scholarly journals Chronic Disturbance in a Tropical Dry Forest: Disentangling Direct and Indirect Pathways Behind the Loss of Plant Richness

2021 ◽  
Vol 4 ◽  
Author(s):  
Andrea Jara-Guerrero ◽  
Diego González-Sánchez ◽  
Adrián Escudero ◽  
Carlos I. Espinosa
Keyword(s):  
Species Richness ◽  
Structural Equation ◽  
Structural Equation Models ◽  
Woody Species ◽  
Biodiversity Loss ◽  
Dry Forest ◽  
Seasonally Dry ◽  
Causal Pathways ◽  
Large Trees ◽  
Chronic Disturbance

Chronic disturbance is widely recognized as one of main triggers of diversity loss in seasonally dry tropical forests (SDTFs). However, the pathways through which diffuse disturbance is acting on the forest are little understood. This information is especially demanded in the case of vanishing Neotropical seasonally dry forests such as the Tumbesian ones. We proposed a conceptual model to analyze the factors behind the loss of woody species richness along a forest disturbance gradient, explicitly considering the existence of direct and indirect causal pathways of biodiversity loss. We hypothesized that the chronic disturbance can act on the woody species richness directly, either by selective extraction of resources or by browsing of palatable species for livestock, or indirectly, by modifying characteristics of the forest structure and productivity. To test our model, we sampled forest remnants in a very extensive area submitted to long standing chronic pressure. Our forests cells (200 × 200 m) were characterized both in terms of woody species composition, structure, and human pressure. Our structural equation models (SEMs) showed that chronic disturbance is driving a loss of species richness. This was done mainly by indirect effects through the reduction of large trees density. We assume that changes in tree density modify the environmental conditions, thus increasing the stress and finally filtering some specific species. The analysis of both, direct and indirect, allows us to gain a better understanding of the processes behind plant species loss in this SDTF.

scholarly journals Aboveground impacts of a belowground invader: how invasive earthworms alter aboveground arthropod communities in a northern North American forest

2021 ◽  
Author(s):  
Malte Jochum ◽  
Lise Thouvenot ◽  
Olga Ferlian ◽  
Romy Zeiss ◽  
Bernhard Klarner ◽  
...  
Keyword(s):  
Species Richness ◽  
Structural Equation ◽  
Structural Equation Models ◽  
Trophic Levels ◽  
Arthropod Community ◽  
Arthropod Communities ◽  
Earthworm Invasion ◽  
Invasive Earthworms ◽  
Invasion Impacts ◽  
Arthropod Abundance

AbstractDeclining arthropod communities have recently gained a lot of attention with climate and land-use change among the most-frequently discussed drivers. Here, we focus on a seemingly underrepresented driver of arthropod-community decline: biological invasions. For ∼12,000 years, earthworms have been absent from wide parts of northern North America, but they have been re-introduced with dramatic consequences. Most studies investigating earthworm-invasion impacts focus on the belowground world, resulting in limited knowledge on aboveground-community changes. We present observational data on earthworm, plant, and aboveground-arthropod communities in 60 plots, distributed across areas with increasing invasion status (low, medium, high) in a Canadian forest. We analyzed how earthworm-invasion status and biomass impact aboveground arthropod community abundance, biomass, and species richness, and how earthworm impacts cascade across trophic levels. We sampled ∼13,000 arthropods, dominated by Hemiptera, Diptera, Araneae, Thysanoptera, and Hymenoptera. Total arthropod abundance, biomass, and species richness declined significantly from areas of low to those with high invasion status with reductions of 61, 27, and 18%, respectively. Structural Equation Models unraveled that earthworms directly and indirectly impact arthropods across trophic levels. We show that earthworm invasion can alter aboveground multitrophic arthropod communities and suggest that belowground invasions can be important drivers of aboveground-arthropod decline.

scholarly journals Threatened Neotropical seasonally dry tropical forest: evidence of biodiversity loss in sap-sucking herbivores over 75 years

2021 ◽  
Vol 8 (3) ◽  
Author(s):  
J. A. Pinedo-Escatel ◽  
G. Moya-Raygoza ◽  
C. H. Dietrich ◽  
J. N. Zahniser ◽  
L. Portillo
Keyword(s):  
Tropical Forest ◽  
Tropical Forests ◽  
Biodiversity Loss ◽  
Distribution Patterns ◽  
Dry Forest ◽  
Data Matrix ◽  
Dry Tropical Forest ◽  
Seasonally Dry ◽  
Strong Trend ◽  
Arthropod Species

Tropical forests cover 7% of the earth's surface and hold 50% of known terrestrial arthropod species. Alarming insect declines resulting from human activities have recently been documented in temperate and tropical ecosystems worldwide, but reliable data from tropical forests remain sparse. The sap-sucking tribe Athysanini is one herbivore group sensitive to anthropogenic perturbation and the largest within the diverse insect family Cicadellidae distributed in America's tropical forests. To measure the possible effects of deforestation and related activities on leafhopper biodiversity, a survey of 143 historic collecting localities was conducted to determine whether species documented in the Mexican dry tropical forests during the 1920s to 1940s were still present. Biostatistical diversity analysis was performed to compare historical to recent data on species occurrences. A data matrix of 577 geographical records was analysed. In total, 374 Athysanini data records were included representing 115 species of 41 genera. Historically, species richness and diversity were higher than found in the recent survey, despite greater collecting effort in the latter. A strong trend in species decline was observed (−53%) over 75 years in this endangered seasonally dry ecosystem. Species completeness was dissimilar between historic and present data. Endemic taxa were significantly less important and represented in the 1920s–1940s species records. All localities surveyed in the dry tropical forest are disturbed and reduced by modern anthropogenic processes. Mexico harbours highly endemic leafhopper taxa with a large proportion of these inhabiting the dry forest. These findings provide important data for conservation decision making and modelling of distribution patterns of this threatened seasonally dry tropical ecosystem.

scholarly journals Consistent drivers of plant biodiversity across managed ecosystems

2016 ◽  
Vol 371 (1694) ◽  
pp. 20150284 ◽  
Author(s):  
Vanessa Minden ◽  
Christoph Scherber ◽  
Miguel A. Cebrián Piqueras ◽  
Juliane Trinogga ◽  
Anastasia Trenkamp ◽  
...  
Keyword(s):  
Species Richness ◽  
Plant Species ◽  
Real World ◽  
Structural Equation ◽  
Structural Equation Models ◽  
Biomass Productivity ◽  
Plant Species Richness ◽  
Ecosystem Functions ◽  
Total Biomass ◽  
Managed Ecosystems

Ecosystems managed for production of biomass are often characterized by low biodiversity because management aims to optimize single ecosystem functions (i.e. yield) involving deliberate selection of species or cultivars. In consequence, considerable differences in observed plant species richness and productivity remain across systems, and the drivers of these differences have remained poorly resolved so far. In addition, it has remained unclear if species richness feeds back on ecosystem functions such as yield in real-world systems. Here, we establish N = 360 experimental plots across a broad range of managed ecosystems in several European countries, and use structural equation models to unravel potential drivers of plant species richness. We hypothesize that the relationships between productivity, total biomass and observed species richness are affected by management intensity, and that these effects differ between habitat types (dry grasslands, grasslands, and wetlands). We found that local management was an important driver of species richness across systems. Management caused system disturbance, resulting in reduced productivity yet enhanced total biomass. Plant species richness was directly and positively driven by management, with consistently negative effects of total biomass. Productivity effects on richness were positive, negative or neutral. Our study shows that management and total biomass drive plant species richness across real-world managed systems.

scholarly journals Hydraulic diversity stabilizes productivity in a large-scale subtropical tree biodiversity experiment

2021 ◽  
Author(s):  
Florian Schnabel ◽  
Xiaojuan Liu ◽  
Matthias Kunz ◽  
Kathryn E. Barry ◽  
Franca J. Bongers ◽  
...  
Keyword(s):  
Climate Change ◽  
Species Richness ◽  
Tree Species ◽  
Structural Equation ◽  
Large Scale ◽  
Structural Equation Models ◽  
Forest Productivity ◽  
Climate Mitigation ◽  
Climate Change Effects ◽  
Tree Species Richness

AbstractExtreme climatic events threaten forests and their climate mitigation potential globally. Understanding the drivers promoting ecosystems stability is therefore considered crucial to mitigate adverse climate change effects on forests. Here, we use structural equation models to explain how tree species richness, asynchronous species dynamics and diversity in hydraulic traits affect the stability of forest productivity along an experimentally manipulated biodiversity gradient ranging from 1 to 24 tree species. Tree species richness improved stability by increasing species asynchrony. That is at higher species richness, inter-annual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was mediated by the diversity of species’ hydraulic traits in relation to drought tolerance and stomatal control, but not the community-weighted means of these traits. Our results demonstrate important mechanisms by which tree species richness stabilizes forest productivity, thus emphasizing the importance of hydraulically diverse, mixed-species forests to adapt to climate change.

scholarly journals BIOLOGICAL DIVERSITY IN COLOMBIAN CARIBBEAN DRY FOREST REMNANTS IN ATLÁNTICO: LICHEN COMMUNITIES IN THE DISTRITO REGIONAL DE MANEJO INTEGRADO LURIZA AND THE RESERVA FORESTAL PROTECTORA EL PALOMAR

Caldasia ◽  
2019 ◽  
Vol 41 (1) ◽  
pp. 194-214 ◽  
Author(s):  
Robert Lücking ◽  
Bibiana Moncada ◽  
María Cristina Martínez-Habibe ◽  
Beatriz E. Salgado-Negret ◽  
Marcela Celis ◽  
...  
Keyword(s):  
Species Richness ◽  
Woody Plants ◽  
Biological Diversity ◽  
New Records ◽  
Dry Forest ◽  
Central American ◽  
Seasonally Dry ◽  
Forest Remnants ◽  
High Level ◽  
First Time

We present a first study of the diversity and community composition of lichens in seasonally dry tropical forest (DTF) remnants in the Atlántico department, Colombia. Lichens were sampled in two of the three protected areas of the department: Distrito de Manejo Integrado (DMI) Luriza and Reserva Forestal Protectora (RFP) El Palomar. The inventory revealed 61 species, including four new to science: Fissurina linoana Lücking, Moncada & G. Rodr. sp. nov., Graphis lurizana Lücking, Moncada & Celis sp. nov., G. mokanarum Lücking, Moncada & M.C. Martínez sp. nov., and Phaeographis galeanoae Lücking, Moncada & B. Salgado-N. sp. nov. Arthonia erupta and Coenogonium saepincola are new to South America, whereas thirteen species are recorded for Colombia for the first time. Further 37 species are new records for Atlántico, raising the total of species known from the department from 27 to 84. With 42 species at Luriza and 31 at El Palomar, species richness was comparable to that of other DTF sites in the Neotropics. Overlap in species composition between the two sites was remarkably low, with only twelve shared species (20 %), indicating a high level of heterogeneity. Biogeographical affinities lie with Central American DTF, which is in line with those of woody plants. These results underline the importance of the remaining fragments of DTF in Colombia in conserving partially unknown biodiversity and the necessity for their continuing conservation.

scholarly journals The Use of Mixed Models for the Analysis of Mediated Data with Time-Dependent Predictors

2011 ◽  
Vol 2011 ◽  
pp. 1-12 ◽  
Author(s):  
Emily A. Blood ◽  
Debbie M. Cheng
Keyword(s):  
Longitudinal Data ◽  
Mixed Models ◽  
Structural Equation ◽  
Structural Equation Models ◽  
Type I Error ◽  
Time Dependent ◽  
Type I ◽  
Delayed Effects ◽  
Causal Pathways ◽  
Observational Cohort

Linear mixed models (LMMs) are frequently used to analyze longitudinal data. Although these models can be used to evaluate mediation, they do not directly model causal pathways. Structural equation models (SEMs) are an alternative technique that allows explicit modeling of mediation. The goal of this paper is to evaluate the performance of LMMs relative to SEMs in the analysis of mediated longitudinal data with time-dependent predictors and mediators. We simulated mediated longitudinal data from an SEM and specified delayed effects of the predictor. A variety of model specifications were assessed, and the LMMs and SEMs were evaluated with respect to bias, coverage probability, power, and Type I error. Models evaluated in the simulation were also applied to data from an observational cohort of HIV-infected individuals. We found that when carefully constructed, the LMM adequately models mediated exposure effects that change over time in the presence of mediation, even when the data arise from an SEM.

scholarly journals Determinants of genetic diversity and species richness of North American amphibians

2021 ◽  
Author(s):  
Chloé Schmidt ◽  
Jason Munshi-South ◽  
Colin J Garroway
Keyword(s):  
Genetic Diversity ◽  
Species Richness ◽  
Structural Equation ◽  
Structural Equation Models ◽  
The United States ◽  
Energy Availability ◽  
Temperature Dependent ◽  
Frog Species ◽  
Species Groups ◽  
Underlying Mechanisms

AbstractWe know little about the general links between broad-scale biodiversity patterns at the nuclear genetic and species levels. Recent work in mammals suggests environmental carrying capacity and ecological opportunity link these two base levels of biodiversity. Energy- and resource-rich environments are thought to support larger populations with higher genetic diversity and species richness. Niche availability is expected to limit population size causing drift while increasing genetic differentiation due to environmental specialization. Several of the processes underlying these links are temperature-dependent, so we might expect different patterns for endotherms and ectotherms. We use a database comprised of raw microsatellite genotypes for 13616 individuals of 18 species sampled at 548 locations in the United States and Canada. We analyzed salamander and frog species separately and simultaneously fit our hypotheses with structural equation models. Similar to mammals, niche availability was the primary contributor to diversity at both the genetic and species levels in frogs, and energy availability was an important predictor of species richness for both taxa. Different than mammals, environmental energy availability was not linked to genetic diversity. There are shared underlying mechanisms linking genetic and species-level diversity but the processes are not entirely general across these species groups.

scholarly journals Endemics and Cosmopolitans: Application of Statistical Mechanics to the Dry Forests of Mexico

Entropy ◽  
2019 ◽  
Vol 21 (6) ◽  
pp. 616
Author(s):  
Michael G. Bowler ◽  
Colleen K. Kelly
Keyword(s):  
Species Richness ◽  
Statistical Mechanics ◽  
Alien Species ◽  
Tropical Forests ◽  
Dry Forest ◽  
Single Site ◽  
Seasonally Dry ◽  
Forest Sites ◽  
Seasonally Dry Tropical Forests ◽  
Dry Tropical Forests

Data on the seasonally dry tropical forests of Mexico have been examined in the light of statistical mechanics. The results suggest a division into two classes of species. There are drifting populations of a cosmopolitan class capable of existing in most dry forest sites; these have a statistical distribution previously only observed (globally) for populations of alien species. We infer that a high proportion of species found only at a single site are specialists, endemics, and that these prefer sites comparatively low in species richness.

scholarly journals Fitness consequences of centrality in mutualistic individual-based networks

2011 ◽  
Vol 279 (1734) ◽  
pp. 1754-1760 ◽  
Author(s):  
José M. Gómez ◽  
Francisco Perfectti
Keyword(s):  
Species Richness ◽  
Social Interactions ◽  
Structural Equation Modelling ◽  
Structural Equation ◽  
Structural Equation Models ◽  
Complex Relationship ◽  
Flower Visitors ◽  
Equation Modelling ◽  
Fitness Consequences ◽  
Network Metrics

The relationships among the members of a population can be visualized using individual networks, where each individual is a node connected to each other by means of links describing the interactions. The centrality of a given node captures its importance within the network. We hypothesize that in mutualistic networks, the centrality of a node should benefit its fitness. We test this idea studying eight individual-based networks originated from the interaction between Erysimum mediohispanicum and its flower visitors. In these networks, each plant was considered a node and was connected to conspecifics sharing flower visitors. Centrality indicates how well connected is a given E. mediohispanicum individual with the rest of the co-occurring conspecifics because of sharing flower visitors. The centrality was estimated by three network metrics: betweenness, closeness and degree. The complex relationship between centrality, phenotype and fitness was explored by structural equation modelling. We found that the centrality of a plant was related to its fitness, with plants occupying central positions having higher fitness than those occupying peripheral positions. The structural equation models (SEMs) indicated that the centrality effect on fitness was not merely an effect of the abundance of visits and the species richness of visitors. Centrality has an effect even when simultaneously accounting for these predictors. The SEMs also indicated that the centrality effect on fitness was because of the specific phenotype of each plant, with attractive plants occupying central positions in networks, in relation to the distribution of conspecific phenotypes. This finding suggests that centrality, owing to its dependence on social interactions, may be an appropriate surrogate for the interacting phenotype of individuals.

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