Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, predator-prey size ratios (PPSRs) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from optimal foraging theory. We analyzed >6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.

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Species of Temnomastax have wide morphological similarities, and differentiation is usually based on male and female genitalia. In this study, we tested whether morphometric differences contribute to differentiation of species of Temnomastax, proposed an identification key for males, and morphometrically studied the sexual dimorphism of Temnomastax hamus and Temnomastax ricardoi. Analysis was performed using 204 specimens belonging to six species; fifteen morphometric variables were used. We used MANOVA and ANOVA to test the morphometric differences among species and Discriminant Analysis for sexual distinction. Temnomastax sp. nov. 1 had the highest values in ⅓ of all analyzed variables used for morphometric distinction of males, followed by Temnomastax latens, T. ricardoi and Temnomastax sp. nov. 2, and T. hamus and Temnomastax tigris. Two groups were formed by the MANOVA, with length of body, length of hind femur, and length of tegmen as the main variables that distinguished them. Overall, females of T. hamus and T. ricardoi presented higher averages for measurement values used in morphometric distinction between sexes than conspecific males and based on discriminant analysis we found significant differences between sexes. There are significant differences in morphometric variations and the ratio between body length and tegmen length provided reliable evidence for differentiation among species, which can be used as a valid tool that complements the identification of Temnomastax species.

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Three species of Conocephalus and two of Euxiphidion from several localities of the Central-West Region of Brazil were studied. Conocephalus goianus Piza, 1977, C. saltator (Saussure, 1859) and C. versicolor (Redtenbacher, 1891) are recorded for the first time from Mato Grosso do Sul, one new species Euxiphidion veroni sp. nov. is described, and a new combination, Euxiphidion caizanum comb. nov. is proposed. The calling songs of C. saltator, C. versicolor, and E. veroni sp. nov. are described. All these three species call very continuously, also in the daytime. The three species of Conocepha-lus have mitotic metaphases with 2n♂ = 33 = 32 + X and 2n♀ = 34 = 32 + XX. Euxiphidion caizanum comb. nov. and    E. veroni sp. nov. have 2n♂ = 31 = 30 + X and 2n♀ = 32 = 30 + XX. Most of the autosomes of C. saltator and C. versicolor are meta/submetacentric, differing from C. goianus that has seven biarmed and nine monoarmed autosomes. Both Euxiphidion species present mostly telo/subtelocentric autosomes. The X chromosome is metacentric, and the largest element of the karyotype in the five species. No interstitial telomeric site (ITS) was observed in mitotic metaphases submitted to telomeric fluorescent in situ hybridization. Ecological aspects of the studied species are discussed.