An international team of scientists has established that red-eared turtles – popular pets – have spread throughout the waters of all of Eurasia, “capturing” the mainland from two sides at once. Having become unnecessary to their owners, they end up in water bodies, where they displace native species, but at the same time they cannot always form self-reproducing populations, that is, those in which replenishment occurs due to the birth of turtles. The results of the study, supported by a grant from the Russian Science Foundation (RSF), were published in the journal NeoBiota.
Red-eared turtles are popular pets and ornamental pond animals. Juveniles are small and very bright, so they attract the attention of people. However, with age, a lot changes: turtles grow up and become not so beautiful, besides aggressive, they are not averse to biting the owner’s finger. Because of this, people often release grown-up pets into the nearest body of water.
These turtles adapt very well to new conditions and displace representatives of the local fauna. They happily begin to feed on tadpoles, attack adult frogs and ducklings, successfully compete with native species for food and places for sunbathing and laying eggs. Moreover, red-eared turtles interbreed with natives, which leads to “genetic pollution”, and are also carriers of diseases, including those dangerous to humans, such as salmonellosis.
To prevent changes in ecosystems, people are trying to stop the spread of this animal around the world. For example, trade in small individuals was banned in the 1970s in the United States, and the import of this reptile into Europe has been completely stopped since 1997. However, these measures did not help – today the red-eared turtle has settled on all continents except Antarctica. She is comfortable living in a variety of conditions, as adults tolerate a wide range of temperatures and are able to eat almost anything they find.
Researchers from the A.N. Severtsov RAS (Moscow), together with domestic (from 25 specialized scientific organizations) and foreign colleagues (representatives of 19 countries), from 2002 to 2020 collected data on the distribution of red-eared turtles in water bodies throughout Eurasia. In addition, they used information about the range of these animals from scientific papers since 1968. The scientists carefully checked all the information received, and in controversial cases, when there were no location coordinates or there were doubts about whether there was a turtle of the desired species, the experts requested additional data from research centers. Biologists also used data from the Global Biodiversity Information System with records from 1978–2020.
As a result, scientists have traced how the red-eared turtles captured the waters of Eurasia. It turned out that the geographical expansion of these reptiles began at the turn of the 1960s and 1970s from two sides: from Europe and East Asia. Whereas other invasive species tend to spread from a limited number of foci, the characteristic feature of the red-eared sliders is to spread from many points on the mainland. By the beginning of 2020, the range of this reptile covered 68 countries of Eurasia.
Turtles that settled in the coastal regions and on the islands of Eurasia turned out to be the most successful. It is here that individuals now live, which effectively breed and even form populations. Their less fortunate relatives create predominantly “pseudopopulations”, in which the number grows not due to natural reproduction, but due to the fact that people throw their pets into local water bodies. If released into the wild, this species can live up to 30 years.
“A cost-effective strategy for controlling the invasive ruby-eared turtle in large countries with different climate zones should be different for the three geographic areas. This is, firstly, the area of true invasion (within the potential breeding area), secondly, the area of conditional invasion (within the potential wintering area, but outside the potential breeding area) and, thirdly, the area without the potential for breeding and wintering. . However, some protective measures, such as a ban on imports and trade, are only effective at the level of the entire country and therefore should be applied at the national level, ”says Andrey Reshetnikov, the main implementer of the project supported by the RSF grant, Ph.D. in Biology and Senior Researcher IPEE RAS.