Variation in isotopic niche, digestive tract morphology, and mercury concentrations in two sympatric waterfowl species wintering in Atlantic Canada

Abstract

Sympatric communities of organisms may exploit different ecological niches to avoid intra- and interspecific competition. We examined the isotopic niches of American black ducks ( Anas rubripes) and mallards ( A. platyrhynchos) wintering in coastal and urban areas of Atlantic Canada and compared isotopic niche with digestive tract morphologies and blood mercury (Hg) concentrations. Isotopic niche width (for δ13C and δ15N) varied between the three groups of ducks studied, with coastally foraging black ducks exhibiting the widest isotopic niche, followed by coastal mallards, while urban feeding black ducks had a narrow isotopic niche. These niche differences had physical and chemical consequences: coastal black ducks had longer digestive tracts, a larger range in gizzard sizes, and higher and more variable Hg concentrations than urban black ducks and coastal mallards. This plasticity in ecological niche may reduce competition among and within species, and subsequently explain why winter numbers of black ducks and mallards have increased in Atlantic Canada.

Differential bioaccumulation patterns of heavy metals and organochlorine pesticides in the Northern Shoveler and Northern Pintail (Avian: Anatidae) related to blood parameters and body condition

“…These findings are consistent with those reported by White and Stickel (1975) and Ohlendorf and Miller (1984), who measured higher levels of OCPs in waterfowl species that consumed a higher proportion of animal (invertebrate) foods. We expected higher Pb concentrations in A. acuta tissues compared to those of S. clypeata because grain ingestion has been related to high ingestion rates of Pb pellets (Mateo et al 2000) English et al 2020). Considering that different types of contaminants and different tissues were analyzed, it seems that both sexes are similarly exposed to Hg and Pb during the fall migratory period and to OCPs throughout the entire year, but each species exhibits distinctive exposure and accumulation patterns.…”

Interspecific differences in feeding selectivity shape isotopic niche structure of three ophiuroids in the Arctic Ocean

“…The co-occurrence of ecologically similar species is founded on the partitioning of their ecological niches or in exploiting different niches driven in some part by diet shifts (Lush et al 2017, English et al 2020). Some studies have been conducted in the Arctic Ocean based on approaches using multiple biomarkers to assess how benthic species co-occur using common resources (Stasko et al 2018a, Yunda-Guarin et al 2020.…”