Intraspecific variability modulates interspecific variability in animal organismal stoichiometry.

Interspecific differences in organismal stoichiometry (OS) have been documented in a wide range of animal taxa and are of significant interest for understanding evolutionary patterns in OS. In contrast, intraspecific variation in animal OS has generally been treated as analytical noise or random variation, even though available data suggest intraspecific variability in OS is widespread. Here, we assess how intraspecific variation in OS affects inferences about interspecific OS differences using two co-occurring Neotropical fishes: Poecilia reticulata and Rivulus hartii. A wide range of OS has been observed within both species and has been attributed to environmental differences among stream systems. We assess the contributions of species identity, stream system, and the interactions between stream and species to variability in N:P, C:P, and C:N. Because predation pressure can impact the foraging ecology and life-history traits of fishes, we compare predictors of OS between communities that include predators, and communities where predators are absent. We find that species identity is the strongest predictor of N:P, while stream or the interaction of stream and species contribute more to the overall variation in C:P and C:N. Interspecific differences in N:P, C:P, and C:N are therefore not consistent among streams. The relative contribution of stream or species to OS qualitatively changes between the two predation communities, but these differences do not have appreciable effects in interspecific patterns. We conclude that although species identity is a significant predictor of OS, intraspecific OS is sometimes sufficient to overwhelm or obfuscate interspecific differences in OS

Environmental and Organismal Predictors of Intraspecific Variation in the Stoichiometry of a Neotropical Freshwater Fish

The elemental composition of animals, or their organismal stoichiometry, is thought to constrain their contribution to nutrient recycling, their interactions with other animals, and their demographic rates. Factors that affect organismal stoichiometry are generally poorly understood, but likely reflect elemental investments in morphological features and life history traits, acting in concert with the environmental availability of elements. We assessed the relative contribution of organismal traits and environmental variability to the stoichiometry of an insectivorous Neotropical stream fish, Rivulus hartii. We characterized the influence of body size, life history phenotype, stage of maturity, and environmental variability on organismal stoichiometry in 6 streams that differ in a broad suite of environmental variables. The elemental composition of R. hartii was variable, and overlapped with the wide range of elemental composition documented across freshwater fish taxa. Average %P composition was ∼3.2%(±0.6), average %N∼10.7%(±0.9), and average %C∼41.7%(±3.1). Streams were the strongest predictor of organismal stoichiometry, and explained up to 18% of the overall variance. This effect appeared to be largely explained by variability in quality of basal resources such as epilithon N∶P and benthic organic matter C∶N, along with variability in invertebrate standing stocks, an important food source for R. hartii. Organismal traits were weak predictors of organismal stoichiometry in this species, explaining when combined up to 7% of the overall variance in stoichiometry. Body size was significantly and positively correlated with %P, and negatively with N∶P, and C∶P, and life history phenotype was significantly correlated with %C, %P, C∶P and C∶N. Our study suggests that spatial variability in elemental availability is more strongly correlated with organismal stoichiometry than organismal traits, and suggests that the stoichiometry of carnivores may not be completely buffered from environmental variability. We discuss the relevance of these findings to ecological stoichiometry theory

Fish introductions and light modulate food web fluxes in tropical streams: a whole-ecosystem experimental approach

Decades of ecological study have demonstrated the importance of top-down and bottom-up controls on food webs, yet few studies within this context have quantified the magnitude of energy and material fluxes at the whole-ecosystem scale. We examined top-down and bottom-up effects on food web fluxes using a field experiment that manipulated the presence of a consumer, the Trinidadian guppy Poecilia reticulata, and the production of basal resources by thinning the riparian forest canopy to increase incident light. To gauge the effects of these reach-scale manipulations on food web fluxes, we used a nitrogen (N-15) stable isotope tracer to compare basal resource treatments (thinned canopy vs. control) and consumer treatments (guppy introduction vs. control). The thinned canopy stream had higher primary production than the natural canopy control, leading to increased N fluxes to invertebrates that feed on benthic biofilms (grazers), fine benthic organic matter (collector-gatherers), and organic particles suspended in the water column (filter feeders). Stream reaches with guppies also had higher primary productivity and higher N fluxes to grazers and filter feeders. In contrast, N fluxes to collector-gatherers were reduced in guppy introduction reaches relative to upstream controls. N fluxes to leaf-shredding invertebrates, predatory invertebrates, and the other fish species present (Hart\u27s killifish, Anablepsoides hartii) did not differ across light or guppy treatments, suggesting that effects on detritus-based linkages and upper trophic levels were not as strong. Effect sizes of guppy and canopy treatments on N flux rates were similar for most taxa, though guppy effects were the strongest for filter feeding invertebrates while canopy effects were the strongest for collector-gatherer invertebrates. Combined, these results extend previous knowledge about top-down and bottom-up controls on ecosystems by providing experimental, reach-scale evidence that both pathways can act simultaneously and have equally strong influence on nutrient fluxes from inorganic pools through primary consumers

Data from: Bony traits and genetics drive intraspecific variation in vertebrate elemental composition

Interspecific variation in elemental composition is well known and often leads to predictable differences in ecosystem interactions, but little is known about the extent, causes and importance of intraspecific variation in elemental composition. If intraspecific variation is substantial and has a genetic basis, it may underlie an important mechanism of evolutionary interplay with ecology as individuals compensate for evolutionary changes in elemental demand. To investigate the extent and causes of intraspecific elemental variation in vertebrates, we sampled evolutionary model species Gasterosteus aculeatus (Threespine Stickleback) from 12 locations in British Columbia, Canada. Fish were phenotyped, genotyped for Eda alleles underlying lateral plate variation and assayed for elemental content (C, N, P). We found stickleback vary widely in elemental composition (2.2 – 6.5%P; 3.0 – 9.4:1 N:P). Phenotypic models explained the majority of this variation using bony armour traits (pelvis length, lateral plate count), bone mineralization, body size and condition. Subsequent genetic models found allelic variation at Eda generates a 7-14% change in whole organism N:P. As Eda allele frequencies are commonly changed through strong natural selection in freshwater habitats, we infer that stickleback elemental composition can evolve rapidly. Further, as genetics are known to drive variation in many of the other influential traits, we conclude that genetic variation constitutes a major source of variation in the elemental composition of Gasterosteus aculeatus. As such, we find that elemental composition has a large evolutionary potential which may underlie important evo-eco interactions

Data from: Decay patterns of invasive plants and plastic trash in urban streams

Urban streams are impacted by invasion of exotic riparian plants and the accumulation of plastic trash, which alter in-stream litter subsidies, and cause changes that cascade up the aquatic food web. The impacts of these factors on urban streams is poorly understood. We compared decay rates and invertebrate colonizers of 5 litter pack types in 4 urban streams in Victoria, British Columbia, Canada: Native Red alder (Alnus rubra) and Sitka willow (Salix sitchensis), invasive English ivy (Hedera sp.), Himalayan blackberry (Rubus armeniacus) and plastic trash (i.e. Styrofoam (polystyrene (PS)), plastic bag (high-density polyethylene (HDPE)), and Mylar (polyethylene terephthalate (PET). We tested 4 hypotheses: 1) exotic ivy and blackberry leaves would decay more slowly than native leaves; 2) exotic ivy and blackberry leaves would attract fewer and less diverse stream invertebrates than native leaves; 3) plastic trash would decay more slowly than leaves; and, 4) plastic trash would attract fewer and less diverse stream invertebrates than leaves. We found no difference between the leaf litter decay rates, however plastic trash decayed more slowly than leaves. Trash decay rates were faster than reported in marine environments, suggesting that plastic trash removal should be a management priority. Stream invertebrates colonized all pack types equally. We observed significant differences in litter decay rates and invertebrate assemblage alpha and Shannon–Wiener diversities across the 4 streams - likely related to differences in stream-specific environmental attributes including flashiness, stream discharge, and biological decay. We conclude that site-specific decay forces supersede litter quality in Pacific Coast urban streams

Durston and El-Sabaawi - Stickleback Composition

From Durston and El-Sabaawi 2017, this file contains morphological, genetic, environmental and elemental data for 375 Threespine Stickleback from 12 populations. The file contains separate tabs for data from all locations, Kennedy and Miami. The Kennedy and Miami data is also present in the all locations tab, but the size adjustment and standardization are different

Stoichiometric phenotype of stickleback

Data from stickleback (adults or juveniles) raised in two environments (lab and mesocosms) from different populations (Constance, Geneva, Constance x Geneva hybrid). Standard Length, Wet weight, Fulton K, %N, %P and N:P are shown as well as lateral plate number for adults