This document discusses key concepts related to populations and population growth. It defines populations as all individuals of a given species in a habitat, and communities as all organisms in an area. An ecosystem includes both living communities and non-living environmental components. Population density is measured as the number of individuals per unit area, and is influenced by factors like natality, mortality, immigration and emigration. Population growth can be exponential under ideal conditions, but is typically sigmoidal with natural restraints like competition, predators, parasites and environmental resistance approaching the carrying capacity.

1. Populations

2. Populations All individuals of a given species in a particular habitat

3. Communities All the organisms in a defined area Ecosystem A community plus all the non-living (abiotic) components in a habitat

4. Populations Measuring Populations How populations are regulated

5. Measuring Populations Population Density Number of individuals per unit area

6. Population Density Influenced by Mortality Emigration Natality Immigration

7. Population Growth Population density fluctuates Natality + immigration = mortality + emigration Mortality is usually high

8. Types of Populations Open Natality, mortality, immigration and emigration affect population size Closed Only natality and mortality affect population size

9. Exponential Growth Under favourable conditions No predators, parasites or competition

10. Sigmoid Growth Natural conditions Curve flattens because of Competition Predators Parasites Environmental resistance Carrying capacity

11. Closed Population Growth No immigration or emigration Population slowly kills itself Lack of Food Space Oxygen Water Poisons itself

12. J Curve Closed population Upper limit Seasonal conditions Never reaches carrying capacity

13. Survivorship The chance of remaining alive to pass on your genes to the next generation Life expectancy Life span

14. Survival of the species Most energy is put into survival of species

15. Age Group structure

16. Population Distribution Clumped Random Evenly spread out

17. Clumped Populations Increases competition for food and space Reduces drying out Greater defence Easier to find mates May also be due to substrate

18. Evenly Spread Animals By competition or aggression Defended territories Limits population density Plants Shading Competition Allelopathy

19. Population Regulation Abiotic Tolerance Acclimation Geographical Barriers Liebig’s Law of Minimum Biotic Predation, paracitism Disease, toxic wastes Competition, Humans

20. Tolerance

21. Acclimation When tolerance limits for an organism change they acclimatise Slow process Usually to seasons

22. Liebig’s Law The functioning of an organism in limited or controlled by whatever essential environmental factor is in the least favourable amount

23. Geographical Barriers Mountain ranges Seas and oceans Rivers

24. Predation

25. Humans Over-hunting Extinction

26. Destroy habitats Draining swamps Clearing forests

27. Over-use of pesticides

28. Toxic wastes