environmental factors and fish ecology. environmental factors affecting organisms and local...
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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
ResultsMean CSS in cm/sec (SE)
Low complexity High complexity
Central stoneroller 35.51 (2.52) 37.40 (8.40)
Cardinal shiner 31.70 (2.38) 26.48 (4.59)
Orangethroat darter 22.49 (3.02) 17.25 (4.49)
Longear sunfish 14.40 (0.18) 15.74 (3.67)
Green sunfish 13.89 (0.59) 11.41 (5.77)
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CDS CSR GSF LES OTD
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CDS CSR GSF LES OTD
Low complexity
Half-CSS speed
Low complexity
CSS speed
High complexity
Half-CSS speed
High complexity
CSS speed
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eloc
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CDS CSR GSF LES OTD
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CDS CSR GSF LES OTD
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
S amplen=56 7
Runn=18 9
S t ream S ect ionn=6 3
S t reamn=21
S ub-wat ershedn=7• 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 km2
• Streams 2nd or 3rd order.
• Stream sections at least 500 m apart defined as 3 consecutive runs separated by riffle or pool habitats.
Spring RiverWatershed
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
Effect Variance % explainedSub-watershed 0.033 27.0
Stream 0.029 23.8
Stream section 0.026 21.3
Run 0.018 14.8
Sample 0.016 13.1
TSS 0.122
Variable Watershed Stream StreamSection
% Cobble ** ** *Depth ** N. S. *% Pebble ** N. S. N. S.Conductivity ** N. S. N. S.Temperature ** * N. S.Width ** ** N. S.pH * N. S. N. S.% Gravel N. S. ** **% Boulder N. S. N. S. N. S.Velocity N. S. N. S. N. S.% Bedrock N. S. N. S. N. S.
Importance of Environmental Variables with Scale
** < 0.005 * < 0.05 N. S. = Not Significant
Contribution to Crayfish Species Relationships
Effect SS % varianceexplained
F p
Sub-watershed 0.189 18.9 21.7 0.002Stream 0.123 12.3 6.95 0.002Stream section 0.158 15.8 3.59 0.002Run 0.195 19.5 1.74 0.005Sample (RSS) 0.335 33.5 - -
TSS 1.00
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.
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