Trouble in Paradise

Rachel & Celeste

Biological Diversity Decreases as Human Development Increases!

      The Department of Nature and Island Resources of the West Indies have become concerned with the loss of biological diversity on St.Kitts. We were hired to help recover the rodents on St. Kitts. Our plan consisted of bringing in similar rodents from the Nevis Island. We tried to breed the St.Kitts rodent with the Nevis rodent but even after 240 tries it still did not work. We have come to discover that we have been trying to breed two distinct species.

      Thousands of years ago, the islands of St.Kitts and Nevis in the West Indies were connected as one large island. On the island, there was a population of rodents that flourished. Over time, ocean levels began to rise and water began to separate the island into two distinct islands. This event isolated the rodents geographically.

      Before the islands were split the rodent population had various leg lengths from 4 to 8 cm. Rodents with longer limbs were able to run faster and jump higher than those with shorter limbs. Rodents who had the ability to run faster were able to escape predators more efficiently. Their ability to jump allowed them to climb and reach food more efficiently. Over time, natural selection by directional selection transformed the rodent population on the St. Kitts island to be completely long legged rodents. However, in recent years, habitat destruction has drastically reduced the size of this rodent population.

      Although long legs were the more favorable attribute, the Nevis island’s all had short legs. When the original population became geographically isolated, a smaller percentage of the rodents were left on the Nevis Island. In a smaller population, genotypes are more likely to be lost by chance and can change the genetic composition over time. Genetic drift was responsible to the diminishing of long legs in the rodent population. By random mating, the trait was lost and the population of small legged rodents flourished on their own without the competition of the long legged rodents.

     Through natural selection (directional selection) and random processes (genetic drift), the population became two distinct species. Because of Allopatric speciation, they became separated not only by geographic isolation but also by reproductive isolation. This is why when we were tried we tried to breed them, they were no longer able to interbreed. The Nevis Island rodent is a squirrel named Sciurus-brakhu (short squirrel) and the St. Kitts island squirrel was named Sciurus-makro (long squirrel).

West Indies. Britannica Kids. Web. 12 Nov. 2014. <>.

Traveler View. Travelers' Health. Web. 12 Nov. 2014. <>.