The interaction between plant competition and disease

It is well documented that pathogens can affect the survival, reproduction, and growth of individual plants. Drawing together insights from diverse studies in ecology and agriculture, we evaluate the evidence for pathogens affecting competitive interactions between plants of both the same and different species. Our objective is to explore the potential ecological and evolutionary consequences of such interactions. First, we address how disease interacts with intraspecific competition and present a simple graphical model suggesting that diverse outcomes should be expected. We conclude that the presence of pathogens may have either large or minimal effects on population dynamics depending on many factors including the density-dependent compensatory ability of healthy plants and spatial patterns of infection. Second, we consider how disease can alter competitive abilities of genotypes, and thus may affect the genetic composition of populations. These genetic processes feed back on population dynamics given trade-offs between disease resistance and other fitness components. Third, we examine how the effect of disease on interspecific plant interactions may have potentially far-reaching effects on community composition. A host-specific pathogen, for example, may alter a competitive hierarchy that exists between host and non-host species. Generalist pathogens can also induce indirect competitive interactions between host species. We conclude by highlighting lacunae in our current understanding and suggest that future studies should (1) examine a broader taxonomic range of pathogens since work to date has largely focused on fungal pathogens; (2) increase the use of field competition studies; (3) follow interactions for multiple generations; (4) characterize density-dependent processes; and (5) quantify pathogen, as well as plant, population and community dynamics.     

Effect of soil nutrients,neighbor identities and root separation types on intra‐ and interspecific interaction among three clonal plant species

In natural environments, plants frequently interact with both heterospecific and conspecific neighbors. The intensity of belowground plant interaction with neighboring species commonly varies with the availability of soil nutrients in the habitats. According to classical ecological theory, competition between conspecific neighbors may be more severe than competition between unrelated species due to the similar nutrient requirements of close relatives, especially when nutrients are scarce in the habitat. However, many recent studies have shown the opposite pattern, and suggested an alternative mechanism based on species recognition. Taking Zoysia sinica as the focal species, we conducted a controlled experiment to test the results of intraspecific and interspecific interactions among three clonal species Zoysia sinica, Zoysia japonica and Alternanthera philoxeroides, which represent a conspecific, a close relative and a distant relative of the focal species, respectively, and at different root treatments (no separation NS, clone separation CS and ramet separation RS) and two nutrient levels. The results showed that Z. sinica recognized conspecific plants in the NS and CS treatments, and did not show above or belowground competition with these. The performance of the focal plant (Z. sinica) was better when it was grown with a conspecific neighbor as compared to all other types of neighbors. In all root separation treatments, the competition was more intense when Z. sinica grew with a close relative (Z. japonica) than when growing with a distant relative (A. philoxeroides). Generally, competition between plants was more intense at the high nutrient level than at the low nutrient level, suggesting that both soil nutrients and a species recognition mechanism play a significant role for the intra‐ and interspecific interaction and fitness of these three neighboring clonal species.     

The interaction between predation and competition: a review and synthesis

This review discusses the interface between two of the most important types of interactions between species, interspecific competition and predation. Predation has been claimed to increase, decrease, or have little effect on, the strength, impact or importance of interspecific competition. There is confusion about both the meaning of these terms and the likelihood of, and conditions required for, each of these outcomes. In this article we distinguish among three measures of the influence of predation on competitive outcomes: short‐term per capita consumption or growth rates, long‐term changes in density, and the probability of competitive coexistence. We then outline various theoretical mechanisms that can lead to qualitatively distinct effects of predators. The qualitative effect of predators can depend both on the mechanism of competition and on the definition of competitive strength/impact. In assessing the empirical literature, we ask: (1) What definitions of competitive strength/impact have been assumed? (2) Does strong evidence exist to support one or more of the possible mechanisms that can produce a given outcome? (3) Do biases in the choice of organism or manipulation exist, and are they likely to have influenced the conclusions reached? We conclude by discussing several unanswered questions, and espouse a stronger interchange between empirical and theoretical approaches to this important question.     

Guidelines for a priori grouping of species in hierarchical community models

Recent methodological advances permit the estimation of species richness and occurrences for rare species by linking species‐level occurrence models at the community level. The value of such methods is underscored by the ability to examine the influence of landscape heterogeneity on species assemblages at large spatial scales. A salient advantage of community‐level approaches is that parameter estimates for data‐poor species are more precise as the estimation process “borrows” from data‐rich species. However, this analytical benefit raises a question about the degree to which inferences are dependent on the implicit assumption of relatedness among species. Here, we assess the sensitivity of community/group‐level metrics, and individual‐level species inferences given various classification schemes for grouping species assemblages using multispecies occurrence models. We explore the implications of these groupings on parameter estimates for avian communities in two ecosystems: tropical forests in Puerto Rico and temperate forests in northeastern United States. We report on the classification performance and extent of variability in occurrence probabilities and species richness estimates that can be observed depending on the classification scheme used. We found estimates of species richness to be most precise and to have the best predictive performance when all of the data were grouped at a single community level. Community/group‐level parameters appear to be heavily influenced by the grouping criteria, but were not driven strictly by total number of detections for species. We found different grouping schemes can provide an opportunity to identify unique assemblage responses that would not have been found if all of the species were analyzed together. We suggest three guidelines: (1) classification schemes should be determined based on study objectives; (2) model selection should be used to quantitatively compare different classification approaches; and (3) sensitivity of results to different classification approaches should be assessed. These guidelines should help researchers apply hierarchical community models in the most effective manner.     

An empirical assessment of tree branching networks and implications for plant allometric scaling models

Several theories predict whole‐tree function on the basis of allometric scaling relationships assumed to emerge from traits of branching networks. To test this key assumption, and more generally, to explore patterns of external architecture within and across trees, we measure branch traits (radii/lengths) and calculate scaling exponents from five functionally divergent species. Consistent with leading theories, including metabolic scaling theory, branching is area preserving and statistically self‐similar within trees. However, differences among scaling exponents calculated at node‐ and whole‐tree levels challenge the assumption of an optimised, symmetrically branching tree. Furthermore, scaling exponents estimated for branch length change across branching orders, and exponents for scaling metabolic rate with plant size (or number of terminal tips) significantly differ from theoretical predictions. These findings, along with variability in the scaling of branch radii being less than for branch lengths, suggest extending current scaling theories to include asymmetrical branching and differential selective pressures in plant architectures.     

丛枝菌根真菌和植物寄生线虫

本文综述了土壤微生物中丛枝菌根真菌和植物寄生线虫的互作关系及其互作机理,并阐述了丛枝菌根真菌在防治植物线虫病害方面的应用前景和实际操作中应注意的技术环节。     

植物群落构建的生态过滤机制研究进展

生物多样性的形成和维持机制,即群落构建机制,一直以来都是群落生态学研究的核心问题。植物群落构建的确定性过程主要是生态过滤机制(包括环境过滤和生物过滤,其中生物过滤包括种间竞争和种内功能性状变异)作用的结果。学者们构建了大量的理论、方法、模型来解释和验证生态过滤机制对群落构建的影响,并取得了显著的成果。然而,关于生态过滤机制在不同尺度的作用、生态过滤机制的各要素分解和量化等方面的研究仍有诸多疑问。重点综述了环境过滤、种间竞争和种内功能性状变异的最新研究进展,并指出了现有研究的不足之处。在未来的研究中,应注重生态过滤机制的各要素分解和量化,加强研究手段的综合运用,关注时空动态变化对植物群落构建的影响,重视对不同植物群落构建机制的共性和个性特征的认识,同时强调与其他生态过程、群落构建机制的整合。通过这些尝试,有助于人们更好的理解植物群落构建过程中的生态过滤机制的作用。     

Patterns of species interaction strength in assembled theoretical competition communities

Strength of interactions between species may be an important tool in our effort to understand community structure. Recent theoretical and empirical findings suggest that despite the presence of some strong interactions, weak interactions prevail in communities. Here, we examine how mean interaction strengths change as theoretical competition communities assemble and what the distribution of interaction coefficients is in the communities that are formed during the assembly process. Our results show that the mean competition strengths fall as assembly progresses and that most interactions in the communities formed are weak. Communities that are invulnerable to further invasions are those where interspecific interactions are weaker than the average interaction strength between species in the pool. If these results can be generalized to more than one trophic level, implications for management and conservation of natural communities are substantial.     

Lopesia indaiensis (Diptera,Cecidomyiidae), a new species of gall midge feeding on Andira fraxinifolia Benth (Fabaceae), an endemic plant in Brazil

Lopesia indaiensis (Diptera, Cecidomyiidae), a new species of gall midge found causing galls on Andira fraxinifolia (Fabaceae), an endemic plant species in Brazil, is described based on larva, pupa, male and female. L. indaiensis galls were collected in Dores do Indaiá, State of Minas Gerais, Southeastern Brazil. Larvae were removed from the galls and pupae and adults were obtained by rearing. The specimens were mounted on slides and the most important morphological characters were illustrated. The new species was compared to the other species of Lopesia.     

Tolerance to drought and flooding events provides a competitive advantage for an invasive over a native plant species

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Experimental evidence for root competition effects on community evenness in one of two phytometer species

AimsPlant–plant interactions, being positive or negative, are recognized to be key factors in structuring plant communities. However, it is thought that root competition may be less important than shoot competition due to greater size symmetry belowground. Because direct experimental tests on the importance of root competition are scarce, we aim at elucidating whether root competition may have direct or indirect effects on community structure. Indirect effects may occur by altering the overall size asymmetry of competition through root–shoot competitive interactions.     

Assessment of uncertainty in functional-structural plant models

Background and Aims

Constructing functional–structural plant models (FSPMs) is a valuable method for examining how physiology and morphology interact in determining plant processes. However, such models always have uncertainty concerned with whether model components have been selected and represented effectively, with the number of model outputs simulated and with the quality of data used in assessment. We provide a procedure for defining uncertainty of an FSPM and how this uncertainty can be reduced.

Methods

An important characteristic of FSPMs is that typically they calculate many variables. These can be variables that the model is designed to predict and also variables that give indications of how the model functions. Together these variables are used as criteria in a method of multi-criteria assessment. Expected ranges are defined and an evolutionary computation algorithm searches for model parameters that achieve criteria within these ranges. Typically, different combinations of model parameter values provide solutions achieving different combinations of variables within their specified ranges. We show how these solutions define a Pareto Frontier that can inform about the functioning of the model.

Key Results

The method of multi-criteria assessment is applied to development of BRANCHPRO, an FSPM for foliage reiteration on old-growth branches of Pseudotsuga menziesii. A geometric model utilizing probabilities for bud growth is developed into a causal explanation for the pattern of reiteration found on these branches and how this pattern may contribute to the longevity of this species.

Conclusions

FSPMs should be assessed by their ability to simulate multiple criteria simultaneously. When different combinations of parameter values achieve different groups of assessment criteria effectively a Pareto Frontier can be calculated and used to define the sources of model uncertainty.     

Lopesia leandrae (Diptera,Cecidomyiidae), a new species of gall midge associated with Leandra ionopogon (Mart.) Cogn. (Melastomataceae), a native plant to Brazil

Lopesia leandrae (Diptera, Cecidomyiidae), a new galling species associated with Leandra ionopogon (Melastomataceae), a native plant species to Brazil, is described based on larva, pupal exuvia, male and female. L. leandrae galls were collected in an area of Atlantic Forest in Bertioga, state of São Paulo, Southeastern Brazil. The new species was compared to the other species of Lopesia.     

Modeling impacts of human footprint and soil variability on the potential distribution of invasive plant species in different biomes

Human footprint and soil variability may be important in shaping the spread of invasive plant species (IPS). However, until now, there is little knowledge on how human footprint and soil variability affect the potential distribution of IPS in different biomes. We used Maxent modeling to project the potential distribution of 29 IPS with wide distributions and long introduction histories in China based on various combinations of climatic correlates, soil characteristics and human footprint. Then, we evaluated the relative importance of each type of environmental variables (climate, soil and human footprint) as well as the difference in range and similarity of the potential distribution of IPS between different biomes. Human footprint and soil variables contributed to the prediction of the potential distribution of IPS, and different types of biomes had varying responses and degrees of impacts from the tested variables. Human footprint and soil variability had the highest tendency to increase the potential distribution of IPS in Montane Grasslands and Shrublands. We propose to integrate the assessment in impacts of human footprint and soil variability on the potential distribution of IPS in different biomes into the prevention and control of plant invasion.     

Biogeographic multi‐species occupancy models for large‐scale survey data

Ecologists often seek to infer patterns of species occurrence or community structure from survey data. Hierarchical models, including multi‐species occupancy models (MSOMs), can improve inference by pooling information across multiple species via random effects. Originally developed for local‐scale survey data, MSOMs are increasingly applied to larger spatial scales that transcend major abiotic gradients and dispersal barriers. At biogeographic scales, the benefits of partial pooling in MSOMs trade off against the difficulty of incorporating sufficiently complex spatial effects to account for biogeographic variation in occupancy across multiple species simultaneously. We show how this challenge can be overcome by incorporating preexisting range information into MSOMs, yielding a “biogeographic multi‐species occupancy model” (bMSOM). We illustrate the bMSOM using two published datasets: Parulid warblers in the United States Breeding Bird Survey and entire avian communities in forests and pastures of Colombia''s West Andes. Compared with traditional MSOMs, the bMSOM provides dramatically better predictive performance at lower computational cost. The bMSOM avoids severe spatial biases in predictions of the traditional MSOM and provides principled species‐specific inference even for never‐observed species. Incorporating preexisting range data enables principled partial pooling of information across species in large‐scale MSOMs. Our biogeographic framework for multi‐species modeling should be broadly applicable in hierarchical models that predict species occurrences, whether or not false absences are modeled in an occupancy framework.     

Relative need for conservation assessments of vascular plant species among ecoregions

Aim (1) To determine the relative need for conservation assessments of vascular plant species among the world’s ecoregions given under‐assessed species distributions; (2) to evaluate the challenge posed by the lack of financial resources on species assessment efforts; and (3) to demonstrate the utility of nonlinear mixed‐effects models with both homoscedastic and heteroscedastic error structures in the identification of species‐rich ecoregions. Location Global. Methods We identified the world’s ecoregions that contain the highest vascular plant species richness after controlling for area using species–area relationship (SAR) models built within a mixed‐effects multi‐model framework. Using quantitative thresholds, ecoregions with the highest plant species richness, historical habitat loss and projected increase in human population density were deemed to be most in need of conservation assessments of plant species. We used generalized linear models to test if countries that overlap with highly important ecoregions are poorer compared with others. Results We classed ecoregions into nine categories based on the relative need for conservation assessments of vascular plant species. Ecoregions of highest relative need are found mostly in the tropics, particularly Southeast Asia, Central America, Tropical Andes and the Cerrado of South America, and the East African montane region and its surrounding areas. Countries overlapping with ecoregions deemed important for conservation assessments are poorer as measured by their capita gross national income than the other countries. The nonlinear mixed modelling framework was effective in reducing residual spatial autocorrelation compared with nonlinear models comprised of only fixed effects. In contrasting multiple SAR models to identify species‐rich ecoregions, there was not one SAR model that fitted best across all biomes. Not all SAR models displayed homoscedastic errors; therefore it is important to consider models with both homoscedastic and heteroscedastic error structures. Main conclusions We propose that conservation assessments should be conducted first in ecoregions with the greatest predicted species richness, historical habitat loss and future human population increase. As ecoregions deemed to be important for conservation assessments are located in the poorest countries, we urge international aid agencies and botanic gardens to cooperate with both local and international scientists to fund and implement conservation assessment programmes there.     

The impact of plant secondary compounds on primate feeding behavior

The recent literature on plant secondary compounds and their influence on primate feeding behavior is reviewed. Many studies of nonhuman primates document the extreme selectivity that primates, particularly herbivorous species, demonstrate in their food choice. Until quite recently investigators interpreted this to mean that herbivorous primates were not food limited. This view has been challenged in the past 10 years by researchers concentrating on the primate–plant interaction. Chemical analyses have demonstrated that plant parts are of varying quality due to differences in nutrient and secondary compound content. The assumption that all leaves (or fruits, flowers, and insects) are potential foods of equal value to the primates eating them is refuted. The observed selectivity and preferences of primates for specific plant or insect species and parts are now viewed as strategies for dealing with the nutrient and secondary compound content variation in these foods.