Why_Are_Most_of_the_World's_Species_Tropical_

Why are most of the world’s species tropical' Provide a detailed analysis of the latitudinal gradient in species richness. Latitudinal gradients in species diversity have been recognized for over a century (Wallace 1878). The cause of these gradients has been the subject of debate since then. This has produced several theories and hypotheses about what factors are dependent in the regulation of diversity (Pianka 1966). Nowadays theories think about many factors such as competition, disturbance (natural and human disturbance) fragmentation, invasion and many others. It is difficult to test the separate causes and to test them individually and also to make hypotheses including all of them. The main theory at this time is the hypothesis of latitudinal gradients of diversity. (Stevens 1989) He produced a rule called ‘rapoport’s rule’ which states that “latitudinal ranges of plants and animals are generally smaller at low than at high latitudes. This rule was used to explain why there is higher species diversity in the tropics than at the poles because narrower ranges in the tropics would facilitate more species to coexist. He later expanded the rule to included altitudinal gradients also. The temperature gradient has been known for many years with temperature being as low as -40C to -70C in the poles and normally over 25C all year round at the tropics. This high temperature does not only affect the heat, it also increases the speed of evaporation which then produces a more humid area and also more precipitation. This means more energy is put into these communities by the sun (the source of earths energy) and this is what many people think could make the tropics much more suitable for species richness. If the plants get more sunlight they can grow bigger and for more time over the year. The arctic is a very harsh environment. In the tundra it is very cold: the average winter temperature is -25° C, and in the summer it is rarely over 10° C. The summertime only lasts six to eight weeks. In the winter it is dark most of the time, and even in the summer it is usually cloudy and overcast; therefore plants get little sunlight. There is also a low amount of rainfall because it is cold. Even though some organisms have adapted to living in such harsh environments there are considerably more species in the tropics. The reason for there being so many species in the tropics is a combination of factors. Firstly organisms can live well there due to the extra energy that this part of earth receives. Also secondly it is due to isolation and islandation which promotes evolution into new species by sexual selection. For example, Darwin and his Galapagos finches. There were there are thirteen species of Darwin's finch, a small sparrow-like bird, each species has evolved depending on the type of food that it feeds on. This is shown by the different beak shapes. These birds all had a common ancestor and must have been isolated from each other. This has eventually produced thirteen different types of one bird. This could be how many of the species arose. In the rainforests isolation can be due to a river or possibly a fallen tree. This would result in many patches of species all over the tropics. All of these plant species makes it difficult for animals. Animals can evolve to only eat of one exact species of plant or not eat plants at all. Tropical plants are not only those widely recognized crops that are limited to production in the tropics, such as bananas, cacao, coconuts, coffee, oil palm, rubber, and sugarcane but those that originated in and continue to be widely grown in the tropics, and have also been adapted and are mainstay commodity crops in subtropical and temperate zones, such as beans, cassava, citrus, maize, millet, potatoes, rice, sorghum, and tomatoes. Tropical plants provide food, clothing, and shelter for hundreds of millions of people, including the worlds poorest. They are the sources of energy, industrial biomaterials, and pharmaceutical products. They are also widely diverse, possessing characteristics and genes of potential value for numerous other plants. Unfortunately, the resources of tropical plants are not only underutilized but in danger of being lost due to destruction of habitat at their sites of origin, the high costs of conservation programs, and our lack of knowledge of the value of these genetic resources. Despite their critical importance, most tropical species receive so little attention from established research organizations and the journal publishing industry that they have been referred to as “orphans.” Many of the animals in the tropics specifically eat one certain thing. This is not good if the thing they eat goes extinct. In England most animals eat a variety of food substances because of the availability of food. I think that human activities in the rainforest could result as more species evolving, this is because of the way that people are deforesting the rainforest. They make a backbone in the forest for a road. Trees get felled in straight lines coming off from the backbone. In my opinion this is isolating parts of the forest from other parts.