Consumer‐resource stoichiometry in detritus‐based streams

Abstract

Stoichiometric relationships between consumers and resources in detritus‐based ecosystems have received little attention, despite the importance of detritus in most food webs. We analysed carbon (C), nitrogen (N), and phosphorus (P) content of invertebrate consumers, and basal food resources in two forested headwater streams (one reference and the other nutrient‐enriched). We found large elemental imbalances between consumers and food resources compared with living plant‐based systems, particularly in regard to P content, which were reduced with enrichment. Enrichment significantly increased nutrient content of food resources (consistent with uptake of N and P by detritus‐associated microbes). P content of some invertebrates also increased in the enriched vs. reference stream, suggesting deviation from strict homeostasis. Nutrient content varied significantly among invertebrate functional feeding groups, orders and, to some extent, size classes. Future application of stoichiometric theory to detritus‐based systems should consider the potential for relatively large consumer‐resource elemental imbalances and P storage by insect consumers.

Unifying ecological stoichiometry and metabolic theory to predict production and trophic transfer in a marine planktonic food web

“…Phototrophs, unlike herbivores, can adjust their elemental composition depending on nutrient stoichiometry, resulting in different food quality and thus affecting consumption rates and consumer nutrient recycling [8]. In community ecology, ES has successfully been used to explain consumer performance (food uptake rate, assimilation, growth rate and efficiency; [9][10][11]), competition between consumer species [12,13], and consumer effects on prey nutrient composition [14,15]. In contrast to ES, MTE [16] focuses on consumer body mass and temperature as determinants of metabolic rates, which control growth and consumption rates as well as population and community productivity.…”

Food type and temperature constraints on the fitness of a dominant freshwater shredder

“…A Kruskal-Wallis ANOVA was used to test for significant differences in elemental ratios of larvae between different treatments. In addition, we plotted the elemental ratios of larvae and food resources (C:N, C:P and N:P) to check the relative stoichiometric constraints (i.e., elemental imbalances) naturally existing in these ecosystems and go through potential changes due to alterations of environmental and dietary conditions (Sterner and Elser, 2002;Cross et al, 2003).…”

“…Recent studies have shown that the degree to which shredders modify FPOM stoichiometry from CPOM stoichiometry may also vary across shredder species depending on traits such as nutritional requirements or feeding behaviour when reared under different leaf types and temperatures (Villanueva et al, 2011;Mas-Martı´et al, 2015;Correa-Araneda et al, 2015). The order Diptera is known to have a high P content, although paradoxically, detritus is among the most P-deficient of food resources (Cross et al, 2003;Evans-White et al, 2005). In our detritus-based system, we confirmed that B. bifida larvae are clearly far out of stoichiometric balance with their food resources, mostly in eucalypt treatments (where the highest elemental imbalances occurred).…”

“…In addition, oil-based and polyphenolic substances contained in mesophyll cells Grac¸a, 1995, 1999;Canhoto et al, 2002) act as barriers to fungal colonization and shredder consumption, leading to altered detritus processing and shredding activity Abelho and Grac¸a, 1996;Pozo et al, 1998;Lo´pez et al, 2001) and thus, the structure and functioning of forested headwater streams. There are many studies that have demonstrated how stream invertebrates may evolve developmental adaptations for the utilization of available resources (Rowe and Ludwig, 1991) and/or change their internal elemental ratios in response to resource quality (Cross et al, 2003;Small and Pringle, 2010). These responses are manifested at the physiological, behavioural or genetic level and depend on individual requirements (Slansky and Scriber, 1985;Sterner and Elser, 2002;Swan and Palmer, 2006).…”

“…These responses are manifested at the physiological, behavioural or genetic level and depend on individual requirements (Slansky and Scriber, 1985;Sterner and Elser, 2002;Swan and Palmer, 2006). Therefore, consumers with high body N or P content and high growth rates (GR) seem to require food that is high in N or P, respectively, to maintain optimal growth (Cross et al 2003;Frost et al, 2005). The extent to which individuals can compensate for elemental imbalances will ultimately determine their life history traits as well as alterations in the nutrient cycling of consumers (Sterner and Elser, 2002).…”