Diet of Leptodactylus ocellatus

Herpetology Notes, volume 2: 9-15 (2009) (published online on 16 February 2009)
Diet of Leptodactylus ocellatus (Anura: Leptodactylidae) from a
cacao plantation in southern Bahia, Brazil
Mirco Solé1*, Iuri R. Dias1, Erika A. S. Rodrigues1, Euvaldo Marciano-Jr1, Samuel M. J. Branco1, Kaoli P.
Cavalcante1 and Dennis Rödder2,3
Abstract. We studied the diet of Leptodactylus ocellatus in a cacao plantation in southern Bahia state, Brazil and compared our
results with data available from populations inhabiting natural and human modified habitats. Stomachs of 117 specimens were
flushed whereby 77 stomachs revealed at least one prey item. Our results indicate that L. ocellatus consumes a great variety of
food items at the study site, whereby Lepidoptera larvae, Coleoptera and Araneae dominated its diet. The presence of vertebrates
including Teleostei and Anura in the diet revealed in previous studies was confirmed, although these items made up only minor
parts of the diet. The index of relative importance showed that the diet of L. ocellatus was dominated by Lepidoptera larvae,
followed by Coleoptera and Araneae. The Levins index observed in our samples was 8.51 and the standardized Shannon-Weaver
index was 0.56. Apparently, the structure of the trophic niche of L. ocellatus is not affected by habitat alteration. The present study
provides evidence for the opportunistic feeding behaviour and broad trophic niche breadth of L. ocellatus.
Keywords. Amphibia, diet, trophic niche, cacao plantation, predation.
Introduction
Trophic interactions are a crucial component of life
history strategies and contribute to the population
regulation (Duellman and Trueb, 1994; Wells, 2007).
In the Neotropics, habitat loss is still the primary
threat to amphibian populations (Young et al., 2001;
Stuart et al., 2004). Other indirect effects associated to
landscape fragmentation may cause alteration of trophic
interactions, due to changes in microclimate, causing
abundance variations in available prey items, what
might contribute to the decline of amphibians (Carey et
al., 2001; Young et al., 2001). A profound knowledge
about trophic relationships in tropical communities is
essential for the development of successful conservation
strategies. An assessment of possible shifts in trophic
niches of species inhabiting natural and human altered
habitats is currently lacking for the vast majority of
anuran taxa.
The family Leptodactylidae is distributed from the
extreme southern USA throughout tropical Mexico,
Central America and South America (Frost et al., 2006),
1 Department of Biological Sciences, Universidade Estadual
de Santa Cruz, Rodovia Ilhéus-Itabuna, km 16, 45662-000
Ilhéus, Bahia, Brazil; e-mail: [email protected]
2 Zoological Research Museum Alexander Koenig, Department
of Herpetology, Adenauerallee 160, 53113 Bonn, Germany
3 Trier University, Department of Biogeography, 54286 Trier,
Germany
* corresponding author
whereby the genus Leptodactylus currently comprises
76 species mainly distributed in South America (Frost,
2008). Compared to other members of the genus,
Leptodactylus ocellatus (Fig. 1) is a large nocturnal frog,
which is widely distributed throughout South America
east of the Andes (Cei, 1980). The species inhabits all
varieties of ponds, rivers and even lakes and can often
be found in strongly anthropogenized areas. Heyer,
Caramaschi and de Sá (2006) recently designated a
neotype for this species and stated that there are both
reproductive and molecular differences that suggest the
presence of more than one species under the name L.
ocellatus.
Regarding L. ocellatus, previous studies have mainly
dealt with growth, reproductive (Vaz-Ferreira and
Gehrau, 1975), behavioral aspects (Strüssmann et al.,
1984), food habits of tadpoles (Lajmanovich, 1994) and
juveniles (Lajmanovich, 1996). The diet of L. ocellatus
has been studied in several Neotropical countries
(Strüssmann et al., 1984; Teixeira and Vrcibradic, 2003;
França, Facure and Giaretta, 2004; Maneyro et al., 2004;
Sanabria, Quiroga and Acosta, 2005) and in several
populations the species has been found to be a potential
predator of amphibians (Teixeira and Vrcibradic, 2003;
França, Facure and Giaretta, 2004; Sanabria, Quiroga
and Acosta, 2005).
Our study provides data on the diet of L. ocellatus from
a cacao plantation in southern Bahia. We report some
prey categories that have not been previously identified
as part of the frog’s diet and we discuss our data with
10
available data from both natural and human modified
habitats in Uruguay, Peru, the Brazilian Pantanal and
the Brazilian states of Espírito Santo, Minas Gerais and
Rio Grande do Sul.
Material and methods
Sampling
Frogs were collected manually from December 2006 to April
2007 at night (from 20:00 to 22:00) near a temporary pond (Fig.
2A) and a small stream (Fig. 2B) in a cocoa plantation (5 ha),
which is located behind the campus of the Universidade Estadual
de Santa Cruz (14°47’45’’S, 39°10’20’’W), municipality of
Ilhéus, southern Bahia, Brazil. In the cacao plantations of
southern Bahia the shelter of trees of the original Atlantic
rainforest vegetation is used to shade the cacao trees. This
shading allows the plantation to conserve similar humidity
indexes as the less impacted Atlantic forest patches. Faria et
al. (2007) found these plantations to harbor over 81% of the
amphibian diversity found in not anthropogenized forests.
Frogs were captured and transferred to the nearby laboratory.
Snout-vent length (SVL; to nearest 0.1 mm) and mouth width
(MW) were measured using a digital caliper. Body mass
(BM; to nearest 0.1g) was recorded using a digital balance.
Each frog’s stomach was flushed following the methodology
proposed by Solé et al. (2005) and specimens were released at
the capture site during the same night, about two to four hours
after having been captured. Stomach contents were transferred
Figure 1. Leptodactylus ocellatus, adult female.
Mirco Solé et al.
to vials, fixed in 70% ethanol and later analyzed under a
stereomicroscope. Prey items were classified following order
level, with exception of Hymenoptera, which were classified
as Formicidae and Non-Formicidae. Completely preserved
items were measured and had their volume calculated using
V
4S L § W ·
¨ ¸
3 2© 2 ¹
2
the formula for ellipsoid bodies (Griffith and Mylotte, 1987):
with L = prey length and W = prey width. If partially digested
body parts were retrieved, the regression formulae proposed
by Hirai and Matsui (2001) were used to estimate the original
prey size, followed by the volume calculation using the above
mentioned formula. For regression analyses XLSTAT 2008
(www.addinsoft.de) was used. To meet statistical assumptions
prey volume was log+1 transformed (Zar, 1999). �������������
The index of
relative importance (IRI) was applied as a measure that reduces
bias in description of animal dietary data. It was introduced
by ������������������������������������������������������
Pianka, Oliphant and Iverson (1971)�������������������
and Pianka (1973):
IRI t
( POt )( PI t PVt )
where POt is the percentage of occurrence (100 x number
of stomachs contained t item / total number of stomachs),
PIt is the percentage of individuals (100 x total number of
individuals of t in all stomachs/total number of individuals of
all taxa in all stomachs), and PVt is the percentage of volume
(100 x total volume of individuals of t in all stomachs/total
Diet of Leptodactylus ocellatus from Southern Bahia, Brazil
volume of all taxa in all stomachs). In order to compare
the trophic niche breath the standardized Shannon-Weaver
entropy index J was used (Weaver and Shannon, 1949):
J
H
log(n)
whereby,
H ¦ pi log( pi )
pi is the relative abundance of each prey category, calculated
as the proportion of prey items of a given category to the total
number of prey items (n) in all compared studies. To calculate
the trophic niche breadth, the Levins index (B) was used (Krebs,
1989):
1
B
¦ pi2
where pi = fraction of items in the food category i; range = 1 to
N.
Results
A total of 117 frogs were captured including
predominately adult and subadult specimens measuring
from 32.01 mm to 142.29 mm SVL (mean ± SD 91.33
± 15.05 mm; Fig. 3) and with a weight of 8.27–159.25
g (mean ± SD 85.63 ± 31.35 g). Mouth width measured
13.99 to 38.52 mm (mean ± SD 30.60 ± 4.33 mm).
Data on the diet of L. ocellatus at the study area are
11
summarized in Table 1. A total number of 77 stomachs
revealed at least one prey item and 38 stomachs were
empty. The mean number of prey items per stomach
was 7.52 ± 9.46 (min= 1; max= 44). Volume of prey
items ranged from 1.02 – 25481.11 mm3 (mean ± SD
634.56 ± 2915.79 mm3). Most frequent prey items
were Lepidoptera larvae (N= 304, N%= 53.52),
followed by Araneae (N= 39, N%= 6.87) and Diptera
larvae (N= 35, N%= 6.16). Regarding the frequency
of occurrence, Lepidoptera larvae, Araneae, and
Coleoptera were most important (each F= 21, F%=
27.27). Lepidoptera larvae (V= 113317.7 mm3, V%=
63.15), Coleoptera (V= 16492.2 mm3, V%= 9.19) and
Hemiptera (V= 13291.3 mm3, V%= 7.14) resulted
to be the most important prey categories in terms of
volume. The index of relative importance showed that
the diet of L. ocellatus was dominated by Lepidoptera
larvae (IRI = 3182.07), followed by Coleoptera (IRI
= 394.72) and Araneae (IRI= 276.53). S�������������
imple linear
regression analyses revealed no significant relationships
between SVL or mouth width of L. ocellatus and
prey volume, minimum lengths of prey items and
maximum length of prey items in our study (Fig. 4).
The Levins index observed in our samples was 8.51
and the standardized Shannon-Weaver index was 0.56.
Figure 2. Study site. Temporary pond (A) and small stream (B), where specimens of Leptodactylus ocellatus were collected.
12
Discussion
Our sample was biased toward adults, which were
frequently found on the margins of the temporary pond
and the small river in open areas as well as in denser
vegetation, whereas juveniles were rare suggesting
microhabitat segregation between adults and juveniles.
A similar observation was reported from a pit fall
survey in Uruguay, where most of the juveniles of L.
ocellatus were found far away from ponds (Maneyro,
pers. comm.).
Dietary composition as observed in our study was
similar to those reported for conspecific populations by
Stüssmann et al. (1984)
�������������������������������������
������������������������������
in Pará (Brazil), Lajmanovich
������������
(1996) in Paraná (Argentina), Teixeira and Vrcibradic
(2003) in Espírito Santo (Brazil), França,
�������������������
Facure and
Giaretta (2004) in Minas Gerais (Brazil), �����������
Maneyro et
al. ����������������������������������������������
(2004) in Maldonado Department (Uruguay), and
Sanabria, Quiroga and Acosta (2005) in east Argentina
where Coleoptera, Formicidae, Araneae and Orthoptera
made up major parts, and small percentages of ingested
vertebrates were also found. Presence of vertebrates in
the diet of anurans is mainly restricted to large species
and was previously reported for several Leptodactylus
species including L. labyrinthicus (Cardoso and
Sazima, 1977; França, Facure and Giaretta, 2004), L.
wagneri (Duellman, 1978), and L. chaquensis (Duré,
1999) besides L. ocellatus. Teixeira and Vrcibradic
Mirco Solé et al.
(2003) found, respectively, one specimen of the anurans
Hypsiboas albomarginatus, Leptodactylus ocellatus and
Physalaemus crombiei and one fish (Poecilia vivipara)
ingested by specimens of L. ocellatus studied in Espírito
Santo, Brazil. Maneyro et al. (2004) detected three
anuran specimens ingested by Uruguayan L. ocellatus,
França, Facure and Giaretta (2004) found adult anuran
specimens (each one Leptodactylus funarius, Rhinella
granulosa and one unidentified hylid) and tadpoles in
stomachs of L. ocellatus at Minas Gerais, and Sanabria,
Quiroga and Acosta (2005) found six bufonids in
stomach contents of Argentinean specimens. All studies
revealed that vertebrates commonly make up only minor
parts of the diet of L. ocellatus.
Terrestrial invertebrates usually dominate the diet of
most anurans, even in those species which are aquatic or
semiaquatic (e.g. Hirai and Matsui, 2001; Stewart and
Sandison, 1972). However, the presence of completely
aquatic organisms such as belostomatid beetle (Teixeira
and Vrcibradic, 2003), fishes and tadpoles (França,
Facure and Giaretta, 2004; Teixeira and Vrcibradic,
2003; this study) in the diet suggest that L. ocellatus
occasionally forage in the water and might be even
capable of capturing prey under water as reported for
one other neotropical frog (Solé and Miranda, 2006).
The presence of decapod crustaceans as stomach
content observed during our study is another hint for
Figure 3. Relative frequency of SVL classes in Leptodactylus ocellatus.
13
Diet of Leptodactylus ocellatus from Southern Bahia, Brazil
Table 1. Prey types consumed by Leptodactylus ocellatus (N= 117) from a cacao plantation in southern Bahia, Brazil. N= number
of prey items; N%= percentage of total number; F= frequency of occurrence; F%= relative frequency of occurrence; V= volume
in mm3; V%= relative volume in mm3; IRI= index of relative importance.
Prey items
Annelida
Mollusca
Oligochaeta
N
N%
F
F%
V
V%
IRI
3
0.53
1
1.30
1547.43
0.86
1.81
Bivalvia
1
0.18
1
1.30
27.91
0.02
0.25
Gastropoda
2
0.35
2
2.60
32.07
0.02
0.96
Crustacea
Decapoda
1
0.18
1
1.30
415.50
0.23
0.53
Arachnida
Acari
4
0.70
4
5.19
6.20
0.00
3.68
Araneae
39
6.87
21
27.27
5872.86
3.27
276.53
Opiliones
34
5.99
17
22.08
4966.85
2.77
193.27
Chilopoda
6
1.06
6
7.79
1817.31
1.01
16.12
Diplopoda
13
2.29
12
15.58
2396.84
1.34
56.49
394.72
Myriapoda
Insecta
Coleoptera
30
5.28
21
27.27
16492.24
9.19
Dermaptera
1
0.18
1
1.30
39.93
0.02
0.26
Diptera
6
1.06
3
3.90
189.12
0.11
4.53
Diptera Larvae
35
6.16
4
5.19
8059.32
4.49
55.34
Hemiptera
12
2.11
9
11.69
13291.25
7.41
111.28
Hymenoptera (Formicidae)
17
2.99
13
16.88
596.11
0.33
56.14
Hymenoptera (Non-Formicidae)
27
4.75
18
23.38
3275.38
1.83
153.79
Isoptera
13
2.29
3
3.90
909.82
0.51
10.89
4
0.70
4
5.19
432.94
0.24
4.91
304
53.52
21
27.27
113317.74
63.15
3182.07
Lepidoptera
Lepidoptera Larvae
Odonata
Orthoptera
1
0.18
1
1.30
2971.56
1.66
2.38
13
2.29
8
10.39
2165.12
1.21
36.32
Pisces
Teleostei
1
0.18
1
1.30
226.02
0.13
0.39
Amphibia
Anura (tadpole)
1
0.18
1
1.30
379.50
0.21
0.50
100
173
179429.02
100
4563.15
Plant Remains
Total
38
568
this sporadic feeding behavior. Decapods were not
previously reported as part of the diet in L. ocellatus.
Plant remains were detected in half of the examined
stomachs. The ingestion of plants is generally considered
accidental in anurans (Brandão et al. 2003; Solé and
Pelz, 2007), but folivory (Das, 1996) or frugivory
(�������������������������������������������������������
Silva and Britto-Pereira, 2006) have been reported for
a few species. During our studies we retrieved a seed
of a jack tree (Artocarpus heterophyllus) from one of
the examined frog stomachs. The seed measured 31.37
mm in length and 17.81 mm in width, and the mouth
width of the frog was 32.14 mm. Rotting jackfruits
are usually covered by a wide variety of arthropods,
and we do not know if the ingestion of this seed by the
frog was accidental while preying on the arthropods or
intentional.
Other studies reported that SVL and mouth width was
49.35
100
significantly correlated with prey size and volume
(França, Facure and Giaretta, 2004; Maneyro et al.,
2004). However, in our study simple linear regression
analyses revealed no significant relationships between
SVL or mouth width of L. ocellatus and prey volume,
minimum lengths of prey items and maximum length
of prey items in our study (Fig. 4). Since variation in
size was low in our sample (Fig. 3), it is likely that the
failure to detect significant relationships between SVL
(and mouth width) and prey size was caused by the high
proportion of adult specimens included. Maneyro et al.
(2004) and França, Facure and Giaretta (2005) sampled
frogs in different habitats including a higher proportion
of juveniles enhancing size variation.
The Levins index (8.51) observed in our samples was
most similar to those obtained from population of L.
ocellatus analyzed in a human altered lagoon in Espírito
14
Mirco Solé et al.
Figure 4. Simple linear regression analyses revealed no significant relationships between SVL and prey volume (log(Vol); R2= 0.000,
p= 0.970; 4A), maximum length of prey items (R2= 0.002, p= 0.747; 4B) and minimum lengths of prey items (R2= 0.012, p= 0.419; 4C)
and mouth width and prey volume (R2= 0.002, p= 0.704; 4D), maximum length of prey items (R2= 0.002, p= 0.718; 4E) and minimum
lengths of prey items (R2= 0.018, p= 0.326; 4F).
Santo (8.52, Teixeira and Vrcibradic, 2003), whereas
values in other studies were slightly lower (7.74,
França, Facure and Giaretta, 2004; 7.26,
����������������������
Maneyro et al.,
2004; 7.40, �����������������������������������������
Sanabria, Quiroga and Acosta, 2005�������
). The
standardized Shannon-Weaver index observed in our
study was 0.56. It was slightly lower than reported in
other studies (0.71, Teixeira and Vrcibradic, 2003; 0.74
França, Facure and Giaretta, 2004������������������������
; 0.66, Maneyro et al.,
2004; 0.63 Sanabria,
�����������������������������������������
Quiroga and Acosta, 2005�������
). The
observed differences may be attributed to differences in
body size and/or prey availability in the studied habitats.
However, the available data suggest that differences in
trophic niche breadth and prey diversity in the diet of L.
ocellatus inhabiting natural and human modified habitats
are small. �����������������������������������������������
Apparently, the structure of the trophic niche
of L. ocellatus is not affected by habitat alteration.
Acknowledgements
We are grateful to the Instituto Brasileiro do Meio Ambiente
e dos Recursos Naturais Renováveis (IBAMA) for issuing
necessary permits (No. 10830-1 (IBAMA-SISBIO) and
Licença permanente 13708-1 (ICMBio)). Raul Maneyro, Axel
Kwet and Vincenzo Mercurio kindly improved the manuscript
with many valuable suggestions. Work of IRD was funded by
FAPESB, EARS by ICB-UESC, EMJ by PIBIC-CNPq and DR
by “Graduiertenförderung des Landes Nordrhein-Westfalen”.
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