Wednesday, February 16, 2011

Large Lake--Fierce Competitors

Lake Malawi holds many secrets in its deep crevasses that reach up to 700 meters. This lake was formed when the plates that make up the earth's crust tore apart in the eastern part of Africa. This tearing of the earth's crust forms areas called rift zones where land is pulled apart and stretches out much like a warm piece of taffy, leaving a thin crust and valley like area in the center with the ends remaining thick. Malawi is located in a particular rift valley called the Great African Rift Valley. It is the southern most lake in a chain of lakes with a surface area of 38,000 square kilometers. As the 8th largest lake in the world and the 2nd deepest lake in Africa, Malawi is home to many interesting and diverse creatures including the aggressive African cichlids that are often kept as pets in tropical fish tanks.

Over a period of a few million years, which is a short time in evolution years, over 22 cichlid species developed with up to 500 individuals in a 50 square mile area. The large amount of different species of the same fish was a result of a process called speciation. Normally, this process occurs when there is only one species of fish, or other animal, in an area where there are many different habitats that can be lived in. In order to reduce competition, or the fight between individuals to get foot or shelter, a member of the species might change their normal preference to fill a new habitat in order to lessen competition. This change occurs over millions of years and eventually the species can no longer mate with the individual that it changed from. Essentially, this is a new species. The cichlid species in Lake Malawi live in an area called the littoral zone which is characterized by a rocky bottom, plant life, and shallow water. The interactions between species, also called interspecific competition, is often studied in these waters in attempt to discover how they partition the habitat for maximum resources.

A process called niche partitioning is often accounted for as the main reason why the diversity of cichlid species has been maintained. Niche partitioning is when members of similar species inhabit different types of habitats in order to lessen competition. It has also been argued that the speciation event of this fish occurred so quickly that members of different cichlid species act as equal. In reality it has been observed male cichlids in Lake Malawi actively guard three different types of territories from different types of other cichlids. The first territory that is guarded by the male is the feeding territory which is characterized by areas where algae and microbes are attached to rocks. Males guard this territory against many fish of their species and not of their species that feed on similar foods. The second territory is the mating territory. A male will actively and aggressively guard this territory from males of the same species and attempt to attract females of the same species while allowing any species of cichlid to travel through this area as long as they have a different diet. The spawning territory is the third and final territory and it is also the smallest. The male will not allow any fish, whether it be a male or female from the same species, to enter this territory in fear that the area will be jeopardized for future spawning activity. All of this information on African cichlids is just a small piece of the story of and I challenge you to go out and research more!

1 comment:

  1. Haha, that second picture is really funny. It made me laugh. :)