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.