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The invasive shrub Buddleja davidii performs better in its introduced range
Abstract
It is commonly assumed that invasive plants grow more vigorously in their introduced than in their native range, which is then attributed to release from natural enemies or to microevolutionary changes, or both. However, few studies have tested this assumption by comparing the performance of invasive species in their native vs. introduced ranges. Here, we studied abundance, growth, reproduction, and herbivory in 10 native Chinese and 10 invasive German populations of the invasive shrub Buddleja davidii (Scrophulariaceae; butterfly bush). We found strong evidence for increased plant vigour in the introduced range: plants in invasive populations were significantly taller and had thicker stems, larger inflorescences, and heavier seeds than plants in native populations. These differences in plant performance could not be explained by a more benign climate in the introduced range. Since leaf herbivory was substantially reduced in invasive populations, our data rather suggest that escape from natural enemies, associated with increased plant growth and reproduction, contributes to the invasion success of B. davidii in Central Europe.
... This species is native to Western and Central China and became invasive in Europe and various other parts of the world within the last century (Kriticos et al. 2011). In the field, plants of native Chinese populations of B. davidii suffer significantly more herbivore damage (14.6% mean leaf herbivory across ten populations) than plants of invasive European populations (0.5%, mean of ten populations), suggesting enemy release in the invasive range (Ebeling et al. 2008). The shrub produces multiple classes of defence compounds such as iridoid glycosides, caffeoyl phenylethanoid glycosides, flavonoids and lignans (Houghton 1985;Jensen 2000;Houghton et al. 2003), that may contribute to plant resistance against herbivores or pathogens. ...
... As indicated by very few signs of herbivore damage in the common garden experiment, both native Chinese and invasive European plants of B. davidii were quite resistant against leaf herbivory, but invasive populations were even less damaged than native populations. Our results are in line with field observations that report less than 1% of leaf herbivory on B. davidii in the invasive range, but about 15% of leaf damage by herbivores in the native range (Ebeling et al. 2008). Thus, in the native range, populations may be under high natural selection for anti-herbivore defences. ...
... Thus, in the native range, populations may be under high natural selection for anti-herbivore defences. In the invasive range, B. davidii plant populations are obviously very well defended against herbivores (or released from herbivores that attack this species) and show at the same time higher plant vigour and reproduction compared to native populations (Ebeling et al. 2008). Likewise, in our laboratory bioassays consumption, RCR, RGR and final biomass of L. dispar larvae were more negatively affected when feeding on leaves of invasive B. davidii compared to native populations (Table 2). ...
The local invasion success of invasive plants can be strongly influenced by reduced antagonist pressure and changes in resistance-mediating traits, but information about comprehensive metabolic backgrounds of native versus invasive populations and their functions is lacking. We examined the defence potential of ten native (Chinese) and ten invasive (European) populations of the shrub Buddleja davidii (Scrophulariaceae) grown in a common garden in the invasive range. We compared the chemical defence arsenal of these plant populations, scored their herbivore damage in the field and determined effects on a generalist herbivore species in the laboratory. Moreover, we isolated compounds that mediate resistance against two potential generalist herbivore species and a pathogenic fungus using bioassay-guided fractionation. Metabolic fingerprinting revealed that invasive populations were chemically very similar to one native population (Mupingzhen, Sichuan Province), which may indicate the geographic region from where the species was introduced. Herbivore damage and herbivore performance were reduced on plants of invasive populations. Different chemical compounds provided distinct resistance against the herbivore and fungus species. Based on our results we suggest that the diverse cocktail of chemical compounds, potentially together with physical leaf features, may provide this plant species with an effective defence arsenal against antagonists. In particular, advantageous pre-adaptations and/or shifted profiles of the chemical bouquet may contribute to the success of invasive plants.
... As a consequence, introduced species may provide valuable information on trait evolution and species responses to novel environments (e.g., Colautti & Lau, 2015;Parker et al., 2003). Numerous studies that have compared plant traits between native and introduced populations have reported differences (e.g., Buckley et al., 2003;Ebeling et al., 2008;Turner et al., 2014;Zhang et al., 2018), with introduced plants tending to be larger and more fecund than their conspecifics from the native range (reviewed in Parker et al., 2013). Given that these traits can affect population dynamics, such trait changes can contribute to a higher population growth rate and faster population spread in species' introduced ranges. ...
... As these results indicate, in order to reveal the potential genetic basis (if any) for the success of invasive populations, a comparison under standardized conditions is necessary (Moloney et al., 2009). Plant traits are highly variable within species, with a significant proportion of the variability arising from differences among populations within both native and introduced ranges (e.g., Ebeling et al., 2008;Rosche et al., 2019); for this reason, it is necessary to sample multiple populations from each range. Climate can be the main selective force for plant traits, resulting in phenotypic variation along climatic clines. ...
Introduced species, which establish in novel environments, provide an opportunity to explore trait evolution and how it may contribute to the distribution and spread of species. Here, we explore trait changes of the perennial herb Lupinus polyphyllus based on 11 native populations in the western USA and 17 introduced populations in Finland. More specifically, we investigated whether introduced populations outperformed native populations in traits measured in situ (seed mass) and under common garden conditions during their first year (plant size, flowering probability, and number of flowering shoots). We also explored whether climate of origin (temperature) influenced plant traits and quantified the degree to which trait variability was explained collectively by country and temperature as compared to other population‐level differences. Three out of four plant traits differed between the native and introduced populations; only seed mass was similar between countries, with most of its variation attributed to other sources of intraspecific variation not accounted for by country and temperature. Under common garden conditions, plants originating from introduced populations were larger than those originating from native populations. However, plants from the introduced range flowered less frequently and had fewer flowering shoots than their native‐range counterparts. Temperature of a population's origin influenced plant size in the common garden, with plant size increasing with increasing mean annual temperature in both native and introduced populations. Our results of the first year reveal genetic basis for phenotypic differences in some fitness‐related traits between the native and introduced populations of L. polyphyllus. However, not all of these trait differences necessarily contribute to the invasion success of the species and thus may not be adaptive, which raises a question how persistent the trait differences observed in the first year are later in individuals’ life for perennial herbs. We explored trait changes in the perennial herb Lupinus polyphyllus based on 11 native populations in the western USA and 17 introduced populations in Finland. Our results of the first‐year reveal genetic basis for phenotypic differences in some fitness‐related traits between the native and introduced populations of L. polyphyllus, but also raise a question how persistent the trait differences observed in the first year are later in individuals’ life for perennial herbs.
... Release from leaf herbivores has widely been assumed as a key reason for the vigorous growth of invasive plants in non-native ranges (Ebeling et al. 2008). This may not be the case for A. trifida where only 3% of leaf area was damaged in the native range. ...
... In future studies, taxonomic surveys of both above-and belowground enemies should be conducted in both ranges to test the enemy release hypothesis further and to optimize the experiment design by accounting for the potential issues such as seed provenance and differences in glasshouse conditions. While many studies have generated evidence supporting the enemy release hypothesis (Callaway et al. 2004;Dostálek et al. 2016;Ebeling et al. 2008;Gundale et al. 2014;Liu and Stiling 2006), few studies have considered the effects of both above-and belowground enemies simultaneously. Furthermore, direct evidence for a causal link between enemy release and plant growth is still rare for invasive plants (Engelkes et al. 2008;Liu and Stiling 2006;Meijer et al. 2016). ...
Aims Efforts to concurrently test for enemy release of both above- and belowground enemies for invasive plants in non-native range are limited. Moreover, direct evidence for the causal link between enemy release and performance is rare for invasive plants. Thus, we sought to investigate if above- and/or belowground enemies are involved in the enemy release mechanisms at various life stages of a temperate invader and their consequences on plant community properties.
Methods We conducted field surveys of enemy damage and plant performance, and plant-soil feedback experiments in the glasshouses using Ambrosia trifida in both its non-native and native ranges across the seed, seedling, and adult life stages.
Results Field surveys showed that seeds of A. trifida were more severely damaged by aboveground enemies in the native relative to the non-native range, while the difference in leaf damage between ranges was small. Plant-soil feedback experiments showed that release from belowground enemies was also important, as seed germination and plant growth were significantly reduced in soils fromthe native range compared with soils from the non-native range. Consistent with the above results, A. trifida was larger, produced more seeds, had higher density, and exerted stronger impacts on co-occurring native plants in the non-native relative to the native range.
Conclusion Our results demonstrated that release from both above- and belowground enemies at various life stages contributed to the invasion success of A. trifida in its non-native range and highlighted the importance of considering both above- and belowground enemy release when studying plant invasions.
... Slope (b), r 2 and P are provided for significant linear regressions the invasion, from stochastic events (e.g. introduction of large seeds; Ebeling et al. 2008), and/or from recent crop to wild gene flow (Keller and Taylor 2008;Presotto et al. 2012Presotto et al. , 2017Colautti and Lau 2015). With the exception of one population with unusually large seeds, all the native populations have smaller seeds than each of the invasive populations (Fig. 3b, c). ...
... size of seedlings, competition ability) may be acting on seed mass and size in sunflower. In this sense, the role of biotic and abiotic factors on the evolution of increased seed size in invasive populations has been explored with contrasting results (Ebeling et al. 2008;Hierro et al. 2013). In addition, we found no correlation between seed mass and germination traits in either native or invasive groups, indicating no constraints for the independent evolution of seed size and dormancy. ...
Invasive plants represent a valuable model system for studying contemporary evolution and predicting evolutionary responses to global climate change. Rapid adaptation to climate during range expansion has been recently recognised as a major factor in biological invasions. In this study, by using complementary approaches (common garden studies and the presence of parallel geographic clines), we tested for rapid, adaptive evolution of seed traits in wild sunflower (Helianthus annuus L.). Seeds from 22 wild sunflower populations from native (North America) and invasive (Argentina and Australia) groups were grown in a common garden for 2 years (experiments) and used for evaluating genetic differences in seed traits. Seed germination at two times after harvest, seed mass, and size (length and width) were recorded. In addition, 25 climatic variables were used to characterize the local environment of each population and to evaluate the geographic variation in the traits. Seeds from the invasive group showed larger mass and size and higher germination (lower seed dormancy) than seeds from the native group. Latitudinal cline explained most of the group variation in seed dormancy, but not in seed mass or size. Invasive sunflower from Argentina (but not from Australia) re-established the latitudinal cline observed in the native group. We provide evidence that support rapid, adaptive evolution (< 70 years) of seed dormancy in the invasive Argentinean sunflower in response to warmer environments found in Argentina, suggesting that crop wild relatives can quickly evolve in response to novel abiotic conditions.
... Increased performance of invasive plants in their invasive range has been well documented 1,2 , with many performance comparisons between invasive and native species pairs 3 . However, few studies have compared performance differences among invasive populations 4,5 , which is surprising since quantifying the relative performance of different populations should indicate their invasive potential. Consequently, studies that compare performance differences among invasive populations will help to identify populations that present a higher risk of becoming invasive, and this evidence should be used to guide management of emerging and existing invasive species 6 . ...
... A pragmatic solution to this problem is to collect trait data in situ 9,15 . Indeed, traits measured in situ have been important for studying performance differences between native and invasive populations of several shrub species, such as Buddleja davidii and Rosa rubiginosa 5,16 . ...
Increased performance of invasive plant species in their introduced range vs. their native range has been previously documented. However, performance differences among invasive populations have rarely been explored, despite this information being central to understanding the evolution of invasiveness as well as being a useful basis to inform management of invasive species. To examine variation in performance among populations of Rosa rugosa in its introduced range, and whether introduced populations perform better than native populations, we quantified growth and reproductive traits in five invasive populations in northwest Europe and two native and declining populations in China. Overall, we found that the introduced R. rugosa populations we sampled performed significantly better than the sampled native populations for growth and reproductive traits (2 to 4 fold increase). However, there was significant variation for most traits among the five invasive populations, demonstrating that some introduced populations we sampled were more successful invaders than others. Our findings provide a useful foundation for management of invasive R. rugosa in Europe, and support the recent call for more intra-species research in invasive species biology.
... Towards its absence, all resources can be invested in biological potential "unlocking" (faster and longer growth, higher reproduction, more offspring, larger sizes, better seed vigor) (Brzosko et al. 2016). Idea fairness confirmation are, among others results presented by Ebeling et al. (2008) Smaller vulnerability to pathogens, including fungi and viruses -their natural enemies, in the new environment was noted. Some publications whose results ambiguously relate to hypothesis validity are also available; smaller pressure from natural enemies is pointed out, however, this does not translate into alien species condition, as observed for creeping thistle Cirsium arvense, invasive plant in New Zealand (Cripps et al. 2010). ...
... stawia w pierwotnym miejscu występowania. Wobec jego braku całe swoje zasoby może zainwestować w "uwolnienie" potencjału biologicznego (szybszy lub dłuższy wzrost, wyższa rozrodczość, liczniejsze potomstwo, większe rozmiary, większy wigor nasion)(Brzosko i in. 2016). Potwierdzeniem słuszności tego poglądu są, między innymi wyniki prezentowane przezEbeling i in. (2008), którzy badali populacje rodzime (10 populacji w Chinach) oraz inwazyjne (10 populacji w Niemczech) krzewu budleja Dawida Buddleja davidii; gatunku inwazyjnego w skali Europy i potencjalnie inwazyjnego w Polsce (Tokarska-Guzik i in. 2012, Baza DAISIE). Autorzy wykazali większą żywotność i rozrodczość roślin inwazyjnych, co skutkowało wy ...
The problem of invasive alien species is currently one of the greatest threats to native biotopes and generates significant economic losses and often also risks to human health and life (Vitousek et al. 1996, Regulation... 2014). Despite efforts to implement systemic solutions at both national and international levels, there are still no effective methods for large scale eradication and control of many invasive alien species (Park 2004, Skorupski 2016). This problem concerns not only species representing different systematic groups, but also their parts or products capable of survival and reproduction. The overarching legal document of the European Union is the Regulation (EU) No 1143/2014 of the European Parliament and of the Council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species. This Regulation defines an alien species as any live specimen of a species, subspecies or lower taxon of animals, plants, fungi or micro-organisms introduced outside its natural range; it includes any part, gametes, seeds, eggs or propagules of such species, as well as any hybrids, varieties or breeds that might survive and subsequently reproduce (Regulation... 2014). Invasive alien species means an alien species whose introduction or spread has been found to threaten or adversely impact upon biodiversity and related ecosystem services (Regulation... 2014). Of the 12,000 alien species found in Europe, only 10-15% are invasive (Sundseth 2014). This apparently small proportion is responsible for economic losses of around € 12 billion (Kettunen et al. 2009). The damage caused by invasive alien species in the natural sense is much more difficult to estimate in the monetary sense. For example, it is known that invasive alien species are associated with 54% extinctions of animals for which the causes of extinction have been identified. In 20% of cases, invasive alien species were the only cause of extinction (Clavero and García-Berthou 2005). The immediate causes of the threat of invasive alien species to biodiversity and related ecosystem services are their impact on habitat change, predation on indigenous species, cross-species competition, disease transmission, substitution of native species for much of their range, and hybridization (Sundseth 2014). Abovementioned facts illustrate the scale of the problem of biological invasions of alien species. In the monograph „Invasive alien species – identification ofthreats to protect biodiversity” are presented examples of invasive alien species in Poland, representing various systematic groups, with different causes and pathways for introduction, as well as different history of invasions, degree of spread across the country, status and scale of negative impact on native fauna and flora. The aim of the publication is not only to describe the phenomenon of biological invasions, but also to provide examples of counter-measures based on the best practices supported by scientific research. The monograph is published within the international project “Exchange of knowledge, experiences and best practices in study and control of the invasive alien species populations in Iceland and Poland”, financed by the Financial Mechanism of the European Economic Area (EEA) 2009-2014 and the National Fund for Environmental Protection and Water Management (Poland), and implemented by the Green Federation “GAIA” in partnership with the West-Iceland Nature Research Centre and in cooperation with the Polish Society for Conservation Genetics LUTREOLA, West Pomeranian University of Technology, Szczecin and the Foundation AQUARIUS.
... Invasive plant species are often regarded as being more successful than native species in the introduced range, including increased biomass (Prati and Bossdorf 2004;Kleunen et al. 2011), fecundity (Erfmeier and Bruelheide 2004;Caño et al. 2008;Ebeling et al. 2008), density (Jakobs et al. 2004) and a wider geographical distribution than their native congeners (Crawley 1987;Jakobs et al. 2004). A number of hypotheses have been proposed to explain why introduced populations show increased performance, where the common denominator for most is the escape from regulation coupled with the ability to adapt and exploit decreased regulation in the introduced range (Hierro et al. 2005). ...
... The increased performance of I. glandulifera in the introduced range, coupled with the diminished associated natural enemies, is consistent with other nativeintroduced range comparison studies (Erfmeier and Bruelheide 2004;Widmer et al. 2007;Ebeling et al. 2008). The height of individual plants showed variation between populations in both ranges, for both sampling periods, but consistently the natural populations of Solang and Rohtang were shorter compared to the semi-natural site Chandrkhani. ...
... Consequently, clear patterns of seed size with range type may not be observed. This is reflected in the literature with some studies finding smaller seeds in the introduced range (Oduor et al. 2011), while others found larger seeds (Buckley et al. 2003;Ebeling et al. 2008;Graebner et al. 2012) or no difference (Buckley et al. 2003;Mason et al. 2008). ...
... Therefore, single variable studies (e.g. Buckley et al. 2003;Erfmeier & Bruelheide 2004;Ebeling et al. 2008) may be problematic for the broader understanding of a species invasion success. In this study, we assessed how the reproductive variables that define life-cycle stages differ between the native and introduced ranges of five woody Fabaceae species. ...
Understanding differences in the components of life-cycle stages of species between their native and introduced ranges can provide insights into the process of species transitioning from introduction to naturalization and invasion. We examined reproductive variables of the germination (seed predation, seed viability, time to germination), seed output (crown projection, seed production, seed weight) and dispersal (seed weight, dispersal investment) stages of five woody Fabaceae species, comparing native and introduced ranges. We predicted that each species would differ in reproductive variables of at least one life-cycle stage between their native and introduced ranges, thus allowing us to determine the life-cycle stage most associated with invasion success in the introduced range. Acacia melanoxylon and Paraserianthes lophantha had reduced seed predation in their introduced ranges while P. lophantha also had higher seed viability indicating that the germination life-cycle stage is most strongly associated with their invasion success in the introduced range. Only Acacia longifolia varied between ranges for the seed output stage due to larger plant size, greater seed production and smaller seed size in its introduced range. Similar to A. longifolia, Acacia cyclops had smaller seed size in its introduced range but did not have any other variable differences between ranges suggesting that the dispersal stage is best associated with its invasion success in the introduced range. Surprisingly, Acacia saligna was the only species without a clear life-cycle stage difference between ranges despite it being one of the more invasive acacia species in Australia. Although we found clear differences in reproductive variables associated with life-cycle stages between native and introduced ranges of these five species, these differences were largely species-specific. This suggests that a species invasion strategy into a novel environment is complex and varies among species depending on the environmental context, phenotypic plasticity and genotypic variation in particular traits.
... A more benign climate does therefore not explain the better performance and higher density of L. vulgare in North America. Similarly, several other studies found better performance of invasive plants in their introduced compared to their native range and that these differences could not be explained by different environmental conditions between ranges (Jakobs et al. 2004;Ebeling et al. 2008;Hinz et al. 2012). Vegetation height, vegetation cover as well as species richness of co-occurring species were higher in L. vulgare populations in Europe than in North America, suggesting that invasive L. vulgare populations experience reduced competition. ...
... Leaf-and root herbivory was significantly reduced and flower head herbivores were completely absent in the invaded range, as predicted by the enemy release hypothesis. Reduced herbivore attack in the invaded compared to the native range has also been found by several other biogeographical studies (Wolfe 2002;Bossdorf et al. 2005;Vilà et al. 2005;Ebeling et al. 2008;Adams et al. 2009;Cripps et al. 2010;Alba and Hufbauer 2012;Castells et al. 2013;Maurel et al. 2013;Blaisdell and Roy 2014;Cronin et al. 2015). One reason for the low herbivore attack in the invaded range might be that there are no congeneric species native to North America (USDA, NRCS 2015), which decreases the probability for native specialist insect herbivores to extend their host range to include L. vulgare as a new host plant. ...
Enemy release is a commonly accepted mechanism to explain plant invasions. Both the diploid Leucanthemum vulgare and the morphologically very similar tetraploid Leucanthemum ircutianum have been introduced into North America. To verify which species is more prevalent in North America we sampled 98 Leucanthemum populations and determined their ploidy level. Although polyploidy has repeatedly been proposed to be associated with increased invasiveness in plants, only two of the populations surveyed in North America were the tetraploid L. ircutianum. We tested the enemy release hypothesis by first comparing 20 populations of L. vulgare and 27 populations of L. ircutianum in their native range in Europe, and then comparing the European L. vulgare populations with 31 L. vulgare populations sampled in North America. Characteristics of the site and associated vegetation, plant performance and invertebrate herbivory were recorded. In Europe, plant height and density of the two species were similar but L. vulgare produced more flower heads than L. ircutianum. Leucanthemum vulgare in North America was 17 % taller, produced twice as many flower heads and grew much denser compared to L. vulgare in Europe. Attack rates by root- and leaf-feeding herbivores on L. vulgare in Europe (34 and 75 %) was comparable to that on L. ircutianum (26 and 71 %) but higher than that on L. vulgare in North America (10 and 3 %). However, herbivore load and leaf damage were low in Europe. Cover and height of the co-occurring vegetation was higher in L. vulgare populations in the native than in the introduced range, suggesting that a shift in plant competition may more easily explain the invasion success of L. vulgare than escape from herbivory.
... Plusieurs études comparatives aboutissent à la conclusion qu'une espèce envahissante est plus grande, produit plus de matière végétale et de graines dans son aire d'accueil que dans son aire d'origine (e.g. Crawley 1987;Willis & Blossey 1999;Jakobs et al. 2004;Ebeling et al. 2008). Crawley (1987) attribue ces différences à une diminution de la pression d'herbivorie, due à l'absence des phytophages naturels de l'espèce dans la région d'accueil. ...
... Moreover, field measurements showed that introduced B. davidii performs better than in its native range (Ebeling et al. 2008). Large water supply during the experiment could have encouraged I. glandulifera biomass production, as this species growth appears to be proportional to water availability (Beerling & Perrins 1993). ...
The objective of this work is to evaluate plant species origin importance for biological invasion consequences, through the analysis of the influence of native and exotic dominant plant species for ecosystem functioning. Five pairs of native dominant species (Agrostis stolonifera, Rubus caesius, Populus nigra, Urtica dioica et Salix alba) and exotic invasive species (Paspalum distichum, Fallopia japonica, Buddleja davidii, Impatiens glandulifera et Acer negundo) were compared for litter breakdown process and primary production. A more detailed analysis evaluates the consequences of A. negundo invasion for riparian forests. Our results indicate that the lack of coevolution between exotic species and the organisms of recipient areas has little implications for ecosystem functioning, even if exotic invasive species can be more efficient in some ecological processes. No general pattern can be drawn for functional consequences of native dominant species replacement by exotic invasive ones.
... Understanding the ecological factors that regulate an invasive species in its native range can help resource managers develop appropriate control strategies in the introduced range (Harris et al. 2011; St. Quinton et al. 2011). Invasive plant species are often regarded as being more successful than native species in the introduced range, including increased biomass (Prati and Bossdorf 2004; Kleunen et al. 2011), fecundity (Erfmeier and Bruelheide 2004; Caño et al. 2008; Ebeling et al. 2008), density (Jakobs et al. 2004) and a wider geographical distribution than their native congeners (Crawley 1987; Jakobs et al. 2004). A number of hypotheses have been proposed to explain why introduced populations show increased performance, where the common denominator for most is the escape from regulation coupled with the ability to adapt and exploit decreased regulation in the introduced range (Hierro et al. 2005). ...
... The increased performance of I. glandulifera in the introduced range, coupled with the diminished associated natural enemies, is consistent with other nativeintroduced range comparison studies (Erfmeier and Bruelheide 2004; Widmer et al. 2007; Ebeling et al. 2008 ). The height of individual plants showed variation between populations in both ranges, for both sampling periods, but consistently the natural populations of Solang and Rohtang were shorter compared to the semi-natural site Chandrkhani. ...
Understanding the ecology of plant species in their whole range (native and introduced) can provide insights into those that become problematic weeds in the introduced range despite being benign components of the vegetative community in the native range. We studied the morphological traits of Impatiens glandulifera in the native (Indian Himalayas) and introduced (UK) range and evaluated what influences natural enemies and arbuscular mycorrhizal fungi (AMF) have on plant performance. We compared height, total leaf area, root: shoot ratio, natural enemy damage and the colonisation of AMF from individual plants within and between ranges twice in 2010 during the months of June and August. In addition, in August 2010, we estimated the number of reproductive units (expressed as the sum of flowers, seed capsule and seeds) at each site. We found that all morphological traits varied between populations and countries, though in general introduced populations, and the semi-natural population in India, showed higher performance compared to natural native populations. There was only an indication that natural enemy damage, which was significantly higher in the native range, negatively affected reproductive units. Within the introduced range, the percentage colonisation of AMF was negatively associated with plant performance indicating that I. glandulifera may associate with an incompatible AMF species incurring a cost to invasive populations. We conclude that species which are heavily regulated in the native range, though still show high levels of performance, should be considered undesirable introductions into similar ecoclimatic ranges due to the potential that these species will become highly invasive species.
... Indeed, recent work by Firn et al. (2011), which compared native and introduced populations of plants that are not particularly problematic invaders, showed that a broad range of patterns exists, including introduced populations performing better, similarly, or worse than native populations. However, because data on performance are only sometimes coupled with data describing environmental differences between ranges (Edwards et al. 1998;Jakobs et al. 2004;Ebeling et al. 2008;Cripps et al. 2010), the factors most often associated with increased performance are not immediately clear for most species. ...
... However, despite their increased prevalence, grasshoppers have only partially filled the role of the leaf-feeding specialist C. verbasci, as evidenced by the significant decrease in damage incurred by introduced plants. This pattern reveals that enemy escape has occurred in this system, and is consistent with the findings of others who have estimated leaf damage in a biogeographic context (Vilá et al. 2005;Adams et al. 2009;Ebeling et al. 2008). ...
Biogeographic data describing performance differences in native and introduced populations of invasive species are increasingly coming to light, revealing that introduced populations often perform better than their native conspecifics. However, this pattern is not universal, nor is it well studied in species that fall on the more “benign” end of the invasion spectrum. Furthermore, performance data are infrequently linked with variation in key environmental factors experienced by populations in each range, making it difficult to assess which factors are typically associated with shifts in performance. Here we assessed performance in native and introduced populations of Verbascum thapsus (common mullein), an herbaceous biennial that was initially introduced to the eastern US from Europe, but which has subsequently expanded its range into semi-arid mountainous regions of the western US, where it appears to be more problematic. Indeed, we found that introduced populations were larger than native populations, with over half of them comprising more than 500 individuals, a size seldom achieved in the native range. We further explored the role that abiotic factors (latitude, elevation, and precipitation) might serve in shaping performance in European and western US populations, and quantified variation in two biotic factors relevant to invasion: herbivory, and the potential for competition from co-occurring vegetation (as well as its inverse, the availability of bare ground). When the influence of abiotic factors was not considered, introduced mullein performed better than native mullein in terms of plant density and plant size (i.e., number of leaves and area covered by the basal rosette). When the influence of abiotic factors was statistically taken into account, the difference in the density of native and introduced populations remained strong, while the difference in number of leaves was reduced, though it remained significant. In contrast, controlling for abiotic factors reversed the pattern for plant area such that plants in introduced populations performed less well than natives. These results suggest that the difference in climate experienced by native and introduced populations is an important driver of mullein performance only for plant area. Thus, increased performance in western US population likely hinges in part on shifts in biotic factors. Indeed, we found a reduction in the prevalence of several herbivore guilds on introduced relative to native mullein, accompanied by a significant decrease in chewing damage in introduced populations. We also found differences in the potential for competition: cover of vegetation is significantly higher in native mullein populations than in introduced populations, and increasing cover of vegetation is associated with declining performance (i.e., density) of native populations but not introduced populations. In sum, the introduced populations performed better than the native populations in several respects; thus, although mullein is considered a relatively ‘benign’ introduced species, it has the potential to differentially impact resident communities in its native and introduced ranges. Additionally, despite the disparity in abiotic conditions experienced by native and introduced populations, these factors do not appear to consistently drive differences in performance. Instead, evidence suggests that enemy escape and shifts in the competitive regime may facilitate mullein invasion. We use our data to propose hypotheses to be tested experimentally.
... Effect on enemy diversity: Distantly related exotics typically experience greater reductions in enemy diversity (Figure 3h, blue line), as the ability for enemies to switch from co-occurring natives is lower (Ebeling et al., 2008). In contrast, exotics with congeners in the invaded range tend to accumulate enemies quickly (Mitchell et al., 2006; Figure 3h, black line) or are targeted by enemies to such an extent they show no evidence for release at all (Ivison et al., 2023;Figure 3h, red line). ...
The enemy release hypothesis (ERH) is the best-known hypothesis explaining high performance (e.g. rapid population growth) of exotic species. However, the current framing of the ERH does not explicitly link evidence of enemy release with exotic performance. This leads to uncertainty regarding the role of enemy release in biological invasions. Here, we demonstrate that the effect of enemy release on exotic performance is the product of three factors: enemy impact, enemy diversity, and host adaptation. These factors are modulated by seven contexts: time since introduction, resource availability, phylogenetic relatedness of exotic and native species, host–enemy asynchronicity, number of introduction events, type of enemy, and strength of growth–defence trade-offs. ERH-focused studies frequently test different factors under different contexts. This can lead to inconsistent findings, which typifies current evidence for the ERH. For example, over 80% of meta-analyses fail to consider ecological contexts which can alter study findings; we demonstrate this by re-analysing a recent ERH synthesis. Structuring the ERH around factors and contexts promotes generalisable predictions about when and where exotic species may benefit from enemy release, empowering effective management. Our mechanistic factor–context framework clearly lays out the evidence required to support the ERH, unifies many enemy-related invasion hypotheses, and enhances predictive capacity.
... Effect on enemy diversity: Distantly related exotics typically experience greater reductions in enemy diversity (Figure 3h, blue line), as the ability for enemies to switch from co-occurring natives is lower (Ebeling et al., 2008). In contrast, exotics with congeners in the invaded range tend to accumulate enemies quickly (Mitchell et al., 2006; Figure 3h, black line) or are targeted by enemies to such an extent they show no evidence for release at all (Ivison et al., 2023;Figure 3h, red line). ...
The enemy release hypothesis (ERH) is the best-known hypothesis explaining high performance (e.g., rapid population growth) of exotic species. However, the current framing of the ERH does not explicitly link evidence of enemy release with exotic performance. This leads to uncertainty regarding the role of enemy release in biological invasions. Here we demonstrate that the effect of enemy release on exotic performance is the product of three factors: enemy impact, enemy diversity, and host adaptation. These factors are modulated by seven contexts: time since introduction, resource availability, phylogenetic relatedness of exotic and native species, host-enemy asynchronicity, number of introduction events, type of enemy, and strength of growth-defence trade-offs. ERH-focused studies frequently test different factors under different contexts, leading to inconsistent findings, which characterise current evidence for the ERH. For example, over 80% of meta-analyses fail to consider ecological contexts that can modulate study findings; we demonstrate this by re-analysing a recent ERH synthesis. Structuring the ERH around factors and contexts promotes generalisable predictions about when and where exotic species may benefit from enemy release, empowering effective management. Our mechanistic factor-context framework clearly lays out the evidence required to support the ERH, unifies many enemy-related invasion hypotheses and enhances predictive capacity.
... A more formal but less commonly applied observational approach is to deploy 'randomized surveys' using a random sampling design to locate populations (e.g. spatially stratifying and randomly assigning sites across the range; Ebeling et al., 2008, Herrera et al., 2011 for comparing metrics between ranges. Finally, in situ 'field experiments' facilitate experimental manipulation of factors to better isolate confounding factors and formally test postulated invasion and disturbance effects, but poor recruitment in the native range and ethical constraints on growing invaders in the introduced range hindered comparisons of performance and plant-fungal interactions. ...
Understanding the causes of plant invasions requires that parallel field studies are conducted in the native and introduced ranges to elucidate how biogeographical shifts alter the individual performance, population success and community‐level impacts of invading plants. Three primary methods deployed in in situ biogeographical studies are directed surveys, where researchers seek out populations of target species, randomized surveys and field experiments. Despite the importance of these approaches for advancing biogeographical research, their relative merits have not been evaluated.
We concurrently deployed directed surveys, randomized surveys and in situ field experiments for studying six grassland plant species in the native and introduced ranges. Metrics included plant size, fecundity, recruitment, abundance and invader impact, as well as soil properties and root associations with putative fungal mutualists and pathogens.
Consistent with key invasion hypotheses, Bromus tectorum experienced increased size and fecundity in the introduced range linked to population increases and significant invader impacts, along with altered fungal associations. However, performance differences did not predict population increases and invader impacts across species. A notable finding was that disturbance facilitated greater recruitment in the introduced range for most species, thereby playing a crucial, though underappreciated, role in driving invader success.
Directed surveys consistently generated information on plant performance and fungal associations. However, soil sampling suggested that directed surveys may have been biased towards disturbed conditions for half the species. Randomized surveys generated robust data for population comparisons and impact, but generally failed to produce performance metrics for species that were uncommon or flowered outside the peak sampling window. Field experiments controlled for bias and confounding factors and provided rare information on recruitment and disturbance effects, but poor recruitment in the native range and ethical constraints on growing invaders in the introduced range hindered comparisons of performance and plant–fungal interactions.
Synthesis . Each method had strengths and weaknesses. However, when combined they provided complementary information to paint the most complete biogeographical picture to date for several introduced plants. We propose a hybrid approach to optimize biogeographical studies.
... It was introduced to North America, South America, Europe, Africa, and New Zealand as an ornamental plant (Tallent-Halsell & Watt 2009). The naturalization and invasion of B. davidii have been confirmed in many European countries (Ebeling et al. 2008;Randall 2017). In Poland, it is a locally established alien species treated as potentially invasive in semi-natural dry grasslands and scrubland facies on calcareous substrates (Tokarska- Guzik et al. 2012). ...
The presented eighth part of the series includes thirteen new chorological records of vascular plants, one from Hungary, six from Poland and six from Slovakia. In Hungary, Ventenata dubia is reported. In Poland, two native taxa Bolboschoenus planiculmis and Najas marina subsp. marina and four alien taxa Buddleja davidii, Lupinus ehrenbergii var. ehrenbergii, Miscanthus sacchariflorus and Sedum sarmentosum are reported. In Slovakia, two native taxa Taraxacum paucilobum with distribution map and Cotoneaster integerrimus are reported as well as four alien taxa Azolla filiculoides, Eichhornia crassipes, Euphorbia prostrata and Pistia stratioites.
... In soybean field, the invasion is realized through increased plasticity of stem length, but the decreased plasticity in corn field, through adaptation mechanism (Weining, 2000). Plants occupying a wide ecological range and diverse habitats often have phenotypic variations in morphology, phenology, physiology, and life history, according to changes in local ecological environment factors (Blossey and Notzold, 1995;Siemann and Rogers, 2001;Ebeling et al., 2008). However, it is unclear if this variation is a simple response of plants to climatic conditions, or an adaptive evolution based on local environmental conditions. ...
Extensive studies have shown that the success of invasive plants in large environmental gradients can be partly attributed to related factors, including phenotypic plasticity and rapid evolution. To enhance their ability to compete and invade, invasive plants often show higher morphological and physiological plasticity to adapt to different habitat conditions. In the past two decades, invasive species have expanded to some new habitats in North and Northwest China, including arid oasis agricultural zones, which are disturbed by human activities, and the ecosystem itself is very fragile. To evaluate the ecological adaptability of invasive plants widely distributed in North and Northwest China, we studied the physiological response and tolerance mechanism of different geographical populations of Solanum rostratum Dunal to different drought-stress gradients in extremely arid regions (Xinjiang population) and semi-arid regions (Inner Mongolia population). The results showed that with the aggravation of drought stress, S. rostratum from different geographical populations adopted different physiological mechanisms to drought stress. Xinjiang population was mostly affected by root/shoot ratio and chlorophyll fluorescence characteristics, showing higher plasticity in the net and total photosynthetic rates, while the Inner Mongolia population mainly relied on the accumulation of osmotic adjustment substances, higher leaf dry matter content, and increased malondialdehyde to cope with drought stress. Based on these results, we concluded that the physiological responses of S. rostratum invading different habitats in northern China to drought stress were significantly different. The drought resistance of the Xinjiang population was higher than that of the Inner Mongolia population. In general, S. rostratum can be widely adapted to both harsh and mild habitats through phenotypic plasticity, threatening agricultural production and ecological environment security in northern China.
... Ecological factors such as human disturbance may regulate populations similarly in both ranges for A. platanoides and naturalization may not necessarily involve evolutionary changes . Introduced individuals may not be better interspecific competitors relative to their native conspecifics , and the size of the recipient habitats available for the species may be too variable and limited, i.e. the forests in southern Ontario are very fragmented (Ebeling et al. 2008). ...
... Correia et al. (2016) reported an absence of pre-dispersal predation of A. dealbata and A. longifolia seeds in the alien range as well as a lower proportion of aborted seeds compared to the native range, resulting in the formation of denser seed banks in the abroad than home range for these two species. Similarly, lower levels of herbivory and higher fecundity have been reported in alien populations (Germany) of the invasive shrub Buddleja davidii compared to native range populations from China (Ebeling et al. 2008), which may explain the consistently denser seed banks observed for this species in its alien range Osborne 2009a, 2010;Li et al. 2011;Kundell et al. 2014). The extent to which lower seed predation affects the seed bank of this species in the alien range, however, remains unclear. ...
The ability to form persistent seed banks might contribute substantially to determine the invasion potential of alien plants in their new distribution ranges, given the role of seed banks as sources of propagules, genetic diversity, and in spreading the risk of germination failure over time. Using the largest seed bank dataset collated to date, comprising 14,293 records for 2566 species, we examined whether the type (transient vs persistent) and density of the seed banks of invasive species differ in their native (home) and alien (abroad) range, and whether these attributes differ among invasive and non-invasive congeners, at home and abroad. A lower probability of forming a persistent seed bank in the alien range was identified when analyzing data for 140 invasive species, although phylogenetic analyses run for 104 of those species did not confirm such differences. However, invasive woody species formed denser seed banks in the alien range, suggesting greater seed production and/or lower seed predation or mortality in the alien than native range. Interestingly, invasive species consistently showed a higher probability of forming persistent seed banks as well as denser seed banks than their non-invasive congeners in their native range, but not in their alien range. These findings provide the first quantitative evidence, based on a large number of species globally, of preadaptation with respect to species life-history traits resulting in the formation of a persistent seed bank in invasive species compared to their non-invasive congeners. The fact that both invasive and non-invasive congeners have similar probabilities of forming persistent seed banks abroad suggests that this might be an important attribute for the establishment of alien species in new ranges (naturalization phase), but not for their spread (invasion phase). Our findings also indicate that the characteristics of native seed banks should be an important component of risk assessments aimed at identifying species that are more likely to become invasive if introduced in new ranges.
... The flowers of porterweed are semi-immersed in depressions or furrows in the rachis of the spike making it possible to estimate total seed production, even after dehiscence. In other studies, stem count has been used to predict the number of inflorescences and the inflorescence length has been used to predict the number of seed capsules (Ebeling et al., 2007). Also, seed capsule weight has been used to project number of seeds per plant (Wilson et al., 2004b). ...
Nettleleaf porterweed ( Stachytarpheta cayennensis ) is a potentially invasive ornamental plant in Florida. Plant growth, visual quality, flowering, and seed viability were assessed for nettleleaf porterweed and eight closely related alternatives planted in northern and southern Florida. In northern Florida, ‘Mario Pollsa’ porterweed ( Stachytarpheta spp.), ‘Violacea’ porterweed ( Stachytarpheta mutabilis ), ‘Naples Lilac’ porterweed ( Stachytarpheta spp.), ‘Red Compact’ porterweed ( Stachytarpheta speciosa ), and nettleleaf porterweed ( Stachytarpheta cayennensis ) achieved high flower ratings between 4 (average to good flowering) and 5 (abundant flowering, peak bloom) during 4 or more months. Also, jamaican porterweed ( Stachytarpheta jamaicensis ), ‘Violacea’ porterweed, ‘Red Compact’ porterweed, and nettleleaf porterweed achieved visual quality ratings between 4 and 5 (good to excellent quality) throughout most of the study. In southern Florida, the same cultivars received high flower ratings but generally for shorter periods of time. Also, ‘Violacea’ porterweed and ‘Red Compact’ porterweed consistently received visual quality ratings that were above 4 (good quality, very desirable). During the course of the 28-week study, nettleleaf porterweed produced the greatest number of spiked inflorescences with 39% to 80% seed viability. At both locations, ‘Violacea’ porterweed did not produce any viable seed and seed viability was less than 10% for ‘Mario Pollsa’ porterweed, coral porterweed ( Stachytarpheta mutabilis ), and ‘Naples Lilac’ porterweed.
... Er ist seit den 1920ern im Gartenbau als Zierpflanze in Verwendung. Die Art ist ein invasiver Neophyt, also eine nicht heimische Pflanzenart, die sich rasch massenhaft ausbreitet und heimische Ökosysteme gefährdet(Kowarik and Starfinger 2002;Ebeling, Hensen and Auge 2008). Außerhalb von Gärten und Parkanlagen, kommt der Sommerflieder an vielen ruderalen Standorten, Kiesflächen und entlang von Wasserflächen vor(Essl, Rabitsch and Breuss 2002). ...
St. Stephen's Cathedral in Vienna (more commonly known as the “Stephansdom”) is not just a popular landmark of the city but also an eminent part of its World Heritage. This study documents the monitoring of the north-eastern roof of the Stephansdom with the goal of assessing the condition of the roofing itself as well as surveying the vegetation growing on the roof. The first visual assessment of the north-eastern roof of the cathedral occurred in May 2017, and the roof vegetation was surveyed in mid-June 2017 with the help of four professional climbers who roped down from the gable. In the course of the vegetation survey in June 2017, 14 plant species from 7 families were found on St. Stephen’s north-eastern roof. The most common species was Asplenium ruta-muraria (wall-rue), which exclusively inhabits the crevices between the roof tiles where wind-blown sediment collects. Horse hair and tile fragments were found in the adult A. ruta-muraria individuals. Most of the tree species discovered were pioneer species of the genus Populus (poplar tree). Discovered damage to the roof included broken and missing tiles as well as flaking and spalling of the ceramic and paint. To facilitate sustained preservation of the historic cathedral roof, regular monitoring of the entire roof surface and removal of the vegetation at an early stage without the use of chemical agents are urgently recommended. This study represents an excellent example of how unconventional means, e.g. the cooperation with a company like HOLZCO, can be employed to survey urban vegetation.
... Key vegetative and reproductive traits of Lantana, considered in the study emerged as prominent traits that potentially benefit species' range expansion. Ebeling et al. (2008) suggested that larger plant size and higher fecundity confer rapid adaptation to the species in the introduced range. Larger plant size of Lantana in India might be advantageous in highly competitive communities. ...
Lantana camara L. (sensu lato), one of the world’s worst invaders has disseminated rapidly and continues to expand in its invaded range. Invasiveness of a species can broadly be gauged by determining trait values, considered as manifestation of performance ability. In spite of vast range expansion, performance of Lantana in its different invaded ranges is under-studied. We measured vegetative and reproductive traits of Lantana in two of its invaded ranges with differential residence timeframes viz. India and South Africa. Comparative field observations revealed that the Indian populations were more vigorous than those in South Africa in terms of key traits. NMS ordination revealed that traits of Lantana in both ranges were significantly related to climatic variables. Substantially different mean annual temperature and/or residence timeframe in the two invaded ranges might have driven contrasting performance ability of Lantana. Results highlight that plant invaders may experience disproportionate success in varied invaded ranges owing to distinction in time elapsed since initial introduction in tandem with environmental factors, which may have crucial implications for their management. However, the study calls for further disentangling the factor(s) which contribute to species’ invasive success in the invaded range.
... Despite several previous studies on how global invaders respond to new environments (Ebeling et al. 2008;Alba & Hufbauer 2012;Kumschick et al. 2013), few have addressed the question of where and why they are able to germinate (Hou et al. 2014;Leiblein-Wild et al. 2014;Menge et al. 2016), grow and establish . A quantification of their early stage performance would allow predictions on the future range expansion of global invaders (Parker et al. 2003;Bossdorf et al. 2005). ...
Successful germination and seedling emergence in new environments are crucial first steps in the life history of global plant invaders and thus play a key role in processes of range expansion.
We examined the germination and seedling emergence success of three global plant invaders – Lupinus polyphyllus, Senecio inaequidens and Verbascum thapsus – in greenhouses and climate chambers under climate regimes corresponding to seven eco‐regions. Seed materials were collected from one non‐native population for L. polyphyllus and S. inaequidens , and from 12 populations for V. thapsus (six natives and six non‐natives).
Experimental climates had significant effects on species responses. No species germinated in the dry (humidity ≤ 50%) and cool (≤ 5 °C) experimental climates. But all species germinated and emerged in two moderately cool (12–19 °C) and in three warm (24–27 °C) experimental climates. In general, V. thapsus showed higher fitness than S. inaequidens and L. polyphyllus . The climate of the seed source region influenced responses of native and non‐native populations of V. thapsus . Non‐native populations of V. thapsus , originating from the warmer seed source, showed higher performance in warm experimental climates and lower performance in moderately cool experimental climates compared to native populations. Responses of V. thapsus populations were also related to precipitation of the seed source region in moderately dry experimental climates.
The warm, semi‐arid and humid experimental climates are suitable for the crucial first steps of invasion success for L. polyphyllus , S. inaequidens and V. thapsus . The species adaptation to its source region modified the responses of our studied plants under different experimental climates representing major eco‐regions of the world.
... That is, inferences derived from studies from other ecosystems with more typical invasion processes may not shed much light on the ecological reality of our study system. For example, Lima Junior et al. (2015), also working with fishes from the upper Paraná floodplain, found no support for the general hypothesis that body size of non-native species is larger in invaded habitats (a general trend reported for plants and animals, e.g., Ebeling et al., 2008;Darling et al., 2011). Perhaps the upper Paraná River floodplain is at an advanced stage of invasional meltdown (Simberloff & Von Holle, 1999) which precludes other mechanisms such as biotic resistance from having a significant influence on the establishment of non-native species. ...
The invasion paradox refers to the existence of biotic resistance and biotic acceptance hypotheses. According to the biotic resistance hypothesis, the higher the richness present in a community, the more resistant it is against invaders. In contrast, the biotic acceptance hypothesis states that if the environment is suitable for a high richness of native species, it will be similarly suitable for establishment of non-native species. Previous studies on terrestrial plant communities considered the scale-dependent nature of native and non-native relationships: the relationship tends to be negative at small scales (biotic resistance) and positive at broader scales (biotic acceptance). We tested the hypothesized role of spatial scale on the relationship between non-native and native species richness using a spatially nested design and a long-term dataset (146 communities sampled during 13 years) of fish species richness from the upper Paraná River floodplain, Brazil. Contrary to expectations, non-native fish species richness was positively correlated with native species richness at all spatial scales. Mobility of vertebrates, mode of invasion, and environmental disturbance may affect the role of spatial scale in potentially mediating relative importance of biotic acceptance versus resistance. In this context, the present study provides a unique contribution towards resolving the invasion paradox.
... Several of these criteria suggest native species will make inferior biofuel feedstocks compared with exotic alternatives. Firstly, bioenergy crops planted in their native bioregion will retain their full suite of pests and diseases, whereas exotic species planted in novel habitats have the potential to escape some, if not all, of their natural enemies (herbivores and plant pathogens) resulting in increased growth rates (Ebeling et al. 2008). However, exotic plants are not always free of natural enemies as similarities between congeners may facilitate host shifts of native herbivores to exotic plants (Frenzel and Brandl 2003). ...
Bioenergy at its most fundamental level is about burning the accumulated proceeds of photosynthesis. Fossil bioenergy, in the form of coal, fueled the early industrial revolution and today, along with oil, sustains contemporary human civilization. In the early 20th century, these concentrated and conveniently packaged fossil fuels largely replaced wood, tallow, and dung as sources of heat and animal traction as a source of power; 200 years ago, 20% of U.S. agricultural land was devoted to growing “fuel” to feed livestock (Sexton et al. 2007). Today, many in the world recognize the many environmental, geopolitical, and economic costs of fossil fuel dependence, and the growing immediacy of the exhaustion of our fossil fuel reserves. As a result of this recognition, we find ourselves reconsidering bioenergy, primarily from living plants, as a partial solution to these problems. Despite the recent attention paid to liquid biofuels, all biomass allocated to energy worldwide currently represents only approximately 10% of the total of 11,410 million tons of oil equivalent used per annum (IEA 2007).
... Increased seed production and heavier seeds were also shown for other invasive plants including Buddleja davidii Franch. (Ebeling et al., 2008) and Cytisus scoparius (L.) Link (Buckley et al., 2003). Specialist herbivores in the native range may affect seed size either through reduced vigour of the parent plants and consequent maternal effects (Agrawal, 2001) or through selection against large seeds (Moegenburg, 1996). ...
Understanding why some plant species become invasive is important to predict and prevent future weed threats and identify appropriate management strategies. Many hypotheses have been proposed to explain why plants become invasive, yet few studies have quantitatively compared plant and population parameters between native and introduced range populations to gain an objective perspective on the causes of plant invasion. The present study uses a biogeographical field survey to compare morphological and reproductive traits and abundance between the native range (USA) and two introduced ranges (Australia and South Africa) of Sagittaria platyphylla (Engelm.) J.G. Sm (Alismataceae), a highly invasive freshwater macrophyte. Introduced and native populations differed in sexual reproductive output with the number of achenes per fruiting head and individual achene weight found to be 40% and 50% greater in introduced populations respectively. However, no other morphological traits were found to be consistently different between the native and both introduced ranges, especially after taking into account differences in environmental conditions between the three ranges. Although populations in introduced regions were larger and occupied greater percentage cover, no differences in plant density were evident. Our results suggest that, apart from sexual reproduction, many of the trait patterns observed in S. platyphylla are influenced by environmental and habitat conditions within the native and invaded ranges. We conclude that the enemy release hypothesis best explains the results observed for sexual reproduction. In particular, we hypothesise that a release from natural enemies, specifically a pre-dispersal seed predator, may induce reproductive plasticity in S. platyphylla.
... The Scrophulariaceae, which mostly consisted in the exotic Butterfly bush (Buddleja davidii, 65% of the samples from this plant family), also attracted rich and specialized flower visitor community, in line with previous work suggesting that using both native and non-native species may lead to an optimal management strategy (Salisbury et al. 2015). Such scheme however requires careful consideration because exotic species invading native ecosystems (as does the Butterfly bush) may have negative consequences (Ebeling et al. 2008). ...
Land-use intensification and resulting habitat loss are put forward as the main causes of flower visitor decline. However, the impact of urbanization, the prime driver of land-use intensification in Europe, is poorly studied. In particular, our understanding of whether and how it affects the composition and functioning of flower visitor assemblages is scant, yet required to cope with increasing urbanization worldwide. Here, we use a nation-wide dataset of plant–flower visitor (Coleoptera, Diptera, Hymenoptera, Lepidoptera) interactions sampled by citizen scientists following a standardized protocol to assess macroecological changes in richness and composition of flower visitor communities with urbanization. We measured the community composition by quantifying the relative occurrence of generalist and specialist flower visitors based on their specialisation on flowering plant families. We show that urbanization is associated with reduced flower visitor richness and a shift in community composition toward generalist insects, indicating a modification of the functional composition of communities. These results suggest that urbanization affects not only the richness of flower visitor assemblages but may also cause their large-scale functional homogenization. Future research should focus on designing measures to reconcile urban development with flower visitor conservation.
... Likewise, where multiple introductions from differing sites of origin have occurred, genetic diversity of the introduced populations can equal or be even higher than that of the native populations (Bossdorf et al., 2005;Harris et al., 2012;Wolf et al., 2012). Detailed insights into these aspects of invasion can often be gained by comparing non-native and native populations of the invasive species (Bossdorf et al., 2005;Hierro et al., 2005;Ebeling et al., 2008;Hirsch et al., 2011;Harris et al., 2012;Cahill & Viard, 2014). ...
It is commonly assumed that plants have more genetic diversity in their native range than in areas where they have been introduced due to founder effects. However, few studies have proven this assumption and included the comparison between non-native and native ranges. We analyzed AFLP fingerprint patterns of 149 individuals from five native (China) and five non-native (Argentina) populations of Cotoneaster franchetii, a shrub which successfully invades different habitats and forms extensive monospecific stands. We compared genetic diversity estimates and assessed genetic differentiation among populations by inspecting FST values and conducting a PCoA, an AMOVA and a Mantel test. No evidence was found for reduced genetic diversity in non-native populations while the PCoA revealed two distinct groups, reflecting their Chinese and Argentine origin. The exceptions were ten individuals from two Chinese populations that clustered within the Argentine populations, supporting the idea of multiple introductions from China to Argentina.
... Nevertheless, the physiological processes of growth and resource acquisition are likely to be particularly crucial in invasions. Physiological plasticity is explicitly included in the EICA hypothesis, as invasive species under reduced enemy pressure may reallocate resources to growth and reproduction (Ebeling et al. 2008). Invasive species may outcompete natives through a jack-of-all-trades strategy, where the invasive species is able to maintain fitness in unfavorable environments; through a master-of-some strategy, where the invasive species succeeds by having particularly high fitness in favorable environments; or through a combination of the two, known as a jack-and-master strategy (Richards et al. 2006). ...
Premise of research. Invasive plants usually have growth and reproductive abilities that allow them to cope with new habitats and environments. The small balsam, Impatiens parviflora, is one of the most widespread annual invasive species in Europe. As no precise physiological assessment for this species has been performed, we compared physiological traits linked to growth performance in contrasting environments. Methodology. Plants were cultivated in growth chambers under four different treatments varying by light and water conditions. We assessed the impact of water stress and low light levels on traits related to plant growth, leaf physiology, photosynthesis, and water status. Pivotal results. Tolerance of low light level was reflected by several morphological and physiological characteristics. The number of leaves initiated was not affected by light condition, whereas specific leaf area increased for plants grown under low light. In addition, the chlorophyll fluorescence parameters revealed that low light did not affect the light-dependent reactions of photosynthesis. Although the net rate of photosynthesis was reduced, plant growth was not markedly affected. Our results thus suggest that I. parviflora generally copes well with shady conditions. The traits involved in efficiency of water use and water conservation indicated that I. parviflora is also highly tolerant to water stress. Although a reduction in plant growth and abscission of old leaves were observed after 4 wk of stress, I. parviflora demonstrated several mechanisms to maintain the light-dependent reactions of photosynthesis under water-stress conditions. Water use efficiency strongly increased in response to water stress, and plants adjusted their water potential to maintain their water supply. Conclusions. Impatiens parviflora shows physiological traits that allow plant growth under contrasting and stressful environments. These physiological traits may contribute to its invasive ability.
... For example, body size is an important biological characteristic related to different physiological and ecological processes, such as metabolic rates (Brown et al. 2004), patterns of distribution and abundance (White et al. 2007), trophic position of species (Woodward and Warren 2007) and vulnerability to extinction (Olden et al. 2007). Considering biological invasions, a reported tendency, regardless of taxonomic group, is that non-native species have larger body sizes in invaded areas when compared with native habitats (Blossey and Nötzold 1995;Roy et al. 2002;Grosholz and Ruiz 2003;Leger and Rice 2003;Ebeling et al. 2008;Darling et al. 2011). However, other studies have found contradictory patterns or have identified significant variability among species (Thébaud and Simberloff 2001;Miller et al. 2002;Vilà et al. 2005;Parker et al. 2013). ...
There is a purported tendency for non-native species to have larger body sizes in their introduced range, commonly attributed to mechanisms such as enemy release or reduced competition. However, results are equivocal and this tendency may also result from ecosystem differences and/or the selective introduction of larger individuals. For most invasions it is difficult to separate the human from biological influences on body size. In this study, we utilize a natural experiment caused by the elimination of a semi-porous biogeographical barrier to test for body size differences in 12 Neotropical fish species in native and invaded ranges, unbiased by human influence in selecting introduced individuals. Our analyses include an additional 25 fish species native to both basins, enabling tests of consistency of body size patterns across native and non-native species in both ecosystems. Twenty-two species (9 non-native, 13 native), irrespective of life-history or trophic guild, had an interaction of population length-weight relationships which indicated inconsistency in relative body sizes in donor and recipient regions across age classes. Of the 15 species with similar slopes of the length-weight relationships between basins, all non-native species (n = 3) and five species native to both basins exhibited significantly larger body sizes (i.e. body mass at a given length) in the more productive donor ecosystem, and the remaining native species were either larger in the recipient system (n = 3) or were not significantly different between basins (n = 4). Our findings contribute to the growing literature that suggests perceived tendencies of larger body sizes in invaded ranges should not be generalized, especially when environmental conditions differ greatly among regions and when dealing with populations that exhibit significant age structure.
... A long-standing goal in invasion biology is to understand what causes a species to be particularly successful in its introduced range. Once established, many species attain higher abundances or greater biomass in their introduced range compared to con-specific populations in their native range (i.e., "invasion success") ; e.g., , Ebeling et al. 2008). This increased vigor enables some species to become invasive and negatively impact native species and ecosystems (e.g., Lodge et al. 1994, Prior and. ...
... A key challenge in invasion biology is to determine what enables species to be particularly successful in their introduced ranges. Many introduced species attain higher abundances or greater biomass compared to conspecific populations in their native range (Elton 1958;Keane and Crawley 2002;Parker et al. 2013;e.g., Torchin et al. 2001;Ebeling et al. 2008;Prior and Hellmann 2013). This increased success enables some species to become invasive, if they negatively affect species, ecosystems, or society (e.g., D'Antonio and Vitousek 1992; Lodge et al. 1994;Prior and Hellmann 2010). ...
The enemy release hypothesis (ERH) predicts that the success of invasive species is caused by reduced enemy pressure in species’ introduced ranges. The ERH is a highly-cited explanation for invasion success, yet rigorous evidence is lacking for most species and ecosystems. Most evidence comes from observations of enemies in native and introduced ranges. These studies assess one aspect of the ERH—“enemy loss.” They do not provide a direct test of the ERH and overlook the assumption of “native enemy effects.” This is a critical limitation as enemy release will not occur if enemies do not affect species in their native ranges, even if enemy loss occurs. Biogeographical experiments, providing a direct test of the ERH, are largely restricted to terrestrial plants. We present a synthesis of community ecology and invasion biology studies, including a novel meta-analysis of native enemy effects, to assess the potential for release for species in different taxonomic groups and ecosystems. We suggest that species that are subject to strong enemy effects in their native range will have a high potential for enemy release. We found that native enemy effects were stronger in aquatic systems than in terrestrial systems. They were particularly weak for terrestrial plants; and strong for marine organisms, and freshwater plants. Studies are needed for species that have strong potential for release, such as for aquatic invasive species. Alternative explanations should be explored for invasive species that are not affected by enemies in their native range, and future studies should emphasize native enemy effects rather than only enemy loss.
... Therefore, size and time to maturity in field populations may be poor measurements for contrasting native and introduced differences in performance. Population abundance and individual reproductive rates may be more informative performance metrics, but these have rarely been sampled in native and introduced populations even though these measurements are not difficult to obtain, particularly for plants (Vilà et al. 2005;Pergl et al. 2006;Ebeling et al. 2008). Measuring abundance, survival rates, and reproductive output of introduced species across their native and introduced ranges should be a priority for the field of invasion biology, as it would allow a quantitative comparison of different performance measures for assessing invasiveness. ...
The success of invasive species has been explained by two contrasting but non-exclusive views: (i) intrinsic factors make some species inherently good invaders; (ii) species become invasive as a result of extrinsic eco-logical and genetic influences such as release from natural enemies, hybridization or other novel ecological and evolutionary interactions. These viewpoints are rarely distinguished but hinge on distinct mechanisms leading to different management scenarios. To improve tests of these hypotheses of invasion success we introduce a simple mathematical framework to quantify the invasiveness of species along two axes: (i) interspecific differences in performance among native and introduced species within a region, and (ii) in-traspecific differences between populations of a species in its native and introduced ranges. Applying these equations to a sample dataset of occurrences of 1,416 plant species across Europe, Argentina, and South Africa, we found that many species are common in their native range but become rare following introduc-tion; only a few introduced species become more common. Biogeographical factors limiting spread (e.g. biotic resistance, time of invasion) therefore appear more common than those promoting invasion (e.g. enemy release). Invasiveness, as measured by occurrence data, is better explained by inter-specific varia-tion in invasion potential than biogeographical changes in performance. We discuss how applying these Copyright Robert I. Colautti et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
... The flowers of porterweed are semi-immersed in depressions or furrows in the rachis of the spike making it possible to estimate total seed production, even after dehiscence. In other studies, stem count has been used to predict the number of inflorescences and the inflorescence length has been used to predict the number of seed capsules (Ebeling et al., 2007). Also, seed capsule weight has been used to project number of seeds per plant (Wilson et al., 2004b). ...
Nettleleaf porterweed (Stachytarpheta cayennensis) is a potentially invasive ornamental plant in Florida. Plant growth, visual quality, flowering, and seed viability were assessed for nettleleaf porterweed and eight closely related alternatives planted in northern and southern Florida. In northern Florida, 'Mario Pollsa' porterweed (Stachytarpheta spp.), 'Violacea' porterweed (Stachytarpheta mutabilis), 'Naples Lilac' porterweed (Stachytarpheta spp.), 'Red Compact' porterweed (Stachytarpheta speciosa), and nettleleaf porterweed (Stachytarpheta cayennensis) achieved high flower ratings between 4 (average to good flowering) and 5 (abundant flowering, peak bloom) during 4 or more months. Also, jamaican porterweed (Stachytarpheta jamaicensis), 'Violacea' porterweed, 'Red Compact' porterweed, and nettleleaf porterweed achieved visual quality ratings between 4 and 5 (good to excellent quality) throughout most of the study. In southern Florida, the same cultivars received high flower ratings but generally for shorter periods of time. Also, 'Violacea' porterweed and 'Red Compact' porterweed consistently received visual quality ratings that were above 4 (good quality, very desirable). During the course of the 28-week study, nettleleaf porterweed produced the greatest number of spiked inflorescences with 39% to 80% seed viability. At both locations, 'Violacea' porterweed did not produce any viable seed and seed viability was less than 10% for 'Mario Pollsa' porterweed, coral porterweed (Stachytarpheta mutabilis), and 'Naples Lilac' porterweed.
... In particular, researchers can use seed collection sites at similar latitudes to partially control for photoperiod and climate (e.g., Blumenthal and Hufbauer 2007). Whether a study incorporates seed collections from separate continents or uses a smaller study area within a continent, a description of the environmental characteristics across the study system, including plant community composition, would inform comparisons across studies (e.g., Ebeling et al. 2008). ...
Citation: Atwood JP, Meyerson LA (2011) Beyond EICA: understanding post-establishment evolution requires a broader evaluation of potential selection pressures. NeoBiota 10: 7–25. Abstract Research on post-establishment evolution in nonnative plant populations has focused almost exclusively on testing the Evolution of Increased Competitive Ability (EICA) hypothesis, which posits that the lack of specialized herbivores in the invaded range drives evolution in nonnative plant populations. Fifteen years of conflicting EICA test results suggest that selection pressures other than specialized herbivory are important in driving post-establishment evolution in invasive species. Alternative hypotheses, such as the Evolution of Reduced Competitive Ability (ERCA) hypothesis, have been proposed but have received little attention or testing. We argue that the lack of consensus across studies that test EICA may be due in part to the lack of consistent definitions and varying experimental design parameters, and that future research in this field would benefit from new methodological considerations. We examined previous work evaluating post-establishment evolution and evaluated the range of study systems and design parameters used in testing the EICA hypothesis. Our goal was to identify where different uses of ecological terms and different study parameters have hindered consensus and to suggest a path forward to move beyond EICA in post-establishment evolution studies. We incorporated these methods into a design framework that will increase data harmony across future studies and will facilitate examinations of any potential selection pressure driving evolution in the invaded range. Copyright Joshua P. Atwood, Laura A. Meyerson. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
... For example, body size is an important biological characteristic related to different physiological and ecological processes, such as metabolic rates (Brown et al. 2004), patterns of distribution and abundance (White et al. 2007), trophic position of species (Woodward and Warren 2007) and vulnerability to extinction (Olden et al. 2007). Considering biological invasions, a reported tendency, regardless of taxonomic group, is that non-native species have larger body sizes in invaded areas when compared with native habitats (Blossey and Nötzold 1995;Roy et al. 2002;Grosholz and Ruiz 2003;Leger and Rice 2003;Ebeling et al. 2008;Darling et al. 2011). However, other studies have found contradictory patterns or have identified significant variability among species (Thébaud and Simberloff 2001;Miller et al. 2002;Vilà et al. 2005;Parker et al. 2013). ...
Background/Question/Methods
Biological invasions are a serious modern ecological problem with many negative impacts to invaded communities. However, an invasion can be considered a natural experiment and allows for testing different hypotheses. Body size is an important trait of organisms that can influence, for instance, dispersal ability, demographic parameters, and home range. Current literature indicates a tendency for invaders’ body size to be larger in non-native habitats. This tendency can be explained by an increase in resources utilization and/or adecrease inparasitism rates and competitive pressures in the non-native habitat. However, human action can also influence body size as a result of human’s propensity to introduce larger bodied individuals, making it difficult to separate human and ecological influences. The invasion of freshwater fishes in the Paraná River floodplain allows us to separate direct human influences from ecological responses. After the construction of the Itaipu Dam, the unintentional union of distinct ichthyofauna provinces occurred as species from the Lower Paraná River basin invaded theUpper Paraná River basin. Using data sets gathered during the period of 2000-2004 in the Upper Paraná River Floodplain (non-native range) and in the Manso Reservoir (native range), for fifteen species, we evaluated the support for the hypothesis stated above. Differences in body size (for each species) and environmental characteristics (conductivity, dissolved oxygen, pH, water temperature and transparency) were tested using ANCOVA and an Analysis of Similarity (ANOSIM), respectively.
Results/Conclusions
Most species were significantly larger in their native habitat. Only Potamotrygon motoro (freshwater stingray) was large in the non-native habitat and Astronotus crassipinis (oscar) and Hypophthalmus edentatus (highwaterman catfish) did not showed differences between habitats. The environmental conditions were dissimilar between native and non-native ranges (R=0.0108. p=0.001). The observed differences in body size can be attributed to differences in environmental conditions as well as possible changes in ecological interactions. However, the use of low-quality resources in the non-native habitat or fisheries pressure for some species may also influence body size.
... Invasive species are often observed to grow larger or produce more offspring in areas where they have been introduced than in their native range. Possible reasons for this include that they escape natural enemies from their native range, alter resource allocation, exhibit novel allelopathic compounds, or they are fortuitously introduced to more favourable environmental conditions (Crawley, 1987;Blossey & N€ otzold, 1995;Callaway & Aschehoug, 2000;Jakobs et al., 2004;Ebeling et al., 2008;Alba et al., 2011;Flory et al., 2011;Parker et al., 2013). Differences in performance have been attributed to both evolutionary changes and phenotypic plasticity (Lee, 2002;Parker et al., 2003;Blair & Wolfe, 2004;Bossdorf et al., 2005). ...
Aim
We evaluated whether the performance of individuals and populations of the invasive plant Verbascum thapsus differs between its native and non‐native ranges, across climate gradients, and in response to its position in a global‐scaled niche model.
Location
India (Kashmir) and Switzerland (native range) and Australia and USA (Hawaii, Montana and Oregon) (non‐native range).
Methods
We measured population characteristics (density of flowering individuals, population size), plant traits (plant height, number of flowering branches) and seed germination for 50 populations of V. thapsus growing along elevational gradients in six mountain regions around the world (two in the native range, and four in the non‐native range). We fitted linear regression models to determine the relationship of plant and population level performance variables to range, region, climate and probability of occurrence from a global niche model.
Results
Plant height, number of flowering branches and population density of V. thapsus did not differ consistently between the native and non‐native ranges, but the area covered by populations in the non‐native range was on average two orders of magnitude larger than the area of native populations. Within and among regions, individual plant performance traits responded variably to precipitation and mean annual temperature, depending on the climatic range of the observed populations; however, performance was greater for populations that had a greater modelled probability of occurrence. Seed germination under controlled conditions was highest between 20 and 35 °C and consistent across populations, although germination at low temperatures was substantially higher for native populations from Kashmir.
Main conclusions
The introduction of V. thapsus to its non‐native range is not associated with consistent increases in plant performance. Instead, plant performance is more strongly influenced by position within the climate niche of the species, position along environmental gradients, and climatic or other differences among regions. We demonstrate that individual‐level and population‐level performance traits can yield different predictors of plant performance. Therefore, future studies comparing plant performance in native and non‐native ranges should include both plant and population characteristics and should also sample the target species from multiple regions in both ranges and along environmental gradients that comprehensively represent the niche of the species.
... Some studies have suggested a direct causal link between reduced herbivory in the exotic range and increased plant growth and reproductive output (e.g. Ebeling et al., 2008) while other studies have found reduced herbivory but no evidence of increased growth (e.g. Cripps et al., 2010). ...
Understanding the processes underlying the transition from introduction to naturalization and spread is an important goal of invasion ecology. Release from pests and pathogens in association with capacity for rapid growth is thought to confer an advantage for species in novel regions.
We assessed leaf herbivory and leaf‐level traits associated with growth strategy in the native and exotic ranges of 13 invasive plant species from 256 populations. Species were native to either the Western Cape region of South Africa, south‐western Australia or south‐eastern Australia and had been introduced to at least one of the other regions or to New Zealand. We tested for evidence of herbivore release and shifts in leaf traits between native and exotic ranges of the 13 species.
Across all species, leaf herbivory, specific leaf area and leaf area were significantly different between native and exotic ranges while there were no significant differences across the 13 species found for leaf mass, assimilation rate, dark respiration or foliar nitrogen.
Analysis at the species‐ and region‐level showed that eight out of 13 species had reduced leaf herbivory in at least one exotic region compared to its native range.
Six out of 13 species had significantly larger specific leaf area ( SLA ) in at least one exotic range region and five of those six species experienced reduced leaf herbivory. Increases in SLA were underpinned by increases in leaf area rather than reductions in leaf mass.
No species showed differences in the direction of trait shifts from the native range between different exotic regions. This suggests that the driver of selection on these traits in the exotic range is consistent across regions and hence is most likely to be associated with factors linked with introduction to a novel environment, such as release from leaf herbivory, rather than with particular environmental conditions.
Synthesis . These results provide evidence that introduction of a plant species into a novel environment commonly results in a reduction in the top‐down constraint imposed by herbivores on growth, allowing plants to shift towards a faster growth strategy which may result in an increase in population size and spread and consequently to invasive success.
... B. globosa has particular value due to its orange flowers borne in small spherical clusters. Buddleja has come under international scrutiny because of its potential for invasiveness (Ebeling et al. 2008;Tallent-Halsell, Watt 2009). Few molecular and cytogenetic data for Buddleja have been published. ...
2011. Introgression of yellow flower colour in Buddleja davidii by means of polyploidisation and interspecific hybridisation. Hort. Sci. (Prague), 38: 96–103. To introduce yellow colour in the commercial Buddleja davidii (2n = 4x = 76) assortment, an interspecific breeding programme with B. globosa (2n = 2x = 38) was started. The first step was to perform chromosome doubling in B. glo-bosa. Two of the obtained tetraploid B. globosa plants were subsequently used as male parent in interspecific crosses with the white flowering B. davidii cv. Nanhoensis Alba. In total 182 interspecific crosses were made and 18 F1 hybrids were obtained. Genome size measurements, chromosome counts and genomic in situ hybridisation (GISH) analysis proved the hybrid nature of most of the F1 hybrids. Plant morphology also expressed hybrid characteristics. F1 seedlings inherited the yellowish flower colour from B. globosa. As for many other woody ornamentals, the creation of hybrids through interspecific hybridisation along with polyploidisation offers new opportunities for breeding in Buddleja.
... However, there are also cases when invasive populations have adapted to the new environment in the introduced range, presenting higher mean values for various life-history traits (e.g., size, carbon assimilation rates, and fecundity) when growing under the same conditions as their native or non-invasive counterparts (Maron et al. 2004;Blumenthal and Hufbauer 2007), or having evolved towards a greater plasticity (Lavergne and Molofsky 2007;Zou et al. 2009). Heterogeneous environments in the introduced range of a species may also result in local adaptation of invasive populations (Alexander et al. 2009;Eriksen et al. 2012), even though genetic differentiation between native and invasive populations can also be the result of non-adaptive processes (i.e., environmental maternal effects and genetic drift; Dybdahl and Kane 2005;Ebeling et al. 2008Ebeling et al. , 2011Geng et al. 2007;Monty et al. 2013). ...
Although the genetic aspects of biological invasions are increasingly receiving more attention in the scientific literature, analyses of phenotypic plasticity and genotype-by-environment interactions are still seldom considered in tree invasion biology. Previous studies have shown that invasions of tree species can be affected by intraspecific phenotypic plasticity, pre-adaptation, and post-introduction evolution, and we suggest there are opportunities for new developments in this field. Here, we present a description of the use of quantitative and molecular genetics in tree invasion biology, and propose an approach based on common garden experiments, quantitative and molecular genetic methods to investigate the role of adaptive evolution, phenotypic plasticity, and genotype-by-environment interactions in tree invasions, particularly at the infraspecific level. We illustrate the utility of this approach using examples from quantitative genetic studies of Pinus and an example from a classical reciprocal common garden experiment with Acer species. By using this approach, researchers can test hypotheses about the role and strength of genetic and environmental effects on population-level invasiveness and gain insights into evolutionary processes that occur during biological invasions. Moreover, knowledge of phenotypic plasticity and local adaption of tree populations may help researchers improve assessments of invasion risk.
This datasheet on Buddleja davidii covers Identity, Overview, Distribution, Dispersal, Hosts/Species Affected, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.
Invasive species are a global concern impacting biodiversity, community structure, and ecological function of entire ecosystems. Elodea canadensis (Canadian Waterweed) is a submerged aquatic macrophyte native to southern Canada and the 48 contiguous United States but invasive in Alaska. The purpose of our study was to compare aquatic macroinvertebrate communities associated with E. canadensis in native (Illinois) and invasive (Alaska) areas. Functional feeding group community structure of E. canadensis-associated macroinvertebrates was different in the invasive and native range. Collector-filterer relative abundance was higher in the invasive range, whereas predator-engulfer relative abundance was higher in the native range. Furthermore, shredder-herbivore density in E. canadensis beds was higher in the native range than in the invasive range. Our results suggest that the successful establishment of E. canadensis in Alaska is likely facilitated by reduced herbivory and that the continued spread of E. canadensis will alter ecosystem structure and function of the Copper River Delta, AK and the ecosystem services it provides.
Theory to explain how plants defend themselves against herbivorous insects is rich, but can be difficult to test. Biological invasions provide unique opportunities to test and improve upon plant defense theory, as plants experience predictable shifts in insect herbivory after introduction to a new range. Here, we use an invasion to evaluate the power of three cornerstone hypotheses to predict the evolution of defense against herbivorous insects. These three hypotheses represent increasing refinements of classic plant‐insect theory regarding optimal defense, and each rests on the same three assumptions: that introduced plant populations escape natural enemies, that insect herbivory reduces plant fitness, and that putative defenses decrease herbivory. These assumptions remain untested in most invasions, which likely contributes to conflicting support for many plant defense hypotheses. We provide evidence that these assumptions are met in common mullein, Verbascum thapsus L. (Scrophulariaceae), which we propose can thus be used as a model system to test plant defense theory. We find that the hypothesis that integrates predictions of within‐plant optimal defense theory and the evolutionary dilemma model (i.e., the ‘shifting defense allocation’ hypothesis) provides strong insights into both invasion and evolution of plant defense. Specifically, we show that introduced populations that escape important specialist herbivores increase the concentration of secondary compounds in high‐quality tissue in particular, in this case protecting valuable young leaves from generalist herbivores that dominate in the introduced range. We would not have detected this shift without exploring within‐plant defense allocation across native and introduced populations, a task rarely undertaken when assessing evolutionary change in plant defenses. This finding provides broad insight into how native and introduced plant populations alike may respond to shifts in herbivore pressure. We close by highlighting future directions of inquiry using introduced plant populations to develop and test plant defense theory more generally.
The butterfly bush or summer lilac (Buddleja davidii) is a popular ornamental garden bush, planted also because it attracts many types of butterflies in the time of flowering. Due to successful vegetative and sexual reproduction it has escaped from gardens and became invasive in Slovenia. We present the current knowledge about its distribution. The species is most frequent in central Slovenia in the pre-Alpine phytogeographical region and in western part of Slovenia, in the sub-Mediterranean phytogeographical region. Some scattered localities are known also from other parts of Slovenia. The butterfly bush predominantly invades disturbed natural habitats mostly on rocky or gravel substrate, as quarries, ruderal sites in urban areas and river banks. We have written the instructions for gardeners and for handling with cut shoots of butterfly bush to prevent further escapes from gardens.
Invasive alien species (IAS) has a very significant impact on aquatic environments. In Spain these ecosystems are home to a large number of IAS and to a high diversity and endemism of fauna, especially inland fish. The threat posed by IAS and the difficulty of working in rivers and streams requires the use of different tools for their control and possible eradication, as well as the development of new methodologies for their application. The methodology for a pilot project was designed to allow the application and assessment of the use of rotenone as an instrument for control and possible eradication of IAS in a river system. This methodology, which currently being implemented, has not been previously tested for rivers in
Spain. The methodology was designed for its application on Pseudorasbora parva, IAS inhabiting some rivers in the Guadiana Basin, Extremadura. It’s included in the Spanish Catalog of Invasive Exotic Species (legally developed by Royal Decree 630/2013). A typical Mediterranean stream (low flow rate, marked dry season), where this IAS inhabits, was selected and the methodology was applied once the relevant authorizations for the use of this biocide were available. It’s considered relevant to present the methodology applied in this pilot project due to the wide possibilities to apply this tool in Spain.
Zusammenfassung Zu verwilderten Vorkommen von Taxa der Gattung Cotoneaster in Deutschland gibt es nur wenige Untersuchungen. Oft basieren diese aufgrund taxonomischer und nomenklatorischer Unsicherheiten und wegen Problemen bei der Einschätzung des floristischen Status bisher nur auf sporadischen Beobachtungen. In der Dölauer Heide, einem Stadtwald von Halle (Saale), wurden subspontane Vorkommen von Cotoneaster bullatus BOIS, C. cornifolius (REHDER et H. E. WILSON) FLINCK et B. HYLMÖ, C. dielsianus E. PRITZ. ex DIELS, C. divaricatus REHDER et H. E. WILSON, C. lucidus SCHLTDL., C. aff. multiflorus, C. villosulus (REHDER et H. E. WILSON) FLINCK et B. HYLMÖ und C. zabelii C. K. SCHNEID. festgestellt. In der weiteren Umgebung von Halle wurde auch subspontanes Auftreten von C. horizontalis DECNE. und C. nitens REHDER et H. E. WILSON ermittelt. Insbesondere C. villosulus und C. divaricatus werden als invasive Arten eingeschätzt. Cotoneaster cornifolius und C. lucidus sind fest eingebürgert und haben das Potenzial, invasiv werden zu können. Die synanthropen Vorkommen mehrerer Cotoneas-ter-Arten haben überwiegend auffallend höheren Wuchs sowie größere Blätter und Früchte als in den Originalbeschreibungen angegeben.. lucidus are permanently naturalised and are able to become invasive. Invasive populations show increased plant size and leaf area relative to original description of the species.
Nursery catalogues have recently been used as a method for tracing the introduction history of invasive plants. Information on species, cultivars, plant size and price can help quantify historical changes in propagule pressure. Propagule pressure of invasive ornamentals has to be combined with climatic data to understand shifting distribution patterns of (potentially) invasive plants. In this study the spread of Ilex aquifolium L. cultivars was investigated at the edge of its distribution margin in Denmark. Danish nursery catalogues from 1841-2007 were studied to 1) reconstruct the introduction history of potentially invasive ornamental genotypes of I. aquifolium in Denmark; 2) explore potential factors that could explain naturalization of the species, i.e. nursery location, plant size, hardiness, price and year; 3) investigate whether or not marketing has been more common inside the historical range of the species in western Denmark; and 4) test the hypothesis that marketing of this frost-sensitive species has increased parallel with higher temperatures in the past 100 years. Price, plant size, hardiness, location, and year were recorded for a total of 3213 entries. Through time, increasing prices and the availability of frost-hardy cultivars were the most significant factors contributing to the sale of I. aquifolium in Denmark. The number of nurseries per area, and hence propagule pressure, was higher in eastern Denmark, outside the natural range of the species. The proportion of very frost-hardy cultivars increased with milder winter temperatures. The main conclusion from this combined nursery catalogue and climate study are that nurseries in an indirect way play an important role in increasing the propagule pressure of potentially invasive ornamentals and thus can affect distribution of native species.
Invasive plants are expected to perform better and consequently be more abundant in their introduced compared to their native ranges. However, few studies have simultaneously compared plant and population traits along with biotic and abiotic environmental parameters for invasive and native plant populations. We compared 17 native Eastern European, 14 expanded Western European and 31 introduced US populations of the invasive Lepidium draba over 2 years. Most parameters were similar between the two European ranges, but differed for the US. Density, cover, and biomass of L. draba were greater in the US while cover of other vegetation was lower. Bare-ground and litter cover were greater for US populations in 1 year, as was L. draba shoot height and seed output. Availability of labile soil nitrogen was also greater in the US range. Endophagous shoot herbivory was greater in Western Europe compared to the US in 1 year. As expected, specialist herbivores were only found in Europe. Differences between ranges were not explained by varying environmental conditions (climate, altitude and latitude). In summary our results indicate that lower interspecific competition, higher resource availability and the lack of specialist natural enemies may all contribute to the increased performance of L. draba in its introduced US range. Additionally, L. draba is well adapted to disturbance events, which may further benefit its competitiveness at degraded sites. In general our results were consistent between years, which reinforces their validity. However, some of the differences were only significant in one of the 2 years, which, on the other hand, emphasizes the importance to ideally conduct biogeographic comparisons over multiple years.
This chapter examines the value of natural experiments for studying aspects of alien tree invasions in South Africa. It presents case studies involving species of Acacia, Hakea, Pinus, Eucalyptus, and Metrosideros. It explores the contributions of natural experiments towards generalizations in plant invasion ecology and the extent to which such studies can reduce the harmful effects of tree invasions.
ADDITIONAL INDEX WORDS. exotic plants, invasive, ornamentals, but-terfl y bush, Buddleja davidii, Buddleja japonica, Buddleja lindleyana, Buddleja ×weyeriana SUMMARY. Because of its weedy nature, extensive use in the landscape, numer-ous cultivars, and history as an inva-sive plant in other countries, butterfl y bush (Buddleja) was an appropriate candidate to evaluate for seed pro-duction and germination in Florida. Seed production was quantifi ed for 14 butterfl y bush taxa planted in western Florida (Milton) and central southern Florida (Fort Pierce). Each of the 14 taxa evaluated produced seed. In Fort Pierce, japanese butterfl y bush (B. japonica) had the greatest capsule weight and 'Gloster' butterfl y bush (B. lindleyana) had the second greatest capsule weight as compared to other taxa. In Milton, 'Gloster' had the greatest capsule weight and japanese butterfl y bush and 'Nanho Alba' butterfl y bush (B. davidii var.
Plant growth, visual quality and flowering were assessed for 14 butterfly bush (Buddleja) taxa planted in western Florida (Milton) and central southern Florida (Fort Pierce). In both locations, 'Violet Eyes' butterfly bush (B. weyeriana x B. lindleyana), 'Honeycomb' butterfly bush (B. x weyeriana), 'Moonlight' butterfly bush (B. x weyeriana), and 'Sungold' butterfly bush (B. x weyeriana) generally had the greatest growth index and shoot dry weight of all cultivars. In Fort Pierce and Milton, flower dry weights of 'White Profusion' butterfly bush (B. davidii), 'Nanho Alba' butterfly bush (B. davidii var. nanhoensis), and 'Dartmoor' butterfly bush (B. davidii x B. davidii var. nanhoensis) were among the highest as compared to other cultivars at each site, although in Milton, 'Gloster' butterfly bush (B. lindleyana), japanese butterfly bush (B. japonica) and 'Honeycomb' butterfly bush also had high flower dry weights. Peak plant performance varied by month, cultivar and location. At 12 weeks, plant form and color were above average for each cultivar with the exception of 'Black Knight' butterfly bush (B. davidii), lindley's butterfly bush (B. lindleyana), and 'Gloster' butterfly bush in the Fort Pierce location only. After 24 weeks at each location, visual quality was above average for 'Black Knight', 'Dartmoor', 'Gloster', 'Honeycomb', 'Violet Eyes', and Japanese butterfly bush. Peak flowering times varied with cultivar and location. At 24 weeks, flowering of 'White Profusion', 'Nanho Alba', 'Nanho Blue', and 'Nanho Purple' butterfly bush grown in Fort Pierce was 25% to 40% less than that of the same cultivars grown in Milton. At 24 weeks, 'Dartmoor' had the most flowers in both locations, covering 75% of the plant canopy.
We studied 28 alien tree species currently planted for forestry purposes in the Czech Republic to determine the probability of their escape from cultivation and naturalization. Indicators of propagule pressure (number of administrative units in which a species is planted and total planting area) and time of introduction into cultivation were used as explanatory variables in multiple regression models. Fourteen species escaped from cultivation, and 39% of the variance was explained by the number of planting units and the time of introduction, the latter being more important. Species introduced early had a higher probability of escape than those introduced later, with more than 95% probability of escape for those introduced before 1801 and <5% for those introduced after 1892. Probability of naturalization was more difficult to predict, and eight species were misclassified. A model omitting two species with the largest influence on the model yielded similar predictors of naturalization as did the probability of escape. Both phases of invasion therefore appear to be driven by planting and introduction history in a similar way. Our results demonstrate the importance of forestry for recruitment of invasive trees. Six alien forestry trees, classified as invasive in the Czech Republic, are currently reported in nature reserves. In addition, forestry authorities want to increase the diversity of alien species and planting area in the country.
ABSTRACT Invading non-indigenous species in the United States cause major environmental damages,and losses adding up to more than $138 billion per year. There are approximately 50,000 foreign species and the number is increasing. About 42% of the species on the Threatened or Endangered species lists are at risk primarily because of non-indigenous species. In the history of the United States, approximately 50,000 non-indigenous (non-native)
ABSTRACT Introduced plant species that became successful invaders appear often more vigorous and taller than their conspecifics in the native range. Reasons postulated to explain this better performance in the introduced range include more favourable environmental conditions and release from natural enemies and pathogens. According to the Evolution of Increased Competitive Ability hypothesis (EICA hypothesis) there is a trade-off between investment into defence against herbivores and pathogens, and investment into a stronger competitive ability. In this study, we conducted field surveys to investigate whether populations of the invasive perennial Solidago gigantea Ait (Asteraceae) differ with respect to growth and size in the native and introduced range, respectively. We assessed size and morphological variation of 46 populations in the native North American range and 45 populations in the introduced European range. Despite considerable variation between populations within continents, there were pronounced differences between continents. The average population size, density and total plant biomass were larger in European than in American populations. Climatic differences and latitude explained only a small proportion of the total variation between the two continents. The results show that introduced plants can be very distinct in their growth form and size from conspecifics in the native range. The apparently better performance of this invasive species in Europe may be the result of changed selection pressures, as implied by the EICA hypothesis.
It is shown that invading species are most likely to establish where levels of competition among the resident species are lowest. Thus, of the higher trophic levels, herbivores are more likely to establish than carnivores or detritivores. Invading plants are most likely to establish in communities where the average level of cover is low. Competition is certainly not the only important process involved in establishment, however. Analysis of invasions by insects released as biocontrol agents against weeds, where exploitation and interference are likely to be negligible, show that the probability of successful establishment is closely related to the insect's intrinsic rate of increase. The main biological causes of failure are generalist predators, with parasites and diseases rather less important. For herbivorous insects, host-plant incompatibility is a major cause of failure in establishment. A general model for the dynamics of an invading species is proposed, which stresses: (a), the importance of distinguishing explicitly between exploitation and interference competition; (b), the potential importance of generalist natural enemies; (c), the role of mutualists; (d), the importance of refuges of various kinds in affecting the probability of establishment. Examples are provided to emphasize how far we still are from real, predictive ability in relation to the likely success of proposed or anticipated invasions.
Biological invasions are a widespread and significant component of human-caused global environmental change. The extent of invasions of oceanic islands, and their consequences for native biological diversity, have long been recognized. However, invasions of continental regions also are substantial. For example, more than 2,000 species of alien plants are established in the continental United States. These invasions represent a human-caused breakdown of the regional distinctiveness of Earth's flora and fauna - a substantial global change in and of itself. Moreover, there are well-documented examples of invading species that degrade human health and wealth, alter the structure and functioning of otherwise undisturbed ecosystems, and/or threaten native biological diversity. Invasions also interact synergistically with other components of global change, notably land use change. People and institutions working to understand, prevent, and control invasions are carrying out some of the most important - and potentially most effective - work on global environmental change.
Cleopus japonicus Wingelmüller (Coleoptera: Curculionidae) has been investigated as a potential biocontrol agent against Buddleja davidii Franchet (Buddlejaceae), an invasive weed of exotic and indigenous forests in New Zealand. The impact of feeding damage by C. japonicus, at densities of 0, 3, 10 or 20 larvae per plant (from 2 nd instar), on the growth of buddleia plants was assessed in a quarantine laboratory. Matured larvae were replaced every 11 days until, after seven weeks, the effects of defoliation were assessed. Grazing damage increased with larval density and in the high density treatment (20 larvae per plant), 83% of expanded leaves had more than 50% of the leaf area grazed. One third of the plants in the high density treatment died, presumably as a result of grazing, whereas there was no mortality in the control and light grazing (3 larvae per plant) treatments. Grazing resulted in a significant reduction in main stem height, total stem and branch length, and dry weight of roots and shoots, primarily in the medium and high density treatments. The results suggest that, following permission to release and successful establishment, C. japonicus should successfully suppress buddleia growth.
Replacement patterns under buddleia (Buddleja davidii) groves aged between 2 and 17 years were studied in streambeds in the western Ikawhenua Range and in the upper Waioeka catchment, Te Urewera National Park. Height and basal diameter growth followed an exponential pattern, with rapid early growth (0.5 m/year and 1 cm/year respectively), levelling off after 15 years or more. Intense self- thinning occurred in younger stands. Typical forest floor vegetation was developing within 15 years of colonisation by buddleia. Seedlings of ten indigenous trees and shrubs were widespread under buddleia, with primary colonising species (e.g. Hebe stricta, Kunzea ericoides) more common under young stands, and other seral species (e.g. Pseudopanax arboreus, Melicytus ramiflorus, Aristotelia serrata) more common under older stands. Buddleia quickly displaces primary native colonisers, herbaceous and woody, where it occurs en masse, accelerating successions to forest on fresh alluvium by replacing longer-lived species such as K. ericoides. It is a very effective coloniser of new surfaces, and is likely to continue spreading in the Park and persist indefinitely in lowland catchments subject to frequent flooding and alluviation.
■ Abstract Contributions from the field of population biology hold promise for understanding and managing invasiveness; invasive species also offer excellent oppor- tunities to study basic processes in population biology. Life history studies and demo- graphic models may be valuable for examining the introduction of invasive species and identifying life history stages where management will be most effective. Evolution- ary processes may be key features in determining whether invasive species establish and spread. Studies of genetic diversity and evolutionary changes should be useful for
Two hypotheses that have been put forward to explain the success of invasive plants, the enemy release hypothesis and the evolution of increased ability (EICA) hypothesis, are based on observations of greater vigour of invasive plants in their range. In this study, we found support for this phenomenon in field populations of the invasive South African Ragwort, Senecio inaequidens: In the introduced range, plants were individually larger and built up larger populations than in the native range. Moreover, invasive populations showed a reduced incidence of parasitizing insects suggesting that enemy release may play a role in the success of this invader. We also found that among-population variation in seed mass was significantly reduced in European population, implying that the species underwent a population bottleneck when introduced to Europe. These first results will serve as a starting point for further studies on the influence of herbivory in this invasive species.
Two venerable hypotheses, widely cited as explanations for either the success or failure of introduced species in recipient communities, are the natural enemies hypothesis and the biotic resistance hypothesis. The natural enemies hypothesis posits that introduced organisms spread rapidly because they are liberated from their co‐evolved predators, pathogens and herbivores. The biotic resistance hypothesis asserts that introduced species often fail to invade communities because strong biotic interactions with native species hinder their establishment and spread. We reviewed the evidence for both of these hypotheses as they relate to the importance of non‐domesticated herbivores in affecting the success or failure of plant invasion.
To evaluate the natural enemies hypothesis, one must determine how commonly native herbivores have population‐level impacts on native plants. If native herbivores seldom limit native plant abundance, then there is little reason to think that introduced plants benefit from escape from these enemies. Studies of native herbivore‐native plant interactions reveal that plant life‐history greatly mediates the strength with which specialist herbivores suppress plant abundance. Relatively short‐lived plants that rely on current seed production for regeneration are most vulnerable to herbivory that reduces seed production. As such, these plants may gain the greatest advantage from escaping their specialist enemies in recipient communities. In contrast, native plants that are long lived or that possess long‐lived seedbanks may not be kept “in check” by native herbivores. For these species, escape from native enemies may have little to do with their success as exotics; they are abundant both where they are native and introduced.
Evidence for native herbivores providing biotic resistance to invasion by exotics is conflicting. Our review reveals that: 1) introduced plants can attract a diverse assemblage of native herbivores and that 2) native herbivores can reduce introduced plant growth, seed set and survival. However, the generality of these impacts is unclear, and evidence that herbivory actually limits or reduces introduced plant spread is scarce. The degree to which native herbivores provide biotic resistance to either exotic plant establishment or spread may be greatly determined by their functional and numerical responses to exotic plants, which we know little about. Generalist herbivores, through their direct effects on seed dispersal and their indirect effects in altering the outcome of native–non‐native plant competitive interactions, may have more of a facilitative than negative effect on exotic plant abundance.
Invading species are most likely to establish where levels of competition among the resident species are lowest. Thus, of the higher trophic levels, herbivores are more likely to establish than carnivores or detritivores. Invading plants are most likely to establish in communities where average level of cover is low. Competition is not the only important process involved in establishment, however. Analysis of invasions by insects released as biocontrol agents against weeds, where exploitation and interference are likely to be negligible, show that the probability of successful establishment is closely related to the insect's intrinsic rate of increase. The main biological causes of failure are generalist predators, with parasites and diseases rather less important. For herbivorous insects, host-plant incompatibility is a major cause of failure in establishment. A general model for the dynamics of an invading species is proposed, which stresses 1) the importance of distinguishing explicitly between exploitation and interference competition; 2) the potential importance of generalist natural enemies; 3) the role of mutualists; 4) the importance of refuges of various kinds in affecting the probability of establishment. -from Author
The suitability of biological control for B. davidii lies in the weed's invasion of relatively stable habitats, of modest economic value, where containment or suppression of the target, rather than eradication, is acceptable. The costs of undertaking a biological control programme based on the importation of natural insect enemies from China are calculated as being of the order of $NZ 0.6 million. -from Authors
For a variety of reasons, hundreds of tree species have been planted well outside their natural ranges. In numerous parts of the world, alien trees are the foundation of commercial forestry and agroforestry enterprises, and many are planted for a wide range of other uses.A small sample of tree species that are widely cultivated as aliens have spread from planting sites, and some taxa are among the most damaging of invasive alien plants. The configuration of alien tree plantings-many species planted in a wide range of habitats, subject to many types, intensities, and combinations of natural and human-mediated disturbances across continents-provides us with a series of "natural" (i.e., nonmanipulative) experiments, with opportunities for gaining useful insights on central issues in invasion ecology. For long-lived organisms like trees, such natural experiments are usually the only available source of information for management, especially in the face of rapid global change. This chapter reviews the value of natural experiments for studying aspects of alien tree invasions, with special reference to South Africa. Case studies, involving mainly species of Acacia, Hakea, Pinus, Eucalyptus, and Metrosideros, are reviewed to explore the extent to which natural experiments have improved (or could improve) our ability to understand and manage these invasions. Suggestions are made on further insights that could be gained through the careful evaluation of natural experiments. Innovations in remote sensing and statistics for spatial data are providing us with new tools.
Discussion 1
The author highlights the original axes of Kari Hauge’s clinical presentation: which combines an accommodation of the regression of the adolescent girl as in the treatment of a child with an encountering technique based on the specificity of the adolescent dimension – the formulation of interpretations both of unconscious content and of the actual relation between the patient and the analyst. This practice allows for an elaboration of infantile Oedipus complexes re-actualized by adolescence while facilitating a resumption of the process of subjectivation, once the needs of dependence have been acknowledged.
Ecological studies typically involve comparison of biological responses among a variety of environmental conditions. When the response variables have continuous distributions and the conditions are discrete, whether inherently or by design, then it is appropriate to analyze the data using analysis of variance (ANOVA). When data conform to a complete, balanced design (equal numbers of observations in each experimental treatment), it is straightforward to conduct an ANOVA, particularly with the aid of the numerous statistical computing packages that are available. Interpretation of an ANOVA of balanced data is also unambiguous. Unfortunately, for a variety of reasons, it is rare that a practicing ecologist embarks on an analysis of data that are completely balanced. Regardless of its cause, lack of balance necessitates care in the analysis and interpretation. In this paper, our aim is to provide an overview of the consequences of lack of balance and to give some guidelines to analyzing unbalanced data for models involving fixed effects. Our treatment is necessarily cursory and will not substitute for training available from a sequence of courses in mathematical statistics and linear models. It is intended to introduce the reader to the main issues and to the extensive statistical literature that deals with them.
When the response variables have continuous distributions and the conditions are discrete, whether inherently or by design, then it is appropriate to analyze the data using analysis of variance (ANOVA). When data conform to a complete, balanced design (equal numbers of observations in each experimental treatment), it is straightforward to conduct an ANOVA. This paper provides an overview of the consequences of lack of balance and gives some guidelines to analyzing unbalanced data for models involving fixed effects. -from Authors
All vascular plants recorded in the lower Orongorongo Valley DSIR study area (1100 ha) are listed with notes on their status and distribution. Of the 501 taxa, 355 are native, 128 are naturalised, and 18 have probably been deliberately introduced or cultivated. Ofthe native taxa, 35% are woody plants, but only 75 of these (or 60% of woody native taxa) are common and thus make up the bulk of the vegetation structure. By contrast, less than 9% of the naturalised species are woody plants, and all except two — gorse and buddleia — are either uncommon or rare. Annuals comprise 5.6% of all native dicotyledon herbs and 49% of the naturalised dicotyledon herbs. The history of the study area, public use, introduced animals, and tectonic events, particularly the earthquake-induced landslides of the mid-nineteenth century, are outlined and discussed in relation to the native and adventive flora. Exotic herbivores, especially possums (Trichosurus vulpecula), have greatly reduced the abundance of some plants which were common 30 years ago, including Alectryon excelsus, Fuchsia excontcata, Coriaria arborea, and Pseudopanax arboreus. Some other species, although probably never common, have been orought to the verge of extinction. Naturalised plants — especially daisies and grasses — have been able to colonise extensive open habitats created by earthquake slipping in 1855, and the reactivated terraces and river flood plain. If current selection pressures continue, it is predicted that other species such as Metrosideros robusta. Weinmannia racemosa, and Sphaeropteris medullaris will become rare, at least in lowland forest. Spread of Pinus radiata into mid-altitude communities will accelerate as exotic forests to windward mature.
This paper considers key issues in plant invasion ecology, where findings published since 1990 have significantly improved our understanding of many aspects of invasions. The review focuses on vascular plants invading natural and semi-natural ecosystems, and on fundamental ecological issues relating to species invasiveness and community invasibility. Three big questions addressed by the SCOPE programme in the 1980s (which species invade; which habitats are invaded; and how can we manage invasions?) still underpin most work in invasion ecology. Some organizing and unifying themes in the field are organism-focused and relate to species invasiveness (the tens rule; the concept of residence time; taxonomic patterns and Darwin's naturalization hypothesis; issues of phenotypic plasticity and rapid evolutionary change, including evolution of increased competitive ability hypothesis; the role of long-distance dispersal). Others are ecosystem-centred and deal with determinants of the invasibility of communities, habitats and regions (levels of invasion, invasibility and propagule pressure; the biotic resistance hypothesis and the links between diversity and invasibility; synergisms, mutualisms, and invasional meltdown). Some theories have taken an overarching approach to plant invasions by integrating the concepts of species invasiveness and community invasibility (a theory of seed plant invasiveness; fluctuating resources theory of invasibility). Concepts, hypotheses and theories reviewed here can be linked to the naturalization-invasion continuum concept, which relates invasion processes with a sequence of environmental and biotic barriers that an introduced species must negotiate to become casual, naturalized and invasive. New research tools and improved research links between invasion ecology and succession ecology, community ecology, conservation biology and weed science, respectively, have strengthened the conceptual pillars of invasion ecology.