Herpetologica Romanica
Vol. 2, 2008, pp.21-26
The analysis of the trophic spectrum of a Pelophylax ridibundus population
from Vadu area, Constanta county, Romania
Anamaria, DAVID1,*, Nicoleta DIMANCEA2, Adrian PAL1 and Katalin CSERVID1
1. University of Oradea, Faculty of Sciences, Department of Biology, Universitatii str.1, Oradea 410087, Romania
2. University of Oradea, Faculty of History and Geography, Department of Geography, Universitatii str.1, Oradea 410087, Romania
* Coppersponding author: A. David, E-mail: [email protected]
Abstract. The 43 analysed individuals were captured from a habitat near Vadu, Constanta county. All the frogs
presented stomachal content, which suggests optimum feeding conditions in the biotope inhabited by this population.
The most important categories of prey taxa are represented by the terrestrial Crustacean Isopoda, Arahnidae-Araneidae
and Coleopteras. The remains of vegetales and shed-skin were also present in the frogs' stomach.
Key words: Pelophylax ridibundus, differences between the sexes, trophic spectrum
Introduction
Although the components of the trophic spectrum
are more or less identical for all of the amphibians,
the role of some trophic objects are different.
Moreover data of this kind offers valuable
information regarding the condition of the habitat,
the available resources which can ensure a lasting
development of the Amphibian populations which
are found here.
Pelophylax ridibundus is an almost exclusively
aquatic species, a good swimmer, being seen only in
the water or in the nearby area (Berger 1973). It lives
in permanent waters, prefering especially the deep
and big lakes (Rybacki & Berger 1994 ;
Cogălniceanu et al. 2000).
The trophic spectrum of this species was studied
especially in the western part of the country, in this
region a series of studies have been conducted
regarding the trophic spectrum of some
nonhibernating populations of Pelophylax ridibundus
(Covaciu-Marcov et al. 2003, 2005; Sas et al. 2004a,
Peter et al. 2005). In Constanta county the food
composition was also analysed from a frog
population from Dobromir locality (Szeibel et al.
2008).
In this study we observed the feeding
particularities depending on the sex and on the
ontogenetic development stage.
Materials and methods
The study took place in April 2007,when we preserved the
stomachal contents of 43 individuals :22 females, 15 juveniles,
and only 6 males.
The habitat from which we analysed the population is
found near the beach, so the altitude is therefor low (5
metres). We also mention that the investigated area is part of
the Danube Delta Biosphere Reservation, which is affected by
man.
We used the stomach-flushing method (Cogalniceanu
1997) in order to preserve the stomachal contents. This
method has the advantage that one can perform feeding
studies without killing the individuals. The samples were
preserved separately, in a 4% formaldehyde solution and
stored in airtight test tubes, which contained labels with the
frog's sex. After the conservation of the stomachal contents,
the studied individuals were released as close as possible to
the place where they were captured, in order to reduce the
impact of our activity.
We analysed and determined the samples in the
laboratory using a magnifying glass and scientific literature
(Crisan & Cupsa 1999; Radu & Radu 1967).
The aim of the study was to determine the differences
that appear between the sexes, the amount and the frequency
Herpetol. Rom, 2,
2008, Romania
22
of the prey taxa, the feeding intensity and the origin of the
prey.
Results and discussions
From a total of 330 consumed prey, 186 were
identified in the stomachal contents of the females,
84 in the case of the juveniles and 60 in that of the
males. Besides animal prey, in the stomachal
contents were also identified vegetales and shedskin.
The amount of the vegetales is 100% in the case
of the males, followed by the females with 63.6%
and the juveniles with 60%. We consider that the
analysed individuals swallowed them together
with the animal prey, in the case of the males the
high value of the vegetal fragments is due to the
smaller amount of analysed individuals.
The accidental consumption of vegetal fragments
is suggested by the observation that adult
Amphibians are, as far as the feeding habits are
concerned, carnivore-insectivore, and that only their
larvae are phytophagous-detritivore (Reeder 1964)
and stressed by the fact that amphibians consume
mainly mobile prey (Zimka 1966). There are theories
that state that amphibians consume vegetal
fragments for the water found in them, or in order
to eliminate intestinal parasites or crush the
exoscheleton of the swallowed prey (Evans &
Lampo 1996).
The amount of stomachal contents with shedskin is higher in the case of the males
16.7%,followed by the juveniles with 13.3%, and the
females with 9.09%. The consumption of shed-skin
is considered by some authors as a way of recycling
epidermal protein (Weldon et al. 1993), these can be
easily swallowed from the water, or ingested as a
result of the confusion between the prey and other
amphibians which are in motion. Shed-skin don't
represent a trophic basis that amphibians search,
but are rather consumed in the nonfavourable
periods, as a result of the absence of other categories
of trophic elements. Shed-skin have also been
identified in the stomachal contents of other
amphibians, such as Rana arvalis (Sas et al. 2003a),
Herpetol. Rom, 2, 2008
David, A. et al.
Rana dalmatina (Aszalos et al. 2005), Bombina bombina
(Sas et al. 2003b), Bombina variegata (Sas et al. 2004b,
Peter et al. 2006), Hyla arborea (Kovacs et al. 2007)
Pelophylax lessonae (Sas et al. 2005) Pelophylax kl.
esculentus (Sas et al. 2007, 2009-online.first).
As far as the feeding intensity is concerned, all of
the analysed frogs present stomachal contents, the
necessary prey being available in order to satisfy the
frog's
energetic
needs.
The
average
number/individual is 10 in the case of the males,
which consumed a small number of prey categories
(14 categories) in a large amount; in the case of the
females this is 8.45 (the prey taxa were grouped in
19 categories), their food being more diverse; and in
the case of the juveniles the average number of
prey/individual is 5.6 (Table 1).
The amount of the prey taxa emphasizes certain
differences between the sexes, respectively
depending on the stage of ontogenetic development.
This fact shows that there are distinctions regarding
the way of obtaining food among the males, females
and juveniles.
In the case of the males the highest value is
occupied by the aquatic Gasteropodes and the
terrestrial Isopodas with a percentage of 25%.
Unlike the males, in the case of the females the
aquatic snails have a vey low rate, 0.54%, the
majority being held by the terrestrial Isopoda, 27.4%
(Table 2), in a whole the females consumed a higher
amount of terrestrial-originated taxa.
The second place, both in the case of the males
and females, is occupied by the Arahnida-Araneida,
their value being 20%, and 17.7% in the case of the
females. This categorie of prey is mentioned in the
scientific literature as important in another
population of Pelophylax ridibundus (Ylmaz &
Kutrup 2006). In the case of the juveniles, the
spiders hold first place with a value of 29.8%.The
Araneida represent an important group which can
be easily captured from the vegetation from the
habitat and therefore are accesible for both adults
and juveniles.
Heteropteras have a lower value in the case of
the males, 5%, followed by other taxons such as
Coleopteras
Carabidae
(6.67%),
Arahnidae
The analysis of the trophic spectrum of a Pelophylax ridibundus population from Vadu area (Romania)
Pseudoscorpionidae (3.33%) and undetermined
Coleoptera s ( 3.33%).
In the case of the females the majority of the
taxons have terrestrial origin. Thus, we determined
terrestrial Heteroptera (4.84%), Lepidoptera larvae
(3.23%),
undetermined
Coleoptera
(9.68%),
Coleoptera Carabidae (3.23%) and Diptera Brahicera
(4.84%).
It is noticeable the appearance of larger preys in
the case of the females, such as Coleopteras,
Araneida, Isopoda, but also the presence of
Lepidoptera larvae. These are more profitable from
an energetic point of view. On the other hand, the
larvae are richer in lipide contents and thus have a
higher nutritive value (Brooks et al. 1996).
In the case of the males the terrestrial Crustacean
Isopoda have the highest frequency, which were
easily captured from the wet ares near the pond,
followed by the Arahnidae Araneidae, aquatic
Heteropteras, undetermined Coleopteras and
Coleopteras Carabidae, which have a lower
frequency.
In the case of the females first place is occupied
by the Arahnidae Araneidae, which are followed by
the undetermined Coleopteras and the terrestrial
Heteropteras. The Crustacean Isopoda have a very
low frequency rate. This fact presents great interest
because of the first place held by them in the case of
the amount of taxons. They were consumed in a
23
large quantity only by certain individuals from the
population, and the spiders are available for a larger
number of frogs, but in a smaller amount.
In the case of the juveniles the situation is
simmilar to that of the adults, thus in the first place
one can find the Arahnidae Araneidae, followed by
the undetermined Coleopteras, the Nematocera
Diptera and the aquatic Heteropteras.
The Arahnidae Araneidae have the highest value
in the case of the females, 72.7%. The same category
holds first place in the case of the juveniles, 86.7%
and the terrestrial Crustacean Isopoda in the case of
the males, 83.3%.
In the third place we can find the terrestrial
Crustacean Isopoda with a relatively high
frequency, 37.2%, followed by the aquatic
Heteropteras, 25.6%, terrestrial Heteropteras, 23.3%,
Coleopterae Carabidae, 20.9%.
The relation between the frequency and the
amount of the prey taxa emphasizes an almost
homogeneous distribution of the trophic resources,
which are relatively abundant in the habitat and are
accesible for most of the individuals, and the fact
that they don't select a certain prey taxa, but the
most abundant one.The high value of both the
frequency and the amount of the same taxa
indicates that the whole population depends on the
same feeding resources (Cogălniceanu et al. 2000b).
Table 1. The total number of prey and the average number of prey/individual,
the amount of the aquatic and terrestrial prey, the frequency of the vegetales and shed-skin
Males
Females
Juveniles
The total no. of prey/individual
60
186
84
The average no. of prey/individual
10
8.45
5.6
% aquatic prey
35.01
20.97
17.85
% terrestrial prey
65.01
79
82.16
vegetales
100
63.6
60
shed-skin
16.7
9.09
13.3
Herpetol. Rom, 2, 2008
David, A. et al.
24
Table 2. The amount prey taxa in the case of the males, females and juveniles
Males
Females
Juveniles
Gasteropode-melci(t)
1.67
2.69
-
Gasteropode-melci(a)
25
0.54
-
Crustacee-Gamaride
-
4.3
8.33
Crustacee-Izopode(a)
-
7.53
1.19
Crustacee-Izopode(t)
25
27.4
10.7
3.33
-
-
Arahnide-Acarieni
-
-
1.19
Arahnide-Araneide
20
17.7
29.8
Colembole
-
0.54
2.38
Heteroptere(a)
5
2.69
4.76
Heteroptere(t)
-
4.84
2.38
Homoptere-Afidine
-
-
1.19
Lepidoptere (L)
1.67
3.23
2.38
Coleoptere-Dytiscide
1.67
5.91
1.19
Coleoptere-Dytiscidae (L)
1.67
-
-
Coleoptere-nedet.
3.33
9.68
13.1
Coleoptere-Carabide
6.67
3.23
1.19
Coleoptere-Coccinelide
1.67
-
-
Coleoptere-Curculionide
-
1.08
-
Coleoptere-Scarabeide
-
0.54
-
Coleoptere-Stafilinide
-
1.61
1.19
1.67
-
2.38
Diptere-Nematocere
-
1.08
8.33
Diptere-Brahicere
-
4.84
7.14
1.67
0.54
1.19
Arahnide-Pseudoscorpionide
Diptere-Nematocere (L)
Hymenoptere-Formicide
As far as the origin of the environment of the
prey is concerned, we can observe that most of the
prey have a terrestrial origin, despite the fact that
this species is considered to be the most aquatic of
the Ranide (Fuhn 1960). The capturing of the prey is
not necessarely made from the terrestrial
environment, these being accesible from the plants
on the water, or even from the lustre of the water, or
from its shores. In our study, the amount of the prey
taxa is high in the cases when they are accesible
from the plants (Araneida, Curculionidae). The
Herpetol. Rom, 2, 2008
majority of terrestrial prey has been observed in
other populations of Pelophylax ridibundus (Cicek &
Mermer 2006, 2007). The males are those that
consumed a larger amount of aquatic prey, 35.01%,
this fact is due to the high value of aquatic
Gasteropodes, which have been swallowed by
these.
The differences that appear in the feeding rate of
the males, females and juveniles of Pelophylax
ridibundus, indicate a more intensive feeding in the
case of the females, respectively a higher fluctuation
The analysis of the trophic spectrum of a Pelophylax ridibundus population from Vadu area (Romania)
of the prey taxa in their contents, in comparison to
the males and juveniles. This situation is due to the
fact that the females need more energy in the laying
of the eggs. Because of the larger body dimensions,
they can consume different types of prey. They also
have a higher mobility than the juveniles, which,
due to the smaller size are limited to the
consumption of prey of certain categories and
which don't have capturing strategies as performed
as the adults do.
Conclusions
The Crustacean Isopoda, Arahnidae, aquatic
Gasteropoda and Coleopteras represent the most
important prey taxa for the analysed population.
The composition of the food is influenced by the
environmental conditions, which can affect the
developing rate of the potential prey, thus
determining the constituing elements of the trophic
spectrum of the analysed population. The
similarities of the males, females and juveniles
trophic spectrum indicate that the lake frog has a
time-serving method of feeding, capturing the most
abundant preys from the habitat.
With regards to the origin of the prey taxa's
environment we established that the majority of the
studied individuals consumed terrestrial prey
captured from the surface of the vegetation, or from
the near-situated ares of the shore.
As a result of the study, we concluded that the
Pelophylax ridibundus population presents optimum
feeding conditions in this habitat.
Considering the fact that the habitat, from which
the studied individuals belong to, is situated near a
beach, the development of the turistic zones could
lead to the disappearance of the Amphibian
populated habitats, which will afterwards result in
the extinction of them, thus studies dedicated to the
analysis of the ecological requirements will help in
understanding the necessities that they have, in
order to ensure a lasting development.
25
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