Effects of climate-induced distributional shifts in caddisfly larvae on detritus processing and ecosystem function in high-elevation ponds and wetlands

Background/Question/Methods

Ecologists have reported shifts in species distributions at both regional and local scales as a result of climate change. Over the past several decades, we have observed how changes in snowpack, the timing of snowmelt, and summer temperatures and patterns of precipitation in the Elk Mountains in central Colorado have affected the hydrology of high elevation ponds and wetlands, and in turn the distribution of aquatic invertebrates. Specifically, the elevational ranges of several species of detritivorous caddisfly larvae have shifted upslope, and within elevations, along local permanence gradients. Previous research suggests that the detritivorous larvae of these caddisflies might be considered foundational species in the sense they are 1) the only abundant animals that feed primarily on vascular plant detritus in high elevation ponds and wetlands, 2) among the biomass-dominant prey resources for predators, and 3) mobilizing nutrients from detrital-microbial substrates via excretion that in turn stimulates algal productivity. Thus, shifts in the species composition of this detritivore guild could affect energy and nutrient fluxes through both the brown (detrital) and green (algal) trophic paths in pond foodwebs. The overall goal of our research is to predict how climate-change induced changes in species composition in this detritivore guild will affect basic ecosystem processes in ponds and wetlands.

Results/Conclusions

Here we focus on quantifying species-specific rates of excretion of ammonium- nitrogen and total soluble phosphorus obtained pond-side using an incubation technique conducted in closed microcosms (plastic bags).  We found that 1) within species, there is little time-of-day variation in the per-unit biomass rate of excretion 2) many of the species have remarkably similar per-unit biomass excretion rates with similar N/P ratios, and 3) that background levels of these nutrients decrease with elevation. These data combined with survey data on abundance and nutrient/chlorophyll-a regressions will be used to parametrize models that can be used to make predictions for how shifts in species composition along local and regional gradients will affect overall pond productivity. Preliminary models suggest that shifts in the species composition of this detritivore guild will indeed lead to significantly different ambient levels of algal nutrients in ponds along permanence gradients and at different elevations. This work was enhanced by the collaborative expertise of the mentor’s long-term data on changing patterns of caddisfly distribution and abundance, and the student’s proficiency with the analytical techniques for quantifying how changes in community composition affect basic ecosystem processes.