Moon phases influence encounters of anurans in the Brazilian semi-arid region of Piauí
Description
The lunar cycle is associated with the behaviour of amphibians, influencing vocalization, reproductive behaviours, and environmental choices. In the present work, we aimed to answer some questions regarding the influence of lunar phases and their interference with the behaviours of semiarid anuran species in Piauí, Brazil. The work was carried out in the municipality of Floriano (S 6°30’; W 43°42’), and an active search was carried out for the inventory, with weekly campaigns from June 2018 to June 2019. The days were transformed into Julian days, and the sampling corresponding to 365.25 Julian days were transformed into degrees (Julian Day*360/365). The absolute occurrence by species was classified as constant, accessory, and accidental. In the circular statistics the Rayleigh test (Z) was applied to verify that there is no randomness, with the sample being considered unidirectional if the calculated interval corresponds to z≥z (α) and P=0.01. Sample sufficiency was estimated using the RAO’S (U) spacing test, with the value considered random when U<U (α) and P= 0.01. During the 13 months of sampling, 1,921 individuals were recorded in 12 species. Rhinella diptycha was the species with the highest record (constant species), and Physalaemus albifrons was the one with the lowest record of occurrence (accidental species). It was possible to deduce that most of the species (60%=6 of 10 species evaluated) present a greater occurrence between 270°–0°–90°, that is, the lunar albedo with less clarity. Four species were considered constant; two were considered accessory species and six, species with accidental occurrence. Studies with the lunar synodic cycle are important, as they help to understand the mechanisms of interaction between anuran species and the environment.
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Statistical and ecological analyses Uniformity and accuracy of the sample period The days were transformed into Julian days using the formula: Julian Days = Day-32075+1461*(Year+4800+(Month-14)/12)/4 + 367*(Month-2-(Month-14)/12*12)/12-3*((Year+4900+(Month-14) /12)/100)/4, where day is 1 to 31, Month is 1 to 12, and Year is 1,801 to 2,099. In this way, the days were considered as intervals from noon until the subsequent noon, disregarding time intervals of weeks, months, and years. Thus, the sampling corresponded to 365.25 Julian days. The Julian day values were transformed into degrees (Julian Day*360/365) (Costa, 2000). Absolute and relative frequencies The absolute frequency of individuals per sampling period was recorded, and the relative frequency of individuals was calculated using Prevalence, which consisted of P=(n/N) *100, where the n=number of specimens found and N = total number of species (Neto, 1976; Lima et al., 2022). Constancy To calculate Constancy, the absolute values of specimens and species were submitted to the formula C=p*100/N, where p = number of samples containing the species and N= total number of samples, these classified as C=>50% – Constant, C=25–50% – Accessory and C=<25% –Accidental (Neto, 1976). Frequency polygon The Frequency Polygon was established through the absolute frequency of specimens per species to the lunar synodic cycle to demonstrate the effects between linear interpretation and circular analysis of sample occurrence (Zar, 2010). Circular statistics The zero azimuth was the new moon, the angular direction being clockwise in the module, the mean vector (μ) was established through the mean location of the peak occurrence of the anuran species to the lunar influence, the length of the mean vector (r) was calculated to determine the direction of unidirectionality. The Rayleigh test (Z) was applied to verify that there is no randomness causing bias, with the sample being considered unidirectional if the calculated interval corresponds to z≥z (α) and P=0.01. Sample sufficiency was estimated using the RAO’S (U) spacing test, with the value considered random when U<U (α) and P= 0.01. If there is not enough data to meet the corollary of the test, the sample is considered insufficient (IS). To develop the tests, we used the ORIANA 4.02 program (Batschelet, 1981; Jammalamadaka, 2001).