapidly and the majority of people live in poverty. Medical care and technological advances are not readily available, food is scarce and levels of education are low. A high social value is placed on large families.2. The more developed countries (MDC) like North America, Australia and Europe. Population growth is low and people enjoy a good standard of living. Medical care and technology is readily available. Food and technology are available, level of education is high.

A comparison of less developed countries with more developed countries

Discuss the differences between the gender-age pyramids for Japan & Zimbabwe.

Use these graphs to discuss the changing trends in the SA population. Indicate the working group (20 – 60 years), mention how their economical contributions will support the non-economical groups (children and old people). Take the % of jobless people into consideration and the fact that only 5.6% of the population pays tax

The effect of high population growth on the environment

The effect of high population growth on the environment (depletion of resources and increased pollution)

The effect of a growing population on resources, pollution, industrial output and the availability of food

Ecological footprint: the impact of a person, city, or country on the ecology of a local area or the whole planet. It is a measure of how much land and water a person, city or country needs and the wastes that are produced.

We do not know what the carrying capacity of the world is. The United Nations has predicted a

global human population of over 10 billion people by 2050 – therefore an estimated 4

billion people will be added to the population in the next 40 years.

One approach to estimate the carrying capacity of the earth is to look at the ecological footprint

of different groups of humans.

• According to the Global Footprint Network, humanity uses the equivalent of 1.3 planets to provide the amount of resources we consume and absorb the waste we produce. This means it now takes the Earth one year and four months to regenerate what we deplete in a year.

To calculate the ecological footprint of a population all their needs need to be taken into account, e.g. food, water, fuel, building materials, clothing and

medical care. The impact, to produce the needs, on the environment is then calculated. An ecological footprint represents the area of land and water

utilised by a particular nation. It takes into account the resources used by wastes produced by that country. It measures how much land an water a human population requires to produce what it

consumes, and to absorb its wastes using current technology. It compares human demand with the

earth’s capacity to regenerate

What are we doing?

The effect of high population growth on the environment. The darker the colour, the greater the ecological footprints.

The following categories affect your ecological footprint:

Ecological “footprint" for different countries

It is likely that the countries and regions with surplus ecological reserves, and not the ones relying on continued ecological deficit spending, will emerge as the robust and sustainable economies and societies of the future.

What will happen if this trend continue?•If everyone lived like me, we'd need 3.5 planets to provide enough resources. •To support my lifestyle, it takes 15.4 acres of the Earth's productive area. •If everyone lived like me, we'd need 3.5 planets to provide enough resources. •To support my lifestyle, it takes 15.4 acres of the Earth's productive area.

What can you do to save the world?

Sustainable: careful use of natural and human resources so that they will also be available to future generationsConservation: the management of the Earth’s resources so that it yields the greatest sustainable benefit to future generations while maintaining its potential to meet the needs of future generations

Human demands versus conservation in the harvesting of natural resources

Abalone poaching is illegal

Human demands versus conservation in the harvesting of natural resources

Oysters need to be a specific size before it may be harvested

Human demands versus conservation in the harvesting of natural resources

During 2010 more than 300 rhino’s have been pouched and killed for their horns in South Africa. The sad truth is that a rhino is worth more

dead than alive. A rhino horn is valued at $20 000 (R14 000) per kg and a rhino horn weigh up to 5 kg. Currently a live rhino is sold at

R130 000 – R300 000.

Social organisation enhance survival of species

• Animals that live in herds, schools, swarms, and flocks typically give up on their individual defences because they pursue another survival strategy.

• If you are a member of a herd, you do not need to run faster than your predator; you only need to run faster than the slowest member of your herd.

• The individual defence IS forming the herd where the weak are daily sacrificed to earn the others one more day of untroubled life, until it is their turn. I

Herds of wildebeest

School of fish

Some Predators form packs as an efficient hunting strategy like wild

dogs

African wild dogs form packs of up to 40 members, each with a dominant breeding pair that remain monogamous for life. These gregarious animals are co-operative hunters, relying on sight rather than smell to pinpoint their prey. Hunts tend to occur at dawn and dusk, but on occasion the dogs will venture out if there is a full moon.

They chase until their prey tires, reaching speeds up to 55 kmph, and sometimes disembowelling prey while it is still running

African wild dogs live in packs of 6 to 20. The aggression exhibited towards prey is completely nonexistent between members of the pack and there is little intimidation among the social hierarchy. Their large range of vocalizations includes a short bark of alarm, a rallying howl and a bell-like contact call that can be heard over long distances. Elaborate greeting rituals are accompanied by twittering and whining. The entire pack is involved in the welfare of the pups, which are born in thick brush or in a den.

Sharks also hunt in groups

Group hunting improves efficiency. By hunting in groups a predator can kill larger animals than

a single animal can kill

Animals with dominant breeding pairs: the giant otter

Giant otters live in groups with one breeding pair. There is one dominant female in the group She has many offspring and is also the top fish catcher and the leader of the hunt.

Animals with dominant breeding pairs – Lions

The advantages of dominant breeding pairs are:- offspring are cared for by many members of the group- dominant males and females are usually the strongest and most efficient members of the group, their genetic material will be carried to the next generation

Division of labour within a colony:bees

There is one queen to each colony, and she is much larger in size than the other bees. Her main task is to lay eggs. No other females are able to mate with the drone males. In addition to laying eggs, the queen also secretes important communicative substances that maintain the unity of the colonyDrones develop only from unfertilized eggs. Their only function is to fertilize the queen. Worker bees develop from fertilised eggs and perform all the functions in the hive, making the waxen combs in the hive, eg gathering food, producing royal jelly, regulating the temperature in the hive, cleaning it of debris and defending it

Division of labour among members of a colony, e.g. an ant colony

Sociality is more advanced in bees, ants, and termites. As a rule, only one female (a queen) lays eggs in a colony, and numerous workers are sterile. Workers are involved in other functions like construction, defence and taking care of juveniles. They often have a division of labour and corresponding morphological differences.

Termites with different members and division of labour

This picture shows some forms (casts) of termites. Social insects have very complicated behaviour. Their success largely depends on coordinated actions of many individuals. For example, leaf-cutting ants have underground fungus gardens. Ants bring foliage to this garden and collect fungus for food.