Relationships between alien plants and organisms of other trophic levels results from centuries of interaction

When studying determinants of invasiveness of plant species, it needs to be taken into account that the relationships between plants and organisms at other trophic levels result from centuries of mutual interactions. Pollination mode is one of the most important mutualistic relationships. Our study shows that alien flora introduced to Central Europe contained a higher proportion of insect-pollinated species than did the Central European native flora and hosted a higher diversity of pollinators per species. However, the frequency of pollination modes in the introduced alien flora gradually changed during the process of naturalization, becoming more similar to that of native species (Fig. 1), and eventually, the naturalized species that became invasive did not differ in their frequency of pollination modes from native species. The results further suggest a remarkable role of the pollination mode in successful invasion; self pollination tends to support the spread of invasive species more than any other mode of pollination. Moreover, groups of plants that have been provided with longer time to sample a wider range of habitats than recently arriving alien species have formed more associations with native pollinator species occurring in those habitats (Pyšek et al. 2011). To obtain insights into an opposite type of historical relationship, we analysed fungal and viral pathogen species richness on 124 plant species in both their native European range and introduced North American range. Plants introduced 400 years ago supported six times more pathogens than those introduced 40 years ago. In the native range, pathogen richness was greater on host plants occurring in more habitat types, with a history of agricultural use, and adapted to greater resource supplies. In hosts’ introduced range, pathogen richness was correlated with host geographic range size, agricultural use, and time since introduction, but not with any measured biological traits (Fig. 2). Introduced species have accumulated pathogens at rates that are slow relative to most ecological processes, and contingent on geographic and historic circumstance (Mitchell et al. 2010).

Figure 1.
Observed and expected frequencies of pollination modes for casual and naturalized neophytes. Expected frequencies are based on the observed values for invasive neophytes and significantly differ from the observed values both for casual and naturalized neophytes. Invasive species do not differ from native (from Pyšek et al., Ecological Monographs 2011).
Figure 2.
Historic and geographic factors explain pathogen species richness in hosts’ introduced range. Pathogen richness was greater on European plants that had a larger introduced geographic range size in North America, a longer residence time in the introduced range (they were introduced earlier) and had a history of agricultural use. The same pattern holds for not only for the absolute numbers of pathogen species but also for the proportional release from pathogens in the introduced range (from Mitchell et al. 2011).


Pyšek, P.Jarošík, V. – Chytrý, M. – Danihelka, J. – Kühn, I. – Pergl, J. – Tichý, L. – Biesmeijer, J. – Ellis, W. N. – Kunin, W. E. – Settele, J.: Successful invaders co-opt pollinators of native flora and accumulate insect pollinators with increasing residence time. Ecological Monographs. Roč. 81 (2011), s. 277–293.

Mitchell, C. E. – Blumenthal, D. – Jarošík, V. – Puckett, E. E. – Pyšek, P.: Controls on pathogen species richness in plants’ introduced and native ranges: roles of residence time, range size, and host traits. Ecology Letters. Roč. 13 (2010), s. 1525–1535.


 Impact of biological invasions and approach to their management: the origin matters

A global meta-analysis of 1041 field studies that in total describe the impacts of 135 alien plant taxa on resident species, communities and ecosystems revealed that alien plants had a significant effect on 11 of 24 different types of impact assessed. Abundance, diversity and fitness of resident species generally decreased in invaded sites, whereas primary production and several ecosystem processes were enhanced (Fig. 3); however, by the time changes in nutrient cycling are detected, major impacts on plant species and communities are likely to have already occurred. Overall, alien species impacts are heterogeneous and not unidirectional even within particular impact types (Vilà et al. 2011). Currently, Europe is the only continent with solid information on impacts of its invasive species (Pyšek & Hulme 2011). When assessing the risks associated with ongoing global change, one cannot ignore the differences between native and alien species (Hulme et al. 2011, van Kleunen et al. 2011). Change in approach to the management of invasive species, recently suggested by some authors, overlooks that the majority of researchers and managers do not target all alien species but focus on those with serious impacts; neither they ignore the fact that some alien species are beneficial to humans. We should not ignore risks associated with invasions just because impacts of some species can manifest after decades since introduction (Simberloff et al. 2011a). The success of eradication campaigns has been improving due to new technologies; over a thousand of successful eradications of invasive plants are documented from all over the world, some resulting in improved state of endangered animal species. Yet, eradication needs to be viewed as the last solution should the preventive measures fail (Simberloff et al. 2011b).

Figure 3.
Results of the metanalysis of the impacts of invasive plants on (a) plant species and communities and (b) animal species and communities. Mean effect size (Hedges’ d) of differences between alien plant species impacts are used as measures, indicating significant effects where the 95% confidence interval do not bracket zero. Invasive species increase the total production of biomass, but decrease species plant and animal fitness, diversity and/or abundance (from Vilà et al. 2011).


Vilà, M. – Espinar, J. L. – Hejda, M. – Hulme, P. E. – Jarošík, V. – Maron, J. L. – Pergl, J. – Schaffner, U. – Sun, Y. – Pyšek, P.: Ecological impacts of invasive alien plants: a meta-analysis of their effects on species, communities and ecosystems. Ecology Letters. Roč. 14 (2011), s. 702–708.

Pyšek, P. – Hulme, P. E.: Biological invasions in Europe 50 years after Elton: time to sound the ALARM. In: Richardson D. M. (ed.), Fifty years of invasion ecology: the legacy of Charles Elton. Oxford: Blackwell Publishing, 2011. s. 73–88.

Hulme, P. E. – Pyšek, P. – Duncan, R. P.: Don’t be fooled by a name: a reply to Thompson and Davis. Trends in Ecology and Evolution. Roč. 26 (2011), s. 318.

van Kleunen, M. – Dawson, W. – Dostál, P.: Research on invasive-plant traits tells us a lot. Trends in Ecology and Evolution. Roč. 26 (2011), s. 317.

Simberloff, D. – Alexander, J. – Allendorf, F. et al. (incl. Jarošík, V., Pergl, J., Pyšek, P.): Non-natives: 141 scientists object. Nature. Roč. 475 (2011a), s. 36.

Simberloff, D. – Genovesi, P. – Pyšek, P. – Campbell, K.: Recognizing conservation success. Science, Roč. 332 (2011b), s. 419.


 Studies of phylogenetic trends of microscopic lignicolous fungi (Pezizomycotina)

When studying evolutionary relationships of lignicolous microscopic fungi, we successfully identified a group of organisms accommodated in the Glomerellales, which mimic fungi of the distantly related Chaetosphaeriales, especially in the microscopic teleomorphic (sexual) characters and similar development of asexual spores. The impossibility to reliably identify them complicated study of their biology and ecology worldwide. Thanks to a broad spectrum of applied methods, including light and electron microscopy, cultivation experiments, phylogeny of protein- and RNA-coding genes, bioinformatics and prediction of secondary structures we could successfully clarify taxonomic structure of the Glomerellales. We could study evolutionary trends in the fungal class Sordariomycetes and describe relationships among morphologically similar, though evolutionary distant fungal groups (Fig. 4). Our study resulted in definition of three families within the Glomerellales; two of them described as novelties. We also addressed the relationship of members of the Microascales, whose conidial states were in the past incorrectly interpreted and linked with members of the Chaetosphaeriales (Réblová et al. 2011a). A study of evolutionary relationships of asexually reproducing fungi traditionally referred to the Glomerellales, we identified three monophyletic genera (Fig. 5), which are correctly placed in different order and class (Réblová et al. 2011b). When studying microscopic fungi of the Ceratostomella-complex, we discovered new organisms and new evolutionary relationships. A monograph of the genus Jattaea of the Calosphaeriales (Fig. 6) was published (Réblová 2011) and a new sexual stage was discovered in the life history of Sterigmatobotrys macrocarpa (Réblová & Seifert 2011).

Figure 4
Phylogram based on three genes (small and large subunits ribosomal RNA and second largest subunit RNA polymerase) clearly shows current systematic treatment of the Sordariomycetes and placement of the Glomerellales, Microascales and Chaetosphaeriales.


Figure 5
Representatives of three asexually reproducing genera of the Helotiales (Leotiomycetes) Infundichalara, Exochalara and Brachyalara, distinguished from morphologically similar taxa in the Glomerellales and Chaetosphaeriales.
Figure 6
Jattaea discreta, a typical representative of the genus Jattaea (Calosphaeriales).


Réblová, M. – Gams, W. – Seifert, K. A.: Monilochaetes and allied genera of the Glomerellales, and a reconsideration of families in the Microascales. Studies in Mycology. Roč. 68 (2011a), s. 163−191.

Réblová, M. – Gams, W. – Štěpánek, V.: The new hyphomycete genera Brachyalara and Infundichalara, the similar Exochalara and species of ‘Phialophora sect. Catenulatae’ (Leotiomycetes). Fungal Diversity. Roč. 46 (2011b), s. 67−87.

Réblová, M.: New insights into the systematics and phylogeny of the genus Jattaea and similar fungi of the Calosphaeriales. Fungal Diversity. Roč. 49 (2011), s. 167−198.

Réblová, M. – Seifert, K. A.: Discovery of the teleomorph of the hyphomycete, Sterigmatobotrys macrocarpa, and epitypification of the genus to holomorphic status. Studies in Mycology. Roč. 68 (2011), s. 193−202.


 Prepared to win? Pre-adaptations of exotic species for competitive interactions

The invasion success of introduced plants is frequently explained as a result of better competitive ability than that of resident species. The rise of novel genotypes in new ranges or production of phytototoxic compounds are both believed to improve exotics competitiveness (Fig. 7). In a common garden experiment I assessed whether exotic species are indeed better competitors than native species. However, species origin was a poor predictor of competitive ability. A capacity to reduce the biomass of target plants was positively correlated with a larger size but not origin of neighbors (Dostál 2011). In the same experiment an effect of relatedness of interacting species was examined. According to Darwin’s naturalization hypothesis, exotic species should use more similar resources and thus be less successful when competing with more- rather than less-related native species. This hypothesis was not supported (Fig. 8) (Dostál 2011). In the second study (Dostál & Palečková 2011) further assumption of naturalization hypothesis was tested, specifically the sharing of specialized enemies between exotic and closely related native species. Here, an effect of soil biota collected at sites with/out native congener was tested. Although soil microorganisms had an overall negative effect on performance of exotic species, effect of soil inoculum was not linked to congener’s presence at the sites.

Figure 7
An overview of hypotheses testing the effect of plant relatedness (i, ii) and origin (iii, iv) on competition intensity between exotic (exo) and native species (nat) in a study of Dostál (2011).

Figure 8
Results indicated that ability to reduce biomass of target plants (T) was independent on the origin or relatedness of neighbor plants (N).


Dostál, P.: Plant competitive interactions and invasiveness: searching for the effects of phylogenetic relatedness and origin on competition intensity. American Naturalist. Roč. 177 (2011), s. 655–667.

Dostál, P. – Palečková, M.: Does relatedness of natives used for soil conditioning influence plant-soil feedback of exotics? Biological Invasions. Roč. 13 (2011), s. 331–340.


 Integrated framework for the invasion process: the effect of pathways of introduction and global change

A mature understanding of the field of biological invasions has been hampered because invasion biologists concerned with different taxa and different environments have largely adopted different model frameworks for the invasion process, resulting in a confusing range of concepts, terms and definitions. We proposed a unified framework for biological invasions that reconciles and integrates the key features of the most commonly used invasion frameworks into a single conceptual model that can be applied to all human-mediated invasions. The unified framework combines previous stage-based and barrier models (Fig. 9; Blackburn et al. 2011), and provides a terminology and categorization for populations at different points in the invasion process (Richardson et al. 2011). Understanding the initial stage of invasion process provides important insights into determinants of invasion success. Pathways introducing alien species in the Czech Republic deliberately as commodities result in easier naturalization and invasion than pathways of unintentional introduction. The proportion of naturalized and invasive species among all introductions delivered by a particular pathway decreases with a decreasing level of direct assistance from humans associated with that pathway, but those species that are introduced via unintentional pathways and become invasive are as widely distributed as deliberately introduced species and invade an even wider range of seminatural habitats (Pyšek et al. 2011a). In the spread stage, invasions reflect ongoing global change, effects of which can be delayed by decades (Essl et al. 2011). In the last 250 years, the spread of alien plants to higher altitudes in the Czech Republic (Fig. 10) was becoming easier due to the increasing disturbance and propagule pressure associated with greater influence of humans at higher altitudes, as well as due to climate change manifested by an increase in temperature (Pyšek et al. 2011b).

Figure 9
The proposed unified framework for biological invasions, dividing the invasion process into a series of stages. In each stage there are barriers that need to be overcome for a species or population to pass on to the next stage, species are referred to by different terms depending on where in the invasion process they have reached, and different management interventions apply at different stages. Different parts of this framework emphasise views of invasions that focus on individual, population, process, or species (from Blackburn et al. 2011).
Figure 10
The relationship between altitudinal range of 65 alien plant species regressed on their minimum residence time (i.e., time since their first record in the Czech Republic) indicates that over the last centuries, alien species gradually penetrated into higher altitudes than where introduced (from Pyšek et al., PNAS 2011).

Blackburn, T. M. – Pyšek, P. – Bacher, S. – Carlton, J. T. – Duncan, R. P. – Jarošík, V. – Wilson, J. R. U. – Richardson, D. M.: A proposed unified framework for biological invasions. Trends in Ecology and Evolution. Roč. 26 (2011), s. 333–339.

Richardson, D. M. – Pyšek, P. – Carlton, J. T.: A compendium of essential concepts and terminology in biological invasions. In: Richardson, D. M. (ed.), Fifty years of invasion ecology: the legacy of Charles Elton. Oxford: Blackwell Publishing, 2011. s. 409–420.

Pyšek, P. – Jarošík, V. Pergl, J.: Alien plants introduced by different pathways differ in invasion success: unintentional introductions as greater threat to natural areas. PLoS ONE. Roč. 6 (2011a), s. e24890.

Essl, F. – Dullinger, S. – Rabitsch, W. – Hulme, P. E. – Hülber, K. – Jarošík, V. – Kleinbauer, I. – Krausmann, F. – Kühn, I. – Nentwig, W. – Vilà, M. – Genovesi, P. – Gherardi, F. – Desprez-Lousteau, M.-L. – Roques, A. – Pyšek, P.: Reply to Keller and Springborn: No doubt about invasion debt. Proceedings of the National Academy of Sciences of the United States of America. Roč. 108 (2011), s. E221.

Pyšek, P.Jarošík, V.Pergl, J.Wild J.: Colonization of high altitudes by alien plants over the last two centuries. Proceedings of the National Academy of Sciences of the United States of America. Roč. 108 (2011b), s. 439–440.