What Is A Species? Species = individuals that are capable of producing viable/fertile offspring Variations, Differential Reproduction & Speciation Different variations, acted upon by the selective pressures of the environment, cause differential reproduction within a population Changes in the variations of a species or the selective pressures may lead to speciation Types of Speciation Allopatric Speciation A population is split into two groups due to geographic isolation If the two environments are different, the selective pressures on each sub- population will differ Differential reproduction will result as different variations are favored in each environment Kaibab v. Abert Squirrel = Allopatric Speciation Peripatric Speciation Like allopatric speciation, population is split by geographic isolation However, the second, new population is much smaller and has a more limited range of variations 2 nd population more likely to exhibit Founders Effect Sympatric Speciation Unlike allopatric speciation, population is NOT split by geographic isolation Due to variations that develop within the population, members become reproductively isolated Ex: mating behaviors, different # chromosomes Different Models For Rate of Evolutionary Change Gradualism Slow, incremental changes in allele frequency and phenotype over time Punctuated Equilibrium Long periods of no change in allele frequency and/or phenotype interrupted by rapid bursts of drastic change Gradualism Species tend not to diverge drastically, but modify existing body plans, behaviors, etc. to fit small changes in the environment Punctuated Equilibrium As mutation and environmental change are random, so is the rate of change in allele frequencies Model supported by most evidence and research (i.e. Stephen Jay Gould) Lab: Origin of Species Purpose: To determine the mode of evolution affecting a sexually reproducing population in regard to abiotic and biotic factors, geographic and reproductive isolation, differential rates of reproduction and selective pressures Protocol Research the changes on each part of the archipelago (Windsor, Norcross, etc.) over the course of 5 million years Record your observations, share your results and answer the analysis questions on the Google Document recently shared with you Notes: For each location, what changes occurred in regard to the Geospizas (i.e. pollenpeepers) variations? For each location, what were the primary selective pressures directing those changes Was the evolution divergent to the point of speciation? Why or why not? If so, what type of speciation best describes these changes: allopatric, peripatric, sympatric?
