Ecological drift and competitive interactions predict unique patterns in temporal fluctuations of population size

Area of Science:

• Ecology
• Population Dynamics
• Community Ecology

Background:

• Higher-order competitive interactions are crucial for stabilizing multi-species communities.
• The structure of competitive hierarchies significantly influences population dynamics and extinction processes.

Purpose of the Study:

• To investigate how transitive versus intransitive competitive hierarchies affect extinction rates and population dynamics.
• To explore the impact of probabilistic competition on community stability.

Main Methods:

• Spatially explicit simulations of ecological drift with 10 species in a 64-patch homogeneous landscape.
• Modeling birth rates influenced by interspecific competition under transitive and intransitive hierarchies.
• Analyzing extinction rates, population fluctuations (synchrony/asynchrony), and population size distributions (noise spectra).

Main Results:

• Transitive competition increased extinction rates and synchronous population fluctuations, generating white noise.
• Intransitive competition decreased extinction rates and caused asynchronous fluctuations, generating brown noise.
• Probabilistic competition models showed density-dependent trajectories and brown noise but had extinction rates similar to neutral models.

Conclusions:

• Intransitive competition has a strong stabilizing effect on local populations, particularly in species-poor communities.
• The stabilizing effect of intransitive competition diminishes with increased species richness.
• Empirical evidence of brown noise, density-dependent regulation, and asynchronous population fluctuations may signal intransitive competitive interactions.