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Population size and genetic drift
- 5. All of thepeople inhabiting a specified area. OR A group of individuals or items that share one or more characteristics living in the same area.
- 6. EXAMPLE A colony ofants A crowd of people
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- 8. The world’s populationis expected to reach seven billion at the turn of 2011-12
- 9. The term: Population size TheActual counting of a total population, the census method, is not often possible in large animal populations. Census method collection of data from the whole population rather than just a sample. The population size is expressed as the population present at a particular instant.
- 10. Population is of twotypes 1. Absolute population size (N) 2. Effective population size (Ne)
- 11. The actual abundanceof a population or species. Absolute population size Absolute population
- 12. The effective population size (Ne) Thenumber of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift. Ne
- 13. There are four Factorsaffecting the population size
- 14. 1. BIRTH RATE 2.DEATH RATE 3. IMMIGRATION 4. EMIGRATION
- 15. BIRTH RATE -the numberof live births per 1000 in a year. Birth rates are affected by such factors as nutrition ,fertility, government policies and social value.
- 16. DEATH RATE -the numberof deaths per 1000 in a year. Death rates are affected by disease, war, medical technology, improved health care, transportation development and nutrition
- 17. -The number ofpeople moving into a country IMMIGRATION EMIGRATION
- 19. Determining population size Four steps 1.Direct observation 2. Indirect observation 3. Sampling 4. Mark- and –recapture
- 20. Counting each individualorganism .It is useful if there are few organisms in the study area , or they don’t move or they are large. NOT useful if the study area is very large, many organisms, organisms are small or move around a lot. 1
- 21. observe tracks ,nestsor other signs that the organism have been there . Useful if organisms move around a lot, are small and or hard to find or if study area is large.
- 22. Useful if popoulationis very large, or covers a large area or is hard to remember which have been counted. count the number of individuals in small area ,then multiply to find the number in the larger study area
- 23. Animals are capturedand marked and released into the environment.
- 24. Genetic drift Genetic driftis the random change in the genetic composition of a population due to chance events causing unequal participation of individuals in producing succeeding generations
- 25. BB individuals havebig beaks , Bb individuals have medium-sized beak and bb individuals have small beaks. These birds live in a place where large and small seeds are abundant, but no medium- sized seeds are available . Populations of all big- beaked individuals have a very high average fitness they can crack open big seeds. Populations of all small-beaked individuals do well— but not quite as well as the big-beaked individual. Medium-beaked individuals have the lowest fitness .and no medium sized beaks available.
- 26. A graph ofthese gene frequencies and the population's resulting fitness levels is shown. This sort of graph is called an adaptive landscape A graph of these gene frequencies and the population's resulting fitness levels is shown. This sort of graph is called an adaptive landscape.
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- 29. Founder effects A foundereffect occurs when a new colony is started by a few members of the original population
- 32. Bottlenecks Effect Population bottlenecksoccur when large numbers of a population are removed by disease, overhunting, overfishing or natural disasters.
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Editor's Notes
- #25 due to chance event occur