PS 4-48 - CANCELLED - Citizen science data reveal spatial patterns in invertebrate assemblages across the Sky Island ecoregion, USA

Abstract: The Madrean Sky Islands of southern Arizona house some of the richest biodiversity in North America. Invertebrates comprise a substantial portion of that biodiversity and function as an essential trophic linkage between aquatic and terrestrial biomes. Sky Island invertebrates are supported by the region’s diverse topographic, climatic, and vegetational features, as well as its aquatic habitats, such as springs, streams, rivers, and spring-fed wetlands (cienegas). But changes to the region’s disturbance regimes, land use, seasonal temperature ranges, and its bimodal monsoon season may jeopardize the long-term sustainability of invertebrate communities along the aquatic—terrestrial continuum.

This study focuses on Sky Island invertebrate species assemblages using springs as survey locations. Using citizen science data, we establish a baseline of springs-associated species assemblages and analyze community structure both within and among mountain ranges (n=8). 331 springs are included in the study, comprising ~40% of the total number of mapped springs in Arizona’s portion of the Sky Island ecoregion. Springs were surveyed using protocols developed by Stevens et al (2016) of the Spring Stewardship Institute, a 501(c)3 based in Flagstaff, AZ, USA. Surveys were conducted from 2012-2019 by dozens of volunteers, including lay public and science professionals, who took part in the “Sky Island Project” (SIP).

For this analysis, we extracted SIP survey data from the Springs Online database, including: spring type, location, and elevation; pH, specific conductance, water temperature, and flow rate; and macroinvertebrate species presence. We extracted additional data from other sources, including mid-scale vegetation dominance type (n=79; USDA), aspect (USGS digital elevation model), and time-since-fire (ignition dates and fire perimeters; NIFC).

We used NMDS to assess invertebrate community structure and found that hillslope springs were more constrained in species composition, while rheocrene springs supported a wider variety of species assemblages. NMDS plots also revealed that invertebrate communities were more similar within a mountain range than across mountain ranges, suggestive of dispersal limitations across the Sky Island landscape. These differences tracked changes in specific conductance, indicating that water chemistry likely plays an important role in structuring invertebrate communities. This was best illustrated in the Huachuca Mountains, which exhibited the largest variation in specific conductance and the greatest turnover (ß diversity) among springs, regardless of spring type. The relative isolation of communities within mountain ranges and their sensitivity to water chemistry indicate changes in local factors driven by climate and disturbance regimes may significantly alter these communities in the future.