Species-specific traits predict whole-assemblage detritus processing by pond invertebrates

Consequences of climate-induced range expansions on multiple ecosystem functions

“…Furthermore, excretion declines predictably with developmental instar, though differences among species-specific instars are small relative to interspecific differences. In addition, there is comparable interspecific variation in detritus processing rates measured in laboratory microcosms over the course of larval development 20 , and species’ microcosm processing rates are generally within 20% of species-specific processing rates measured in-situ with littoral cages 27 , 45 . Furthermore, this previous work demonstrates that additive predictions of caddisfly assemblage detritus processing calculated by summing the products of species’ mass-specific processing rate and biomass provide accurate estimates of in situ assemblage-total detritus processing 20 .…”

“…In addition, there is comparable interspecific variation in detritus processing rates measured in laboratory microcosms over the course of larval development 20 , and species’ microcosm processing rates are generally within 20% of species-specific processing rates measured in-situ with littoral cages 27 , 45 . Furthermore, this previous work demonstrates that additive predictions of caddisfly assemblage detritus processing calculated by summing the products of species’ mass-specific processing rate and biomass provide accurate estimates of in situ assemblage-total detritus processing 20 . Thus, we predicted caddisfly species’ contribution to ecosystem processes over time as the products of average density, final instar mass, larval development rate, and either nutrient excretion rate or detritus processing rate.…”

“…In this larger community context, redundancy in animal-driven nutrient supply conferred by other invertebrate taxa would likely preclude any changes in total supply caused by arrival of range expanding caddisflies. However, other taxa are unlikely to provide comparable redundancy for multiple ecosystem processes, such as coarse detritus processing which is driven by larval caddisflies in this system 20 , 24 . Thus, ecosystem outcomes of range shifts and subsequent changes to animal or plant assemblages are likely to vary among ecosystem processes.…”

“…Instead, the bulk of animal-driven supply was provided by dipterans and zooplankton with higher mass-specific excretion rates. Although the caddisfly assemblage is biomass-dominant among benthic invertebrates 18 , their low nutrient excretion rates may be constrained by the nutrient-poor coarse sedge detritus that comprises 78–95% of their diets 19 , or by the need to rapidly attain large body sizes to consume more detritus 20 , evade predation 26 , 39 , and complete larval development 25 . Indeed, low detritivore nutrient supply contributions are consistent with slower energy and material transfer to higher trophic levels through detrital pathways relative to autotrophic pathways 43 .…”

“…1A, B ). Including the range expanding species, this caddisfly assemblage has high interspecific trait variation in species-specific N and P excretion and detritus processing rates 19 , 20 . The influence of interspecific variation in invertebrate functional traits on fundamental ecosystem processes like nutrient cycling and detritus breakdown is increasingly recognized in aquatic 21 , 22 and terrestrial ecosystems 11 .…”