MATERIALS Life Sciences 1

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. J Gerber and J Goliath 2

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. J Gerber and J Goliath 3

Graph of repeated growth pattern J Gerber and J Goliath 4

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. J Gerber and J Goliath 5

Geometric and logistic growth phase J Gerber and J Goliath 6

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. J Gerber and J Goliath 7

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 J Gerber and J Goliath 8

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. J Gerber and J Goliath 9

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. J Gerber and J Goliath 10

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. J Gerber and J Goliath 11

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 population There 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 population There 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.

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