麻豆淫院

Amphibians are land animals, but can only reproduce in water. They prefer to live in and around small bodies of water. But this habitat is becoming increasingly rare鈥攊n Germany alone, more than half of this type of body of water has disappeared in the last century.

Anyone who wants to protect amphibians must therefore also maintain, improve or create new ponds and pools. But what does an amphibian pond look like in which as many species as possible feel at home?

Researchers led by the Catalan University of Vic and with the participation of the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) have determined in a Europe-wide study which factors promote a high diversity of amphibians in small bodies of water.

The research was published in two articles, one in and another in .

Climatic factors play an important role here, but are often not locally controllable. But there is still room for maneuver, because local factors are also important, as the study shows: low nutrient load, medium-sized and rather shallow, no fish鈥攖hat would be ideal. But be careful with the fish: many species of them are also threatened, so in each individual case a balance must be struck between fish protection and amphibian protection.

A pond or pool is by definition a standing body of water with a water surface of less than 5 hectares. In Germany, artificially created small bodies of water are usually called ponds (the water level of which can usually be regulated) and naturally formed small bodies of water are called pools or ponds. These make up an estimated 30% of inland water areas worldwide.

They have suffered particularly from water shortages in recent years. Across Europe, they are at historic lows, and many are drying out permanently. They are small oases for amphibians that live on land and in water.

"But water shortages, increasing pressure on the surrounding landscape and climate change with its extreme weather are taking a heavy toll on these ecosystems and therefore also on the amphibians that depend on them," explains IGB Director Prof. Dr. Luc De Meester, co-author of the study.

Amphibians are the most threatened group of vertebrates. In Europe, around a quarter of species are classified as threatened (i.e., in the categories "vulnerable," "critically endangered" or "critically endangered") according to the Red List of the International Union for Conservation of Nature (IUCN). "We therefore need to better understand which factors we can use to positively influence amphibian populations," says IGB scientist Dr. Thomas Mehner, co-author of the study.

Thirty different amphibian species were recorded in the total of the water bodies studied. The average number of species per water body was three species, with Spain having the highest average local richness with about five species and the United Kingdom the lowest, with around two species. Some species were restricted to a single country, with Spain having the highest number of unique species (nine), followed by Turkey (five), Switzerland (one) and Germany (one).

The most common species was the smooth newt (Lissotriton vulgaris), which occurred in 41.8% of all small water bodies in the countries studied, followed by the northern crested newt (Triturus cristatus, 30.4%), the common toad (Bufo bufo, 27.9%) and the common frog (Rana temporaria, 25.4%).

Latitude matters, but local factors also play a role

It is known from other studies that the species diversity of amphibians is related to latitude, since climatic factors such as water availability and temperature are important factors that limit the range of these cold-blooded and highly moisture-dependent animals. The current study also shows this relationship to climatic factors.

"Apart from that, however, we show that local characteristics of the ponds and pools play just as important a role as the climatic factors. And these can of course be better influenced," says Mehner.

The researchers found the highest diversity of amphibian species in small bodies of water with few nutrients, no fish, medium size, shallow water and extensive bank vegetation. Ponds located in protected areas had a slightly higher diversity of amphibian species. The following measures can be used to create a species-rich amphibian pond by taking local factors into account:

Reduce nutrient load

The most important indicator to explain the variation in amphibian species richness in this study was chlorophyll-a concentration. Chlorophyll-a concentration indicates algal biomass and is therefore also an indicator of nutrient pollution. This is because when there are many nutrients in the water, algae can grow particularly well. Nutrient pollution in ponds can reduce amphibian species richness by reducing the survival rate of eggs and larvae, reducing reproductive success and increasing susceptibility to disease.

"Nutrient pollution is a common problem in ponds that are located near agricultural land and are exposed to increased amounts of artificial and natural fertilizers. Therefore, management options to increase amphibian species richness should focus on implementing measures to reduce nutrient pollution and on livestock management that restricts the access of grazing animals to the respective water bodies," says Mehner.

This is especially true for waters that have previously been exposed to only low levels of nutrients: at low concentrations, even a small increase in chlorophyll-a content has a strong negative impact on amphibian abundance, according to one result.

Pond area and depth are also important factors for amphibian richness: the highest species richness was observed in medium-sized (200鈥�2,500 square meters) and shallow (less than 1.5 meters deep) waters. This pattern could be due to the fact that smaller and shallower ponds are more likely to dry out, while fish live or survive more frequently in larger and deeper waters. "These mechanisms can lead to amphibian richness reaching its peak at intermediate values of pond size and depth," says Mehner.

Fish: Balancing amphibian and fish protection

The number of fish species was found to be a significant factor in the decline in amphibian diversity, especially when three or more fish species were present in a small pond. Predatory fish are generally considered to be the cause of the decline in amphibian diversity. Amphibian eggs, tadpoles and adults are vulnerable to predation by several fish species found in the study (e.g., the alien species gibel and sunfish, or northern pike).

Although pond plants are important for the amphibian community, such as providing shelter, protection and food, they explained only a very small part of the variation in amphibian species richness in this study. This observation is in contrast to other studies that show that vegetation is a reliable determinant of amphibian richness. Also, direct land use factors within 100 meters, such as an urban environment, agriculture, roads or protected areas, did not have as strong an influence on amphibian species richness as the other factors.

"The study shows that species-rich amphibian waters can occur anywhere鈥攅ven in urban contexts. This study can directly feed into the development of Europe-wide initiatives such as the European Pond Conservation Network and provides important information for pond projects at the local level, enabling decision-makers to take better-informed amphibian conservation measures," says Mehner.

The research team included 201 small bodies of water in seven European countries in the study and defined certain characteristics for each pond. The species diversity of the amphibians was determined using eDNA from water samples. eDNA stands for environmental DNA. This allows the genetic fingerprints that organisms leave behind in their habitat to be determined.

The relative influence of climate, local inanimate and animate factors and land use variables on the variation in amphibian species richness in the ponds was quantified using boosted regression trees. Ecologists use this statistical model to explain relationships between different environmental factors and to make predictions. It is flexible enough to take into account typical properties of their data, such as nonlinearities and interactions.

What the study did not take into account

While the study considered current climatic drivers, it did not consider historical climate variables. Previous research has shown that paleoclimatic processes have a major impact on the present-day gradient of amphibian species richness. Future studies incorporating these data could therefore provide an even more comprehensive understanding of how historical and present processes interact in shaping amphibian diversity.

In addition, not all influencing factors were taken into account, such as food availability (density of large invertebrates), shading or connectivity between small water bodies, the presence of environmental chemicals and their effects. Field studies have limited ability to establish clear cause-effect relationships.

Nevertheless, the use of boosted regression trees is reliable in this context of a complex data structure and the results provide a clear pattern of how multiple water body features play a role in explaining the amphibian species richness of pond ecosystems on a large geographical scale.