Resource use and ecological interactions of invertebrate communities in springs of central and west Texas

Authors: Weston Nowlin, Parvathi Nair, Nina Noreika, Pete Diaz, Chad Norris

Year: 2019

Abstract

Spring ecosystems serve as ecotones (i.e., transition zones between adjacent ecosystem types) between surface and subterranean as well as terrestrial and aquatic habitats. As ecotones, spring ecosystems often contain complex assemblages from multiple habitat and ecosystem types including spring obligate (crenic) taxa, subterranean taxa (hypogean), and more widespread surface water associated (epigean) species. This study examines patterns of resource and habitat use in the invertebrate communities at spring ecosystems in semi-arid and arid areas of central and west Texas, USA. We examined invertebrate food web structure and function at Comal Springs (central Texas), Finegan Springs (Devils River in west Texas) using stable isotopes of carbon (d13C), nitrogen (d15N) in organisms and their potential food sources. In the Comal and Finegan spring systems, endemic crenic and hypogean invertebrate species generally relied upon inputs of terrestrial organic matter (leaves and woody material) as their primary organic matter source, but more cosmopolitan epigean taxa relied upon algal-derived resources. We also found that the ecological niche (as determined by stable isotope values) of endemic crenic and hypogean species were narrow and exhibited little overlap with other species. We conducted a comparable study in several spring systems in the Davis Mountains region of west Texas (i.e., San Solomon systems) and similarly found that endemic and endangered spring obligate snail and amphipod fauna exhibit narrow ecological niches with little overlap with non-native invertebrates. Overall, our results indicate that invertebrate food webs found in spring ecotones exhibit a substantial trophic complexity and endemic fauna are finely partitioning food resources and exhibit narrow feeding niches. Results also highlight the importance of lateral connections to riparian zones as a source of organic matter for the macroinvertebrate communities in spring systems.