Browsing by Autor "M. Isabel Loza"

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Commonness and rarity determinants of woody plants in different types of tropical forests
(Springer Science+Business Media, 2014) Gabriel Arellano; M. Isabel Loza; J. Sebastián Tello; Manuel J. Macía
Constructing sympatry networks to assess potential introgression pathways within the major oak sections in the contiguous US states
(Wiley, 2024) Charles H. Cannon; John Kartesz; Sean Hoban; M. Isabel Loza; Emily Beckman Bruns; Andrew L. Hipp
Societal Impact Statement Increasing evidence indicates gene flow commonly occurs between closely related species in diverse plant genera and can involve numerous species. Here, we present a simple method to quantify and characterize the potential for gene flow among “sympatric” species (they share some part of their geographic distribution), using oaks as a case study. The resulting sympatry networks provide insight into potential interspecific gene flow, from the perspective of each species and across the entire suite of interfertile species. In a rapidly changing world, interspecific gene flow will play an increasingly important role in the conservation of endangered species, both positive and negative. Summary We provide a simple method, using geographic distribution data, to quantify and characterize sympatry networks among a suite of interfertile species to assess potential routes for introgressive hybridization (IH). Sympatry is a necessary condition for IH and is easily determined from widely available geographic distribution data. Oaks, famous for hybridization, present an excellent case study. We use county‐level data for 94 oak species in the contiguous US states to determine patterns of sympatry of species within the four sections, assumed to be interfertile. The pairwise sympatry relationships can generate species‐centric local networks or a syngameon‐wide network. Two different measures of sympatry are used: proportional and relative. Most oak species are exposed to IH from many species, with red oaks having slightly higher local levels of sympatry (5.7 vs. 3.8 spp per county) than white oaks but lower total numbers of sympatric species (13.7 vs. 14.8). The nature of potential IH generally differs for threatened species, which are often embedded in the much larger distributions of widespread species. Potential IH within oak sections is widespread and disproportionately affects rare species. Given that IH has potentially positive or negative impacts on species cohesion, persistence, and adaptation, the geographic connections among species and the ‘local sympatry effect’ can serve as a springboard for hypothesis generation and genetic investigation of introgression patterns.
Disentangling environmental and spatial processes of community assembly in tropical forests from local to regional scales
(Wiley, 2015) Gabriel Arellano; J. Sebastián Tello; Peter M. Jørgensen; A C.; M. Isabel Loza; Vania Torrez; Manuel J. Macía
Understanding patterns and mechanisms of variation in the compositional structure of communities across spatial scales is one of the fundamental challenges in ecology and biogeography. In this study, we evaluated the effects of spatial extent (i.e. size of study region) on: 1) whether community composition can be better explained by environmental (i.e. niche‐based) or spatial (e.g. dispersal‐based) processes ; and 2) how climate and soils contribute to the influence of environment on plant community composition. We surveyed community composition across a network of 398 forest plots spanning a ∼4000 m elevational gradient in the Madidi region in northwestern Bolivia. Using redundancy analyses and hierarchical variation partitioning, we disentangled the effects of environmental and spatial predictors on species composition, further decomposing the environmental effect between its climatic and soil components. We repeated analyses for 200 sub‐regions ranging in spatial extent from ∼250 to ∼17 500 km 2 . Our analyses show a high degree of idiosyncrasy in results that come from different sub‐regions. Despite this variability, we were able to identify various important patterns in the structure of tropical plant communities in our study system. First, even though sub‐regions varied in size by nearly two orders of magnitude, the total amount of explained variation in community composition was scale independent; at all spatial scales, environment and space accounted for about 25% of the differences in community composition among plots. Second, the measured environmental effect was higher than the spatial effect on average and in the vast majority of sub‐regions. This was true regardless of the spatial extent of analysis. Finally, we found that both climatic and soil variables accounted for significant fractions of variation, but climate was always more important than soils.
Elevational Gradients in β-Diversity Reflect Variation in the Strength of Local Community Assembly Mechanisms across Spatial Scales
(Public Library of Science, 2015) J. Sebastián Tello; Jonathan A. Myers; Manuel J. Macía; A C.; Leslie Cayola; Gabriel Arellano; M. Isabel Loza; Vania Torrez; Maritza Cornejo; Tatiana B. Miranda
Despite long-standing interest in elevational-diversity gradients, little is known about the processes that cause changes in the compositional variation of communities (β-diversity) across elevations. Recent studies have suggested that β-diversity gradients are driven by variation in species pools, rather than by variation in the strength of local community assembly mechanisms such as dispersal limitation, environmental filtering, or local biotic interactions. However, tests of this hypothesis have been limited to very small spatial scales that limit inferences about how the relative importance of assembly mechanisms may change across spatial scales. Here, we test the hypothesis that scale-dependent community assembly mechanisms shape biogeographic β-diversity gradients using one of the most well-characterized elevational gradients of tropical plant diversity. Using an extensive dataset on woody plant distributions along a 4,000-m elevational gradient in the Bolivian Andes, we compared observed patterns of β-diversity to null-model expectations. β-deviations (standardized differences from null values) were used to measure the relative effects of local community assembly mechanisms after removing sampling effects caused by variation in species pools. To test for scale-dependency, we compared elevational gradients at two contrasting spatial scales that differed in the size of local assemblages and regions by at least an order of magnitude. Elevational gradients in β-diversity persisted after accounting for regional variation in species pools. Moreover, the elevational gradient in β-deviations changed with spatial scale. At small scales, local assembly mechanisms were detectable, but variation in species pools accounted for most of the elevational gradient in β-diversity. At large spatial scales, in contrast, local assembly mechanisms were a dominant force driving changes in β-diversity. In contrast to the hypothesis that variation in species pools alone drives β-diversity gradients, we show that local community assembly mechanisms contribute strongly to systematic changes in β-diversity across elevations. We conclude that scale-dependent variation in community assembly mechanisms underlies these iconic gradients in global biodiversity.
Elevational range sizes of woody plants increase with climate variability in the Tropical Andes
(Wiley, 2023) Flavia Montaño‐Centellas; A C.; Leslie Cayola; Manuel J. Macía; Gabriel Arellano; M. Isabel Loza; Beatriz Nieto‐Ariza; J. Sebastián Tello
Abstract Aim The climate variability hypothesis proposes that species subjected to wide variation in climatic conditions will evolve wider niches, resulting in larger distributions. We test this hypothesis in tropical plants across a broad elevational gradient; specifically, we use a species‐level approach to evaluate whether elevational range sizes are explained by the levels of thermal variability experienced by species. Location Central Andes. Time Period Present day. Taxon Woody plants. Methods Combining data from 479 forest plots, we determined the elevational distributions of nearly 2300 species along an elevational gradient (~209–3800 m). For each species, we calculated the maximum annual variation in temperature experienced across its elevational distribution. We used phylogenetic generalized least square models to evaluate the effect of thermal variability on range size. Our models included additional covariates that might affect range size: body size, local abundance, mean temperature and total precipitation. We also considered interactions between thermal variability and mean temperature or precipitation. To account for geometric constraints, we repeated our analyses with a standardized measure of range size, calculated by comparing observed range sizes with values obtained from a null model. Results Our results supported the main prediction of the climate variability hypothesis. Thermal variability had a strong positive effect on the range size, with species exposed to higher thermal variability having broader elevational distributions. Body size and local abundance also had positive, yet weak effects, on elevational range size. Furthermore, there was a strong positive interaction between thermal variability and mean annual temperature. Main Conclusions Thermal variability had an overriding importance in driving elevational range sizes of woody plants in the Central Andes. Moreover, the relationship between thermal variability and range size might be even stronger in warmer regions, underlining the potential vulnerability of tropical montane floras to the effects of global warming.
Elevational Range Sizes of Woody plants Increase with Climate Variability in the Tropical Andes
(2023) Flavia Montaño‐Centellas; Alfredo F. Fuentes; Leslie Cayola; Manuel J. Macía; Gabriel Arellano; M. Isabel Loza; Beatriz Nieto‐Ariza; J. Sebastián Tello
Abstract Aim The climate variability hypothesis proposes that species subjected to wide variation in climatic conditions will evolve wider niches, resulting in larger distributions. We test this hypothesis in tropical plants across a broad elevational gradient; specifically, we use a species-level approach to evaluate whether elevational range sizes are explained by the levels of thermal variability experienced by species. Location Central Andes Time period Present day Major taxa studied Woody plants Methods Combining data from 479 forest plots, we determined the elevational distributions of nearly 2300 species along an elevational gradient (∼209 – 3800 m). For each species, we calculated the maximum annual variation in temperature experienced across its elevational distribution. We used phylogenetic generalized least square models to evaluate the effect of thermal variability on range size. Our models included additional covariates that might affect range size: body size, local abundance, mean temperature and total precipitation. We also considered interactions between thermal variability and mean temperature or precipitation. To account for geometric constraints, we repeated our analyses with a standardized measure of range size, calculated by comparing observed range sizes with values obtained from a null model. Results Our results supported the main prediction of the climate variability hypothesis. Thermal variability had a strong positive effect on the range size, with species exposed to higher thermal variability having broader elevational distributions. Body size and local abundance also had positive, yet weak effects, on elevational range size. Furthermore, there was a strong positive interaction between thermal variability and mean annual temperature. Main conclusions Thermal variability had an overriding importance in driving elevational range sizes of woody plants in the Central Andes. Moreover, the relationship between thermal variability and range size might be even stronger in warmer regions, underlining the potential vulnerability of tropical montane floras to the effects of global warming.
Functional traits mediate the effect of environmental conditions on tree growth of common Andean trees
(Elsevier BV, 2025) Eduardo Aguirre-Mazzi; Carla Maldonado; Leslie Cayola; Alfredo F. Fuentes; M. Isabel Loza; Christine E. Edwards; J. Sebastián Tello
Understanding how plant functional strategies interact with environmental variation is essential to predict the impacts of global change on forest communities. Here we investigated how resource-acquisition strategies, captured by branch and leaf traits, interact with environmental gradients, including climate, soil fertility, and solar radiation exposure, to influence relative growth rates (RGR) in 224 tree species from tropical montane forests in the Madidi region of the Bolivian Andes. Using data from 33 permanent forest plots and Bayesian hierarchical models, we found that the effects of environmental conditions on tree growth were modulated by species’ resource-acquisition strategies. Our findings reveal that acquisitive species, with higher specific leaf area (SLA), larger leaf size, and lower tissue density, performed better in cooler, drier, thermally variable, nutrient-rich sites with low solar radiation. In contrast, conservative species, characterized by stress-tolerant traits (higher tissue density and smaller leaves), grew better in nutrient-poor, high-radiation environments and tended to be less responsive to climatic gradients. Our analysis relied on two major PCA axes of functional trait covariation that captured distinct mechanistic pathways but aligned with survival-growth trade-off. Our results suggest that whole-plant allocation strategies, reflected by a leaf-area vs wood density trade-off may be more important than leaf-level traits (e.g., SLA) under closed canopies, highlighting the multidimensionality of trait-growth relationships. Our results underscore the role of trait–environment matching in shaping species performance and community assembly, and highlight the importance of trait-based approaches for forecasting forest responses to climate and land-use change. • Plant traits and environmental gradients interact to drive tree growth in the Andes. • Acquisitive species are more sensitive to climatic gradients than conservative ones. • Soil fertility favors acquisitive species whereas conservatives tolerate poor soils. • High solar exposure favors conservative species growth, limits acquisitive species. • Leaf area and wood density better predict growth compared to SLA in adult trees.
Insights on biodiversity drivers to predict species richness in tropical forests at the local scale
(Elsevier BV, 2022) Rubén G. Mateo; Gabriel Arellano; Virgilio Gómez‐Rubio; J. Sebastián Tello; Alfredo F. Fuentes; Leslie Cayola; M. Isabel Loza; Victoria Cala Rivero; Manuel J. Macía
Disentangling the relative importance of different biodiversity drivers (i.e., climate, edaphic, historical factors, or human impact) to predict plant species richness at the local scale is one of the most important challenges in ecology. Biodiversity modelling is a key tool for the integration of these drivers and the predictions generated are essential, for example, for climate change forecast and conservation planning. However, the reliability of biodiversity models at the local scale remains poorly understood, especially in tropical species-rich areas, where they are required. We inventoried all woody plants with stems ≥ 2.5 cm in 397 plots across the Andes-Amazon gradient. We generated and mapped 19 uncorrelated biodiversity drivers at 90 m resolution, grouped into four categories: microclimatic, microtopographic, anthropic, and edaphic. In order to evaluate the importance of the different categories, we grouped biodiversity drivers into four different clusters by categories. For each of the four clusters of biodiversity drivers, we modelled the observed species richness using two statistical techniques (random forest and Bayesian inference) and two modelling procedures (including or excluding a spatial component). All the biodiversity models produced were evaluated by cross-validation. Species richness was accurately predicted by random forest (Spearman correlation up to 0.85 and explained variance up to 67%). The results suggest that precipitation and temperature are important driving forces of species richness in the region. Nonetheless, a spatial component should be considered to properly predict biodiversity. This could reflect macroevolutionary underlying forces not considered here, such as colonization time, dispersal capacities, or speciation rates. However, the proposed biodiversity modelling approach can predict accurately species richness at the local scale and detailed resolution (90 m) in tropical areas, something that previous works had found extremely challenging. The innovative methodology presented here could be employed in other areas with conservation needs.
Oligarchic patterns in tropical forests: role of the spatial extent, environmental heterogeneity and diversity
(Wiley, 2015) Gabriel Arellano; Peter M. Jørgensen; A C.; M. Isabel Loza; Vania Torrez; Manuel J. Macía
Abstract Aim Oligarchic patterns can vary from weak (i.e. little difference between rare and common species) to strong (i.e. a set of dominant species is immediately evident). Our aim was to understand the relationships between the strength of the oligarchic patterns, diversities (alpha, beta and gamma), and five potential causes (elevational variability, soil heterogeneity, elevation, soil conditions and geographical extent). Location The Amazon–Andes transition in the Madidi region (Bolivia). Methods We established 398 plots of 0.1 ha each, containing 121,183 individual woody plants belonging to 2390 species. Then we defined 500 sub‐regions (= unique overlapping subsets of 50 plots from the pool of 398 plots) so they varied in extent from 220 to 17,700 km 2 within the study area. We employed two independent path analyses to relate environmental characteristics and geographical extent of sub‐regions to (1) oligarchic strength and (2) alpha, beta and gamma diversities. We used generalized linear models to relate diversities to different measures of oligarchic strength. Results Oligarchies at larger extents were weaker, a trend strongly driven by the pure effect of area and, secondarily, by environmental heterogeneity. Oligarchies at higher elevations were weaker than expected, and oligarchies in acidic and nutrients‐poor soils were not stronger than those in less stressful soils. Trends in oligarchic strength were inversely correlated with those of gamma and beta diversity: weaker oligarchies were found in species‐rich and heterogeneous communities. Main conclusions Environmental heterogeneity and low landscape connectivity limit the strength of the oligarchic pattern. Although diversities (particularly beta diversity) and oligarchic strength are closely related, they are somewhat differently driven by external factors. In particular, oligarchic strength is more sensitive to spatial extent and less sensitive to environmental heterogeneity than beta diversity. Finally, the study of oligarchic patterns should consider a priori expectations based on species richness and turnover.
Phylogenetic patterns of rarity in a regional species pool of tropical woody plants
(Wiley, 2017) M. Isabel Loza; Iván Jiménez; Peter M. Jørgensen; Gabriel Arellano; Manuel J. Macía; Vania Torrez; Robert E. Ricklefs
Abstract Aim Rarity, which is believed to influence extinction risk, can be defined in terms of local abundance, geographical range size and habitat breadth. Phylogenetic patterns in these attributes provide insight into the extent to which rarity and extinction risk are conserved during evolution and the potential for species‐level heritability. We evaluated phylogenetic signal (i.e., related species resembling each other more than species drawn at random) and evolutionary conservatism (similarity among related species exceeding that expected from a Brownian model of evolution) in three axes of rarity (local abundance, geographical range size and habitat breadth) among species in a regional pool of tropical woody plants. Location The Madidi region in Bolivia. Time period 2001–2010. Major taxa studied Lignophyta clade. Methods We used a network of 48 1‐ha forest plots and 442 0.1‐ha forest plots to measure local abundance and habitat breadth of 1,700+ woody plant species (from 100+ plant families). We estimated geographical range size from occurrence records of individual species across the Neotropics. We characterized overall phylogenetic patterns of rarity using Blomberg's K and applied variance partitioning among taxonomic levels, as well as disparity analysis, to describe patterns of trait distribution at different depths in the phylogeny. Results We found phylogenetic signal, but not evolutionary conservatism, in the three axes of rarity. The variance in rarity among supra‐specific taxa, particularly families and genera, exceeded that calculated from random draws of species from the Madidi region. Phylogenetic signal, estimated by the proportion of variance among supra‐specific taxonomic levels, varied between 23 and 36% for local abundance and geographical range size, and between 9 and 10% for habitat breadth. Main conclusions The regional pool of woody plant species in Madidi exhibits phylogenetic signal in rarity that is consistent with biologically significant species‐level heritability.
Relative effects of edaphic conditions and climate on palm communities in the Central Andes
(2021) Fabiola Montoya; Moraes R. Mónica; A C.; Leslie Cayola; Ana Antezana; Tatiana Lopes de Miranda; Esther Mosqueira-Meneses; M. Isabel Loza; J. Sebastián Tello
ABSTRACT Palms (family Arecaceae) are conspicuous and structural elements in forests ecosystems of tropical regions and mountain forests in South America. Additionally, many species of palms are culturally and economically important to human populations. Because of their ecological and ethnobotanical significance, understanding the drivers of palm distribution and diversity is critical. However, most past research has focused in tropical lowland palm communities, while our understanding of montane tropical palm ecology and biogeography is comparatively lacking. We investigate the environmental factors that influence patterns of richness, composition, and abundance of palms in the Central Andes. In particular, we are interested in the relative effects that soil edaphic conditions and climate have on palm community structure. For these analyses, we used a network of 88 forest plots distributed along a broad elevational gradient (1,000 – 3,200 meters), which are part of the Madidi Project in north-western Bolivia. We carried out palm community-level analysis, as well as species-specific analyses for each of the 16 most common species. We found that soils and climate contribute differentially to shaping Andean palm diversity and distributions. We found that soils explain more variation in species composition (14.4%) than climate (3.45%), but that climate explains more variation in species richness (13%) than soils (6.1%). Moreover, species-specific analyses reveal that there is great variation in how different common species respond to their abiotic environment. Our results contribute to understanding the drivers of biodiversity for a highly important group of plants in one of the most important hotspots for biodiversity. RESUMEN En el neotrópico, las palmeras (Arecaceae) son un grupo diverso y abundante de plantas que constituyen elementos estructurales en bosques tropicales tanto de tierras bajas como de montaña. Además, muchas especies de palmeras son culturalmente y economicamente importantes para muchas poblaciones humanas. Debido a su importancia ecológica y etnobotánica, entender los mecanismos que controlan la diversidad y la distribución de las palmeras es extremadamente importante. Sin embargo, la mayoría de la investigación hasta el momento se ha enfocado en comunidades de palmeras de tierras bajas, mientras que la ecología y biogeografía de las palmeras de montañas es relativamente poco entendida. En este estudio, nosotros investigamos los factores ambientales que influencian la riqueza, composición y abundancia de palmeras en los Andes Centrales. En particular, estamos interesados en entender los efectos relativos de las condiciones edáficas del suelo y el clima en la estructura de comunidades de palmeras. Para nuestros análisis, usamos una red de 88 parcelas de árboles distribuidas a lo largo de un gradiente elevacional (1,000 – 3,200 metros), la misma que es parte del Proyecto Madidi en Bolivia. Encontramos que el suelo y el clima tienen efectos diferentes. El suelo explica más variación en la composición de especies (14.4%) que el clima (3.45%), pero el clima explica más variación en la riqueza de especies (13%) que los suelos (6.1%). Además, análisis independientes para las 16 especies más comunes demuestran gran variación en como cada especie responde a las condiciones ambientales. Nuestros resultados contribuyen a entender los factores que controlan la diversidad de un grupo importante de plantas en una de las regiones más diversas del planeta.
The role of niche overlap, environmental heterogeneity, landscape roughness and productivity in shaping species abundance distributions along the Amazon–Andes gradient
(Wiley, 2016) Gabriel Arellano; María N. Umaña; Manuel J. Macía; M. Isabel Loza; A C.; Victoria Cala Rivero; Peter M. Jørgensen
Abstract Aim Statistical and ecological mechanisms shape species abundance distributions (SADs). A lack of correlation between ecological gradients and SAD shape would suggest that SADs are caused by purely statistical reasons. We evaluated the variation in the shape of SADs for communities in landscapes of differing variable connectivity, environmental heterogeneity, species niches overlap and productivity. Location Rainforests in the Madidi region (Bolivia). Methods We compiled biological and environmental information on 65 sites (a site being a group of two to six 0.1‐ha plots where woody plants of a diameter at breast height ≥ 2.5 cm were inventoried). We built unveiled (complete) SADs for each site and fitted Gambin models to those SADs. The Gambin α parameter served as a metric of SAD shape. Low α values characterize logseries‐like SADs, while high α values characterize lognormal‐like SADs. For each site, we estimated landscape roughness, environmental heterogeneity, species niche overlap and productivity. These variables were related to SAD shape by means of variation partitioning. Results SADs changed from logseries‐like to lognormal‐like along the elevational gradient. Many of our predictor variables were correlated: 40.4% of the variation in SAD shape could not be attributed to specific factors. However, 50.62% of the variation in the SAD shape could be assigned to individual predictor matrices: 28.4% was explained exclusively by niche overlap, 15.41% exclusively by environmental heterogeneity, 5.20% exclusively by landscape roughness and 1.6% exclusively by productivity. Main conclusions Ecological processes related to the topographical/environmental complexities that vary across the elevational gradient are correlated with the SAD shape. Purely statistical mechanisms are apparently not sufficient to explain the changes in SAD shape. The most important factor is the mean overlap of the niches of the species of an assemblage: avoiding competition with co‐occurring species could be the most important mechanism driving species relative success at the ≤100 km 2 scale.