Order of arrival promotes coexistence via spatial niche preemption by the weak competitor

Historical contingency, such as the order of species arrival, can modify competitive outcomes via niche modification or preemption. However how these mechanisms ultimately modify stabilising niche and average fitness differences remains largely unknown. By experimentally assembling two congeneric spider mite species feeding on tomato plants during two generations, we show that order of arrival interacts with species’ competitive ability to determine competitive outcomes. Contrary to expectations, we did not observe that order of arrival cause priority effects. In fact, coexistence was predicted when the inferior competitor (Tetranychus urticae) arrived first. In that case, T. urticae colonized the preferred feeding stratum (leaves) of T. evansi leading to spatial niche preemption, which equalized fitness but also increased niche differences, driving community assembly to a close-to-neutrality scenario. Our study demonstrates how the spatial context of competitive interactions interact with species competitive ability to influence the effect of order of arrival on species coexistence.

Order of arrival promotes coexistence via spatial niche preemption by the weak competitor

Historical contingency, such as the order of species arrival, can modify competitive outcomes via niche modification or preemption. However, how these mechanisms ultimately modify stabilising niche and average fitness differences remains largely unknown. By experimentally assembling two congeneric spider mite species feeding on tomato plants during two generations, we show that order of arrival interacts with species' competitive ability to determine competitive outcomes. Contrary to expectations, we did not observe that order of arrival cause priority effects. In fact, coexistence was predicted when the inferior competitor (Tetranychus urticae) arrived first. In that case, T. urticae colonized the preferred feeding stratum (leaves) of T. evansi leading to spatial niche preemption, which equalized fitness but also increased niche differences, driving community assembly to a close-to-neutrality scenario. Our study demonstrates how the spatial context of competitive interactions interact with species competitive ability to influence the effect of order of arrival on species coexistence.

Proliferation of Isoëtalean Lycophytes During the Permo-Triassic Biotic Crises: A Proxy for the State of the Terrestrial Biosphere

Throughout their 420-Ma-long history, Lycopodiopsida have played a subordinate role at the landscape level with very few exceptions. One being the arborescent Lepidodendrales that dominated Pennsylvanian peat swamps in equatorial regions. Another is the enigmatic world-wide proliferation of sub-arborescent Isoëtales during, and in the aftermath of the Permo-Triassic terrestrial biosphere crisis that extended deep into the Triassic. Palynological as well as megafossil data shows that in a great proportion of locations around the globe that produced a fossil record, the provincial floras characteristic for the latest Permian were replaced by communities dominated by Isoëtales such as Pleuromeia and its allies. Our analysis of the isoëtalean biology, especially of the genus Pleuromeia, reveals an unusual suite of physiological and life-history traits, all indicating that it was an excellent stress-tolerator, but also a slow-growing weak competitor. This enabled Pleuromeia to thrive during environmental crises and occupy diverse habitats following the decline of other plants groups. Given their unusual biology, Isoëtales’ repeated ubiquity throughout the Early Triassic implies prolonged and repeated environmental stress in localities worldwide. Additionally, it demonstrates that the cosmopolitan isoëtalean-dominated systems produced a low-productivity, low-diversity terrestrial trophic base of the food web that no longer provided the same level of ecological and evolutionary goods and services (energy source, niche construction, ecosystem engineering, etc.) as the communities they replaced.

Drastic changes of the amphipod fauna in northern Germany and the displacement of Gammarus lacustris G.O. Sars, 1864 to relict habitats/status

The amphipod fauna of Central Europe has changed dramatically over the last century. This change has increased dramatically over the past 30 years. This dynamic is well documented in northeast Germany. This study places it in a landscape-ecological context. An example of a displacement is Gammarus lacustris G.O. Sars, 1864, a circumpolar species with a variety of habitats, but relegated to relic habitats. The species turns out to be a very weak competitor. Already with the immigration of Gammarus roeselii Gervais, 1835 (probably in the 1960s), it became a relic species in northeast Germany. Massive waves of introduction of Pontocaspian species of the genera Dikerogammarus, Pontogammarus and Echinogammarus a few decades later intensified this process for this and other species.

Effectiveness of Soil-Applied and Post-Emergence Herbicides in Crops of Scarlet Grosbeak (Erythrina Erythrina) of the Northern Steppe of Ukraine

The results of research on the effectiveness of action of herbicides on weeds incrops of Scarlet grosbeak of the Linza variety, conducted on the experimental field of the educationaland research center of the Dnipro State Agrarian and Economic University, located inthe Dniprovskyi district of Dnipropetrovsk region are presented. The soil is represented by chernozemordinary low in humus full-profile. The potential soil contamination in the arable layer byvegetative organs of reproduction of perennial suckering weeds was average (100–120 thousandpieces / m2), and high (800–900 million pieces / ha) by seeds of annual weeds. Scarlet grosbeakwas placed after winter wheat. Soil-applied and post-emergence herbicides were applied in therecommended time by a small-sized sprayer OM-4, developed by the Department of GeneralAgriculture and Soil Science of the State Agrarian and Economic University and limited liabilitycompany “Agromodul”. Years of Scarlet grosbeak growing were characterized as typical for theSteppe zone of Ukraine, but differed in the amount of precipitations. The main reasons for thesmall area of distribution of Scarlet grosbeak are identified. The attention was paid to the needfor integrated weed control for the successful growing of this legume crop. It is found that in thesegetal сommunity of Scarlet grosbeak the dominant position was occupied by common ragweedand annual cereals, which at the beginning and end of the growing season accounted for about90% of the total number of weeds. The presence of a small amount of white orache, lesser bindweed,redroot amaranth and others was also noted. In accordance with the evaluations of the technicalefficacy of herbicides in crops of Scarlet grosbeak, which are a weak competitor to weeds,indicate the need to take into account their effect on the weight of weeds. The best results in thecontrol of common ragweed in the crops of the studied culture were provided by preparationsbased on Prometryn 400 g / l + Metribuzin 100 g / l, Imazethapyr 100 g / l and Imazamox 40 g / l,which helped to reduce its weight in the air-dry state by 67.9; 64.4 and 62.1%, respectively, comparedwith the control. The least effective was the insurance (post-emergence) herbicide based onMetribuzin 600 g / l, which helped to reduce the mass of common ragweed in the air-dry state byonly 10.7% compared to the control. The technical efficiency of herbicides action and their tankmixtures on dicotyledonous annual weeds was almost the same and ranged from 50.0% to 87.5%.The use of herbicides and their tank mixtures in general allowed to save from 0.03 t / ha to 0.26 t/ ha grain of Scarlet grosbeak compared to the control without herbicides. Herbicide preparationsdiffered insignificantly in terms of the effect on grain yield. The insurance (post-emegence) herbicidesbased on Imazamox 40 g / l and Imazethapyr 100 g / l should be distinguished. The use ofthis herbicides provided yielding capacity on the level 1.19 and 1.23 t / ha, which was more thancontrol by 22.7 and 26.8%, respectively.

In Vitro Interactions between Eutypella parasitica and Some Frequently Isolated Fungi from the Wood of the Dead Branches of Young Sycamore Maple (Acer pseudoplatanus)

The ten most frequently isolated fungi from the wood of the dead branches of Acer pseudoplatanus L. were tested in dual cultures to evaluate their in vitro antagonistic activity against Eutypella parasitica R.W. Davidson and R.C. Lorenz, the causative agent of a destructive disease of maples in Europe and North America. The tested fungi, treated also as challenge isolates, were Diaporthe sp., Eutypa sp., Eu. maura, E. parasitica, Fusarium avenaceum, Neocucurbitaria acerina, Neonectria sp., Peniophora incarnata, Petrakia irregularis, and Phomopsis pustulata. The antagonistic ability of each challenge isolate was evaluated by calculating an index of antagonism (AI) based on the interaction type in the dual cultures. The results of competition between the fungal isolates were quantified after re-isolations from the interaction zone (s). The dual cultures revealed two main types of competitive interactions: Deadlock, consisting of mutual inhibition after mycelial contact or at a distance, and replacement, reflecting in the inhibition of E. parasitica, followed by partial overgrowth by the replacing fungus. Statistical analysis showed significant differences in average AI and s of challenge isolates between different dual culture assays. Based on the results of the antagonism index, Eutypa sp., Eu. maura, Neonectria sp., and P. incarnata had the highest inhibitory effect on E. parasitica growth and were recognized as the most promising candidates for further biocontrol studies of E. parasitica. The mycelium of E. parasitica at the interaction zones remained mostly viable, except in dual cultures with Eutypa sp., F. avenaceum, and Neonectria sp., where re-isolations did not yield any colony of the E. parasitica isolate. Based on the results, we assume that E. parasitica is a weak competitor, which invests less energy in direct mycelial competition. We discuss the potential of the observed antagonists as a possible biocontrol of Eutypella canker of maple. Nevertheless, additional experiments should be performed for a solid conclusion about competitive ability of E. parasitica and usefulness of antagonists as biocontrol.

A duration estimator for a continuous time war of attrition game

We developed a maximum likelihood estimator corresponding to the predicted hazard rate that emerges from a continuous time game of incomplete information with a fixed time horizon (i.e., Kreps and Wilson, 1982, Journal of Economic Theory27, 253–279). Such games have been widely applied in economics and political science and involve two players engaged in a war of attrition contest over some prize that they both value. Each player can be either a strong or weak competitor. In the equilibrium of interest, strong players do not quit whereas weak players play a mixed strategy characterized by a hazard rate that increases up to an endogenous point in time, after which only strong players remain. The observed length of the contest can therefore be modeled as a mixture between two unobserved underlying durations: one that increases until it abruptly ends at an endogenous point in time and a second involving two strong players that continues indefinitely. We illustrate this estimator by studying the durations of Senate filibusters and international crises.

Ranunculus schmalhausenii (section Batrachium, Ranunculaceae), a neglected water crowfoot endemic to Fennoscandia—a case of rapid hybrid speciation in postglacial environment of North Europe

The taxa of Ranunculus section Batrachium (Ranunculaceae) have been variably and unsatisfactorily treated in North Europe. Since the description of Ranunculus schmalhausenii (Batrachium dichotomum), probably the most common species in the area, its taxonomic status and identity have been unclear and differently implied. In the majority of treatments, individuals of R. schmalhausenii were ascribed to R. peltatus but sometimes also to the other morphologically similar, heterophyllous taxa. Based on detailed morphological study combined with geographical, ecological and biological evaluation the separate species status of this taxon was finally evidenced. The additive ITS polymorphism pattern of R. schmalhausenii confirmed its hybridogenous origin, however identification of the parental species was impeded by the heterogeneous character of the polymorphism detected. Genetic variation expressed by R. schmalhausenii samples may provide evidence of its multiple origin and suggests sexual reproduction of the taxon. Analysis of a sequence variation of two noncoding cpDNA regions, namely psbE-petL and rpl32-trnL, showed that individuals of R. schmalhausenii inherited cpDNA from two lineages of Batrachium, indicating that this taxon was created at least in two separate hybridization events. Ranunculus schmalhausenii may have originated from sexual ancestral species as multiple created hybrids which have been stabilized by polyploidisation. Genetic structure of R. schmalhausenii is somehow similar to also hybridogenous R. penicillatus. In this study, a detailed morphological, geographical, ecological, and biological description of R. schmalhausenii was presented and the differences between this species and similar taxa were outlined. The name was lectotypified and its synonymy was provided. In contrast to many other heterophyllous species of Ranunculus section Batrachium, R. schmalhausenii occurs mainly in young, postglacial landscapes of Fennoscandia, prefering deep and clear waters with current or wave action and a hard bottom, which perfectly corresponds with a relict, postglacial nature of the species. The species probably presents an example of rapid hybrid speciation (less than 10 000 years) in postglacial environment of North Europe and may be considered as endemic to Fennoscandia. Moreover, R. schmalhausenii, as a weak competitor and pollution sensitive taxon, can be regarded as an indicator of clean waters. Phylogenetic relations within section Batrachium indicates convergent evolution of some species and two cases of possible cpDNA capture.