Abstract
AbstractUnderstanding the amount of variation in functional traits between closely related species within guilds is critical for understanding links between community composition and ecosystem processes. Nutrient excretion is an important link between animals and their environments, and aquatic invertebrate communities can supply a considerable proportion of ecosystem nutrient demand via excretion. We quantified nitrogen (N) and phosphorus (P) excretion rates of 10 species of larval caddisflies that inhabit high‐elevation ponds and wetlands to determine the magnitude of variation in nutrient excretion within this guild. We found considerable interspecific variation in biomass‐specific excretion of nitrogen (eightfold differences), phosphorus (sevenfold differences), and the stoichiometric N:P ratios (fivefold differences). Through a meta‐analysis, we compared the variation within this guild to the variation found in other family‐level species assemblages to determine the overall range in the variation of nutrient excretion that could be expected across guilds and to determine whether the variation in this caddisfly guild is comparatively extreme, average, or low. The meta‐analysis revealed a large range in variation among guilds, and comparatively, the variation within this caddisfly guild is high for N excretion and intermediate for P excretion. The considerable variation within guilds revealed by our meta‐analysis suggests that functional redundancy among guild members is difficult to predict. Thus, some natural or human‐caused species gains or losses within biological groupings such as guilds and trophic levels could have little or no effect on ecosystem processes, whereas others could have very large effects.
Highlights
Combining taxonomically or functionally related species into groups, such as trophic levels, functional groups, and guilds, is often used to explore the relationships between biological diversity and ecosystem function (Tilman 1997, Boyero et al 2007, Slade et al 2007, O’Connor et al 2017)
We found that differences among guilds can explain much of the variation in animal nutrient excretion, and that within a guild of caddisflies, variation in nutrient excretion was intermediate for P and high for N compared to the variation in excretion within guilds of other aquatic invertebrates and vertebrates
We have shown that there is substantial variation in nutrient excretion rates for ten closely related species of larval caddisflies that inhabit high-elevation ponds and wetlands. These excretion rates are consistent throughout the day, and for taxa with broad distributions, rates are consistent at different sites along an elevational gradient from montane (e.g., 2800 m) to subalpine (e.g., 3400 m)
Summary
Combining taxonomically or functionally related species into groups, such as trophic levels, functional groups, and guilds, is often used to explore the relationships between biological diversity and ecosystem function (Tilman 1997, Boyero et al 2007, Slade et al 2007, O’Connor et al 2017). Other studies have found that species are not functionally equivalent, and there are many examples of how the loss or addition of a single species can dramatically affect carbon flow and nutrient cycling (e.g., Hall et al 2003, Taylor et al 2006, McIntyre et al 2007, Small et al 2011) This suggests that within assemblages of closely related species, which are commonly grouped into ecological guilds and assumed to fulfill similar functional roles in ecosystems, there could be substantial variation in traits such as nutrient excretion. The purpose of this study was to compare the variation in nutrient excretion among species within guilds of aquatic animals to explore the range in variation in this particular functional trait
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