Natural population variability may be masking the more-individuals hypothesis

Area of Science:

• Ecology
• Biodiversity Science
• Population Dynamics

Background:

• Species richness and ecosystem productivity are globally correlated, but the underlying mechanisms remain debated.
• The more-individuals hypothesis (MIH) suggests higher productivity supports more individuals, thus more species.
• Existing empirical evidence for the MIH is mixed, prompting further investigation into potential confounding factors.

Purpose of the Study:

• To investigate if interannual population variability masks the true relationship proposed by the more-individuals hypothesis (MIH).
• To assess the impact of varying sampling durations on the detection of the MIH relationship using simulation.

Main Methods:

• Simulations were conducted with fixed linear relationships between productivity, species richness, and average abundance.
• Population abundance was simulated with annual variability and sampled over durations of 1 to 40 years.
• Linear regressions of species richness on sampled abundance were used to evaluate the detection of the MIH relationship.

Main Results:

• High interannual population variability combined with short-term sampling (1-3 years) significantly reduced the ability to detect the simulated MIH relationship.
• Nearly all current MIH studies employ sampling durations and face population variability levels that hinder accurate detection.
• Long-term sampling (5+ years) substantially improved the detection of the underlying MIH relationship in simulations.

Conclusions:

• Interannual population variability is a critical factor that can obscure the true relationship between productivity and species richness.
• Current research practices in MIH studies, often relying on short-term data, may lead to erroneous conclusions.
• Future research on the more-individuals hypothesis must incorporate long-term ecological monitoring to account for population dynamics and reliably test its validity.