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.