DISCUSSION
The results of the present study indicate a high
probability of competition for calling or prey-am-
bushing perches (but see below) and a relatively low
probability of competition over food between D. mi-
crocephalus and S. vigilans at the study site. Both spe-
cies use emergent plants and show identical vertical
distribution. The species share approximately 42% of
the prey categories identified (15 out of 36) but their
relative importance varies between them; the most im-
portant categories in one species are usually amongst
the least important in the other. In D. microcephalus,
arachnids of Agelenidae and dipterans of Thachinidae
are the most important (RII ≈ 10%), while the most
important prey in S. vigilans are orthopterans of the
family Grillydae. Our results contrast with those of
Muñoz-Guerrero et al. (2007) with regards to micro-
habitat use and diet composition; we discuss potential
factors favoring the differences between studies.
At our study locality, we found total micro
spatial overlap between D. microcephalus and S. vigi-
lans; both species occupy the same type of perch and
their vertical distribution coincides. We often found
individuals of both species on the same plant sepa-
rated by as much as 20 cm, as well as on neighboring
plants less than one meter apart. In addition, during
the study season, the abundance of both species (esti-
mated from acoustic surveys and captures) was simi-
lar, despite the fact that D. microcephalus has often
been regarded as more abundant than S. vigilans (S.
Boher, pers. comm.). While habitat use suggests high
potential for space competition between these spe-
cies, we do not take this for granted because competi-
tion depends on resource abundance (Pianka, 1994)
and nightly activity rhythms. If suitable perches are
abundant and/or their activity patterns are disjointed
(within the night and/or along the season), both spe-
cies might coexist without major interference. We did
not estimate perch abundance in relation to popula-
tion numbers, but qualitatively, at the height of the
rainy season, emergent vegetation formed a con-
tinuous cover along the lagoon margins; thus calling
perches did not seem to be limited. Additionally, dur-
ing the study period we never observed any type of ag-
gressive interaction (vocal or physical) between D. mi-
crocephalus and
S. vigilans. We believe that acoustical
cues may help to avoid direct interspecific encounters
and maintain interindividual distances much as it has
been demonstrated in intraspecific spacing (Whitney
& Krebs, 1975; Wilczynski & Brenowitz, 1988). We
understand, however, that our characterization of the
microhabitat was not detailed enough because we did
not identified plants to species level, or estimated the
size and shape of the leaves and stems. For instance,
Jiménez & Bolaños (2012) found similitude in mi-
crohabitat use between D. ebraccatus and D. phlebodes
but they detected microhabitat segregation when they
considered other more specific variables such as leaf
size and shape (long-thing, short-wide) and plant type
(herb, sedge, shrub, vine).
Our results contrast with those of Muñoz-Guer-
rero et al. (2007), who found some evidences of spatial
segregation between D. microcephalus and S. vigilans
at a locality in a dry forest in Colombia; while both
species preferentially perched from 40-50 cm above
shallow water, D. microcephalus preferred herbaceous
plants whereas S. vigilans preferred heliconias (al-
though it also used herbs). We propose that floristic
and physiognomic differences between sites (Colom-
bia and Venezuela) may explain these differences.
Nevertheless, the striking differences in microhabitat
species-segregation between our study and that of Mu-
ñoz-Guerrero et al. (2007) identify the need of more
extensive studies encompassing more habitat and mi-
crohabitat types to better understand potential space
interactions between D. microcephalus and S. vigilans.
While the microhabitat-niche dimension of
D. microcephalus and
S. vigilans at our study locality
coincides, the food dimension differentiates. Both
species rely on arthropods, but at the taxonomic level
TABLE 3:
Comparison of the diet of of Dendropsophus microcephalus
and Scarthyla vigilans at two localities: La Guáquira (Venezuela, this
study) and El Botillero, Colombia (Muñoz-Guerrero et al., 2007)
based on RII (%). RII for El Botillero were calculated from data
shown in Table 1. pp 420, Muñoz-Guerrero et al. (2007). Other
includes unidentified items and larvae. “?” indicates incomplete
data not allowing calculation. RII > 15% are shown in bold.
Order
D. microcephalus
S. vigilans
This study El Botillero This study El Botillero
Acari
1.46
Araneae
26.56
17.74
11.02
24.37
Collembola
10.62
Coleoptera
14.41
15.68
3.56
11.51
Dyctioptera
6.1
19.80
Diptera
15.68
16.55
10.60
4.21
Hemiptera
?
5.54
4.87
Homoptera
15.79
27.67
Hymenoptera
5.28
9.52
3.64
19.07
Lepidoptera
10.26
10.31
Neuroptera
6.31
Mantodea
?
Orthoptera
5.93
10.31
22.95
16.68
Psocoptera
?
Isopoda
4.7
Other
2.64
8.66
Fonseca-Pérez, K.A.
et
al
.: Diet and microhabitat Hylinae
100