ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum und die Fitness positiv beeinflussen. Die vorliegende Studie untersucht den seltener bekannten Fall der intraspezifischen Facilitation. Dabei... more
ABSTRACT Unter ungünstigen Umweltbedingungen können benachbarte Pflanzen das Überleben, Wachstum und die Fitness positiv beeinflussen. Die vorliegende Studie untersucht den seltener bekannten Fall der intraspezifischen Facilitation. Dabei beeinflussen bereits etablierte Gehölzpflanzen die Etablierung von gleichartigen Sämlingen positiv. In Erweiterung der üblichen Betrachtungsweise wird dabei das Zusammenspiel von positiven und negativen Interaktionen während der Keim- und Anwuchsphase betrachtet. Felduntersuchungen wurden auf einer hypersalinen Fläche auf der Halbinsel Bragança (Nordbrasilien) durchgeführt, die durch ein gestörtes hydrologisches Regime gekennzeichnet ist. Nach mehreren Dekaden, siedelten sich Büsche der Mangrovenart Avicennia germinans in einigen Teilen der Fläche an. Während der hier vorgestellten Studie wurden drei verschiedene Entwicklungsstadien der Wiederbesiedlung (geringe, mittlere und hohe Vegetationsbedeckung) auf Grundlage von Satellitenbildern bestimmt. Verschiedene Pflanzenparameter(Pflanzenhöhe und Kronenradius), wurden von jedem Busch gemessen. Die Pflanzen wurden in Sämlinge und größere Pflanzen unterteilt und die Stammposition jeder Pflanze aufgenommen. Für die Messung der lokalen Interaktionsintensität wurde der Hegyi-Index benutzt. Dieser ermöglicht die gleichzeitige Betrachtung von positiven (facilitation) und negativen (Konkurrenz) Interaktionen zwischen Nachbarpflanzen. Räumliche Punktmusteranalysen wurden mit dem Interaktionsindex kombiniert, um die Bedeutung und die Stärke der Interaktionstypen für verschiedene Wiederbesiedlungsphasen zu untersuchen. Das räumliche Muster der Pflanzen ist in allen Entwicklungsstadien aggregiert, was sich auch im Interaktionsindex für Sämlinge widerspiegelte. Darüber hinaus zeigte der Index ein frühes Umschalten von Facilitation zu Konkurrenz mit zunehmendem Entwicklungsstadium. Dieses Ergebnis spiegelt sich nicht im räumlichen Muster wider, was auf Selbstausdünnungsprozesse zurückzuführen ist. Diese sind mit den individuellen Wachstumsprozessen gekoppelt und benötigen mehr Zeit für messbare Veränderungen. Die aktuelle Studie erweitert das ökologische Konzept sowohl von intraspezifischen als auch interspezifischen positiven Pflanzeninteraktionen, da die Bedeutung und Stärke im Vergleich zu simultan vorhandenen Konkurrenzprozessen betrachtet werden. Darüber hinaus liefern die Ergebnisse Empfehlungen für die Planung von Renaturierungsprojekten degradierter Flächen, da diese bisher keine positiven Interaktionen berücksichtigen: bei ungünstigen Umweltbedingungen sollte das Pflanzmuster von regelmäßigen Abständen hin zu mehr aggregierten Anpflanzungen umgestellt werden, um die Erfolgschancen der Etablierung zu vergrößern.
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ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, generally applicable, and have well-known properties. These standard models are widely used as building blocks for all kinds of theoretical and... more
ABSTRACT In classical theoretical ecology there are numerous standard models which are simple, generally applicable, and have well-known properties. These standard models are widely used as building blocks for all kinds of theoretical and applied models. In contrast, there is a total lack of standard individual-based models (IBM's), even though they are badly needed if the advantages of the individual-based approach are to be exploited more efficiently. We discuss the recently developed ‘field-of-neighborhood’ approach as a possible standard for modeling plant populations. In this approach, a plant is characterized by a circular zone of influence that grows with the plant, and a field of neighborhood that for each point within the zone of influence describes the strength of competition, i.e., growth reduction, on neighboring plants. Local competition is thus described phenomenologically. We show that a model of mangrove forest dynamics, KiWi, which is based on the FON approach, is capable of reproducing self-thinning trajectories in an almost textbook-like manner. In addition, we show that the entire biomass-density trajectory (bdt) can be divided into four sections which are related to the skewness of the stem diameter distributions of the cohort. The skewness shows two zero crossings during the complete development of the population. These zero crossings indicate the beginning and the end of the self-thinning process. A characteristic decay of the positive skewness accompanies the occurrence of a linear bdt section, the well-known self-thinning line. Although the slope of this line is not fixed, it is confined in two directions, with morphological constraints determining the lower limit and the strength of neighborhood competition exerted by the individuals marking the upper limit.
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ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shaping forces in forest succession and spatio-temporal processes. In this study, we simulated different disturbance regimes using the... more
ABSTRACT Disturbances play a crucial role in various forest ecosystems and represent major shaping forces in forest succession and spatio-temporal processes. In this study, we simulated different disturbance regimes using the individual-based mangrove forest model KiWi. Frequent small-scaled gaps caused by lightning strikes and rare medium-sized patches caused by hurricanes were produced with varying size, severity and frequency. Additionally, a mixed regime including both lightning strikes and hurricanes was simulated. All three scenarios produced the same tree mortality rate over the simulation periods. We analyzed the temporal and spatial variations in these disturbances, taking into account their homogenizing or heterogenizing effects on the forest structure of a simulated area of 25 ha. All disturbance regimes produced significantly more homogenizing effects on the spatial forest structure than an undisturbed scenario. The hurricane regime produced a temporal heterogenization of the forest structure, while the small-scaled frequent lightning strike gaps were not able to contribute to additional heterogeneity. This shows that the explicit implementation of the disturbances generates different forest structures. The simulation results were integrated into an existing conceptual model for mangrove forest dynamics.
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Research Interests: Engineering, Conservation, Ecology, Population Dynamics, Sensitivity Analysis, and 11 morePredator-prey interaction, Mathematical Sciences, Design method, Early development, Conceptual Understanding, Growth rate, Model Analysis, Design Sensitivity Analysis, Population dynamic, Population Persistence, and Individual Based Model
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Research Interests: Zoology, Plant Biology, Ecology, Competition, Biological Sciences, and 14 moreEnvironmental Sciences, Forest, Succession, Ecological, Species Diversity, Species Richness, Mangrove forest, Vegetation Science, Evolutionary Algorithm, Forestry Sciences, Simulation experiment, Intermediate disturbance hypothesis, Plant Community, and Indexation
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The recovery of fishing grounds of Ucides cordatus populations in the Caeté Peninsula is a recurrent process due to individual movements. However, these movements could not be observed in the field. A pattern-oriented modeling approach... more
The recovery of fishing grounds of Ucides cordatus populations in the Caeté Peninsula is a recurrent process due to individual movements. However, these movements could not be observed in the field. A pattern-oriented modeling approach was used to infer on U. cordatus individual behaviors from population-level observations. An individual-based model was specifically developed for this purpose. The model results informed
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Metabolic scaling theory (MST) is an attempt to link physiological processes of individual organisms with macroecology. It predicts a power law relationship with an exponent of -4/3 between mean individual biomass and density during... more
Metabolic scaling theory (MST) is an attempt to link physiological processes of individual organisms with macroecology. It predicts a power law relationship with an exponent of -4/3 between mean individual biomass and density during density-dependent mortality (self-thinning). Empirical tests have produced variable results, and the validity of MST is intensely debated. MST focuses on organisms' internal physiological mechanisms but we hypothesize that ecological interactions can be more important in determining plant mass-density relationships induced by density. We employ an individual-based model of plant stand development that includes three elements: a model of individual plant growth based on MST, different modes of local competition (size-symmetric vs. -asymmetric), and different resource levels. Our model is consistent with the observed variation in the slopes of self-thinning trajectories. Slopes were significantly shallower than -4/3 if competition was size-symmetric. W...
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The growing concern over these organohalogens, some of which have been found in human blood and appear to be widespread in the environment, led researchers to gather in Hamburg, Germany, in 2003 to evaluate the current state of methods to... more
The growing concern over these organohalogens, some of which have been found in human blood and appear to be widespread in the environment, led researchers to gather in Hamburg, Germany, in 2003 to evaluate the current state of methods to analyze for the organic contaminants. Jonathan Martin of the University of Toronto and 20 colleagues from industry, government, and academia