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Dispersal and local abundances of the predatory edible frog (Pelophylax esculentus) in Scania – A potential threat to the vulnerable green tree frog (Hyla arborea)?

Liu, Jiate (2017) BION01 20162
Degree Projects in Biology
Abstract
Amphibian populations are declining globally due to several abiotic factors such as climate, pH, water permanence and biotic factors including predation by exotic species, competition and the spread of diseases. Habitat destruction caused by humans is also an important factor. Several species of amphibian have been declining in Sweden, and in most cases explained by habitat destruction and isolation. Thus, creation of new breeding ponds has reversed the trend for many species, including the green tree frog. In recent years however, the spread of the edible frog (Pelophylax esculentus) in Scania has raised some concern. It is a predatory amphibian and has wide distribution in Europe. It can be found in a broad range of habitats and could... (More)
Amphibian populations are declining globally due to several abiotic factors such as climate, pH, water permanence and biotic factors including predation by exotic species, competition and the spread of diseases. Habitat destruction caused by humans is also an important factor. Several species of amphibian have been declining in Sweden, and in most cases explained by habitat destruction and isolation. Thus, creation of new breeding ponds has reversed the trend for many species, including the green tree frog. In recent years however, the spread of the edible frog (Pelophylax esculentus) in Scania has raised some concern. It is a predatory amphibian and has wide distribution in Europe. It can be found in a broad range of habitats and could potentially have negative impacts on other amphibians including the previously endangered European green tree frog (Hyla arborea). The aim of this study was to summarize the past and present distribution of P. esculentus in Scania and relate this pattern to the distribution of H. arborea. Furthermore, I studied the environmental factors affecting the co-existence and the numbers of both species in an area (the Frihult) where P. esculentus first appeared in 2011. In the Frihult area, 30 wetlands were investigated, and the overall results show that P. esculentus has increased their distribution range to include most parts of south-western and central parts of Scania in the past 20 years. In the Frihult area, P. esculentus was abundant in comparatively small, eutrophic ponds with a low coverage of emergent plants. Furthermore, P. esculentus and H. arborea shared similar habitats but there was no negative relation between the numbers of P. esculentus and H. arborea in these ponds. The results from this study show that P. esculentus is spreading rapidly in Scania and it is co-existing with other amphibians of concern, such as H. arborea. The potential for negative effects of P. esculentus on H arborea is there, but the patterns observed in this study cannot support this hypothesis. (Less)
Popular Abstract
Potential threat of an edible frog in Sweden

Declining amphibian populations are reported globally in recent decades, and in most cases explained by habitat destruction and isolation. Thus many breeding ponds are created and restored in Sweden to prevent amphibians from extinction. In recent years however, the spread of the edible frog (Pelophylax esculentus) in Scania has raised some concern. It is a predatory amphibian and can be found in a broad range of habitats. Therefore it could potentially have negative impacts on other amphibians. The aim of this study was to summarize the past and present distribution of P. esculentus in Scania and relate this pattern to the distribution of the vulnerable green tree frog (Hyla arborea).... (More)
Potential threat of an edible frog in Sweden

Declining amphibian populations are reported globally in recent decades, and in most cases explained by habitat destruction and isolation. Thus many breeding ponds are created and restored in Sweden to prevent amphibians from extinction. In recent years however, the spread of the edible frog (Pelophylax esculentus) in Scania has raised some concern. It is a predatory amphibian and can be found in a broad range of habitats. Therefore it could potentially have negative impacts on other amphibians. The aim of this study was to summarize the past and present distribution of P. esculentus in Scania and relate this pattern to the distribution of the vulnerable green tree frog (Hyla arborea). Furthermore, I studied the co-occurrence of these species in an area recently colonized by the edible frog.

Four periods (year 1995-2000, year 2001-2005, year 2006-2010 and year 2011-2017) were selected to map the spread of P. esculentus in Scania. Individual species data for P. esculentus and H. arborea in year 2016 from Artportalen were used to compare their current distribution. As these two species show greatest overlap in the Frihult area, the abundance data for individual species in the same ponds were then used to study the relationship between these two frogs. Thirty ponds in the Frihult area were selected to investigate factors influencing densities of adult P. esculentus. The inventory was made by following the specific survey manual and filling in protocols. Data analyses including a chi-squared test, a principal components analysis (PCA) and a linear regression were performed in either SPSS or Excel.

Distribution of P. esculentus was becoming increasing larger in the last 20 years. Back in 1995-2000, P. esculentus was only reported at a small area in the south-western part of Scania. Nowadays this species has increased their distribution range to also encompass the central and eastern parts of Scania. The numbers of individuals reported was also increasing since 1995. From 1995-2000, there were only 3 recordings of this species. Until 2005, 33 ponds were found with P. esculentus. In the latter 5 years, 219 more sites were noted with the species, and until 2017, this number raised to 391. In the Frihult area, 28 out of 30 ponds were found to be colonized by P. esculentus. The number of adult edible frogs at different wetlands in this area varied between 0 and 28. P. esculentus densities increase linearly with small circumference, higher conductivity, higher turbidity, higher pH and lower coverage of emersed-vegetation. This corresponds to comparatively small wetlands with eutrophic conditions, but that are not overgrown by emersed-vegetation.

Both P. esculentus and H. arborea are found in the southern parts of Scania. P. esculentus mainly occurs at south-western and middle Scania whereas H. arborea mainly occurs in south-eastern and central parts of Scania. In the Frihult area, more than 20 ponds were found with both P. esculentus and H. arborea. The occurrence of H. arborea was not dependent on whether P. esculentus was present or not. And the number of calling males of H. arborea in spring was not significantly related to the number of P. esculentus per 10 meters of shore in late summer.

The results of this project will be valuable when assessing and reducing the effects of P. esculentus on other amphibians.

Master’s Degree Project in Biology, 45 credits, 2017
Department of Biology, Lund University

Advisor: Per Nyström
Advisors Unit/Department (or Company or Authority): Department of Biology/Ekoll AB (Less)
Please use this url to cite or link to this publication:
author
Liu, Jiate
supervisor
organization
course
BION01 20162
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8909781
date added to LUP
2017-05-31 13:21:00
date last changed
2017-05-31 13:21:00
@misc{8909781,
  abstract     = {Amphibian populations are declining globally due to several abiotic factors such as climate, pH, water permanence and biotic factors including predation by exotic species, competition and the spread of diseases. Habitat destruction caused by humans is also an important factor. Several species of amphibian have been declining in Sweden, and in most cases explained by habitat destruction and isolation. Thus, creation of new breeding ponds has reversed the trend for many species, including the green tree frog. In recent years however, the spread of the edible frog (Pelophylax esculentus) in Scania has raised some concern. It is a predatory amphibian and has wide distribution in Europe. It can be found in a broad range of habitats and could potentially have negative impacts on other amphibians including the previously endangered European green tree frog (Hyla arborea). The aim of this study was to summarize the past and present distribution of P. esculentus in Scania and relate this pattern to the distribution of H. arborea. Furthermore, I studied the environmental factors affecting the co-existence and the numbers of both species in an area (the Frihult) where P. esculentus first appeared in 2011. In the Frihult area, 30 wetlands were investigated, and the overall results show that P. esculentus has increased their distribution range to include most parts of south-western and central parts of Scania in the past 20 years. In the Frihult area, P. esculentus was abundant in comparatively small, eutrophic ponds with a low coverage of emergent plants. Furthermore, P. esculentus and H. arborea shared similar habitats but there was no negative relation between the numbers of P. esculentus and H. arborea in these ponds. The results from this study show that P. esculentus is spreading rapidly in Scania and it is co-existing with other amphibians of concern, such as H. arborea. The potential for negative effects of P. esculentus on H arborea is there, but the patterns observed in this study cannot support this hypothesis.},
  author       = {Liu, Jiate},
  language     = {eng},
  note         = {Student Paper},
  title        = {Dispersal and local abundances of the predatory edible frog (Pelophylax esculentus) in Scania – A potential threat to the vulnerable green tree frog (Hyla arborea)?},
  year         = {2017},
}