RESUMO
Invasions often accelerate through time, as dispersal-enhancing traits accumulate at the expanding range edge. How does the dispersal behaviour of individual organisms shift to increase rates of population spread? We collate data from 44 radio-tracking studies (in total, of 650 animals) of cane toads (Rhinella marina) to quantify distances moved per day, and the frequency of displacement in their native range (French Guiana) and two invaded areas (Hawai'i and Australia). We show that toads in their native-range, Hawai'i and eastern Australia are relatively sedentary, while toads dispersing across tropical Australia increased their daily distances travelled from 20 to 200 m per day. That increase reflects an increasing propensity to change diurnal retreat sites every day, as well as to move further during each nocturnal displacement. Daily changes in retreat site evolved earlier than did changes in distances moved per night, indicating a breakdown in philopatry before other movement behaviours were optimised to maximise dispersal.
Assuntos
Bufo marinus/fisiologia , Bufonidae/fisiologia , Espécies Introduzidas , Distribuição Animal/fisiologia , Migração Animal/fisiologia , Animais , Austrália , Ecossistema , Guiana Francesa , Havaí , Modelos Biológicos , Tecnologia de Sensoriamento RemotoRESUMO
Snakes of the tribe Dipsadini feed mostly on annelids, slugs, and snails. Some species that feed exclusively on snails are able to de-shell their prey prior ingestion. On the basis of dissection of preserved specimens from museums, we report the dietary habits of three species of Sibynomorphus from Brazil. Eighteen to 26% of the snakes had stomach contents, varying from 1-8 items, and the number of prey was not correlated with snake size. Prey mass was positively correlated with snake mass, but relative prey mass decreased with increasing snake size. Prey mass represented less than 5% of the predator mass for all species. Sibynomorphus neuwiedi and S. mikanii only had Veronicellidae slugs in their digestive tract, whereas S. ventrimaculatus also included snails in their diet. Sibynomorphus mikanii ingested most prey rear-first, but there was no difference in direction of prey ingestion by the other two species. Snake morphology differed among species and provided insights into habitat use and feeding habits. Sibynomorphus neuwiedi was the largest species and had the longest tail. Its eyes were also larger than those of S. mikanii, which, together with tail size, suggests more arboreal habits. Sibynomorphus ventrimaculatus had the largest head relatie to the body, which might facilitate ingestion of snails. In summary, the three species of Sibynomporphus are slug specialists. Like other goo-eaters, these snakes feed on very small and low caloric prey, which might require them to feed frequently. This hypothesis is supported by the larger number of prey ingested by these snakes compared to non-goo-eater species of Dipsadini.
RESUMO
Reproductive biology and food habits of Pseudoboa nigra (Serpentes: Dpsadidae) from the Brazilian cerrado. Herein we provide data on body size, sexual size dimorphism, reproductive cycle, and food habits of the pseudoboini snake Pseudoboa nigra, wich is dissections of 147 preserved specimens, it is shown that femmales attain, and mature at, larger body sizes than males. There is no significant sexual dimorphism in head lenght, but males have longer tails to their body sizes. Vitellogenesis, egg-laying, and sperm production occur throughout the year, but males do not exhibit long-term sperm storage. The main prey of P. nigra is lizards; there is no evidence of ontogenetic change or sex differences in the diet of this species.
Biologia reprodutiva e hábitos alimentares de Pseudoboa nigra (Serpentes: Dipsadidae) do cerrado brasileiro. Neste trabalho fornecemos informações sobre tamanho corporal, dimorfismo sexual, ciclo reprodutivo e hábitos alimentares da serpente Pseudoboini Pseudoboa nigra, que corre no domínio do Cerrado na região Central da América do Sul. Com base na dissecção de 147 espécimes preservados, mostramos que as fêmeas são em média maiores e atinguem maturidade sexual com maior tamanho corporal que os machos. O dimorfismo sexual não foi significativo para o tamanho da cabeça, mas os machos possuem caudas relativamente mais longas que as fêmeas. A vitelogênese, a postura de ovos e a espermatogênese ocorrem durante todo o ano, e os machos não armazenam esperma no ducto deferente por longos períodos. A principal presa dessa espécie são lagartos; não há evidencias de variação ontogenética ou de diferenças relacionadas ao sexo na dieta dessa espécie.
Assuntos
Masculino , Feminino , Animais , Caracteres Sexuais , Colubridae , Serpentes/classificação , América do Sul , Brasil , Dieta , ReproduçãoRESUMO
If selective forces on locomotor ability and reproductive biology differ among habitats, we expect to see relationships between habitat, morphology, and life-history traits. Comparative (phylogenetically based) analysis of data from 12 pythonid and 12 boid snake species reveals multiple evolutionary shifts in habitat use, notably in the evolution of arboreal habits. Compared to terrestrial and aquatic taxa of the same overall body size, arboreal species have narrower and more laterally compressed bodies and relatively longer tails. Offspring sizes are not affected by arboreality, but presumably reflecting space constraints within their narrow bodies, arboreal species (1) produce smaller clutch sizes relative to maternal body length and (2) have left and right ovaries that overlap little if at all along the length of the body (i.e., the right ovary is positioned anterior to the left ovary) whereas in terrestrial snakes the two ovaries overlap along much of their length. This modification of ovarian morphology in arboreal snakes presumably reduces the degree of bodily distension during vitellogenesis and pregnancy, thus enhancing climbing ability and camouflage among the branches.