The literature on biological invasions is biased in favour of invasive species – those that spread and often reach high abundance following introduction by humans. It is, however, also important to ...understand previous stages in the introduction'naturalization invasion continuum (‘the continuum’), especially the factors that mediate naturalization. The emphasis on invasiveness is partly because most invasions are only recognized once species occupy large adventive ranges or start to spread. Also, many studies lump all alien species, and fail to separate introduced, naturalized and invasive populations and species. These biases impede our ability to elucidate the full suite of drivers of invasion and to predict invasion dynamics, because different factors mediate progression along different sections of the continuum. A better understanding of the determinants of naturalization is important because all naturalized species are potential invaders. Processes leading to naturalization act differently in different regions and global biogeographical patterns of plant invasions result from the interaction of population-biological, macroecological and human-induced factors. We explore what is known about how determinants of naturalization in plants interact at various scales, and how their importance varies along the continuum. Research that is explicitly linked to particular stages of the continuum can generate new information that is appropriate for improving the management of biological invasions if, for example, potentially invasive species are identified before they exert an impact.
It is increasingly recognized that the factors facilitating plant invasions depend on the stage along the introduction–naturalization–invasion continuum. Adaptative strategies, that is, combinations ...of functional traits that represent overall fitness in the face of one or more selection pressures, have shown promise in explaining plant invasions. However, whether adaptive strategy patterns change with stages of plant invasion is not yet known.
Using the Pladias Database of the Czech Flora and Vegetation, we explored how Grime's adaptive strategies (competitors, stress‐tolerators, ruderals; CSR) and introduction pathways (deliberate vs. accidental) relate to plant invasion along the introduction–naturalization–invasion continuum.
Phylogenetically corrected ANOVAs showed that naturalized species (referring to non‐invasive naturalized species in this study) were mostly R‐selected, whereas invasive species tended to be C‐selected. The results of phylogenetic regression analysis further confirmed that across the deliberately and accidentally introduced species, R‐ and C‐selection were positively related to naturalization and invasion success respectively. We also found that deliberate introduction was negatively related to naturalization success and grid‐cell occupancy of naturalized species, likely due to the different CSR strategies of deliberately and accidentally introduced aliens.
Our study provides empirical evidence that different adaptive strategies are associated with species that have reached different invasion stages and confirms the usefulness of the CSR strategy framework for understanding plant invasion. This has implications for predicting and preventing potential high‐impact invaders. For example, our results show that naturalized C‐selected species have a higher probability of becoming invasive than naturalized R‐selected species. Therefore, management actions are essential to prevent further introductions and spread of competitors.
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•Patterns of introduction, naturalisation, invasion, and impact in the plant family Myrtaceae are similar to other plant groups previously screened for invasiveness, but there are differences between ...dry-fruited and fleshy-fruited Myrtaceae.•A higher proportion of dry-fruited Myrtaceae have been introduced than fleshy-fruited species.•Fleshy- and dry-fruited taxa of Myrtaceae differ in rate of transition along the invasion continuum and where invasions and impacts occur.•On islands, invasions of fleshy-fruited taxa seem to be more common than those of dry-fruited taxa.
Recent studies on patterns of biological invasions in several plant families have confirmed general findings (e.g., taxa with larger native range sizes are more likely to become invasive; and taxa with longer residence time in new regions are more likely to naturalise) and highlighted some context-specific findings relevant for management (e.g., resistance to Phytophthora is a pre-requisite for successful naturalisation in Proteaceae). We explore these issues for the plant family Myrtaceae, specifically by contrasting taxa with fleshy fruits with those with dry fruits to develop hypotheses around the role of seed dispersal in the invasion process. To this end we: 1) compiled a comprehensive list of introduced Myrtaceae; 2) determined the degree of establishment of each species in its introduced range; 3) compared the distribution of native, introduced, and invasive ranges; 4) assessed traits associated with the degree of establishment; and 5) assessed the magnitude and types of impacts of invasive Myrtaceae. A slightly higher proportion of dry-fruited species have been introduced than fleshy-fruited species 170 out of 2257 (7.5 %) vs. 236 out of 3741 (6.7 %), though the difference was not significant. However, introduced dry-fruited Myrtaceae have naturalised more frequently than fleshy-fruited taxa 90 out of 170 (53 %) vs. 40 out of 236 (17 %), whereas naturalised dry-fruited taxa have become invasive at a lower rate 22 out of 90 (24 %) vs. 18 out of 40 (46 %). Invasions of fleshy-fruited taxa seem to be more common on islands. Although invasions by fleshy- and dry-fruited species had similar impact mechanisms and magnitudes, naturalised fleshy-fruited Myrtaceae are more likely to have impacts on islands than dry-fruited confamilials.
Synthesis Fleshy- and dry-fruited taxa of Myrtaceae differ in rates of transition along the invasion continuum and where invasions and impacts occur. We speculate that seed dispersal abilities, lack of competitors, and the availability of areas suitable for germination might explain these differences.
The ability to predict which alien plants will transition from naturalized to invasive prior to their introduction to novel regions is a key goal for conservation and has the potential to increase ...the efficacy of weed risk assessment (WRA). However, multiple factors contribute to plant invasion success (e.g., functional traits, range characteristics, residence time, phylogeny), and they all must be taken into account simultaneously in order to identify meaningful correlates of invasion success. We compiled 146 pairs of phylogenetically paired (congeneric) naturalized and invasive plant species in Australia with similar minimum residence times (i.e., time since introduction in years). These pairs were used to test for differences in 5 functional traits (flowering duration, leaf size, maximum height, specific leaf area SLA, seed mass) and 3 characteristics of species’ native ranges (biome occupancy, mean annual temperature, and rainfall breadth) between naturalized and invasive species. Invasive species, on average, had larger SLA, longer flowering periods, and were taller than their congeneric naturalized relatives. Invaders also exhibited greater tolerance for different environmental conditions in the native range, where they occupied more biomes and a wider breadth of rainfall and temperature conditions than naturalized congeners. However, neither seed mass nor leaf size differed between pairs of naturalized and invasive species. A key finding was the role of SLA in distinguishing between naturalized and invasive pairs. Species with high SLA values were typically associated with faster growth rates, more rapid turnover of leaf material, and shorter lifespans than those species with low SLA. This suite of characteristics may contribute to the ability of a species to transition from naturalized to invasive across a wide range of environmental contexts and disturbance regimes. Our findings will help in the refinement of WRA protocols, and we advocate the inclusion of quantitative traits, in particular SLA, into the WRA schemes.
Biological invasion is a long process that starts with humans introducing intentionally (most of the time) species into a new environment to benefit from the ecosystem services that these species ...provide. Increasing evidence suggests that species providing ecosystem services might be phylogenetically closer than expected, but only a few studies actually demonstrate this. Also, recent studies indicate that naturalized and invasive species are two functionally distinct groups, but evidence that they are also two phylogenetically distinct groups is mixed. Using the set of Australian Acacia species known to have been introduced intentionally by humans to several parts of the world for the ecosystem services they provide, we first tested whether there is a phylogenetic pattern in the subset of introduced species. We found that species moved beyond Australia are phylogenetically more closely related than expected at random, suggesting that the ecosystem services that guide human-mediated introduction of these species into new areas (e.g. famine food, medicines, fuel, fodder, ornament) may be shared between closely related species. We also found that naturalized non-invasive and naturalized invasive species are closely related and both are not a phylogenetically random subset of introduced species based on mean phylogenetic distance, suggesting that naturalization and invasion processes may be phylogenetically mediated. Collectively, our study indicates that phylogeny might play different roles at different stages of the biological invasion process.
In spite of the several studies trying to identify the biological traits that are generally associated with the success of alien plant species, only a few traits are consistently shown to be ...important. Dividing the species into meaningful sub-categories may improve our ability to distinguish successful alien species. We asked whether there are differences between short-lived and long-lived herbaceous aliens regarding the biological traits associated with their success in their introduced range. We used the source-area approach to answer the question by performing a comparative study with those Central-European herbaceous plant species which are invasive or non-invasive aliens in the United States. Biological traits used in the analysis were extracted from European databases. The significant traits (with one exception) conferred invasiveness for only one of the two life history groups. These results outline a particular combination of competition and colonization in both groups, although achieved in different ways. Short-lived invasive species, which are supposed to be good colonizers with effective reproduction and dispersal, are backed by some kind of competitive ability conferred by height; while in the case of competitive and persistent long-lived species, the successful aliens are equipped with traits that make them better colonizers than other perennial alien species (e.g., tolerance for a wide range of anthropogenic disturbance, dispersal through water).
A complete list of all alien taxa ever recorded in the flora of the Czech Republic is presented as an update of the original checklist published in 2002. New data accumulated in the last decade are ...incorporated and the listing and status of some taxa are reassessed based on improved knowledge. Alien flora of the Czech Republic consists of 1454 taxa listed with information on their taxonomic position, life history, geographic origin (or mode of origin, distinguishing anecophyte and hybrid), invasive status (casual; naturalized but not invasive; invasive), residence time status (archaeophyte vs neophyte), mode of introduction into the country (accidental, deliberate), and date of the first record. Additional information on species performance that was not part of the previous catalogue, i.e. on the width of species’ habitat niches, their dominance in invaded communities, and impact, is provided. The Czech alien flora consists of 350 (24.1%) archaeophytes and 1104 (75.9%) neophytes. The increase in the total number of taxa compared to the previous catalogue (1378) is due to addition of 151 taxa and removal of 75 (39 archaeophytes and 36 neophytes), important part of the latter being the reclassification of 41 taxa as native, mostly based on archaeobotanical evidence. The additions represent taxa newly recorded since 2002 and reported in the national literature; taxa resulting from investigation of sources omitted while preparing the previous catalogue; redetermination of previously reported taxa; reassessment of some taxa traditionally considered native for which the evidence suggests the opposite; and inclusion of intraspecific taxa previously not recognized in the flora. There are 44 taxa on the list that are reported in the present study for the first time as aliens introduced to the Czech Republic or escaped from cultivation: Abies concolor, A. grandis, A. nordmanniana, Avena sterilis subsp. ludoviciana, A. ×vilis, Berberis julianae, B. thunbergii, Bidens ferulifolius, Buddleja alternifolia, Buglossoides incrassata subsp. splitgerberi, Buxus sempervirens, Corispermum declinatum, Cotoneaster dielsianus, C. divaricatus, Euphorbia myrsinites, Gleditsia triacanthos, Helleborus orientalis, Hieracium heldreichii, Koelreuteria paniculata, Lonicera periclymenum, Lotus ornithopodioides, Malus baccata, M. pumila, Miscanthus sacchariflorus, Morus alba, Muscari armeniacum, Paeonia lactiflora, Pennisetum alopecuroides, Pinguicula crystallina subsp. hirtiflora, P. grandiflora subsp. rosea, Podophyllum hexandrum, Pyracantha coccinea, Rhodotypos scandens, Rumex patientia × R. tianschanicus ‘Uteuša’, Salix cordata, Sarracenia purpurea, Sasa palmata ‘Nebulosa’, Scolymus maculatus, Spiraea japonica, Tagetes tenuifolia, Thuja occidentalis, Trifolium badium, Vaccinium corymbosum and Viburnum rhytidophyllum. All added and deleted taxa are commented on. Of the total number of taxa, 985 are classified as casuals, 408 as naturalized but not invasive, and 61 as invasive. The reduction in the number of invasive taxa compared to the previous catalogue is due to a more conservative approach adopted here; only taxa that currently spread are considered invasive. Casual taxa are strongly overrepresented among neophytes compared to archaeophytes (76.7% vs 39.4%), while naturalized but non-invasive taxa follow the reversed pattern (18.8% vs 57.4). However, these two groups do not significantly differ in the proportion of invasive taxa. Of introduced neophytes, 250 taxa (22.6%) are considered vanished, i.e. no longer present in the flora, while 23.3% became naturalized, and 4.5% invasive. In addition to the traditional classification based on introduction–naturalization–invasion continuum, taxa were classified into 18 population groups based on their long-term trends in metapopulation dynamics in the country, current state of their populations, and link to the propagule pressure from cultivation. Mapping these population groups onto the unified framework for biological invasions introduced by Blackburn et al. in 2011 made it possible to quantify invasion failures, and boom-and-busts, in the Czech alien flora. Depending on inclusion criteria (whether or not extinct/vanished taxa and hybrids are considered), alien taxa ever recorded in the Czech Republic contribute 29.7–33.1% to the total country’s plant diversity; taking into account only naturalized taxa, a permanent element of the country’s flora, the figure is 14.4–17.5%. Analysis of the dates of the first record, known for 771 neophytes, indicates that alien taxa in the flora have been increasing at a steady pace without any distinct deceleration trend; by extrapolating this data to all 1104 neophytes recorded it is predicted that the projected number would reach 1264 in 2050. Deliberate introduction was involved in 747 cases (51.4%), the remaining 48.6% of taxa are assumed to have arrived by unintentional pathways. Archaeophytes are more abundant in landscapes, occupy on average a wider range of habitat types than neophytes, but reach a lower cover in plant communities. The alien flora is further analysed with respect to representation of genera and families, origin and life history.
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