Interactions at surface–subterranean ecotones: structure and function of food webs within spring orifices

A bstract Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for...

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Bibliographic Details
Published in:Oecologia 2021-05, Vol.196 (1), p.235-248
Main Authors: Nair, Parvathi, Diaz, Peter H., Nowlin, Weston H.
Format: Article
Language:English
Subjects:
Algae
Amino acids
Aquatic crustaceans
Aquatic ecosystems
Aquatic invertebrates
Associated species
Bacteria
Biomedical and Life Sciences
Coexistence
Conditional probability
Diet
Ecology
Ecosystem Ecology–Original Research
Ecotones
Endemic species
Food
Food chains
Food chains (Ecology)
Food resources
Food sources
Food webs
Fungi
Hydrology/Water Resources
Invertebrates
Isotopes
Life Sciences
Niche overlap
Niches
Organic matter
Orifices
Partitioning
Periphyton
Plant Sciences
Probability theory
Resource partitioning
Riparian land
Spring
Stable isotopes
Structure-function relationships
Terrestrial environments
Underground structures
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Summary:A bstract Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for population coexistence in these presumably low resource environments are not well understood. We examined invertebrate communities at two spring complexes in Texas, USA and assessed resource use and food web structure at spring orifices using stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N). Using bulk δ 13 C and δ 15 N of organisms and potential food sources, we elucidated dietary sources and found that invertebrate communities exhibited resource partitioning and contained two main food chains (periphyton versus terrestrial organic matter [OM]). In both spring complexes, several endemic spring orifice associated and subterranean taxa derived most of their diet from terrestrial OM. Analysis of compound-specific stable isotopes (i.e., δ 13 C of essential amino acids, EAAs) from two co-occurring elmid species indicated that the endemic spring orifice-associated species ( Heterelmis comalensis ) derived > 80% of its EAAs from bacteria, whereas the widespread surface species ( Microcylloepus pusillus ) derived its EAAs from a more equitable mix of bacteria, fungi, and algae. We additionally calculated niche overlap among of several taxonomically related groups (aquatic beetles and amphipods) that co-occur in spring ecotones and posterior probability estimates indicated little to no niche overlap among related species. Results indicate that invertebrates at subterranean—surface aquatic ecotones are partitioning food resources and highlight the importance of connections to riparian zones for persistence of several endemic invertebrates.
ISSN:0029-8549
1432-1939
DOI:10.1007/s00442-021-04912-z