velikost textu

Communitiy level impacts of alien invasive plants and the role of native range habitats in plant invasions

Upozornění: Informace získané z popisných dat či souborů uložených v Repozitáři závěrečných prací nemohou být použity k výdělečným účelům nebo vydávány za studijní, vědeckou nebo jinou tvůrčí činnost jiné osoby než autora.
Název:
Communitiy level impacts of alien invasive plants and the role of native range habitats in plant invasions
Název v češtině:
Vliv invazivních druhů na invadovaná společenstva a role stanoviště v invazích rostlin
Typ:
Disertační práce
Autor:
RNDr. Martin Hejda, Ph.D.
Školitel:
prof. RNDr. Petr Pyšek, CSc.
Oponenti:
Mgr. Miloš Duchoslav
Mgr. Lubomír Tichý, Ph.D.
Id práce:
31053
Fakulta:
Přírodovědecká fakulta (PřF)
Pracoviště:
Katedra ekologie (31-162)
Program studia:
Ekologie (P1514)
Obor studia:
-
Přidělovaný titul:
Ph.D.
Datum obhajoby:
12. 12. 2008
Výsledek obhajoby:
Prospěl/a
Informace o neveřejnosti:
Příloha práce byla vyloučena ze zveřejnění.
Jazyk práce:
Angličtina
Abstract v angličtině:
Conclusions Categorization of the species studied according to their impact on invaded communities This study focused on neophytes, species introduced after 1500 A.D., because their impact on native vegetation is higher and more obvious than that of archaeophytes, introduced before that date, due to considerable invasion dynamics and relatively short residence time (Pyšek et al. 2002). The target neophytes, included in the study, differ strongly in their community level impacts. Impatiens glandulifera had a miniscule impact on species diversity and composition, both in the removal experiment and comparative study (Chapter I). This small impact is likely to be associated with this annual species’ lower competitive strength, which has a modest root system and forms stands that are not homogeneous in terms of cover. The density of I. glandulifera populations is known to decrease during the vegetation season, as plants fall due the weight of climbers, which are common in invaded riparian communities (Calystegia sepium, Cuscuta europaea – see Beerling & Perrins 1993). Moreover, the character of communities in which I. glandulifera invades, mostly riparian nitrophilous vegetation, does not provide opportunities for competitively weak species even if they are not invaded. This vegetation is dominated by tall, competitive native nitrophilous species (Urtica dioica, Carduus crispus, Chaerophyllum bulbosum) and competitively weak species, which would be otherwise prone to competitive exclusion by I. glandulifera, cannot thrive in these communities due to the suppression by these native nitrophilous dominants. Similarly, Mimulus gutattus has no impact on species diversity and composition both in the removal experiment (Chapter II) and comparative study (Chapter III). The invasion of this species in the Czech Republic is restricted to heavily disturbed riparian terraces, which is the only place where M. gutattus forms dense stands. Even though the cover of M. guttatus exceeded 70% in some of the experimental plots, the overal cover of all plant species rarely reached 100%, which suggests that the development of the closed vegetation cover is limited by the riparian disturbance regime rather than the invasion by M. guttatus. At the same time, the intensive disturbance could reduce the competitive effect of native vegetation and enable the alien species to form stands, which are otherwise rarely observed in Central Europe. The situation is different in the Atlantic part of Europe, where M. guttatus is often seen invading wet meadows and dense riparian vegetation (Truscott et al. 2008). It is very likely that the species thrives in the Atlantic climate of the British Isles and is more competitive there which allows it to successfully penetrate into dense native vegetation. The parts of the Czech Republic where M. guttatus is found invading riparian vegetation (SW and N Bohemia, NE Moravia – Slavík 2000) are climatically somewhat similar to the Atlantic Europe because of high summer 73 precipitation. However, the neophytes are supposed to go through a rapid adaptation process during the invasion (Lee 2002; Daehler 2003; Bossdorf et al. 2005), so it is possible that populations of M. guttatus better adapted to Central European climatic conditions will appear in the future. The comparative study measuring the community level impact of 13 neophytes alien to Central Europe (Chapter III) revealed that these neophytes differ strongly in their impacts. The stands of Fallopia sachalinensis harboured on average almost 90% less species than adjacent uninvaded vegetation, and the effect of this species on β diversity was similarly supressive. Low similarity between invaded and uninvaded vegetation indicates also severe impact on species composition. The other species from the genus Fallopia (F. japonica and F. x bohemica) and Heracleum mantegazzianum all exhibited more than 50% reduction of both α and β diversity and are alien invaders with the most severe impact on the invaded community. Rudbeckia laciniata, Solidago gigantea, Imperatoria ostruthium, Lupinus polyphyllus represent species with moderate impact on invaded vegetation; their invasion resulted in less than 40% reduction of both α and β diversity. Their effect on floristic similarity was also moderate. The invasion by Aster novi-belgii resulted in a similar reduction of α and β diversity, but was associated with a strong impact on species composition. The opposite was true for Helianthus tuberosus: invasion of this species was assocaited with moderate impact on α and β diversity, but relatively modest impact on species composition. Measures and determinants of the community-level impact The impacts of invading neophytes on α diversity correlates with that on β diversity and on species composition. The fact that the impact on α diversity is negatively correlated with abundance-based Sørensen similarity between invaded and uninvaded vegetation proves the time for space substitution approach to be right: when the impact of invasion is low, the species composition of invaded vegetation resembles that of the vegetation which is uninvaded and was considered to mimic the situation before the invasion. The impact of the invader is determined by its height and cover; these characteristics can be used as surrogates for biomass production. The spatial homogeneity of the invaded stands is another important factor, since non-homogeneous populations of the invading species, such as I. glandulifera, provide opportunities for native species to survive in the invaded vegetation. This is likely to be the mechanism behind the assumption that the impacts of the invasive species are scale dependent. The impact on diversity differs according to its measure. When the differences in species numbers are considered, the impact depends mostly on the identity of the invading species. On the 74 other hand, when the differences in Shannon evenness and diversity are used as the measures, the impact positively correlates with the differences in height and cover of the invading neophyte and that of the native species dominating the adjacent uninvaded community, hence assumed to dominate the community before the invasion. In other words, if the invader imposes substantialy stronger dominance over the community than the native dominant species present prior to invasion, the community level impact of invasion is especially strong. In this way, the character of the community prior to invasion determines the overall community level impact of the invasion as well – the communities with strong dominants prior to the invasion tend to be impacted less, because such communities do not contain many competitively weak species, that would be easily eliminated following the invasion. The species actually present in such communities are less likely to be excluded from the community, because the competitive influence of the invader is not much different from that of the native species dominating the community prior to invasion. In contrary, communities without strong native dominants tend to be impacted more, because they contain more species that cannot cope with the competitive effect of the invader. Similar pattern was observed for the influence of invasion on soil (Dassonville et al. 2008). In this study, soils that were oligotrophic prior to invasion were affected more and the impact of invasion was context-dependent. Considering that the community level impacts are likely to be context-dependent, hence to a large extent determined by the characteristics of the community prior to invasion, the impact of I. glandulifera might change in the future. When the data for this study were collected (season 2004– 2005), I. glandulifera was observed to form dense stands almost exclusively in riparian vegetation. Nowadays, it is observed to colonize wet meadows, submontane tall forb vegetation and wet hemerobic vegetation (Drescher & Prots 2003). If this species continues to invade such vegetation in the future, its community level impact might be different from that observed in the riparian vegetation. The character of uninvaded vegetation also needs to be considered when evaluating conservation hazards associated with invasion. Most target neophytes were found to invade disturbed and/or nitrophilous habitats and their dominance was mostly at the expense of ruderal species and other neophytes (see also Hulme & Bremner 2006). On the other hand, some neophytes with relatively mild impact, assessed in quantitative terms, can seriously deprive communities of a high conservation value, harbouring rare native species. This is the case of Lupinus polyphyllus, Heracleum mantegazzianum and Rumex alpinus that were most often found to invade semi-natural and natural communities. 75 The role of habitats in the native range The link between the character of the native range habitats and invasion success in Central Europe is distinctive, even though it is masked by the efect of other factors, such as residence time, life form, and geographical origin. Species recruited from (i) riverine terraces, eroded slopes and banks and avalanche tracks and (ii) deciduous forests and, at the same time, from riparian scrubs are, in relative terms, most likely to become successful invaders. Another native range habitats with a high proportion of succesful invaders are (iii) subalpine tall forbs, (iv) cultivated gardens and parks, (v) trampled and other intensively disturbed areas and (vi) wet grasslands. In contrary, most of the neophytes recruited from (i) coastal sand and dune habitats, (ii) sedge and reedbeds, (iii) dry grasslands and (iv) ruderal and other anthropogenic habitats only occur as casuals in the invaded range. From their native habitats, these neophytes seem to be adapted to effective dispersal and possess competitive strength resuting from vigorous growth. In their native range, they usually grow on nutrient-rich sites with a high intensity of disturbance, rapid succession and therefore intensive competition, such as riparian habitats or subalpine tall forbs. The riverine terraces and riparian scrub can be seen as one habitat in different part of a successional sere – the riparian scrub develops on riverine terraces. In this contex, an ideal invader seemes to be an opportunistic colonizer of newly exposed substrata, which is, at the same time, competitive enough so as to persist in the rapidly developing nitrophilous vegetation. The importance of the rapid dispersal is likely to be connected with the fact that random disturbance events, such as floods, promote the invasion (Truscott et al. 2006). Similar habitats in Central Europe suffer from the invasions most intensively (Chytrý et al. 2005). The character of native range habitats with the highest proportions of casual neophytes (i.e., the least successful invaders) suggests that neophytes recruited from such habitats are more adapted to tolerating stressfull factors rather than towards effective dispersal and competitiveness. The correspondence between the habitats in the native and invaded ranges changes with the invasive success. Casual neophytes invade a limited spectrum of habitats compared to that they occupy in the native range. This is rather trivial fact, associated with the limited spread of casual neophytes – limited distribution is correlated with a limited spectrum of habitats occupied in the invaded range. Naturalized neophytes invade a spectrum of habitats comparable to that they inhabit in the native range; the naturalisation process is most likely to be successful in the same conditions as the species occupies in the native range, since those are the site conditions it is best adapted to. The most successful invaders seem to expand their original niche and invade a broader scale of habitats than they occupy in their native ranges. Although these succesful invaders typically recruit from a few habitats described above, the spectrum of habitats they occupy in the invaded range is 76 broader. Part of this phenomenon can be attributed to them being widespread – the larger the area a species occupies, the more types of habitats it is likely to sample and colonize, although this relationship is not straightforward and linear. However, besides this, it is likely that invasive neophytes expand their original niche during invasion. This “primary niche expansion“ of the most successful invaders can be explained by ecological plasticity of these species as well as their ability to adapt rapidly to the conditions encountered in the invaded range. The rapid evolution, assumed to take place during the invasion process (Lee 2002, Daehler 2003, Bossdorf et al. 2005) may be an important factor responsible for the rapid spread of the invasive species. References Alcock K. G. (2002): Effect of phosphorus on growth and competitive interactions of native and introduced species found in White Box woodland. Austral Ecology 27: 438–446. Alvarez M. E. & Cushman J. H. (2000): Community-level consequences of a plant invasion: effects on three habitats in coastal California. Ecological Applications 12: 1434–1444. Badano E. I. & Pugnaire F. I. (2004): Invasion of Agave species (Agavaceae) in south-east Spain: invader demographic parameters and impacts on native species. Diversity and Distributions 10: 493–500. Beerling D. J. & Perrins J. M. (1993): Impatiens glandulifera Royle (Impatiens Roylei Walp.). Journal of Ecology 81: 367–382. Bímová K., Mandák B. & Kašparová I. (2004): How does Reynoutria invasion fit the various theories of invasibility? Journal of Vegetation Science 15: 495–504. Bossdorf O., Auge H., Lafuma L., Rogers W. E., Siemann E. & Prati D. (2005): Phenotypic and genetic differentiation between native and introduced plant populations. Oecologia 144:1– 11. Brockerhoff E. G., Ecroyd C. E., Leckie A. C. & Kimberley M. O. (2003): Diversity and succession of adventive and indigenous vascular understorey plants in Pinus radiata plantation forests in New Zeeland. Forest Ecology and Management 185: 307–326. Chao A., Chazdon R. L., Colwell R. K. & Shen T. J. (2005): A new statistical approach for assessing similarity of species composition with incidence and abundance data. Ecology Letters 8: 48–159. Chytrý M., Pyšek P., Tichý L., Knollová I. & Danihelka J. (2005): Invasions of the Czech Republic by alien plants: a quantitative assessment across habitats. Preslia 77: 339–354. 77
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