Abstract
Ecological networks are commonly applied to depict general patterns of biotic interactions, which provide tools to understand the mechanism of community assembly. Commensal interactions between epiphytes and their hosts are a major component of species interactions in forest canopies; however, few studies have investigated species assemblage patterns and network structures of epiphyte–host interactions, particularly non-vascular epiphytes in different types of forest. To analyze the characteristics of network structures between epiphytes and their hosts, composition and distribution of epiphytic bryophytes were investigated from 138 host individuals using canopy cranes in a tropical lowland seasonal rain forest (TRF) and a subtropical montane moist evergreen broad-leaved forest (STF), in Southwest China. We structured binary networks between epiphytic bryophytes and their hosts in these two forests, which presented 329 interactions in the TRF and 545 interactions in the STF. Compared to TRF, the bryophyte–host plant networks were more nested but less modular in the STF. However, both forests generally exhibited a significantly nested structure with low levels of specialization and modularity. The relatively high nestedness may stabilize the ecological networks between epiphytic bryophytes and their hosts. Nevertheless, the low modularity in epiphyte–host networks could be attributed to the lack of co-evolutionary processes, and the low degree of specialization suggests that epiphytes are less likely to colonize specific host species. Vertical distribution of the bryophyte species showed structured modules in the tree basal and crown zones, probably attributing to the adaptation to microclimates within a host individual. This study highlights the nested structure of commensal interaction between epiphytic bryophytes and host trees, and provides a scientific basis to identify key host tree species for conservation and management of biodiversity in forest ecosystems.
Highlights
Human disturbance and climate change induce a severe biodiversity crisis, which directly leads to species extinction, and indirectly causes community collapse as species co-extinction through interspecific interactions
We found that epiphytic bryophyte species such as Taxiphyllum taxirameum in the tropical lowland seasonal rain forest (TRF) and Thuidium cymbifolium in the subtropical montane moist evergreen broad-leaved forest (STF) commonly occurred on the base of host individuals, and these species may prefer shade and high humidity habitat
Our study shows that the STF supports a higher diversity of epiphytic bryophytes and more complex structures of bryophyte– host networks in comparison to the TRF in southwest China
Summary
Human disturbance and climate change induce a severe biodiversity crisis, which directly leads to species extinction, and indirectly causes community collapse as species co-extinction through interspecific interactions. Biotic interactions remain a core theme to understand the general mechanisms of community assembly and disassembly in order to scientifically guide biodiversity conservation and restoration (Taylor et al, 2016; Naranjo et al, 2019). Ecological networks provide a powerful tool to elucidate complex interspecific interactions in different types of communities (Borrett et al, 2014; Landi et al, 2018). Much effort is required to understand general structures of interaction networks and to clarify the underlying mechanisms that mediate ecological networks
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