Reconnecting plants and pollinators: challenges in the restoration of pollination mutualisms

Ecological restoration of plant-pollinator interactions has received surprisingly little attention, despite animal-mediated pollination underpinning reproduction of the majority of higher plants. Here, we offer a conceptual and practical framework for the ecological restoration of pollination mutualisms. Through the use of targeted restoration plantings to attract and sustain pollinators and increased knowledge of the ecological requirements of pollinators, we propose that pollination could be successfully restored in degraded ecosystems. The challenge for pollination biologists is to integrate their findings with those of plant restoration ecologists to ensure sustainable pollination in restored ecosystems.     

Ant visitation of extrafloral nectaries of Passiflora: the effects of nectary attributes and ant behavior on patterns in facultative ant-plant mutualisms

Extrafloral nectary (EFN) plants are widespread and can be quite species-rich in some communities. Thus, ants that utilize extrafloral nectar may have the opportunity to discriminate among a wide variety of nectar sources, resulting in variation in the ant attention EFN plants receive. In this study, we compare ant visitation rates of three Passiflora species that coexist in an early successional neotropical forest. These three vine species (Passiflora auriculata, P. biflora, and P. oerstedii) differ in their extrafloral nectary structure and placement, and thus may attract different numbers or species of ants. Through censuses of ants tending extrafloral nectaries, we found that P. auriculata received significantly higher numbers of ant visitors than P. oerstedii, but did not differ significantly from P. biflora in its attractiveness to ants. We also found that termite worker baits (simulating herbivores) placed on P. auriculata and P. biflora were discovered by ants significantly more quickly than baits placed on P. oerstedii. In both ant visitation censuses and in termite bait trials, we found no significant associations between Passiflora species and the species of ant visitors. We also performed experimental manipulations of several characteristics of P. auriculata, which resulted in changes in levels of ant visitation. When petiolar nectaries of P. auriculata were experimentally blocked, visitation by the common ant Ectatomma ruidum declined, even though nectaries on the leaf surfaces were still functional. Connections with other vegetation also had an effect on ant visitation. Though experimental creation of connections between growing P. auriculata shoots and other vegetation did not enhance ant visitation, eliminating connections resulted in a significant decline in the number of ant visitors. The results of this study suggest factors that may contribute to variation in ant visitation of extrafloral nectary plants. In addition, this study demonstrates that extrafloral nectary plants co-occurring in a habitat and available to the same ants may differ in patterns of visitation by ants and perhaps in the quality of protection from herbivores that they receive.     

Diversity of ant-plant interactions: protective efficacy in Macaranga species with different degrees of ant association

The pioneer tree Macaranga in SE Asia has developed manyfold associations with ants. The genus comprises all stages of interaction with ants, from facultative relationships to obligate myrmecophytes. Only myrmecophytic Macaranga offer nesting space for ants and are associated with a specific ant partner. The nonmyrmecophytic species are visited by a variety of different ant species which are attracted by extrafloral nectaries (EFN) and food bodies. Transitional Macaranga species like M. hosei are colonized later in their development due to their stem structure. Before the colonization by their specific Crematogaster partner the young plants are visited by different ant species attracted by EFN. These nectaries are reduced and food body production starts as soon as colonization becomes possible. We demonstrated earlier that obligate ant partners can protect their Macaranga plants against herbivore damage and vine cover. In this study we focused on nonspecific interactions and studied M. tanarius and M. hosei, representing a non-myrmecophyte and a transitional species respectively. In ant exclusion experiments both M. tanarius and M. hosei suffered significantly higher mean leaf damage than controls, 37% versus 6% in M. hosei, 16% versus 7% in M. tanarius. M. tanarius offers both EFN and food bodies so that tests for different effects of these two food rewards could be conducted. Plants with food bodies removed but with EFN remaining had the lowest mean increase of herbivore damage of all experimental groups. Main herbivores on M. hosei were mites and caterpillars. Many M. tanarius plants were infested by a shootborer. Both Macaranga species were visited by various ant species, Crematogaster spp. being the most abundant. We found no evidence for any specific relationships. The results of this study strongly support the hypothesis that non-specific, facultative associations with ants can be advantageous for Macaranga plants. Food bodies appear to have lower attractive value for opportunistic ants than EFN and may require a specific dietary adaptation. This is also indicated by the fact that food body production in the transitional M. hosei does not start before stem structure allows a colonization by the obligate Crematogaster species. M. hosei thus benefits from facultative association with a variety of ants until it produces its first domatia and can be colonized by its obligate mutualist.     

Benefits and harms of erythropoiesis-stimulating agents for anemia related to cancer: a meta-analysis

Background

Erythropoiesis-stimulating agents are used to treat anemia in patients with cancer. However, their safety and effectiveness is controversial. We did a systematic review of the clinical efficacy and harms of these agents in adults with anemia related to cancer or chemotherapy.

Methods

We conducted a systematic review of published and unpublished randomized controlled trials (RCTs) using accepted methods for literature searches, article selection, data extraction and quality assessment. We included RCTs involving anemic adults with cancer. We compared the use of erythropoiesis-stimulating agents with nonuse and assessed clinical outcomes (all-cause mortality, cardiovascular events and hypertension, health-related quality of life, blood transfusions and tumour response) and harms (serious adverse events) between groups.

Results

We identified 52 trials (n = 12 006) that met our selection criteria. The pooled all-cause mortality during treatment was significantly higher in the group receiving erythropoiesis-stimulating therapy than in the control group (relative risk [RR] 1.15, 95% confidence interval [CI] 1.03 to 1.29). Compared with no treatment, use of erythropoiesis-stimulating agents led to clinically detectable improvements in disease-specific measures of quality of life. It also reduced the use of blood transfusions (RR 0.64, 95% CI 0.56 to 0.73). However, it led to an increased risk of thrombotic events (RR 1.69, 95% CI 1.27 to 2.24) and serious adverse events (RR 1.16, 95% CI 1.08 to 1.25).

Interpretation

Use of erythropoiesis-stimulating agents in patients with cancer-related anemia improved some disease-specific measures of quality of life and decreased the use of blood transfusions. However, it increased the risk of death and serious adverse events. Our findings suggest that such therapy not be used routinely as an alternative to blood transfusion in patients with anemia related to cancer.Anemia related to cancer may be due to the cancer itself or it may be a complication of chemotherapy. Because anemia is associated with adverse clinical outcomes in people with cancer, including impaired quality of life¹ and decreased survival,² treatment with erythropoiesis-stimulating agents has been widely used. These agents are costly, and reimbursement policies for their use in patients with cancer-related anemia vary across Canadian jurisdictions. Recent studies suggest that their use in such patients may be associated with an increased risk of adverse events such as thromboembolism.³ Potential adverse effects have also been identified in patients with chronic kidney disease.^4,5Therefore, an assessment of the efficacy and harms of erythropoiesis-stimulating agents in patients with cancer-related anemia would be useful to clinicians, and to jurisdictions that seek to develop an evidence-based reimbursement policy for these drugs. We conducted a systematic review based on work done for the Canadian Agency for Drugs and Technologies in Health⁶ to summarize the clinical efficacy and harms of these agents in adults with anemia related to cancer.     

Ants as diaspore removers of non-myrmecochorous plants: a meta-analysis

Diaspore (e.g. seeds, fruits) dispersal is pivotal for plant communities and often involves several steps and different dispersing agents. Most studies focusing on diaspore dispersal by animals have highlighted the role of vertebrates, neglecting the role of ants in the diaspore dispersal of non-myrmecochorous plants. Diaspore dispersal by ants is especially relevant in the current scenario of declining of vertebrate populations and, consequently, collapse of the dispersal system of large-seeded plants. Although ants can never compensate for the dispersal service provided by vertebrates, they can mitigate the impact of vertebrate decline via removal of diaspores deposited on the ground. We have used a meta-analytical approach to investigate the contribution of ants in the removal of non-myrmecochorous diaspores (through vertebrate exclusion experiments). We considered the number of diaspore removal as effect size and factors such as plant growth forms, diaspore and ant size, habitat type as moderators. In addition, we investigated the role of such factors on the diaspore removal distance by ants. Ants played complementary role to non-myrmecochorous diaspore removal services provided by vertebrates (mean Hedges’ g of −0.30). The ant diaspore removal was 69% higher for diaspores from shrubs than that of tree diaspores and removal of small-sized diaspores were 69% and 70% higher in comparison to medium- and large-sized diaspores, respectively. Regarding the diaspore removal distance by ants, those of tree species were removed 32% farther than those of shrub species, and diaspores were removed three- times farther in the savanna than in rainforest ecosystems. Our results highlight the shrubs and small-sized diaspores. Regarding the diaspore removal distance, the ants can be crucial for the dispersal of tree diaspores and in the savanna ecosystems. Finally, considering the biodiversity crisis, the ants may play an even more important role than appreciated in diaspores dispersal.     

Responses of plants in polar regions to UVB exposure: a meta-analysis

We report a meta‐analysis of data from 34 field studies into the effects of ultraviolet B (UVB) radiation on Arctic and Antarctic bryophytes and angiosperms. The studies measured plant responses to decreases in UVB radiation under screens, natural fluctuations in UVB irradiance or increases in UVB radiation applied from fluorescent UV lamps. Exposure to UVB radiation was found to increase the concentrations of UVB absorbing compounds in leaves or thalli by 7% and 25% (expressed on a mass or area basis, respectively). UVB exposure also reduced aboveground biomass and plant height by 15% and 10%, respectively, and increased DNA damage by 90%. No effects of UVB exposure were found on carotenoid or chlorophyll concentrations, net photosynthesis, F_v/F_m or Φ_PSII, belowground or total biomass, leaf mass, leaf area or specific leaf area (SLA). The methodology adopted influenced the concentration of UVB absorbing compounds, with screens and natural fluctuations promoting significant changes in the concentrations of these pigments, but lamps failing to elicit a response. Greater reductions in leaf area and SLA, and greater increases in concentrations of carotenoids, were found in experiments based in Antarctica than in those in the Arctic. Bryophytes typically responded in the same way as angiosperms to UVB exposure. Regression analyses indicated that the percentage difference in UVB dose between treatment and control plots was positively associated with concentrations of UVB absorbing compounds and carotenoids, and negatively so with aboveground biomass and leaf area. We conclude that, despite being dominated by bryophytes, the vegetation of polar regions responds to UVB exposure in a similar way to higher plant‐dominated vegetation at lower latitudes. In broad terms, the exposure of plants in these regions to UVB radiation elicits the synthesis of UVB absorbing compounds, reduces aboveground biomass and height, and increases DNA damage.     

A general framework for effectiveness concepts in mutualisms

A core interest in studies of mutualistic interactions is the ‘effectiveness’ of mutualists in providing benefits to their partners. In plant‐animal mutualisms it is widely accepted that the total effect of a mutualist on its partner is estimated as (1) a ‘quantity’ component multiplied by (2) a ‘quality’ component, although the meanings of ‘effectiveness,’ ‘quantity,’ and ‘quality’ and which terms are applied to these metrics vary greatly across studies. In addition, a similar quantity × quality = total effect approach has not been applied to other types of mutualisms, although it could be informative. Lastly, when a total effect approach has been applied, it has invariably been from a phytocentric perspective, focussing on the effects of animal mutualists on their plant partner. This lack of a common framework of ‘effectiveness’ of mutualistic interactions limits generalisation and the development of a broader understanding of the ecology and evolution of mutualisms. In this paper, we propose a general framework and demonstrate its utility by applying it to both partners in five different types of mutualisms: pollination, seed dispersal, plant protection, rhizobial, and mycorrhizal mutualisms. We then briefly discuss the flexibility of the framework, potential limitations, and relationship to other approaches.     

Clonal plants as cooperative systems: Benefits in heterogeneous environments

All natural environments are spatially and temporally heterogeneous. Consequently, their ability to provide essential resources for the growth of plants is variable. Modular plant species produce repeated basic structures which, in the case of clonal species, are called ramets. Ramets belonging to the same clone are distributed throughout the environment in space and time, and therefore they may be located in sites which differ in resource-providing quality. The connections between ramets may allow resources to be shared, enabling the clone to behave as a cooperative system. As a result of such physiological integration, ramets can survive in conditions where there is lethal shortage of a resource because they are connected to, and supported by, ramets located in conditions where there is ample supply of the same resource. Physiological integration between connected ramets presents opportunities for heterogeneous environments to be exploited to an extent that is only just becoming apparent. As heterogeneity is ubiquitous in natural environments, it may be expected that plants, as relatively immobile organisms, will have evolved the capacity to cope with it by making appropriate localized morphological and/or physiological plastic responses. Recent studies suggest that such responses not only enable clonal species to cope with environmental heterogeneity, but that under some circumstances they can benefit more from environments which are heterogeneous rather than homogeneous, even when both types of environment contain the same amount of resources. Studies on Glechoma hederacea (Lamiaceae) that illustrate this phenomenon are described.     

Variation in mutualisms: the spatiotemporal mosaic of a pollinator assemblage

Variation in time (annual and seasonal) and space (between- and within-population) is examined for the pollinator assemblage of Lavandula latifolia (Labiatae), an insect-pollinated, summer- flowering, evergreen shrub of Mediterranean woodlands in southeastern Spain. Lavandula latifolia is pollinated there by nearly 85 species of comparatively long-tongued Hymenoptera, Diptera and Lepidoptera. The diversity, composition and abundance of pollinators varied markedly between years. Lepidopteran taxa prevailed numerically in one year, hymenopterans in four years, and both groups had similar abundance in the remaining year. The vast majority of pollinators exhibited significant annual differences in average abundance. Only 35.7% of taxa were recorded in all of the six study years. The pollinator assemblage had marked seasonal dynamics. Important changes in species richness, abundance and composition took place over the flowering season of L. latifolia (nearly 3 months). Only 21.7% of insect taxa occurred throughout the flowering season. Lavandula latifolia populations at different distances from water courses differed broadly in the abundance and composition of pollinators. Hymenopterans dominated numerically at the water-distant sites, whereas lepidopterans prevailed in populations growing in the vicinity of streams. Only 40.7% of taxa were recorded at all of the four study populations. Within the same plant population, horizontal distances of the order of 25 m resulted in significant changes in pollinator composition. Variations at the four scales considered combine to produce, from the viewpoint of L. latifolia, a spatio-temporal mosaic of pollinators. As these differ broadly in frequency of pollen transfer, size of pollen loads deposited, and between-flower flight distance patterns, spatio-temporal variation will predictably result in inconsistent or contradictory selective pressures on the plant, thus hindering specialization in relation to particular pollinators.     

Insights into a novel three-partner interaction between ants,coreids (Hemiptera: Coreidae) and extrafloral nectaries: implications for the study of protective mutualisms

Extrafloral nectar of plants and honeydew of hemipterans are the common mediators of facultative interactions that involve ants as a mobile strategy of defence. The outcome of these interactions can vary from mutualistic to commensalistic or even antagonistic, depending on the ecological context and the interacting species. Here, we explore a novel, three-partner interaction involving ants, the coreid Dersagrena subfoveolata (Hemiptera) and the extrafloral nectaries (EFNs) bearing plant Senna aphylla (Fabaceae) in semi-arid Northwest Argentina. We surveyed natural areas and conducted ant exclusion experiments, to understand how each pairwise interaction influences the overall outcome among the three interacting parts. The outcome of the interactions was assessed for experimental plants as the reproductive output and herbivore abundances and for coreids as predator abundances. We found that the coreids occurred exclusively on S. aphylla plants and that at least nine ant species interacted with the EFNs as well as with the coreids. Coreid occurrence and abundance depended on ant densities, which in turn, was determined by the presence of actively secreting EFNs. Coreid and ant presence did not influence plant reproductive success, and ants provided to coreids some biotic defence, mainly against vespid wasp predators, but had no effect on non-coreid herbivores. We conclude that the interaction outcome is commensalistic between ants and plants (assuming that EF nectar is not costly for the plant), antagonistic between coreids and plants, and mutualistic between coreids and ants. The sum of all outcomes is net positive effect for ants and coreids, and net slightly negative to neutral for plants.     

The protective role of coastal marshes: a systematic review and meta-analysis

Background

Salt marshes lie between many human communities and the coast and have been presumed to protect these communities from coastal hazards by providing important ecosystem services. However, previous characterizations of these ecosystem services have typically been based on a small number of historical studies, and the consistency and extent to which marshes provide these services has not been investigated. Here, we review the current evidence for the specific processes of wave attenuation, shoreline stabilization and floodwater attenuation to determine if and under what conditions salt marshes offer these coastal protection services.

Methodology/Principal Findings

We conducted a thorough search and synthesis of the literature with reference to these processes. Seventy-five publications met our selection criteria, and we conducted meta-analyses for publications with sufficient data available for quantitative analysis. We found that combined across all studies (n = 7), salt marsh vegetation had a significant positive effect on wave attenuation as measured by reductions in wave height per unit distance across marsh vegetation. Salt marsh vegetation also had a significant positive effect on shoreline stabilization as measured by accretion, lateral erosion reduction, and marsh surface elevation change (n = 30). Salt marsh characteristics that were positively correlated to both wave attenuation and shoreline stabilization were vegetation density, biomass production, and marsh size. Although we could not find studies quantitatively evaluating floodwater attenuation within salt marshes, there are several studies noting the negative effects of wetland alteration on water quantity regulation within coastal areas.

Conclusions/Significance

Our results show that salt marshes have value for coastal hazard mitigation and climate change adaptation. Because we do not yet fully understand the magnitude of this value, we propose that decision makers employ natural systems to maximize the benefits and ecosystem services provided by salt marshes and exercise caution when making decisions that erode these services.     

Decreasing water availability across the globe improves the effectiveness of protective ant–plant mutualisms: a meta‐analysis

Abiotic conditions can increase the costs of services and/or the benefits of rewards provided by mutualistic partners. Consequently, in some situations, the outcome of mutualisms can move from beneficial to detrimental for at least one partner. In the case of protective mutualisms between ant bodyguards and plants bearing extrafloral nectaries (EFNs), plants from arid environments face a trade‐off between EFN production and maintenance and water and carbon economy. This trade‐off may increase EFN costs and decrease their value as a defensive strategy to plants in such environments. Despite this, the presence of EFNs is an ubiquitous trait in plants from arid environments, suggesting that they provide greater benefits to plants in these environments to compensate for their higher costs. We used a meta‐analysis to investigate if such benefits do increase with decreasing water availability and the possible underlying causes (such as ant behaviour or ant diversity). As predicted, ant effect on EFN plants performance increased as mean annual precipitation decreased. We also found that the frequency of dominant ants on EFN plants increased in drier areas. Due to the more aggressive behaviour of dominant ants, we suggest that they represent an important factor shaping the adaptive value of EFNs to plants in arid environments.     

Implications of newly-formed seed-dispersal mutualisms between birds and introduced plants in northern California,USA

I examined the role of bird dispersal in invasiveness of three non-native plant species in California, USA: Triadica sebifera, Ligustrum lucidum, and Olea europaea. I selected these species because their invasiveness in California is uncertain, but a survey of ornithologists highlighted them as likely bird-dispersed. I quantified bird frugivory of these plants, compared them with a native species (Heteromeles arbutifolia), and explored the management implications of dispersal mutualisms for these and other incipient invasive plants. Fruit removal by birds was sufficient to permit spread for all study species. Seed dispersers (rather than seed predators) and pulse feeders (flocking species with potential for long distance dispersal) performed most fruit removal for the non-native species, a pattern indicative of an effective dispersal regime. The number of fruiting trees per stand was a significant predictor of bird visitation. Founding population size may thus be important in management of invasive, bird-dispersed plants. Disperser-defined niches were relatively narrow because a few disperser species performed the majority of fruit removal from study trees, but each fruit species was consumed by a variety of potential dispersers. This results in strong pairwise niche overlap between some plant species. Ordinated by bird use, study site-species combinations clustered more by geographic location than by plant species, emphasizing the opportunistic nature of bird foraging. None of the non-native focal plant species appears dispersal limited, and all have formed novel mutualisms in California. It is possible that these plants are now in lag phases preceding bird-mediated invasion. Consideration of bird dispersal when evaluating invasiveness is therefore an imperative.     

Host discrimination in modular mutualisms: a theoretical framework for meta-populations of mutualists and exploiters

Plants in multiple symbioses are exploited by symbionts that consume their resources without providing services. Discriminating hosts are thought to stabilize mutualism by preferentially allocating resources into anatomical structures (modules) where services are generated, with examples of modules including the entire inflorescences of figs and the root nodules of legumes. Modules are often colonized by multiple symbiotic partners, such that exploiters that co-occur with mutualists within mixed modules can share rewards generated by their mutualist competitors. We developed a meta-population model to answer how the population dynamics of mutualists and exploiters change when they interact with hosts with different module occupancies (number of colonists per module) and functionally different patterns of allocation into mixed modules. We find that as module occupancy increases, hosts must increase the magnitude of preferentially allocated resources in order to sustain comparable populations of mutualists. Further, we find that mixed colonization can result in the coexistence of mutualist and exploiter partners, but only when preferential allocation follows a saturating function of the number of mutualists in a module. Finally, using published data from the fig–wasp mutualism as an illustrative example, we derive model predictions that approximate the proportion of exploiter, non-pollinating wasps observed in the field.     

Mutualism, hybrid inviability and speciation in a tropical ant-plant

Although biotic interactions are particularly intricate in the tropics, few studies have examined whether divergent adaptations to biotic interactions lead to speciation in tropical organisms. Ant-plant mutualisms are widespread in the tropics. Within Leonardoxa africana, two subspecies present contrasting defences against herbivores. Young leaves of subsp. africana are defended by mutualistic ants, whereas subsp. gracilicaulis satiates herbivores by synchronized leaf production. Subsp. africana possesses hollow internodes and many large foliar nectaries, housing and feeding ants. We detected no genetic introgression between the two subspecies in the contact zone between them. F1 hybrids were present. They were intermediate in phenotype, expressing reduced, nonfunctional but costly myrmecophilic traits. However, they suffered more herbivory than their parents. Hybrids remained small, failing to reach reproductive size, probably due to their maladapted defence phenotype. Hence, there could be a direct link between adaptation to mutualism and reproductive isolation: biotic interactions could be a driver of tropical diversity.     

Modelling nutritional mutualisms: challenges and opportunities for data integration

Nutritional mutualisms are ancient, widespread, and profoundly influential in biological communities and ecosystems. Although much is known about these interactions, comprehensive answers to fundamental questions, such as how resource availability and structured interactions influence mutualism persistence, are still lacking. Mathematical modelling of nutritional mutualisms has great potential to facilitate the search for comprehensive answers to these and other fundamental questions by connecting the physiological and genomic underpinnings of mutualisms with ecological and evolutionary processes. In particular, when integrated with empirical data, models enable understanding of underlying mechanisms and generalisation of principles beyond the particulars of a given system. Here, we demonstrate how mathematical models can be integrated with data to address questions of mutualism persistence at four biological scales: cell, individual, population, and community. We highlight select studies where data has been or could be integrated with models to either inform model structure or test model predictions. We also point out opportunities to increase model rigour through tighter integration with data, and describe areas in which data is urgently needed. We focus on plant‐microbe systems, for which a wealth of empirical data is available, but the principles and approaches can be generally applied to any nutritional mutualism.     

Expression of protective antigen in transgenic plants: a step towards edible vaccine against anthrax

Protective antigen (PA) is the most potent molecule for vaccination against anthrax. In the present study, we have successfully integrated protective antigen gene in nuclear genome of tobacco plants by Agrobacterium mediated leaf-disc transformation method. Expression of protective antigen gene was detected by immunoblot analysis using antisera raised against purified PA. A distinct band of approximately 83kDa lighted up in the protein extracted from transformed plants while there was no such band in untransformed plants. The plant expressed PA showed biological activity just like native PA, which was demonstrated by cytolytic assay on macrophage like cell lines with lethal factor. This study establishes for the first time expression of PA gene in a plant system and thus marks the first milestone towards developing edible vaccine against anthrax.     

The occurrence and abundance of plants with extrafloral nectaries, the basis for antiherbivore defensive mutualisms, along a latitudinal gradient in east Asia

Abstract. The occurrence and abundance of indigenous plants with extrafloral nectaries was evaluated within local communities and regional floras along a north to south gradient from tundra in northeastern Russia (64–70°N) through temperate types in eastern Russia and Korea to subtropical vegetation in the Bonin Islands (26–27°N) south of Japan. Moving from tundra to subtropical vegetation, there is a pattern of increasing abundance of extrafloral bearing plants as a function of total plant cover (from 10.25 to 40.18%), number of species per sampled area (from 0.11 to 1.13/100 m), and proportion of species within regional floras (from 0.32 to 7.46%). There were some plants with extrafloral nectaries in all communities but their abundance varied greatly, c. 1–25% in the four northern latitudes and c. 7–70% in the subtropical region. Ants, the primary mutualists associated with plants bearing extrafloral nectaries, have a similar pattern of increasing abundance (species richness, nest density, and colony size) along the same north–south latitudinal gradient.     

Damage-induced changes in woody plants and their effects on insect herbivore performance: a meta-analysis

We conducted a meta‐analysis of 68 studies published between 1982 and 2000 in which the responses of woody plants to natural or simulated herbivore damage and/or insect herbivore performance on control and damaged plants were measured. Cumulative meta‐analyses revealed dramatic temporal changes in the magnitude and direction of the plant and herbivore responses reported during the last two decades. Studies conducted in the 1980s reported increase in phenolic concentrations, reduction in nutrient concentrations and negative effect on herbivore performance, consistently with the idea of induced resistance. In contrast, in the early 1990s when the idea that some types of plant damage may result in induced susceptibility was generally accepted, studies reported non‐significant results or induced susceptibility, and smaller effects on herbivores. The above changes may reflect paradigm shifts in the theory of induced defenses and/or the differences between study systems used in the early and the more recent studies. Overall, plant growth and carbohydrate concentrations were reduced in damaged plants despite enhanced photosynthetic rates. Damage increased the concentrations of carbon and phenolics, while terpene concentrations tended to decrease after damage; changes in nutrient concentrations after damage varied according to nutrient mobility, inherent plant growth rate, ontogenetic stage and plant type (deciduous/evergreen). Early season damage caused more pronounced changes in plants than late season damage, which is in accordance with the assumption that vigorously growing foliage has a greater capacity to respond to damage. Insect growth rate and female pupal weight decreased on previously damaged plants, while herbivore survival, consumption and male pupal weight were not significantly affected. The magnitude and direction of herbivore responses depended on the type of plant, the type of damage, the time interval between the damage and insect feeding (rapid/delayed induced resistance), and the timing of the damage.     

Persistence of mutualisms with bidirectional interactions in a two-species system

In Lotka–Volterra equations (LVEs) of mutualisms, population densities of mutualists will increase infinitely if the mutualisms between them are strong, which is called the divergence problem. In order to avoid the problem, a mutualism system of two species is analyzed in this work. The model is derived from reactions on lattice and has a form similar to that of LVEs. Population densities of species will not increase infinitely because of spatial limitation on the lattice. Stability analysis of the model demonstrates basic mechanisms by which the mutualisms lead to coexistence/extinction of the species. When in coexistence, intermediate mutualistic effect is shown to lead to the maximal density in certain parameter ranges, while a strong or weak mutualistic effect is not so good. Furthermore, the stability analysis exhibits that extremely strong/weak mutualisms will result in extinction of one/both species.