Adaptation to a limiting environment: the phosphorus content of terrestrial cave arthropods

Abstract

Stoichiometric imbalances (mismatches between elemental ratios of consumers and their food) are expected to be especially important in detritus-based systems because poor resource quality may impose severe growth constraints. Such imbalances have been highlighted in producer-based food webs and detritusbased aquatic systems, but similar investigations of detritus-based terrestrial ecosystems are absent. Cave animals are dependent on detrital subsidies from the surface and display adaptations to caves (e.g., decreased growth and metabolic rates). Here we examined how nutrient quality may constrain consumer strategies in caves. We found that the quality of cave resources was comparable to resources on the surface, but there was some evidence that cave animals may face nutritional constraints for at least a part of the year. Such constraints may be especially important for millipedes, whose C:P was particularly low (i.e., nutrient-demanding) relative to cave detritus. Based on the growth rate hypothesis, we predicted that cave-adapted species would have lower %P, lower %RNA, and a lower RNA/DNA ratio relative to surface-dwelling counterparts; however, the differences we discovered between congeneric millipedes may not necessarily be due to P scarcity. Consistent with stoichiometric theory, we found significant negative %P allometry across phylogenetic groupings of 17 cave arthropods. We did not see this allometric relationship in millipedes, perhaps because of the lowered P content of the cave-obligate species. Our results highlight the potential for stoichiometric challenges of caves to influence the adaptations of terrestrial cave animals. This novel explanation for cave adaptation may yield insights into cave biodiversity and biogeography.

Ecological mechanisms and phylogeny shape invertebrate stoichiometry: A test using detritus‐based communities across Central and South America

“…Previous studies have shown that the P content of carnivores is higher (Cross et al, ; González et al, ; Lemoine et al, ; Wiesenborn, ) or the same (Martinson et al, ; Schneider et al, ) as that of detritivores. In this study, trophic group differences in P content depended on site, suggesting that some of the divergent results between previous studies reflect local conditions.…”

“…Similarly, carnivores have access to higher quality resources and may therefore rely more heavily on higher nutrient materials to build their bodies (Fagan et al, 2002;González et al, 2011;Lemoine et al, 2014). Nevertheless, the generalization of an increase in nutrient-rich biomass with increasing trophic position has been recently disputed for arthropods, in particular regarding P content and N:P (Lemoine et al, 2014;Schneider, Kay, & Fagan, 2010;Woods et al, 2004). This suggests that the role of trophic guild in determining the elemental content of arthropods, and perhaps invertebrates in general, may depend on the identity of species in the community.…”

“…While previous studies have provided valuable insights into organismal stoichiometry, most of the work to date has been conducted using either literature-compiled databases (Fagan et al, 2002), or at local scales (González et al, 2011;Schneider et al, 2010;Wiesenborn, 2013;Woods et al, 2004), and has focused on a few closely related species, especially dipterans (Bertram, Bowen, Kyle, & Schade, 2008;Hämback et al, 2009). Very few studies have quantified the contribution of evolutionary history to animal stoichiometry from natural communities (but see González et al, 2011) or across geographical scales (see Kaspari & Powers, 2016).…”

Litter manipulation and the soil arthropod community in a lowland tropical rainforest

“…3), several elements of fundamental importance to arthropod metabolism became limiting (phosphorus and carbon in particular; Medici and Taylor, 1966;Vigh and Dendinger, 1982;Denno and Fagan, 2003;Capinera, 2008;Schneider et al, 2010). However, no corresponding effects of litter addition were observed in terms of arthropod absolute and relative abundances, which suggests that the above elements were in sufficient supply in most control plots, at least in terms of their effects on soil arthropods.…”

Collembolan reproduction in soils from a long-term fertilisation experiment opposes the Growth Rate Hypothesis

“…With higher P availability in the soil, more large-bodied invertebrates were found [19]. Schneider et al [25] compared stoichiometric data of slow-growing cave arthropods (Collembola, Coleoptera, Orthoptera, millipedes, arachnids) to their surfacedwelling counterparts and found lower P contents in their body mass. Hamb€ ack et al [11] compared stoichiometry of Diptera diets and bodies and found that Diptera body N did not directly increase with diet quality.…”