Stratigraphy of stable isotope ratios and leaf structure within an African rainforest canopy with implications for primate isotope ecology

Abstract

The canopy effect describes vertical variation in the isotope ratios of carbon (δ13C), oxygen (δ18O) and partially nitrogen (δ15N) within plants throughout a closed canopy forest, and may facilitate the study of canopy feeding niches in arboreal primates. However, the nuanced relationship between leaf height, sunlight exposure and the resulting variation in isotope ratios and leaf mass per area (LMA) has not been documented for an African rainforest. Here, we present δ13C, δ18O and δ15N values of leaves (n = 321) systematically collected from 58 primate food plants throughout the canopy (0.3 to 42 m) in Côte d’Ivoire, West Africa. Besides leaf sample height and light availability, we measured leaf nitrogen and carbon content (%N, %C), as well as LMA (n = 214) to address the plants’ vertical resource allocations. We found significant variation in δ13C, δ18O and δ15N, as well as LMA in response to height in combination with light availability and tree species, with low canopy leaves depleted in 13C, 18O and 15N and slightly higher in %N compared to higher canopy strata. While this vertical isotopic variation was not well reflected in the δ13C and δ15N of arboreal primates from this forest, it did correspond well to primate δ18O values.

Late Pleistocene to late Holocene palaeoecology and human foraging at Kuumbi Cave, Zanzibar Island

“…Several stable isotope studies have highlighted that δ 18 O values may reflect food resource partitioning among arboreal primates, but that δ 13 C values do not (Krigbaum et al, 2013;Roberts et al, 2017;Lowry et al, 2021). The KC primates and hyrax δ 13 C and δ 18 O values seemingly capture intraspecies vertical food resource partitioning, however (Figure 9).…”

Trait based niche differentiation in tetrakas (Bernieridae) endemic to Madagascar: A multi-isotope approach

“…The canopy height was variable and reached higher than the mistnets in most cases, but capturing birds at greater heights was technically not feasible. Therefore, all capture height data reported in this study refer to birds caught within the mist-nets, at heights between 0 and 5 m. This approach is commonly used on research in habitat usage by ground-dwelling or understory birds (e.g., Rajaonarivelo et al, 2020Rajaonarivelo et al, , 2021Lowry et al, 2021), but its drawback is the lack of information it provides regarding birds inhabiting the strata above the nets.…”

“…Consistently, this produces 13 C-depleted plant values from ground to canopy; the most positive values are usually at the upper vertical portion. Canopy effects on avian studies (understorey or ground-dwelling birds) have been measured as height from the ground, rather than estimating or measuring the vertical distance from the canopy (e.g., Rajaonarivelo et al, 2020Rajaonarivelo et al, , 2021Lowry et al, 2021).…”

A skew in poo: Biases in primate fecal isotope analysis and recommendations for standardized sample preparation

“…However, many primate species are specialized frugivores and important seed dispersers within their habitats (Chapman, 1989). Compared to the taxonomic detail provided by macroscopic identification, stable isotopes tend to assess more categorical differences in primate diet in terms of the predominance of C 3 and C 4 plants (Codron et al, 2006; Tieszen, 1991), the prevalence of fruits versus foliage (Blumenthal et al, 2012; Cernusak et al, 2009), between low and high canopy plant foods (Lowry et al, 2021; Medina & Minchin, 1980; Roberts et al, 2017), or the presence of higher tropic level foods such as insects, meat, or breastmilk (Bădescu et al, 2016; Oelze et al, in preparation; Reitsema, 2012).…”