Bases conceptuales y herramientas gráficas para investigar cómo funcionan los rasgos funcionales

Los rasgos funcionales constituyen una vía de investigación promisoria para explicar y predecir patrones ecológicos en distintos niveles de organización (genotipos, poblaciones, comunidades) porque ligan a las respuestas de los individuos con las condiciones ambientales que los rodean. Sin embargo, los ecólogos y botánicos argentinos parecen no haber explorado esta línea de trabajo tanto como investigadores en otras partes del mundo. Con este trabajo pretendo fomentar el uso de rasgos funcionales entre lectores locales e hispanoparlantes. Amalgamando definiciones propuestas por otros autores (en algunos casos contradictorias), defino a los rasgos funcionales como características morfológicas que luego afectan una cadena de procesos fisiológicos y ecológicos a los que llamé función, tasa vital y éxito ecológico (o fitness) poblacional. El propósito de esta definición es enfatizar la relación mecanística entre estructura y función de las plantas. El beneficio práctico es sumamente importante: poder predecir el futuro de una planta o un grupo de plantas a partir de sus propiedades físicas, las cuales son generalmente más fáciles de conocer que medidas fisiológicas o fenológicas. Luego, utilizo dos tipos de herramientas gráficas para discutir la funcionalidad de cuatro rasgos clave: altura potencial, peso de semilla, peso foliar por área y tamaño de hoja. Estas herramientas graficas son (i) diagramas de influencias que muestran las conexiones positivas o negativas, directas o indirectas, entre rasgos y fitness y (ii) gráficos de coordenadas cartesianas que describen las relaciones funcionales entre rasgos y tasas vitales que, al combinarse, dan lugar a relaciones rasgo fitness de óptimo. La teoría indica que las relaciones de óptimo serían la norma más que la excepción, a pesar de que generalmente se interpreta a los rasgos funcionales como indicadores de las funciones de las plantas, lo que implica relaciones exclusivamente lineales. Estas herramientas gráficas nos pueden ayudar a elaborar predicciones que guíen la generación de datos y llenar vacíos de información importantes respecto del vínculo mecanístico entre morfología y fitness poblacional. Si bien es improbable que los rasgos funcionales usados de manera aislada ofrezcan explicaciones completas o predicciones infalibles, ignorarlos nos negaría una fuente de información irremplazable para entender y predecir las respuestas de poblaciones y comunidades vegetales a las condiciones ambientales en nuestro mundo cambiante.Functional traits constitute a promising research avenue to explain and predict ecological patterns at different levels of organization (genotypes, populations, communities) because they link individual responses to environmental conditions. However, Argentine ecologists and botanists seem not to have explored this line of research as much as colleagues in other parts of the world. With this work I intend to promote the use of functional traits among local and regional readers. Amalgamating often conflicting definitions proposed by other authors, I define functional traits as morphological characteristics that affect a chain of physiological and ecological processes that I refer to as function, vital rate, and population fitness. The purpose of this definition is to emphasize the mechanistic relationship between plant structure and function. The practical benefits are straightforward: predicting the future of a plant or a group of plants from their physical properties, which are generally easier to obtain than physiological or phenological measures. Next, I use two types of graphical tools to discuss the functionality of four key traits: potential plant height, seed mass, leaf mass per area, and leaf size. These graphical tools are (i) path diagrams that show direct or indirect, positive or negative connections between traits and fitness and (ii) cartesian graphs that describe the functional relationships between traits and vital rates that, when combined, result in optimum trait–fitness relationships. Theory indicates that such optimum relationships would be the norm rather than the exception, even though functional traits are generally interpreted as “indicators” of plant functions, which exclusively implies linear relationships. These graphical tools may help us produce predictions that guide data generation and contribute to fill important information gaps regarding the mechanistic link between plant form and population fitness. Although functional traits alone are unlikely to offer complete explanations or infallible predictions, ignoring them would deny us an irreplaceable source of information to understand and predict plant population and community responses to environmental conditions in a changing world.Fil: Rolhauser, Andrés Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. University of Toronto; Canadá. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Bases conceptuales y herramientas gráficas para investigar cómo funcionan los rasgos funcionales

Los rasgos funcionales constituyen una vía de investigación promisoria para explicar y predecir patrones ecológicos en distintos niveles de organización (genotipos, poblaciones, comunidades) porque ligan a las respuestas de los individuos con las condiciones ambientales que los rodean. Sin embargo, los ecólogos y botánicos argentinos parecen no haber explorado esta línea de trabajo tanto como investigadores en otras partes del mundo. Con este trabajo pretendo fomentar el uso de rasgos funcionales entre lectores locales e hispanoparlantes. Amalgamando definiciones propuestas por otros autores (en algunos casos contradictorias), defino a los rasgos funcionales como características morfológicas que luego afectan una cadena de procesos fisiológicos y ecológicos a los que llamé función, tasa vital y éxito ecológico (o fitness) poblacional. El propósito de esta definición es enfatizar la relación mecanística entre estructura y función de las plantas. El beneficio práctico es sumamente importante: poder predecir el futuro de una planta o un grupo de plantas a partir de sus propiedades físicas, las cuales son generalmente más fáciles de conocer que medidas fisiológicas o fenológicas. Luego, utilizo dos tipos de herramientas gráficas para discutir la funcionalidad de cuatro rasgos clave: altura potencial, peso de semilla, peso foliar por área y tamaño de hoja. Estas herramientas graficas son (i) diagramas de influencias que muestran las conexiones positivas o negativas, directas o indirectas, entre rasgos y fitness y (ii) gráficos de coordenadas cartesianas que describen las relaciones funcionales entre rasgos y tasas vitales que, al combinarse, dan lugar a relaciones rasgo fitness de óptimo. La teoría indica que las relaciones de óptimo serían la norma más que la excepción, a pesar de que generalmente se interpreta a los rasgos funcionales como indicadores de las funciones de las plantas, lo que implica relaciones exclusivamente lineales. Estas herramientas gráficas nos pueden ayudar a elaborar predicciones que guíen la generación de datos y llenar vacíos de información importantes respecto del vínculo mecanístico entre morfología y fitness poblacional. Si bien es improbable que los rasgos funcionales usados de manera aislada ofrezcan explicaciones completas o predicciones infalibles, ignorarlos nos negaría una fuente de información irremplazable para entender y predecir las respuestas de poblaciones y comunidades vegetales a las condiciones ambientales en nuestro mundo cambiante.Functional traits constitute a promising research avenue to explain and predict ecological patterns at different levels of organization (genotypes, populations, communities) because they link individual responses to environmental conditions. However, Argentine ecologists and botanists seem not to have explored this line of research as much as colleagues in other parts of the world. With this work I intend to promote the use of functional traits among local and regional readers. Amalgamating often conflicting definitions proposed by other authors, I define functional traits as morphological characteristics that affect a chain of physiological and ecological processes that I refer to as function, vital rate, and population fitness. The purpose of this definition is to emphasize the mechanistic relationship between plant structure and function. The practical benefits are straightforward: predicting the future of a plant or a group of plants from their physical properties, which are generally easier to obtain than physiological or phenological measures. Next, I use two types of graphical tools to discuss the functionality of four key traits: potential plant height, seed mass, leaf mass per area, and leaf size. These graphical tools are (i) path diagrams that show direct or indirect, positive or negative connections between traits and fitness and (ii) cartesian graphs that describe the functional relationships between traits and vital rates that, when combined, result in optimum trait–fitness relationships. Theory indicates that such optimum relationships would be the norm rather than the exception, even though functional traits are generally interpreted as “indicators” of plant functions, which exclusively implies linear relationships. These graphical tools may help us produce predictions that guide data generation and contribute to fill important information gaps regarding the mechanistic link between plant form and population fitness. Although functional traits alone are unlikely to offer complete explanations or infallible predictions, ignoring them would deny us an irreplaceable source of information to understand and predict plant population and community responses to environmental conditions in a changing world.Fil: Rolhauser, Andrés Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. University of Toronto; Canadá. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Complex trait‒environment relationships underlie the structure of forest plant communities

Traits differentially adapt plant species to particular conditions generating compositional shifts along environmental gradients. As a result, community-scale trait values show concomitant shifts, termed trait‒environment relationships. Trait‒environment relationships are often assessed by evaluating community-weighted mean (CWM) traits observed along environmental gradients. Regression-based approaches (CWMr) assume that local communities exhibit traits centred at a single optimum value and that traits do not covary meaningfully. Evidence suggests that the shape of trait‒abundance relationships can vary widely along environmental gradients—reflecting complex interactions—and traits are usually interrelated. We used a model that accounts for these factors to explore trait‒environment relationships in herbaceous forest plant communities in Wisconsin (USA). We built a generalized linear mixed model (GLMM) to analyse how abundances of 185 species distributed among 189 forested sites vary in response to four functional traits (vegetative height—VH, leaf size—LS, leaf mass per area—LMA and leaf carbon content), six environmental variables describing overstorey, soil and climate conditions, and their interactions. The GLMM allowed us to assess the nature and relative strength of the resulting 24 trait‒environment relationships. We also compared results between GLMM and CWMr to explore how conclusions differ between approaches. The GLMM identified five significant trait‒environment relationships that together explain ~40% of variation in species abundances across sites. Temperature appeared as a key environmental driver, with warmer and more seasonal sites favouring taller plants. Soil texture and temperature seasonality affected LS and LMA; seasonality effects on LS and LMA were nonlinear, declining at more seasonal sites. Although often assumed for CWMr, only some traits under certain conditions had centred optimum trait‒abundance relationships. CWMr more liberally identified (13) trait‒environment relationships as significant but failed to detect the temperature seasonality‒LMA relationship identified by the GLMM. Synthesis. Although GLMM represents a more methodologically complex approach than CWMr, it identified a reduced set of trait‒environment relationships still capable of accounting for the responses of forest understorey herbs to environmental gradients. It also identified separate effects of mean and seasonal temperature on LMA that appear important in these forests, generating useful insights and supporting broader application of GLMM approach to understand trait‒environment relationships.Fil: Rolhauser, Andrés Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Waller, Donald M.. University of Wisconsin; Estados UnidosFil: Tucker, Caroline M.. University of North Carolina; Estados Unido

A trait–environment relationship approach to participatory plant breeding for organic agriculture

The extent of intraspecific variation in trait–environment relationships is an open question with limited empirical support in crops. In organic agriculture, with high environmental heterogeneity, this knowledge could guide breeding programs to optimize crop attributes. We propose a three-dimensional framework involving crop performance, crop traits, and environmental axes to uncover the multidimensionality of trait–environment relationships within a crop. We modeled instantaneous photosynthesis (Asat) and water-use efficiency (WUE) as functions of four phenotypic traits, three soil variables, five carrot (Daucus carota) varieties, and their interactions in a national participatory plant breeding program involving a suite of farms across Canada. We used these interactions to describe the resulting 12 trait–environment relationships across varieties. We found one significant trait–environment relationship for Asat (taproot tissue density–soil phosphorus), which was consistent across varieties. For WUE, we found that three relationships (petiole diameter–soil nitrogen, petiole diameter–soil phosphorus, and leaf area–soil phosphorus) varied significantly across varieties. As a result, WUE was maximized by different combinations of trait values and soil conditions depending on the variety. Our three-dimensional framework supports the identification of functional traits behind the differential responses of crop varieties to environmental variation and thus guides breeding programs to optimize crop attributes from an eco-evolutionary perspective.Fil: Rolhauser, Andrés Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. University of Toronto; CanadáFil: Windfeld, Emma. University of Toronto; Canadá. University of Calgary; CanadáFil: Hanson, Solveig. University of British Columbia; CanadáFil: Wittman, Hannah. University of British Columbia; CanadáFil: Thoreau, Chris. University of British Columbia; CanadáFil: Lyon, Alexandra. Kwantlen Polytechnic University; Canadá. University of British Columbia; CanadáFil: Isaac, Marney E.. University of Toronto; Canad

Una aproximación funcional al estudio de las invasiones de plantas anuales en el desierto

Fil: Rolhauser, Andrés Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Escuela para Graduados; Argentina.Las invasiones biológicas pueden, en algunos casos, comprometer la integridad de los sistemas naturales y agropecuarios, lo que ha despertado el interés social en ellas. Nos compete a los ecólogos entender cómo funcionan, para poder controlar las que están ocurriendo y evitar otras futuras. En las últimas décadas, el estudio de las invasiones biológicas se centró en dos preguntas generalmente abordadas por separado: ¿qué condiciones hacen a un hábitat invasible? y ¿qué características hacen a un especie exótica invasiva? A pesar de los esfuerzos, los resultados de esta aproximación han sido inconsistentes. Recientemente, se propuso que la ecología funcional puede ofrecer un marco apropiado para el estudio conjunto de la invasividad de las especies y la invasibilidad de las comunidades. La ecología funcional propone que las características morfo-fisio-fenológicas de los individuos determinan su desempeño ecológico (o "fitness") en términos de supervivencia y reproducción, en el contexto de un ambiente particular. Respecto de las invasiones, tiene sentido entonces preguntarse si las especies exóticas deben ser similares o distintas a las nativas para ser exitosas y si el beneficio de tales similitudes o diferencias cambia con el ambiente. Precisamente, utilizamos estas preguntas como eje directriz para estudiar la invasión de plantas anuales en un desierto del Monte argentino. Para contestarla, realizamos estudios observacionales de campo y experimentales en vivero. Los resultados sugieren que la similitud funcional respecto de las nativas (i) beneficiaría a las exóticas cuando el ambiente es más severo (en nuestro caso, el invierno), mientras que (ii) las perjudicaría cuando el ambiente es más benigno (en nuestro caso, el verano). Estos mecanismos habrían permitido a la invasora Tribulus terrestris (Zygophyllaceae) ser la especie anual dominante en el verano, aparentemente gracias a que se diferencia de las nativas en atributos clave para la ocupación del espacio y la tolerancia al estrés hídrico/térmicoDoctorado en Ciencias Agropecuarias144 p.: tbls., grafs., mapas, fot

Annual plant functional traits explain shrub facilitation in a desert community

Question: For a desert where winter is the driest, harshest season we asked: does the effect of dominant shrubs (Bulnesia retama) on annual species depend on (1) the functional traits of the latter, (2) the season of the year, or (3) the activity of livestock? Location: A low-density goat farm in central-northern Monte Desert, Argentina. Methods: We estimated the effect of shrubs using a log response ratio based on annual species population sizes underneath shrub canopies and in open spaces. We collected density data of annual species in 18 visits between Aug 2010 and Apr 2013 in permanent 50-cm square areas laid out according to a split-plot design, in which the activity of livestock (fenced and unfenced; plots were 10-m squares) was the main factor, and microsite type (shrub and open) was the subordinate factor, with 20 replicates for each combination. We also gathered data on eight functional traits (characterizing whole plants, leaves, roots and seeds) from annual plants collected in the study site following standardized protocols. Results: Annual species with acquisitive attributes (high specific leaf area, intermediate-to-low leaf dry matter content, large leaves and high specific root volume) were more benefited by shrubs compared to species with the opposite, relatively conservative attributes. Facilitative influences of shrubs were pervasive during winter, while competitive influences increased in frequency during summer, when total plant density was higher. This pattern was not affected by livestock. Conclusions: The outcome of species interactions depended on the interplay between plant strategies and abiotic stress: facilitated species were mostly acquisitive, and shrub facilitation was more important during the harshest season (winter). Specific root volume, along with widely used functional traits (specific leaf area, leaf dry matter content, leaf size) delineated such strategies. This underlines the importance of considering below-ground traits when studying plant-plant interactions. Single traits achieved superior explanatory power of shrub effects than composite ones (i.e. principal component axes based on single traits), reinforcing the idea that single functional traits are themselves meaningful indicators of complex physiological trade-offs that ultimately affect community structure and dynamics. Whether functional traits determine species' abundance within a given community remains unresolved. We show that ecological strategies of desert annuals determined their abundance in relation to dominant shrubs: acquisitive species were facilitated, whereas conservative ones were repelled. Specific root volume, along with widely used functional traits (specific leaf area, leaf dry matter content, and leaf size) delineated such annual-plant strategies.Fil: Rolhauser, Andrés Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Biología; ArgentinaFil: Pucheta, Eduardo Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Biología; Argentin

Experimentos factoriales

En este capítulo se presenta una clase de diseños que resultan de gran importancia práctica porque permiten evaluar en forma conjunta los efectos de varios factores sobre una respuesta. Se denomina factor a cada fuente de variación de interés para el experimentador (por ejemplo, herbicidas, especies, dietas, fertilización fosforada). Los niveles del factor son las posibles formas que toma el mismo (distintos herbicidas, diferentes especies, distintas dietas, distintas dosis de fertilización fosforada, respectivamente). En los experimentos factoriales, los tratamientos son las distintas combinaciones de los niveles de los factores en estudio.Fil: Perelman, Susana Beatriz. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Rolhauser, Andrés Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentin

Inferring trait-based mechanisms and variance consequences of abiotic secondary dispersal from the spatio-temporal distribution of a desert soil seed bank

Questions: Quantifying the combined effects of seed traits, microsite types, and abiotic dispersal agents on the mean and variance of seed bank density and composition will help understand vegetation dynamics in deserts. In a site with NE slope and mainly southerly winds, we asked whether large and oblong seeds were more likely to be transported and deposited in water obstructions and underneath the northern part of shrub understories. We also asked whether seed standing crop was less variable in water obstructions than in other microsites less affected by seed deposition. Location: A sand field in San Juan province, Argentina. Methods: We sampled the soil seed banks of four microsite types: water obstructions where debris/litter accumulates, southern and northern shrub understories, and open spaces among shrubs. Sampling was carried out in 11 plots and replicated at six moments between 2010 and 2012. Results: Debris microsites showed the highest levels of seed density, species richness and standing crop; seed density and standing crop were also least variable in these microsites. Debris microsites also contained high seed abundance of stress-intolerant, shrub-dependent species. Seed density, species richness, seed standing crop, and the proportions of both large and oblong seeds were all higher in northern than in southern understories. The relationship between seed mass and the proportion of seeds that were apparently retained (i.e., not washed away and deposited in water obstructions) was more strongly negative in southern than in northern understories. Conclusions: Northern and southern understories appeared to act as water run-on (i.e., seed recipients) and run-off zones (i.e., seed donors), respectively. Seed accumulation under the shelter provided by shrubs may promote seed predation in these microsites. Abiotic dispersal would therefore contribute to the maintenance of vegetation patches when seed arrival underneath shrub canopies saturates granivore consumption.Fil: Rolhauser, Andrés Guillermo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Pucheta, Eduardo Raúl. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; Argentin

From pattern to process: estimating expansion rates of a forest tree species in a protected palm savanna

We assessed the possible influences of dominant tree density (Butia yatay palm trees) and fire on the expansion of a riparian tree population (Myrcianthes cisplatensis) over El Palmar National Park, a protected savanna in Argentina. Our approach is based on Skellam´s model of population expansion, which predicts that populations with density-independent reproduction and random dispersal will exhibit Gaussian-shaped expansion fronts. Using Poisson regression, we fitted Gaussian curves to Myrcianthes density data collected at varying distances from a riparian forest, within four environmental conditions resulting from combinations of palm density (dense and sparse) and fire history (burned and unburned). Based on the estimated parameters, we derived statistics appropriate to compare attained expansion velocity, mean squared effective dispersal distance, and density-independent population growth among environmental conditions. We also analyzed the effects of palm density, fire history, and distance from the riparian forest on local maximum size of Myrcianthes individuals. Gaussian curves fitted the data reasonably well and slightly better than two alternative front models. Palm density and fire history interacted to control Myrcianthes spread, making unburned dense palm savannas the preferential avenue for Myrcianthes population expansion across the landscape. Limitation of Myrcianthes expansion by fire appeared to result from low survival of small individuals to fire, whereas facilitation of Myrcianthes expansion by palm trees may have resulted from increased population growth. Our results stress the interactive role of fire regime and local biotic influences in determining propagule pressure and tree establishment at the forefront, and the overall vulnerability of savannas to colonization by forest species.Fil: Rolhauser, Andrés Guillermo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Batista, William B.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentin

Directional, stabilizing, and disruptive trait selection as alternative mechanisms for plant community assembly

How plant functional traits (e.g., seed mass) drive species abundance within communities remains an unsolved question. Borrowing concepts from natural selection theory, we propose that trait-abundance relationships can generally correspond to one of three modes of trait selection: directional (a rectilinear relationship, where species at one end of a trait axis are most abundant), stabilizing (an n-shaped relationship), and disruptive (a u-shaped relationship). Stabilizing selection (i.e., the functional convergence of abundant species) would result from positive density-dependent interactions (e.g., facilitation) or due to generalized trade-offs in resource acquisition/use, while disruptive selection (i.e., the divergence of abundant species) would result from negative density-dependent interactions (e.g., competition) or due to environmental heterogeneity. These selection modes can be interpreted as proxies for community-level trait-fitness functions, which establish the degree to which traits are truly "functional". We searched for selection modes in a desert annual-plant community in Argentina (which was divided into winter and summer guilds) to test the hypothesis that the relative importance of disruptive mechanisms (competition, disturbances) decreases with the increase of abiotic stress, a stabilizing agent. Average density was analyzed as a function of eight traits generally linked to resource acquisition and competitive ability (maximum plant height, leaf size, specific leaf area, specific root length), resource retention and stress tolerance (leaf dissection, leaf dry matter content, specific root volume), and regeneration (seed mass) using multiple quadratic-regression models. Trait selection was stabilizing and/or directional when the environment was harshest (winter) and disruptive and/or directional when conditions were milder (summer). Selection patterns differed between guilds for two important traits: plant height and seed mass. These results suggest that abiotic stress may drive within-community functional convergence independently of the trait considered, opposing the view that some traits may be inherently convergent while others divergent. Our quadratic model-based approach provides standardized metrics of both linear and nonlinear selection that may allow simple comparisons among communities subjected to contrasting environmental conditions. These concepts, rooted in natural selection theory, may clarify the functional link between traits and species abundance, and thus help untangle the contributions of deterministic and stochastic processes on community assembly.Fil: Rolhauser, Andrés Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; ArgentinaFil: Pucheta, Eduardo Raúl. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Ingeniería Agrícola y Uso de la Tierra; Argentin