Invasion stages and potential distributions of seven exotic terrestrial isopods in Japan

A peer-reviewed open-access journal BioRisk 13: 53–76 (2018) BioRisk53 Invasion stages and potential distributions of seven exotic terrestrial isopods in Japan doi: 10.3897/biorisk.13.23514 RESEARCH ARTICLE https://biorisk.pensoft.net Invasion stages and potential distributions of seven exotic terrestrial isopods in Japan Shigenori Karasawa1, Kensuke Nakata2 1 Department of Life and Environmental Agricultural Sciences, Faculty of Agriculture, Tottori University, 4-101 Koyama-machi Minami, Tottori 680-8553, Japan 2 Kyoto Women’s University, Kitahiyoshi-cho 35, Higashiyama-ku, Kyoto 605-8501, Japan Corresponding author: Shigenori Karasawa () Academic editor: J. Settele | Received 22 January 2018 | Accepted 23 February 2018 | Published 15 March 2018 Citation: Karasawa S, Nakata K (2018) Invasion stages and potential distributions of seven exotic terrestrial isopods in Japan. BioRisk 13: 53–76. https://doi.org/10.3897/biorisk.13.23514 Abstract Evaluating potential distribution areas and limiting factors for the distribution of exotic species in invasive regions are essential to identify risks and protect the native ecosystem. However, less research has been conducted on the underground ecosystem than for above-ground. Factors, limiting the distributions of exotic terrestrial isopods, have been identified and their invasive stages and potential distribution areas in Japan evaluated. A database of distribution data has been developed for 17,412 terrestrial isopod specimens in Japan and two ecological niche models constructed using 19 bioclimatic variables; the regional model was calculated using data from Japan (invasive region) only, whereas a combination of data from Japan and North America (invasive regions) and Europe (native region) was used to construct the global model. The global model predicted that annual mean temperature and mean diurnal-temperature range were the important limiting factors for most exotic isopods. It was found that Armadillidium nasatum Budde-Lund, 1833, A. vulgare Latreille, 1804, Haplophthalmus danicus Budde-Lund, 1880, Porcellio laevis Latreille, 1804, P. scaber Latreille, 1804 and Porcellionides pruinosus (Brandt, 1833) were composed of stabilising and colonising populations, which enabled prediction of the future spread of distribution areas for these species in Japan. Porcellio dilatatus Brandt, 1833 was introduced in unstable environments and thus was found in fewer locations. Keywords Ecological niche model, Maxent, Oniscidea, precipitation, temperature Copyright Shigenori Karasawa, Kensuke Nakata. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.. 54 Shigenori Karasawa & Kensuke Nakata / BioRisk 13: 53–76 (2018) Introduction Populations of exotic species are rapidly increasing worldwide with recent globalisation (Hulme 2009) and such species have become a serious threat to biodiversity and ecological functions (e.g. Gurevitch and Padilla 2004, Simberloff et al. 2013). Ecological niche modelling to predict species distributions, based on environmental variables, has become a valuable tool for preventing the colonisation of invasive species and for designing effective protection activity (Franklin and Miller 2010, Elith 2015). However, this approach is based on the assumptions of population equilibrium and niche stability in space and time (Guisan and Thuiller 2005) and these assumptions often fail (Broennimann et al. 2007, Guisan et al. 2014). Thus, it is important to evaluate the invasive stages of species of interest to predict future distributions and risks of those species. Gallien et al. (2012) developed a methodological framework for evaluating the invasive stage by plotting probabilities of two prediction models to identify the leading edge of an invasion and to determine whether the invasive population had reached the equilibrium (Kumar et al. 2015, Zhu et al. 2017). Soil arthropods have extremely high species richness and serve important ecological functions, such as decomposition, carbon and nutrient cycling, soil structure and maintenance and biological population regulation (Orgiazzi et al. 2016). In addition to being found on the ground, many exotic species inhabit soil ecosystems; however, less information is available about exotic species in soils than for those above ground (e.g. Bardgett and Wardle 2010, McNeill et al. 2017). Terrestrial isopods (Crustacea: Oniscidea) include more than 3,700 species worldwide (Schmalfuss 2003, Sfendourakis and Taiti 2015) and play important ecological functions, e.g. decomposing organic material (Zimmer 2004), facilitating microbial activity (Hassall et al. 1987) and acting as prey for vertebrates (Ihara 1998). Thus, understanding and protecting this group are essential to maintain their diversity and ecological functions in soil ecosystems. A hot spot of isopod diversity is in the Mediterranean region (Sfendourakis and Taiti 2015) and some species from this region were introduced to several other regions through human activity (Schmalfuss 2003). For example, one-third of all terrestrial isopod species in North America were found to be exotic species (Hornung et al. 2015). Lilleskov et al. (2008) investigated the species richness of native and introduced species in North America and found that the peak for introduced species occurred at a higher latitude than that for native species. This result implied that it may be problematic to apply information related to factors controlling the distributions of native species to exotic species. However, few studies have clarified the factors determining the distributions of exotic species in regions to which they have been introduced. About 140 terrestrial isopod species have been reported in Japan (Nunomura 2015), although their taxonomic classification is still considerably confusing (Karasawa 2016, Karasawa and Honda 2012, Karasawa et al. 2016). However, at least seven species, Armadillidium nasatum Budde-Lund, 1833, A. vulgare Latreille, 1804, Haplophthalmus danicus Budde-Lund, 1880, Porcellio dilatatus Brandt, 1833, P. laevis Latreille, 1804, P. scaber Latreille, 1804 and Porcellionides pruinosus (Brandt, 1833), are considered exotic Invasion stages and potential distributions of seven exotic terrestrial isopods in Japan 55 in Japan; their original distributional areas may have been in the Mediterranean region or Europe (Schmalfuss 2003, Nunomura 2007, Cochard et al. 2010). Some researchers have examined the relationship between the distribution of these taxa and land use in Japan (Watanabe 1991, Fujita and Watanabe 1999), but no research has clarified the factors delimiting their distributions at a macro scale. Thus, determining these delimiting factors and predicting potential future distributions and invasive stages are importa (...truncated)