Population

1. Population

2. Learning outcomes for today • Define a population and describe the attributes that make up that population • Describe the 3 types of population distribution • Work in a pair to learn about survivorship curves and age structure

3. Definition • A group of interbreeding individuals of the same species that live in a particular area at a defined time.

4. Natality • Number of births per 1000 people per year births per year crude birth rate = total population X 1000

5. Mortality • Number of deaths per 1000 people per year deaths per year Crude death rate = total population X 1000

6. Density • Number of individuals of a population per unit area of habitat at a specific time. • E.g. Pine trees per hectare of the Urewera forest in 2007 • E.g. Diatoms per cubic metre of sea water taken of Raglan beach in 2006

7. Low Density High Density Individuals crowded together Colonial organisms • Only a few animals per unit area • Highly territorial, solitary animals

8. Distribution • How individuals are spaced in an area • 3 types of distribution • Random • Clumped • Uniform

9. Distribution - Random • Presence of one individual does not directly affect the location of another individual. • Uncommon in animals • Often seen in plants

10. Distribution - Clumped • Individuals are grouped in patches, sometimes around a resource • The presence of one individual increases the probability of finding another • E.g. Herding or highly social species (buffalo)

12. Distribution - Uniform • Individuals are evenly spaced • Presence of one individual decreases the probability of finding another close by

13. Pair Share Class • Describe why some organisms may exhibit a clumped distribution because of • Resources in the environment • A group social behaviour

14. Pair Share Class 2. Describe a social behaviour found in some animals that may encourage a uniform distribution

15. Pair Share Class • Describe the type of environment that would encourage uniform distribution

16. Pair Share Class 4. Give an example of each of the following types of distribution patterns • Clumped • Random • Uniform

17. Age structure and Survivorship Curves

18. Survivorship • There are three types of survivorship curves • Type I • Mortality is very low in the infant and juvenile years, and throughout most of adult life. Mortality increases rapidly in old age. • Type II • Mortality is relatively constant through all life stages (no one age is more susceptible than another) • Type III • Mortality is very high during early life stages, followed by a very low death rate for the few individuals reaching adulthood.

19. Survivorship

20. Your Task: Biozone exercise Survivorship curves 286

21. Population Age Structure • The age structure of a population refers to the relative proportion of individuals in each age group in the population. • The population is usually divided into three groups • Pre-reproductive • Reproductive • Post-reproductive

22. Population Age Structure • This is usually shown as a age pyramid. The shape of the pyramid show different things • True pyramid – an expanding population • Bell shaped – a stable population • Urn shaped – a diminishing population

23. An Expanding Population

24. A Stable Population

25. A Diminishing Population