New World rats and mice
Cotton rat ( Sigmodon hispidus )
The New world are a group of mice -like rodents of the family Cricetidae ( Cricetidae ). It is a form - and species-rich ( about 500 species) group that is spread on the entire American continent. The New world do not have a scientific name, and no systematic rank, but are divided into three subfamilies, Neotominae, Sigmodontinae and Tylomyinae. It is unclear whether the New world form a monophyletic group (that is closer related to each other than with all other animals).
Features
The New world are a diverse group that has occupied a variety of ecological niches and therefore has different body shapes. Many species resemble mice or rats, but there are also vole, mole, mouse racing and shrew -like agents. The body length varies depending on the type from 5 to 35 centimeters and the weight of 6-450 grams. One of the greatest representatives include the South American giant rats ( Kunsia ), the smallest the American harvest mice ( Baiomys ). The texture of the fur varies as does the coloring, but most species are kept in brown, gray or black shades, the bottom and often the feet are lighter. The tail length is variable depending on lifestyle, as well as the construction of the limbs. The individual subfamilies differ in the morphology of the penis.
The dental formula is in almost any case I 1/ 1 - C 0 /0 - P 0 /0 - M 3 /3, a total of 16 teeth. Only the genus Neusticomys has only two molars and a total of 12 teeth per jaw half. The molars have roots, the arrangement of the Kauhöcker is variable, the rearmost molar is usually reduced.
Distribution and habitat
New world are located on the entire American continent, their range extends from Alaska and northern Canada to Tierra del Fuego. There they have colonized almost every habitat, they are found in grasslands and steppes as well as in deserts and tropical rainforests and in mountainous regions to more than 5000 meters above sea level. Some species have adapted to synanthropic to the presence of people and also inhabit fields and plantations.
Way of life
As different body shapes and habitats so varied are the ways of life of the New world. Most species are ground dwellers, but many can climb well and some have specialized in a tree-dwelling lifestyle. There are also species that cause a subterranean grave - lifestyle and also semi- aquatic ( partially aquatic ) forms. You can be night, crepuscular or diurnal, they do not hibernate, but fall during the cool season, sometimes in a hibernation ( torpor ). Also, the social behavior is variable, in addition to solitary there are also groups in wild species.
Nutrition
Many species are herbivores, are linked, inter alia, grasses, seeds, fruits, nuts, mushrooms, tubers and other plant parts to himself. But there are also a number of omnivorous species that supplement their diet to animal food ( insects, spiders, scorpions, crabs, earthworms, small vertebrates, eggs and other ). Some groups such as the grasshopper mice and rats fish have even adapted completely to a carnivorous diet, which is rather unusual for rodents.
Reproduction
New world are generally very fertile animals with a high reproductive rate. In warmer areas, the pairing can generally take place throughout the year, the females have several litters of the year. The load times are usually 20-40 days, very short, the litter sizes are typically two to five pups (in some cases it can be more than ten ). Newborns are altricial, but growing fast. After about one to two weeks their eyes open, after two to four weeks, they are weaned. Sexual maturity occurs one to four months.
The life expectancy is low. Numerous natural enemies like predators, snakes, birds of prey, owls and other ensure that animals are rarely more than a year in the wild old. In captivity, however, are aged up to 5 years possible.
New world and people
Some species have adapted to synanthropic to the people and show already in their name their preference for plantation crops ( cotton rats, rice rats or sugar mice). They are considered a pest in some places and are being pursued. Some species are also feared as a carrier of viruses (such as hantavirus ).
Several species are in their area of distribution of the most common mammals, others only have a small living space and are at risk. Are particularly threatened Inselendemiten - species that occur only on individual islands. Several of these species are already extinct, such as the Caribbean giant rice rat, the rat Neotoma bunkeri Busch, the Fernando de Noronha - rat, the Galapagos giant rat and others. The reasons for their extinction are usually in the introduction of rats, cats and mongooses.
System
The New world, together with the voles ( Arvicolinae ) and hamsters ( Cricetinae ) the family of Cricetidae ( Cricetidae ). With the Altweltmäusen that often occupy the same ecological niche and lead a similar lifestyle, they are, however, more distantly related.
Today the New world be divided into three subfamilies:
- The Neotominae include about 125 species and are widespread in North and Central America.
- The Tylomyinae are a species-poor group (10 species) tree-dwelling animals from Central America.
- The Sigmodontinae are approximately 375 species, the most species-rich group have their main range in South America - only a few species live in North and Central America.
Traditionally, all New world were combined in a common subfamily, Sigmodontinae, the split into three subfamilies today is rooted in differences in the construction of the penis and the hind feet, and was confirmed by molecular genetic studies. Whether the three sub-families form a monophyletic group or not is controversial. The investigation of Jansa and Weksler (2004) might suggest that the Sigmodontinae are more closely related to voles than with the other Neuweltmäusen. However, these similarities are weak, the molecular findings is unclear, so the question of the monophyly of the New world at the present time can not be answered. It is clear that the three subfamilies have separated from each other at about the same time as the other subfamilies.