Results
Results for all hypotheses are summarised in Figures 2 and 3, and Table
1. Fischer’s C, a measurement of conditional independence was 29.23 (p =
0.4, df = 28) for the structural equation model, suggesting no missing
dependencies in the model. For hypothesis one, increases in overall
niche distance reduced species richness, and a path was added from mean
niche volume to species richness, finding greater niche volumes were
associated with greater species richness. Therefore, species richness
decreased with the average distance of a site in niche-space to the
average of the total species pool supporting hypothesis one (Figure 2;
Figure 3a; Table 1), and more species-rich sites contained species with
higher niche volume on average.
Our second hypothesis was that mean abundance will be greater when the
site is nearer to niche centres of the species at the site. This was
supported as we found log mean abundance decreased with niche mismatch
so that species nearer the centre of their range were, on average, more
abundant (Figure 2; Figure 3b; Table 1). Log mean abundance also
increased with mean niche volume and an additional path was added
showing increasing niche overlap was associated with increasing log mean
abundance – we discuss possible reasons for this below.
Our third hypothesis was that synchrony will be reduced if the niches of
the species were more dissimilar. This was less well supported as
species richness decreased synchrony (increased asynchrony), but niche
overlap had no significant effect (Figure 2; Figure 3d; Table 1). We
also found a relationship between species richness and niche overlap,
with overlap decreasing with higher species richness, indicating that
richer communities were composed of species with more dissimilar niches.
Our fourth hypothesis was that average population stability would be
greater when the site was nearer the centre of the species niches and
when the niche breadth of species was larger. This was partly supported
as niche mismatch decreased average population stability, but, contrary
to expectation, increased mean niche volume decreased average population
stability, and mean population abundance had no significant effect
(Figure 2; Figure 3c; Table 1). There was also no significant effect of
log abundance on population stability.
Finally we hypothesised synchrony and average population stability will
explain differences in community stability. Synchrony reduced community
stability while average species stability increased community stability
(Figure 2; Figure 3e,f; Table 1). After accounting for these effects,
species richness and log mean abundance also increased community
stability.