Large species shifts triggered by small forces.

Area of Science:

• Ecology
• Theoretical Ecology
• Systems Ecology

Background:

• Ecosystems can experience rapid shifts in species composition, often without obvious large-scale disturbances.
• Understanding the drivers of these sudden ecological changes is crucial for predicting ecosystem stability.

Purpose of the Study:

• To investigate the mechanisms behind sudden catastrophic shifts in complex ecological communities.
• To determine if gradual environmental changes can trigger abrupt community reorganizations.

Main Methods:

• Development and analysis of randomly generated multispecies models.
• Exploration of community dynamics under symmetrical and asymmetrical competition.
• Inclusion of predator-prey interactions (second trophic level) to assess their impact.

Main Results:

• Complex communities exhibit multiple attractors, leading to occasional catastrophic shifts.
• Alternative attractors robustly emerge, particularly with symmetrical competition where interspecific competition exceeds intraspecific competition.
• The presence of predators slightly reduced the probability of alternative attractors but did not fundamentally alter the findings.

Conclusions:

• Complex species interactions inherently generate alternative attractors, making ecosystems prone to sudden shifts.
• Ecosystem responses to environmental change are characterized by hysteresis and abrupt transitions.
• These findings offer insights into unexplained ecosystem regime shifts and potential causes of ancient mass extinctions.