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Hi These questions are about the evolution of species (speciation). There are a number of models (theories) to describe events leading to the evolutionary emergence of new species. In order to examine how speciation occurs, we need first to define species: most often this is said to be a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions.” Speciation is a lineage-splitting event that produces two or more separate species. The species are separate when they can no longer mate with each other, thus they are said to have reached reproductive isolation - for a good summary description of this see http://evolution.berkeley.edu/evosite/evo101/VC1gReproIsolation.shtml. Reproductive isolation can include occasional matings that produce offspring that do not survive long or that cannot themselves reproduce. From: http://evolution.berkeley.edu/evosite/evo101/VC1aModesSpeciation.shtml: “The key to speciation is the evolution of genetic differences between the incipient species. For a lineage to split once and for all, the two incipient species must have genetic differences that are expressed in some way that causes matings between them to either not happen or to be unsuccessful. These need not be huge genetic differences. A small change in the timing, location, or rituals of mating could be enough. But still, some difference is necessary. This change might evolve by natural selection or genetic drift. Reduced gene flow probably plays a critical role in speciation. Modes of speciation are often classified according to how much the geographic separation of incipient species can contribute to reduced gene flow”. And according to http://en.wikipedia.org/wiki/Speciation : “Speciation refers to the evolutionary process by which new biological species arise. There are three main ideas concerning the emergence of new species (Modes of Speciation), each based on the degree to which populations undergoing this process are geographically isolated from one another (allopatric speciation, sympatric speciation, parapatric speciation, polyploidy speciation”. “Allopatric speciation is speciation by geographic isolation. In this mode of speciation, something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate. Isolation might occur because of great distance or a physical barrier, such as a desert or river. In parapatric speciation there is no specific extrinsic barrier to gene flow. The population is continuous, but nonetheless, the population does not mate randomly. Individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population’s range. In this mode, divergence may happen because of reduced gene flow within the population and varying selection pressures across the population’s range. Sympatric speciation does not require large-scale geographic distance to reduce gene flow between parts of a population. How could a randomly mating population reduce gene flow and speciate? Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche. This may occasionally happen when, for example, herbivorous insects try out a new host plant.” In the first part of question 1, you have a reproductive isolation mechanism driving an allopatric speciation event. In part b, your island species is reproductively isolated from the distant species but can mate with nearby members to form a hybrid species (for more on this see http://biomed.brown.edu/Courses/BIO48/21.Models.HTML) . In your second question, you are looking again at isolated populations with limited interbreeding. These populations are expected to diverge over time and form different species if they become unable to breed with each other through genetic drift alone. You are interested in whether or not the given migration rate generates enough gene flow between the populations to drive evolution away from divergence of the populations into two or more species. Migration tends to increase variability within a population and at the same time prevent populations from diverging to the extent that they become new species by introducing gene flow. The migration rate you have been given is 0.5 breeding individuals every five generations. This turns out to be too low to prevent divergence of allele frequencies within the populations because it requires an average of one immigrant every other generation to counterbalance drift (see http://darwin.eeb.uconn.edu/eeb348/lecture-notes/mutation-drift/node4.html and http://www.ucl.ac.uk/~ucbhdjm/courses/b242/MigEvol/Fst4Nm.pdf. I hope this helps, good luck with your studies.