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■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent opportunities to study basic processes in population biology. Life history studies and demographic models may be valuable for examining the introduction of invasive species and identifying life history stages where management will be most effective. Evolutionary processes may be key features in determining whether invasive species establish and spread. Studies of genetic diversity and evolutionary changes should be useful for

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The Population Biology of Invasive Species

Trichoderma spp. are free-living fungi that are common in soil and root ecosystems. Recent discoveries show that they are opportunistic, avirulent plant symbionts, as well as being parasites of other fungi. At least some strains establish robust and long-lasting colonizations of root surfaces and penetrate into the epidermis and a few cells below this level. They produce or release a variety of compounds that induce localized or systemic resistance responses, and this explains their lack of pathogenicity to plants. These root-microorganism associations cause substantial changes to the plant proteome and metabolism. Plants are protected from numerous classes of plant pathogen by responses that are similar to systemic acquired resistance and rhizobacteria-induced systemic resistance. Root colonization by Trichoderma spp. also frequently enhances root growth and development, crop productivity, resistance to abiotic stresses and the uptake and use of nutrients.

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Trichoderma species--opportunistic, avirulent plant symbionts.

To curb the future economic and environmental impacts of invasive exotic species, we need to understand the mechanisms behind exotic invasions. One commonly accepted mechanism for exotic plant invasions is the enemy release hypothesis (ERH), which states that plant species, on introduction to an exotic region, experience a decrease in regulation by herbivores and other natural enemies, resulting in a rapid increase in distribution and abundance. The success of classical biological control has been used as support for ERH, but this observational evidence does not directly test ERH, and the more experimental evidence is equivocal. Competitive release through greater generalist enemy impact on natives seems to be an important but understudied mechanism of enemy release, but there is a serious need for experiments involving exclusion of natural enemies in invaded plant communities. With a clearer understanding of the role of enemy release in exotic plant invasions, we can begin to build a comprehensive predictive model of exotic plant invasions.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(02)02499-0.pdf

Exotic plant invasions and the enemy release hypothesis

Community ecology theory can be used to understand biological invasions by applying recent niche concepts to alien species and the communities that they invade. These ideas lead to the concept of ‘niche opportunity', which defines conditions that promote invasions in terms of resources, natural enemies, the physical environment, interactions between these factors, and the manner in which they vary in time and space. Niche opportunities vary naturally between communities but might be greatly increased by disruption of communities, especially if the original community members are less well adapted to the new conditions. Recent niche theory clarifies the prediction that low niche opportunities (invasion resistance) result from high species diversity. Conflicting empirical patterns of invasion resistance are potentially explained by covarying external factors. These various ideas derived from community ecology provide a predictive framework for invasion ecology.

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Community ecology theory as a framework for biological invasions

Biotic invaders are species that establish a new range in which they proliferate, spread, and persist to the detriment of the environment. They are the most important ecological outcomes from the unprecedented alterations in the distribution of the earth's biota brought about largely through human transport and commerce. In a world without borders, few if any areas remain sheltered from these im- migrations. The fate of immigrants is decidedly mixed. Few survive the hazards of chronic and stochastic forces, and only a small fraction become naturalized. In turn, some naturalized species do become invasive. There are several potential reasons why some immigrant species prosper: some escape from the constraints of their native predators or parasites; others are aided by human-caused disturbance that disrupts native communities. Ironically, many biotic invasions are apparently facilitated by cultivation and husbandry, unintentional actions that foster immigrant populations until they are self-perpetuating and uncontrollable. Whatever the cause, biotic invaders can in many cases inflict enormous environmental damage: (1) Animal invaders can cause extinctions of vulnerable native species through predation, grazing, competition, and habitat alteration. (2) Plant invaders can completely alter the fire regime, nutrient cycling, hydrology, and energy budgets in a native ecosystem and can greatly diminish the abundance or survival of native species. (3) In agriculture, the principal pests of temperate crops are nonindigenous, and the combined expenses of pest control and crop losses constitute an onerous "tax" on food, fiber, and forage production. (4) The global cost of virulent plant and animal diseases caused by parasites transported to new ranges and presented with susceptible new hosts is currently incalculable. Identifying future invaders and taking effective steps to prevent their dispersal and establishment con- stitutes an enormous challenge to both conservation and international commerce. Detection and management when exclusion fails have proved daunting for varied reasons: (1) Efforts to identify general attributes of future invaders have often been inconclusive. (2) Predicting susceptible locales for future invasions seems even more problematic, given the enormous differences in the rates of arrival among potential invaders. (3) Eradication of an established invader is rare, and control efforts vary enormously in their efficacy. Successful control, however, depends more on commitment and continuing diligence than on the efficacy of specific tools themselves. (4) Control of biotic invasions is most effective when it employs a long-term, ecosystem- wide strategy rather than a tactical approach focused on battling individual invaders. (5) Prevention of invasions is much less costly than post-entry control. Revamping national and international quarantine laws by adopting a "guilty until proven innocent" approach would be a productive first step. Failure to address the issue of biotic invasions could effectively result in severe global consequences, including wholesale loss of agricultural, forestry, and fishery resources in some regions, disruption of the ecological processes that supply natural services on which human enterprise depends, and the creation of homogeneous, impoverished ecosystems composed of cosmopolitan species. Given their current scale, biotic invasions have taken their place alongside human-driven atmospheric and oceanic alterations as major agents of global change. Left unchecked, they will influence these other forces in profound but still unpredictable ways.

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Biotic invasions: causes, epidemiology, global consequences, and control

Contents: Introduction.- Taxonomy of Entomopathogenic Fungi.- Illustrations of Common Fungal Pathogens.- Fungal Pathogenesis.- Natural Control: Ecology and Biology.- Biotechnology.- Biological Control: Past, Present and Future.- Bibliography.- Index.

Atlas of Entomopathogenic Fungi

The main constraint and continuing threat to cocoa production in Latin America is disease caused by two basidiomycete fungi belonging to the genus Crinipellis (Agaricales), both of which are currently on an invasive front Classical biological control, in which coevolved natural enemies are considered to offer the most potential for sustainable control of invasive alien organisms, is investigated as a management strategy Our initial approach has been to search for the suspected coevolved host (Theobroma gileri) of one of these pathogens, Crinipellis roreri, the causal agent of frosty pod rot, in the mesic forests of north-west Ecuador; to isolate the endophytes and mycoparasites associated with both host and pathogen; to screen selected fungi in the greenhouse and laboratory, in order to determine their biocontrol potential Endophytes were isolated directly in the field from healthy tree boles and pods, and over 40 genera were recorded, mainly representing anamorphs of Hypocreales in the genera Acremonium, Clonostachys, Trichoderma and Verticillium, as well as basidiomycetes belonging to the Agaricales and Polyporales Of the endophytic fungi tested, most can be inoculated into and recovered from asymptomatic cocoa seedlings Twenty-eight mycoparasitic species were isolated from diseased pods and selected mycoparasites as well as endophytes were screened against C roreri using the pre-colonised plate method Consistently high mycoparasitism of the C roreri pseudostroma was demonstrated, particularly by a complex of Clonostachys and Trichoderma species

Endophytes and mycoparasites associated with an indigenous forest tree, Theobroma gileri , in Ecuador and a preliminary assessment of their potential as biocontrol agents of cocoa diseases

The neotropical composite, Parthenium hysterophorus, has achieved major weed status in India and Australia within the past few decades. The reasons for its success as an alien invasive weed are discussed, particularly those relating to allelopathy, together with its effect on crop production, animal husbandry, human health and biodiversity. The actual and potential use of natural enemies as classical biological control agents is reviewed and the work undertaken over the last 20 years on screening and evaluating both insect and fungal agents is analysed. It is concluded that successful management of this weed can only be achieved by an integrated approach in which biological control, because of its cost effectiveness, environmental safety and sustainability, could play a significant role.

Parthenium hysterophorus: a review of its weed status and the possibilities for biological control.

A part of the species formerly classified in Verticillium sect. Prostratu is unrelated to the majority subsumed in Lecanicillium on molecular grounds. Most species of this clade have conspicuous dictyochlamydospores (formerly assembled in Diheterospora), while others are distinct only by the tendency to form swollen vegetative hyphae, chromophilic, relatively short conidia, and the lack of crystals. The genus Pochonia which predates Diheterospora is used for this group. The distinctness of I? chlurnyclosporia and f? suchlasporia, each with two varieties, is confirmed. A teleomorph, Cordyceps chlamydosporia, is newly described for the former. Eight anamorph taxa are keyed out, including two new species, f? microbactrosporu and I? rubescen.~. Two species of Rotiferophthom were available for investigation, and their generic distinctness was confirmed. The parasite of rust fungi Verticillium epiphytum and a fungicolous species with conspicuous intercalary chlamydospores, K incurvum, were studied for comparison with Pochonia, but are not formally classified. Verticillium epiphytum is close to but falls outside Pochonia, V incurvum is probably a nectriaceous anamorph. Verticillium pseudohemipterigenum with erect conidiophores bearing numerous tlask-shaped phialides in dense whorls is also not formally reclassified. 4 the

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Harry C. Evans

Papers

Biotic invasions: causes, epidemiology, global consequences, and control

Atlas of Entomopathogenic Fungi

Endophytes and mycoparasites associated with an indigenous forest tree, Theobroma gileri , in Ecuador and a preliminary assessment of their potential as biocontrol agents of cocoa diseases

Parthenium hysterophorus: a review of its weed status and the possibilities for biological control.

A revision of Verticillium section Prostrata. V. The genus Pochonia, with notes on Rotiferophthora.