Albert, M. E., D'Antonio, C. M., & Schierenbeck, K. A. (1997). Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California. I. morphological evidence. American Journal of Botany, 84(7), 896-904. ABSTRACT
Individuals of the invasive non-native plant species Carpobrotus edulis, its native or naturalized congener C. chilensis, and putative hybrids are found throughout coastal California. This study characterized morphological variation within the genus and assessed the extent of hybridization and direction of introgression between C. edulis and C. chilensis. Twelve randomly selected Carpobrotus individuals from each of 49 sample locations were classified as 'C. edulis,' 'C. chilensis,' or one of three intermediate morphotype classes, and compared for clonal, vegetative, and fruit characters. Univariate comparisons showed that C. edulis individuals had deeper mats with more cover within the mat boundary, longer, wider, more serrate leaves, and wider fruits with more carpels than intermediate and C. chilensis morphotype classes. Carpobrotus edulis and intermediates had more lateral branches than did C. chilensis, suggesting that hybrids tend to vary toward C. edulis. Discriminant function analysis (DFA) identified the following characters as discriminating significantly among Carpobrotus groups: leaf length, leaf width, leaf length/width, number of lateral branches, number of carpels, and fruit diameter. Using these characters, DFA correctly classified 98% of apparently pure C. edulis and C. chilensis, but only 76% of all Carpobrotus individuals when putative hybrids were included. Principal components analysis showed that C. edulis and C. chilensis cluster into distinct morphotypes, but that hybrids overlap with both groups, particularly with C. edulis. The genus Carpobrotus in California resembles a large hybrid swarm, with putative hybrids forming a large portion of the overall population and tending to vary toward C. edulis.
 
 
Campos, J. A., Herrera, M., Biurrun, I., & Loidi, J. (2004). The role of alien plants in the natural coastal vegetation in central-northern Spain. Biodiversity and Conservation, 13(12), 2275-2293. ABSTRACT
Alien plants in coastal habitats and their influence on natural vegetation are studied. After 5 years working on this subject in the Basque Country and surrounding areas, a number of results from the coastal ecosystems are presented. These ecosystems are one of the most threatened and affected by the invasion of alien plants, especially shore dunes, saltmarshes and cliffs. These kinds of habitats, especially the dunes, experience significant pressure from human activities which favours the expansion of some of these species: Arctotheca calendula, Sporobolus indicus and Oenothera spp. The presence and abundance of these invasive plants and others such as Baccharis halimifolia, Cortaderia selloana, Spartina patens and Carpobrotus edulis in the plant communities in an area between the French border and the western part of the region of Cantabria have been studied. The degree of invasion of each plant in each syntaxonomic unit has been analysed.
 
 
Conser, C., & Connor, E. F. (2009). Assessing the residual effects of carpobrotus edulis invasion, implications for restoration. Biological Invasions, 11(2), 349-358. ABSTRACT
We examined whether the residual effects on soil caused by the invasion of Carpobrotus edulis, common iceplant, would inhibit the reestablishment of a native plant species. Carpobrotus edulis interacts both directly by suppressing the growth and establishment of other plants and indirectly by altering soil chemistry. We tested whether the residual effects of C. edulis resulted in lowered germination, survival, growth, and reproduction of Gilia millefoliata, a rare dune annual. We compared G. millefoliata planted in plots previously occupied by C. edulis to G. millefoliata planted in plots that previously had native vegetation. Each plot received three treatments: seed, transplant, and unplanted, and were censused every three weeks until senescence. Carpobrotus edulis had strong negative effects on the germination, survival, growth, and reproduction of G. millefoliata. C. edulis lowers soil pH and increases organic content due to the recalcitrance of tissue to decomposition, which may have evolved as a mechanism to facilitate recolonization and invasion..
 
 
D'Antonio, C. M. (1990). Seed production and dispersal in the non-native, invasive succulent Carpobrotus edulis (Aizoaceae) in coastal strand communities of central california. Journal of Applied Ecology, 27(2), 693-702. ABSTRACT
The plant produces a fleshy indehiscent fruit in early spring which remains on the plant until autumn when it is eaten by a variety of native mammals. Uneaten fruits remain on the plants for several years. Deer, brush rabbits and jackrabbits all eat the fruit and pass the seeds intact. The germination potential of ingested seeds was enhanced. Not all seeds in an animal dropping germinate in a given year. Ungerminated seeds remained viable for at least 2 yr, allowing build-up of a seedbank. Seeds were more frequent in the soil beneath adult plants, but showed no correlation in their abundance with distance away from adults over short distances. Viable seeds were found in deer faeces 1 km from the nearest adult plant. Dispersal of C. edulis by a variety of unspecialized consumers may help to explain its success as an invader.
 
 
D'Antonio, C. M., & Mahall, B. E. (1991). Root profiles and competition between the invasive exotic perennial, Carpobrotus edulis and two native shrub species in california coastal scrub. American Journal of Botany, 78(7), 885-894. ABSTRACT
The mat-forming succulent Carpobrotus edulis (Aizoaceae) surrounds and grows over many native plant species in Calfornia coastal communities. Haplopappus ericoides and H. venetus var. sedoides, have shallow root systems that occupied the same soil depths as those of C. edulis. In the presence of C. edulis, the normal rooting profiles of the shrubs were displaced downward, although partial overlap with C. edulis remained. Removal of C. edulis from around individuals of both shrub species resulted in higher predawn xylem pressure potentials, suggesting that the surrounding C. edulis was utilizing water that would otherwise have been available to these shrubs. In H. ericoides, predawn xylem pressure potentials of removal treatment shrubs remained higher than those of the controls throughout the remainder of the dry season even though these shrubs showed a marked increase in canopy area after removal of surrounding C. edulis. Removal of C. edulis from around H. venetus also initially led to higher predawn xylem pressure potentials in the removal shrubs and increased production of new leaves. After this initial period the predawn xylem pressure potentials of the removal shrubs were not significantly different from those of controls, ie demand for water by the increased leaf areas eventually matched the enhanced water availability resulting from C. edulis removal. The morphology of H. venetus changed to that more typical of unaffected individuals. Thus, C. edulis significantly affected not only the water relations of the shrub species but also their shoot sizes and overall morphologies
 
 
de la Peña, E., de Clercq, N., Bonte, D., Roiloa, S., Rodríguez-Echeverría, S., & Freitas, H. (2010). Plant-soil feedback as a mechanism of invasion by carpobrotus edulis. Biological Invasions, 12(10), 3637-3648. ABSTRACT
Invasive plant species have been suggested to change the composition of the soil community in a way that results in a positive feedback for them and a negative feedback for the native plant community. Carpobrotus edulis, a species native to South Africa, is one of the most aggressive exotic species in Mediterranean Europe. Although several aspects of its invasion biology have been studied, the occurrence of plant-soil feedback has been scarcely investigated. We first checked for the existence of biotic resistance in soils from two invaded sites of Mediterranean Europe and one site in the native area. Secondly, we evaluated the effects of soil conditioning on the germination and plant growth of C. edulis and two key species of native dunes. Finally, we tested the effects of short- and long-term soil conditioning on the performance and reproductive effort of C. edulis. Our results show that at first there is a natural resistance to invasion by the soil biota. Later, biotic resistance in invaded soil is suppressed by the establishment of a soil community that enhances the growth of C. edulis and that negatively influences the growth and survival of the native plants. Long-term soil conditioning in the field resulted in shifts in the balance between vegetative growth and sexual reproduction. Long-term invasion was also reflected in high levels of endophyte colonization by chytrids in roots, although the physiological consequences of this colonization remain unknown. The results obtained illustrate a mechanism that explains how C. edulis breaks the initial biotic resistance of newly-invaded landscapes. Finally, this study highlights the importance of studying plant-soil interactions on different members of the plant community and temporal stages in order to fully understand invasion.
 
 
Ferrer Merino, F., & Donat, P. M. (2011). Invasive plants in the coastal vegetal communities in Valencia (spain). Notulae Botanicae Horti Agrobotanici Cluj-Napoca, 39(1), 9-17. ABSTRACT
A botanical survey has been conducted to determine the influence of invasive species on the main indigenous communities in the Spanish Mediterranean coast and evaluate the current status of these communities in the eastern coast of Spain. The work was done in about 35 km of coastline located in Valencia (Spain). A total of 361 species cataloged are present in the study area, belonging to 79 different families. 49 of them have been inventoried invasive species which currently affect 38 plant communities. For this cause, we have developed a map of location finding out the area occupied by the same at every point and key to indigenous communities it affects. The plant communities characteristic of semi-mobile dunes Centaureo maritimae-Echietum sabulicolae and Medicagini marinae-Ammophiletum australis have turned out to have a greater degree of invasion. Carpobrotus edulis, Agave americana, Arundo donax, Oxalis pes-caprae and Cortaderia sellowiana are invasive species that cause further encroachment, both in area as a number of vegetation communities they affect.
 
 
Gallagher, K. G., Schierenbeck, K. A., & D'Antonio, C. M. (1997). Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in california II. allozyme evidence. American Journal of Botany, 84(7), 905-911. ABSTRACT
Morphological evidence has indicated that hybridization and introgression are occurring between Carpobrotus edulis L., a nonindigenous, invasive species in California (Bolus), and its putative native congener, C. chilensis. The identification of allozyme markers has enabled us to quantify hybridization and the extent of introgression between these species. Samples from 20 individuals of each of five morphological types (both parent species and three hybrid phenotypes) were collected from 39 populations along the coast of California from the Mexico to Oregon borders. Ten enzyme systems revealed a total of 17 resolvable loci, eight of which were polymorphic for the genus. Five of the polymorphic loci easily differentiate C. edulis and C. chilensis. Allele frequencies among the morphologically defined types are consistent with estimations of allele frequency changes due to first- and second-generation backcrossing. In comparison to long-lived, herbaceous perennials and widespread species, C. edulis and intermediate types have more variation in their populations (P = 41.73, A(p) = 2.11, H(o) = 0.246, and P = 38.13, A(p) = 2.06, H(o) = 0.216, respectively) than C. chilensis (P = 11.76, A(p) = 2.00, H(o) = 0.082). Indirect estimates of gene flow indicate four of the five morphological types are outcrossing. Gene flow between previously allopatric species may have broad implications if it results in an increase in fitness; further experimentation is needed to determine the ultimate ecological consequences of this phenomenon and its possible threat to limited, remaining natural habitat in California.
 
 
Maltez-Mouro, S., Maestre, F. T., & Freitas, H. (2010). Weak effects of the exotic invasive Carpobrotus edulis on the structure and composition of portuguese sand-dune communities. Biological Invasions, 12(7), 2117-2130. ABSTRACT
Sand dune ecosystems have a high conservation value worldwide, but they are highly threatened by exotic plant invasion. We investigated the impacts of the exotic invasive species Carpobrotus edulis on the composition and structure (spatial pattern, total cover, species diversity and species co-occurrence) of native sand dune communities in the western coast of Portugal. We studied eight sites following a north-south gradient; in each site we established 8-10 transects of 25 contiguous quadrats of one square meter. C. edulis had a significantly clumped pattern in five of the study sites, which, however, was not related to the spatial pattern of native species. The effects of climate on the community structure variables were on average three times stronger than those of C. edulis. This species also had small effects on the floristic composition of native species. Our results indicate that the success and impacts of C. edulis are habitat-dependent and context-specific. They also provide evidence of a strong resilience to the impacts of invasion in the studied sand dune ecosystems: C. edulis did not reach large abundances or exert negative impacts on native communities to the extent expected. These ecosystems provide a unique opportunity to increase our understanding on the origin of impacts by invasive species, and on how particular communities resist the impacts of an invader.
 
 
Roiloa, S. R., Rodríguez-Echeverría, S., de la Peña, E., & Freitas, H. (2010). Physiological integration increases the survival and growth of the clonal invader carpobrotus edulis. Biological Invasions, 12(6), 1815-1823. Schierenbeck, K. A., Symonds, V. V., Gallagher, K. G., & Bell, J. (2005). Genetic variation and phylogeographic analyses of two species of carpobrotus and their hybrids in california. Molecular Ecology, 14(2), 539-547. ABSTRACT
Despite the commonality and study of hybridization in plants, there are few studies between invasive and noninvasive species that examine the genetic variability and gene flow of cytoplasmic DNA. We describe the phylogeographical structure of chloroplast DNA (cpDNA) variation within and among several interspecific populations of the putative native, Carpobrotus chilensis and the introduced, Carpobrotus edulis (Aizoaceae). These species co-occur throughout much of coastal California and form several 'geographical hybrid populations'. Two hundred and thirty-seven individuals were analysed for variation in an approximate 7.0 kb region of the chloroplast genome using PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism) data. Phylogenetic analyses and cpDNA population differentiation were conducted for all morphotypes. Historic geographical dispersion and the coefficient of ancestry of the haplotypes were determined using nested clade analyses. Two haplotypic groupings (I and II) were represented in C. chilensis and C. edulis, respectively. The variation in cpDNA data is in agreement with the previously reported allozyme and morphological data; this supports relatively limited variation and high population differentiation among C. chilensis and hybrids and more wide-ranging variation in C. edulis and C. edulis populations backcrossed with C. chilensis. C. chilensis disproportionately contributes to the creation of hybrids with the direction of gene flow from C. chilensis into C. edulis. The cpDNA data support C. chilensis as the maternal contributor to the hybrid populations.
 
 
Thuiller, W., Richardson, D. M., Pyssek, P., Midgley, G. F., Hughes, G. O., & Rouget, M. (2005). Niche-based modelling as a tool for predicting the risk of alien plant invasions at a global scale. Global Change Biology, 11(12), 2234-2250. ABSTRACT
Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well-known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high-risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first-step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.
 
 
Underwood, E., Ustin, S., & DiPietro, D. (2003). Mapping nonnative plants using hyperspectral imagery. Remote Sensing of Environment, 86(2), 150-161. ABSTRACT
Nonnative plant species are causing enormous ecological and environmental impacts from local to global scale. Remote sensing images have had mixed success in providing spatial information on land cover characteristics to land managers that increase effective management of invasions into native habitats. However, there has been limited evaluation of the use of hyperspectral data and processing techniques for mapping specific invasive species based on their spectral characteristics. This research evaluated three different methods of processing hyperspectral imagery: minimum noise fraction (MNF), continuum removal, and band ratio indices for mapping iceplant (Carpobrotus edulis) and jubata grass (Cortaderia jubata) in California's coastal habitat. Validation with field sampling data showed high mapping accuracies for all methods for identifying presence or absence of iceplant (97%), with the MNF procedure producing the highest accuracy (55%) when the classes were divided into four different densities of iceplant.
 
 
Underwood, E. C., Ustin, S. L., & Ramirez, C. M. (2007). A comparison of spatial and spectral image resolution for mapping invasive plants in coastal california. Environmental Management, 39(1), 63-83. ABSTRACT
We explored the potential of detecting three target invasive species: iceplant (Carpobrotus edulis), jubata grass (Cortaderia jubata), and blue gum (Eucalyptus globulus) at Vandenberg Air Force Base, California. We compared the accuracy of mapping six communities (intact coastal scrub, iceplant invaded coastal scrub, iceplant invaded chaparral, jubata grass invaded chaparral, blue gum invaded chaparral, and intact chaparral) using four images with different combinations of spatial and spectral resolution: hyperspectral AVIRIS imagery (174 wavebands, 4 m spatial resolution), spatially degraded AVIRIS (174 bands, 30 m), spectrally degraded AVIRIS (6 bands, 4 m), and both spatially and spectrally degraded AVIRIS (6 bands, 30 m, i.e., simulated Landsat ETM data). Overall success rates for classifying the six classes was 75% (kappa 0.7) using full resolution AVIRIS, 58% (kappa 0.5) for the spatially degraded AVIRIS, 42% (kappa 0.3) for the spectrally degraded AVIRIS, and 37% (kappa 0.3) for the spatially and spectrally degraded AVIRIS. A true Landsat ETM image was also classified to illustrate that the results from the simulated ETM data were representative, which provided an accuracy of 50% (kappa 0.4). Mapping accuracies using different resolution images are evaluated in the context of community heterogeneity (species richness, diversity, and percent species cover). Findings illustrate that higher mapping accuracies are achieved with images possessing high spectral resolution, thus capturing information across the visible and reflected infrared solar spectrum. Understanding the tradeoffs in spectral and spatial resolution can assist land managers in deciding the most appropriate imagery with respect to target invasives and community characteristics.
 
 
Van Grunsven, R. H. A., Bos, F., Ripley, B. S., Suehs, C. M., & Veenendaal, E. M. (2009). Release from soil pathogens plays an important role in the success of invasive Carpobrotus in the mediterranean. South African Journal of Botany, 75(1), 172-175. ABSTRACT
Introduced plant species can become locally dominant and threaten native flora and fauna. This dominance is often thought to be a result of release from specialist enemies in the invaded range, or the evolution of increased competitive ability. Soil borne microorganisms have often been overlooked as enemies in this context, but a less deleterious plant soil interaction in the invaded range could explain local dominance. Two plant species, Carpobrotus edulis and the hybrid Carpobrotus X cf. acinaciformis, are considered major pests in the Mediterranean basin. We tested if release from soil-borne enemies and/or evolution of increased competitive ability could explain this dominance. Comparing biomass production in non-sterile soil with that in sterilized soil, we found that inoculation with rhizosphere soil from the native range reduced biomass production by 32% while inoculation with rhizosphere soil from the invaded range did not have a significant effect on plant biomass. Genotypes from the invaded range, including a hybrid, did not perform better than plants from the native range in sterile soil. Hence evolution of increased competitive ability and hybridization do not seem to play a major role. We conclude that the reduced negative net impact of the soil community in the invaded range may contribute to the success of Carpobrotus species in the Mediterranean basin.
 
 
Vila, M., & D'Antonio, C. M. (1998). Fruit choice and seed dispersal of invasive vs. noninvasive Carpobrotus (aizoaceae) in coastal california. Ecology, 79(3), 1053-1060. ABSTRACT
Natural hybridization between previously allopatric plant species can produce highly successful lineages. However, the ecological processes controlling the spread of hybrid genotypes have rarely been studied in the field. We compared fruit characteristics, fruit preference, and seed dispersal by native frugivores among the non-indigenous succulent Carpobrotus edulis, the putative native congener C. chilensis, and the hybrids resulting from introgressive hybridization. In this system, the non-native C. edulis and hybrids are known to be very successful invaders of California coastal plant communities. Carpobrotus edulis and hybrids produced more fruits per clone than C. chilensis, primarily as a consequence of larger clone size. Clone size and energy content of fruits were good predictors of fruit removal. Marked fruits of C. edulis and hybrids were removed faster than those of the other morphotypes, and C. edulis fruits were preferred over those of C. chilensis in a fruit transplant experiment. However, total fruit removal by the end of the growing season was very high for all morphotypes. Scats from black-tailed jackrabbit (Lepus californicus) and mule deer (Odocoileus hemionus), the most common frugivores in our sites, contained more seeds from C. edulis and hybrid morphotypes than from C. chilensis, and more than would be expected based on relative fruit abundance. Germination of seeds from C. edulis and hybrids was enhanced after gut passage, whereas germination of C. chilensis decreased after gut passage, compared to seed germination from intact fruits. The results suggest that patterns of fruit preference by native frugivores and seed survival after gut passage facilitate the successful spread of an aggressive introduced species and hybrids in contrast to the less aggressive, apparently native congener.
 
 
Vilà, M., & D'Antonio, C. M. (1998). Hybrid vigor for clonal growth in carpobrotus (aizoaceae) in coastal california. Ecological Applications, 8(4), 1196-1205. ABSTRACT
One of the consequences of the human-caused movement of plant species around the globe is hybridization between previously allopatric species. Introgressive hybridization between the non-native, invasive perennial succulent Carpobrotus edulis and the putative native, non-invasive C. chilensis is occurring throughout coastal California, leading to a high abundance of aggressive hybrid morphotypes and the loss of open space for native species establishment and growth. We test the hypothesis that hybrid vigor for vegetative growth and resistance to herbivory contributes to successful invasion by hybrid morphotypes. We compared survival and vegetative growth of transplanted cuttings of three morphotypes (parental species and hybrids) in three habitats in a factorial watering and caging experiment. Overall Carpobrotus growth was both water and herbivore limited. Hybrids displayed higher growth than either parental species. Hybrids always had higher survival in response to herbivory than C. chilensis, but survived better than C. edulis only in the bluff scrub. Growth of hybrids was higher than C. chilensis in the backdune and grassland but only higher than C. edulis in the backdune. Carpobrotus chilensis had the lowest survival to herbivory and the slowest growth. Our data suggest that greater resistance to mammalian herbivory coupled with hybrid vigor for vegetative growth can contribute to the invasive status of hybrids. High susceptibility to browsing and slow growth of C. chilensis at least partially explain its non-aggressive nature in coastal California.
 
 
Vilà, M., & D'Antonio, C. M. (1998). Fitness of invasive Carpobrotus (aizoaceae) hybrids in coastal California. Ecoscience, 5(2), 191-199. ABSTRACT
Natural hybridization between previously allopatric plant species can produce highly successful lineages. We test the low-fitness-hybrid hypothesis in Carpobrotus and its implications for hybrid invasion. We examine reproductive fitness components of hybrids between the invasive non-native succulent Carpobrotus edulis (L. Bolus) and the non-invasive putative native C. Chilensis (L.) from three populations in California coastal plant communities. Hybrids between the two species are very abundant and aggressive but it is not known if this is a transitory phenomenon. We find no support for the low-fitness-hybrid hypothesis in Carpobrotus. Fruit weight and seed set, mass and germination rate of hybrids were intermediate between or the same as a parental taxon. Survival, growth, and root to shoot ratio of hybrid seedlings did not differ from those of parental taxa. Although hybrid fitness is not superior to that of parental species, we believe that hybrids will continue to persist and invade California caostal communities because recruitment of seedlings did not differ from those of parental species. The highest survival probability of the introduced C. edulis may insure its successful invasion status.
 

 
 
 
 
 
 
 
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