Invasiveness Does Not Predict Impact: Response of Native Land Snail Communities to Plant Invasions in Riparian Habitats

Studies of plant invasions rarely address impacts on molluscs. By comparing pairs of invaded and corresponding uninvaded plots in 96 sites in floodplain forests, we examined effects of four invasive alien plants (Impatiens glandulifera, Fallopia japonica, F. sachalinensis, and F.×bohemica) in the Czech Republic on communities of land snails. The richness and abundance of living land snail species were recorded separately for all species, rare species listed on the national Red List, and small species with shell size below 5 mm. The significant impacts ranged from 16–48% reduction in snail species numbers, and 29–90% reduction in abundance. Small species were especially prone to reduction in species richness by all four invasive plant taxa. Rare snails were also negatively impacted by all plant invaders, both in terms of species richness or abundance. Overall, the impacts on snails were invader-specific, differing among plant taxa. The strong effect of I. glandulifera could be related to the post-invasion decrease in abundance of tall nitrophilous native plant species that are a nutrient-rich food source for snails in riparian habitats. Fallopia sachalinensis had the strongest negative impact of the three knotweeds, which reflects differences in their canopy structure, microhabitat humidity and litter decomposition. The ranking of Fallopia taxa according to the strength of impacts on snail communities differs from ranking by their invasiveness, known from previous studies. This indicates that invasiveness does not simply translate to impacts of invasion and needs to be borne in mind by conservation and management authorities.     

Downregulation of net phosphorus-uptake capacity is inversely related to leaf phosphorus-resorption proficiency in four species from a phosphorus-impoverished environment

Background and Aims

Previous research has suggested a trade-off between the capacity of plants to downregulate their phosphorus (P) uptake capacity and their efficiency of P resorption from senescent leaves in species from P-impoverished environments.

Methods

To investigate this further, four Australian native species (Banksia attenuata, B. menziesii, Acacia truncata and A. xanthina) were grown in a greenhouse in nutrient solutions at a range of P concentrations [P]. Acacia plants received between 0 and 500 µm P; Banksia plants received between 0 and 10 µm P, to avoid major P-toxicity symptoms in these highly P-sensitive species.

Key Results

For both Acacia species, the net P-uptake rates measured at 10 µm P decreased steadily with increasing P supply during growth. In contrast, in B. attenuata, the net rate of P uptake from a solution with 10 µm P increased linearly with increasing P supply during growth. The P-uptake rate of B. menziesii showed no significant response to P supply in the growing medium. Leaf [P] of the four species supported this finding, with A. truncata and A. xanthina showing an increase up to a saturation value of 19 and 21 mg P g⁻¹ leaf dry mass, respectively (at 500 µm P), whereas B. attenuata and B. menziesii both exhibited a linear increase in leaf [P], reaching 10 and 13 mg P g⁻¹ leaf dry mass, respectively, without approaching a saturation point. The Banksia plants grown at 10 µm P showed mild symptoms of P toxicity, i.e. yellow spots on some leaves and drying and curling of the tips of the leaves. Leaf P-resorption efficiency was 69 % (B. attenuata), 73 % (B. menziesii), 34 % (A. truncata) and 36 % (A. xanthina). The P-resorption proficiency values were 0·08 mg P g⁻¹ leaf dry mass (B. attenuata and B. menziesii), 0·32 mg P g⁻¹ leaf dry mass (A. truncata) and 0·36 mg P g⁻¹ leaf dry mass (A. xanthina). Combining the present results with additional information on P-remobilization efficiency and the capacity to downregulate P-uptake capacity for two other Australian woody species, we found a strong negative correlation between these traits.

Conclusions

It is concluded that species that are adapted to extremely P-impoverished soils, such as many south-western Australian Proteaceae species, have developed extremely high P-resorption efficiencies, but lost their capacity to downregulate their P-uptake mechanisms. The results support the hypothesis that the ability to resorb P from senescing leaves is inversely related to the capacity to downregulate net P uptake, possibly because constitutive synthesis of P transporters is a prerequisite for proficient P remobilization from senescing tissues.     

Population genetic structure of the predatory,social wasp Vespula pensylvanica in its native and invasive range

Invasive species cause extensive damage to their introduced ranges. Ocean archipelagos are particularly vulnerable to invasive taxa. In this study, we used polymorphic microsatellite markers to investigate the genetic structure of the social wasp Vespula pensylvanica in its native range of North America and its introduced range in the archipelago of Hawaii. Our goal was to gain a better understanding of the invasion dynamics of social species and the processes affecting biological invasions. We found that V. pensylvanica showed no significant genetic isolation by distance and little genetic structure over a span of 2000 km in its native range. This result suggests that V. pensylvanica can successfully disperse across large distances either through natural‐ or human‐mediated mechanisms. In contrast to the genetic patterns observed in the native range, we found substantial genetic structure in the invasive V. pensylvanica range in Hawaii. The strong patterns of genetic differentiation within and between the Hawaiian Islands may reflect the effects of geographic barriers and invasion history on gene flow. We also found some evidence for gene flow between the different islands of Hawaii which was likely mediated through human activity. Overall, this study provides insight on how geographic barriers, invasion history, and human activity can shape population genetic structure of invasive species.     

Community‐level changes in Banksia woodland following plant pathogen invasion in the Southwest Australian Floristic Region

Question: Does the introduced pathogen Phytophthora cinnamomi change Banksia woodland α‐ or β‐diversity and what are the implications for species re‐colonization? Location: High rainfall zone of the Southwest Australian Floristic Region (SWAFR). Methods: We measured pathogen‐induced floristic change along a disease chronosequence, and re‐sampled historic quadrats in Banksia attenuata woodlands of the SWAFR. The chronosequence represents three disease stages: (1) healthy vegetation with no disease expression; (2) the active disease front; and (3) diseased vegetation infected for at least 15 years. Comparative data were obtained by resampling diseased plots that were historically disease‐free when established in 1990. Results: β‐diversity differed substantially for both chronosequence and historic data, while α‐diversity was maintained, as measured by plot species richness and Simpson's reciprocal index. Species of known pathogen susceptibility were significantly reduced in cover–abundance, including the structurally dominant species; Banksia attenuata, B. ilicifolia and Allocasuarina fraseriana. Although these species remained present on diseased sites, there were overall reductions in canopy closure, leaf litter and basal area. These declines were coupled with an increase of species with unknown susceptibility, suggesting potential resistance and capacity to take advantage of altered site conditions. Conclusions: This study highlights the ability of an introduced plant pathogen to alter community floristics and associated stand variables. Species cover–abundances are unlikely to recover due to a reduced seed source, altered site conditions and pathogen persistence at the landscape level. However, maintenance of α‐diversity suggests continued biological significance of Phytophthora‐affected sites and the formation of novel ecosystems, themselves worthy of conservation.     

Niche partitioning in a sympatric cryptic species complex

Competition theory states that multiple species should not be able to occupy the same niche indefinitely. Morphologically, similar species are expected to be ecologically alike and exhibit little niche differentiation, which makes it difficult to explain the co‐occurrence of cryptic species. Here, we investigated interspecific niche differentiation within a complex of cryptic bumblebee species that co‐occur extensively in the United Kingdom. We compared the interspecific variation along different niche dimensions, to determine how they partition a niche to avoid competitive exclusion. We studied the species B. cryptarum, B. lucorum, and B. magnus at a single location in the northwest of Scotland throughout the flight season. Using mitochondrial DNA for species identification, we investigated differences in phenology, response to weather variables and forage use. We also estimated niche region and niche overlap between different castes of the three species. Our results show varying levels of niche partitioning between the bumblebee species along three niche dimensions. The species had contrasting phenologies: The phenology of B. magnus was delayed relative to the other two species, while B. cryptarum had a relatively extended phenology, with workers and males more common than B. lucorum early and late in the season. We found divergent thermal specialisation: In contrast to B. cryptarum and B. magnus, B. lucorum worker activity was skewed toward warmer, sunnier conditions, leading to interspecific temporal variation. Furthermore, the three species differentially exploited the available forage plants: In particular, unlike the other two species, B. magnus fed predominantly on species of heather. The results suggest that ecological divergence in different niche dimensions and spatio‐temporal heterogeneity in the environment may contribute to the persistence of cryptic species in sympatry. Furthermore, our study suggests that cryptic species provide distinct and unique ecosystem services, demonstrating that morphological similarity does not necessarily equate to ecological equivalence.     

Preference and Prey Switching in a Generalist Predator Attacking Local and Invasive Alien Pests

Invasive pest species may strongly affect biotic interactions in agro-ecosystems. The ability of generalist predators to prey on new invasive pests may result in drastic changes in the population dynamics of local pest species owing to predator-mediated indirect interactions among prey. On a short time scale, the nature and strength of such indirect interactions depend largely on preferences between prey and on predator behavior patterns. Under laboratory conditions we evaluated the prey preference of the generalist predator Macrolophus pygmaeus Rambur (Heteroptera: Miridae) when it encounters simultaneously the local tomato pest Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) and the invasive alien pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae). We tested various ratios of local vs. alien prey numbers, measuring switching by the predator from one prey to the other, and assessing what conditions (e.g. prey species abundance and prey development stage) may favor such prey switching. The total predation activity of M. pygmaeus was affected by the presence of T. absoluta in the prey complex with an opposite effect when comparing adult and juvenile predators. The predator showed similar preference toward T. absoluta eggs and B. tabaci nymphs, but T. absoluta larvae were clearly less attacked. However, prey preference strongly depended on prey relative abundance with a disproportionately high predation on the most abundant prey and disproportionately low predation on the rarest prey. Together with the findings of a recent companion study (Bompard et al. 2013, Population Ecology), the insight obtained on M. pygmaeus prey switching may be useful for Integrated Pest Management in tomato crops, notably for optimal simultaneous management of B. tabaci and T. absoluta, which very frequently co-occur on tomato.     

Benzoic acid induces tolerance to biotic stress caused by Phytophthora cinnamomi in Banksia attenuata

Banksia attenuata plants were treated with soil drenches or foliar sprays of benzoic acid (BZA) to determine induced resistance to Phytophthora cinnamomi. Stems of B. attenuata were inoculated with the pathogen 1 week after treatment with BZA. Resistance was estimated by measuring P. cinnamomi lesions on stems. Treatment with 0.10 mM, 0.25 mM or 0.50 mM BZA caused a reduction in lesion size with 0.50 mM BZA applied as a soil drench being the most effective treatment at suppressing the development of lesions. This is the first report of BZA induced host resistance in any plant species to any pathogen.     

Potential for dissemination of Phytophthora cinnamomi by feral pigs via ingestion of infected plant material

Feral pigs have long been implicated as potential vectors in the spread of the devastating plant pathogen Phytophthora cinnamomi due to their rooting and wallowing activities which may predispose them as vectors of infested soil. In this study, we aim to determine whether feral pigs have the potential to act as vectors of plant pathogens such as P. cinnamomi through their feeding activity. The typically omnivorous diet of feral pigs may also lead to the passage of P. cinnamomi infected plant material through their digestive system. This study investigates the potential for feral pigs to pass viable P. cinnamomi in their faeces following the ingestion of millet seeds, pine plugs and Banksia leptophilia roots inoculated with P. cinnamomi. Recovery rates of P. cinnamomi from the millet seeds, pine plugs and B. leptophilia roots following a single ingested bolus were 33.2, 94.9 and 10.4 %, respectively supported by quantitative PCR analysis. These results demonstrate that P. cinnamomi remain viable within infected plant material following passage through the pig digestive tract, although the digestive processes reduce the pathogen’s viability. An inverse relationship was observed between the viability of infected material and passage time, suggesting that partially digested plant material provides protection for P. cinnamomi against the adverse environmental conditions of the pig digestive tract. Phytophthora cinnamomi remained viable for up to 7 days in larger pieces of colonised woody plant material such as the pine plugs. A plant infection trial using passaged P. cinnamomi colonised pine plugs showed that even material that remained in the digestive tract for 7 days was capable of infecting and killing healthy plants, susceptible to P. cinnamomi. This study provides compelling evidence that feral pigs have the ability to transport viable P. cinnamomi in their digestive tract.     

An Extensive Alien Plant Inventory from the Inhabited Areas of Galapagos

Background

Plant invasions are causing habitat degradation in Galapagos. Problems are concentrated on the four inhabited islands. Plants introduced to rural areas in the humid highlands and urban areas on the arid coast act as foci for invasion of the surrounding Galapagos National Park.

Methodology/Principal Findings

Here we present results of the most comprehensive inventory to date of alien vascular plants in the inhabited areas of Galapagos. The survey was conducted between 2002 and 2007, in 6031 properties (97% of the total) on Floreana, Isabela, San Cristobal and Santa Cruz Islands. In total 754 alien vascular plant taxa were recorded, representing 468 genera in 123 families. Dicotyledons represented 554 taxa, monocotyledons 183, there were 7 gymnosperms and 10 pteridophytes. Almost half (363) of the taxa were herbaceous. The most represented families were Fabaceae (sensu lato), Asteraceae and Poaceae. The three most recorded species in the humid rural areas were Psidium guajava, Passiflora edulis and Bryophyllum pinnatum, and in the dry urban areas, Aloe vera, Portulaca oleracea and Carica papaya. In total, 264 (35%) taxa were recorded as naturalized. The most common use for taxa was ornamental (52%).

Conclusions/Significance

This extensive survey has increased the known alien vascular flora of Galapagos by 257 species, giving a ratio of alien to native taxa of 1.57∶1. It provides a crucial baseline for plant invasion management in the archipelago and contributes data for meta analyses of invasion processes worldwide. A repeat of the survey in the future would act as an effective early detection tool to help avoid further invasion of the Galapagos National Park.     

Microsatellites for eastern Australian Banksia species

We developed eight primer pairs for Banksia microsatellite markers (five using DNA from Banksia oblongifolia and three from Banksia robur) in order to study the processes of speciation within hybridizing B. oblongifolia, B. robur and Banksia paludosa complex. We genotyped four populations of B. oblongifolia and B. robur, and three of B. paludosa. Numbers of alleles ranged from 1 to 13 across the three species and observed average heterozygosities ranged from 0.000 to 0.833. At least four loci completely discriminated B. robur from B. oblongifolia and three discriminated B. paludosa from B. oblongifolia. Seven of these primers amplified DNA from at least two of three other local species.     

Uptake of 32P by Young Plants of Banksia hookeriana Meissner When Healthy and Infected with Phytophthora cinnamomi Rands

Young plants of Banksia hookeriana were grown in acid-washedsand with adequate phosphate and water supply, and a proportionwere inoculated with Phytophthora cinnamomi. There were no majordifferences in growth between uninoculated and infected plants,but there was a large increase in uptake of ³²P with increasingroot disease. In healthy plants ³²P uptake was greatest in youngleaf tissue, but in diseased plants labelled phosphate was directedmore towards older leaves where the activity was almost twicethat of young leaves. Enhanced uptake with disease was ascribed to possible blockageof the ‘message’ or ‘signal’ of phosphatetranslocation from shoot to root, such that the diseased rootincorrectly treated the shoot as P deficient and increased Puptake. Key words: Banksia hookeriana, Proteaceae, ³²P uptake, Phytophthora cinnamomi     

Molecular analysis of interspecific and intergeneric relationships of Banksia using RAPDs and non-coding chloroplast DNA sequences

 Random amplified polymorphic DNA (RAPD) and chloroplast DNA (cpDNA) markers were used to study interspecific and intergeneric relationships of Banksia (Proteaceae) to aid breeding of the genus for cut flower production. The accepted morphological phylogeny of Banksia, with two subgenera, two sections and 13 series, is unclear regarding the relationships of the commercial cut flower species B. coccinea. Fifteen RAPD primers and a non-coding cpDNA sequence between the trnL (UAA) and trnF (GAA) gene were applied to species of Banksia, the related genus Dryandra, and to Musgravea heterophylla as the outgroup, with cluster analysis applied to the results. The two methods were in broad agreement with each other, and with the accepted taxonomy, with closely related species pairs and groups clustering together, but RAPDs were not informative between distantly related species or species pairs. Banksia coccinea clustered with Dryandra and formed a polytomy with 2 Dryandra species and the two sections of subgenus Banksia. Subgenus Isostylis formed a polytomy with D. formosa, basal to subgenus Banksia, but with B. cuneata and B. illicifolia (both in subgenus Isostylis) polyphyletic. Dryandra did not separate as a clade and fell within Banksia, raising questions about the currently accepted view of the two as sister genera with parallel morphological development. The results indicate that interspecific and intergeneric hybridisation with genus Dryandra and subgenus Banksia may be possible routes for improvement of the commercial species B. coccinea. Received: 25 September 1996 / Accepted: 8 November 1996     

Impact of flower and seed predators on seed-set in two Banksia shrubs

A non-systemic Insecticide was used to exclude flower and seed predators from Banksia ericifolia and B. oblongifolia Inflorescenses. In B. ericifolia this treatment doubled the number of inflorescences that set seeds, and increased by 40% the number of seeds produced per Inflorescence. Insecticide treatment did not alter either of these components of seed-set in B. oblongifolia partly because the experiment began too late to exclude flower predators In this species. The results obtained for B. ericifolia support the hypothesis that flower and seed predators explain, in part, the low incidence of seed-bearing cones and the low seed:flower ratios reported for many Banksia species. Each Banksia species supports two guilds of Inflorescence predators. Two Lepidopteran species feed on young flowers; one of these causes tunnel damage to the rachis. Each Banksia species also supports five Lepidopteran and two Curcullonid seed-predators. About 40% of these herbivorous Insects are common to both shrubs.     

遗传多样性与外来物种的成功入侵: 现状和展望

遗传多样性被认为是影响外来种入侵成功的重要因素之一。研究表明, 尽管外来种在入侵过程中可能受到奠基者效应的影响, 但是多次引种、种内或种间杂交等过程使得许多外来种在引入地的遗传多样性水平未必会显著低于原产地, 从而使得外来种可能通过快速进化来适应引入地的新生境。然而, 高水平的遗传多样性并非成功入侵的必要条件, 遗传变异的匮乏对一些外来种的入侵能力没有明显的影响, 甚至在一些生物入侵案例中, 遗传多样性的降低反而促进了入侵成功。针对遗传多样性与入侵成功之间的复杂关系, 本文在评述外来种遗传多样性的研究现状的基础上, 分析了遗传多样性对外来种的短期入侵成功和长期进化的影响机制, 从方法角度探讨了目前研究中存在的若干问题, 并对如何推进入侵生态学研究提出了一些看法。正如一些学者提出的, 入侵生态学需要与生态学其他分支整合起来, 才能加深对生物入侵及其相关的生态和进化过程的理解。     

Grass bud responses to fire in a semiarid savanna system

Increasingly, land managers have attempted to use extreme prescribed fire as a method to address woody plant encroachment in savanna ecosystems. The effect that these fires have on herbaceous vegetation is poorly understood. We experimentally examined immediate (<24 hr) bud response of two dominant graminoids, a C₃ caespitose grass, Nassella leucotricha, and a C₄ stoloniferous grass, Hilaria belangeri, following fires of varying energy (J/m²) in a semiarid savanna in the Edwards Plateau ecoregion of Texas. Treatments included high‐ and low‐energy fires determined by contrasting fuel loading and a no burn (control) treatment. Belowground axillary buds were counted and their activities classified to determine immediate effects of fire energy on bud activity, dormancy, and mortality. High‐energy burns resulted in immediate mortality of N. leucotricha and H. belangeri buds (p < .05). Active buds decreased following high‐energy and low‐energy burns for both species (p < .05). In contrast, bud activity, dormancy, and mortality remained constant in the control. In the high‐energy treatment, 100% (n = 24) of N. leucotricha individuals resprouted while only 25% (n = 24) of H. belangeri individuals resprouted (p < .0001) 3 weeks following treatment application. Bud depths differed between species and may account for this divergence, with average bud depths for N. leucotricha 1.3 cm deeper than H. belangeri (p < .0001). Synthesis and applications: Our results suggest that fire energy directly affects bud activity and mortality through soil heating for these two species. It is imperative to understand how fire energy impacts the bud banks of grasses to better predict grass response to increased use of extreme prescribed fire in land management.     

Low Rate of Between-Population Seed Dispersal Restricts Genetic Connectivity and Metapopulation Dynamics in a Clonal Shrub

Clonal species normally have low seed production, low recruitment rates and long lifespans, and it is expected that the rates of long-distance dispersal (LDD) of seeds will be low as well. Banksia candolleana is a clonal shrub in Mediterranean-type, fire-prone sclerophyll shrublands of southwestern Australia, whose reproductive biology and population dynamics contrast with those of co-occurring nonclonal congeneric species, all of which are restricted to a mosaic of sand dunes set within a matrix of inhospitable swales. Using microsatellite markers, we genotyped 499 plants in all 15 populations of B. candolleana within a 12-km² area, assessed population genetic differentiation, and quantified the effective rate of interpopulation seed dispersal through genetic assignment of individuals to populations. We measured life history, reproductive and demographic attributes, and compared these with two co-occurring Banksia species, a non-clonal resprouter and a nonsprouter. B. candolleana has much higher levels of population genetic differentiation, and one-third the rate of interpopulation seed migration, as the other two species (2.2% vs 5.5−6.8% of genotyped plants inferred to be immigrants), though distances reached by LDD are comparable (0.3−2.3 km). The low rate of interpopulation dispersal was supported by an analysis of the age structure of three populations that suggests a mean interdune migration rate of <800 m in 200 years, and 60% of suitable dunes remain uninhabited. Thus, B. candolleana has poor properties for promoting long-distance dispersal. It is unclear if these are idiosyncratic to this species or whether such properties are to be expected of clonal species in general where LDD is less critical for species survival.     

The influence of cone age on the relative longevity of Banksia seeds

Background and Aims

Serotiny is common in the genus Banksia, so any seed collection is likely to be comprised of seeds that were produced in many different years. This study aimed to determine the impact of cone age and degree of serotiny on longevity in ex situ storage.

Methods

Cones of identifiable age classes were collected from three species of Banksia. Seeds were extracted from cones and the degree of serotiny calculated. An estimate of initial viability (K_i), the time for viability to fall by one probit (σ) and the relative longevity of seeds (p₅₀) for each species and cone age class was determined using a comparative longevity test (50 °C, 63 % relative humidity).

Key Results

The degree of serotiny ranged from moderate (7·9) for Banksia attenuata to strong (40·4) for B. hookeriana. Survival curves for all seed age classes within each species could be described by regressions with a common slope (1/σ), but with different values for K_i. The time taken for viability to fall by one probit (σ) could be described by a common value (29·1 d) for all three species.

Conclusions

Differences in seed longevity between cone age classes and species was related to variation in initial viability (K_i) rather than to differences in σ. While targeting the youngest mature seed cohort on a plant will maximize the viability of seeds collected, a wide range of age classes should be collected (but stored as separate cohorts if possible) for quality conservation/restoration seed collections where genetic diversity is important.     

Drivers of Solidago species invasion in Central Europe—Case study in the landscape of the Carpathian Mountains and their foreground

AimThe invasion process is a complex, context‐dependent phenomenon; nevertheless, it can be described using the PAB framework. This framework encompasses the joint effect of propagule pressure (P), abiotic characteristics of the environment (A), and biotic characteristics of both the invader and recipient vegetation (B). We analyzed the effectiveness of proxies of PAB factors to explain the spatial pattern of Solidago canadensis and S. gigantea invasion using invasive species distribution models.LocationCarpathian Mountains and their foreground, Central Europe.MethodsThe data on species presence or absence were from an atlas of neophyte distribution based on a 2 × 2 km grid, covering approximately 31,200 km² (7,752 grid cells). Proxies of PAB factors, along with data on historical distribution of invaders, were used as explanatory variables in Boosted Regression Trees models to explain the distribution of invasive Solidago. The areas with potentially lower sampling effort were excluded from analysis based on a target species approach.ResultsProxies of the PAB factors helped to explain the distribution of both S. canadensis and S. gigantea. Distributions of both species were limited climatically because a mountain climate is not conducive to their growth; however, the S. canadensis distribution pattern was correlated with proxies of human pressure, whereas S. gigantea distribution was connected with environmental characteristics. The varied responses of species with regard to distance from their historical distribution sites indicated differences in their invasion drivers.Main conclusionsProxies of PAB are helpful in the choice of explanatory variables as well as the ecological interpretation of species distribution models. The results underline that human activity can cause variation in the invasion of ecologically similar species.     

Assessing the risk of invasive success in Pinus and Banksia in South African mountain fynbos

Abstract. South African mountain fynbos has been severely invaded by trees and shrubs introduced from other mediterranean-climate regions. Management of these invasions should involve controlling current invaders and screening future introductions. Invasion windows are described and functional groups are defined for pines based on life history attributes important for invasion in the fire-prone mountain fynbos. The most successful invasive pines here (Pinus halepensis, P. pinaster and P. radiata) are fire-resilient and have small seeds, low seed-wing loadings, short juvenile periods, moderate to high degrees of serotiny and relatively poor fire-tolerance as adults. Other species with these attributes, especially from mediterranean-climate regions, wouldbe high-risk introductions. Taxa in other functional groups have not become major weeds even with widespread man-aided dissemination. Experience with pine invaders was used to define functional groups in western Australian Banksia species (Proteaceae), shrubs and trees which include taxa with similar attributes to fynbos invaders (e.g. Hakea and Pinus spp.). Banksias have only recently been introduced to the Cape, and are likely to be increasingly cultivated for the cut flower market. Tall serotinous shrubs with many small seeds per plant, short juvenile periods and low fire tolerance were identified as high risk introductions. This group includes thicket-forming species which maintain very large viable seed banks, e.g. Banksia burdettii, B. hookeriana and B. leptophylla. Low sprouting shrubs with few large seeds per plant and long juvenile periods are unlikely to become invasive in mountain fynbos. The approach of defining functional groups based on life history attributes and invasion windows is valuable for predicting the probability of invasive success. Chance interactions suchas an opportunistic dispersal mutualism between Pinus pinea and an introduced squirrel sometimes confound these predictions and underscore the idiosyncracies inherent in biological invasions.     

Developing a taxonomic identification system of Phytophthora species based on microsatellites

BackgroundPhytophthora is the most important genus of the Oomycete plant pathogens. Nowadays, there are 117 described species in this genus, most of them being primary invaders of plant tissues. The different species are causal agents of diseases in a wide range of crops and plants in natural environments. In order to develop control strategies against Phytophthoraspecies, it is important to know the biology, ecology and evolutionary processes of these important pathogens.AimsThe aim of this study was to propose and validate a low cost identification system for Phytophthora species based on a set of polymorphic microsatellite (SSRs) markers.MethodsThirty-three isolates representing Phytophthora infestans, Phytophthora andina, Phytophthora sojae, Phytophthora cryptogea, Phytophthora nicotianae, Phytophthora capsici and Phytophthora cinnamomi species were obtained, and 13 SSRs were selected as potentially transferable markers between these species. Amplification conditions, including annealing temperatures, were standardized for several markers.ResultsA subset of these markers amplified in all species, showing species-specific alleles.ConclusionsThe adaptability and impact of the identification system in Colombia, an Andean agricultural country where different Phytophthora species co-exist in the same or in several hosts grown together, are discussed.