In: Biology
Human pressures lead to changes in the life history of organisms, with potentially huge consequences for fitness.
a) Fish harvesting can favor fish that reproduce earlier even if they produce fewer offspring. Suppose that a fish that reprodcues at age 3 years produces 20 eggs that will survive to adulthood, while one that reproduces at age 2 years produces only 5. If fish die after reproducing, which population will grow faster? One way to do this is to figure out which population would be larger after 6 years, which is two generations for those that reproduce every 3 years, and three generations for those that reproduce every 2 years.
b) Suppose half of the fish are harvested between ages 2 and 3 years. Which age of reproduction is now favored? what other effects do you think this would hvae on the population?
c) Compare this scenario to the effects of giving up migration. What information would you need to compute whether birds that spend the winter in cities will do better than those that continue to migrate?
a) The fish that produces egg after 3 years will complete two generations by 6 years. Hence after one generation from one fish 20 fishes are produced. After second generation from these 20 fishes a total of 400 fishes are produced.
In the case of 2nd fish, which produces only 5 fish for every reproduction after 2 years, can complete three generations in 6years. By the completion of three generations, from one fish a total of 125 fishes are produced.
Hence, the population of fish that reproduces once in every 3 years is larger.
2) when fish are harvested between the ages 2 and 3 years, 2 years reproduction is favored as 3 years reproduction is not allowed to reproduce only, because the fish is already harvested before 3 years itself. If after one generation of both the fishes harvesting is carried out, then 3 years reproduction is favored as the number of seed 3 times more than the 2years reproduction fish. As it keep going like this frequency of gene pool of 2 years reproduction will decrease after several generations.
c)The information like number of eggs that are produced at every breeding time and the time of maturity that is needed to attain breeding level by both migratory and non-migratory birds is required to compute whether birds that spend the winter in cities will do better than those that continue to migrate