Highly variable spread rates in replicated biological invasions: fundamental limits to predictability.

Area of Science:

• Ecology
• Evolutionary Biology
• Invasion Biology

Background:

• Mean spread rates of invasive species are well-studied.
• Variance in spread rates, driven by environmental or internal factors, is often overlooked.
• Endogenous variability (demographic/genetic stochasticity) is a key but empirically unstudied driver of spread rate variance.

Purpose of the Study:

• To investigate the role of endogenous variability in driving variance in species' spread rates.
• To empirically test the impact of internal stochasticity on invasion dynamics.
• To assess the predictability of invasion spread in simple ecological systems.

Main Methods:

• Utilized laboratory microcosms for replicated invasions of the flour beetle, Tribolium castaneum.
• Measured and compared spread rates across multiple independent invasion experiments.
• Analyzed variance in spread rates to distinguish between exogenous and endogenous drivers.

Main Results:

• Endogenously generated variance in spread rates was found to be remarkably high among replicate invasions.
• Observed variation exceeded levels attributable to demographic stochasticity alone.
• Inherent unpredictability was evident even in controlled laboratory settings.

Conclusions:

• Endogenous variability significantly contributes to the variance in invasion spread rates.
• Demographic stochasticity alone cannot explain the observed unpredictability.
• Ecological invasion spread is fundamentally less predictable than previously assumed, even under simplified conditions.