Rethinking the nature of intraspecific variability and its consequences
on species coexistence
Abstract
Context Intraspecific variability (IV) has been proposed to explain
species coexistence in diverse communities. Assuming, sometimes
implicitly, that conspecific individuals can perform differently in the
same environment and that IV blurs species differences, previous studies
have found contrasting results regarding the effect of IV on species
coexistence. Objective We aim at showing that the larg IV observed in
data does not mean that conspecific individuals are necessarily
different in their response to the environment and that the role of
high-dimensional environmental variation in determining IV has been
largely underestimated in forest plant communities. Methods and Results
We first used a simulation experiment where an individual attribute is
derived from a high-dimensional model, representing “perfect
knowledge” of individual response to the environment, to illustrate how
a large observed IV can result from “imperfect knowledge” of the
environment. Second, using growth data from clonal Eucalyptus
plantations in Brazil, we estimated a major contribution of the
environment in determining individual growth. Third, using tree growth
data from long-term tropical forest inventories in French Guiana, Panama
and India, we showed that tree growth in tropical forests is structured
spatially and that despite a large observed IV at the population level,
conspecific individuals perform more similarly locally than compared
with heterospecific individuals. Synthesis As the number of
environmental dimensions that are typically quantified is generally much
lower than the actual number of environmental dimensions influencing
individual attributes, a great part of observed IV might be
misinterpreted as random variation across individuals when in fact it is
environmentally-driven. This mis-representation has important
consequences for inference about community dynamics. We emphasize that
observed IV does not necessarily impact species coexistence per se but
can reveal species response to high-dimensional environment, which is
consistent with niche theory and the observation of the many differences
between species in nature.