Ecological stoichiometry of indirect grazer effects on periphyton nutrient content

Abstract

Ecological stoichiometry has been successful in enhancing our understanding of trophic interactions between consumer and prey species. Consumer and prey dynamics have been shown to depend on the nutrient composition of the prey relative to the nutrient demand of the consumer. Since most experiments on this topic used a single consumer species, little is known about the validity of stoichiometric constraints on trophic interactions across consumers and ecosystems. We conducted a quantitative meta-analysis on grazer-periphyton experiments to test (1) if benthic grazers have consistent effects on the nutrient composition of their prey, and (2) whether these effects can be aligned to the nutrient stoichiometry of grazer and periphyton, other environmental factors, or experimental constraints. Grazers significantly lowered periphyton C:N and C:P ratios, indicating higher N- and P-content of grazed periphyton across studies. Grazer presence on average increased periphyton N:P ratios, but across studies the effect size did not differ significantly from zero. The sign and strength of grazer effects on periphyton nutrient ratios was strongly dependent on the nutrient content of grazers and their food, but also on grazer biomass, the amount of biomass removal and water column nutrients. Grazer with low P-content tended to reduce periphyton P-content, whereas grazers with high P-content increased periphyton P-content. This result suggests that low grazer P-content can be an indication of physiological P-limitation rather than a result of having relatively low and fixed P-requirements. At the across-system scale of this meta-analysis, predictions from stoichiometric theory are corroborated, but the plasticity of the consumer nutrient composition has to be acknowledged.

Effect of host-plant genetic diversity on oak canopy arthropod community structure in central Mexico

“…GLM describes the effects of variables in a multivariate-model setting. This analysis has the advantages that even if a variable has a nonsignificant effect on a variable when subjected to univariate analysis, it may still be a significant variable in a multivariate-model setting when accounting for covariance with other factors (Hillebrand et al 2008). We pooled the following genetic data from 20 trees within each locality: the community was quantified at the stand level and the occurrence of individual SSRs and RAPDs markers present in each locality, resulting in a unique genetic diversity value for each locality.…”

Consumer diversity indirectly changes prey nutrient content

“…That is, the relative N content of the periphyton increased in the presence of grazers and increased further with increasing grazer diversity. Whereas positive effects of grazer presence on relative algal nutrient content are frequently reported (Hillebrand et al 2008), the observation that more grazer species further enhance nutrient content (in 2004) is, to our knowledge, an unprecedented result. Moreover, we found significant NDE on periphyton C:N ratios in 2004 and marginally nonsignificant NDE in 2005, which indicates that periphyton C:N ratios in multispecies treatments was not an intermediate of the values observed in species monocultures (supporting Hypothesis 3).…”

“…Excretion by grazers has been shown to enhance nutrient uptake and content of periphytic algae (Evans-White & Lamberti 2005, Liess & Haglund 2007. Higher biomass removal can also increase the bulk periphyton N content by different mechanisms (Hillebrand et al 2008) such as removing N-poor detritus, shifting species composition, promoting mixing in the boundary layers or changing the relationship between available nitrogen concentrations and living algal biomass. In 2005, we mainly saw an averaging effect of multiple grazer species on periphyton stoichiometry, whereas deviations from averaging were weak and marginally non-significant.…”

“…Several mechanisms would explain the increased concentration of nutrients in grazed periphyton (McCormick & Stevenson 1991, Hillebrand & Kahlert 2001, Frost et al 2002b, Hillebrand et al 2008: grazers may promote the uptake of available nutrients by increasing hydrodynamic mixing above the periphyton or by removing nutrient-poor detritus, or grazers may increase the availability of nutrients by excretion or egestion. Hillebrand et al (2008) discuss these mechanisms in more detail.…”

Dieta de Pomacea canaliculata (Gastropoda: Ampullariidae) en su hábitat natural basada en análisis de contenidos digestivos e isótopos estables

“…P. canaliculata has an important status in the energetic balance of sediments of pampean streams due to a high consumption of vascular plants and detritus (Cazzaniga and Estebenet, 1984), since the waste it produces is later used by other secondary consumers. The excretion and/or egestion of nutrients by grazers also increase the supply of nutrients available to the periphyton (Hillebrand et al, 2008).…”