Deviation from strict homeostasis across multiple trophic levels in an invertebrate consumer assemblage exposed to high chronic phosphorus enrichment in a Neotropical stream

Abstract

A central tenet of ecological stoichiometry is that consumer elemental composition is relatively independent of food resource nutrient content. Although the P content of some invertebrate consumer taxa can increase as a consequence of P-enriched food resources, little is known about how ecosystem nutrient loading can affect the elemental composition of entire consumer assemblages. Here we examine the potential for P enrichment across invertebrate consumer assemblages in response to chronic high P loading. We measured elemental ratios in invertebrate consumers and basal food resources in a series of streams in lowland Costa Rica that range widely in P levels (2-135 microg l(-1) soluble reactive P). Streams with high P levels receive natural long-term (over millennia) inputs of solute-rich groundwater while low-P streams do not receive these solute-rich groundwater inputs. P content of leaf litter and epilithon increased fourfold across the natural P gradient, exceeding basal resource P content values reported in the literature from other nutrient-rich streams. Invertebrate consumers from the high-P study stream were elevated twofold in P content across multiple taxonomic and functional feeding groups, including predators. Our results strongly support the hypothesis that elevated P content in consumers feeding on P-enriched food resources is a consequence of deviation from strict homeostasis. In contrast to prior studies, we found that between-stream variation in P content of a given taxon greatly exceeded within-stream variation among different taxa, suggesting that environment may be as important as phylogeny in controlling consumer stoichiometry. Relaxing the assumption of strict homeostasis presents challenges and opportunities for advancing our understanding of how nutrient limitation affects consumer growth. Moreover, our findings may provide a window into the future of how chronic anthropogenic nutrient loading can alter stoichiometric relationships in food webs.

Assessing the Effects of Logging Activities on Avian Richness and Diversity in Different Aged Post-Harvested Hill Dipterocarp Tropical Rainforest of Malaysia

“…During the recovery process many plant species become mature and start flowering and fruiting which attract insects (bees, wasps, butterflies, moths, beetles and flies) which is a major diet of avian species. Invertebrate communities of the tropical rain forest are highly diverse and their distribution and richness is associated with a diversity of vegetation structure and composition such as foliage, flowers, fruits, barks (Small and Pringle, 2010;Batista Matos et al, 2013;Peters et al, 2013). Silva and Brandao (2010) reported that invertebrate density strongly associated with vegetation structure and may vary at spatial scales of a few meters.…”

Widespread natural intraspecific variation in tissue stoichiometry of two freshwater molluscs: Effect of nutrient enrichment

“…For example, zooplankton C:P ratio is strongly correlated to the seston C:P ratio (Hessen et al, 2005). A field study also found that invertebrates across multiple trophic levels in the high-P stream had significantly higher P content and lower C:P compared to the low-P stream (Small and Pringle, 2010). That study found that between-stream variation in P content of a given taxon greatly exceeds in-stream variation among different taxa.…”

“…To date, studies of organismal stoichiometry have mostly focused on characterizing variability and drivers among taxonomic and functional groups (Cross et al, 2003;Evans-White et al, 2005;Small and Pringle, 2010). In contrast, relatively few studies have examined the extent and causes of intraspecific variability in organismal stoichiometry in natural ecosystems .…”

“…If deviation from strict homeostasis is a widespread phenomenon in freshwater invertebrates, then larger variations in nutrient loading could lead to extensive natural intraspecific variations in stoichiometric (C:N:P) composition of freshwater invertebrate such as molluscs. Still, it is less clear how tissue stoichiometry varies along nutrient gradient for many freshwater molluscs Naddafi et al, 2012;Small et al, 2009;Small and Pringle, 2010). One way to elucidate this question is to assess tissue C:N:P stoichiometry of freshwater molluscs among lakes with different nutrient loading (mainly P and N), as higher contents of these may affect tissue stoichiometry via altered food elemental composition (Naddafi et al, 2009).…”

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

“…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).…”