Microbial communities display alternative stable states in a fluctuating environment.

Area of Science:

• Ecology
• Microbiology
• Theoretical Ecology

Background:

• Environmental fluctuations are key drivers in ecological systems.
• While disturbances can increase biodiversity, other outcomes like competitive exclusion are possible.
• Understanding species' responses to fluctuating environments is crucial for ecological theory.

Purpose of the Study:

• To investigate the effects of environmental fluctuations on bacterial community dynamics.
• To explore whether fluctuating environments lead to coexistence or alternative stable states.
• To test the predictions of the Lotka-Volterra model in fluctuating conditions.

Main Methods:

• Utilizing laboratory microcosms with cocultures of two bacterial species (P. putida and P. veronii).
• Manipulating dilution rates (low, high, and alternating) to simulate environmental fluctuations.
• Comparing experimental results with predictions from the Lotka-Volterra model.

Main Results:

• At low dilution rates, P. veronii was excluded; at high rates, P. putida was excluded.
• Alternating dilution rates resulted in alternative stable states, dependent on initial species proportions.
• The Lotka-Volterra model accurately predicted these outcomes, including the effect of time-averaged mortality.

Conclusions:

• Fluctuating environments can lead to alternative stable states rather than guaranteed coexistence or increased biodiversity.
• The timing of environmental fluctuations is critical in determining community structure.
• Simple ecological models, like Lotka-Volterra, can effectively predict community responses to environmental variability.