Plasticity and specialisation in the isotopic niche of African clawless otters foraging in marine and freshwater habitats

Abstract

Individual-level behavioural plasticity resulting from differences in environmental conditions is prevalent in many organisms and may result in phenomena such as dietary-or habitat specialisation. The isotopic niche of African clawless otters, Aonyx capensis, occupying different habitats was investigated with the use of stable isotope techniques. Stable isotope analyses revealed that African clawless otter isotopic niche varied between, as well as within, individuals and varied when compared to conspecifics occupying different habitats. Some otters varied their isotopic niche and foraging areas temporally, whilst others did not. The isotopic niche of African clawless otters in a coastal habitat overlapped substantially with previous reports on otter diet, but illustrated that otters eat more shark and molluscs than previously estimated. In freshwater habitats, not all otters had trout in their isotopic niche, although this prey item was abundantly available in the study area. Our results suggest that the African clawless otters can exhibit substantial behavioural plasticity. Such evident adaptability is likely to benefit otters and allow for extended use of non-pristine environments affected by human disturbance when sufficient quantities of prey remain available.

Abundance, survival and population growth of killer whales Orcinus orca at subantarctic Marion Island

“…Local adaptation and variation in diet, behaviour, morphology and demographic parameters (e.g. survival and reproductive rates) are common among such populations (McMahon et al 2003, Tremblay and Cherel 2003, Gabrey 2010, Jordaan et al 2019b). Yet, these population differences are often overlooked in ecological studies.…”

The diet of spotted-necked otters foraging in trout-stocked waters in Mpumalanga, South Africa

“…We collected three vibrissae at Millstream Farm after spotted-necked otters were captured in baited carnivore cage traps intended for African clawless otters (see Jordaan et al 2019 for details). These traps (1.5m x 0.7m x 0.8m) were baited with fresh African clawless otter spraints and trout and placed at suitable locations within Millstream Farm (e.g.…”

“…The analyses of stable isotope ratios (SIA) is a technique that overcomes many of the limitations associated with spraint analysis and has been used to investigate the diets and isotopic niches of various otter species (Angerbjörn et al 1994;Grey 2001;Newsome et al 2009;Carrasco et al 2019;Jordaan et al 2019). This method makes use of various animal tissues including bone collagen (Angerbjörn et al 1994), red blood cells and blood plasma (Hilderbrand et al 1996), muscle tissue (Grey 2001), teeth (Carrasco et al 2019) and vibrissae (Lübcker et al 2016;Lerner et al 2018).…”

“…The persecution of otters in South Africa takes place despite early evidence suggesting that invasive trout is a relatively unimportant prey species in the diets of both otter species (Butler and du Toit 1994;Rowe-Rowe 1977a). While more recent work suggests that African clawless otters do predate on trout in stocked waters, considerable inter-individual variation is evident in their diet, and not all otters in, and around, stocked waters predate upon trout (Jordaan et al 2019).…”

Pacific marten (Martes caurina) as an apex predator : the habitat and diet ecology of an insular population of mesocarnivore on Haida Gwaii

“…Mesocarnivores are found in the order Carnivora and include small to mid-size (<15 kg) mammals, such as felids, canids, and mustelids (Roemer et al 2009). Mesocarnivores display relatively high trophic plasticity and can perform a variety of ecosystem functions depending on exogenous forces, such as climate, plant species composition, competition and predation, and prey availability (Jordaan et al 2019;Manlick et al 2019). The energetic requirements of smallbodied predators are low, and can be met by omnivorous diets composed of plants, invertebrates, and small vertebrates (Carbone et al 1999).…”