Plant invasions – the role of mutualisms RICHARDSON, DAVID M.; ALLSOPP, NICKY; D'ANTONIO, CARLA M. ...
Biological reviews of the Cambridge Philosophical Society,
02/2000, Letnik:
75, Številka:
1
Journal Article
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Many introduced plant species rely on mutualisms in their new habitats to overcome barriers to
establishment and to become naturalized and, in some cases, invasive. Mutualisms involving ...animal-mediated pollination and seed dispersal, and symbioses between plant roots and microbiota often facilitate
invasions. The spread of many alien plants, particularly woody ones, depends on pollinator mutualisms.
Most alien plants are well served by generalist pollinators (insects and birds), and pollinator limitation does
not appear to be a major barrier for the spread of introduced plants (special conditions relating to Ficus and
orchids are described). Seeds of many of the most notorious plant invaders are dispersed by animals, mainly
birds and mammals. Our review supports the view that tightly coevolved, plant-vertebrate seed dispersal
systems are extremely rare. Vertebrate-dispersed plants are generally not limited reproductively by the lack
of dispersers. Most mycorrhizal plants form associations with arbuscular mycorrhizal fungi which, because
of their low specificity, do not seem to play a major role in facilitating or hindering plant invasions (except
possibly on remote islands such as the Galapagos which are poor in arbuscular mycorrhizal fungi). The lack
of symbionts has, however, been a major barrier for many ectomycorrhizal plants, notably for Pinus spp. in
parts of the southern hemisphere. The roles of nitrogen-fixing associations between legumes and rhizobia and
between actinorhizal plants and Frankia spp. in promoting or hindering invasions have been virtually ignored
in the invasions literature. Symbionts required to induce nitrogen fixation in many plants are extremely
widespread, but intentional introductions of symbionts have altered the invasibility of many, if not most,
systems. Some of the world's worst invasive alien species only invaded after the introduction of symbionts.
Mutualisms in the new environment sometimes re-unite the same species that form partnerships in the native
range of the plant. Very often, however, different species are involved, emphasizing the diffuse nature of
many (most) mutualisms. Mutualisms in new habitats usually duplicate functions or strategies that exist in
the natural range of the plant. Occasionally, mutualisms forge totally novel combinations, with profound
implications for the behaviour of the introduced plant in the new environment (examples are seed dispersal
mutualisms involving wind-dispersed pines and cockatoos in Australia; and mycorrhizal associations
involving plant roots and fungi). Many ecosystems are becoming more susceptible to invasion by introduced
plants because: (a) they contain an increasing array of potential mutualistic partners (e.g. generalist
frugivores and pollinators, mycorrhizal fungi with wide host ranges, rhizobia strains with infectivity across
genera); and (b) conditions conducive for the establishment of various alien/alien synergisms are becoming
more abundant. Incorporating perspectives on mutualisms in screening protocols will improve (but not
perfect) our ability to predict whether a given plant species could invade a particular habitat.
Burkholderia cepacia was originally described as the causal agent of onion sour skin. However, this bacterium is now recognized as a complex of 22 closely related species, commonly referred to as the ...B. cepacia complex (BCC). Only a few taxonomic studies have been undertaken with the aim of understanding the diversity of species associated with onion sour skin. In this study, we used a polyphasic analysis including rep‐PCR assay, biochemical and pathological profiles, and multilocus sequence analysis (MLSA) to characterize the BCC species associated with onion sour skin in the semi‐arid region of north‐east Brazil. Phylogenetic analysis of the recA of strains representing the genetic variability, as determined by rep‐PCR, grouped the strains into four clades. Clades I and II represent B. cenocepacia lineages IIB and IIIA, respectively, while the strains in Clades III and IV clustered more closely to Clades I and II than to strains of any other BCC species. MLSA confirmed the existence of the four clades with a 1.00 posterior probability. A distance matrix indicated a low level of divergence among the strains of the four clades found in the MLSA, proving that B. cenocepacia lineages IIIA, IIIB, and a new lineage of B. cenocepacia are associated with onion sour skin in the semi‐arid region of north‐east Brazil. Also, surprisingly, no strain was identified as B. cepacia, indicating that this species probably does not play a role in this disease in this region.
Onion sour skin in the semi‐arid region of north‐east Brazil is caused by strains of Burkholderia cenocepacia lineages IIIA, IIIB, and a new lineage, while B. cepacia was not found in this region.
Molecular modeling and ultraviolet–visible spectroscopy (UV–vis) studies strongly suggest that the interaction between RCQ and heme is predominant through the quinoline moiety in a mechanism of ...action similar to that observed for chloroquine.
Reversed chloroquine (RCQ) is a multiple ligand compound active against chloroquine-sensitive and resistant falciparum malaria. It is composed by a 4-aminoquinoline moiety (like that present in chloroquine (CQ)) joined to imipramine (IMP), a modulating agent that also showed intrinsic antiplasmodial activity against Brazilian Plasmodium falciparum isolates resistant to CQ. Molecular modeling and ultraviolet–visible spectroscopy (UV–vis) studies strongly suggest that the interaction between RCQ and heme is predominant through the quinoline moiety in a mechanism of action similar to that observed for CQ.
Ecology letters (2011) 14: 274-281 ABSTRACT: Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested ...assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.
We measured spatial and temporal patterns of seed dispersal and seedling recruitment for 58 species in a grassland community to test whether seed dispersal could predict patterns of invasion after ...disturbance. For the 12 most abundant grasses, recruitment of native species was dependent on the propagule supply of both native and exotic species. Variability in seed rain on small spatial (1-10 m) and temporal (within season) scales led to qualitative differences in the outcome of disturbance colonization such that native species dominated disturbances when exotic seed supply was low but failed to establish when exotic seed supply was high. Local dispersal and spatial heterogeneity in species composition promoted coexistence of native and exotic species by creating refuges from high exotic seed supply within native dominated patches. Despite this, copious exotic seed production strongly limited recruitment of native species in exotic dominated patches. Most grasslands in California are presently dominated by exotic species, suggesting that competition at the seedling stage is a major barrier to native species restoration.
The invasion of European perennial grasses represents a new threat to the native coastal prairie of northern California. Many coastal prairie sites also experience anthropogenic nitrogen (N) ...deposition or increased N availability as a result of invasion by N-fixing shrubs. We tested the hypothesis that greater seedling competitive ability and greater responsiveness to high N availability of exotic perennial grasses facilitates their invasion in coastal prairie. We evaluated pairwise competitive responses and effects, and the occurrence of asymmetrical competition, among three common native perennial grasses (Agrostis oregonensis, Festuca rubra, and Nassella pulchra) and three exotic perennial grasses (Holcus lanatus, Phalaris aquatica, and Festuca arundinacea), at two levels of soil N. We also compared the root and shoot biomass and response to fertilization of singly-grown plants, so we could evaluate how performance in competition related to innate plant traits. Competitive effects and responses were negatively correlated and in general varied continuously across native and exotic species. Two exceptions were the exotic species Holcus, which had large effects on neighbors and small responses to them, and competed asymmetrically with all other species in the experiment, and the native grass Nassella, which had strong responses to but little effect on neighbors, and was out-competed by all but one other species in the experiment. High allocation to roots and high early relative growth rate appear to explain Holcus's competitive dominance, but its shoot biomass when grown alone was not significantly greater than those of the species it out-competed. Competitive dynamics were unaffected by fertilization. Therefore, we conclude that seedling competitive ability alone does not explain the increasing dominance of exotic perennial grasses in California coastal prairie. Furthermore, since native and exotic species responded individualistically, grouping species as 'natives' and 'exotics' obscured underlying variation within the two categories. Finally, elevated soil N does not appear to influence competition among the native and exotic perennial grasses studied, so reducing soil N pools may not be a critical step for the restoration of California coastal prairie.
There is growing interest in the addition of carbon (C) as sucrose or sawdust to the soil as a tool to reduce plant‐available nitrogen (N) and alter competitive interactions among species. The ...hypothesis that C addition changes N availability and thereby changes competitive dynamics between natives and exotics was tested in a California grassland that had experienced N enrichment. Sawdust (1.2 kg/m) was added to plots containing various combinations of three native perennial bunchgrasses, exotic perennial grasses, and exotic annual grasses. Sawdust addition resulted in higher microbial biomass N, lower rates of net N mineralization and net nitrification, and higher concentrations of extractable soil ammonium in the soil. In the first year sawdust addition decreased the degree to which exotic annuals competitively suppressed the seedlings of Nassella pulchra and, to a lesser extent, Festuca rubra, both native grasses. However there was no evidence of reduced growth of exotic grasses in sawdust‐amended plots. Sawdust addition did not influence interactions between the natives and exotic perennial grasses. In the second year, however, sawdust addition did not affect the interactions between the natives and either group of exotic grasses. In fact, the native perennial grasses that survived the first year of competition with annual grasses significantly reduced the aboveground productivity of annual grasses even without sawdust addition. These results suggest that the addition of sawdust as a tool in the restoration of native species in our system provided no significant benefit to natives over a 2‐year period.
Biological invasions as global environmental change Vitousek, P.M. (Stanford University.); D'Antonio, C.M; Loope, L.L ...
American scientist,
(Sep-Oct 1996), 19960901, Letnik:
84, Številka:
5
Journal Article
The world's mobile society is redistributing the species on the earth at a pace that challenges ecosystems, threatens human health and strains economies. The extent to which humans manipulate the ...distribution of life on earth is discussed.
The South African succulent Carpobrotus edulis has been invading native and non-native plant assemblages in California since its introduction in the early 1900s. This study was designed to determine ...mechanisms controlling invasion by this species into three different communities: coastal grassland, backdune, and coastal scrub. The communities differed in several factors that influenced invasion by Carpobrotus: soil disturbance, herbivory, and identity of competitors. Disturbances of the soil was required for establishment of Carpobrotus at the grassland site. Soil disturbance did not promote Carpobrotus establishment in the coastal scrub or backdune. Establishment in these sites was restricted by herbivory. The influence of neighboring vegetation on Carpobrotus establishment was site dependent. At the grassland site, Carpobrotus seedling survival was reduced by grasses, and the only surviving seedlings were on gopher mounds. Growth of larger Carpobrotus plants, however, was unaffected by grasses. Proximity to shrubs, the dominant plant type at the backdune and coastal scrub sites, did not affect Carpobrotus seedling survival. It did, however, decrease both root and shoot biomass of seedlings and cuttings. Invasion is expected to occur most rapidly at the grassland site. Although germination and early survival there depend on the occurrence of rodent disturbances, these occur frequently, and seedling recruitment in the grassland was observed during this study. Once established, clonal growth is great and is not affected by herbivory or competition. In contrast, at the coastal growth, intense herbivory prevented successful establishment during this study. Cage experiments suggested that herbivory counteracted the high growth potential of Carpobrotus at this site. At the dune site, even caged plants showed very poor growth. Thus, although seedling recruitment does not occur there, invasion is expected to be slow due to harsh physical conditions that limit both survival and growth. These findings demonstrate strong community differences in the factors governing invasability by Carpobrotus edulis.
To date, studies investigating the association between ACTN3 R577X and ACE I/D gene variants and elite sprint/power performance have been limited by small cohorts from mixed sport disciplines, ...without quantitative measures of performance.
To examine the association between these variants and sprint time in elite athletes.
We collected a total of 555 best personal 100-, 200-, and 400-m times of 346 elite sprinters in a large cohort of elite Caucasian or African origin sprinters from 10 different countries. Sprinters were genotyped for ACTN3 R577X and ACE ID variants.
On average, male Caucasian sprinters with the ACTN3 577RR or the ACE DD genotype had faster best 200-m sprint time than their 577XX (21.19 ± 0.53 s vs. 21.86 ± 0.54 s, p = 0.016) and ACE II (21.33 ± 0.56 vs. 21.93 ± 0.67 sec, p = 0.004) counterparts and only one case of ACE II, and no cases of ACTN3 577XX, had a faster 200-m time than the 2012 London Olympics qualifying (vs. 12 qualified sprinters with 577RR or 577RX genotype). Caucasian sprinters with the ACE DD genotype had faster best 400-m sprint time than their ACE II counterparts (46.94 ± 1.19 s vs. 48.50 ± 1.07 s, p = 0.003). Using genetic models we found that the ACTN3 577R allele and ACE D allele dominant model account for 0.92 % and 1.48 % of sprint time variance, respectively.
Despite sprint performance relying on many gene variants and environment, the % sprint time variance explained by ACE and ACTN3 is substantial at the elite level and might be the difference between a world record and only making the final.
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