Oregon State University · Fisheries & Wildlife · Alkinani 2025

Ecological Interactions Among Non-native Smallmouth Bass, Native & Introduced Crayfishes in Oregon Rivers

Dissertation Conceptual Framework · Interactive Reference
Study Species
🐟
Non-Native · Predator
Smallmouth Bass
Micropterus dolomieu
⟷
🦞
Native · Prey
Signal Crayfish
Pacifastacus leniusculus
⟷
🦀
Non-Native · Prey
Ringed Crayfish
Faxonius neglectus
Study Systems — Oregon, USA
Willamette River Basin
Large, low-gradient mainstem. Agricultural and urban landscape. Dominated by native Signal Crayfish; Ringed Crayfish only localized in upstream sub-basins.
Signal Crayfish Ringed (localized)
Umpqua River Basin
Cooler, steeper, geomorphically heterogeneous. Mixed assemblage. Provides thermal heterogeneity (cold ≤18°C / warm ≥21°C) essential for thermal stratification design.
Signal Crayfish Ringed Crayfish Red Swamp Crayfish
Invasion Hypotheses Tested — Click to Expand
ERH
Enemy Release Hypothesis
Invaders experience reduced predator, parasite, and pathogen pressure in introduced range — enabling population growth and spread.
Chapters 1 · 2
NPH
Naïve Prey Hypothesis
Native prey lack effective antipredator responses to novel predators, increasing vulnerability and altering refuge behavior.
Chapters 2 · 3
IMH
Invasional Meltdown Hypothesis
Positive interactions among invaders — facilitation or habitat modification — amplify establishment and ecosystem impacts.
Chapters 1 · 3
Dissertation Chapters — Mechanistic Scaffold
Chapter 01 · Field
Trophic Ecology of Smallmouth Bass
Stomach Content Analysis
  • Frequency of occurrence (F%)
  • Percent by records (%R)
  • Jacobs' D electivity index
  • NMDS + PERMANOVA ordination
  • Detection-corrected occupancy for prey availability
Hypotheses Tested
ERH IMH
Chapter 02 · Laboratory
Predator–Prey Behavioral Trials
Controlled Tank Experiments
  • Prey choice (Signal vs Ringed, binary)
  • Attack latency + handling time
  • Refuge occupancy duration
  • Temperature × Shelter 2×2 design
  • GLMM with Fish_ID random effect
Hypotheses Tested
NPH ERH (OFT)
Chapter 03 · Lab + Field
Crayfish Competition & Thermal Context
Competition Trials + Thermal Gradients
  • Shelter dominance outcome (binary)
  • Displacement events + aggression
  • Exposure under predator cue
  • Thermal preference (gradient device)
  • Binomial GLMM, Cox PH models
Hypotheses Tested
NPH IMH
Interpretive Logic — What Do the Results Indicate?
📋
Ch. 1 Diet
Ringed or Signal consumed more?
→
🔬
Ch. 2 Trials
Handling vs naïveté mechanism?
→
🏠
Ch. 3 Shelter
Displacement ↑ exposure?
→
→
⚔️
Antagonistic
Bass suppresses non-native crayfish
→
🔥
Meltdown
Invaders facilitate each other; natives decline
Anticipated Outcome Scenarios
Scenario
Empirical Pattern Expected
Invasion Pathway Indicated
Bass consumes Ringed > Signal
Ch. 1 + Ch. 2
Positive electivity for Ringed Crayfish; shorter handling time; Ringed consumed first in trials
Antagonistic
Bass suppresses non-native invader
Signal exposed via displacement
Ch. 3
Ringed dominates shelters → Signal exposed → Signal consumed more under predator cue
Invasional Meltdown
Invader–invader facilitation harms native
Signal consumed despite lower availability
NPH test
Positive electivity for Signal; reduced antipredator behavior; longer exposure time in trials
Naïve Prey
Behavioral naïveté drives native vulnerability
No species preference detected
Null result
Electivity near zero; no behavioral asymmetry; equal handling times
Biotic Resistance
Bass limits both invaders equally