The non-neutral benefits of a diverse world: species richness promotes niche structure through reduced dominance

Understanding how local diversity influences the fundamental dynamics of
communities has become an important and urgent question in community ecology, as
global diversity continues to decrease rapidly. Recent theoretical and experimental work
have provided various perspectives in both how to quantify community dynamics and
how species richness benefits communities and ecosystem function. Increased species
richness has been shown to increase the importance of neutral processes in simulated
communities. However, species richness can also heighten productivity through
increased niche partitioning. There remains a need to clarify the impact of species
richness on fundamental community dynamics. Through three research chapters, I used
various niche-neutral metrics to investigate a cross-section of experimental contexts
and methods of increasing species richness.
In chapter 3, simulations of virtual communities revealed the complementarity of
multiple niche-neutral metrics due to their scale and resulting sensitivity to storage
effects. Chapter 4 used an experimental study in peatland pools to reveal the increased
niche partitioning in communities of filter-feeding zooplankton resulting from lowvolume
dispersal treatments. Chapter 5 focused on a mesocosm experiment, which
artificially assembled zooplankton communities of both low and higher species richness.
Not only did it add weight to the observations of chapter 4, but it further demonstrated
how increased niche structure was achieved through the reduction of single-species
dominance.
Combined, the three research chapters demonstrated the benefits of both
considering multiple community measures in parallel, and using a species heatmap
method – developed for this thesis – to reveal species-level patterns in influencing the
various interpretations of community measures. In conclusion, I suggest that increased
species richness promotes niche structure by tempering dominance post-disturbance.
Low-volume dispersal treatments could thus be used to generate more stable,
v
productive and biodiverse local communities, with potentially little negative impact
from the homogenisation of meta-communities.