Rethinking the nature of intraspecific variability and its consequences on species coexistence

Area of Science:

• Ecology
• Plant Community Dynamics
• Forest Ecology

Background:

• Intraspecific variability (IV) is debated for its role in species coexistence, with assumptions that individual performance differences drive niche overlap.
• Previous studies yield conflicting results on IV's effect on coexistence, partly due to overlooking high-dimensional environmental influences on individual variation.
• Understanding the true drivers of IV is crucial for ecological theory, particularly in diverse forest plant communities.

Purpose of the Study:

• To demonstrate that observed large IV in data does not necessarily imply inherent differences in conspecific individual responses to the environment.
• To explore the significant, yet often overlooked, role of high-dimensional environmental variation in shaping IV within forest plant communities.
• To reassess the impact of IV on species coexistence and community dynamics by accounting for environmental influences.

Main Methods:

• Simulation experiments modeling individual attributes based on high-dimensional environmental data to illustrate IV arising from imperfect environmental knowledge.
• Analysis of clonal Eucalyptus plantation growth data to quantify the environmental contribution to individual growth variation.
• Examination of tree growth data from long-term tropical forest inventories (French Guiana, Panama, India) to assess spatial structuring and local conspecific similarity.

Main Results:

• Simulations showed that 'imperfect knowledge' of a high-dimensional environment can generate substantial observed IV.
• Environmental factors were found to be a major determinant of individual growth in Eucalyptus plantations.
• Tropical tree growth exhibits spatial structuring, with conspecific individuals performing more similarly in local environments than when compared across broader scales, despite overall population-level IV.

Conclusions:

• Observed IV in forest plants is frequently driven by unquantified, high-dimensional environmental variation, not necessarily by inherent differences in individual responses.
• Misinterpreting environmentally driven IV as random variation has significant consequences for inferring community dynamics and species coexistence mechanisms.
• IV can be a marker of species' responses to complex environments, aligning with niche theory and explaining observed biodiversity patterns.