Friday, January 24, 2014

Marine Mammal

Marine Mammal
Marine mammals are widely distributed throughout the globe, but their distribution is patchy and coincides with the productivity of the oceans. Species richness peaks at around 40° latitude, both north and south. This corresponds to the highest levels of primary production around North and South America, Africa, Asia and Australia. Total species range is highly variable for marine mammal species. On average most marine mammals have ranges which are equivalent or smaller than one-fifth of the Indian Ocean. The variation observed in range size is a result of the different ecological requirements of each species and their ability to cope with a broad range of environmental conditions. There is a high degree of overlap between marine mammal species richness and areas of human impact on the environment which is of concern.Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 129 species that rely on the ocean for their existence.They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of dependence on the marine environment for existence varies considerably with species. For example, dolphins and whales are completely dependent on the marine environment for all stages of their life, whereas seals feed in the ocean, but breed on land. Marine mammals can be subdivided into four recognised groups; cetaceans   pinnipeds  sirenians  and fissipeds which are the group of carnivores with separate digits. Both cetaceans and sirenians are fully aquatic and therefore are obligate ocean dwellers. Pinnipeds are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting. In contrast, both otters and the polar bear are much less adapted to ocean living. While the number of marine mammals is small compared to those found on land, their total biomass is large. They play important roles in maintaining marine ecosystems, especially through regulation of prey populations.These two factors make them an integral component of the marine environment. This is of particular concern considering 23% of marine mammal species are currently threatened.


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