Effects of Urbanization on Bothrops jararaca Populations in São Paulo Municipality, Southeastern Brazil
Quantitative and qualitative alterations in the environment may have serious ecological consequences for populations of native species. Isolated forest fragments, such as those surrounded by highly urbanized areas, may function similarly to oceanic islands with differences in species diversity compared to mainland areas. These differences may include changes in prey availability and predator pressure, with consequent effects on growth and size of species that interact with those prey and predators. Here, we investigate body size, prey availability, and predation pressure in populations of Bothrops jararaca in two forest fragments within an urban environment in southeastern Brazil (a completely isolated, small forest fragment and a large, well-connected forest fragment). While we found no differences in mean body size or stoutness between the two populations, we did find larger specimens in the small isolated fragment. Prey availability and predator pressure also were significantly lower in the small isolated fragment. The urban environment significantly changes the population ecology between the two locations. These results suggest that lower food availability in the isolated fragment did not decrease the growth rate of B. jararaca, but the low predator pressure increased longevity, resulting in a higher proportion of large snakes in this population. Alterações quantitativas e qualitativas no ambiente podem ter sérias consequências para a ecologia de populações de espécies nativas. Fragmentos florestais cercados por matriz urbana podem funcionar de modo similar à ilhas oceânicas, tendo menor diversidade de espécies do que áreas maiores. Outras diferenças incluem mudanças na disponibilidade de presas e pressão de predadores, que consequentemente afetam o crescimento e tamanho das espécies. Neste estudo investigamos o tamanho corporal, disponibilidade de presas e pressão de predadores em populações de Bothrops jararaca em dois fragmentos florestais dentro de um ambiente urbano no Sudeste do Brasil (um pequeno fragmento completamente isolado e um grande fragmento conectado). Não encontramos diferenças na média do tamanho corporal, nem na robustez entre as duas populações. Entretanto, espécimes maiores foram encontrados no fragmento menor e isolado. A disponibilidade de presas e pressão de predação também foram significativamente menores no fragmento menor e isolado. O ambiente urbano mudou significativamente a ecologia da população destes dois locais. Os resultados sugerem que a menor disponibilidade de presas não diminui a taxa de crescimento de B. jararaca, mas a menor pressão de predação pode aumentar a longevidade, resultando em uma maior proporção de serpentes maiores nesta população.Abstract
Resumo
Map showing the localities of the two study areas of Bothrops jararaca: Parque Estadual da Cantareira (PEC, yellow) above and Parque Estadual das Fontes do Ipiranga (PEFI, red) below.
Plasticine replicas used in the experiments of predators' pressure on Bothrops jararaca. The replica represents the front portion of an adult individual, and it is placed with a wire to improve substrate fixation. (A) Standard model; (B) mammal attack; (C) bird attack; and (D) rodent bite easily distinguished by the incisive teeth.
Comparison of SVL (mm) between Bothrops jararaca males (M) and females (F) of Parque Estadual das Fontes do Ipiranga (PEFI) and Parque Estadual da Cantareira (PEC). Lines represent averages, boxes are standard deviation, and whiskers are total range.
Stoutness of Bothrops jararaca males and females represented by the relationship between body size and mass of both parks. Open circles = Parque Estadual das Fontes do Ipiranga (PEFI) population; closed circles = Parque Estadual da Cantareira (PEC) population; hashed line = best fit to PEFI population; solid line = best fit to PEC population; MM = males; FF = females.
Proportional distribution of Bothrops jararaca males (MM; left) and females (FF; right) by body size class of both parks: above the population structure and below the cumulative proportion by the increasing size. Black bars = Parque Estadual das Fontes do Ipiranga (PEC); grey bars = Parque Estadual da Cantareira (PEC).
Comparison of Bothrops jararaca potential rodent prey availability between the Parque Estadual das Fontes do Ipiranga (PEC) and Parque Estadual da Cantareira (PEC) over the period of the study. (A) Total Individuals captured and (B) total mass.
Number of models attacked in the two study sites: (A) total number of attacks; (B) by bird (black bar) or mammal (grey bar); and (C) by substrate type: forest floor (black bar) or vegetation (grey bar).
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