Trophic interactions in an austral temperate ephemeral pond inferred using stable isotope analysis
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Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period.
KeywordsEphemeral Generalists Trophic complexity Hydro-period Stable isotope Bayesian analysis in R (SIBER) Specialists
This paper is dedicated to the memory of Sven Kaehler who carried out the stable isotope analysis. This study was made possible through financial and logistical support from Rhodes University and the National Research Foundation (NRF) of South Africa (UID: 77444). We thank PSR Weyl and T Bellingan (Department of Zoology and Entomology, Rhodes University) for assistance with macrophyte and macroinvertebrate identification, respectively, and Eduardo Suárez-Morales of El Colegio La Frontera Sur (ECOSUR), Mexico for copepod identification. In addition, we extend our gratitude to the White family for granting us access to their property. We thank the handling editor Mariana Meerhoff for her patience and two anonymous reviewers for their work and time through providing insightful and useful comments on the manuscript.
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