BIS 2B Study Guide - Final Guide: Allopatric Speciation, Mycorrhiza, Nutrient Density

• School: UC-Davis
• Department: Biological Sciences
• Course: BIS 2B
• Professor: Schreiber, Sebastian

Document Summary

All interactions have costs and benefits but adaptations maximize benefits. Populations under the allee threshold: each individual has decreased fitness and the populations declines or tends towards extinction (population growth rate negative) Populations above the allee threshold: each individual has increased fitness and population grows (population growth rate positive: allee threshold effects are positive-density dependent because when population densities are high the population growth rate increases. Sister species are the same age because they each diverged from one another simultaneously (one lineage separated into two lineages at the node) Genetic incompatibilities create reproductive isolation: gradual accumulation of genetic incompatibilities from allopatric speciation: Chromosomal incompatibilities: new chromosome rearrangements and pairing prevents isolated populations from producing normal pairing chromosomes and gametes. Dobzhansky-miller incompatibility: independent mutations of epistatic genes within isolated populations when populations produce offspring the combination of incompatible alleles reduce fitness: sudden reproductive isolation of polyploid from diploid ancestor.