No difference in competitive ability between invasive North American and native European <Emphasis Type="Italic">Lepidium draba</Emphasis> populations

The evolution of increased competitive ability (EICA) hypothesis states that plants introduced into a new range experience reduced herbivory, which in turn results in a shift in resource allocation from herbivore defense to growth. If genotypes of an invasive plant species from its native and introduced ranges are grown under common conditions, introduced genotypes are expected to grow more vigorously than conspecific native genotypes. We tested predictions of the EICA hypothesis with the invasive species Lepidium draba by comparing the growth of genotypes from its native European and introduced western US ranges under common conditions. To test potential differences in competitive ability, we grew L. draba from both continents with either Festuca idahoensis, a weak competitor native to North America, or Festuca ovina, a strong competitor native to Europe. Contrary to EICA predictions, there were no differences in the performance of native and introduced L. draba, independent of whether plants were grown with F. idahoensis, F. ovina, or alone. The strong competitor, F. ovina impaired the growth of L. draba more than the weak competitor F. idahoensis and conversely, F. idahoensis was generally more impaired by L. draba than was F. ovina. While the native F. idahoensis was equally affected by L. draba regardless of range, F. ovina was not: US L. draba had a stronger negative effect on F. ovina growth than European L. draba. Our data suggest that the EICA hypothesis is not suitable to explain the invasion success of L. draba in the US. Instead, the greater competitive effect of L. draba on the North American F. idahoensis and the asymmetric competitive effect of L draba from different origins on F. ovina may indicate superior competitive ability for resources, or the presence of allelopathic traits in L. draba, to which plant species in non-native ranges are maladapted.     

Invasive leaf resources alleviate density dependence in the invasive mosquito, <Emphasis Type="Italic">Aedes albopictus</Emphasis>

Interactions between invasive species can have important consequences for the speed and impact of biological invasions. Containers occupied by the invasive mosquito, Aedes albopictus Skuse, may be sensitive to invasive plants whose leaves fall into this larval habitat. To examine the potential for interactions between invasive leaf species and larval A. albopictus, we conducted a field survey of leaf material found with A. albopictus in containers in Palm Beach County, Florida and measured density dependent responses of A. albopictus larvae to two invasive and one native leaf species in laboratory experiments. We found increased diversity of leaf species, particularly invasive species, in areas further from the urbanized coast, and a significant positive association between the presence of Schinus terebinthifolious (Brazilian pepper) and the abundance of A. albopictus. In laboratory experiments, we determined that larval growth and survivorship were significantly affected by both larval density and leaf species which, in turn, resulted in higher population performance on the most abundant invasive species (Brazilian pepper) relative to the most abundant native species, Quercus virginiana (live oak). These results suggest invasive leaf species can alleviate density dependent reductions in population performance in A. albopictus, and may contribute to its invasion success and potential to spread infectious disease.     

<Emphasis Type="Italic">Acroptilon repens</Emphasis>, an Asian invader,has stronger competitive effects on species from America than species from its native range

The ability to competitively suppress native species is key to successful invasion. Since invasions involve an increase in abundance or dominance of a species in its non-native range, competitive effects might be expected to be stronger in the non-native range of an invader; however, there have been few comparisons of the competitive effects of invasive plants on species from invaded ranges versus species from native ranges. We compared the competitive and allelopathic effects of Acroptilon repens on native North American species to effects on related species from the native range of Acroptilon in Uzbekistan. We also compared the competitive interactions among these North American and Eurasian species, in the absence of Acroptilon, examining the hypothesis that particular regional species pools may show differences in competitive ability. The results showed that Acroptilon had stronger competitive effects against native North American species than against species native to Uzbekistan. There was no difference in the competitive effects among Eurasians and North Americans. The effects of leachates collected from Acroptilon roots were weak but more negative on species from North America than on species from Uzbekistan. Our results suggest that inherently stronger competitive and allelopathic effects of Acroptilon on North American plants than on plants from its native range may contribute to its invasive success.     

Predatory disturbance and prey species diversity: the case of gray whale (<Emphasis Type="Italic">Eschrichtius robustus</Emphasis>) foraging on a multi-species mysid (family <Emphasis Type="Italic">Mysidae</Emphasis>) community

Why competitive exclusion does not limit the number of coexisting plankton species is a persistent question for community ecology. One explanation, the intermediate disturbance hypothesis (IDH), proposes that elevated species diversity is a product of moderate levels of disturbance that allow the subsequent invasion of less competitive species. Here, we assess the shifts in species diversity in a mysid (Mysidae Dana, 1850) zooplankton community, where at least 10 species have, over the last 15 years, have come to comprise the primary prey base of summer resident gray whales (Eschrictius robustus Lilljeborg, 1861) in Clayoquot Sound, British Columbia. We evaluate trends in the community structure of mysids (species dominance, diversity, and richness) across mysid habitat in the study area during the gray whale foraging season (May–September) for the period 1996 and 2008. Mysid species composition varies among years and diversity has increased as whales shifted their predatory focus from benthic amphipods (Ampeliscidae Costa, 1857) to mysids, near our starting point in 1996. Holmesimysis sculpta Tattersall, 1933 was the dominant species in early years; however, in 2007, the dominance shifted to Neomysis rayi Murdoch, 1885. The habitat restrictions and life history attributes of local populations of coastal mysids leave them vulnerable to the cumulative impacts of increased predation pressure by gray whales. This case study presents a unique examination implicating predation as an agent of disturbance capable of altering the species structure of a local prey community.     

Effects of <Emphasis Type="Italic">Caulerpa racemosa</Emphasis> invasion on soft-bottom assemblages in the Western Mediterranean Sea

The present study aimed at evaluating the effects of Caulerpa racemosa var. cylindracea spread on Mediterranean soft-bottom assemblages. The benthic assemblages colonized by C. racemosa were compared with non invaded assemblages at multiple spatial scales. In addition, a manipulative experiment has been conducted over a one-year period in order to compare the structure of native assemblages invaded by the alga with others where the alga has been manually removed and others that were not invaded. Results of both studies showed that Mediterranean soft-bottom assemblages invaded by C. racemosa differed from non invaded ones in terms of species composition, abundance and patterns of spatial variability. Moreover, in areas cleaned out from the alga, the benthic assemblages begin to recover their structure and after one year they get more similar to the assemblages observed in non invaded areas. The present paper, taking into account different aspects of C. racemosa invasion in Mediterranean soft bottoms, highlighted that the observed increase in alpha diversity did not correspond to an increase in the overall diversity of the studied system. Infact, the loss of beta diversity in invaded sites, together with the spread of species typical of vegetated habitats, may contribute to a homogenization of the Mediterranean coastal system. Furthermore, a possible role of ecosystem engineer for C. racemosa can be hypothesized.     

Genetic differentiation in plants of the genus <Emphasis Type="Italic">Cypripedium</Emphasis> from Russia inferred from allozyme data

Ten gene loci of nine enzyme systems (PGI, 6-PGD, NADHD, SKDH, GDH, PGM, DIA, ADH, GOT-1, and GOT-2) were analyzed in Cypripedium calceolus, C. macranthon, C. shanxiense, and C. × ventricosum plants from the south of the Russian Far East. Alleles of loci 6-PGD, NADHD, GDH, ADH, GOT-1, and PGI proved to be diagnostic for C. calceolus and C. macranthon. Plants of C. shanxiense from Primorye and Sakhalin Island were monomorphic at all of the loci examined, and their allelic structure can be regarded as diagnostic for the species. The allelic structure for fragments of the C. calceolus population from the western and eastern parts of the species range differed in two loci, PGI and SKDH: alleles absent in C. calceolus plants from the western part of the range occurred at a high frequency in the plants of this species from the eastern part of the range (28–41% and 55–68%, respectively). These alleles were found in C. shanxiense. The genetic structure of C. shanxiense was similar to that of C. calceolus from the eastern part of the range, i.e., the region when these species are sympartic. The additional alleles in C. calceolus from the eastern part of the range might have appeared as a result of hybridization with C. shanxiense. Our results indicate that C. calceolus plants occuring on the territory of Russia form two groups that represent two different units of genetic diversity preservation. We suggest that C. × ventricosum plants in southern Primorye were formed by hybridization between C. macranthon and C. calceolus × C. shanxiense hybrids. Thus, they differ from plants inhabiting the Urals and West Siberia, which originated by hybridization between C. macranthon and C. calceolus. The population of C. × ventricosum presumably also consists of two plant groups differing in genetic structure, which should be regarded as two different units of preservation of this taxon.     

Presence of <Emphasis Type="Italic">C. albidus</Emphasis>, <Emphasis Type="Italic">C. laurentii</Emphasis> and <Emphasis Type="Italic">C. uniguttulatus</Emphasis> in Crop and Droppings of Pigeon Lofts (<Emphasis Type="Italic">Columba livia</Emphasis>)

Columba livia is an important reservoir and carrier of Cryptococcus neoformans, Cryptococcus uniguttulatus, Cryptococcus laurentii and Cryptococcus albidus. Upper digestive tract of this species is also known as a habitat for Cryptococcus neoformans. Given the increasing clinical interest of this microorganism, 331 swabs from crop and 174 dropping samples from pigeon lofts in Grand Canary Island have been studied. The obtained results show an extensive presence samples 81 positive (24.47%) of Cryptococcus spp. in analysed crops: 32 (9.66%) for C. neoformans, 24 (7.2%) for C. uniguttulatus, 23 (6.9%) for C. albidus and 2 (0.6%) for C. laurentii. In the same way, Cryptococcus spp was also isolated in 82 (47.13%), dropping samples: C. neoformans in 59 (33.9%), C. uniguttulatus, in 9 (5.17%), C. laurentii in 8 (4.59%) and C. albidus in 6 (3.44%) of the investigated samples, respectively. The cryptococcosis produced by species of cryptococci other than C. neoformans has become more important during the last decade, supporting the study on the role of pigeon in the epidemiology of this disease.     

Multiple host-ant use by the predatory social parasite <Emphasis Type="Italic">Phengaris</Emphasis> (=<Emphasis Type="Italic">Maculinea</Emphasis>) <Emphasis Type="Italic">arion</Emphasis> (Lepidoptera,Lycaenidae)

Phengaris (=Maculinea) arion is an endangered social parasite of Myrmica ants, and for a very long time was considered as specific to Myrmica sabuleti. Previous studies carried out in Poland suggested some discrepancies within this assumption, and therefore a much more intensive survey was undertaken. The host ant use of P. arion was studied at five sites in different types of biotopes in Poland, i.e. xerothermal grasslands where Thymus pulegioides was used as a larval food plant by the butterfly, and more or less sandy biotopes with Thymus serpyllum. Altogether nine Myrmica species were recorded, and considerable variation in species composition and density of nests was recorded. At four localities M. sabuleti proved to be the most common ant. A total of 529 Myrmica nests were examined, and only 20 of them contained larvae and pupae of P. arion. Host ants belonged to five different species, i.e. M. sabuleti, Myrmica scabrinodis, Myrmica schencki, Myrmica lobicornis and Myrmica hellenica. Only at one site (NE Poland) was a significant heterogeneity in parasitation rates among Myrmica species detected. M. lobicornis was the most often infested ant there, which may suggest local specialisation of the butterfly. Overall low parasitism rates may explain the vulnerability of P. arion in Central Europe but further studies are also necessary.     

Soil microbial communities alter allelopathic competition between <Emphasis Type="Italic">Alliaria petiolata</Emphasis> and a native species

Allelopathy has been increasingly invoked as a mechanism facilitating exotic plant invasions. However, studies even on the same target species often yield varying results concerning the strength and importance of allelopathic inhibition, suggesting that the process may depend on the specific environmental context. Here I studied how the allelopathic inhibition of sycamore (Platanus occidentalis) seedlings by garlic mustard (Alliaria petiolata) depended on the presence of a soil microbial community. Using three analytical approaches to quantifying allelopathy, I consistently found allelopathic inhibition only in sterilized soils, suggesting that certain microbial taxa inhibit the process, possibly by degrading the allelochemicals. Determining the environmental contexts that reduce or eliminate allelopathic inhibition could lead to a greater understanding of the spatial variation in invasion success and potentially lead to new avenues for management.     

Exotic grass invasion impacts fitness of an endangered prairie butterfly, <Emphasis Type="Italic">Icaricia icarioides fenderi</Emphasis>

Fender’s blue butterfly is an endangered species restricted to fragmented, grassland remnants that are becoming increasingly dominated by tall, invasive grasses in western Oregon, USA. I performed a removal experiment to assess the impacts of structural degradation accompanying the invasion of Arrhenatherum elatius, tall oat grass, on butterfly fitness and fitness related behaviors. Clipping of A. elatius to native grass sward height resulted in 2.5–5 times as many eggs laid per leaf of host plant. Both male and female butterflies basked more frequently in areas removed of A. elatius inflorescences and upon encountering the treatment edge butterflies had a high rate of return into a large area removed of the grass inflorescences. Although butterfly behavior appeared to be affected by the change in sward height on the treatment edge, there was no evidence for the edge causing a disproportionate egg load. Invasion and dominance by A. elatius appeared to diminish host plant apparency which may result in overloading of eggs on conspicuous host plants, increased incidence of emigration, and a decrease in the likelihood of colonization because female butterflies appeared indifferent to larval resources beneath A. elatius inflorescences. Dominance of natural shortgrass prairies by tall stature grasses like A. elatius may be an insidious form of habitat degradation for grassland Lepidoptera worldwide, but it may go largely unnoticed because larval and adult resources can persist under the unnaturally tall grass canopy.     

Herbivory and population dynamics of invasive and native <Emphasis Type="Italic">Lespedeza</Emphasis>

Some exotic plants are able to invade habitats and attain higher fitness than native species, even when the native species are closely related. One explanation for successful plant invasion is that exotic invasive plant species receive less herbivory or other enemy damage than native species, and this allows them to achieve rapid population growth. Despite many studies comparing herbivory and fitness of native and invasive congeners, none have quantified population growth rates. Here, we examined the contribution of herbivory to the population dynamics of the invasive species, Lespedeza cuneata, and its native congener, L. virginica, using an herbivory reduction experiment. We found that invasive L. cuneata experienced less herbivory than L. virginica. Further, in ambient conditions, the population growth rate of L. cuneata (λ = 20.4) was dramatically larger than L. virginica (λ = 1.7). Reducing herbivory significantly increased fitness of only the largest L. virginica plants, and this resulted in a small but significant increase in its population growth rate. Elasticity analysis showed that the growth rate of these species is most sensitive to changes in the seed production of small plants, a vital rate that is relatively unaffected by herbivory. In all, these species show dramatic differences in their population growth rates, and only 2% of that difference can be explained by their differences in herbivory incidence. Our results demonstrate that to understand the importance of consumers in explaining the relative success of invasive and native species, studies must determine how consumer effects on fitness components translate into population-level consequences. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Overexpression of <Emphasis Type="Italic">WUSCHEL</Emphasis> in <Emphasis Type="Italic">C. chinense</Emphasis> causes ectopic morphogenesis

Capsicum chinense is a recalcitrant species for in vitro morphogenesis, and up to date there is no efficient system for genetic transformation and regeneration of this species via somatic embryogenesis. Here, we carried out an in vitro transformation of C. chinense via Agrobacterium tumefaciens co-cultivation with a system that expresses the heterologous gene WUSCHEL from Arabidopsis thaliana. WUSCHEL has been shown to promote the transition from vegetative to embryogenic state when overexpressed. We tested if the expression of WUSCHEL in C. chinense would promote an embryogenic response in this species. After 15 days of induction, the segments of transformed stems begun to form globular structures, suggesting that heterologus WUSCHEL was active and involved in the process of morphogenesis.     

Comparative ontogenic analysis of <Emphasis Type="Italic">Cyclamen coum</Emphasis> Mill. and <Emphasis Type="Italic">Cyclamen kuznetzovii</Emphasis> Kotov et Czernov

Many issues of ontogeny, morphogenesis, and taxonomy of the Cyclamen genus plants remain poorly studied thus far. Data available on the species native to Crimea and the Caucasus are also contradictory. Here we studied the C. coum populations growing around the Maikop city in the Caucasus and those of C. kuznetzovii in Crimea in order to describe a particular ontogeny of these two taxa and to draw preliminary conclusions concerning their taxonomic location.     

A comparison of the autecology of two seed-taking ant genera, <Emphasis Type="Italic">Rhytidoponera</Emphasis> and <Emphasis Type="Italic">Melophorus</Emphasis>

Members of the genus Rhytidoponera and, to a lesser extent, certain Melophorus spp. are keystone mutualists for the dispersal of seeds in the southwest of Western Australia, with important ramifications for the ecology and speciation of plants in this biodiversity hotspot. For this reason, it is important to understand the autecology of the relevant ant species and the way in which they interact with plant seeds. This paper addresses key aspects of the ecology of three such ant species, Rhytidoponera violacea (Forel), R. inornata Crawley and Melophorus turneri perthensis Wheeler. Data are presented on their geographic distribution, seasonality of foraging, diurnal activity, response to fire, nest site preference, nest structure, colony size, feeding habits, foraging response to seed availability, and seedling emergence from nests. The role of all three species as seed dispersers is confirmed, and all three species have ecologies that are well-suited for dispersal and survival of native plant seeds. Preservation of this interaction is important for the conservation of plants, and it is fortuitous that all three species are able to survive disturbance and return to rehabilitated areas. However, the smaller R. inornata, and to a lesser extent, the larger R. violacea, are vulnerable to invasive ant [Pheidole megacephala (Fabricius)] incursions. M. turneri perthensis is able to coexist with the invasive ant unless this is at high densities, probably as a result of its ability to forage during high temperatures when the invasive species is inactive.     

Does allelopathy explain the invasiveness of <Emphasis Type="Italic">Campuloclinium macrocephalum</Emphasis> (pompom weed) in the South African grassland biome?

Campuloclinium macrocephalum is an Asteraceous alien weed that invades roadside vegetation and grassland in South Africa. The role of allelopathy and competition in its invasiveness was investigated using Eragrostis curvula (weeping lovegrass, an indigenous grass), E. tef and Lactuca sativa (lettuce) as test species. Trials were conducted in Petri-dishes, pots and in the field. Root and shoot extracts of adult C. macrocephalum plants did not inhibit seed germination in any test species. The greatest effect was radicle stunting produced by leaf extracts at 10 and 25% w/v. Eragrostis curvula was less tolerant of the extracts than E. tef. Allelopathic effects could however not be confirmed in pot trials evaluating the interference potential of the weed or weed residue effects against E. curvula. E. curvula growth and biomass was not affected by plant densities of one or five C. macrocephalum per pot, whereas C. macrocephalum suffered a 17% mortality and density-dependant trade-offs of size and biomass for survival. Under field conditions C. macrocephalum had a broader ecological niche than E. curvula, invading hygrophilous and undisturbed grasslands not amenable for E. curvula establishment, this included well drained disturbed soils on which the latter proliferated. Evidence of competitive exclusion of E. curvula by C. macrocephalum or vice versa was not detected. The coexistence of both species irrespective of relative density suggested these species have different resource requirements. Allelopathy was not an adequate causal mechanism to explain invasiveness in Campuloclinium macrocephalum. A more traditional hypothesis such as the absence of natural enemies, at this stage, better justifies the weed’s invasion success.     

<Emphasis Type="Italic">Myrothecium verrucaria</Emphasis> – a potential biological control agent for the invasive ‘old world climbing fern’ (<Emphasis Type="Italic">Lygodium microphyllum</Emphasis>)

One of the greatest threats to the native ecosystems in any part of the world is the invasion and permanent colonization of ecosystems by non-native species. Florida is no exception to this biological invasion, and is currently colonized by an extensive variety of exotic plant species. Originally imported from Asia over 30 years ago, Old World Climbing Fern Lygodium microphyllum (Cavanilles) R. Brown) has become one of the most invasive and destructive weeds in southern Florida. To date different effective control measures of its growth and spread have not been successful; fire and herbicide applications that are currently employed are neither cost effective nor environmentally friendly. In light of the highly delicate ecosystem that is being affected by L. microphyllum, we tested the soil fungus Myrothecium verrucaria (Albertini and Schwein) Ditmar: Fr. for its pathogenicity on the invasive fern. In greenhouse studies the effect of two conidial concentrations of M. verrucaria on L. microphyllum was investigated. Plants were spray inoculated with M. verrucaria which resulted in successful disease development with leaf necrosis symptoms. The higher conidial concentration (1 × 10⁸ ml⁻¹) produced a disease index of approximately 3 on a scale of 0 to 4, day 24 postinitial inoculation, demonstrating the efficacy of this fungus as a severe retardant of Lygodium growth. Preliminary screening of selected native plant species for susceptibility to M. verrucaria showed low disease indices after repeated spray inoculations; the highest index attained was 0.4 by Slash pine (Pinus elliottii).     

Revision of “<Emphasis Type="Italic">Septonema ochraceum</Emphasis>” revealed three new species of <Emphasis Type="Italic">Venturiaceae</Emphasis> and <Emphasis Type="Italic">Herpotrichiellaceae</Emphasis>

Survey of seven strains determined as Septonema ochraceum (Dothideomycetes, inc. sed.) isolated from pine litter or obtained from public collections revealed three new species, Fusicladium cordae, F. sicilianum (Venturiaceae), Cladophialophora matsushimae (Herpotrichiellaceae) and a cryptic species morphologically identical to Devriesia americana (Teratosphaeriaceae), but phylogenetically distinct. Morphological survey and phylogenetic analysis using nucleotide sequence data from the nuclear ribosomal subunit genes indicate a close relationship within three species colonising pine litter needles, F. cordae, F. pini and F. ramoconidii. F. sicilianum is most related to F. rhodense. C. matsushimae represents a species belonging to one of the lineages of the polyphyletic genus Cladophialophora. None of the strains observed can be classified morphologically as S. ochraceum, of which the type material does not exist.     

Shifting invertebrate zooplanktivores: watershed-level replacement of the native <Emphasis Type="Italic">Leptodora</Emphasis> by the non-indigenous <Emphasis Type="Italic">Bythotrephes</Emphasis> in Canadian Shield lakes

The abundance of the native, pelagic macroinvertebrate predator, Leptodora kindtii, is negatively correlated with the abundance of a new invasive competitor, Bythotrephes longimanus, in a small number of Canadian Shield lakes. However, we do not yet know if Bythotrephes is replacing Leptodora on a regional scale. We determined the distribution of both species in 166 lakes in the District of Muskoka, south-central Ontario, Canada—the watershed with the longest history and largest prevalence of Bythotrephes invasions in North America. The frequency of occurrence of Leptodora was substantially reduced (twofold) in the presence of Bythotrephes. We argue that Bythotrephes is responsible for this dramatic reduction in the frequency of occurrence of Leptodora. Lakes in which both species co-occurred could not be distinguished from invaded lakes without Leptodora, suggesting a pattern of species replacement at a watershed level. We believe this is the first account of the widespread replacement of a native, pelagic macroinvertebrate predator by Bythotrephes in North America, and it does not bode well for Leptodora given the rapid, ongoing spread of Bythotrephes.     

Competitive displacement of the native species <Emphasis Type="Italic">Bursaphelenchus mucronatus</Emphasis> by an alien species <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis> (Nematoda: Aphelenchida: Aphelenchoididae): a case of successful invasion

The presence of alien invasive species has serious negative impact on endemic biodiversity, especially on native species that occupy the same niche in the ecosystem. To study the influence of the alien invasive species Bursaphelenchus xylophilus on its native sister species B. mucronatus, the two nematode species were mix-cultured in a fungal mat and mix-inoculated into a susceptible host. By comparing the propagation parameters of both species under competitive and noncompetitive conditions it was shown that the propagation level of B. xylophilus was clearly higher than that of B. mucronatus under laboratory culture. Furthermore, the propagation capacity of B. xylophilus under competitive conditions was much higher than that under noncompetitive conditions, both in laboratory culture and with host inoculation. Bursaphelenchus xylophilus also excluded B. mucronatus when the two species were cultured as a mixture for a longer time. The relative abundance ratios of the two species in natural pinewoods were also determined by random sampling of dying pine trees from regions with different invasion histories. It was noted that with an increase in invasion years the distribution frequency of B. xylophilus increased while that of B. mucronatus decreased. Experimental tests verified our hypothesis that because of its high fecundity and strong competitive ability, the invasive species B. xylophilus out-competed the native species B. mucronatus and displaced it in natural ecosystems. The successful invasion of B. xylophilus is attributed to competitive displacement, which may be one of the ecological invasive mechanisms.