Diet of Dendropsophus microcephalus and Scarthyla vigilans (Anura: Hylidae) at a locality in north-western Venezuela with notes on microhabitat occupation

ta) in northern Venezuela. The ranch spans through 

lowlands (100 masl) and hills (1,400 masl) and veg-

etation varies from mist-forest in the highlands to 

semi deciduous tropical humid forests at the lowlands 

of Cerro Zapatero (Runemark et al., 2005; Lotzkat, 

2007). Large areas of the lowlands have been turned 

into rice and corn fields and cattle ranching. We col-

lected the individuals in two lagoons arbitrarily labeled 

Lagoon A (10°17’49”N, 68°40’08”W; 3,392 m2) and 

B (10°17’46”N, 68°40’11”W; 12,155 m2 approx.) in 

the surroundings of crop and pasture fields.

Dendropsophus microcephalus (Cope, 1886) (Hy-

lidae: Hylinae) is a medium-sized (SVL males: 18-

25 mm; SVL females: 24-31 mm) nocturnal-arboreal 

frog (Duellman, 1970; Savage, 2002). The night col-

or of the dorsum is light yellow with various brown or 

tan markings; the daylight color is tan-yellow, or light 

brown with darker brown or red markings (Duellman, 

1970). The species ranges from Mexico to Peru, and 

in Venezuela it has an ample distribution in the low-

lands north of the Orinoco River (Barrio-Amorós, 

1998). It occupies open lowlands from natural savan-

nas to pasture lands holding ephemeral or long lasting 

ponds (Barrio-Amorós, 1998). During the reproduc-

tive season, males vocalize from emergent vegetation 

in shallow water (Tárano, 2010). The species has been 

labeled as least concern (Bolaños et al., 2008) in view 

of its wide distribution, tolerance of a broad range of 

habitats, presumed large population, and because it is 

not facing any known threats.

Scarthyla vigilans (Solano, 1971) (Hylidae: Hy-

linae) is a medium-sized nocturnal-arboreal frog (av-

erage SVL males: 15.6 mm; SVL females 19.5 mm). 

The dorsum is lime-green with poorly differentiated 

longitudinal stripes and transparent patches in vent 

(Barrio-Amorós  et  al., 2006). The species’ range is 

restricted to northern South America, specifically to 

Venezuela, northern Colombia (including the Mag-

dalena River basin) (Armesto et al., 2009) and Trini-

dad and Tobago (Smith, J.M. et al., 2011). It occupies 

lowlands below 100 masl. Male activity at the study 

site peaks in October (Lotzkat, 2007); calling activity 

peaks at night and it can also occur during the day 

(Lotzkat, 2007). The species has been also labeled as 

least concern (La Marca et al., 2004) because it is a 

very adaptable species, which is not facing any known 

threats.

Diet composition

We used visual and auditory surveys to find 

the individuals during nightly walks from 2000 to 

0000 hrs from July to September 2012. We captured 

the individuals by hand and immediately fixed each 

specimen in formalin 4% to stop digestion (Toft, 

1980a; Caldwell, 1996); we further preserved it in 

ethanol 70% until processed. In the lab, we measured 

the snout-to-vent length (SVL) and mouth width 

(from corner to corner, mouth closed) with a dial cali-

per (Kannon) to the nearest 0.1 mm, before dissecting 

the stomach. Each stomach was preserved in ethanol 

70% until further examination. We determined age 

class and sex by inspection on the gonads; individuals 

with developed gonads were considered adults, other-

wise they were classified as juveniles.

We observed the stomach contents under a ste-

reoscopic microscope (AmScope, Model SE306R-PZ-

E) at 20x, 40x and 80x. We identified prey items to 

the taxonomic level of order, class and family (which 

we called “prey categories”) through the taxonomic 

key developed by Smith, R. & Silva (1970). Then, we 

measured the maximum length and width of all items 

on each prey category with a “hair count” stereoscopic 

microscope to the nearest 0.01 mm. With these mea-

sures we calculated the volume of each prey item by 

using the equation of a prolate spheroid

where l represents the maximum length of the item 

and w its maximum width (Vitt, 1991). Prey volume 

is a gross estimator of the energetic contribution of an 

item (Caldwell, 1996). Broken or partially digested 

items were not measured.

We determined the number of items per prey 

category (Ni), the proportion of non-empty stomachs 

which contained a given category (Fi) and the vol-

ume of each category per stomach (Ni x Vi). With 

these values we estimated the diet richness (number of 

prey categories), diet diversity through the Shannon-

Wiener index

where p

i

 corresponds to the proportion of prey i in 

number, equitability through the Alatalo index (Ala-

talo, 1981)

where

Papéis Avulsos de Zoologia, 57(7), 2017

95

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and

with

the absolute importance index

where

(S means stomach), the niche breath per species 

through the standardized Levins’ index (Levins, 1968)

with the standardization proposed by Hurlbert (1978)

where  n is the number of possible states of the re-

source, and the diet overlap between S. vigilans and 

D. microcephalus through the Pianka’s index (Krebs, 

1999)

where Px,i and Py,i are the frequencies of the i-esim 

category in species x and y, respectively. All these in-

dexes with the exception of H’ vary between 0 and 1.

Microhabitat occupation

We performed visual and acoustic surveys in 

both lagoons by slowly walking amidst vegetation, 

around and within the lagoons at night. For each in-

dividual found, we recorded the horizontal distance 

to the water (in case of being located in the lagoon 

margins), substrate type (emergent vegetation, float-

ing vegetation, soil), plant type (Monocotyledoneae, 

Dicotyledoneae), perch type (leaf, stem, stone), and 

perch height above water or soil. Form these measures 

we estimated vertical and horizontal segregation be-

tween species and segregation by perch type.

Statistical Analysis

We determined the association between SVL and 

mouth width within species through the Spearman 

rank correlation coefficient. Then, we determined the 

association between mouth width and prey length or 

volume (log transformed) within species (Spearman 

rank correlation coefficient). We also compared prey 

size and stomach volume between species through the 

Mann-Whitney U test (Zar, 1999).

We performed a Principal Components Analysis 

(PCA) to explore diet segregation between species. In 

addition, we compared the Shannon-Wienner index 

between species through the Hutchenson t (Hutch-

enson, 1970) as:

where

and S is the variance of H for each species, estimated as

where fi corresponds to Ni. The degrees of freedom of 

t were estimated through

To determine microhabitat preferences we used 

the 

χ2 test (Zar, 1999) and the standardized residuals 

analysis in case we found significant associations (i.e., 

species x distance to water, species x perch type or spe-

cies x perch height). We used PAST 2.17 (Hammer 

et al., 2001) and Statistica 6.0 to perform the statisti-

cal analyses

RESULTS

Morphometry and Diet Composition

We collected 209 individuals, 99 individuals of 

D.  microcephalus (88 males, 6 females, 5 juveniles) 

and 110 individuals of S. vigilans (68 males, 38 fe-

males, 4 juveniles.). In both species, females were 

larger than males (SVL: D.  microcephalus, males: 

Fonseca-Pérez, K.A. 

et

 

al

.: Diet and microhabitat Hylinae

96

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