Differential reproductive allocation can be the cause of seasonality of life-history characteristics in some guppy populations. When food is abundant, they increase brood size. Guppies reduce their fecundity and reproductive allocation in response to scarce food. In addition to senescence pattern, resource availability and density also matter in regulation of guppy populations. They tend to be more abundant in smaller streams and pools than in large, deep, or fast-flowing rivers. Although not typically found there, guppies also have tolerance to brackish water and have colonized some brackish habitats. Field studies reveal that guppies have colonized almost every freshwater body accessible to them in their natural ranges, especially in the streams located near the coastal fringes of mainland South America. The guppies were expected to eat the mosquito larvae and help slow the spread of malaria, but in many cases, these guppies have had a negative impact on native fish populations. Sometimes this has occurred accidentally, but most often as a means of mosquito control. However, guppies have been introduced to many different countries on every continent except Antarctica. Guppies are native to Antigua and Barbuda, Barbados, Brazil, Guyana, Jamaica, the Netherlands Antilles, Trinidad and Tobago, the U.S.
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