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?

Ouachita Highlands, Alum Fork of Saline River

# # # # # # # # # # # # # # Bread Creek North Alum Fork South Alum Fork Changes in Volume dark 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 Assemblages Jaccard’s measure of stability from presence-absence R 2 = 0.744; P < 0.01 VariableStd. Coef.t-valueP-value Distance Upstream < 0.01 Volume (c.v.) Bray-Curtis measure of stability from relative abundances R 2 = 0.906; P < 0.01 VariableStd. Coef.t-valueP-value Volume (c.v.) <0.01 Dissolved Oxygen <0.01 Chlorophyll Temperature <0.01 Specific Conductivity

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 abundances R 2 = 0.927; P < 0.01 Variable Std. Coef.t-valueP-value Specific Conductivity (c.v.) <0.01 Turbidity <0.01 Chlorophyll (c.v.) <0.01 Jaccard’s measure of stability from presence-absence Variables n.s.

Stability of Aquatic Insect Assemblages

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) 0.44 a 0.34 b 0.40 a 0.56 b

Immigration-Extinction Rates: Fishes Immigration R 2 = 0.56; P = 0.01 VariableStd. Coef.t-value P-value Distance Upstream Chlorophyll Extinction R 2 = 0.58; P = 0.01 VariableStd. Coef.t-valueP-value Volume (c.v.) Chlorophyll (c.v.)

Immigration-Extinction Rates: Fishes

Immigration-Extinction Rates: Insects Immigration Variables n.s.; related mainly to life history? Extinction R 2 = 0.69; P = 0.01 VariableStd. Coef.t-value P-value Distance Upstream Chlorophyll (c.v.) <0.01 pH (c.v.)

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

Acknowledgements US Forest Service P. Raelynn Deaton Marceau Ratard Andy Sanderson