Environmental Factors and Fish Ecology

Environmental factors affecting organisms and local assemblages Many factors High complexity Abiotic Large, long Geological strata Climate change Small, short Micro-hydraulics Temperature Biotic Competition Predation From Matthews 1998

Important Abiotic Environmental Variables Affecting Organisms in Streams Current velocity/Discharge Substrate Temperature Dissolved oxygen Relationships between environmental variables can be very important

Organism Adaptations to Flow Streamlined shape –Fusiform shape –Reduced fins and fin location Suckers Benthic habit –Enlarged pectoral fins –Dorsal eyes –Loss of swim bladder

Effect of Current Velocity and Discharge on Substrate

Effect of Current Velocity on Fish Position maintenance –Swimming ability Species, size, life stage –Energy use Food availability –Drift feeders Bioenergetically –Cost/benefit relationship Hill and Grossman 1993

Effect of Substrate on Current Velocity and Flow Eddies Wake interference Quasi-smooth flow

Ozark Highlands Lower gradient Cobble-gravel Spring influence Boston Mountains Higher gradient Bedrock-cobble High flow variation

Research Questions Does fish morphology predict fish swimming ability and refuge use?

Central stoneroller Campostoma anomalum Cardinal shiner Notropis cardinalis Orangethroat darter Etheostoma spectabile Green sunfish Lepomis cyanellus Longear sunfish Lepomis megalotis Pictures by W. N. Roston, from ‘Fishes of Arkansas’ Five Common Arkansas Stream Fish

Two substrate types: 1. Complex (w/ rocks) 2. Smooth plexiglas Velocity increased by 10 cm/s every 15 min until fish exhaustion

Results Mean CSS in cm/sec (SE) Low complexityHigh complexity Central stoneroller (2.52)37.40 (8.40) Cardinal shiner (2.38)26.48 (4.59) Orangethroat darter (3.02)17.25 (4.49) Longear sunfish (0.18)15.74 (3.67) Green sunfish (0.59)11.41 (5.77)

Low complexity Half-CSS speed Low complexity CSS speed High complexity Half-CSS speed High complexity CSS speed Relative Velocity

Temperature Mean, max and min temps. –Survival –Growth –Reproduction Cumulative temperature –Degree-days –Latitude –Stream size –Groundwater influence –Elevation

Effect of Temperature on Egg Hatching

Temp and DO in Lakes and Rivers Allan 1995

Organisms Vary With Abiotic Variables

Longitudinal pattern in streams Rivers generally increase in size as one proceeds downstream –Velocity (U) varies with gradient, depth, and substrate texture Average velocity usually increases downstream! –Gradient decreases, but depth increases and friction decreases Gradient Friction Depth Velocity Distance from headwater Fish species and numbers are related to these changes in stream abiotic variables.

Size (Spatial and Temporal Scale) Matters Relationship between environmental variables and organisms is scale dependent

Questions How do crayfish species-environmental relationships change with spatial scale? How do lotic crayfish species relationships change with spatial scale?

Study Design Balanced, hierarchical design. Replicate units contained within a particular level. Each level represents a different level of spatial scale.

Study Site Drainage area of 3, 926 km 2 Streams 2nd or 3rd order. Stream sections at least 500 m apart defined as 3 consecutive runs separated by riffle or pool habitats. Spring River Watershed

Field Methods Measurements of substrate composition, stream width, current velocity, and depth measured at each sample location. Water temperature, pH, and conductivity measured in each stream section. Crayfish collected identified to species, sexed, and carapace length measured.

Contribution to Species-Environment Relationships

Importance of Environmental Variables with Scale ** < * < 0.05 N. S. = Not Significant

Contribution to Crayfish Species Relationships

Conclusions Importance of environmental variables differed among levels of scale. Largest scale (sub-watersheds) explained most variation in species-environmental relationships (27.0%) and this decreased with decreasing spatial scale. Greatest amount of variation in crayfish species relationships explained (33.5%) attributed to differences at the microhabitat (sample) level.