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The use of data-based species distribution models (SDMs) has increased significantly in recent years. However, studies of determining the minimum requirements of occurrence sites from ecological monitoring datasets used in species distribution modelling remain insufficient. Therefore, this study proposed a framework to determine the threshold of minimum occurrence sites for SDMs by assessing compliance with Benford’s law. The compliance test verified that the national-scale freshwater fish monitoring dataset was natural and reliable. Results derived from true skill statistics (TSS) determined the minimum number of occurrence sites for reliable species distribution modelling was 20 with a TSS value of 0.793 and an overall accuracy of 0.804. The Benford compliance test has shown to be a useful tool for swift and efficient evaluation of the reliability of species occurrence datasets, or the determination of the threshold of occurrence sites before species distribution modelling. Further studies regarding the evaluation of this method’s transferability to other species and validation using SDM performance are required. Overall, the framework proposed in this study demonstrates that Benford compliance test applied to species monitoring datasets can be used to derive a universal and model-independent minimum occurrence threshold for SDMs.

Climate change, which has the potential to alter water flow and temperature in aquatic environments, can influence the freshwater fish habitat. This study used an ecological habitat suitability model (EHSM), which integrates hydraulic (water depth and velocity) and physiologic (water temperature) suitability, to investigate the impact of climate change on two native freshwater fish species (Zacco platypus and Nipponocypris koreanus) in South Korea. The model predicted that in 2080 (2076–2085), the decrease in average ecological habitat suitability (EHS) will be higher for N. koreanus (19.2%) than for Z. platypus (9.87%) under the representative concentration pathway (RCP) 8.5 scenario. Under the same condition, EHS for Z. platypus and N. koreanus at 36.5% and 44.4% of 115 sites, respectively, were expected to degrade significantly (p < 0.05). However, the habitat degradation for Z. platypus and N. koreanus was much lower (7.8% and 10.4%, respectively) under the RCP 4.5 scenario, suggesting a preventive measure for carbon dioxide emission. Partial correlation analysis indicated that the number of hot days (i.e., days on which the temperature exceeds the heat stress threshold) is the variable most significantly (p < 0.05) related to EHS changes for both species. This study suggests that the EHSM incorporating the effect of water temperature on the growth and heat stress of fish can be a promising model for the assessment of climate change impacts on habitat suitability for freshwater fish.

Aedes koreicus (Edward, 1917) (Diptera: Culicidae), a mosquito species native to East Asia, has spread to parts of Europe and Central Asia since 2008. The species shares ecological characteristics with Aedes japonicus (Theobald, 1901) (Diptera: Culicidae), which has already successfully invaded and established in North America and Europe. Given these similarities, it is plausible that Ae. koreicus may also invade North America in the future. However, the invasion of Ae. koreicus may be masked or have delayed detection due to their similar morphologies with Ae. japonicus. This study highlights the potential risks of invasion of Ae. koreicus into North America, especially in the northeastern United States, and for further expansion in Europe. We used the maximum entropy model to identify areas with a high likelihood of presence in North America and Europe using comprehensive occurrence records from East Asia, Central Asia, and Europe. We have identified 15 additional countries in Europe and 7 states in the United States that will likely have suitable environments for Ae. koreicus. Additionally, we reviewed the morphological characteristics of Ae. koreicus and Ae. japonicus and provided morphological keys to distinguish the 2 species. Morphological results contradicting previous studies suggested that finding the origin by morphological comparison between Ae. koreicus populations may need re-evaluation. The information presented here will be useful for researchers and public health professionals in high-risk areas to be informed about morphological characteristics to distinguish Ae. koreicus from similar-looking Ae. japonicus. These tools will allow more careful monitoring of the potential introduction of this highly invasive species.

Invasive non-indigenous species have been reported to cause harm to ecosystems, including freshwater ecosystems, and reduce species abundance. As the world became more alert to the introduction of non-indigenous species, the demands for developing preliminary management measures have also increased. Thus, this study aimed to develop a habitat suitability assessment approach for non-indigenous freshwater fish with cost-effective data access. This approach utilized the Köppen-Geiger climate classification maps and fish occurrence data to predict the present (1980–2016) and future (2071–2100) habitat suitability of Oreochromis niloticus and Poecilia reticulata in South Korea. A fuzzy inference system was applied to relate climatic variables based on the Köppen-Geiger climate classification and species occurrence records. The results indicate that the habitat of the two species is limited to sites near sources of thermal pollution (for overwintering) in the present, and habitable area will expand in the future as the temperature increases. This approach is expected to aid non-experts in decision-making processes regarding non-indigenous freshwater fish management by evaluating potential habitats through the transfer of quantitative climate variables into linguistic or intuitive variables. Further augmentation in the climate zone classification method is expected to aid developing management strategies. Additionally, this approach is anticipated to facilitate the application of habitat prediction results by shortening the gap between experts and non-experts.

Aedes koreicus (Edward, 1917) (Diptera: Culicidae), a mosquito species native to East Asia, has spread to parts of Europe and Central Asia since 2008. The species shares ecological characteristics with Aedes japonicus (Theobald, 1901) (Diptera: Culicidae), which has already successfully invaded and established in North America and Europe. Given these similarities, it is plausible that Ae. koreicus may also invade North America in the future. However, the invasion of Ae. koreicus may be masked or have delayed detection due to their similar morphologies with Ae. japonicus. This study highlights the potential risks of invasion of Ae. koreicus into North America, especially in the northeastern United States, and for further expansion in Europe. We used the maximum entropy model to identify areas with a high likelihood of presence in North America and Europe using comprehensive occurrence records from East Asia, Central Asia, and Europe. We have identified 15 additional countries in Europe and 7 states in the United States that will likely have suitable environments for Ae. koreicus. Additionally, we reviewed the morphological characteristics of Ae. koreicus and Ae. japonicus and provided morphological keys to distinguish the 2 species. Morphological results contradicting previous studies suggested that finding the origin by morphological comparison between Ae. koreicus populations may need re-evaluation. The information presented here will be useful for researchers and public health professionals in high-risk areas to be informed about morphological characteristics to distinguish Ae. koreicus from similar-looking Ae. japonicus. These tools will allow more careful monitoring of the potential introduction of this highly invasive species.

The number of invasive species threatening freshwater habitats are increasing globally, and can be accelerated by climate change. Thus, risk assessments of potential invasive species are required for establishing prevention measures, in which quantitative risk assessments provide results objectively. In this study, the invasion risk of largemouth bass (Micropterus salmoides) in four major river basins (the Han, Nakdong, Geum, and Yeongsan) in South Korea was evaluated using an ensemble of species distribution models (SDMs). A weighted ensemble of the SDMs was developed to predict the probability of largemouth bass occurrence in the present (2011–2015) and two future periods: 2050 (2046–2055) and 2080 (2076–2085). The invasion risk of largemouth bass was evaluated using two approaches: relative and absolute risk assessments. Both approaches predicted an increase in Tier 1 (the highest risk) areas under representative concentration pathway (RCP) 4.5; however, a decrease in the areas of concern under RCP 8.5. In particular, the upper streams of the Nakdong and Han river basins are expected to be at risk in the future. In addition, Tier 1 risk areas are predicted to shift northward under both RCP 4.5 and 8.5 scenarios, especially in the Nakdong River Basin. This study provides a quantitative risk assessment tool based on the SDMs for the management of largemouth bass invasion under climate change.

In this study, water flow rate and quality variables that restrict freshwater fish distribution were incorporated in species distribution modeling to evaluate the impacts of climate change. A maximum entropy model (MaxEnt) was used to predict the distribution of 76 fish species in the present (2012–2014) and in the future (2025–2035 and 2045–2055) based on representative concentration pathway (RCP) 4.5 and RCP 8.5 scenarios for five major river basins (Han, Nakdong, Geum, Seomjin, and Yeongsan) in South Korea. The accuracy of MaxEnt performance was improved from 0.905 to 0.933, and from 0.843 to 0.864 in the model training and test, respectively, by introducing flow rate, total nitrogen, total phosphorus (TP), and total suspended solids (TSS). TSS and TP were ranked as the second and fourth contributing parameters, respectively, among the 17 variables considered in this study. There was a greater decline in species richness index under scenario RCP 8.5 than under scenario RCP 4.5, and in 2050 compared with 2030. However, the tolerance guild index (TGI) was predicted to improve in the future. The increase in TGI coupled with the decrease in species richness index (SRI), indicated that climate change is likely to have adverse effects on freshwater fish. Notably, the habitat of Korean spotted barbel (Hemibarbus mylodon), an endemic species of South Korea, is expected to contract largely in 2050 based on the RCP 8.5 scenario. These findings demonstrate that the incorporation of flow rate and water quality parameters into climatic variables can improve the prediction of freshwater fish distribution under climate change.

This study aimed to evaluate classification algorithms to predict largemouth bass (Micropterus salmoides) occurrence in South Korea. Fish monitoring and environmental data (temperature, precipitation, flow rate, water quality, elevation, and slope) were collected from 581 locations throughout four major river basins for 5 years (2011–2015). Initially, 13 classification models built in the caret package were evaluated for predicting largemouth bass occurrence. Based on the accuracy (>0.8) and kappa (>0.5) criteria, the top three classification algorithms (i.e., random forest (rf), C5.0, and conditional inference random forest) were selected to develop ensemble models. However, combining the best individual models did not work better than the best individual model (rf) at predicting the frequency of largemouth bass occurrence. Additionally, annual mean temperature (12.1 °C) and fall mean temperature (13.6 °C) were the most important environmental variables to discriminate the presence and absence of largemouth bass. The evaluation process proposed in this study will be useful to select a prediction model for the prediction of freshwater fish occurrence but will require further study to ensure ecological reliability.