No abstract

Large‐diameter, tall‐stature, and big‐crown trees are the main stand structures of forests, generally contributing a large fraction of aboveground biomass, and hence play an important role in climate change mitigation strategies. Here, we hypothesized that the effects of large‐diameter, tall‐stature, and big‐crown trees overrule the effects of species richness and remaining trees attributes on aboveground biomass in tropical forests (i.e., we term the “big‐sized trees hypothesis”). Specifically, we assessed the importance of: (a) the “top 1% big‐sized trees effect” relative to species richness; (b) the “99% remaining trees effect” relative to species richness; and (c) the “top 1% big‐sized trees effect” relative to the “99% remaining trees effect” and species richness on aboveground biomass. Using environmental factor and forest inventory datasets from 712 tropical forest plots in Hainan Island of southern China, we tested several structural equation models for disentangling the relative effects of big‐sized trees, remaining trees attributes, and species richness on aboveground biomass, while considering for the full (indirect effects only) and partial (direct and indirect effects) mediation effects of climatic and soil conditions, as well as interactions between species richness and trees attributes. We found that top 1% big‐sized trees attributes strongly increased aboveground biomass (i.e., explained 55%–70% of the accounted variation) compared to species richness (2%–18%) and 99% remaining trees attributes (6%–10%). In addition, species richness increased aboveground biomass indirectly via increasing big‐sized trees but via decreasing remaining trees. Hence, we show that the “big‐sized trees effect” overrides the effects of remaining trees attributes and species richness on aboveground biomass in tropical forests. This study also indicates that big‐sized trees may be more susceptible to atmospheric drought. We argue that the effects of big‐sized trees on species richness and aboveground biomass should be tested for better understanding of the ecological mechanisms underlying forest functioning.

Plant diversity surely determines arthropod diversity, but only moderate correlations between arthropod and plant species richness had been observed until Basset et al. (2012, Science 338: 1481-1484) finally undertook an unprecedentedly comprehensive sampling of a tropical forest and demonstrated that plant species richness could indeed accurately predict arthropod species richness. We now require a high-throughput pipeline to operationalize this result so that we can (1) test competing explanations for tropical arthropod megadiversity, (2) improve estimates of global eukaryotic species diversity, and (3) use plant and arthropod communities as efficient proxies for each other, thus improving the efficiency of conservation planning and of detecting forest degradation and recovery. We therefore applied metabarcoding to Malaisetrap samples across two tropical landscapes in China. We demonstrate that plant species richness can accurately predict arthropod (mostly insect) species richness and that plant and insect community compositions are highly correlated, even in landscapes that are large, heterogeneous, and anthropogenically modified. Finally, we review how metabarcoding makes feasible highly replicated tests of the major competing explanations for tropical megadiversity.3

Aim Phylogeographical studies of Taiwan have advanced our knowledge of the origins of its fauna, but the discrepancies raise issues related to the interpretation of single‐taxon studies. Here, we provide a synthesis of the biogeographical histories of multiple terrestrial vertebrates endemic to Taiwan and infer the colonization processes within the context of geological and climatic events. Location Taiwan and neighbouring land masses. Taxon Terrestrial vertebrates. Methods We conducted a meta‐analysis of 28 phylogenetic studies of 33 endemic Taiwanese terrestrial vertebrates to summarize the insights into their source regions and divergence times. We used dispersal–extinction–cladogenesis models to reconstruct the ancestral ranges of 54 endemic species based on a recently published time‐calibrated phylogenetic tree. By constructing a frequency histogram that quantified the number and timing of divergence events within 1 Myr bins, we inferred the spatiotemporal colonization patterns of endemic Taiwanese species. Results The results from 28 phylogenetic studies revealed that South China is the main source region of endemic Taiwanese species. However, based on a more comprehensive time tree, the ancestral area reconstruction analyses indicated that endemic species are predominately of Eastern Himalayan origin. Both datasets highlighted a temporal pattern that the majority of colonization events of terrestrial vertebrates endemic to Taiwan occurred from the early Pliocene (c. 5 Ma) onwards, and these events were temporally congruent with the geological estimates of the emergence of Taiwan Island. Main conclusions Terrestrial vertebrates endemic to Taiwan reached the island over the last 5 Myr from a variety of zoogeographical regions. In contrast to the traditional notion, the Eastern Himalayas is the most important source region of endemic Taiwanese species, followed by South China and Indochina. In addition to the land bridge, transoceanic dispersal provided another potential mode for species to colonize Taiwan.

Aim Zoogeographical regionalizations have recently seen a revived interest, which has provided new insights into biogeographical patterns. However, few quantitative studies have focused on zoogeographical regions of China. Here, we analyse zoogeographical regions for terrestrial vertebrates in China and how these regions relate to environmental and geological drivers and evaluate levels of cross‐taxon congruence. Location China. Methods We applied hierarchical clustering and non‐metric multidimensional scaling ordination to βsim dissimilarity matrices to delineate zoogeographical regions of China, based on the species distribution of 2102 terrestrial vertebrates in 50 × 50 km grid cells. We used generalized linear models and deviance partitioning to investigate the roles of current climate, past climate change, vegetation and geological processes in shaping the zoogeographical regions. Finally, we used Mantel and Kruskal–Wallis tests to evaluate the levels of cross‐taxon congruence. Results Cluster analyses revealed 10 major zoogeographical regions: South China, the Yungui Plateau, Taiwan, North China, Northeast China, the Inner Mongolia Plateau, Northwest China, the Longzhong Plateau, the Tibetan Plateau and East Himalaya. In contrast to previous regionalizations, a major split was identified by clustering grid cell assemblages and dividing the eastern and western parts of China, followed by the northern part of China. Deviance partitioning showed that current climate and geological processes explained most of the deviance both jointly and independently. Congruence in species composition of endotherms and ectotherms was surprisingly low. Main conclusions We propose new zoogeographical regions for China based on our quantitative methods. In contrast to previous regionalizations, we consider Central China as a part of South China and identify the Longzhong Plateau and Taiwan as independent regions. While our results strongly support the notion of a broad biogeographical transition zone in East Asia, they also suggest a major south–north‐oriented Palaearctic‐Oriental boundary in China.