Seed predation of two alien Opuntia species invading Mediterranean communities

Invasibility depends on the interaction of the introduced species with the abiotic and biotic factors of the recipient community. In particular, the biotic resistance posed by native herbivores has been claimed to be of great importance in controlling plant invasion. We investigated fruit and seed predation of two exotic Opuntia species within and between Mediterranean communities in order to determine how patterns of predation matched patterns of invasion. Predators were small mammals, presumably mice, which could consume more than 50% of the seeds produced. Predators could be equally effective in consuming fruit and single seeds. O. maxima fruits were slightly preferred to O. stricta fruits, but predators did not distinguish between seeds. Seed predation was more intense in invaded than in non-invaded communities. However, there was a high spatial variation in seed predation that did not always match patterns of invasion, suggesting that seed predation alone is not a good predictor of community invasibility to Opuntia. According to these results invasibility to Opuntia is limited in some (but not all) communities by native mice. Seed losses by predation were high for both species. However, we estimated that more than 75% of seeds dispersed by birds to non-invaded areas are not predated.     

中国2种归化植物新记录

报道了发现于辽宁省的2种中国归化植物新记录:白毛马鞭草(Verbena stricta Vent.)和向日葵(Helianthus annuus L.),白毛马鞭草穗状花序粗壮而紧凑,单生枝顶或呈简单的聚伞状或圆锥状排列,且花序轴在果期显著延长,叶卵圆形,无柄,与中国有报道的本属其他物种区别明显。该种原产美国西部至中部地区,近来在辽宁省铁岭市发现有归化。向日葵原产于北美地区,被发现广泛归化于辽宁省大连市,营口市鲅鱼圈也有发现。归化种群形态特征与该地区栽培类型完全不同,其花序极多分枝,头状花序直径较小,瘦果极小,表面纹饰多样性很高。     

Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America

Photosynthetic responses were quantified for two Zostera japonica Aschers. and Graebn. populations from the northern and southern limits of distribution exposed to a range of salinities along the Pacific Coast of North America. Plants were collected from Padilla Bay, Washington (northern) and Coos Bay, Oregon, USA (southern) and cultured together in experimental tanks at 3 salinities (5, 20 and 35) under saturating irradiance for 3 weeks. Subsequently, photosynthesis–irradiance (P vs. E curves) relationships for leaf segments from the two populations were assessed using an oxygen electrode system. We found no evidence for diel rhythms in either light saturated photosynthesis (P_max) or dark respiration (R_d). For the Padilla Bay population, P_max ranged from 192 to 390 μmol O₂ g DW⁻¹ h⁻¹; for the Coos Bay population P_max ranged from 226 to 774 μmol O₂ g DW⁻¹ h⁻¹. Photosynthetic maxima of the Coos Bay plants occurred at a salinity of 20, whereas salinity had no effect on the photosynthetic maxima of the Padilla Bay plants. There were significant differences in leaf tissue R_d among salinity treatments but the two populations responded similarly to salinity. North American populations of Z. japonica are best adapted to intermediate salinities, displaying minimum R_d rates, lower compensation irradiance, higher saturation irradiance, and greater P_max rates at a salinity of 20. Additionally, the southern population may be better adapted to southward expansion along the Pacific Coast and changes associated with global climate change.     

白花鬼针草入侵对植物群落结构及物种多样性的影响

【目的】阐明白花鬼针草入侵对植物群落组成及物种多样性的影响。【方法】调查广东茂名有白花鬼针草入侵(试验样方)和无白花鬼针草生长(对照样方)的植物群落中植物的种类、盖度、高度和密度,计算不同植物重要值及物种多样性指数,通过皮尔逊相关系数及拟合曲线展现白花鬼针草种群特征与其重要值及物种多样性的关系。【结果】白花鬼针草入侵后植物群落的组成和结构显著改变,由对照样方的104种减少到试验样方的63种,双穗雀稗、白花蛇舌草、香膏萼距花等物种消失,胜红蓟、阔叶丰花草、假臭草等恶性杂草的重要值降低,而马唐、薇甘菊、空心莲子草等物种重要值升高。白花鬼针草入侵降低了物种多样性,试验样方的Patrick丰富度指数(R)、Simpson多样性指数(D)和Shannon-Wiener多样性指数(H)均低于对照样方;白花鬼针草的重要值与以上多样性指数(H、D)和丰富度指数(R)呈显著负相关(P<0.001)。【结论】白花鬼针草入侵减少了物种多样性,并形成单一优势种群群落,对植物群落产生了负效应,对生态环境造成了极大的威胁。     

Measuring the trophic ecology of ants using stable isotopes

Ants are prominent components of most terrestrial arthropod food webs, yet due to their highly variable diet, the role ants play in arthropod communities can be difficult to resolve. Stable isotope analysis is a promising method for determining the dietary history of an organism, and has the potential to advance our understanding of the food web ecology of social insects. However, some unique characteristics of eusocial organisms can complicate the application of this technique to the study of their trophic ecology. Using stable isotopes of N and C, we investigated levels of intraspecific variation both within and among colonies. We also examined the effect of a common preservation technique on δ¹⁵N and δ¹³C values. We discuss the implications of our results on experimental design and sampling methods for studies using stable isotopes to investigate the trophic ecology of social insects. Received 4 February 2005; revised 23 June 2005; accepted 4 July 2005.     

Hepatospora eriocheir (Wang and Chen, 2007) gen. et comb. nov. infecting invasive Chinese mitten crabs (Eriocheir sinensis) in Europe

We describe a microsporidian parasite infecting non-native Chinese mitten crabs (Eriochier sinensis) from Europe. Electron microscopy revealed merogonic and sporogonic life stages bound within a plasmalemma. The crab parasite develops polar tube precursors at the sporont stage but does not complete formation of the intact spore extrusion apparatus at the stage of the sporogonial plasmodium like Enterocytozoon bienuesi and other representatives of the Enterocytozoonidae. Its presence within an aquatic crustacean host, and a distinct molecular phylogeny based on partial small subunit ribosomal RNA (SSU rRNA) gene sequences also place it relatively close, though distinct to, existing genera within the Enterocytozoonidae. Consideration of morphological and phylogenetic characteristics of other hepatopancreas-infecting microsporidia from crustaceans suggests that certain ones (e.g. Enterospora canceri) are retained within the clade corresponding to the existing family Enterocytozoonidae, while others, including the parasite described here, may eventually be grouped in a sister taxon potentially of family rank. Based upon morphological and host similarity, it is likely that the parasite described here is the same as Endoreticulatus eriocheir (Wang and Chen, 2007), previously described from Chinese mitten crabs in Asia. However, using a combined taxonomic approach based upon morphological and phylogenetic data, we propose the formation of a new genus (Hepatospora) to replace the previous generic classification of the Asian parasite as Endoreticulatus. The microsporidian from the hepatopancreas of E. sinensis is named Hepatospora eriocheir (Wang and Chen, 2007) gen. et comb. nov. It is assumed that the parasite was introduced during initial invasions of this crab to Europe during the early 20th Century.     

二色仙人掌，中国仙人掌科一新归化种

2019年4-6月,在江苏省西南部句容市郭庄镇虬山,首次发现二色仙人掌(Opuntia cespitosa Rafinesque)归化种群。该种群主要生长在海拔46～90 m的废弃采石场上,分布范围东西长510 m,南北宽260 m,面积约13.26 hm2。二色仙人掌开花结实的成年植株共计910棵,其中最大灌木平卧茎长轴上叶状茎10个,树龄可达10 a,大概在2010年就生长于虬山。在句容虬山采石场关闭时,采石场工作人员可能将盆栽的二色仙人掌就地丢弃,从而导致该归化种群的发展。比较了二色仙人掌与中国仙人掌属已知其余4种归化植物的形态特征,并编制了分种检索表。此外,讨论了二色仙人掌的传播机制及其入侵风险。     

Mycorrhizal fungi and the nutrient ecology of three oldfield annual plant species

Summary Three oldfield annual species (Abutilon theophrasti Medic., Ambrosia artemisiifolia L. and Setaria lutescens (Weigel) Hubb.) were investigated. All three developed substantial mycorrhizal infections when inoculated with Glomus etunicatum Becker & Gerd. Mycorrhizal infection dramatically increased phosphorus content and dry weight of both Abutilon and Ambrosia, but did not significantly affect dry weight and only modestly increased phosphorus content of Setaria. These results were consistent with a lower level of infection and much greater root density in Setaria than in the other species. When Abutilon was grown in the presence of Setaria, mycorrhizal infection had no effect on Abutilon phosphorus content or dry weight. The depressive effect of Setaria on the response to inoculation in Abutilon was probably not caused by water soluble allelopathic chemicals from Setaria roots, but soil leachate from Abutilon plants did inhibit infection in other Abutilon plants. The data were consistent with the hypothesis that the very high root density and effective soil exploitation of Setaria reduced the benefit from mycorrhizal infection in Abutilon via phosphorus depletion in a large proportion of the available soil volume. Furthermore, even if mycorrhizal infection were capable of increasing phosphorus content of Abutilon in the presence of Setaria, the very high competitive ability of Setaria for nitrogen in the soil could have reduced the benefit of an enhanced phosphorus content. Carbon isotope ratios were reduced in Abutilon by mycorrhizal infection, indicating a possible reduction in water use efficiency.     

Saving camels from straws: how propagule pressure-based prevention policies can reduce the risk of biological invasion

Nonnative species that harm or have the potential to cause harm to the environment, economy, or human health are known as invasive species. Propagule pressure may be the most important factor in establishment success of nonnative species of various taxa in a variety of ecosystems worldwide, and strong evidence is emerging that propagule pressure determines both the scale of invasion extent and impact. In a limited way, the US government is applying a “propagule pressure approach” in a variety of prevention policy contexts aimed at minimizing the impact of harmful organisms. However, there are also readily apparent opportunities for enacting propagule pressure-based measures to fill current gaps in invasive species prevention and control at national, state, and local levels. An explicit focus on propagule pressure-based policies could substantially increase the effectiveness of US efforts to prevent the introduction of invasive species through by intentional and unintentional introductions. The views expressed in this paper are solely those of the authors and do not necessarily reflect those of the US government. “As the last straw breaks the laden camel’s back...” -Charles Dickens, Dombey and Son     

Assessing the residual effects of Carpobrotus edulis invasion, implications for restoration

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.     

Migration from plant to plant: an important factor controlling densities of the epiphytic cladoceran <Emphasis Type="Italic">Alona</Emphasis> (Chydoridae,Anomopoda) on lake vegetation

We investigated seasonal changes in the density of epiphytic cladocerans Alona spp. (Chydoridae, Anomopoda) in two habitats, emergent and submerged aquatic plants, in Lake Suwa, Japan, from April to August 1998 and from April to November 2000. Alona had a density peak in early June on reeds (emergent) and in late June on Potamogeton malaianus (submerged). In summer, Alona density remained low in both habitats. Although density was positively correlated with the abundance of epiphytic algae, the birth rate was constant and no correlation between algal abundance and clutch size was detected. In a field experiment using ropes as an artificial substrate covered with high and low densities of epiphytic algae as food, more Alona attached to the ropes with the high density of algae. These results suggest that Alona may select food-rich habitats and migrate seasonally, and that migration is an important factor in the population dynamics of epiphytic chydorid cladocerans such as Alona. In Lake Suwa, Alona may migrate from the reed zone to the submerged macrophyte zone in June.     

Connectivity compensates for low habitat quality and small patch size in the butterfly <Emphasis Type="Italic">Cupido minimus</Emphasis>

Habitat size, habitat isolation and habitat quality are regarded as the main determinants of butterfly occurrence in fragmented landscapes. To analyze the relationship between the occurrence of the butterfly Cupido minimus and these factors, patch occupancy of the immature stages in patches of its host plant Anthyllis vulneraria was studied in the nature reserve Hohe Wann in Bavaria (Germany). In 2001 and 2002, 82 A. vulneraria patches were surveyed for the presence of C. minimus larvae. The occurrence was largely affected by the size of the food plant patches. In a habitat model that uses multiple logistic regression, the type of management and habitat connectivity are further determinants of species distribution. Internal and temporal validation demonstrate the stability and robustness of the developed habitat models. Additionally, it was proved that the colonization rate of C. minimus was significantly influenced by the distance to the next occupied Anthyllis patch. Concerning long-term survival of (meta-) populations in fragmented landscapes, the results show that lower habitat quality may be compensated by higher connectivity between host plant patches. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Flower morphology of the resurrection plant Chamaegigas intrepidus Dinter and some of its potential pollinators

The resurrection plant Chamaegigas intrepidus Dinter (Scrophulariaceae) is a rare endemic species growing in ephemeral rock pools on isolated granite outcrops in Central Namibia. Previous studies suggested a high degree of gene flow within individual pools. Therefore, floral morphology, pollination and potential pollinators of the plant species were studied while the plants were at full flower set.The zygomorphous, intensively scenting flowers carry dense layers of trichomes (400–1600 mm⁻²) on the lower lip, similar to well-known oil-flowers. Four species of potential pollinators could be found. Two of them the Hymenoptera, Apis mellifera and Liotrigona bottegoi, were found to be rare, whereas beetles of the genus Condylops spec. (Condylops erongoensis and a new species) showed up with numbers up to 50 individuals m⁻² in some pools, visiting the flowers most frequently. Individuals of Liotrigona and Condylops were proven to carry pollen of Chamaegigas after their flower visits. The results are discussed in relation to the genetic variability of the plant and the phenomenon of pollen limitation in rare plant species.     

Habitat preferences of cattail species and hybrids (Typha spp.) in eastern Canada

Interspecific hybridization is widespread in plants and is an important evolutionary process. Hybrids may be fitter than their parental species, at least under some environmental conditions, and this may lead to partitioning of taxa by habitat. In eastern Canada, two cattail species (Typha latifolia and Typha angustifolia) and their hybrid (Typha x glauca) are known to have become increasingly widespread in recent decades, although their habitat preferences and patterns of co-existence at the local scale are not well known. We quantified the occurrence of these three taxa in three different habitat types (high traffic, low traffic, and ‘natural’) at 40 different sites along a sampling route of approximately 2000 km in eastern Canada. There were no significant overall associations between habitat type and taxon, although intraspecific comparisons among sites showed that the hybrid was most likely to grow in high traffic (highly disturbed) sites. In addition, pairwise comparisons revealed significant independence of T. latifolia and T. angustifolia, although the hybrid was equally likely to co-exist with either of its parental species. The presence of the three taxa in several habitats, including highly disturbed roadside areas, is consistent with their increasingly invasive tendencies.     

An evolutionary modelling approach to understanding the factors behind plant invasiveness and community susceptibility to invasion

Ecologists have had limited success in understanding which introduced species may become invasive. An evolutionary model is used to investigate which traits are associated with invasiveness. Translocation experiments were simulated in which species were moved into similar but evolutionarily younger communities. The main findings were that species that had previously been the most abundant in their original communities have significantly higher rates of establishment than did species that had previously occurred at low abundance in their original community. However, if establishment did occur, previously abundant and previously low-abundant species were equally likely to become dominant and were equally likely to exclude other species from their new community. There was a suggestion that the species that were most likely to establish and exclude others were 'genetically' different. When species that had evolved in different simulations (but with identical environmental conditions) were transplanted into communities that had also evolved in different simulations of the same conditions, the outcomes were difficult to predict. Observed rates of establishment and subsequent competitive dominance were observed to be species- and community combination-specific. This evolutionary study represents a novel in silico attempt to tackle invasiveness in an experimental framework and may provide a new methodology for tackling these issues.     

Comparing the effects of the exotic cactus-feeding moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) and the native cactus-feeding moth, Melitara prodenialis (Walker) (Lepidoptera: Pyralidae) on two species of Florida Opuntia

This study examined the effects of the native cactus moth borer, Melitara prodenialis, and the invasive cactus moth borer, Cactoblastis cactorum, on two common cactus species, Opuntia stricta and O. humifusa at coastal and inland locations in central Florida. Opuntia stricta were present only at coastal sites and O. humifusa were present at coastal and inland sites. Throughout the duration of the study, coastal plants were subject to damage solely by C. cactorum and inland plants solely by M. prodenialis. Results showed marginally significantly higher numbers of eggsticks on O. stricta than O. humifusa and significantly higher numbers at coastal sites than at inland sites. There was also significantly higher moth damage on O. stricta than O. humifusa and at coastal sites than inland sites, but not significantly so. However, there was a higher level of plant mortality for O. humifusa than for O. stricta and a significantly higher level of cactus mortality at inland sites when compared to coastal sites. This increased mortality may be due to increased attack by true bugs, Chelinidea vittiger, and by Dactylopius sp., combined with attack by M. prodenialis. Inland plants also tended to be smaller than coastal plants and could be more susceptible to the combined effects of all insects. Further long-term research on coastal cactus survival when attacked and unattacked by Cactoblastis is necessary to fully determine the effects of this moth on Opuntia survival.     

The ecology of the Bithynia first intermediate hosts of Opisthorchis viverrini

Opisthorchiasis, together with its associated cholangiocarcinoma, is one of the most important human parasitic diseases on continental Southeast Asia. A great deal of epidemiological data from humans is available on this disease, particularly from the northeast of Thailand, however, only limited information is available on those aspects of the life cycle relating to its Bithynia (Gastropoda) and cyprinid fish intermediate hosts. Here we review the information which is available on the Bithynia hosts of Opisthorchis viverrini. Only one major ecological study has been carried out at one site on a single species of Bithynia. We show not only that detailed ecological studies are required to clarify the epidemiology of opisthorchiasis, but also that the taxonomic status of the Bithynia species transmitting O. viverrini requires clarification.     

Role of topography and soils in grassland structuring at the landscape and community scales

The relative importance of abiotic factors in community assembly is debated and thought to be dependent on the scale. I investigated the relative role of topography and soils as structuring agents at the landscape and the community scales in 126 subalpine calcareous grasslands in the Pyrenees, in terms of species composition and abundance. I wished to know: (1) the role of abiotic factors in the organization of plant communities across the landscape; (2) how much of the variation in community distribution was accounted for by abiotic factors; and (3) how well their role applied to the distribution of dominant species at the landscape and the community scales. The hypothesis was: abiotic factors play an important role in community distribution in the landscape, but species interactions are more important within communities. Multivariate methods generated four communities, organized in two contrasting groups along the main vegetation axis, which explained 13% of the variation: mesic grasslands (Nardus stricta and Festuca nigrescens communities) and xeric grasslands (Carex humilis and Festuca gautieri communities). Mesic communities were more acidic and fertile than xeric communities. Changes in the abiotic environment, accounting for up to 80% of the variation in the vegetation, were smooth, while the transition between xeric and mesic grasslands was sharp in terms of species composition. The distribution in the landscape of the first main species from each community was closely related to abiotic factors, which modeled poorly the abundance of the main species at smaller scales. At the within-community scale, the explanatory power of biotic relationships was community dependent, producing the most significant models for plants highly dominant within their communities, such as N. stricta and F. gautieri. Contrary to current hypothesis, there was a shift from mainly positive relationships among dominant species in fertile mesic communities to mainly negative in infertile xeric ones.     

Multiple gene genealogies and species recognition in the ectomycorrhizal fungus Paxillus involutus

Paxillus involutus (basidiomycetes, Boletales) is a common ectomycorrhizal fungus in the Northern Hemisphere. The fungus displays significant variation in phenotypic characters related to morphology, physiology, and ecology. Previous studies have shown that P. involutus contains several intersterility groups and morphological species. In this study, we have used concordance of multiple gene genealogies to identify genetically isolated species of P. involutus. Fragments from five protein coding genes in 50 isolates of P. involutus collected from different hosts and environments in Europe and one location in Canada were analysed using phylogenetic methods. Concordance of the five gene genealogies showed that P. involutus comprises at least four distinct phylogenetic lineages: phylogenetic species I (with nine isolates), II (33 isolates), III (three isolates), and IV (five isolates). The branches separating the four species were long and well supported compared with the species internodes. A low level of shared polymorphisms was observed among the four lineages indicating a long time since the genetic isolation began. Three of the phylospecies corresponded to earlier identified morphological species: I to P. obscurosporus, II to P. involutus s. str., and III to P. validus. The phylogenetic species had an overlapping geographical distribution. Species I and II differed partly in habitat and host preferences.