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Impacts of exotic species to foodweb structure of Hawaiian streams

Impacts of exotic species to foodweb structure of Hawaiian streams. Richard A. MacKenzie, Tara Holitzki, Karla McDermid. Research objectives. To document how poeciliids are affecting Hawaiian streams. We hypothesized that high densities of omnivorous poeciliids would:

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Impacts of exotic species to foodweb structure of Hawaiian streams

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  1. Impacts of exotic species to foodweb structure of Hawaiian streams Richard A. MacKenzie, Tara Holitzki, Karla McDermid

  2. Research objectives To document how poeciliids are affecting Hawaiian streams. We hypothesized that high densities of omnivorous poeciliids would: H1. shift food resources available for native gobies H2. shift trophic position of native gobies

  3. Study site • Substrate • Riparian canopy • Watershed • Land use • Elevation • Stream width

  4. METHODS • Collected samples for d13C, d15N, dD • Leaf litter • Algae (epilithon scrapes) • Invertebrates (surber) • L. concolorand P. reticulata(dipnets)

  5. Multiple food resources

  6. MacKenzie et al. in review

  7. MacKenzie et al. in review

  8. 41-44% 36-56%

  9. 41-44% 36-56% 32% 68% 93%

  10. ???%

  11. Trophic position of L. concolor Trophicpositionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2 Vander Zanden et al. 1999

  12. Conclusions • Invasion of Hawaiian streams by exotic poeciliids are altering food web structure of native stream fish by shifting food resources from high (i.e., Chironomidae) to low quality food sources (i.e., Cheumatopsyche analis) • Trophic position of L. concolor decreased by 1/2 trophic lengthin poeciliid-invaded streams • The introduction of exotic invertebrates to Hawaiian streams (i.e., C. analis) may be altering food web structure by shifting basal food resources (e.g., increased importance of leaf litter)

  13. Impacts of exotic species to foodweb structure of Hawaiian anchialine ponds Bruce Dudley, Richard A. MacKenzie, Troy Sakihara

  14. kiawe native veg. open (no fish) open (fish)

  15. algae leaf litter leaf litter algae

  16. Oahu Hawai‘i

  17. MacKenzie et al. in review

  18. MacKenzie et al. in review

  19. METHODS METHODS • Calculated percent contributions to diets using ISOSOURCE (Phillips and Gregg 2003) • Calculated trophic position (Vander Zanden et al. 1999) Trophicpositionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2

  20. Cheumatopsyche analis Procambrusclarkii Pomaceacanaliculata Ranacatesbeiana Englund 2002 Bufomarinus Gambusiaaffinis Sarotherodon melanochromis

  21. 60% 40% 20% 80% Vander Zanden et al. 1999

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