Synergy in plant invasions: fast-growing species experience greater enemy release

This research, based on studying 243 European plant species and their fungal and viral pests both in their native Europe and in the invaded range in the United States (Blumenthal et al. 2009), shows that two key causes of plant invasion, escape from natural enemies and increase in plant resources, act in concert. Fast-growing plant species adapted to moist, nitrogen-rich soils in their native region lost many more fungal and viral pathogens upon introduction to the United States than did other types of plants (Fig.­­ 1). Such enemy release is thought to provide alien species with an advantage over native species still burdened by their enemies. This is the first study, however, to show that the strength of enemy release can be predicted from the type of plant: Alien species that are fast-growing and weedy are likely to benefit most from enemy release. Unfortunately, these are the same species most-favored by global change, because fast-growing weedy species thrive in environments with ample plant resources and global change increases key plant resources, such as carbon dioxide and soil nitrogen, through increases in the greenhouse gases carbon dioxide and nitrous oxide, respectively. Alien fast-growing weedy species therefore have a double advantage in today’s world: Increases in resources enable them to outcompete slow-growing plants and unusually strong enemy release enables them to outcompete even fast-growing native plants. As global change proceeds, continuing increases in resource availability are likely to continue to favor fast-growing weedy species, and exacerbate plant invasion (Blumenthal et al. 2009). The results of the study confirm that distinguishing plant species on the basis of their origin, a principle that is sometimes questioned, is justified by differences in performance and traits among native and alien species (Pyšek & Hulme 2009).

Fig. 1

Blumenthal D., Mitchell C.E., Pyšek P. & Jarošík V. 2009. Synergy between pathogen release and resource availability in plant invasion. Proceedings of the National Academy of Sciences of the United States of America 106: 7899–7904.

Pyšek P. & Hulme P.E. 2009. Invasion biology is a discipline that’s too young to die. Nature 160: 324. 

Biological invasions: Europe on a crossroad?

The rates of introductions of alien plants and animals to Europe have been accelerating in the last decades (Fig. 2) and costs associated with invasive organisms are increasing, currently reaching at least 12 bio. € annually (Hulme et al. 2009a). Alien plant invasions threaten native species diversity at various spatial scales, as exemplified by the results of two studies. One of them shows that at the community level, the reduction of diversity of native resident species is associated with the relative dominance of the invader compared to that of the dominant species of the original uninvaded community (Hejda et al. 2009). The second study indicates that plant invasions suppress not only taxonomic but also phylogenetic diversity of regional floras. Despite the huge taxonomic diversity of plants imported into European and American cities, the strong environmental filters imposed by cities constrain the functional diversity of urban floras, which is reflected in their generally low phylogenetic diversity. Urban alien floras are mainly composed of phylogenetically related species that are well adapted to anthropogenic habitats, although these filters are stronger for groups of alien species present for a longer time (Ricotta et al. 2009). The fact that some invasive species provide economic benefits cannot be taken as a strong incentive to their further introduction, despite the potential ecological risks. Economic benefits are often gained by one sector of society while the costs are borne by the wider public. Therefore precautionary approach to biological invasions is necessary in Europe (Hulme et al. 2009b). European data and knowledge, recently acquired during the DAISIE and ALARM projects, provide a strong platform on which to build a European strategy on invasive species, and Europe can therefore serve as a model example for other parts of the world (Hulme et al. 2009c). A possibility to establish a pan-European agency (European Centre for Invasive Species Management) that would integrate all invasion related activities across Europe was suggested; such agency, with a mission to identify, assess and communicate current and emerging threats to the economy and environment posed by invasive species, would help to reduce the influx of invasive organism to Europe and decrease economic costs associated with biological invasions in Europe (Hulme et al. 2009a, d).

Fig. 2

Hulme P., Pyšek P., Nentwig W. & Vilà M. 2009a. Will threat of biological invasions unite the European Union? Science 324: 40–41.

Hejda M., Pyšek P. & Jarošík V. 2009. Impact of invasive plants on the species richness, diversity and composition of invaded communities. Journal of Ecology 97: 393–403.

Ricotta C., La Sorte F.A., Pyšek P., Rapson G.L., Celesti-Grapow L. & Thompson K. 2009. Phyloecology of urban alien floras. Journal of Ecology 97: 1243–1251.

Hulme P.E., Nentwig W., Pyšek P. & Vilà M. 2009b. Biological invasions: benefits versus risk. Response. Science 324: 1015–1016.

Hulme P.E., Nentwig W., Pyšek P. & Vilà M. 2009c. A standardized response to biological invasions. Response. Science 325: 146–147.

Hulme P.E., Nentwig W., Pyšek P. & Vilà M. 2009d. Common market, shared problems: time for a coordinated response to biological invasions in Europe? Neobiota 8: 3–19.

Ecological, taxonomic and evolutionary consequences of genome duplication

Genome duplication is widely acknowledged as a key force in plant evolution. Polyploids differ from their diploid counterparts in several phenotypic, ecological or life-trait characteristics. The former studies of diploid-polyploid plant groups were, however, hampered by non-representative sampling. This limitation was only overcome by the advent of flow cytometry. The prerequisite for comparative studies of polyploid groups is the knowledge of overall ploidy variation and cytotype distribution at various spatial scales. Targeted cytotype screening in several plant groups both in Europe and Africa has markedly changed our perception of ploidy variation and dynamics under natural conditions. Our data showed that genome duplication is much more prolific even in regions traditionally considered to be polyploid-depauperate. An illustrative example is the Cape flora where both genome-wide (e.g., variation in genome copy number and genome size) and chromosomal variation (e.g., different basic chromosome numbers) were detected (Suda et al. 2009; Fig­­. 3). Cytotype distribution is controlled by the synergistic effect of different ecological and evolutionary mechanisms. Evolutionary history (such as the number of independent polyploidization events and place of polyploid’s origin) together with the migration ability largely shape the distribution at large spatial scales (Kolář et al. 2009). On the other hand, ecological preferences (e.g., microhabitat sorting, biotic and abiotic interactions) and competitive abilities of different cytotypes drive ploidy segregation at fine spatial scales (Hülber et al. 2009). Together with molecular markers, flow cytometry represents a powerful tool for gaining insight into the evolutionary history of polyploids, especially allopolyploids combining genomes of different parental taxa. Intraspecific differences in genome size allowed us to identify putative parental species in an important component of the high-altitude Alpine flora (Dixon et al. 2009).

Fig. 3 – Oxalis obtusa

Suda J., Loureiro J., Trávníček P., Rauchová J., Vít P., Urfus T., Kubešová M., Dreyer L.L., Oberlander K.C., Wester P. & Roets F. 2009. Flow cytometry and its applications in plant population biology, ecology and biosystematics: new prospects for the Cape flora. South African Journal of Botany 75: 389.

Kolář F., Štech M., Trávníček P., Rauchová J., Urfus T., Vít P., Kubešová M. & Suda J. 2009. Towards resolving the Knautia arvensis agg. (Dipsacaceae) puzzle: primary and secondary contact zones and ploidy segregation at landscape and microgeographic scales. Annals of Botany 103: 963–974.

Hülber K., Sonnleitner M., Flatscher R., Berger A., Dobrovsky R., Niessner S., Nigl T., Schneeweiss G.M., Kubešová M., Rauchová J., Suda J. & Schönswetter P. 2009. Ecological segregation drives fine scale cytotype distribution of Senecio carniolicus (Asteraceae) in the Eastern Alps. Preslia 81: 309–319.

Dixon C.J., Schönswetter P., Suda J., Wiedermann M. & Schneeweiss G.M. 2009. Reciprocal Pleistocene origin and postglacial range formation of an allopolyploid and its sympatric ancestors (Androsace adfinis group, Primulaceae). Molecular Phylogenetics and Evolution 50: 74–83.

Timing of flowering is an non-trivial result of selection pressure from pollinators and herbivores

The timing of reproduction influences how organisms interact with the environment and can have important effects on fitness. In plants, the evolution of flowering phenology is often interpreted as a response to the selection from mutualists, although antagonistic interactions may also be important. We examined direct and indirect phenotypic selection on the start of flowering via mutualistic and antagonistic interactions in the perennial herb Lathyrus vernus over seven years. Flowering start influenced seed set, predispersal seed predation, and risk of grazing. These effects acted in opposite directions and partly influenced different components of fitness. Combining information on the effects on fitness components with that on links between fitness components and average life-time fitness, in terms of population growth rate, showed that earlier flowering was associated with a higher life-time fitness in all years. These relationships were, however, mediated largely by the variation in flower number, and the direct selection on the date of first flowering was more variable among years. Thes results point that long-term studies correcting for indirect selection and environmental covariance are needed to understand selection on reproductive phenology and that demographic approaches are necessary to assess selection mediated by several agents and influencing several components of fitness (Ehrlén & Münzbergová2009).

Ehrlén J. & MünzbergováZ. 2009. Timing of flowering: Opposed selection on different fitness components and trait covariation. American Naturalist 173: 819–830.

Survival strategies of plants in disturbed environments

Plants, as sedentary organisms, are daily coping with unfavourable conditions of the environment. The study of plant adaptations to stress can contribute to understanding of their ecology and evolution. Plants possess two main systems of dealing with severe disturbances: they either do not survive and the population survival relies on regeneration from seed, or they tolerate the disturbance by means of vegetative regeneration from intact or fragmented parts of their body. Our research focused on mechanisms related to the varying success of regenerative strategies in different environments. We demonstrated that vegetative regeneration after disturbance plays an important role not only in perennials but also in short-lived species, such as widespread weeds (Sosnová & Klimešová 2009; Latzel et al. 2009). Such regeneration ability of weeds should be taken into account in conducting their mechanical removal, especially in organic farming. The mechanical removal of weeds is likely to be less efficient if target weeds are capable of vegetative regeneration. The nutrient level of the environment affects plants’ regenerative strategies in a different way (Latzel & Klimešová 2009), being an important factor determining preference for either seeding or resprouting strategy under given conditions. A novel result is that the success of individual regeneration strategies depends not only on ambient conditions of disturbed plants (e.g. nutrients) but also on the quality of environment experienced by preceding generations (Latzel et al. 2009). We have demonstrated that maternal plants affect the photosynthesis of their progeny (Fig­­. 4a), the growth of which therefore depends on nutrient levels experienced by their mothers. Due to maternal effects, the progeny of mothers that experienced severe disturbance grew better in nutrient-poor conditions whereas that of not disturbed mothers in nutrient-rich conditions (Fig. 4b). This indicates that maternal effects play an important role in different success of seeding and resprouting strategies after disturbance, hence also in the evolution of plant populations.

Fig. 4a
Fig. 4b

Sosnová M. & Klimešová J. 2009. Life-history variation in the short-lived herb Rorippa palustris: The role of carbon storage. Acta Oecologica 35: 691–697.

Latzel V., Dospělová L. & Klimešová J. 2009. Annuals sprouting adventitiously from the hypocotyl: Their compensatory growth and implications for weed management. Biologia 64: 923–929.

Latzel V. & Klimešová J. 2009. Fitness of resprouters versus seeders in relation to nutrient availability in two Plantago species. Acta Oecologica 35: 541–547.

Latzel V., Hájek T., Klimešová J. & Gómez S. 2009. Nutrients and disturbance history in two Plantago species: maternal effects as a clue for observed dichotomy between resprouting and seeding strategies. Oikos 118: 1669–1678.