ENVIRONMENTAL STUDIES (60 marks) Population Ecology • 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
Terminology c:Population and Community structure • Habitat: • Ecological niche: the functional position of an organism in its environment
1.Use the following diagram to list:1.1 A few species 1.2 A population 1.3 A community2. What kind of ecosystem is illustrated here?
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
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
Aspects of population fluctuation and regulation 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).
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 area 1. 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
Question : growth patterns 4. 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 ]
Methods to determine population size2. Indirect method: simple sampling
Simple sampling can be used to determine the number of plants in an area
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 sampling Method 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 Why is it necessary to repeat the investigation a number of times? 2. How is this investigation limited?
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
Answer : Simple sampling Ave. number of worms in a plot = 120+100+150+130+100 = = 120 worms/plotEstimate number of = number of individuals in sample x habitat sizeindividuals in the __________________________population sample size = = 24 000 worms
Methods to determine population size2. Indirect method: mark recapture A number of animals are caught and marked
Mark recapture • 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.
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
Activity 2: Mark -recapture Method: Get into groups of 4. 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. Mark 30 of your fish with a pen. Discuss how you should mark real fish. Put the marked fish back into your dam and mix them up with the rest of the fish. Take a handful of the mixed fish out of the dam. Count the marked and the unmarked fish. Estimate the size of your fish population by using the formula: Repeat your estimate at least 5 times and calculate the estimated average fish in your dam. Tabulate your results. List possible shortcomings of your investigation
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
Human population age and gender distribution in:1. an increasing populationA 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 pyramid3. 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.
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