Mammals play a vital role in forest ecosystems mainly through their effects on food web dynamics, micro-habitats formation, nutrients and biomass flow, pollination and seed dispersal (Fricke et al., 2022; Lacher et al., 2019). However, the sixth biological mass extinction is now underway (Ceballos et al., 2017; Cowie et al., 2022). Specifically, over 300 mammal species have died out since the Late Pleistocene (Davis et al., 2018). According to the IUCN Red List, 26% of mammals are at risk of extinction (IUCN, 2021). Notably, when compared to other habitats, forest habitat has the highest diversity of mammal species, as well as the highest proportion of threatened mammals (Cox et al., 2022). However, an assessment found that only 40% of the world's forests with high landscape level integrity were still existent in 2019 (Grantham et al., 2020). This massive loss and fragmentation of intact forest habitat has significantly reduced the forest mammal diversity and threatened the functioning and biodiversity of other taxon groups of forest ecosystems. For example, forest area and habitat configuration were the two important factors on the occurrence declining of koala (Phascolarctos cinereus), which has highly specific habitat requirements and low migration capacity (McAlpine et al., 2006). Additionally, the widespread mammal defaunation could significantly decrease the plant seed's dispersal ability to follow climate change (Fricke et al., 2022). Therefore, the understanding of forest mammal diversity distribution patterns and potential drivers is fundamental for ecosystem management and biodiversity conservation in forest ecosystems.
Recently, a growing number of studies have found that species richness alone cannot fully capture changes in biodiversity (Hillebrand et al., 2018). However, multi-dimensional diversity indices, such as phylogenetic diversity and functional diversity, make it possible to evaluate biodiversity in a comprehensive manner and to reflect the evolutionary history of the species and differences in ecosystem functions (Liu et al., 2021; Safi et al., 2011). For example, the extinction of functional redundant species had little effect on ecosystem functioning (Pimiento et al., 2020). However, if an ancestor or functionally unique species was lost, evolutionary history and ecosystem functioning would be more impacted (Brodie et al., 2021). In addition, the studies of phylogenetic diversity and functional diversity are critical for exploring the mechanisms of the community assembly (e.g. inter-specific competition or habitat filtering; Cardillo, 2011) and the mechanisms of geographic distribution patterns of biodiversity (Oliveira et al., 2016).
Notably, many classical theories have been proposed to explain the impacts of environmental factors on the geographic distribution patterns of biodiversity (Currie et al., 2004; Fjeldsaå and Lovett, 1997; McGlone, 1996). The energy related hypothesis proposes that contemporary temperature and precipitation could affect the biodiversity patterns through their effects on the speciation, extinction, evolutionary rate as well as resources availability, such as the productivity hypothesis and the water-energy hypothesis (Currie et al., 2004; Hawkins et al., 2003). For example, a study found that annual mean precipitation was the best predictor for small mammal phylogenetic diversity and functional diversity in Mount Kenya (Onditi et al., 2022). In addition, long term climate stability also has strong legacy on distributions of contemporary biodiversity (McGlone, 1996). For example, the history climate stability hypothesis proposes that the species richness increases with the increasing climate stability because of the lower extinction rate and the higher speciation rate (McGlone, 1996; Svenning et al., 2015). Moreover, habitat heterogeneity hypothesis proposes that regions with higher habitat heterogeneity could harbor higher species diversity by providing more ecological niches, more geographic isolation opportunities for speciation, as well as more refuges (Stein et al., 2015).
In addition to these natural environmental factors, the massive and rapid increasing anthropogenic activities, e.g., agricultural development, large human populations, urbanization and biological invasions, also have strong direct and indirect impacts on mammal diversity (Dirzo et al., 2014; Bogoni et al., 2020). For example, a study in Colombia found that mammal diversity and evenness deceased due to agriculture expansion (Boron et al., 2019). In addition, a study based on fossils of 351 mammal species, which were extinct since the beginning of the Late Pleistocene, found that the human population density can predict the past mammal extinction patterns with 96% accuracy (Andermann et al., 2020).
Since the 21st century, camera traps have been widely used by researchers to monitor wildlife as a non-invasive monitoring technology (Delisle et al., 2021). Camera traps have several advantages over other monitoring systems, including less expensive, unaffected by harsh environmental conditions, and are able to do large-scale and long-term monitoring (Hamel et al., 2013; Silveira et al., 2003). In recent years, camera traps have been widely used in assessing species richness (O’Brien, 2008), estimating population density (Hedges et al., 2015), monitoring behavior (Rowcliffe et al., 2014). In addition, global mammal monitoring databases by cameras traps have been established, such as TEAM (Jansen et al., 2014) and Emammal (Forrester et al., 2017). It is worth mentioning that there are also many studies using camera traps to monitor mammals and some established monitoring networks in China (Li, 2020). However, using mammal data monitored by camera traps to perform a analysis on geographic distribution pattern of forest mammal diversity have been less conducted, particularly in China.
China has high mammal species richness, diverse forest types, as well as wide climate range and elevation range (Lin et al., 2021). In addition, ten existing camera traps networks in China provide an ideal opportunity to evaluate the patterns and multiple drivers of geographic distributions of forest mammal diversity. Therefore, this study firstly searched the literatures with mammal species list recorded by camera traps in forest ecosystems in China. Then different biodiversity indices, including species richness, phylogenetic and functional diversity, phylogenetic and functional structure of these mammal communities were calculated. Finally, the relationships between these biodiversity indices and natural environmental factors (contemporary climate, paleoclimate changes, habitat heterogeneity) and anthropogenic factors (cropland area and human population size) were assessed.