4.1 Taxonomic, functional and phylogenetic diversity
Our findings revealed
no
difference in
the
TD, PD and FD of small mammals among the three forest types at the
landscape scale, indicating that secondary and plantation forests can
play an important role in the maintenance of small mammal communities
after deforestation. Our results were consistent with those of most
previous studies on small mammals (Suchomel et al., 2012; Suchomel et
al., 2014; Wu et al., 2019). The studied secondary forests, with a
particularly high diversity and abundance of broadleaf vegetation, can
support a higher diversity of small mammals by providing more food
resources (Suchomel et al., 2014). Small mammal diversity in the studied
plantation forests was slightly higher than that in the secondary
forests and was similar to that in the primary forests. This phenomenon
may result from two mechanisms: (1) In our study area, secondary and
plantation forests are closed to the primary forests, which acts as
reservoir of species (Partel et al. 1996; Bernard et al., 2009). Small
mammals can spread from primary forests to secondary or/and plantation
forest, resulting in the high similarity of the assemblage. (2) Although
the structure and composition of vegetation in the plantation forests
were simpler than those in the primary and secondary forests, some
shrubs and understorey vegetation were also present in the plantation
forests, which can provide food resources and shelter. Meanwhile, small
mammals can quickly adapt to environmental change (Graham et al., 2019).
At the site scale, the TD, FD and PD of small mammals were highest in
the primary forests and lowest in the planation forests during all three
seasons. These results indicated that although small mammals can survive
in the three forest types, they prefer primary and secondary forests
when more food resources and shelter are available (Carey & Johnson,
1995; Gray et al., 2019; Rebelo et al., 2019).
Zhang et al. (2020) found that the TD, FD and PD of avian communities in
secondary forests were higher than those in primary and plantation
forests in the same study region, which was inconsistent with our
results. Therefore, different taxa may respond differently to forest
conversion. Such an inconsistency may be caused by the higher
adaptability of small mammals to forest conversion than birds (Graham et
al., 2019). In addition, secondary forests with more plant species,
including berry plant, can attract more bird species
(Zhang
et al., 2020).
4.2
Phylogenetic and functional structure
Our study further indicated that random ecological processes were
dominant
in the assembly of the small mammal communities across different forest
types. Our results were different from those reported for the avian
communities in Mt. Liangshan, where habitat filtering was the primary
mechanism in the primary forest (Zhang et al., 2020). We propose two
possible explanations for this result: 1) forest habitats with high
productivity and sufficient niches allow the settlement of lineages with
different ecological attributes, and 2) small mammals usually have wide
niche breadths (strong adaptability), so they
are typically more successful in
accommodating to forest conversion than other taxa (Wu et al., 2019;
Graham et al., 2019). Most of the small mammal species were captured in
more than one forest type, and only a few species were found in a single
forest type (Appendix). In addition, the phylogenetic structure of the
small mammal communities were clustered among the three forest types,
and there were no differences in the phylogenetic structure among the
three forest types. Our results were different from previous studies
that conformed to “assembly rules” (Table S2), as species interact
based on their phenotypic similarities and differences, and that
phenotypic variation has a basis in evolutionary history (Hanz et al.,
2019; Sobral & Cianciaruso, 2016; Webb et al., 2002; Zhang et al.,
2020). The clustered phylogenetic structure in all forest types may be
attributed to in situ diversification and low dispersal rates within
regions (dispersal filter; Cardillo, 2011), followed by the maintenance
of this phylogenetic structure pattern by random ecological processes.
Overall,
random
ecological processes dominated the small mammal communities in forest
habitats, and forest conversion had no significant effect on the random
ecological processes.