Vulnerabilidade de pequenos mamíferos de áreas abertas a vertebrados predadores na estação ecológica de Itirapina, SP

Abstract

Prey selection studies may result in different conclusions depending on the analysed forager. Predators with different foraging modes, such as raptors and carnivorous mammals, may select different prey types. Certain prey morphological and behavioural patterns could explain selection. Predation would be favouring morphological/functional adaptations, such as inflated auditory bullae, saltatorial locomotion, use of habitat with shelters and higher activity levels during moonless nights. This kind of study is still scarce in Brazil. So, the goal of this research was the analysis of small mammal selection in the diet of three predators at Itirapina Ecological Station, SP, as well as to verify the vulnerability of small mammals in relation to hearing, locomotion, use and activity in different physiognomies during nights with varying lunar illumination. Analysis of prey selection by the Barn Owl (Tyto alba) was conducted in relation to species, size, age and sex. The Burrowing Owl (Athene cunicularia) was studied in relation to the consumption of small mammal species, size and age. The Maned Wolf (Chrysocyon brachyurus) was only evaluated concerning prey species selection. Remains of bones (mandibles and pelvic girdles) found in pellets and faeces of predators were utilized to identify prey species, sex and to quantify number of consumed individuals. Analysis of prey species selection was conducted by comparisons between proportion of prey found in the diet and in environment, applying G test and Bonferroni confidence intervals. Differential sex consumption was evaluated by G test and Fisher exact test. Mann-Whitney test was employed to compare prey size in the diet and in the environment. Rodent ages found in pellets/ faeces and in the field were compared by G test. The volumes of auditory bullae were obtained by injection of water in these structures using micro-syringe. Bipedalism index (ratio between fore and hind limb lengths) was calculated to find the best potential escape response among the studied rodents. Small mammal abundance/activity in three different physiognomies was assessed by pitfall traps during full or no moon nights. The Barn Owl was more selective than the Burrowing Owl in relation to prey species consumption, though both of them include the same small mammal species in their diets. Calomys tener and Oligoryzomys nigripes were the most preyed on rodents by the two owls. Small-sized and juvenile

Behavioural and morphological strategies by small savannah rodents to avoid predation

“…For all analyses, statistical significance was set at ˛ = 0.05. For more detailed information on methods and analysis on diet and prey selection by the maned wolf and the owls in the EEI, see Bueno (2003) and Bueno andMotta-Junior (2006, 2008).…”

“…Motta-Junior 2000; Bueno andMotta-Junior 2006, 2008;Queirolo and Motta-Junior 2007). Furthermore, analyses on prey vulnerability to predation remain unexplored.…”

Dieta e seleção de coleópteros copro-necrófagos (Scarabaeidae: Scarabaeinae) pela coruja-buraqueira (Athene cunicularia, Strigiformes: Strigidae) em campos da Estação Ecológica de Itirapina, Estado de São Paulo, Brasil

“…Neste estudo foi estimada a massa corporal média dos invertebrados predados a partir de valores de massa de indivíduos adultos e juvenis pertencentes à coleção de referência (Motta Junior, 1996) e de exemplares coletados nas armadilhas cujas massas foram obtidas em balança de precisão de até 0,0001g. Para estimar a massa corporal de vertebrados foram utilizadas equações de Correlação log-log base 10, elaboradas no estudo de Motta Junior (1996) e Bueno (2003). Utilizou-se como medida para roedores e marsupiais o comprimento da mandíbula, desde a borda superior do alvéolo do incisivo até a concavidade entre os processos mandibular e angular (cf.…”