Geographical and intrapopulation variation in the diet of a threatened marine predator, Pontoporia blainvillei (Cetacea)

Abstract

Understanding diet variation is a major concern when developing conservation guidelines for threatened species, especially for marine predators whose prey availability can be reduced by commercial fisheries. Diet can vary in geographically structured populations due to variation in prey availability and within a location due to the effects of season, sex, age, and individual. However, these sources of variation are seldom considered together in dietary studies. We analyzed diet variation at the geographical and intrapopulation levels in the franciscana dolphin (Pontoporia blainvillei) by analyzing samples of stomach contents from individuals incidentally caught by artisanal fisheries. We investigated the geographical (Northern, Central, and Southern regions of the São Paulo State coast, Brazil) and intrapopulation effects of season, sex, and age. We used the leave-one-out cross-validation method to test for significance of the proportional similarity index, which measures the overlap between diet compositions. We found that diet varied across different levels, from the geographical to the individual level, including the effects of season, sex, and age. Diet variation as a function of age suggests an ontogenetic diet shift. Our findings indicate that ecological processes within local stocks should inform management at the local geographic scale. Evidence for ecological differences between franciscana stocks is of great significance for the conservation of this threatened species.Abstract in Portuguese is available with online material.

Spatial and temporal variation in the diet of the sandy beach gastropod Olivella minuta

“…It is well‐known that consumers’ activities may regulate nutrient cycling and mixing of materials (Griffiths et al, ; Levinton, ), change community composition (Gergs, Grey, & Rothhaupt, ; Posey, Lindberg, Alphin, & Vose, ), alter the behavior of the preyed species (Atkinson, Vaughn, Forshay, & Cooper, ; Wohlgemuth, Filip, Hillebrand, & Moorthi, ), or induce physical and chemical defenses (Naiman, ). To better understand the consumer's effect on ecosystem functioning, it is essential to correctly characterize their diet to know which food resources they consume and their role in food webs (Henning et al, ). Nonetheless, dietary studies are rarely performed (e.g., Courant et al, ; Fontoura‐da‐Silva, Dantas, & Caetano, ), or are constrained in space and time (Li, Gerth, Van Driesche, Bateman, & Herlihy, ).…”

“…Grazing species, in turn, may reduce plant community biomass or stimulate primary production by accelerating nitrogen cycling, depending on the grazing pressure (Connor & Robert, ; Kelaher et al, ). While the top‐down effects of foraging activities of marine species have been widely examined (e.g., Cheverie, Hamilton, Coffin, & Barbeau, ; Paine, ), little is known about whether or how environmental differences in space and time may affect the feeding behavior of a given species (Henning et al, ). This uncertainty is highlighted for soft‐bottom coastal ecosystems such as sandy beaches.…”

Relações tróficas e uso de área da toninha, >i<Pontoporia blainvillei>/i< (Gervais e d\'Orbigny, 1844) e do boto-cinza, >i<Sotalia guianensis>/i< (Van Bénéden, 1864) da costa sudeste do Brasil determinados pela composição de isótopos estáveis de carbono e nitrogênio

“…PA significa Projeto Atlantis, SGD significa Sotalia guianensis amostrados dentro do estuário, CT é o comprimento total, as idades foram definidas em anos e os sexos foram definidos em M para machos e F para fêmeas pelas aberturas das fendas da genitália durante a dissecção. ................................................................................................... 62 Tabela 3 -Principais presas nos hábitos alimentares das toninhas e dos botos-cinza segundo Lopes et al (2012), Campos (2015) e Henning et al (2018) , estudos realizados na região sul da costa do Estado de São Paulo e norte do Paraná. Hábitos das presas:…”

“…Para a realização deste estudo foram processadas amostras de predadores botos-cinza e toninhas, assim como de seus principais itens alimentares avaliados em estudos pretéritos realizados na região de estudo e envolvendo a investigação dos hábitos alimentares desses dois cetáceos (LOPES, 2012;LOPES et al, 2012;CAMPOS, 2015;HENNING et al, 2018). A outra parte das amostras que envolveu os cetáceos foi obtida por meio de biopsias realizadas dentro do estuário de Cananéia em março e em maio de 2018, utilizando uma balestra de 120 lbs.…”

“…A última parte das amostras e que envolveu as principais presas consumidas por estes cetáceos localmente (LOPES et al, 2012;CAMPOS, 2015;HENNING et al, 2018)…”