an animal, plant, or microorganism that is to some extent associated with man. The term “synanthropic organism” is used rarely in relation to pathogenic microorganisms.
The life cycles of synanthropic organisms are adapted to conditions created or modified by human activity. There are many different types of associations between man and synanthropic organisms. The internal and external parasites of man, including helminths, ticks, fleas, and mosquitoes, are completely synanthropic if they live in human abodes and partially synanthropic if they live outside homes but in areas inhabited by humans. Some synanthropic invertebrates, for example, many protozoans, worms, anthropods, and mollusks, and some synanthropic vertebrates, for example, many amphibians, reptiles, birds, and mammals, find shelter, a favorable microclimate, and food in populated areas, often in buildings. Other organisms, including swallows and swifts, use buildings only as shelters.
Susliks, hamsters, many steppe insects, and other organisms have become adapted to living in fields, meadows, parks and other lands used by man and have spread to roads and pastures outside their original home range. Obligatory synanthropic organisms, including house mice, rats, pigeons, true bugs, and cockroaches, are closely associated with humans and not found outside population centers. Their ties to humans have promoted their widespread distribution, as a result of which some of them have become cosmopolitan. In the taiga and tundra, mice and rats are found only in cities, and in southern forests, steppes, and deserts they form large populations. In temperate zones they winter in buildings, which they usually abandon in the summer.
Facultative synanthropes, including common microtines, found in forest belts, certain small predators, and passeriform and galliform birds, have weaker ties to humans, avoid populated areas, and live on plantings. The adaptation of such animals to conditions that have been changed by human activity promotes an increase in their numbers at the expense of wild species that have been driven back. The development of sea, land, and air transportation has been accompanied by the movement of synanthropic organisms over enormous distances, resulting in their broad distribution.
N. P. NAUMOV