Impacts of exotic species to foodweb structure of Hawaiian streams

Richard A. MacKenzie, Tara Holitzki, Karla McDermid

Research objectivesTo document how poeciliids are affecting Hawaiian streams.

We hypothesized that high densities of omnivorous poeciliids would:H1. shift food resources available for native gobiesH2. shift trophic position of native gobies

Study site

1. Substrate2. Riparian canopy3. Watershed4. Land use5. Elevation6. Stream width

• Collected samples for d13C, d15N, dD

1) Leaf litter2) Algae (epilithon scrapes)3) Invertebrates (surber)4) L. concolor and P. reticulata

(dipnets)

METHODS

13C (‰)

-26 -24 -22 -20 -18 -16 -14

1

5N

(‰

)

2

4

6

8

ChironomidaeC. analisL. concolor

13C (‰)

-26 -24 -22 -20 -18 -16 -14

1

5N

(‰

)

2

4

6

8

ChironomidaeC. analis (Green)C. analis (Brown)

Dugesia sp. Col 25 vs Col 26 L. concolor

Multiple food resources

Chironomid

C. analis (G)

C. analis (B)

Dugesia

Per

cen

t co

ntr

ibu

tio

n

0

20

40

60

80

100Gobies in poeciliid-free streamsGobies in poeciliid-invaded streams

*

A

MacKenzie et al. in review

FCL INV

Chiron

omid

C. ana

lis (G

)

C. ana

lis (B

)

Duges

ia

Per

cen

t co

ntr

ibu

tio

n

0

20

40

60

80

100Exotic poeciliids in poeciliid-invaded streamsNative gobies in poeciliid-invaded streams

B

*

MacKenzie et al. in review

41-44%36-56%

41-44%36-56%

93% 68%32%

???%

Trophic position of L. concolor

Trophic positionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2

Vander Zanden et al. 1999

Poeciliid-free Poeciliid-invaded

Fo

od

Ch

ain

Len

gth

0

1

2

3

4p < 0.05

Conclusions1. 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 lengthin 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

kiawe native veg.

open (no fish)

open (fish)

Anchialine pool food web

D (‰)

-220 -200 -180 -160 -140 -120 -100

1

3C

(‰

)

-26

-24

-22

-20

-18

-16

-14

-12

-10

kiawemiloopen (no fish)open (fish)

algae

algae

leaflitter

leaflitter

Chironomidae65%

Diptera15%

JV Atyids12%

Larval Atyids5%

C. analis3%

Lentipes concolor gut content

Hawai‘i

Oahu

D (‰)

-170 -160 -150 -140 -130 -120 -110 -100 -90

15N

(‰

)

3

4

5

6

7

8

9

10 Midge fly (chironomid)

Caddisfly

L. concolor (non-invaded stream)

MacKenzie et al. in review

D (‰)

-170 -160 -150 -140 -130 -120 -110 -100 -90

15N

(‰

)

3

4

5

6

7

8

9

10 Midge fly (chironomid)CaddisflyL. concolor (invaded stream)L. concolor (non-invaded stream)P. reticulata

MacKenzie et al. in review

Trophic positionconsumer = (d15Nconsumer – d15Nbaseline)/3.4 + 2

• Calculated percent contributions to diets using ISOSOURCE (Phillips and Gregg 2003)

• Calculated trophic position (Vander Zanden et al. 1999)

METHODSMETHODS

Invasive taxa in Pearl Harbor

No.

Aquatic insects 49

Crustaceans 5

Mollusks 10

Amphibians 3

Fish 18

Cheumatopsyche analisProcambrus clarkii

Pomacea canaliculata

Englund 2002

Rana catesbeiana

Bufo marinus

Sarotherodon melanochromis

Gambusia affinis

40%

60%

80%20%

Vander Zanden et al. 1999

13C (‰)

-26 -24 -22 -20 -18 -16 -14

1

5N

(‰

)

2

4

6

8

ChironomidaeC. analis

13C (‰)

-26 -24 -22 -20 -18 -16 -14

1

5N

(‰

)

2

4

6

8

ChironomidaeC. analisL. concolor

13C

-26 -24 -22 -20 -18 -16 -14

1

5N

(‰

)

2

4

6

8

ChironomidaeC. analisL. concolor