Urban plums and toads: do fleshy fruits affect the post-metamorphic growth of amphibians?

Abstract

BackgroundThe main aim of the study was to analyse the influence of fleshy fruits (plums) on the post-metamorphic growth and feeding behaviour of the green toad Bufotes viridis. We tested the following two hypotheses: (1) juveniles of the green toad are characterised by faster growth in conditions involving fallen plums Prunus cerasifera due to the associated presence of more varied food such as invertebrates; (2) green toads exhibit more active feeding behaviour in the presence of fleshy fruits.MethodsA total of 120 fresh metamorphs of the green toad were randomly assigned to one of four groups: two experimental groups with fleshy plums and two other groups as controls (without fruits). Each group was kept in an enclosure to which wild invertebrates had free access. Each individual toad was measured for snout-vent length (mm) and body mass (g) every other day for 30 days. In order to determine whether fallen plums influence the feeding behaviour of toads, the number of active and hidden (under an artificial shelter) individuals was also noted.ResultsThe results showed that green toads from both enclosures with plums were characterised by more rapid growth than individuals from the control treatments. Simultaneously, in the enclosure with fleshy fruits, greater species richness of wild invertebrates was observed. No differences in active feeding behaviour were noted between control groups and groups with plums.DiscussionFleshy fruits, upon falling, attract many types of invertebrates; thus they may represent good dietary supplements for fresh amphibian metamorphs. Therefore, the presence of fruit trees close to a breeding site might influences the post-metamorphic growth of amphibians, but not their feeding behaviour. The presence of insects associated with fallen fruit seems to favour the occurrence of amphibian populations, which is particularly important, since, due to political and social pressure, numbers of fruit trees are currently being reduced. To our knowledge, no previous study has investigated the potential influence of the presence of fruit trees on the growth and behaviour of anurans.

Among the trees: shade promotes the growth and higher survival of juvenile toads

“…In line with a previous study, we used the cherry plum (also commonly known as the myrobalan plum, Fig. 2), as a fleshy fruit lying on the ground (Kaczmarski et al, 2019b). Artificial fruits were purchased from a commercial supplier offering decorative items, while the myrobalan plums were collected near the study sites.…”

“…Juvenile toads were collected near natal water bodies on the same day (July 19) during post-metamorphic dispersion. All individuals originated from a city centre population living in a fountain and a small patch of a green area (52°24'04.7"N, 16°54'54.9"E; more details: Kaczmarski et al, 2019b;Zawadzki et al, 2017). We adopted an experimental design from a previous study (for more details, see: Kaczmarski et al, 2019b).…”

“…All individuals originated from a city centre population living in a fountain and a small patch of a green area (52°24'04.7"N, 16°54'54.9"E; more details: Kaczmarski et al, 2019b;Zawadzki et al, 2017). We adopted an experimental design from a previous study (for more details, see: Kaczmarski et al, 2019b). However, we have made some modifications to the earlier research protocol.…”

“…Previous research indicated that cherry plum Prunus cerasifera Ehrh. fruits lying on the ground in experimental conditions in a partly shaded site have a supporting effect on the growth of juvenile green toads, possibly due to the attracted insects that are then eaten by the toads (Kaczmarski et al, 2019b). Prunus cerasifera is a non-native tree species, kenophyte, that was initially a cultivated plant and nowadays has entered the landscape to various habitats.…”

Generalist, selective or ‘mixed’ foragers? Feeding strategies of two tropical toads across suburban habitats

“…For example, European green toads (Bufotes viridis) preferentially consume insects attracted to artificial street lighting in urban environments (Covaciu-Marcov et al, 2010). Green toads can also benefit from fallen fruits from trees typically planted in urban and suburban localities, becoming an important food source just after metamorphosis and also during the period of intensive growth preceding the first hibernation (Kaczmarski et al, 2019). The Cururu toad Rhinella diptycha in Brazil is also reported to eat fruits in urban settings (Severgnini et al, 2020).…”