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Sea Lions report

Sea Lions report - Greg Reynolds Bio 1B Section 123 7 May...

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Greg Reynolds Bio 1B Section 123 7 May 2008 California Sea Lions The California Sea Lion ( Zalophus californianus ), a member of the Otariid family, is a complex organism with a rich evolutionary and ecological history. As a recent entrant to the marine environment these amphibious mammals are good examples of evolution’s continuing action. In terms of ecological impact the sea lion acts as both a secondary-tertiary predator of fish and squid and as occasional prey to killer whales and large sharks (Aurioles-Gamboa 2007). Living on the coast of California, parts of Mexico and Canada the Zalophus californianus has a noticeable interaction with humans and its natural habitat (Wilson 2005). Reviewing this background requires the exploration of many faucets of the sea lions’ existence including their environment, life cycle, taxonomic data, adaptive advantages, interaction with humans and ecological impacts. Belonging to the Otariid family, that reentered the ocean only approximately twenty-five million years ago, the California Sea Lion shows many evolutionary characteristics that reveal its path to becoming the animal it is today. The closest living relative to the Otariids is the bear and the family diverged from the other pinnipeds, phocids (seals) and odobenids (walrus), in North America where the other two groups headed for colder environments (Arnason 2006). Starting off as a land based mammal with few characteristics fit for aquatic life, the Otariids eventually evolved flippers from the paws of their ancestors and little by little adapted greater and greater oxygen capacities to dive deeper and take advantage of a greater food supply. With the development of blubber in addition to these other advancements, the Otariids undertook their current position of living the majority of their lifetime in the water and reproducing on land (Kohno 2005). An important part of Otariid evolution is
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that both front and back limbs can still rotate under the body which allows them to get up on docks and walk to a certain degree, unlike true seals, phocids, that can no longer walk on land. This awkward walk was easily observable in the Pier 39 sea lions and their surprising grace in the water just emphasized the direction of their evolution: into the water. This characteristic means that the Otariids maintain muscular front limb muscles that are used as the main source of propulsion. This set of evolutionary characteristics, flipper limbs, oxygen capacity, blubber and walking dictate the behavior of Otariids and allow their survival. Each characteristic evolved in response to environmental requirements like the cold water, speedy predators and prey distributions of the new aquatic environment. These same factors are still present in today’s environment, hence the perseverance of Otariid species throughout the world. Despite the climate changes of the last twenty-five million years, the Otariids have evolved to meet all
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Sea Lions report - Greg Reynolds Bio 1B Section 123 7 May...

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