scholarly journals Pathogens, density dependence and the coexistence of tropical trees

2006 ◽  
Vol 273 (1604) ◽  
pp. 2909-2916 ◽  
Author(s):  
Robert P Freckleton ◽  
Owen T Lewis
Keyword(s):  
Density Dependence ◽  
Natural Enemies ◽  
Plant Pathogens ◽  
Plant Density ◽  
Experimental Studies ◽  
Careful Analysis ◽  
Tropical Trees ◽  
Species Identity ◽  
Intraspecific Density Dependence ◽  
Whole Life Cycle

There is increasing interest in the role played by density-dependent mortality from natural enemies, particularly plant pathogens, in promoting the coexistence and diversity of tropical trees. Here, we review four issues in the analysis of pathogen-induced density dependence that have been overlooked or inadequately addressed. First, the methodology for detecting density dependence must be robust to potential biases. Observational studies, in particular, require a careful analysis to avoid biases generated by measurement error, and existing studies could be criticized on these grounds. Experimental studies manipulating plant density and pathogen incidence will often be preferable, or should be run in parallel. Second, the form of density dependence is not well understood and, in particular, there are no data indicating whether pathogens cause compensating or overcompensating density responses. Owing to this, we argue that the potential for pathogen-induced density dependence to generate diversity-enhancing outcomes, such as the Janzen–Connell effect, remains uncertain, as coexistence is far more probable if density dependence is overcompensating. Third, there have been few studies examining the relative importance of intra- or interspecific density dependence resulting from pathogens (or, more widely, natural enemies). This is essentially equivalent to asking to what extent pathogens are host-specific. If pathogens are generalists, then mortality rates will respond to overall plant density, irrespective of plant species identity. This will weaken the intraspecific density dependence and reduce the diversity-promoting effects of pathogens. Finally, we highlight the need for studies that integrate observations and experiments on pathogens and density dependence into the whole life cycle of trees, because as yet it is not possible to be certain of the degree to which pathogens contribute to observed dynamics.

scholarly journals Enemies mediate distance- and density-dependent mortality of tree seeds and seedlings: a meta-analysis of fungicide, insecticide and exclosure studies

2021 ◽  
Vol 288 (1943) ◽  
pp. 20202352
Author(s):  
Xiaoyang Song ◽  
Richard T. Corlett
Keyword(s):  
Density Dependence ◽  
Natural Enemies ◽  
Natural Enemy ◽  
Plant Pathogens ◽  
Meta Analysis ◽  
Seedling Stage ◽  
Forest Community ◽  
Density Dependent ◽  
Density Dependent Mortality ◽  
Dependent Mortality

Conspecific negative distance- and density-dependence is often assumed to be one of the most important mechanisms controlling forest community assembly and species diversity globally. Plant pathogens, and insect and mammalian herbivores, are the most common natural enemy types that have been implicated in this phenomenon, but their general effects at different plant life stages are still unclear. Here, we conduct a meta-analysis of studies that involved robust manipulative experiments, using fungicides, insecticides and exclosures, to assess the contributions of different natural enemy types to distance- and density-dependent effects at seed and seedling stages. We found that distance- and density-dependent mortality caused by natural enemies was most likely at the seedling stage and was greater at higher mean annual temperatures. Conspecific negative distance- and density-dependence at the seedling stage is significantly weakened when fungicides were applied. By contrast, negative conspecific distance- and density-dependence is not a general pattern at the seed stage. High seed mass reduced distance- and density-dependent mortality at the seed stage. Seed studies excluding only large mammals found significant negative conspecific distance-dependent mortality, but exclusion of all mammals resulted in a non-significant effect of conspecifics. Our study suggests that plant pathogens are a major cause of distance- and density-dependent mortality at the seedling stage, while the impacts of herbivores on seedlings have been understudied. At the seed stage, large and small mammals, respectively, weaken and enhance negative conspecific distance-dependent mortality. Future research should identify specific agents of mortality, investigate the interactions among different enemy types and assess how global change may affect natural enemies and thus influence the strength of conspecific distance- and density-dependence.

Analysis of Polygonal Vortex Flows in a Cylinder with a Rotating Bottom

2021 ◽  
Vol 11 (3) ◽  
pp. 1348
Author(s):  
A. Rashkovan ◽  
S.D. Amar ◽  
U. Bieder ◽  
G. Ziskind
Keyword(s):  
Experimental Studies ◽  
Free Surface Flow ◽  
Careful Analysis ◽  
Numerical Approach ◽  
Surface Flow ◽  
Initial Water ◽  
Eddy Simulation ◽  
Disk Rotation ◽  
Inner Radius ◽  
Liquid Flows

The present paper provides a physically sound numerical modeling of liquid flows experimentally observed inside a vertical circular cylinder with a stationary envelope, rotating bottom and open top. In these flows, the resulting vortex depth may be such that the rotating bottom disk becomes partially exposed, and rather peculiar polygon shapes appear. The parameters and features of this work are chosen based on a careful analysis of the literature. Accordingly, the cylinder inner radius is 145 mm and the initial water height is 60 mm. The experiments with bottom disk rotation frequencies of 3.0, 3.4, 4.0 and 4.6 Hz are simulated. The chosen frequency range encompasses the regions of ellipse and triangle shapes as observed in the experimental studies reported in the literature. The free surface flow is expected to be turbulent, with the Reynolds number of O(105). The Large Eddy Simulation (LES) is adopted as the numerical approach, with a localized dynamic Subgrid-Scale Stresses (SGS) model including an energy equation. Since the flow obviously requires a surface tracking or capturing method, a volume-of-fluid (VOF) approach has been chosen based on the findings, where this method provided stable shapes in the ranges of parameters found in the corresponding experiments. Expected ellipse and triangle shapes are revealed and analyzed. A detailed character of the numerical results allows for an in-depth discussion and analysis of the mechanisms and features which accompany the characteristic shapes and their alterations. As a result, a unique insight into the polygon flow structures is provided.

scholarly journals Dynamics and Management of Rising Outbreak Spruce Budworm Populations

Forests ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 748 ◽  
Author(s):  
Jacques Régnière ◽  
Barry Cooke ◽  
Ariane Béchard ◽  
Alain Dupont ◽  
Pierre Therrien
Keyword(s):  
Population Growth ◽  
Density Dependence ◽  
Natural Enemies ◽  
Choristoneura Fumiferana ◽  
Regional Scale ◽  
Adult Emergence ◽  
Spruce Budworm ◽  
Migration Activity ◽  
Larval Stages ◽  
The Impact

Management of spruce budworm, Choristoneura fumiferana (Clem.), outbreak spread requires understanding the demographic processes occurring in low, but rising populations. For the first time, detailed observations were made in the early stages of outbreak development. We sampled populations over a three-year period in both treated and untreated populations in the Lower St-Lawrence region of Quebec, Canada, and measured the density-dependence of survival and population growth rates, and the impact of natural enemies and insecticides. Insecticides tested were Bacillus thuringiensis (Berliner 1915) and tebufenozide. We recorded strong density-dependence of survival between early larval stages and adult emergence, explained largely by the variation of natural enemy impacts and overcrowding. We also observed inverse density-dependence of apparent fecundity: net immigration into lower-density populations and net emigration from the higher, linked to a threshold of ~25% defoliation. Because of high migration rates, none of the 2013 treatments reduced egg populations at the end of summer. However lower migration activity in 2014 allowed population growth to be reduced in treated plots. This evidence lends support to the conclusion that, for a budworm population to increase to outbreak density, it must be elevated via external perturbations, such as immigration, above a threshold density of ~4 larvae per branch tip (L4). Once a population has increased beyond this threshold, it can continue growing and itself become a source of further spread by moth migration. These findings imply that populations can be brought down by insecticide applications to a density where mortality from natural enemies can keep the reduced population in check, barring subsequent immigration. While we recognize that other factors may occasionally cause a population to exceed the Allee threshold and reach outbreak level, the preponderance of immigration implies that if all potential sources of significant numbers of moths are reduced on a regional scale by insecticide applications, a widespread outbreak can be prevented, stopped or slowed down by reducing the supply of migrating moths.

scholarly journals The Influence of Tree Diversity on Natural Enemies—a Review of the “Enemies” Hypothesis in Forests

2020 ◽  
Vol 6 (4) ◽  
pp. 243-259 ◽  
Author(s):  
Michael Staab ◽  
Andreas Schuldt
Keyword(s):  
Species Richness ◽  
Natural Enemies ◽  
Natural Enemy ◽  
Tree Species ◽  
Tree Diversity ◽  
Pest Species ◽  
Top Down ◽  
Species Identity ◽  
Enemies Hypothesis ◽  
Functional And Phylogenetic Diversity

Abstract Purpose of Review Natural enemies are an important component for forest functioning. By consuming herbivores, they can be effective top-down regulators of potential pest species. Tree mixtures are generally expected to have larger predator and parasitoid populations compared to monocultures. This assumption is based on the “enemies” hypothesis, a classical ecological concept predicting a positive relationship between plant diversity (and complexity) and natural enemies, which, in turn, should increase top-down control in more diverse environments. However, the “enemies” hypothesis has mostly been tested and supported in relatively simple agricultural ecosystems. Until recently, research in forests was sparse. We summarize the upcoming knowledge-base for forests and identify forest characteristics likely shaping relationships between tree diversity, natural enemies (abundance, species richness, diversity), and top-down control. We further identify possible implications for mixed species forestry and key knowledge gaps. Recent Findings Tree diversity (almost exclusively quantified as tree species richness) does not consistently increase enemy abundance, diversity, or result in herbivore control. Tests of the “enemies” hypothesis are largely based on aboveground natural enemies (mainly generalists) and have highly variable outcomes across taxa and study systems, sometimes even finding a decrease in predator diversity with increasing tree diversity. Recurrent effects of tree species identity and composition indicate that a closer focus on tree functional and phylogenetic diversity might help to foster a mechanistic understanding of the specific circumstances under which tree diversity can promote top-down control. Summary Our review suggests that the “enemies” hypothesis may not unambiguously apply to forests. With trees as structurally complex organisms, even low-diversity forests can maintain a high degree of habitat heterogeneity and may provide niches for many predator and parasitoid species, possibly blurring correlations between tree and natural enemy diversity. Several further factors, such as latitude, identity effects, intraguild predation, or functional and phylogenetic components of biodiversity, may confound the predictions of the “enemies” hypothesis. We identify topics needing more research to fully understand under which conditions tree diversity increases natural enemy diversity and top-down control—knowledge that will be crucial for forest management.

scholarly journals Influence of distance from adjacent forest fragments on aphids (Hemiptera: Aphididae) parasitoidism in wheat fields in Parana State, Brazil

2016 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
Orcial Ceolin Bortolotto ◽  
Ayres De Oliveira Menezes Jr. ◽  
Adriano Thibes Hoshino ◽  
Hugo Reis Medeiros
Keyword(s):  
Density Dependence ◽  
Natural Enemies ◽  
Neotropical Region ◽  
Agricultural Landscapes ◽  
Clear Relationship ◽  
Forest Fragments ◽  
The North ◽  
Inverse Density Dependence ◽  
Planting Season ◽  
Aphid Abundance

In agricultural landscapes, non-crop habitats, such as forest fragments, may not only play an important role for natural enemies, but may also favor some pests. However, there is a lack of studies in Neotropical regions about these interactions. Thus, the aim of this study was to investigate aphid parasitoidism at two distances (25 m and 525 m) from edges of forest fragments adjacent to wheat crops. This research was carried out in four wheat fields in the north of the Parana state, Brazil, during the planting season of 2009. In total, 8,392 aphids were counted, representing two species. There were 589 total aphid-parasitized (“mummies”), represented by six species. In all four areas, aphid abundance and parasitoidism showed no clear relationship to distance from forest fragments (25 m and 525 m). In addition, inverse density dependence between aphids and parasitoidism was observed. In summary, this study does not support the hypothesis of higher parasitoidism of aphids near edges of forest fragments. However, this is the first study in the Neotropical region and more research must be done to better understand this tritrophic interaction.

scholarly journals OPTIMIZATION OF THE OF SUNFLOWER CROPS STRUCTURE IN TECHNOLOGIES WITH RETARDANTS APPLICATION

2021 ◽  
Vol 2 (7(71)) ◽  
pp. 22-26
Author(s):  
V. Yatsenko ◽  
H. Zhatova ◽  
I. Kolosok
Keyword(s):  
Seed Treatment ◽  
Plant Density ◽  
Experimental Studies ◽  
Treatment Plant ◽  
Forest Steppe ◽  
Stem Height ◽  
Technological Parameters ◽  
Crop Density ◽  
Basic Level ◽  
Plant Treatment

The results of experimental studies to determine the actual changes in stem height, plant productivity and sunflower yield depending on the plant density and different variants of retardant application are presented in the article. The research was carried out in a model field experiment with a density gradient from 19.84 to 160.0 thousand plant / ha. The aim of the research was to determine the optimal parameters of the crop structure of new sunflower Choral hybrid in the technology with retardant application. It has been established that the optimal variant for ensuring the technological parameters of the plant height of the Choral hybrid in the northeastern Forest-Steppe of Ukraine was the complex application of Moddus retardant according to the scheme "seed treatment + plant treatment in the phase of 8-10 leaves". To maintain the basic level of yield, it is proposed to increase the calculated indicators of the final (pre-harvest) crop density from 56.5 to 73.1 thousand plants / ha.

scholarly journals Strong whole life-cycle inbreeding depression in Daphnia magna enhanced by partial asexuality

2020 ◽  
Author(s):  
Valentina G. Tambovtseva ◽  
Anton A. Zharov ◽  
Christoph R. Haag ◽  
Yan R. Galimov
Keyword(s):  
Life Cycle ◽  
Daphnia Magna ◽  
Inbreeding Depression ◽  
Experimental Studies ◽  
Life Cycles ◽  
Mating Strategies ◽  
Breeding Systems ◽  
Similar Species ◽  
Entire Life ◽  
Whole Life Cycle

ABSTRACTInbreeding depression is a key factor in the evolution of mating strategies and breeding systems across the eukaryotic tree of life. Yet its potential impact in partially asexual species has only received little attention. We studied inbreeding depression in the cyclical parthenogen Daphnia magna by following mixtures of inbred and outbred genotypes from an early embryonic stage through hatching to adulthood and then across several asexual generations. We found that, across asexual generations, the frequency of inbred genotypes strongly and constantly decreased, until the experimental populations were almost entirely made up of outbred genotypes. The resulting estimate of inbreeding depression across the entire life cycle was almost 100 %, much higher than previous estimates for this and other similar species. Our results illustrate that the magnitude of inbreeding depression may be severely underestimated in studies that use fitness components or proxies instead of compound fitness estimates across the entire life, as well as in experimental studies with substantial pre-experimental mortality. More generally, our results suggest that inbreeding depression may play an important role in the evolution of partially asexual life cycles because clonal reproduction maintains inbreeding levels, and hence the negative effects of inbreeding accumulate across subsequent asexual generations.

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