•The relationship between acoustic indices, vegetation, and topographic characteristics was investigated at two spatial scales in a forest plot network.•Topographic complexity and horizontal ...vegetation, including tree density and basal area, were important variables significantly related to bird acoustic indices.•The relationship between acoustic indices, vegetation, and topographic characteristics of the tropical forest was spatial scale dependent.
The soundscape of different habitats can be discriminated by multiple acoustic indices as they have previously been related to vegetation characteristics. However, the relationship between acoustic indices and topography still needs to be thoroughly evaluated, as well as the variance in the relationship at different spatial scales within the same research system. Networks of forest dynamics plots constructed under the same protocol provide an ideal research platform for addressing the above issue. Our study investigated the relationship between acoustic indices, vegetation, and topographic characteristics at two spatial scales. We recorded soundscapes using autonomous recorders across a tropical forest dynamics plot network consisting of 22 plots in Xishuangbanna, Yunnan Province, southwest China. To exclude recordings with geophony and with biotic sounds from non-avian species, especially from cicadas and frogs, the recordings were previewed aurally and visually, with 9110 min of “clear” bird acoustic recordings chosen for final analysis. We assessed the relative importance of tree species richness, six vegetation characteristics, and three topographic characteristics for five acoustic signal complexity indices, and three statistical indices which describe the properties of frequency spectrum, at 25 m and 50 m spatial scales. We found that topographic complexity was the most significant factor influencing acoustic indices. The variation explained by topographic complexity ranged from 13.2 % to 47.2 % for the seven best-fitted models at both spatial scales. Horizontal vegetation characteristics, including tree density and basal area, were also important variables related to acoustic indices. The Acoustic Diversity Index (ADI) and Bioacoustic Index (BIO) were not associated with vegetation or topographic characteristics at either spatial scale. Three out of seven significant relationships between acoustic indices and vegetation or topographic characteristics disappeared as the spatial scale increased from 25 m to 50 m. In contrast, the significant relationship between Acoustic entropy (H), the centroid (CENT) and skewness (SKEW) and topographic complexity remained stable. Our results suggest that both acoustic signal complexity indices and acoustic statistical indices showed a different relationship to vegetation and topographic characteristics in tropical forests, and the strength of these relationship was scale-dependent. This study revealed that topographic complexity might be an effective predictive variable for further ecoacoustic research.
One of the few rules in ecology is that communities are composed of many rare and few common species. Trait‐based investigations of abundance distributions have generally focused on species‐mean ...trait values with mixed success. Here, using large tropical tree seedling datasets in China and Puerto Rico, we take an alternative approach that considers the magnitude of intraspecific variation in traits and growth as it relates to species abundance. We find that common species are less variable in their traits and growth. Common species also occupy core positions within community trait space indicating that they are finely tuned for the available conditions. Rare species are functionally peripheral and are likely transients struggling for success in the given environment. The work highlights the importance of considering intraspecific variation in trait‐based ecology and demonstrates asymmetry in the magnitude of intraspecific variation among species is critical for understanding of how traits are related to abundance.
Chromolaena odorata
(L.) R. M. King and H. Robinson (Asteraceae), originally from the Neotropics, has become a serious weed in the humid tropics and subtropics of Southeast Asia, Africa and Pacific ...Islands. In its introduced distributions,
C. odorata
has been recognised as two biotypes, the Asian/West African (AWA) biotype and South African (SA) biotype, with independent distribution, morphology and ecological characters. To characterise the genetic variability and identify the likely source regions in the native distributions of the two biotypes, we carried out an extensive phylogeographic study using chloroplast and nuclear DNA sequences and microsatellite DNA markers. The analysis of both DNA sequences and nuclear markers showed that native populations possessed high genetic diversity, while both the AWA and SA biotypes in invaded regions appeared to have low genetic diversity. The AWA and SA biotypes were genetically distinct. Strong competitive ability and environmental adaptability may have facilitated the invasion AWA and SA biotypes in its respective invasive regions. We conclude that the source of AWA biotype may be Trinidad and Tobago, while the SA biotype was from Cuba and Jamaica. For a better outcome of biocontrol, the potential biological control agents for the two biotypes should be collected from these native regions, respectively.
Trait‐based studies in community ecology have generally focused on the community as a unit where all species occur due to stochasticity, determinism or some mixture of the two. However, the processes ...governing population dynamics may vary greatly among species. We propose a core‐transient framework for trait‐based community studies where a core group of species has a strong link to the local environment while transient species have weaker responses to the environment. Consistent with the expectations of the framework, we found that common species exhibit clear linkages between performance and their environment and traits while rare species tend to have weaker or non‐significant relationships. Ultimately, trait‐based ecology should move beyond applying a set of processes to a community as a whole and towards quantifying inter‐specific variation in the drivers of population dynamics that ultimately scale up to determine community structure.
Climate is widely recognised as an important determinant of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate, ...which substantially hinders our understanding of how climate constrains biodiversity globally. Using data from 35 large forest plots, we test hypothesised relationships amongst climate, topography, forest structural attributes (stem abundance, tree size variation and stand basal area) and tree species richness to better understand drivers of latitudinal tree diversity patterns. Climate influences tree richness both directly, with more species in warm, moist, aseasonal climates and indirectly, with more species at higher stem abundance. These results imply direct limitation of species diversity by climatic stress and more rapid (co‐)evolution and narrower niche partitioning in warm climates. They also support the idea that increased numbers of individuals associated with high primary productivity are partitioned to support a greater number of species.
1. Density‐dependent survival is prevalent in tropical forests and is recognized as a potentially important mechanism for maintaining tree species diversity. However, there is little knowledge of how ...density dependence changes in fluctuating environments. 2. Across the 20‐ha Xishuangbanna tropical seasonal rain forest dynamics plot in southwest China, which has distinct dry and wet seasons, we monitored seedling survival in 453 1‐m2 quadrats over 2 years. Density dependence was assessed using generalized linear mixed models with crossed random effects. 3. When pooling all species at the community level, there were strong negative effects of conspecific tree neighbours on seedling survival over the dry‐season, wet‐season and 2‐year intervals. The proportion of conspecific seedling neighbours had a significant negative effect in the dry season, but not in the wet season. 4. At the species level, the effects of conspecific tree and seedling neighbours varied widely among species in the community and were significantly positively related to population basal area in the community over the dry‐season interval. In contrast, over the wet‐season interval, the effects of conspecific tree and seedling neighbours did not significantly vary among species in the community. Overall community‐ and species‐level results suggest that local‐scale negative density dependence (NDD) tends to be stronger in the dry than wet season in the Xishuangbanna tropical forest. 5. At the scale of the 20‐ha plot, we found a community compensatory trend (CCT), in which rare species had relatively higher seedling survival than common species in both the wet and dry seasons. A positive association between potential NDD and population basal area suggests that the CCT results from local‐scale NDD, specifically because of negative effects of conspecific tree neighbours. 6. Synthesis. Our results demonstrate that the strength of density‐dependent seedling survival can vary between seasons and among species in tropical forests. Future research is needed to assess the underlying mechanisms of this temporal and interspecific variation in NDD and its consequences for species coexistence and community composition.
1. Individual-level interactions with neighbours and their surrounding environments are key factors influencing performance that ultimately shape and maintain diversity in tropical plant communities. ...Theory predicts that the strength of these interactions depends on the similarity among neighbours, the turnover in composition caused by individuals that enter as new recruits and individuals that die, and fitting to local conditions. Despite considerable phenotypic variation among individuals and high community dynamics, these three factors have rarely been considered together for understanding growth variation, especially for seedling communities in the tropics. 2. We address this outstanding challenge by quantifying the influence of trait dissimilarity among neighbours, temporal turnover in neighbours, and individual trait variation on seedling growth, based on an unprecedented dataset containing individual-level demographic and functional trait data for tropical tree seedlings. 3. The results showed that trait dissimilarity associated with resource acquisition does not influence growth. However, conspecific negative density-dependent effects on growth were evident through the initial density of conspecif ics and the increase in conspecifics during the study period. Also, individuals with relatively larger investments in leaf biomass allocation attained higher growth rates, suggesting that seedlings adjust their resource allocation to tissues related with light capture. 4. Synthesis. Together, these findings indicate that tropical seedling communities are structured by local abiotic factors that ultimately result in individual variation in resource acquisition traits and by biotic interactions driven by negative density dependence. These biotic interactions are highly dynamic and depend on conspecifics turnover, even at short temporal scales. Thus, to gain further insights into the forces structuring seedling communities, future studies should account for temporal variability in immediate neighbours and individual-level phenotypic variation that influence individual interactions.
Increasingly, ecologists are using functional and phylogenetic approaches to quantify the relative importance of stochastic, abiotic filtering and biotic filtering processes shaping the pattern of ...species co‐occurrence. A remaining challenge in functional and phylogenetic analyses of tropical tree communities is to successfully integrate the functional and phylogenetic structure of tree communities across spatial and size scales and habitats in a single analysis. We analysed the functional and phylogenetic structure of tree assemblages in a 20‐ha tropical forest dynamics plot in south‐west China. Because the influence of biotic interactions may become more apparent as cohorts age, on local scales, and in resource‐rich environments, we perform our analyses across three size classes, six spatial scales and six distinct habitat types, using 10 plant functional traits and a molecular phylogeny for the >400 tree taxa found in the plot. All traits, except leaf area and stem‐specific resistance, had significant, albeit weak phylogenetic signal. For canopy species, phylogenetic clustering in small and medium size classes turned to phylogenetic overdispersion in the largest size class and this change in dispersion with size was found in each habitat type and across all spatial scales. On fine spatial scales, functional dispersion changed from clustering to overdispersion with increasing size classes. However, on larger spatial scales assemblages were functionally clustered for all size classes and habitats. Phylogenetic and functional structure across spatial and size scales and habitats gave strong support for a deterministic model of species co‐occurrence rather than for a neutral model. The results also support the hypothesis that abiotic determinism is more important at larger scales, while biotic determinism is more important on smaller scales within habitats.
Evaluating the relative importance of deterministic and stochastic processes underlying taxonomic and functional beta diversity is crucial in community ecology, because it can reveal the dominant ...processes of community assembly. However, studies of bird communities remain rare and of limited spatial extents. In this study, we described the taxonomic and functional beta diversity patterns of 32 passerine bird assemblages of Yunnan Province, China. We constructed null models based on observed species beta diversity and used multiple regressions on distance matrices to evaluate the relative contributions of deterministic and stochastic processes to passerine bird assemblage dissimilarity. Our results showed significant geographic distance decay in taxonomic and functional similarity, with passerine bird assemblages located in the northwest and southwest of the province having higher functional beta diversity values than expected. Environmental distance and geographic distance explained a similar amount taxonomic beta diversity, but environmental distance explained much more functional beta diversity. Our results suggest that both deterministic and stochastic processes drive taxonomic beta diversity, but that deterministic processes, particularly environmental filtering, play a dominant role in driving functional beta diversity of passerine bird assemblages at sub‐national scale.
Chinese forests cover most of the representative forest types in the Northern Hemisphere and function as a large carbon (C) sink in the global C cycle. The availability of long-term C dynamics ...observations is key to evaluating and understanding C sequestration of these forests. The Chinese Ecosystem Research Network has conducted normalized and systematic monitoring of the soil-biology-atmosphere-water cycle in Chinese forests since 2000. For the first time, a reference dataset of the decadal C cycle dynamics was produced for 10 typical Chinese forests after strict quality control, including biomass, leaf area index, litterfall, soil organic C, and the corresponding meteorological data. Based on these basic but time-discrete C-cycle elements, an assimilated dataset of key C cycle parameters and time-continuous C sequestration functions was generated via model-data fusion, including C allocation, turnover, and soil, vegetation, and ecosystem C storage. These reference data could be used as a benchmark for model development, evaluation and C cycle research under global climate change for typical forests in the Northern Hemisphere.
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