Effects of Gopher Mounds on Plant Species Diversity in a Meadow

System

Nina GriffinEcoInformatics Summer InstituteHJ Andrews Experimental Forest

August 24, 2007

Advisor: Dr. Charlie Halpern

University of Washington

Introduction

• Pocket Gophers– Small rodents that tunnel

underneath the soil and deposit as mounds.

– Diet: Forbs mostly, and some grasses

• Mounds=Disturbance– Reduces competition– Increases diversity

http://snohomish.wsu.edu/photos/gopher2.jpg

The Intermediate Disturbance Hypothesis

• When disturbance is too small and infrequent OR too large and frequent = Little/no species diversity.

• At intermediate sizes and frequencies = Maximum species diversity

http://www.epa.gov/watertrain/ecology/s18.jpg

Previous Research: Diversity-Disturbance Relationship

• IDH modeled in tropical rain forests, coral reef systems, phytoplankton marine communities

• Positive relationship• Negative relationship• No relationship• Bimodal curve* Each ecosystem is unique and needs to

be studied individually.

Previous Research: Gopher Mounds and Plant Diversity

• Little research with conflicting results on gopher mounds in meadow systems.

• Rogers et al (2001) - Prairies Decrease

• Olff and Ritchie (1998) – Grasslands Increase or

decrease

• Huntly (1994) – Meadows Increase

Objectives

• Relationship between mound activity and plant species diversity in a meadow ecosystem.

• Test IDH for this ecosystem.

Methods

• Site: Lodgepole Pine Meadow, Bunchgrass Ridge, Oregon.

Methods

• Collection: Ten - 2mx2m plots randomly– 1mx1m subplots within

– Plant species and abundance

– Mound size and age–Fresh, Young, Old

• Used Excel to analyze data

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

(m)

(m)

.

Grasses Abundance(%)

Agropyron repens 2.6

Bromus carinatus 12.8

Danthonia intermedia 4

Elymus glaucus <1

Festuca idahoensis 44.6

Poa prantensis 1

Forbs

Achillea millefolium 8.3

Agoseris aurantiaca <1

Aster occidentalis 1

Cirsium callilepis 4.1

Erigeron aliceae 5

Fragaria vesca 4

Hieracium gracile 3

Lupinus latifolius 1

Orthocarpus imbricatus 2.8

Phlox diffusa 12.5

Pteridium aquilinum 7

http://www.baynatives.com/plants/Festuca-idahoensis/

http://www.fs.fed.us/database/feis/plants/graminoid/brocar/all.html

http://www.larkspurbooks.com/Polem1.html

Results• No clear relationship between species richness and

disturbance. • IDH is NOT followed.

4

5

6

7

8

9

10

11

12

0 10 20 30 40 50 60 70 80 90 100

Disturbance (%)

Spec

ies

rich

nes

s .

4

6

8

10

12

0 20 40 60

Disturbance (%)

Spec

ies

rich

nes

s

.Fresh mounds, 1mx1m subplots

4

6

8

10

0 20 40 60 80 100

Disturbance (%)

Spec

ies

rich

nes

s

.

Young mounds, 1mx1m subplots

0.8

1

1.2

1.4

1.6

1.8

0 10 20 30 40 50 60 70 80 90

Disturbance (%)

H'

Fresh

Young

Old

Shannon-Weiner, 1mx1m subplots

IDH is not followed by this system on the scale of one meadow.

Plant Cover• Graminoids=grasses

– Dominant plant type in meadow– Lowest abundance on “Fresh” mounds– Greatest on “Old” mounds

• Forbs=non-grasses– Greatest abundance on “Fresh” mounds – Lowest on “Old” mounds

• Fresh mounds DO reduce competition and alter the composition of the plots.

Factors that Affect Diversity

Disturbance• Soil composition• Nutrient availability• Precipitation• Snow Pack• Distance

Spatial Analysis

• Pairs of 1mx1m subplots (M:M, N:N, M:N)

– Distance (meters) between

– Difference in species richness

– Difference in Shannon-Weiner Index

– Number of species shared

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

(m)

(m)

.

2

3

4

5

6

7

8

0 5 10 15 20 25 30 35 40 45 50

Distance (m)

Spec

ies

shar

ed

.

M, M

N, N

M, N

Number of species shared decreases with distance

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 5 10 15 20 25 30 35 40 45 50

Distance (M)

Diffe

rence

in s

pec

ies

rich

nes

s

.

M, M

N, N

M, N

Difference in species richness increases

with distance.

Plot typeDistance (m)

Mean

M, M 0-2 0.38

N, N 0-2 0.46

M, N 0-2 1.00

Spatial Analysis: Conclusions

• Distance IS a confounding factor:– Subplots closer together shared more species

than those further apart.– Subplots further apart had a greater

difference in species richness.

• Although mounds alone do not increase diversity, they contain different species and so add diversity.

Why is this important?

• Grassland and meadow biodiversity

• Herbivores controlling species diversity

• Gophers labeled as “pests”

• This study suggests that they aren’t!

Future Studies

• Look at other factors: soil, precipitation.

• Larger spatial scale: multiple meadows

• Create a model to show succession in the system over time and the effects on plant species.

Acknowledgements

• National Science Foundation

• Charlie Halpern, Desiree Tullos, Nicole Czarnomski, Julia Jones, and Jorge Ramirez.

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