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Abstract Freshwater turtles are often used as terrarium pets, especially juveniles of exotic species. At the adult stage they are often released by their owners into the wild despite their high invasion potential. In Europe these thermophilic potentially invasive alien species occupy the habitats of the native European pond turtle Emys orbicularis (Linnaeus, 1758), with new records from the wild being made specifically in Eastern Europe (Latvia and Ukraine) during recent decades. Assessing the potential of alien freshwater turtles to establish in new territories is of great concern for preventing invasion risks while preserving native biodiversity in the present context of climate change. We explored this issue by identifying the present and future (by 2050) suitable habitats of the European pond turtle and several potentially invasive alien species of freshwater turtle already settled in Europe, using a geographic information system (GIS) modelling approach based on datasets from CliMond for climate, Near-global environmental information (NGEI) for freshwater ecosystems (EarthEnv) and Maxent modelling using open-access databases, data from the literature and original field data. Modelling was performed for seven species of alien freshwater turtles occurring from the extreme northern to southern borders of the European range of E. orbicularis: the pond slider Trachemys scripta (Thunberg and Schoepff, 1792), the river cooter Pseudemys concinna (Le Conte, 1830), the Florida red-bellied cooter Pseudemys nelsoni (Carr, 1938), the false map turtle Graptemys pseudogeographica (Gray, 1831), the Chinese softshell turtle Pelodiscus sinensis (Wiegmann, 1835), the Caspian turtle Mauremys caspica (Gmelin, 1774) and the Balkan terrapin Mauremys rivulata (Valenciennes, 1833). In Ukraine, the most Eastern limit of E. orbicularis distribution, were previously reported northern American originated T. scripta, M. rivulata, M. caspica, whereas in Latvia, Emys’ most northern limit, were additionally reported P. concinna, P. nelsoni, G. pseudogeographica and Asia originated P. sinensis. The resulting Species Distribution Models (SDM) were of excellent performance (AUC > 0.8). Of these alien species, the most potentially successful in terms of range expansion throughout Europe were T. scripta (34.3% of potential range expansion), G. pseudogeographica (24.1%), and M. caspica (8.9%) and M. rivulata (4.3%) mainly in Eastern Europe, especially in the south of Ukraine (Odesa, Kherson, Zaporizhzhia regions, and Crimean Peninsula). Correlation between the built SDMs for the native E. orbicularis and the invasive alien T. scripta was reliably high, confirming the highly likely competition between these two species in places they cooccur. Moreover, a Multiple Regression Analysis revealed that by 2050, in most of Europe (from the western countries to Ukraine), the territory overlap between E. orbicularis and potentially invasive alien species of freshwater turtles will increase by 1.2 times, confirming higher competition in the future. Importantly, by 2050, Eastern Europe and Ukraine are predicted to be the areas with most suitable habitats for the European pond turtle yet with most limited overlap with the invasive alien species. We conclude that Eastern Europe and Ukraine are the most relevant priority conservation areas for the European pond turtle where it is now necessary to take protective measures to ensure safe habitat for this native species on the long-term.

Calling amphibian male counts (CAMC) is a cost-effective non-invasive acoustic monitoring method that needs amphibian community quality assessment system. In our survey we considered breeding amphibian assemblages as entities having three main ecological traits, size, richness and evenness, and tested the reliability of potentially suitable metrics that each characterize separate ecological trait. We also aimed at finding out the site and surrounding land-use characteristics linked to low or high-quality amphibian community state assessments, and studied differences in responses of community traits to these external factors.In this CAMC study that covered 400 amphibian breeding sites across Latvia, we tested responses of 11 metrics (5 CAMC for community size, 2 richness metrics, 4 evenness and dominance indices) to five sets of predictors (two sets of anthropogenic land use variables, two natural/mixed effect sets, and a climate variable set) using GLMs, to find out statistically significant anthropogenic factors, site and surrounding land use characteristics and model ranks according to their corrected Akaike information criterions. Then, we used anthropogenic factors to classify sites with natural and strongly impacted site groups, compared their metrics by Wilcoxon rank-sum tests and Box plots, and assessed metric congruences in site classifications.Based on their properties, we recommend using three metrics, each being the best in representing their own breeding amphibian assemblage trait in the communities of temperate Europe: the total number of calling males (CAMCtot), the community completeness, and the reciprocal form of Berger-Parker dominance index.Despite of good responses to anthropogenic pressure indicators showed by the metrics, local site characteristics were still the highest-ranked factor, with waterbody dimensions being the most important for amphibian population size, and macrophyte vegetation largely determining their taxonomic richness and community evenness. Among anthropogenic threats, the strongest effects were from the transportation corridors (roads) and infrastructure developments that had particularly adverse effects on community richness and evenness, and on CAMC for some taxa. Wetlands in surrounding areas were more important for CAMCtot. The climate factor was generally among the least important in ranks, probably due to its general similarity among the study sites throughout Latvia.Our study shows opportunities for using amphibian-based metrics in ecological indicator systems, where they may substitute fish metrics in some waterbody types, and suggests the necessity of paying more attention to wetland size and location against the road network in amphibian habitat restoration projects.

The European eel (Anguilla anguilla (L.)) is a unique catadromous euryhaline fish and the only anguillid eel species classified as ‘critically endangered’. The Baltic Lakeland area contains naturally recruited and introduced eels. There is great uncertainty regarding a baseline for the location and number of naturally dispersed eels in the region. Little is known about the genetic structure of the European eel populations in Baltic countries. The estimation of population genetic structure is important for the efficient management of naturally recruited and introduced eels. Two mitochondrial regions were used to investigate the genetic structure within and between eel samples from 11 waterbodies. In this study, new, unique, and widely distributed haplotypes were revealed. The studied eel population in the Baltic Lakeland shows high genetic diversity, which is possibly a result of intensive restocking programs. Sequences characterized for Anguilla rostrata were revealed in both mitochondrial regions. Understanding the genetic structure of eel populations worldwide is crucial for conservation efforts. Eel restocking in waterbodies where natural migration is restricted contributes to diversity loss for the world gene pool of eels.

Abstract Semi-aquatic European water frogs (Pelophylax spp.) harbour rich helminth infra-communities, whose effects on host population size in nature are poorly known. To study top-down and bottom-up effects, we conducted calling male water frog counts and parasitological investigations of helminths in waterbodies from different regions of Latvia, supplemented by descriptions of waterbody features and surrounding land use data. We performed a series of generalized linear model and zero-inflated negative binomial regressions to determine the best predictors for frog relative population size and helminth infra-communities. The highest-ranked (by Akaike information criterion correction, AICc) model explaining the water frog population size contained only waterbody variables, followed by the model containing only land use within 500 m, while the model containing helminth predictors had the lowest rank. Regarding helminth infection responses, the relative importance of the water frog population size varied from being non-significant (abundances of larval plagiorchiids and nematodes) to having a similar weight to waterbody features (abundances of larval diplostomids). In abundances of adult plagiorchiids and nematodes the best predictor was the host specimen size. Environmental factors had both direct effects from the habitat features (e.g., waterbody characteristics on frogs and diplostomids) and indirect effects through parasite-host interactions (impacts of anthropogenic habitats on frogs and helminths). Our study suggests the presence of synergy between top-down and bottom-up effects in the water frog–helminth system that creates a mutual dependence of frog and helminth population sizes and helps to balance helminth infections at a level that does not cause over-exploitation of the host resource.

Aquaculture’s role in addressing food security has grown, with a spotlight on Asian carp species. Polyculture, i.e. cultivating multiple fish species in a single system, is being increasingly adopted for its resource efficiency and economic benefits. This practice for Asian fish for food and ornamental purposes is gaining traction in Europe despite their invasive potential. Rising temperatures due to climate change offer an opportunity for thermophilic Asian carps (Hypophthalmichthys molitrix and Aristichthys nobilis). Using GIS modeling (Maxent), we identified the possible settlement of Asian carp in Northern Europe amidst climate change. We analyzed carp global distribution centers, assessed the potential carp spread in Europe, and evaluated their potential suitability for polyculture systems. By 2050, H. molitrix may extend its range to 58–62° N latitude, with a potential 1.7-fold habitat increase, while A. nobilis, which are more heat-tolerant, may move north to 52–58° N latitude, with a 1.3-fold potential increase. Despite the slight ecological differences in their native habitats, niche modeling indicates that these carp can occupy similar niches in Europe (proven statistically). The eventuality of using Asian species for polyculture in Europe presents both opportunities and challenges in the face of a changing climate as long as invasion risks are prevented. Envisaging such polyculture, yet very carefully for the protection of ecosystems, can help food security.

Amphibians are the most threatened group of vertebrates. While habitat loss poses the greatest threat to amphibians, a spreading fungal disease caused by Batrachochytrium dendrobatidis Longcore, Pessier & D.K. Nichols 1999 (Bd) is seriously affecting an increasing number of species. Although Bd is widely prevalent, there are identifiable heterogeneities in the pathogen’s distribution that are linked to environmental parameters. Our objective was to identify conditions that affect the geographic distribution of this pathogen using species distribution models (SDMs) with a special focus on Eastern Europe. SDMs can help identify hotspots for future outbreaks of Bd but perhaps more importantly identify locations that may be environmental refuges (“coldspots”) from infection. In general, climate is considered a major factor driving amphibian disease dynamics, but temperature in particular has received increased attention. Here, 42 environmental raster layers containing data on climate, soil, and human impact were used. The mean annual temperature range (or ‘continentality’) was found to have the strongest constraint on the geographic distribution of this pathogen. The modeling allowed to distinguish presumable locations that may be environmental refuges from infection and set up a framework to guide future search (sampling) of chytridiomycosis in Eastern Europe.

The aim of our study was to provide a first overview of the population genetic structure of the invasive Chinese sleeper, Perccottus glenii, (Actinopterygii: Odontobutidae) in European water bodies. This species originates from inland waters of north-eastern China, northern North Korea and the Russian Far East. The 1172 bp long portion of the cytochrome b gene was sequenced from Chinese sleeper specimens collected from a variety of water bodies in Belarus, Bulgaria, Hungary, Germany, Latvia, Lithuania, Poland, Russia (European part) and Ukraine. Our study revealed that the invasive Chinese sleeper in Europe consists of at least three distinct haplogroups that may represent independent introduction events from different parts of its native area; i.e. three founding populations: (1) Baltic haplogroup that may originate either from fish introduced inadvertent from Russia or from some unidentified source (release by aquarists). So far, this haplogroup has been found only in the Daugava basin in Latvia. (2) East-European haplogroup that may originate from an unintentional introduction to the Volga basin in Russia and has expanded westward. So far, this group was recorded in the Volga, Upper Dnieper and Neman drainages in Belarus, Lithuania, and Russia. (3) Carpathian haplogroup, that originated from individuals unintentionally introduced with Asian cyprinid fishes to Lviv region in Ukraine and are now widely distributed in Central Europe.

Wetlands are of great importance for biodiversity and nature conservation, especially geographically isolated wetlands (GIW). Yet literature about the ecological value of such GIW is missing, especially at the edge of the distribution of endangered species such as amphibians. In 2018 and 2022, we monitored amphibian communities in 15 isolated (GIW) and 12 non-isolated (nGIW) ponds by counting individuals using three methods: (1) capturing with hand nets, (2) visual counting, and (3) capturing with fyke traps. The three methods provided similar results, showing the great importance of GIW for amphibians, especially newts, whose abundance was 5–13 times greater in GIW compared to nGIW. The largest numbers of species and individuals (adults and larvae) were found in isolated wetlands (GIW). In non-isolated water bodies (nGIW) where more than 10 individuals of the Chinese sleeper Perccottus glenii, an alien invasive fish, were found, amphibians were not found at all. Importantly, between 2018 and 2022, the northern crested newt, T. cristatus, dramatically decreased in the nGIW. As a result of our work, it was revealed that the reconstruction of geographically isolated wetlands is very important for the conservation of amphibian biodiversity in a changing climate. One of the most effective measures aimed at protecting amphibians from negative factors—the spread of alien invasive fish species and diseases—is the reconstruction of wetlands in historically exploited landscapes with the creation of a wide range of water bodies yet broadly dominated by geographically isolated ponds.

In the modern world, when the problems of the environment are most acutely associated with climate change, amphibians are considered to be the most vulnerable group of anamniotes as an indicator of the state of wetlands. Along with a decrease of numbers among amphibians in Europe, nowadays newts especially suffer from the impact of invasive species, in particular predators such as the Chinese sleeper, Perccottus glenii. This predatory fish species has recently spread to areas of primary relevance for newt reproduction. This fish consumes eggs, larvae, and even adult newt individuals. Using an ecological niche approach and climate based species distribution models (SDM), we applied the coefficient of determination (R2) for comparing the level of similarity of the built SDM for the newts Triturus cristatus and Lissotriton vulgaris, and the Chinese sleeper. We show that by 2050, the level of climatic niche similarity for these native and invasive species will increase from 12% to 22% throughout Europe, and from 44% to 66% in Eastern Europe. This study highlights the expansion of the Chinese sleeper as a real threat to European biodiversity of wetlands in the near future, especially in their most northeastern distribution range.

The spread and outbreaks of phytophagous pests are often associated with global warming. In addition to economic interest, these species may be of interest in terms of biological indication of climate changes. In this context, we considered the locust digitate leafminer Parectopa robiniella Clemens, 1863 (Lepidoptera: Gracillariidae). This phytophage was first discovered in Europe in 1970 near Milano in Italy. Since then, it has been spreading across the continent. In Ukraine, it was recorded for the first time in 2003. In 2020–2021, we found areas of massive leaf damage caused by the black locust (Robinia pseudoacacia) in locations on Trukhaniv Island in Kyiv and some places in the Kyiv administrative region. Using 1041 georeferenced records of P. robiniella across Europe and a Bayesian additive regression trees algorithm (BART), we modeled the distribution of the moth. Predictors of current climate (WorldClim v.2, CliMond v.1.2 and ENVIREM) and a black locust habitat suitability raster were employed. Sets of SDMs built for P. robiniella with and without the habitat suitability raster for the host tree performed equally well. Amongst the factors that determine the niche of the locust digitate leafminer, most important are temperature-related conditions assumed to facilitate the spread and naturalization of the pest. In Ukraine, the appearance of the moth has coincided with increasing mean annual temperatures. Particularly favorable for the species are areas in the west and south-west of the country, and Transcarpathia. In the near future, the moth could reach locations in Nordic countries, Estonia, the British Isles, Black Sea coastal areas in Turkey, further into Russia, etc.

The spread of phytophagous pests are often associated with global warming. These species may be of interest in terms of biological indications of climate change. We considered the locust digitate leafminer P. robiniella. In Ukraine it was first recorded in 2003. In 2020–2021, we found areas of massive R. pseudoacacia leaf damage caused by the pest on Trukhaniv island (Kyiv) and some places in the region. Using 592 georeferenced records of P. robiniella across Europe and a Bayesian additive regression trees algorithm, we modeled the distribution of the moth. As predictors, a current climate (WorldClim v.2) and a black locust habitat suitability map were employed. Western and south-western regions of Ukraine and Transcarpathia are considered the most favorable for the pest. Amongst the factors determining its niche, summer moisture and warm conditions are the most important for facilitating the spread and naturalization of the moth. Under progressing climate change, the species is expected to move eastward.

The potential distribution of tropical fish species in Eastern Europe—Gambusia holbrooki (introduced for biological control) and Poecilia reticulata (aquarium species, found in waste waters of big cities)—tend to be of particular interest in terms of global climate change. After GIS modeling of our own data and findings listed in the GBIF databases (2278 points for G. holbrooki and 1410 points for P. reticulata) using the Maxent package and ‘ntbox’ package in R, 18 uncorrelated variables of 35 Bioclim climatic parameters from CliMond dataset, it was found out that by 2090 guppies will appear in the south of Ukraine (Danube river’s estuary, as well as in several places in the Caucasus and Turkey with habitat suitability > 0.3–0.5). G. holbrooki will also slightly expand its range in Europe. Limiting factors for G. holbrooki distribution are: bio1 (Annual mean temperature, optimum +12–+24 °C) and bio19 (Precipitation of coldest quarter (mm). Limiting factors for P. reticulata are: bio1 (optimum +14–+28 °C), bio4 (Temperature seasonality), bio3 (Isothermality). Unlike G. holbrooki, guppies prefer warmer waters. Such thermophilic fish species do not compete with the native ichthyofauna, but they can occupy niches in anthropogenically transformed habitats, playing an important role as agents of biological control.

In order to use an integrated approach for studying the influence of risk factors on the distribution of the native turtle species E. orbicularis and accompanying invasive species (T. scripta and N. procyonoides) in the northeast of their range, we used GIS modelling and a database (GAEZ, human footprint, CliMond) of 55 preselected variables, which represent a system of bioclimatic and anthropogenic factors. The main variables that influenced the results were factors related to temperature. There was a high correlation (r = 0.6) between the species distribution model’s habitat suitability for E. orbicularis and the corresponding “human footprint” values within the European part of the species’ natural range. Its unpretentiousness towards anthropogenic factors would likely help the further expansion of its range in eastern Europe, because the areas with the highest habitat suitability (r > 0.7) were projected to increase 3.3-fold. When comparing the E. orbicularis model to those obtained for N. procyonoides and T. scripta, we concluded that N. procyonoides could be dangerous because it occupies similar habitats (the degree of correlation is reasonably high in the north of their range (r = 0.5) in Latvia). An expansion of the range of Trachemys scripta is also possible in the future within the northern territories. Therefore, when developing the turtles’ protection algorithms, it is also necessary to take into account the influence of invasive species.

The study of the dynamics of the European pond turtle’s Emys orbicularis range and distribution as an indicator of climate change in the past, present, and future is most relevant in connection with the protected status of this species in Europe. Based on our original finds, 25 archaeological sites yielding 1623 remains of 1504 individuals of subfossil pond turtles, current marginal distribution in Latvia, Ukraine, Russia, and literature data, we analyzed 437 records of Holocene turtles and 2847 current records of pond turtles. We identified areas that could serve as refugia for E. orbicularis, as a result of GIS modeling, while using 19 bioclimatic variables from the Worldclim and PaleoClim data bases. The data obtained confirm current hypotheses regarding the origin of more than 10 mtDNA lineages of E. orbicularis and the existence of multiple glacial refugia, and considerable Holocene home range dynamics.

The aim of the research was to investigate the presence of allochthonous species of turtles in the nature of Latvia, as well as to withdraw them from the nature according to the "Plan on protection of Emys orbicularis in Latvia", officially approved by the Latvian Ministry of Environment (Pupiņš & Pupiņa 2007a). The methods of the research were: 1) information campaign and survey; 2) interviews with inhabitants; 3) field expeditions; 4) laboratory study of viability of found turtles. In course of research, five new allochthonous species and subspecies of the turtles were recorded for the first time, and new data were obtained about finding Trachemys scripta elegans in the nature of Latvia. Most of the registered animals (80%) were removed from the nature. Since allochthonous turtles get there in the result of escape from pet-lovers and, apparently, illegal introduction into nature by their owners, education of population is of great importance.