Chapter 4 Population Dynamics

Need to know Outline the contributory factors or variables in the Predator/Prey Relationships State the effects on the Human Population due to: Famine Disease War Contraception

Factors that contribute to Predator-Prey relationships The availability and abundance of food Large number of prey will increase the number of predators. This will in turn cause a decrease in the number of prey and then predators.

E. g. Large number of deer will increase the number of wolves E.g. Large number of deer will increase the number of wolves. This will decrease the number of deer and then wolves. When wolves decrease deer will increase again.

Concealment Prey can conceal / hide themselves, this allows population of prey to survive. A prey may achieve camouflage through background matching and through disruptive coloration.

Movement of Prey & Predators If there is not enough food the prey will move to a more abundant location; predator moves then to the area with more prey. A prey may achieve camouflage through background matching and through disruptive coloration.

Population Dynamics Population Dynamics is the study of changes that occur in a population & the factors that cause these changes. A population is a group of organisms of the one species.

Human population curve Note: 1 billion = 1,000 million Year (AD) Population 400 100 million 1650 500 million 1930s >2 billion 1970s 4 billion 2000 >6 billion Population is now increasing by about 85 million per year = 230,000 per day = 160 per minute = 2.7 per second

Human Population Curve Has not been susceptible to the normal constraints of nature and looks very different

Most population numbers tend to fluctuate in the short term, but find an overall balance in the long term where births and immigrations are equal to deaths and emigrations. Mortality rates are high in nature – many organisms die before they can reproduce. The factors affecting global human population are very simple. They are fertility, mortality, initial population, and time.

Factors affecting Human Population Numbers Food Disease War Contraception

1. Famine A lack of food leads to malnutrition and death due to disease or starvation. Great Irish Famine of 1845 – 47, about 1 million people died. Some countries still suffer from famine, but it is often a problem of food distribution rather than food shortages. Advances in agricultural techniques have so far allowed food supplies to match population growth.

2. Disease Vaccines – reduce the incidence of diphtheria, whooping cough, tetanus, polio, meningitis, TB, etc. Sanitation + insecticides – have controlled malaria, yellow fever and sleeping sickness. Anaesthetics have improved surgical methods & new drugs have saved many lives. Antibiotics have prevented deaths that would have been caused by bacteria.

The human population growth of the last century has been truly phenomenal. It required only 40 years after 1950 for the population to double from 2.5 billion to 5 billion. This doubling time is less than the average human lifetime. The world population passed 6 billion just before the end of the 20th century.  Present estimates are for the population to reach 8-12 billion before the end of the 21st century. During each lecture hour, more than 10,000 new people enter the world, a rate of ~3 per second!

Personal hygiene and improved methods of sanitation have played a major role and preceded the impact of modern medicine and, in particular, the development of antibiotics capable of reducing death due to infection.

3. War Reduces the human population. Increased birth rates (baby booms) often follow wars.

4. Contraception Since the 1960s increased availability has reduced birth rates.

Population Dynamics Population increases are due to increases in the birth rate and immigration. Population decreases are due to increases in the mortality rate and emigration.

Somewhere around 180 million people have been killed in one Twentieth Century atrocity or another -- a far larger total than for any other century in human history.

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