Range expansion of Pallas's squirrel (Callosciurus erythraeus) introduced in southern France: Habitat suitability and space use

Successful eradication of an invasive alien Pallas’s squirrel (Callosciurus erythraeus Pallas 1779) population in the Netherlands with support of the local community

The Pallas’s squirrel (Callosciurus erythraeus) is an invasive alien species in several countries in Europe, but also in Argentina and Japan. The species is a threat to indigenous squirrel species and difficult to eradicate. In 2008 a population of this species was discovered in the south of the Netherlands, close to the Belgian border. The range and number of Pallas’s squirrels in the area was determined using sightings of local citizens, foresters and an extensive inventory with hair tubes and camera traps. The population was successfully eradicated during an eradication campaign with several stages from 2011 till 2015. The population appeared to be larger than expected. In total, 249 individuals were trapped in an area as large as 50 km2. Trapped squirrels were not killed, but sterilized and rehomed in animal parks across Europe. The eradication campaign was successful due to the cooperation and support of the general public, who were informed by flyers, lectures and several appeals in local media and on social media platforms. Both helped in getting support of the general public, but sterilization and rehoming must be properly supervised. The total costs of eradication summed up to at least €330,000. No Pallas’s squirrels were reported after October 2015, however sightings of ‘dark colored’ squirrels from the area are still reported by the general public and verified by an expert of the Dutch Mammal Society until today.

Exotic Pet Trade as a Cause of Biological Invasions: The Case of Tree Squirrels of the Genus Callosciurus

Simple Summary

The pet industry is a growing global multibillion dollar market. The increase of exotic and non-domesticated animal ownership has led to an increase in the number of non-native pets released that create invasive alien species (IAS) populations in the wild. IAS negatively impact the biodiversity, human health and countries’ economies. We use tree squirrels of the genus Callosciurus as a well-documented case study of pets that become IAS. We review the pathways and range of introduction and the challenge and legal importance of species identification. Next, we document how they negatively affect native plants and animals, their parasitic infections that can threat native wildlife and human health and their impact on human activities and productive systems. We discuss the diverse biological, social, political and economic reasons that make control/eradication of these charismatic species difficult in most countries. However, we also highlight the successful management of the IAS in two countries where the early detection and engagement of stakeholders were key to successful eradication. We conclude that efforts to educate and involve the broader public by actively engaging a diversity of stakeholders are more likely to build a consensus toward IAS management and should be a priority for each country.

Abstract

The trade of non-native pets, especially of non-domesticated and exotic animals, and their subsequent release and establishment of populations is one of the major pathways of introduction for invasive alien reptiles, amphibia, birds and mammals. Here, we use a group of arboreal mammals, tree squirrels of the genus Callosciurus, as a well-documented case study, reviewing the pathways of introduction, the current areas of non-native distribution, the rate of establishment success and the challenge and legal importance of species identification. We further illustrate the importance of early detection and effective monitoring methods and plans. Next, we document how they interfere with native species, their risk of acting as vectors for emerging infectious diseases and their potential role in maintaining parasitic infections that can affect human health. We conclude by reviewing the current management, or the lack of it, and highlight the diverse biological, social, political and economic reasons that make control/eradication of these charismatic species difficult or even impractical in most countries. However, reviewing the only two successful eradications of the IAS, we highlight the need to acknowledge the public opinion and the importance of communication, transparency and the engagement of a diversity of stakeholders to create a consensus about the actions to undertake.

Habitat selection of invasive alien Pallas’s squirrels (Callosciurus erythraeus) in an urban habitat with small fragmented green spaces

The distribution of invasive alien Pallas’s squirrels (Callosciurus erythraeus) has expanded mainly toward the southeast with continuous forest in Kanagawa Prefecture, Japan. Recently, however, squirrels have been sighted in residential areas with only a few green spaces. We examined the habitat selection of squirrels in a city with small fragmented green spaces by censusing the animals along a 6.7 km route. Twenty-three presence data were obtained in 10 grids, which were much larger than the mean home ranges of the species, suggesting that a squirrel population had already been established in this area. Although woods of <5 ha were reported to be unsuitable squirrel habitats, the study area only had two green spaces with >5 ha, and 90% of presence data were obtained in green spaces with <5 ha. This indicates that squirrels can establish a population even in areas with small fragmented green spaces. The squirrels selected areas close to evergreen and deciduous woods, but they avoided those closer to residential areas. Since small fragmented woods, such as evergreen trees, are widely distributed in the central parts of Kanagawa Prefecture, the squirrels may use them as stepping stones to expand their range.

Advances in population ecology and species interactions in mammals

The study of mammals has promoted the development and testing of many ideas in contemporary ecology. Here we address recent developments in foraging and habitat selection, source–sink dynamics, competition (both within and between species), population cycles, predation (including apparent competition), mutualism, and biological invasions. Because mammals are appealing to the public, ecological insight gleaned from the study of mammals has disproportionate potential in educating the public about ecological principles and their application to wise management. Mammals have been central to many computational and statistical developments in recent years, including refinements to traditional approaches and metrics (e.g., capture-recapture) as well as advancements of novel and developing fields (e.g., spatial capture-recapture, occupancy modeling, integrated population models). The study of mammals also poses challenges in terms of fully characterizing dynamics in natural conditions. Ongoing climate change threatens to affect global ecosystems, and mammals provide visible and charismatic subjects for research on local and regional effects of such change as well as predictive modeling of the long-term effects on ecosystem function and stability. Although much remains to be done, the population ecology of mammals continues to be a vibrant and rapidly developing field. We anticipate that the next quarter century will prove as exciting and productive for the study of mammals as has the recent one.