Stable isotope evidence for trophic niche partitioning in a South African savanna rodent community

Abstract

Species’ partitioning of resources remains one of the most integral components for understanding community assembly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning because these proxies represent the individual’s diet and trophic niche, respectively. Using free-ranging rodents in a southern African savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, species with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel analytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices.

Dietary niche separation of rodents and shrews in an African savanna

“…But both interpretations imply competition as an important component in rodent communities of Kafue National Park, as found in other parts of southern Africa (Codron et al . ). Crocidura fuscomurina shows the opposite pattern (wider niche under low than under high fire recurrence).…”

“…, Codron et al . ). Using rodent and shrew assemblages of termitaria, grassland, and Miombo woodland as the three most species‐rich habitats of KNP in Zambia, we employ the conceptual framework of competition over limited resources resulting in limiting similarities (MacArthur & Levins ) and reconstruction of diet composition based on stable isotopes to investigate the following questions.…”

Resource partitioning and functional diversity of worldwide freshwater fish communities

“…This might be especially true for isotopic niches as species with highly overlapping niches may also display microhabitat or temporal niche partitioning (e.g., Codron et al. ). Coupling stable isotope data with behavioral and habitat use information should allow to gain a better understanding of the mechanisms underlying the observed variation in species’ isotopic niches.…”

Trends in behavioural ecology: Putting South African research in a global perspective

“…South African and international authors largely agreed in terms of the top three thematic areas: foraging, reproductive and social behaviour (Table 1, Figure 1). In contrast to international trends, in which indirect analysis of foraging behaviour was rarely represented 37 , many South African researchers use indirect methods such as scat 38 and isotope analyses 39 to describe foraging behaviour. Foraging ecology in the South African literature is therefore often restricted to dietary studies, with nuanced assessments of foraging behaviour -such as habitat selection 13 or strategic responses to environmental variation 40 -remaining uncommon.…”

“…Furthermore, while South African researchers already display a positive tendency to study heterospecific interactions, these studies are often performed on either a population level (e.g. Codron et al 39 ), or much smaller scale 58 . It is likely that collaborative research across study sites would enable us to assess inter-specific competition and collaboration on both a fine and large scale.…”