Space resource utilization of dominant species integrates abundance- and functional-based processes for better predictions of plant diversity dynamics

Sustainable ecosystem management relies on our ability to predict changes
in plant diversity and to understand the underlying mechanisms. Empirical
evidence demonstrates that abundance- and functional-based processes
simultaneously explain the loss of plant diversity in response to human
activities. Recently, a novel indicator based on percent cover (CoverD)
and maximum height (HeightD) of the dominant plant species – Space
Resource Utilization (SRUD) – has proven to give robust and better
predictions of plant diversity dynamics than community biomass. Whether
the superior predictive ability of SRUD is due to its capacity to
simultaneously capture abundance- and functional-based processes remains
unknown. Here, we tested this hypothesis by quantifying mechanistic links
between changes in SRUD and biodiversity in response to nutrients and
herbivores. Furthermore, we assessed the relative contribution of
dominant, intermediate, and rare species to reduced density of individuals
by combining null model analysis with field experiments. We found that
SRUD successfully captured changes in ground-level light availability and
changes in the number of individuals to predict plant diversity dynamics,
and each of CoverD and HeightD partly and independently contributed to
both processes. Comparative results from null model analysis and field
experiments confirmed that individual losses of dominant, intermediate,
and rare species followed non-random processes. Specifically, compared
with random loss process, rare species lost proportionally more
individuals and thus disproportionately contributed to species loss, while
dominant and intermediate species lost less. Our results demonstrate that
SRUD captures both abundance- and functional-based processes thus
explaining why SRUD provides more accurate predictions of changes in
species diversity. Given that rare species can play an important role in
shaping community structure, resisting against invasion, impacting higher
trophic levels, and providing multiple ecosystem functions, reducing the
SRU of dominant species could alleviate the risk of exclusion of rare
species by mitigating abundance- and functional-based competition
processes.