Background As number of species varies with volume (Taylor, 1997, and others), how is assemblage...

Background• As number of species varies with volume

(Taylor, 1997, and others), how is assemblage stability affected when isolated pools shrink during summer?

• Across years and seasons, extinction rates of fish assemblages are related positively to flow variation; immigration rates are greatest downstream (Taylor and Warren, 2001). Are patterns of extinction and immigration rates within a season (i.e., at smaller scales) similar to those at larger scales?

Lak e W ino na

Alu m Fo rk

Mid dl e F or k

Bre ad C re ekNo rth A lum F or k

So uth A lum F or k

Ouachita Highlands, Alum Fork of Saline River

Stream Flow data for Alum Fork Saline River

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Str

eam

flow

(ft3

/s)

-50

0

50

100

150

200

250R

ainfall (mm

)

80

90

100

110

120

130

140

150

Stream flow (1990 - 2000) Rainfall (1931 - 1995) Stream flow (2002)

#

#

#

#

#

#

#

##

#

#

#

#

#

Bread Creek

North Alum Fork

South Alum Fork

Changes in Volumedark shade = greater changes

Objectives

• Characterize changes in stability of fish and aquatic insect assemblages from intermittent streams during summer dry-down

• Estimate site-specific immigration and extinction rates to investigate why these processes differ across sites

Methods• Fishes sampled for 48 hours with metal Gee minnow traps and a plastic floating minnow trap; once a month, June – Sept

Methods• Aquatic invertebrates: Hester-Dendy traps and a d-frame sweep net (6, 10 second passes along edge of pools); once a month, July - Sept

Environmental variables recorded between 10 am and 2 pm (pool size, temperature, DO, chlorophyll a, conductivity, pH, turbidity)

Stability of Fish AssemblagesJaccard’s measure of stability from presence-absenceR2 = 0.744; P < 0.01Variable Std. Coef. t-value P-valueDistance Upstream -0.61 -3.82 < 0.01Volume (c.v.) -0.46 -2.89 0.01

Bray-Curtis measure of stability from relative abundancesR2 = 0.906; P < 0.01Variable Std. Coef. t-value P-valueVolume (c.v.) 0.64 4.30 <0.01Dissolved Oxygen -0.48 -4.07 <0.01Chlorophyll -0.39 -3.20 0.01Temperature -0.51 -3.91 <0.01Specific Conductivity 0.36 2.13 0.07

coefficient of variation for volume

0 1

Sta

bilit

y

0.0

0.2

0.4

0.6

0.8Bray-Curtis; unbroken; r2 = 0.44; P = 0.01

Jaccard's; broken; r2 = 0.44; P = 0.02

Stability of Fish Assemblages

Distance Upstream (m)

0 2000 4000 6000 8000 10000 12000 14000 16000

Ass

embl

age

Sta

bilit

y

0.0

0.2

0.4

0.6

0.8

r2 = 0.66P < 0.05

Stability of Fish Assemblages

#

#

#

#

#

#

#

##

#

#

#

#

#

Bread Creek

North Alum Fork

South Alum Fork

dark shade = higher stability

Stability of Fish Assemblages

Stability of Aquatic Insect Assemblages

Bray-Curtis measure of stability from relative abundancesR2 = 0.927; P < 0.01Variable Std. Coef. t-value P-valueSpecific Conductivity (c.v.) 0.91 -10.22 <0.01Turbidity 0.75 8.27 <0.01Chlorophyll (c.v.) -0.98 6.83 <0.01

Jaccard’s measure of stability from presence-absence

Variables n.s.

Stability of Aquatic Insect Assemblages

coefficient of variation for specific conductivity

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Ass

em

blag

e S

tab

ility

0.0

0.1

0.2

0.3

0.4

0.5

0.6

r2 = 0.39P < 0.05

Immigration-Extinction Rates

Fishes(p = 0.02)

Aquatic Insects(p = 0.06)

Immigration Rate Extinction Rate

Average probabilities of immigration and extinction calculated for each site following Taylor and Warren (2001)

0.44a 0.34b

0.40a 0.56b

Immigration-Extinction Rates:Fishes

Immigration R2 = 0.56; P = 0.01Variable Std. Coef. t-value P-valueDistance Upstream 0.44 2.19 0.05Chlorophyll 0.54 2.66 0.02

Extinction R2 = 0.58; P = 0.01Variable Std. Coef. t-value P-valueVolume (c.v.) 0.53 2.68 0.03Chlorophyll (c.v.) -0.48 -2.42 0.02

Distance upstream (m)

0 2000 4000 6000 8000 10000 12000 14000 16000

Pro

babi

lity

of im

mig

ratio

n (f

ishe

s)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Immigration-Extinction Rates: Fishes

Immigration-Extinction Rates: Fishes

coefficient of variation for volume

0 1

Pro

babi

lity

of e

xtin

ctio

n (f

ishe

s)

0.2

0.4

0.6

0.8

1.0

1.2

Immigration-Extinction Rates: Insects

Immigration

Variables n.s.; related mainly to life history?

Extinction R2 = 0.69; P = 0.01Variable Std. Coef. t-value P-valueDistance Upstream -0.54 -3.01 0.01Chlorophyll (c.v.) -0.72 -3.86 <0.01pH (c.v.) -0.34 -1.84 0.10

Paraleptophelibia spp.Jy

4A

u4S

e4 Jy5

Au5

Se5 Jy6

Au6

Se6 Jy9

Au9

Se9

Jy11

Au1

1S

e11

Jy12

Au1

2S

e12

Jy14

Au1

4S

e14

Jy15

Au1

5S

e15

Jy17

Au1

7S

e17

Jy18

Au1

8S

e18

Jy24

Au2

4S

e24

Log

Abu

ndan

ce

0

2

4

6

8

10

12

14

16

Immigration-Extinction Rates: Insects

Distance upstream (m)0 2000 4000 6000 8000 10000120001400016000

Pro

babi

lity

of e

xtin

ctio

n (in

sect

s)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Immigration-Extinction Rates: Insects

Summary• Fish assemblage stability is sensitive to changes in

habitat size, quality, and position • During summer, fish assemblage stability was

lowest and immigration, highest at upstream sites• Aquatic insect assemblage stability is sensitive to

changes in habitat quality, and changes in structure related to species-specific life histories

• Insect assemblage stability generally exhibited patterns different from those of fishes, and were less influenced by pool size or position

AcknowledgementsUS Forest Service

P. Raelynn DeatonMarceau RatardAndy Sanderson