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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
Impacts of exotic species to foodweb structure of Hawaiian streams

Richard A. MacKenzie, Tara Holitzki, Karla McDermid

research objectives
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
Study site
  • Substrate
  • Riparian canopy
  • Watershed
  • Land use
  • Elevation
  • Stream width
slide5

METHODS

  • Collected samples for d13C, d15N, dD
    • Leaf litter
    • Algae (epilithon scrapes)
    • Invertebrates (surber)
    • L. concolorand P. reticulata(dipnets)
slide10

41-44%

36-56%

slide11

41-44%

36-56%

32%

68%

93%

slide13

Trophic position of L. concolor

Trophicpositionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2

Vander Zanden et al. 1999

slide14

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)
impacts of exotic species to foodweb structure of hawaiian anchialine ponds
Impacts of exotic species to foodweb structure of Hawaiian anchialine ponds

Bruce Dudley, Richard A. MacKenzie, Troy Sakihara

slide16

kiawe

native veg.

open (no fish)

open (fish)

slide17

algae

leaf

litter

leaf

litter

algae

slide19

Oahu

Hawai‘i

slide22

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

slide23

Cheumatopsyche analis

Procambrusclarkii

Pomaceacanaliculata

Ranacatesbeiana

Englund 2002

Bufomarinus

Gambusiaaffinis

Sarotherodon melanochromis

slide24

60%

40%

20%

80%

Vander Zanden et al. 1999