11.3 Other Mechanisms of Evolution Updates: Tonight –Reading 14.2 –Review gene flow, speciation Unit 8 test Friday; vocab Keystone Makeups: May 23 rd – June 2 nd Final exam: Tues June 10 th – Wed June 11 th

11.3 Other Mechanisms of Evolution LEQ: Why are biologists concerned about small population size? Activator: –If natural selection designs organisms for optimal survival and reproductive success (Darwinian fitness), so why does evolution not prevent aging in the first place? Key terms – bottleneck effect, genetic drift, founder effect, population density, population dispersion, survivorship curve

11.3 Other Mechanisms of Evolution natural selection cannot select against the effects of deleterious mutations that are confined to advanced age

11.3 Other Mechanisms of Evolution Effective populations have certain characteristics. Population density is a measurement of the number of individuals living in a defined space. Calculation:

11.3 Other Mechanisms of Evolution Population dispersion refers to how a population is spread in an area. Geographic dispersion of a population shows how individuals in a population are spaced.

11.3 Other Mechanisms of Evolution There are three types of dispersion. –clumped

11.3 Other Mechanisms of Evolution There are three types of dispersion. –uniform

11.3 Other Mechanisms of Evolution There are three types of dispersion. –random

11.3 Other Mechanisms of Evolution Life tables profile the demographics of a population

11.3 Other Mechanisms of Evolution Survivorship curves help to describe the reproductive strategy of a species. A survivorship curve is a diagram showing the number of surviving members over time from a measured set of births.

11.3 Other Mechanisms of Evolution Type I has low level of infant mortality and an older population common to large mammals and humans Type II survivorship rate is equal at all stages of life common to birds and reptiles Type III has very high birth rate, very high infant mortality –common to invertebrates and plants

11.3 Other Mechanisms of Evolution Genetic drift changes allele frequencies from one generation to the next due to chance

11.3 Other Mechanisms of Evolution Genetic drift: “a sample error” Populations of all sizes change in allele frequency due to chance events involving reproduction –The effects of drift grow as a population shrinks

11.3 Other Mechanisms of Evolution Bottlenecks and founder effect reduce variation Population bottlenecks can greatly reduce genetic variation: –Greater chance that harmful alleles increase –Negative selection effects can become extreme –Organisms that start new small populations, founder effect, have similar problems