Drivers of community composition
Although no consistent evidence of deterministic succession in endophyte
communities was observed; there was some evidence of deterministic
processes shaping the community assembly of fungal endophyte
communities. Host identity had the largest impact on endophyte community
composition (Figure xx, Table xx). Host identity alone explained
~23% of the total ~29% variation in
turnover of endophyte composition explained by the final model. Host
identity is known to be a major determinant of the composition of foliar
fungal endophyte communities (Christian et al. , 2016; Davidet al. , 2016; Vincent et al. , 2016; Liu et al. ,
2019; Yao et al. , 2019). The specificity of endophytes to a
particular host or group of taxonomically related hosts ranges from
extremely narrow to relatively wide (Arnold and Lutzoni, 2007; Põlmeet al. , 2018). This may explain why, even though host identity
was the important factor structuring foliar fungal endophyte
communities, the identity of only two host species was retained in the
final model, with C. inerme consistently being removed as one of
the variables which explained the least turnover in endophyte community
composition.
Geographic distance between samples was the only significant variable
consistently retained in every GDM (i.e. the full dataset and each of
the three hosts individually) (Figure 2 & Figure 3)). This indicates
that the similarity in composition of foliar fungal endophytes decays
with increasing distance, a pattern commonly observed in ecological
communities (Nekola and White, 1999; Soininen et al. , 2007).
Indeed, others have shown that foliar fungal endophytes are dispersal
limited over distances from 10km to >100km (David et
al. , 2016; Koide et al. , 2017; Oono et al. , 2017).
However, here we show that even over a shorter spatial distance, i.e.
<1500m, there is consistent evidence for distance decay
driving turnover in endophyte community composition.
The GDMs performed for each host individually, showed that the factors
responsible for the turnover in foliar fungal endophyte community
composition within a host is variable as is the rate and magnitude of
this turnover (Figure 3, Supporting information Table S5-S7). For
example, distance to the indigenous forest, the difference in minimum
temperature and geographic separation were the most important variables
explaining the turnover in foliar fungal endophyte communities forE. crispa, C. inerme and S. chirindensis respectively,
holding all other variables constant in their individual models. Others
have shown how the distance to a potential inoculum source, in our case
a large indigenous forest, can be important for causing compositional
differences in fungal communities (Glassman et al. , 2017). It has
also been shown how abiotic conditions, like temperature differences,
can shape endophyte community composition due to differences in the
physiological performance of endophyte species in dealing with the
prevailing conditions (Arnold and Herre, 2003; Peay et al. , 2016;
Unterseher et al. , 2016). Such findings highlight how both
deterministic (i.e. temperature differences) and stochastic (i.e.
distance to an inoculum source or geographic separation) forces can be
important factors causing turnover in foliar fungal endophyte
communities in the same system but for different hosts.