Masatoshi Katabuchi

A global meta‐analysis of the relative extent of intraspecific trait variation in plant communities

Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.

Robustness of trait distribution metrics for community assembly studies under the uncertainties of assembly processes

Numerous studies have revealed the existence of nonrandom trait distribution patterns as a sign of environmental filtering and/or biotic interactions in a community assembly process. A number of metrics with various algorithms have been used to detect these patterns without any clear guidelines. Although some studies have compared their statistical powers, the differences in performance among the metrics under the conditions close to actual studies are not clear. Therefore, the performances of five metrics of convergence and 16 metrics of divergence under alternative conditions were comparatively analyzed using a suite of simulated communities. We focused particularly on the robustness of the performances to conditions that are often uncertain and uncontrollable in actual studies; e.g., atypical trait distribution patterns stemming from the operation of multiple assembly mechanisms, a scaling of trait-function relationships, and a sufficiency of analyzed traits. Most tested metrics, for either convergence or divergence, had sufficient statistical power to distinguish nonrandom trait distribution patterns without uncertainty. However, the performances of the metrics were considerably influenced by both atypical trait distribution patterns and other uncertainties. Influences from these uncertainties varied among the metrics of different algorithms and their performances were often complementary. Therefore, under the uncertainties of an assembly process, the selection of appropriate metrics and the combined use of complementary metrics are critically important to reliably distinguish nonrandom patterns in a trait distribution. We provide a tentative list of recommended metrics for future studies.

Vulnerability of moorland plant communities to environmental change: consequences of realistic species loss on functional diversity

Understanding the consequences of realistic species loss on the functioning and persistence of vulnerable ecosystems is key to devising conservation strategies when environmental changes are immediate threats. Yet, few studies have provided direct evidence for conservation prioritization and decision-making. We incorporated the quantification of functional diversity based on the Rao index of diversity (FDrao) into this applied context and examined the consequences of realistic species loss on functional diversity in moorland plant communities widely interspersed within a subalpine zone in northern Japan. The realistic order of species loss was derived from the nested subset pattern in the moorland communities, which was corroborated by selective species tolerance and selective extinction. We analysed the relationships between the FDrao half-life, as an index of each moorlands vulnerability to species loss, and a range of environmental variables describing the moorlands. We then mapped this index across the entire landscape. At most sites, ordered species loss caused a relatively small decline in FDrao until a certain number of species was lost and an accelerating decline thereafter, suggesting relatively low initial vulnerability to species loss. At the other sites, however, ordered species loss caused an approximately proportional decrease in FDrao, suggesting relatively high vulnerability to species loss. The model indicated that sites with higher elevation, higher carrying capacities, or increasing isolation have a shorter FDrao half-life. The mapping of this index allowed us to identify the geographical distribution of sites of high conservation priority.Synthesis and applications. We performed fine-scale assessments of the vulnerability of moorland plant communities to species loss, which is likely to occur under future environmental conditions, by simulating the consequences of realistic species loss for functional diversity. The methods used here can provide urgently needed information to support the prioritization and decision-making involved in conserving ecosystems in the face of global biodiversity loss. We performed fine-scale assessments of the vulnerability of moorland plant communities to species loss, which is likely to occur under future environmental conditions, by simulating the consequences of realistic species loss for functional diversity. The methods used here can provide urgently needed information to support the prioritization and decision-making involved in conserving ecosystems in the face of global biodiversity loss.

Relative importance of habitat use, range expansion, and speciation in local species diversity of Anolis lizards in Cuba

Variations in species richness of local assemblages may be explained by local ecological processes or large-scale evolutionary and biogeographical processes. In Anolis lizards, species with different ecomorphs can coexist by occupying different niches. In addition, several species with the same ecomorph (e.g., trunk-ground) can coexist, and the number of trunk-ground anole species varies among local species assemblages. In this study, we assessed the importance of ecological interactions, number of speciation events, and range expansion for local and regional species diversity of these lizards. We examined the species richness and thermal microhabitat partitioning (considered to be a measure of ecological interaction) of 12 trunk-ground anole species in 11 local assemblages in Cuba. The results indicated that the phylogenetic structure of trunk-ground anole lizard assemblages was random. However, there was an overdispersion of preferences for thermal microhabitat use, which indicates that differences in microhabitat use are likely to occur within assemblages. We suggest that the number of speciation events within regions and the number of sympatrically coexisting species increases species richness at the local level. Migration appeared to be limited, leading to the range expansion of only three species with different thermal requirements. The thermal niches of species were conserved within Anolis allogus clade, whereas species within the Anolis homolechis and Anolis sagrei clades tended to change their thermal niches. Our results suggest that the species composition and richness in local assemblages could be explained by evolutionary history (the number of speciation events and limits to range expansion) and ecological processes (habitat partitioning). Of the ecological factors, the number of thermal (microhabitat use) and structural niches (e.g., vegetation) could limit the potential number of coexisting species within a local assemblage n

Variations in Species Composition of Moorland Plant Communities Along Environmental Gradients Within a Subalpine Zone in Northern Japan

Despite the ecological, conservation, and cultural significance of Japan’s alpine and subalpine moorland ecosystems, the patterns of species composition in plant communities in these ecosystems have not been fully described. The objectives of this study were to classify and describe the species composition of moorland plant communities and to examine the relationships between the classified community types and measured environmental variables within the subalpine zone of northern Japan. Plant communities were sorted into six types, whose strongest indicator species were Sieversia pentapetala, Schizocodon soldanelloides, Moliniopsis japonica, Vaccinium oxycoccos, Carex thunbergii, and Hosta sieboldii, respectively. The differences in species composition among these types were mainly related to the variations in soil solution pH and electric conductivity and in elevation and temperature. Each community type represented a unique combination of plant species, with some rare and endangered species. Describing and classifying the vegetation by providing indicators for a representative range of moorland community types should facilitate the identification and conservation of these valuable communities.

Contrasting outcomes of species- and community-level analyses of the temporal consistency of functional composition

Multiple anthropogenic drivers affect every natural community, and there is broad interest in using functional traits to understand and predict the consequences for future biodiversity. There is, however, no consensus regarding the choice of analytical methods. We contrast species- and community-level analyses of change in the functional composition for four traits related to drought tolerance using three decades of repeat censuses of trees in the 50-ha Forest Dynamics Plot on Barro Colorado Island, Panama. Community trait distributions shifted significantly through time, which may indicate a shift toward more drought tolerant species. However, at the species level, changes in abundance were unrelated to trait values. To reconcile these seemingly contrasting results, we evaluated species-specific contributions to the directional shifts observed at the community level. Abundance changes of just one to six of 312 species were responsible for the community-level shifts observed for each trait. Our results demonstrate that directional changes in community-level functional composition can result from idiosyncratic change in a few species rather than widespread community-wide changes associated with functional traits. Future analyses of directional change in natural communities should combine community-, species-, and possibly individual-level analyses to uncover relationships with function that can improve understanding and enable prediction.

Habitat filtering determines the functional niche occupancy of plant communities worldwide

How the patterns of niche occupancy vary from species-poor to species-rich communities is a fundamental question in ecology that has a central bearing on the processes that drive patterns of biodiversity. As species richness increases, habitat filtering should constrain the expansion of total niche volume, while limiting similarity should restrict the degree of niche overlap between species. Here, by explicitly incorporating intraspecific trait variability, we investigate the relationship between functional niche occupancy and species richness at the global scale. 2.We assembled 21 datasets worldwide, spanning tropical to temperate biomes and consisting of 313 plant communities representing different growth forms. We quantified three key niche occupancy components (the total functional volume, the functional overlap between species and the average functional volume per species) for each community, related each component to species richness, and compared each component to the null expectations. 3.As species richness increased, communities were more functionally diverse (an increase in total functional volume), and species overlapped more within the community (an increase in functional overlap) but did not more finely divide the functional space (no decline in average functional volume). Null model analyses provided evidence for habitat filtering (smaller total functional volume than expectation), but not for limiting similarity (larger functional overlap and larger average functional volume than expectation) as a process driving the pattern of functional niche occupancy. 4.Synthesis. Habitat filtering is a widespread process driving the pattern of functional niche occupancy across plant communities and coexisting species tend to be more functionally similar rather than more functionally specialized. Our results indicate that including intraspecific trait variability will contribute to a better understanding of the processes driving patterns of functional niche occupancy

Divergent drivers of leaf trait variation within species, among species, and among functional groups

Significance Leaf traits, such as photosynthetic capacity, nitrogen concentration, and leaf mass per area, strongly affect plant growth and nutrient cycles. Understanding relationships among leaf traits is, therefore, a fundamental challenge in plant biology, crop science, and ecology. Different groups of leaves exhibit distinct relationships among pairs of traits. For example, photosynthetic capacity per unit leaf area increases strongly with leaf mass per area from sun to shade within species, but these same traits are only weakly related across global species. Our analysis suggests that divergent trait relationships can be understood by partitioning leaf mass into photosynthetic and structural support components. Our paper clarifies the causes of relationships among traits and why those relationships differ among different groups of plants. Understanding variation in leaf functional traits—including rates of photosynthesis and respiration and concentrations of nitrogen and phosphorus—is a fundamental challenge in plant ecophysiology. When expressed per unit leaf area, these traits typically increase with leaf mass per area (LMA) within species but are roughly independent of LMA across the global flora. LMA is determined by mass components with different biological functions, including photosynthetic mass that largely determines metabolic rates and contains most nitrogen and phosphorus, and structural mass that affects toughness and leaf lifespan (LL). A possible explanation for the contrasting trait relationships is that most LMA variation within species is associated with variation in photosynthetic mass, whereas most LMA variation across the global flora is associated with variation in structural mass. This hypothesis leads to the predictions that (i) gas exchange rates and nutrient concentrations per unit leaf area should increase strongly with LMA across species assemblages with low LL variance but should increase weakly with LMA across species assemblages with high LL variance and that (ii) controlling for LL variation should increase the strength of the above LMA relationships. We present analyses of intra- and interspecific trait variation from three tropical forest sites and interspecific analyses within functional groups in a global dataset that are consistent with the above predictions. Our analysis suggests that the qualitatively different trait relationships exhibited by different leaf assemblages can be understood by considering the degree to which photosynthetic and structural mass components contribute to LMA variation in a given assemblage.

LeafArea: an R package for rapid digital image analysis of leaf area

Measuring leaf area is essential to quantifying other leaf functional traits. This paper introduces a new R package, LeafArea, which allows one to conveniently run ImageJ (http://imagej.nih.gov/ij/) within R. The functions in this package analyze multiple scanned leaf images in the target directory, generate multiple output files containing the leaf area of each leaf image, and then process and combine these files into a single file in a format that is convenient for subsequent analyses. Leaf area data from multiple images from the same sample can be combined automatically. This function allows users to cut large leaves into several pieces during scanning. The package provides a user-friendly, automated tool for measuring leaf area from scanned images.

Climate sensitive size-dependent survival in tropical trees

Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four ‘survival modes’ that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories.Data from 2 million individual trees spanning 1,781 species reveal that tropical forests can be grouped into four size-dependent life-history survival modes, the application of which in demographic simulations predicts biomass change.