Individual size distributions (ISD; also known as size spectra), are an empirical relationship describing the decline in relative abundance from small to large individuals. ISD relationships are incredibly consistent across ecosystems and habitats and have been proposed as a simple, universal metric for assessing ecological status. Increased environmental temperatures are expected to favor small individuals leading to steeper ISDs supporting fewer large individuals. The Teton Alpine Stream Research (TASR) project has been monitoring alpine streams since 2015. Streams are grouped based on water sources: glacier, rock glacier, and snowfield. Monitoring includes hourly stream temperature measurements and annual collection of quantitative benthic macroinvertebrate samples. Temperature analyses have indicated summer temperatures in glacier and rock glacier streams are consistent across years, but snowfield streams are warming rapidly. This system presents a unique opportunity to test if ISD relationships change or are consistent in response to increased environmental temperatures.
ISD relationships were estimated from quantitative macroinvertebrate samples from two time points (first and last sample) from the three stream categories, and will be analyzed with a two-way ANOVA to test for effects of stream group, time point, and their interactive effects.
We hypothesize that the ISD relationships will remain consistent through time in both the glacier and rock glacier streams. However, we predict steeper ISD relationships in the snowfield stream due to a higher relative abundance of small individuals.
The long-term and repeatable data collection offers a unique opportunity to assess ISD pattern changes in response to rapidly rising temperatures. The information from this research is widely applicable across mountain and alpine environments which are experiencing rapid climate warming.