Environmental changes can be very hard on numerous species in an ecosystem, as it can have a very powerful impact on natural selection. A common environmental pressure is survival of the fittest. In survival of the fittest, only the organisms best suited to the environment will survive and reproduce. Before giraffes adapted to having very long necks, this was extremely prevalent because the taller giraffes could reach higher food supply when the food supply grown lower was scarce, whilst the shorter necked giraffes could not reach the food, as shown in Picture A, and thus would not survive. The graph (Picture B) shown below represents this with the shorter giraffes being those with less survival and less reproduction and the taller giraffes would be those with more survival and more reproduction.
Evolution of the giraffe coincides with natural selection as overtime, the giraffes with shorter necks died out and only the giraffes with longer necks could survive and find mates to successfully reproduce with. It has also been reported that, as shown in Picture C, the giraffe and the okapi evolved from a common ancestor referred to as the pre-okapi. Summary: As shown in the evolutionary tree (Picture C), giraffes and okapis evolved from a common ancestor, the pre-okapi. This has substantial evidence as the okapi is the only close relative to the giraffe and their skulls, as shown in picture D, are very identical. Darwin explained that change occurs over time and, because of survival of the fittest, those more adapted to the environment will be the ones who survive and reproduce, passing their genes to their offspring. Of course this relates the the size of the giraffes necks again, as the ones with longer necks could not only reach the higher, abundant food source but attracted more mates, and therefore reproduced while the short-necked giraffes did not. There are now nine giraffe subspecies including the Reticulated giraffe and the Nigerian giraffe. While there are not many differences between the sub-species, some have adapted to different climates or weather patterns. For example, the Nigerian giraffe has adapted to the rainy Nigerian climate and the Reticulated giraffe has adapted to the dry savanna climate. |
Picture APicture BPicture CPicture D (okapi skull right, giraffe left) |