Variation in diet of hatchlings, juveniles and sub-adults of Caiman crocodilus chiapasius in La Encrucijada, Chiapas, Mexico

Abstract

Little is known about the diet of the Chiapas spectacled caiman, Caiman crocodilus chiapasius (Bocourt, 1876), in the southern coast of Mexico. Herein, we analyzed the stomach content of 44 caimans divided into 3 size classes in La Encrucijada, Chiapas, Mexico. Within the contents we identified insects, crustaceans, arachnids, fishes, and birds. Hatchlings fed mainly on insects and arachnids, juveniles on crustaceans and insects and sub-adults on crustaceans and fish. Our data show that while the invertebrate intake decreased along different size classes, vertebrates intake increased, and that diet overlapped greater in adjacent size classes. No differences were found in niche breadth (p > 0.05), diet composition (Q = 2.0, p = 0.3678) and prey abundance (X 2 = 1.9756, p = 0.3759) among size classes. Caiman crocodilus chiapasius is protected by the Mexican law in the category of "special protection". ResumenPara entender la dieta del caimán de anteojos de Chiapas Caiman crocodilus chiapasius (Bocourt, 1876) en la costa sur de México, analizamos el contenido estomacal de 44 caimanes de 3 clases de tamaño en La Encrucijada, Chiapas, sur de México. En los contenidos, identificamos insectos, crustáceos, arácnidos, peces y aves. Las crías se alimentaron principalmente de insectos y arácnidos, los juveniles de crustáceos e insectos, y los subadultos de crustáceos y peces. Nuestros resultados muestran que mientras le ingestión de invertebrados disminuye con el aumento del tamaño de los individuos, la ingestión de vertebrados se incrementa y que el solapamiento de dietas es más importante entre clases de tamaño adyacentes. No encontramos diferencias entre clases de tamaño a nivel de ancho de nicho (p > 0.05), composición de dieta (Q = 2.0, p = 0.3678) y abundancia de presa (X 2 = 1.9756, p = 0.3759). Caiman crocodilus chiapasius está catalogado como especie con protección especial por la ley mexicana.Palabras clave: Caimán; Dieta; Desarrollo; Nicho alimenticio G.J. Soria-Ortiz et al. / Revista Mexicana de Biodiversidad 91 (2020): e912852 2 https://doi.

Sources of intraspecific variation in the isotopic niche of a semi-aquatic predator in a human-modified landscape

“…Caimans have a well-documented ontogenetic dietary shift ( Da Silveira & Magnusson, 1999 ; Magnusson, Da Silva & Lima, 1987 ; Thorbjarnarson, 1993 ). There is a significant change in the prey types and sizes with increasing body size in crocodilians ( Grigg & Kirshner, 2015 ; Radloff, Hobson & Leslie, 2012 ; Thorbjarnarson, 1993 )—for instance, from 85 g in hatchlings to 20 kg in our study, but with some conventional dietary studies reporting a high niche overlap of prey items among size classes (through prey diversity indexes) that indicates some degree of intraspecific competition ( Soria-Ortiz, Charruau & Reynoso, 2020 ). Alternatively, isotopic studies show niche divergence through ontogenetic variation along stable isotopes or in the isotopic niches ( Adame et al, 2018 ; Caut et al, 2019 ; Marques et al, 2013 ; Radloff, Hobson & Leslie, 2012 ).…”

“…Further, juveniles demonstrated remarkable plasticity by occupying a substantial isotopic niche space. Considering that food type intake relates to prey available as the habitat and season ( Magnusson, Da Silva & Lima, 1987 ; Soria-Ortiz, Charruau & Reynoso, 2020 ; Thorbjarnarson, 1993 ), differences in the isotopic niches of size classes indicate that caimans are partitioning food resources with distinct isotopic composition on a habitat or microhabitat scale ( Marques et al, 2013 ). Factors of hierarchical social organization and agonistic behaviors driven by body size can influence movements and home ranges in crocodilians ( Grigg & Kirshner, 2015 ).…”