Compensatory dynamics are rare in natural ecological communities.

Area of Science:

• Ecology
• Population Dynamics
• Community Ecology

Background:

• A central debate in ecology concerns whether population sizes are regulated by competition (density-dependent) or by abiotic factors (e.g., temperature, precipitation).
• Theoretical models, including Hubbell's neutral theory, emphasize the role of interspecific competition in shaping community structure and dynamics.
• If competition is a primary driver, species abundances should exhibit compensatory dynamics, leading to negative covariance.

Purpose of the Study:

• To empirically test the prevalence of compensatory dynamics in natural communities.
• To determine whether interspecific competition or abiotic factors are more significant drivers of year-to-year fluctuations in species abundance.

Main Methods:

• Analysis of community covariance measures across 41 diverse natural communities.
• Inclusion of various taxa and spatial scales to ensure broad applicability.
• Statistical assessment of the direction (positive or negative) of species covariance.

Main Results:

• Species within natural communities exhibited positive covariance, contrary to expectations for strong compensatory dynamics.
• The observed positive covariance was the opposite of what would be predicted if interspecific competition were the dominant regulatory force.
• Abiotic factors appear to exert a stronger influence on species abundance fluctuations.

Conclusions:

• Interspecific competition is less important than abiotic factors in driving short-term fluctuations of species abundance in most natural communities.
• Community dynamics are more likely shaped by common responses to environmental variables than by direct competitive interactions.
• The findings challenge the centrality of compensatory dynamics in explaining community-level population regulation.