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: H1. shift food resources available for native gobies H2. shift trophic position of native gobies

Study site 1.Substrate 2.Riparian canopy 3.Watershed 4.Land use 5.Elevation 6.Stream width

Collected samples for  13 C,  15 N,  D 1)Leaf litter 2)Algae (epilithon scrapes) 3)Invertebrates (surber) 4)L. concolor and P. reticulata (dipnets) METHODS

Multiple food resources

MacKenzie et al. in review

41-44% 36-56%

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

???%

Trophic position of L. concolor Trophic position consumer = (  15 N consumer –  15 N baseline )/ Vander Zanden et al. 1999

Conclusions 1.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) 2.Trophic position of L. concolor decreased by 1/2 trophic length in poeciliid-invaded streams 3.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)

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

kiawenative veg. open (no fish) open (fish)

algae leaf litter leaf litter

Hawai ‘i Oahu

MacKenzie et al. in review

Trophic position consumer = (  15 N consumer –  15 N baseline )/ Calculated percent contributions to diets using ISOSOURCE (Phillips and Gregg 2003) Calculated trophic position (Vander Zanden et al. 1999) METHODS

Invasive taxa in Pearl Harbor No. Aquatic insects49 Crustaceans5 Mollusks10 Amphibians3 Fish18 Cheumatopsyche analis Procambrus clarkii Pomacea canaliculata Englund 2002 Rana catesbeiana Bufo marinus Sarotherodon melanochromis Gambusia affinis

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