2.6 Inferring local community assembly mechanisms
To quantify the relative importance of ecological processes in
structuring the bacterial and fungal metacommunity, the iCAMP approach
was employed(Ning et al., 2020), which is
a more sophisticated development of the approach proposed by Stegen et
al. (Stegen et al., 2013;
Stegen, Lin, Konopka, & Fredrickson,
2012). The iCAMP approach uses a quantitative framework to infer
community assembly mechanisms through a phylogenetic-bin-based null
model analysis. Within this framework, ecological processes are divided
into five processed, including homogeneous selections (HoS),
heterogeneous selections (HeS), dispersal limitation (DL), homogenizing
dispersal (HD) and drift (DR) processes. In the approach, multiple
phylogenetic bins were generated based on the phylogenetic tree. The
null model analysis within each bin is calculated by beta Net
Relatedness Index (βNRI) and modified Raup–Crick metric (RC). The
fraction of pairwise comparisons with βNRI < − 1.96 is
considered as the percentages of homogeneous selection, whereas those
with βNRI > +1.96 as the percentages of heterogeneous
selection. Next, taxonomic diversity metric RC is used to partition the
remaining pairwise comparison with |βNRI| ≤ 1.96. The
fraction of pairwise comparisons with RC < − 0.95 is treated
as the percentages of homogenizing dispersal, while those with RC
> + 0.95 as dispersal limitation. The remaining ones with
|βNRI| ≤ 2 and | RC | ≤ 0.95
represent the percentages of drift. The βNRI and RC are calculated using
the “picante” package(Kembel et al.,
2010) and “iCAMP”(Ning et al., 2020)
package in R.