Effects of Gopher Mounds on Plant
Species Diversity in a Meadow
System
Nina Griffin
EcoInformatics Summer Institute
HJ 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
70
60
(m)
.
50
40
30
20
10
0
0
10
20
30
40
(m)
50
60
70
Grasses
Abundance(%)
Agropyron repens
2.6
Bromus carinatus
12.8
Danthonia intermedia
Elymus glaucus
Festuca idahoensis
Poa prantensis
4
<1
44.6
1
http://www.baynatives.com/pla
nts/Festuca-idahoensis/
http://www.fs.fed.us/database/feis/
plants/graminoid/brocar/all.html
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
Phlox diffusa
Pteridium aquilinum
2.8
12.5
7
http://www.larkspurbooks.com/Polem1.html
Results
.
• No clear relationship between species richness and
disturbance.
• IDH is NOT followed.
12
Species richness
11
10
9
8
7
6
5
4
0
10
20
30
40
50
Disturbance (%)
60
70
80
90
100
Fresh mounds, 1mx1m subplots
Young mounds, 1mx1m subplots
10
Species richness
10
8
6
4
8
6
4
0
20
40
60
0
20
Disturbance (%)
40
60
80
100
Disturbance (%)
Shannon-Weiner, 1mx1m subplots
1.8
1.6
1.4
Fresh
H'
Species richness
.
.
12
Young
1.2
Old
1
0.8
0
10
20
30
40
50
60
70
80
90
Disturbance (%)
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
70
60
(m)
.
50
40
30
20
10
0
0
10
20
30
40
(m)
50
60
70
8
7
Species shared
.
6
M, M
N, N
5
M, N
4
3
2
0
5
10
15
20
25
30
35
40
45
Distance (m)
Number of species shared decreases with distance
50
4.5
Difference in species richness
.
4
3.5
3
2.5
M, M
N, N
M, N
2
1.5
1
0.5
0
0
5
10
15
20
25
30
35
40
45
50
Distance (M)
Difference in species
richness increases
with distance.
Plot type
Distance
(m)
M, M
0-2
0.38
N, N
0-2
0.46
M, N
0-2
1.00
Mean
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.
Works Cited
Aronson, R.B., and Precht, W.F. 1995. Landscape patters of reef coral diversity: a test of the intermediate disturbance
hypothesis. Journal of Experimental Marine Biology and Ecology 192:1-14.
Coggins, S.T. and Conover, M.R. 2005. Effects of pocket gophers on the herbaceous vegetation growing in aspen meadows.
Wildlife Society Bulletin 33:1210-1215.
Fox, J.F., and Connell, J.H. 1979. Intermediate-Disturbance Hypothesis. Science 204: 1344-1345.
Gibson, D.J. 1989. Effects of Animal Disturbance on Tallgrass Prairie Vegetation. American Midland Naturalist 121:144-154.
Huntly, N., and Reichman, O.J. 1994. Effects of subterranean mammalian herbivores on vegetation. Journal of Mammalogy
75: 852-859.
Inouye, R.S., N. Huntly, and Wasley G.A. 1997. Effects of pocket gophers (Geomys bursarius) on microtopographic variation.
Journal of Mammalogy 78: 1144-1148.
Inouye, R.S., N.J. Huntly, D. Tilman, and Tester, J.R. 1987. Pocket gophers (Geomys bursarius), vegetation, and soil nitrogen
along a successional sere in east central Minnesota. Oceologia 73: 178-184.
Johst, K., and Huth, A. 2005. Testing the Intermediate Disturbance Hypothesis: When will there be two peaks of diversity?
Diversity and Disturbances 11:111-120.
Jones, C. C., Halpern, C. B., and Niederer, J. In review. Plant succession on gopher
mounds in western Cascade meadows: consequences for species diversity and heterogeneity. American Midland Naturalist.
Klaas, B.A., Danielson, B.J., Moloney, K.A. 1998. Influence of pocket gophers on meadow boles in a tallgrass prairie. Journal
of Mammalogy 79:942-952.
Kondoh, M. 2001. Unifying the relationships of species richness to productivity and disturbance. Biological Sciences 268:269271.
Kovacs, M. ed. 1992. Biological Indicators in Environmental Protection. Ellis Horwood, London, England, pgs 23-24.
Molino, J-F., and Sabatier, D. 2001. Tree diversity in tropical rain forests: a validation of the Intermediate Disturbance
Hypothesis. Science 294:1702-1704.
Olff H. and Ritchie, M.E. 1998. Effects of herbivores on grassland plant diversity. TREE 13:261-266.
Pain. R.T. 1966. Food web complexity and species diversity. The American Naturalist 100:65-75.
Proulx, M., and Mazumder, A. 1998. Reversal of grazing impact on plant species richness in nutrient-poor vs. nutrient-rich
ecosystems. Ecology 79:2581-2592.
Rogers, W.E., Hartnett D.C., and Elder, B. 2001. Effects of plains Pocket Gopher (Geomys bursarius) disturbances on
tallgrass-prairie plant community structure. American Midland Naturalist 145:344-357.
Sommer, U. 1995. An experimental test of the intermediate disturbance hypothesis using cultures of marine phytoplankton.
Limnology and Oceanography 40:1271-1277.
Teipner, C.L., Garton, E.O., and Nelson, L. 1983. Pocket Gophers in Forest Ecosystems. Ogden, Utah : U.S. Dept. of
Agriculture, Forest Service, Intermountain Forest and Range Experiment Station.