The edaphic control of plant diversity Hulshof, Catherine M.; Spasojevic, Marko J.; Schrodt, Franziska
Global ecology and biogeography,
October 2020, 2020-10-00, 20201001, Letnik:
29, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Background
The central thesis of plant ecology is that climate determines the global distribution of vegetation. Within a vegetation type, however, finer‐scale environmental features, such as the ...physical and chemical properties of soil (edaphic variation), control patterns of plant diversity and distributions.
Aims
Here, we review the literature to provide a mechanistic framework for the edaphic control of plant diversity. First, we review three examples where soils have known, prevalent effects on plant diversity: during soil formation, on unusual soils and in regions with high edaphic heterogeneity. Second, we synthesize how edaphic factors mediate the relative importance of the four key processes of community assembly (speciation, ecological drift, dispersal and niche selection). Third, we review the potential effects of climate change in edaphically heterogeneous regions. Finally, we outline key knowledge gaps for understanding the edaphic control of plant diversity. In our review, we emphasize floras of unusual edaphic areas (i.e., serpentine, limestone, granite), because these areas contribute disproportionately to the biodiversity hotspots of the world.
Taxa
Terrestrial plants.
Location
Global.
Conclusion
Edaphic variation is a key driver of biodiversity patterns and influences the relative importance of speciation, dispersal, ecological drift, niche selection and interactions among these processes. Research is still needed to gain a better understanding of the underlying mechanisms by which edaphic variation influences these community assembly processes, and unusual soils provide excellent natural systems for such tests. Furthermore, the incorporation of edaphic variation into climate change research will help to increase the predictive power of species distribution models, identify potential climate refugia and identify species with adaptations that buffer them from climate change.
1. Patterns of species co-existence and species diversity in plant communities remain an important research area despite over a century of intensive scrutiny. To provide mechanistic insight into the ...rules governing plant species co-existence and diversity, plant community ecologists are increasingly quantifying functional trait values for the species found in a wide range of communities. 2. Despite the promise of a quantitative functional trait approach to plant community ecology, we suggest that, along with examining trait variation across species, an assessment of trait variation within species should also be a key component of a trait-based approach to community ecology. Variability within and between individuals and populations is likely widespread due to plastic responses to highly localized abiotic and biotic interactions. 3. In this study, we quantify leaf trait variation within and across ten co-existing tree species in a dry tropical forest in Costa Rica to ask: (i) whether the majority of trait variation is located between species, within species, within individuals or within the leaves themselves; (ii) whether trait values collected using standardized methods correlate with those collected using unstandardized methods; and (iii) to what extent can we differentiate plant species on the basis of their traits? 4. We find that the majority of variation in traits was often explained by between species differences; however, between leaflet trait variation was very high for compound-leaved species. We also show that many species are difficult to reliably differentiate on the basis of functional traits even when sampling many individuals. 5. We suggest an ideal sample size of at least 10, and ideally 20, individuals be used when calculating mean trait values for individual species for entire communities, though even at large sample sizes, it remains unclear if community level trait values will allow comparisons on a larger geographic scale or if species traits are generally similar across scales. It will thus be critical to account for intraspecific variation by comparing species mean trait values across space in multiple microclimatic environments within local communities and along environmental gradients. Further, quantifying trait variability due to plasticity and inheritance will provide a better understanding of the underlying patterns and drivers of trait variation as well as the application of functional traits in outlining mechanisms of species co-existence.
Beyond the study of the mean, functional ecology lacks a concise characterization of trait variance patterns across spatiotemporal scales. Traits are measured in different ways, using different ...metrics, and at different spatial (and rarely temporal) scales. This study expands on previous research by applying a ubiquitous and widely used empirical model—Taylor's Power Law—to functional trait variance with the goal of identifying general patterns of trait variance scaling (the behavior of trait variance across scales). We compiled data on tree seedling communities monitored over 10 years across 213 2 m2 plots and functional trait data from a subtropical forest in Puerto Rico. We examined trait‐based Taylor's Power Law at nested spatial and temporal scales. The scaling of variance with the mean was idiosyncratic across traits suggesting that the drivers of variation are likely to differ across traits that may make variance scaling theory elusive. However, slopes varied more in space than through time, suggesting that spatial environmental variability may have a larger role in driving trait variance than temporal variability. Empirical models that characterize taxonomic patterns across spatiotemporal scales, like Taylor's Power Law, can provide an insight into the scaling of functional traits, a necessary next step toward a more predictive trait‐based ecology.
Despite being recognized as a promoter of diversity and a condition for local coexistence decades ago, the importance of intraspecific variance has been neglected over time in community ecology. ...Recently, there has been a new emphasis on intraspecific variability. Indeed, recent developments in trait-based community ecology have underlined the need to integrate variation at both the intraspecific as well as interspecific level. We introduce new T-statistics (‘T’ for trait), based on the comparison of intraspecific and interspecific variances of functional traits across organizational levels, to operationally incorporate intraspecific variability into community ecology theory. We show that a focus on the distribution of traits at local and regional scales combined with original analytical tools can provide unique insights into the primary forces structuring communities.
A challenge
Variation is ubiquitous in nature across all spatial and temporal scales and underlies prominent ecological and evolutionary theories. Although understanding the causes and consequences ...of trait variation is a central goal of trait‐based ecology, the scaling of trait variance across space and time (variance scaling) is unresolved.
A solution
We argue that characterizing trait variance across spatio‐temporal scales using a combination of prominent power laws can elucidate the role of environmental variability in trait variation and potential mechanisms driving trait patterns. In particular, the species–time–area relationship and Taylor's power law help to establish a generalizable framework for developing and testing variance scaling theory. Finally, we outline priority research questions and tractable systems for answering them. Successional forests, long‐term forest monitoring networks and censuses of short‐lived taxa are ideal for coupling high‐resolution environmental data with measurements of trait variance across scales to test the models proposed here.
Main conclusions
Characterizing the behaviour of variance across spatio‐temporal scales is feasible and a prerequisite for developing a predictive theory of trait‐based ecology.
Summary
A longstanding goal of ecology and conservation biology is to understand the environmental and biological controls of forest succession. However, the patterns and mechanisms that guide ...successional trajectories, especially within tropical forests, remain unclear.
We collected leaf functional trait and abiotic data across a 110‐year chronosequence within a tropical dry forest in Costa Rica. Focusing on six key leaf functional traits related to resource acquisition and competition, along with measures of forest stand structure, we propose a mechanistic framework to link species composition, community trait distributions and forest structure. We quantified the community‐weighted trait distributions for specific leaf area, leaf dry matter concentration, leaf phosphorus concentration, leaf carbon to nitrogen ratio and leaf stable isotopic carbon and nitrogen. We assessed several prominent hypotheses for how these functional measures shift in response to changing environmental variables (soil water content, bulk density and pH) across the chronosequence.
Increasingly, older forests differed significantly from younger forests in species composition, above‐ground biomass and shifted trait distributions. Early stages of succession were uniformly characterized by lower values of community‐weighted mean specific leaf area, leaf stable nitrogen isotope and leaf phosphorus concentration. Leaf dry matter concentration and leaf carbon to nitrogen ratio were lower during earlier stages of succession, and each trait reached an optimum during intermediate stages of succession. The leaf carbon isotope ratio was the only trait to decrease linearly with increasing stand age indicating reduced water use efficiency in older forests. However, in contrast with expectations, community‐weighted trait variances did not generally change through succession, and when compared to null expectations were lower than expected.
The observed directional shift in community‐weighted mean trait values is consistent with the ‘productivity filtering’ hypothesis where a directional shift in water and light availability shifts physiological strategies from ‘slow’ to ‘fast’. In contrast with expectations arising from niche based ecology, none of the community trait distributions were over‐dispersed. Instead, patterns of trait dispersion are consistent with the abiotic filtering and/or competitive hierarchy hypotheses.
Lay Summary
Much ecological research aims to explain how climate impacts biodiversity and ecosystem-level processes through functional traits that link environment with individual performance. However, the ...specific climatic drivers of functional diversity across space and time remain unclear due largely to limitations in the availability of paired trait and climate data. We compile and analyze a global forest dataset using a method based on abundance-weighted trait moments to assess how climate influences the shapes of whole-community trait distributions. Our approach combines abundance-weighted metrics with diverse climate factors to produce a comprehensive catalog of trait–climate relationships that differ dramatically—27% of significant results change in sign and 71% disagree on sign, significance, or both—from traditional species-weighted methods. We find that (i) functional diversity generally declines with increasing latitude and elevation, (ii) temperature variability and vapor pressure are the strongest drivers of geographic shifts in functional composition and ecological strategies, and (iii) functional composition may currently be shifting over time due to rapid climate warming. Our analysis demonstrates that climate strongly governs functional diversity and provides essential information needed to predict how biodiversity and ecosystem function will respond to climate change.
Over the past three decades, there has been a concerted effort to study the long-term dynamics of tropical forests throughout the world. Data regarding temporal trends in species diversity, species ...composition, and species-specific demographic rates have now been amassed. Such data can be utilized to test predictions regarding the roles the environment and demographic stochasticity play in driving forest dynamics. These analyses could be further refined by quantifying the temporal trends in the functional composition and diversity in tropical forests. For example, we have only a handful of studies that quantify directional shifts in the functional composition in tropical forests in response to global change drivers. The present study uses data from three censuses spanning 30 yr in a Neotropical dry forest dynamics plot to provide novel insights into how the functional diversity and composition of a tropical forest has changed through time. Specifically, here we aim to (1) quantify population dynamics and compare it to that expected from environmental or demographic variance; (2) quantify long-term trends in species richness and functional diversity; (3) test whether there have been directional changes in the functional composition of the forest though time and the population changes that are responsible for these changes; and (4) place these long-term results into the context of the successional and climatic history of the forest.
The relationship between tree height and diameter is fundamental in determining community and ecosystem structure as well as estimates of biomass and carbon storage. Yet our understanding of how tree ...allometry relates to climate and whole organismal function is limited. We used the Forest Inventory and Analysis National Program database to determine height–diameter allometries of 2,976,937 individuals of 293 tree species across the United States. The shape of the allometric relationship was determined by comparing linear and nonlinear functional forms. Mixed‐effects models were used to test for allometric differences due to climate and floristic (between angiosperms and gymnosperms) and functional groups (leaf habit and shade tolerance). Tree allometry significantly differed across the United States largely because of climate. Temperature, and to some extent precipitation, in part explained tree allometric variation. The magnitude of allometric variation due to climate, however, had a phylogenetic signal. Specifically, angiosperm allometry was more sensitive to differences in temperature compared to gymnosperms. Most notably, angiosperm height was more negatively influenced by increasing temperature variability, whereas gymnosperm height was negatively influenced by decreasing precipitation and increasing altitude. There was little evidence to suggest that shade tolerance influenced tree allometry except for very shade‐intolerant trees which were taller for any given diameter. Tree allometry is plastic rather than fixed and scaling parameters vary around predicted central tendencies. This allometric variation provides insight into life‐history strategies, phylogenetic history, and environmental limitations at biogeographical scales.
Tree height‐diameter allometry is plastic and scaling parameters vary around predicted central tendencies due to climatic variation. The magnitude of allometric variation due to climate depends largely on differences between angiosperms and gymnosperms.
Questions: Are patterns of intra- and inter-specific functional trait variation consistent with greater abiotic filtering on community assembly at high latitudes and elevations, and greater biotic ...filtering at low latitudes and elevations? Locations: Area de Conservación Guanacaste, Costa Rica; Santa Catalina Mountains, Arizona; Siskiyou Mountains, Oregon. Methods: We measured woody plant species abundance and a key functional trait associated with competition for resources and environmental tolerance (specific leaf area, SLA) along elevational gradients in low-latitude tropical (Costa Rica), mid-latitude desert (Arizona) and high latitude mediterranean (southern Oregon) biomes. We explored patterns of abiotic and biotic filtering by comparing observed patterns of community-weighted means and variances along elevational and latitudinal gradients to those expected under random assembly. In addition, we related trait variability to niches and explored how total trait space and breadth vary across broad spatial gradients by quantifying the ratio of intra- to inter-specific variation. Results: Both the community-wide mean and variance of SLA decreased with increasing latitude, consistent with greater abiotic filtering at higher latitudes. Further, low-elevation communities had higher trait variation than expected by chance, consistent with greater biotic filtering at low elevations. Finally, in the tropics and across latitude the ratio of intra- to inter-specific variation was negatively correlated to species richness, which further suggests that biotic interactions influence plant assembly at low latitudes. Conclusions: Intra- and inter-specific patterns of SLA variation appeared broadly consistent with the idea that the relative strength of biotic and abiotic drivers on community assembly changes along elevational and latitudinal gradients; evidence for biotic drivers appeared more prominent at low latitudes and elevations and evidence for abiotic drivers appeared more prominent at high latitudes and elevations.
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