The Dynamics of Changes in the Amphibian (Amphibia) Population Size in the Masurian Landscape Park Monitoring Results of Spring Migration Monitoring from the Years 2011–2019

In Poland, 18 amphibian species live in Poland. They represent two orders, namely, salamanders – Caudata and frogs – Anura, and six families: true frogs (Ranidae), true toads (Bufonidae), true salamanders and newts (Salamandridae), European spadefoot toads (Pelobatidae), Firebelly toads (Bombinatoridae) and Tree frogs (Hylidae). All of them are subject to species protection and, with the exception of the common toad and smooth newt, to protection under the EU Habitats Directive (Table 1) [Sura P., Głowaciński Z., 2018; Herczek A., Gorczyca J., 2004].

Amphibians are among the most endangered vertebrate species worldwide. At the European level, nearly 23% of the amphibians have been recognised as endangered, of which 2.4% as critically endangered, 7.2% as endangered and 13.3% as vulnerable. A similar situation is observed throughout the EU-27 (22.0% endangered, including 2.4% critically endangered, 6.1% endangered and 13.4% vulnerable). In general, almost a quarter of amphibians are regarded as endangered on the European continent. Further, 16.9% of the amphibians are regarded as near threatened. By way of contrast, 19.4% of the reptiles, 15.2% of the mammals and 13% of the European birds are endangered [Temple, H.J., Cox, N.A., 2009].

As regards amphibians, the greatest threat is the loss of habitats, which affects a total of 76 species. Contaminants are the second major threat that affects 62 species. They are followed by invasive alien species, which pose a threat to almost half of the European amphibian species. These invasive species include predators, such as the salmonids, and pathogens, such as a fungal disease chytridiomycosis, which is associated with a reduction in the amphibian population numbers, and the extinction of amphibians in many parts of the world

ec.europa.eu/environment/nature/conservation/species/redlist/amphibians/major_threats.htm

Another serious threat is the uptake of water resources (particularly for agricultural purposes), which changes the hydrology of surface waters of the habitats inhabited by amphibians [Mathwin R. et al., 2002]. The fragmentation of habitats, which contributes to the loss of biological diversity worldwide, is also of extreme importance. The fragmentation implies a reduced gene flow, an increase in the inbreeding levels, the loss of diversity in populations, an increased differentiation between populations and the increased risk of extinction and the dispersion (i.e. from the site of birth to the reproduction in other population) [Pabijan M. et al., 2020; Winter M. et al., 2016; Testud G. et al., 2020].

One of the factors contributing to the fragmentation of habitats is the network of roads, particularly the local ones. Amphibians are dependent on the complex landscape structure when moving between breeding and feeding habitats. Roads act as barriers: they increase the imperviousness of habitats and mortality of amphibians. Unfortunately, the mass mortality of amphibians on the roads increases with the development of infrastructure and occurs faster than mitigating measures [Kolenda K. et al., 2019]. Consequently, the fragmentation of habitats results in the fragmentation of population, modification of animals’ behaviours and a reduction in gene flow [Puky M., 2006; Sillero N. et al., 2019; Wittbrodt K., 2011; Sjögren-Gulve P., 2020]. In addition, the roads, due to the need for maintaining them (e.g., sand or salt spreading on icy roads), change and pollute the habitats located in the immediate vicinity, which can have a lasting effect on the biology of organisms, the population dynamics and the distribution of species [Grzybowski M., Glińska-Lewczuk, 2019]. The fragmentation of habitats in the form of road infrastructure development has an adverse effect on: -

an amphibian’s individual characteristics within the same species (certain individuals, especially females, mature earlier, while others do it later),

It is believed that it is the climate change that is of significance in the shaping of amphibian population. Ectothermic animals such as amphibians and reptiles are particularly sensitive to the rapidly rising global temperature [Bodensteiner B.L., 2020; Taylor E.N. et al., 2020]. According to Bucciarelli G.M. et al. [2020], although the amphibians have developed life strategies in order to mitigate the adverse consequences of varying precipitation patterns, their ability to adapt to the simultaneous drought and rapid increased in the temperature as well as the greater environmental variability in general, may be insufficient to maintain viable populations, given the rate and intensity of these changes. A study by Cohen J. M. et al. [2018] demonstrated that global warming may have consequences for the amphibians adapted to relatively cold conditions, which are most vulnerable to the interactions between an increase in the average temperature and the emerging infectious diseases. Yiming LI Y et al. [2012] express a different opinion, as they claim that there is little evidence of climate change being lethal to amphibians. These authors believe that the information on thermal tolerance of amphibians, their thermal preferences and the actual temperature and humidity ranges in which amphibians live is too limited.

The examples provided above have resulted in eight out of 18 species having been awarded the UI (unfavourable-inadequate) status in the European Union. These species include: European common spadefoot (Pelobatesfuscus), European fire-bellied toad (Bombinabombina), European tree frog (Hylaarborea), Northern crested newt (Trituruscristatus), pool frog (Pelophylaxlessonae), moor frog (Rana arvalis), common frog (Rana temporaria) and Carpathian newt (Triturusmontandoni).

nature-art17.eionet.europa.eu/article17/species/report/?period=5&group=Amphibians&country=PL&region=

In Poland, all amphibian species are subject to legal protection, of which three species are under strict protection, while for six species, active protection was proposed (Table 1).

The unfavourable situation in the context of changes in populations of individual amphibian species necessitates taking remedial measures such as the development of programmes for construction/reconstruction of water bodies, which increase the diversity of plants and invertebrates as well as amphibians, programmes for Eurasian beaver reintroduction and the construction of road-crossing tunnels for amphibians in the road infrastructure [Downie J.R. et al., 2019; Klimaszewski K. et al., 2015; Dalbeck L. et al., 2020].

It is very important to create natural buffers between wetlands and the surrounding areas, which will consequently have a positive effect on water quality and biological diversity. Buffer zones are contact zones between aquatic and terrestrial ecosystems, which help regulate the ecological functions of both systems. As regards the amphibians, an effective buffer zone should be approximately 50 m wide [Lind L. et al., 2019; Guzy J.C. et al., 2019].

However, the research conducted in Canada, the United States and Italy showed that the guidelines concerning the protection of true frogs (Ranidae) and true toads (Bufonidae) in agricultural landscapes should focus on the protection of terrestrial habitats at the landscape level, and not on the maintenance of narrow buffers in wetlands [Sawatzky M.E. et al., 2019; Ficetola G.F., 2009; Semlitsch R.D. et al., 2003]. Such a strategy, however, requires the cooperation between naturalists with broadly understood local communities and professional groups due to the emerging conflicts of interest [Preisser E. et al., 2000]. Further measures to protect amphibians include the restoration of flow capacity of the wildlife river corridors and the abandonment or limitation of the removal of aggradate mud and sandy deposits (amphibian overwintering in the mud) [Biedroń I. et al., 2020].

The aim of monitoring was to determine the dynamics of changes in population numbers of amphibians (Amphibia) during the spring migrations. Field research was conducted from 2011 to 2019 in the vicinity of the “Krutynia Górna” Nature Reserve located in the Masurian Landscape Park in Warmińsko-MazurskieVoivodeship (Fig. 1).

Figure 1

The reserve was established on 22 April 1983 by Order of the Minister of Forestry and Wood Industry. The main aim of the reserve’s protection is to protect forest, aquatic and peat bog biocenoses associated with the Upper Krutynia River Valley and the Lake Krutyńskie and the natural landscape features. The reserve has a landscape park character, and its area is 271.01 ha. The reserve protects the Lake Krutyńskie and the upper section of the Krutynia River, which flows out from the lake, and the leafy and mixed forests located by the river banks [Wittbrodt K., et al., 2020].

Order of the Minister of Forestry and Wood Industry of 22 April 1983 on the recognition as nature reserves [M.P. of 1983, No 16, item 91].

In the years 2011–2019, at the turn of February and March, barriers were placed on both sides of a 200-m-long section of the district road 1773N adjacent to the reserve, in order to prevent amphibians from crossing the road (Fig. 2). Along the barrier, from the inside, plastic traps were embedded in the ground (8 on each side). The traps had holes in them so that no water accumulated in them during rainfalls; moreover, branches were placed in them to allow insects and small-sized mammals to escape from the trap [Information and educational materials..., 2014].

Figure 2

Depending on the air temperature and humidity, the monitoring was conducted 2–3 times a day. The temperature was measured, and the weather conditions were determined. The monitoring personnel checked the traps located on one side of the road, identified the species composition and counted the trapped individuals and then transferred them to the other side of the road. The barriers were removed in the first half of May, when amphibians finish their migration to breeding sites.

Each year, before commencing the monitoring, the Regional Director for Environmental Protection in Olsztyn was applied to for permission to trap the protected species individuals.

The results of amphibian monitoring carried out in the years 2011–2019 in the Masurian Landscape Park, in the vicinity of the “Krutynia Górna” Nature Reserve, showed the occurrence of 13 out of the 18 domestic amphibian species, including the Northern crested newt (Triturus cristatus) categorized as a Near Threatened (NT) species. Despite the unfavourable situation with regard to the humidity conditions in the habitats under monitoring, no clear correlations were noted between the population abundance of amphibian species occurring in the Masurian Landscape Park and the climatic factors in individual years. In view of the situation of amphibians at the domestic and global levels, presented in the study, it is necessary to continue the monitoring along with an extended assessment of the (biotic and abiotic) factors affecting the fluctuations of individual populations.