The role of habitat connectivity in the assembly of the Golden
Oak metacommunity
Habitat fragmentation has been shown to alter the relative importance of
spatial vs. environmental processes as drivers of metacommunity
structure (Jamoneau, Chabrerie, Closset-Kopp, & Decocq, 2012), but the
way we measure spatial distances among habitat patches and account for
the effects of the surrounding matrix may affect our interpretation of
the predominant processes (Resasco & Fletcher, 2021; Watling,
Nowakowski, Donnelly, & Orrock, 2011). In the case of the highly
fragmented Golden Oak (Qa) habitat, circuit theory-based
connectivity modelling demonstrated that isolation estimates accounting
for fragmentation and matrix resistance consistently performed better at
explaining turnover than those based on topography, with the latter
performing better than null models assuming a homogeneous matrix (Table
3; Table S7). This finding aligns with recent studies that have
documented the ecological importance of dispersal corridors for
community assembly across different taxonomic groups (Firmiano et al.,
2021; Marrec et al., 2021; reviewed in Fletcher, Burrell, Reichert,
Vasudev, & Austin, 2016). However, this approach relies on the
assumption that all species of the metacommunity respond similarly to
landscape heterogeneity. Future studies integrating metabarcoding with
morphological information derived from local ‘voucher’ reference
collections could facilitate the implementation of species-specific
analyses accounting for ecological and trait variation (Brodie &
Newmark, 2019; Hartfelder et al., 2020). Despite these limitations, our
results provide empirical evidence of an important effect of habitat
fragmentation on soil microarthropod metacommunity structure across the
Golden Oak forest patches, with the role of environmental filtering
remaining equally significant (Table 3). Interestingly, we also obtained
equivalent distance-decay of community similarity curves based on
connectivity or on topoclimatic distances (Figure 5), although the
topoclimatic variables were not spatially autocorrelated (Mantel test, r <0.103, p-value >0.188) and their
shared variance with connectivity-based predictors was very low
(<2%; Table 3). The similar slopes of the decay curves for
ASVs and OTUs based on spatial distances are compatible with a neutral
dispersal-constrained model (Baselga et al., 2015), while the equivalent
pattern based on topoclimatic distances could be generated under certain
scenarios of high dispersal and narrow ecological niches (Baselga et
al., 2013). Taken together our results suggest that dispersal limitation
and niche-based processes have jointly shaped turnover patterns across
the Qa habitat, although each process may affect different
fractions of the metacommunity (e.g., some species and/or
intraspecific entities may have low dispersal propensity and wide
topoclimatic niches, while others might be good dispersers with narrow
niches). Future species-specific analyses may help to refine these
conclusions.