Abiotic and biotic variation has been shown to be important in regulating nutrient cycling and belowground communities in natural systems. However, genetic variation in dominant plants as a driver of rates of nutrient cycling is still poorly understood and few studies have looked at genotype interactions across multiple environments. Using Populus angustifolia and a common garden approach, we hypothesized that all three factors: tree genetic variation, environmental conditions and genetic by environment (G x E) interactions would affect soil carbon (C) storage and nitrogen (N) cycling. Replicated copies of five different reciprocally planted Populus genotypes were studied in three separate 18-21 year old common gardens at different elevations (1300m, 1384m and 1587m) in northern Utah, to measure the genotype and environmental effects on pools of soil C and N as well as rates of soil net N nitrification and net mineralization. Our results indicate that genotypes influence pools of soil C, total N and C:N, but genotype did not influence net rates of nitrogen mineralization. Environmental variation significantly influenced pools of soil C, total N, soil C:N and rates of net nitrification and net N mineralization. As predicted, G x E interactions significantly influenced both pools and processes of soil C and N cycling. Overall, we found that genetic variation in plant traits (tree diameter and leaf/root chemistry) as well as soil texture across gardens were significant predictors of soil C and N pools and fluxes across seasons. These data help us understand the relative role of genotypic variation on above- and belowground interactions in different environments and the consequences of these interactions on ecosystem processes. The results from this study show that across an environmental gradient Populus angustifolia genotypes can influence nitrogen mineralization through feedbacks between environmental variation, tree phenotype and soils.

Abiotic and biotic variation has been shown to be important in regulating nutrient cycling and belowground communities in natural systems. However, genetic variation in dominant plants as a driver of rates of nutrient cycling is still poorly understood and few studies have looked at genotype interactions across multiple environments. Using Populus angustifolia and a common garden approach, we hypothesized that all three factors: tree genetic variation, environmental conditions and genetic by environment (G x E) interactions would affect soil carbon (C) storage and nitrogen (N) cycling. Replicated copies of five different reciprocally planted Populus genotypes were studied in three separate 18-21 year old common gardens at different elevations (1300m, 1384m and 1587m) in northern Utah, to measure the genotype and environmental effects on pools of soil C and N as well as rates of soil net N nitrification and net mineralization. Our results indicate that genotypes influence pools of soil C, total N and C:N, but genotype did not influence net rates of nitrogen mineralization. Environmental variation significantly influenced pools of soil C, total N, soil C:N and rates of net nitrification and net N mineralization. As predicted, G x E interactions significantly influenced both pools and processes of soil C and N cycling. Overall, we found that genetic variation in plant traits (tree diameter and leaf/root chemistry) as well as soil texture across gardens were significant predictors of soil C and N pools and fluxes across seasons. These data help us understand the relative role of genotypic variation on above- and belowground interactions in different environments and the consequences of these interactions on ecosystem processes. The results from this study show that across an environmental gradient Populus angustifolia genotypes can influence nitrogen mineralization through feedbacks between environmental variation, tree phenotype and soils.

The encroachment of woody species into grassland and savanna ecosystems has been well document since the early 1800s. Within the parkland ecoregion of western Canada, trembling aspen (Populus tremuloides Michx.) has been one of the key tree species increasing in dominance. Aspen encroachment is best explained not by single mechanism, but rather by a number of interacting ecological factors. In this study I examined the ecological consequences of the clonal biology in aspen as a means to explain persistence and observed tree-grass ratios within grassland savannas of western Canada. Results suggest that aspen stands cycle between a “stable” phase characterized by a dense mature canopy, and an “unstable” phase characterized by canopy breakup and increased regeneration from root suckers. It is during this unstable phase that clonal encroachment is likely to occur. Within these mature stands, different-aged ramets promote persistence by maximizing developmental variation. Such a mechanism overcomes the functional phenotypic uniformity of ramets within a single age-structured stand. Results from my study indicate that physiological integration is beneficial to the growth and survivorship of regenerating and encroaching aspen ramets. My results also suggest that the benefits of physiological integration are greatest in more stressful environments, and in recently established post-fire ramets. Finally, the consequences of variation in adaptive ecological relevant traits among individuals was examined by determining differences in vigor among aspen clones in relation to the production of secondary compounds (phenolic glycosides). My results demonstrate a high degree of variation in leaf phenolic glycosides production among clones. A significant amount of this variation was accounted for by differences in clone vigor (within population: individual susceptibility hypothesis), with a smaller amount related to environmental differences (among populations). In all instances, vigorous clones were significantly higher in levels of phenolic glycosides compared with dieback clones, suggesting that some individuals may be predisposed to undergo density-independent mortality. This has important ecological implications, because it implies that one of the key mechanisms regulating population dynamics, community interactions and biodiversity may be related to intrinsic adaptive differences in susceptibility among individuals.

The encroachment of woody species into grassland and savanna ecosystems has been well document since the early 1800s. Within the parkland ecoregion of western Canada, trembling aspen (Populus tremuloides Michx.) has been one of the key tree species increasing in dominance. Aspen encroachment is best explained not by single mechanism, but rather by a number of interacting ecological factors. In this study I examined the ecological consequences of the clonal biology in aspen as a means to explain persistence and observed tree-grass ratios within grassland savannas of western Canada. Results suggest that aspen stands cycle between a “stable” phase characterized by a dense mature canopy, and an “unstable” phase characterized by canopy breakup and increased regeneration from root suckers. It is during this unstable phase that clonal encroachment is likely to occur. Within these mature stands, different-aged ramets promote persistence by maximizing developmental variation. Such a mechanism overcomes the functional phenotypic uniformity of ramets within a single age-structured stand. Results from my study indicate that physiological integration is beneficial to the growth and survivorship of regenerating and encroaching aspen ramets. My results also suggest that the benefits of physiological integration are greatest in more stressful environments, and in recently established post-fire ramets. Finally, the consequences of variation in adaptive ecological relevant traits among individuals was examined by determining differences in vigor among aspen clones in relation to the production of secondary compounds (phenolic glycosides). My results demonstrate a high degree of variation in leaf phenolic glycosides production among clones. A significant amount of this variation was accounted for by differences in clone vigor (within population: individual susceptibility hypothesis), with a smaller amount related to environmental differences (among populations). In all instances, vigorous clones were significantly higher in levels of phenolic glycosides compared with dieback clones, suggesting that some individuals may be predisposed to undergo density-independent mortality. This has important ecological implications, because it implies that one of the key mechanisms regulating population dynamics, community interactions and biodiversity may be related to intrinsic adaptive differences in susceptibility among individuals.

The overarching goal of my dissertation is to explore the potential and limits of a trait-based approach to plant ecology. Together, the different studies presented here address two explicit and implicit foundational assumptions underpinning the trait-based approach: (1) that the correlation patterns and biological significance of traits transfer across scales and (2) that the phenotypic complexity of plants can accurately be synthesized into a few meaningful traits to study their ecology. Moreover, the last chapter focuses on a third key assumption: (3) that traits are strong predictors of plant performance (Shipley et al. In Press). I examine these assumptions by exploring multivariate patterns of phenotypic variation and integration across different ecological scales (e.g., individuals, populations, species) while explicitly considering the phenotypic complexity of trees, both in terms of their multidimensional and integrated nature. Two themes thus permeate this body of work: scales and phenotypic complexity. Much of what we know about the relationships among key traits comes from species-scale studies. Trait variation at smaller scales are often interpreted in the context of these interspecific relationships, but it is not clear that interspecific patterns observed at global scales apply to smaller scales. Moreover, although plants are complex, integrated organisms with intricate relationships among their traits, single traits are often studied and interpreted without considering the rest of the phenotype. Yet, examining individual traits outside of their phenotypic context might provide limited insight or be misleading. To address these shortcomings, this body of work examines multidimensional patterns of trait variation and correlation across ecological scales. It uses (1) a set of six ecophysiological leaf traits from mature trees in a lowland tropical rainforest, and (2) a set of twenty leaf, root, stem, branch and whole-plant ecophysiological traits from deciduous saplings in a temperate forest. The combination of our findings point to three main conclusions: (i) local interspecific and intra-population trait integration structures differ from each other and from the global interspecific patterns reported in the literature, such that global-scale interspecific patterns cannot readily be transferred to more local scales; (ii) considering the complexity of the plant phenotype provides better insights into ecological patterns and processes than what we can learn from considering individual or a handful of traits; and (iii) traits strongly affect individual plant performance, although there is no relationship between a species' trait correlation structure and its environmental niche, which suggests that there are multiple alternative optimal phenotypes in a given environment.

O presente trabalho avalia a variação não-geográfica de Necromys lasiurus (Lund, 1840) dentro do território brasileiro, utilizando a morfometria craniana. Os dados foram obtidos a partir de 20 medidas craniodentárias tomadas de 1.572 indivíduos depositados em diversas coleções brasileiras. Foram descritas classes etárias baseadas exclusivamente no desgaste dos molares superiores e as mesmas foram utilizadas como índices etários para a avaliação da variação etária. Foram realizadas análises uni e multivariadas para descrever a variação sexual e etária de N. lasiurus considerando primeiramente toda a amostra e, em seguida, separadamente para cada localidade ou agrupamento cujo número amostral se mostrou suficiente para a condução dos testes estatísticos. N. lasiurus revelou dimorfismo relacionado às classes etárias intermediárias tanto na amostra total quanto nas amostras locais. No entanto, a ocorrência de dimorfismo sexual não se repetiu em todas as localidades avaliadas. A análise da variação etária com a amostra total revelou importantes padrões de variação craniana, como o rápido desenvolvimento da região orofacial em relação a outras regiões do crânio. No entanto, a avaliação da ontogenia nas amostras locais revelou diversos padrões ontogenéticos distintos. Além disso, as análises multivariadas apontam para a existência de uma estruturação geográfica da variação, corroborando estudos anteriores com a espécie. Os resultados obtidos indicam que futuras análises de cunho geográfico e taxonômico sobre N. lasiurus devem abordar os sexos de maneira separada e as classes etárias podem ser homogeneizadas para a formação de amostras com indivíduos suficientes para permitir a realização de análises estatísticas. / The present study assess the non-geographic variation of Necromys lasiurus (Lund, 1840) in Brazil, using skull morphometrics. A total of 20 craniometric measurements were taken from 1,572 specimens deposited in many Brazilian zoological collections. Age classes were described based on the wear stage of the superior molars and used as index to asses the variation due to age. Uni and multivariate analyses were used in order to describe the sexual and ontogenetic variation of N. lasiurus, first using the total sample and then using geographic samples that contained sufficient individuals for the application of the statistical tests. N. lasiurus presented sexual dimorphism related to intemediate age classes in total and in some local samples. The age assessment revealed important ontogenetic patterns of the skull development, like the rapid growth of orofacial region compared to other parts. The local analyses revealed individual patterns of variation for each sample. Besides, the multivariate approach showed geographic patterns of variation, just like previous studies said. The results of this study indicate that future geographic and taxonomic investigations on N. lasiurus should keep both sexes separated and the age classes could be homogenized in order do form adequate samples that allow the application of statistical tests.

Traditionally, the study of biodiversity has focused on quantifying patterns of species diversity, or species richness, by simply counting the number of species across environmental gradients. This approach has been fundamental to ecological investigations and thinking with regards to identifying patterns of biodiversity. Although species diversity is the most commonly used dimension of biodiversity, species diversity alone does not provide a mechanistic understanding of biodiversity gradients. By also quantifying the genetic and phylogenetic diversity of a population, community or ecosystem, ecologists can become more informed on the relationships organisms have with one another, as well as their potential to adapt to changes in their environment. While each of these approaches provides methods for characterizing biodiversity, they do not offer direct insight into what species do, how they function, or how they will respond to changes in their environment. Functional, or trait-based ecology, provides an informative alternative to species-centric approaches that seeks to understand patterns of biodiversity in terms of functional traits. Functional traits capture fundamental tradeoffs in life history strategies that can be used to determine species ecological roles and can be used to scale from organisms to ecosystems to ask broad ecological questions. The overarching goal of my dissertation is to add additional links to trait-based ecology by identifying potential sources of trait variation across different spatial and temporal gradients between varying levels of biological organization. By assessing variation across spatial-temporal scales, I tested two prominent assumptions of trait-based ecology. First, I tested the trait-environment assumption wherein traits affect ecosystem processes. Therefore, there should be a predictable relationship between traits, their environment, and ecosystem function across large ecological gradients and between broad taxonomic groups. Second, I tested the assumption that interspecific trait variation exceeds intraspecific trait variation; thus, the species mean trait value captures much of the variation for a given trait. My study systems include the latitudinal diversity gradient of North America, forests of varying successional age in the tropical dry forests of Costa Rica, and a subalpine meadow of Colorado. First, we collected leaf trait data and soil microbial data at six sites across the latitudinal diversity gradient to test a central hypothesis of trait-based ecology, primarily that shifts in plant traits associated with decomposition and nutrient availability ramify to influence microbial functioning. We found that changes in plant traits not only reflect nutrient limitation across broad ecological gradients, but also have important regional effects on biogeochemical processes, microclimates, and energy fluxes that influence microbial diversity. Furthermore, changes in plant function correspond to changes in bacterial functional traits related to carbon, nitrogen, and phosphorus cycling, although only fungal functional traits related to nitrogen cycling change across the gradient. Our results represent one of the first comparisons of functional diversity within and across bacterial, fungal, and plant communities across a latitudinal gradient. Next, we collected leaf functional trait and abiotic data across a 110-year chronosequence within a tropical dry forest in Costa Rica. We focused on six leaf functional traits for woody plants within 14 plots that have varying times since disturbance in the tropical dry forests of Guanacaste, Costa Rica. When we compare species composition and community function, we find that older tropical dry forest communities differ significantly from younger forests in species composition, above ground biomass, and functional traits. Species in younger forests have traits better adapted to hotter temperatures and increased drought. For example, young forests are characterized by thicker leaves with higher water use efficiency. In contrast, older forests have thinner broader leaves more susceptible to desiccation. Interestingly, in contrast to expectations, variation in these functional traits does not generally change through succession. This means that the different species within each community are converging on similar functional strategies. Our results also suggest that regenerating tropical dry forests are resilient and can be restored within a human lifetime. Finally, we evaluated patterns of trait variation within and between three years to understand the widely-ignored source of temporal variation associated with seasonality and test the assumption that interspecific trait variation exceeds intraspecific variation and the species means account for the overall variation of a trait. To do this, we collected leaf data from eight species at a local site in Colorado throughout the growing season, over three years, as well as extracted data from a global database and made comparisons to assess sources trait variation. We found that, although the timing of collection influences one’s ability to capture fine-scale processes occurring on short time scales, collecting data locally throughout the growing season and across multiple years does not significantly influence species ranking. However, species ranking is not conserved for comparisons between local and global databases. This suggests that extra care should be taken when applying global data for species-specific studies and that ‘snap-shot’ sampling designs may over- or underestimate community trait distributions, reducing predictability. Overall, this body of work extends beyond understanding patterns of species diversity through the inclusion of species function. It contributes to our understanding of variation in biodiversity across broad ecological gradients and between diverse taxonomic groups, how communities assemble via functional traits, and the importance of temporal variation on functional traits for detecting fine-scale patterns.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第19324号 / 農博第2145号 / 新制||農||1036(附属図書館) / 学位論文||H28||N4952(農学部図書室) / 32326 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 縄田 栄治, 教授 北山 兼弘, 教授 北島 宣 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

No description available.

The trait based approach has been proposed as a way to reconcile community ecology. Despite recent advances in trait based ecology, such as the development of global trait databases and standardized methodology for trait collections, it remains unclear to what degree traits vary across individuals, species, and communities. In addition, the drivers of trait variation may shed light on the underlying processes that maintain species diversity and community assembly at local to continental scales yet these have been poorly studied. In this study, I examine both the magnitude of trait variation as well as the patterns of trait variation at local to continental scales in order to understand the drivers of diversity patterns across environmental gradients. First, I quantified the magnitude of trait variation at local scales in a dry tropical forest and determined that intraspecific variation is not negligible and can be quite large for compound-leaved species. However, I showed that the sample sizes necessary for quantifying trait variation are tractable and should encourage the adoption of trait variation in trait based ecology. Second, I tested whether climatic variables are predominantly responsible for observed trait variation across dry tropical forests in the Americas. I showed that climatic variability, specifically variability in precipitation, explained a large degree of observed trait variation across dry tropical forests and may provide a unique approach for classifying dry tropical forests based on their inherent degree of climatic seasonality. Third, I quantified patterns of trait variation at continental scales across elevational gradients at high to low latitudes. I showed that climatic variables largely drive patterns of trait variation at high latitudes while biotic factors largely drive patterns of trait variation at low, tropical latitudes. This finding has implications for understanding large-scale patterns of species diversity across elevational and latitudinal gradients. Finally, I apply trait variation to life history theory by quantifying variation in two life history traits (growth and reproduction) in a tropical tree species using a legacy dataset. I showed that variation in these two life history traits is due to both resource availability and allometric related effects on both traits. In sum, this study advances our understanding of the magnitude and underlying drivers of trait variation at local to continental scales.