Consistent performance of invasive plant species within and among islands of the Mediterranean basin

Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk. Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to test how the same invasive species perform in different habitats within a single island, and to scale up differences among islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity). The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary, Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight the risk to other islands not yet invaded.     

Assessing the risk of potentially invasive plant species in central Europe

A risk assessment system was developed to assess the invasion potential of new environmental weeds in central Europe. A pre-evaluation step excludes species that are officially controlled, widespread, or intended for use in protected cultures only. Species eligible for risk assessment are classified into three categories (high risk, further observation required, low risk) by rating them according to various biogeographical and ecological aspects. The rating system was validated by testing 47 well-known invasive plant species of temperate Europe and 193 exotic plants which have failed to establish themselves in Switzerland. The overall accuracy was 65%. Accuracy of correctly predicting invasive species was 77%, while accuracy of correctly predicting non-invasive species was 62%. The proposed risk assessment protocol should be understood as a first attempt for a European country and needs modifications. These can only be achieved by applying the system in practice.     

Consistency in the habitat degree of invasion for three invasive plant species across Mediterranean islands

Habitats are known to vary in their vulnerability to invasion by alien plants and different species often colonise distinct habitats. To assess the consistency in the degree of invasion of particular habitats, this study examined the frequency of occurrence and local abundance of three invasive plant taxa: Ailanthus altissima, Carpobrotus spp., and Oxalis pes-caprae across different habitat types on four representative Mediterranean islands. We conducted systematic field surveys recording the presence-absence and cover of these taxa on the islands of Mallorca, Corsica, Sardinia and Crete. Drawing on the results of 5,285 sample points, the frequency of occurrence of the three invaders tends to be higher than expected in urban, ruderal and roadside habitats. In contrast, scrub habitats rarely contain any of the three invaders, indicating that they may be more resistant to invasion. The degree of invasion, determined by the local abundance of an invasive plant in any one habitat, varies according to the identity of the invader and the island. However, based on average abundance, Oxalis pes-caprae exhibits the highest degree of invasion, and Carpobrotus spp. the least. There is no indication that any one of the four islands is more prone to either higher frequencies or abundances of the three invaders. These patterns suggest that anthropogenic changes in Mediterranean islands will increase the vulnerability of certain habitats to invasion and increase the distribution of these three invasive taxa at any of the four islands.     

Persistence, extinction and different species pools within the flora of lake islands in western Ireland

The vascular flora on twenty-nine lake islands in Lough Corrib, western Ireland was surveyed in 1992–93. Thirteen of these islands had been surveyed by the author in 1974 (Roden, 1979). Data on species–area curves and species turnover between 1974 and 1992 are presented. Species numbers on each island did not change greatly in the 18-year interval and extinctions were most common on smaller islands. It is known that six of the islands surveyed are less than 150 years old and their flora must have immigrated over open water during that period. It is shown that this group of species has a different log species/log area regression than the remaining flora, with a much shallower slope (low Z value). The proportion of less widespread species was greatest on islands nearest to the mainland. The implication of different slopes in different species groups and the restriction of turnover to rare species is discussed with reference to the island Theory of Biogeography.     

Natives adapting to invasive species: ecology,genes, and the sustainability of conservation

Contemporary anthropogenic evolution is common. Biological invasions are an especially dynamic form of novel selection. This paper considers how native species evolve in response to biological invasions and the potential consequences of such evolution. Among numerous recent cases, the most widely reported instances are of phytophagous insects shifting onto introduced host plants. For example, our studies show that in North America and Australia, soapberry bugs evolved substantially after colonizing introduced hosts. Such cases permit close estimation of evolution’s direction and rate, and we have used cross-rearing studies of derived and ancestral-type populations to measure changes in reaction norms and performance tradeoffs. Different fitness traits have followed very different paths in evolving to their current phenotypic values. Our hybridization studies show that the genetic architecture of these adaptations involves a surprising degree of non-additive variation (epistasis, dominance). The importance of non-additive genetic variation in rapid evolution will be clarified as more studies take advantage of similar situations. As appreciation grows for the deep contemporary interplay of evolution and ecology, debate about qualitative terms describing evolution’s rate will become less relevant. From a conservation standpoint, contemporary evolution in native species presents challenges for ecologically appropriate and sustainable management. Evolving natives and invaders may reconfigure contemporary and future communities. Adaptive evolution may also enhance native communities’ capacity to control invasive populations.     

Gap analysis revealed a low efficiency of Natura 2000 network for the conservation of endemic species in Mediterranean temporary freshwater habitats

Listed and rare species are abundant in temporary freshwater habitats. Among them, the endemic contingent represents a crucial conservation target particularly in the areas characterized by abundant endemic flora for which the local administrations have a high level of responsibility. The aim of this research was to test how the endemic plants found in Mediterranean temporary ponds were represented in Natura 2000 network in a biodiversity hotspot of the Mediterranean region. The results of our research at regional scale pointed out that the existing Nature 2000 sites provide a limited degree of protection and that the gap analysis should be taken into account when conservation priorities are set.     

The role of zoological parks in biodiversity conservation in the Gulf of Guinea islands

Modern zoological institutions are devoting more of their resources to research, education and conservation than they have in the past. Many zoos recently have become increasingly involved in external or field (in situ) projects, with a view to conserving species and their habitats where they occur naturally. An opportunity to practice in situ conservation exists on Bioko, the largest and biologically the most diverse of the Gulf of Guinea islands. Although urgent political and economic problems confront Equatorial Guinea, of which Bioko is part, external aid will be needed if the infrastructure is to be developed to protect and maintain two important nature reserves on the island. Several initiatives are suggested for the involvement of zoos in this process.     

Patterns of butterfly distribution in the Andaman islands: implications for conservation

Twenty-five islands of different sizes were rapidly surveyed in the Andaman islands for patterns of butterfly distribution and abundance. The surveys were conducted in the dry seasons of 1992 in the South Andaman islands, 1994 in the North Andaman islands and on both these years on the Little Andaman Island. Different habitat types were identified on each island and butterflies were sampled by the line transect method in each habitat type. Sixty-five species of butterflies were recorded from six families. Fifty-one species were less common and contributed to 25 % of the total count. Six species were very common. The overall distribution patterns of the species were nested. This suggests that small islands share their species with the larger islands but not vice versa. Many uncommon species were found exclusively on large islands. The presence of evergreen forest on islands significantly influenced the species encountered. Small and medium sized islands with evergreen forests had significantly more species than those without evergreen forests. Loss of primary forests due to logging and encroachment will result in the loss of many butterfly species. It is recommended that the large patches of primary evergreen forests be protected on a priority basis on large islands.     

The mismeasure of islands: implications for biogeographical theory and the conservation of nature

The focus on place rather than space provides geography with a powerful raison d’être. As in human geography, the functional role of place is integral to the understanding of evolution, persistence and extinction of biotic taxa. This paper re‐examines concepts and biogeographical evidence from a geographical rather than ecological or evolutionary perspective. Functional areography provides convincing arguments for a postmodern deconstruction of major principles of the dynamic Equilibrium Theory of Island Biogeography (ETIB). Endemic oceanic island taxa are functionally insular as a result of long‐term island stability, confinement, isolation, and protection from continental invasion and disturbance. Most continental taxa persist in different, more complex and open spatial systems; their geographical place is therefore fundamentally distinct from the functional insularity of oceanic island taxa. This creates an insular‐continental polarity in biogeography that is currently not reflected in conservation theory. The focus on the biogeographical place leads to the development of the eigenplace concept defined as the functional spatial complex of existence. The application of still popular ETIB concepts in conservation biology is discouraged. The author calls for the integration of functional areography into modern conservation science.     

The value of small habitat islands for the conservation of genetic variability in a steppe grass species

The habitat loss and fragmentation due to agricultural land-conversion affected the steppe throughout its range. In Ukraine, 95% of steppe was destroyed in the last two centuries. Remaining populations are confined to few refuges, like nature reserves, loess ravines, and kurgans (small burial mounds), the latter being often subject to destruction by archeological excavations.Stipa capillata L. is a typical grass species of Eurasian steppes and extrazonal dry grasslands, that was previously used as a model species in studies on steppe ecology. The aim of our research was to assess genetic diversity of S. capillata populations within different types of steppe refuges (loess ravines, biosphere reserve, kurgan) and to evaluate the value of the latter group for the preservation of genetic diversity in the study species.We assessed genetic diversity of 266 individuals from 15 populations (nine from kurgans, three from loess ravines and three from Askania-Nova Biosphere Reserve) with eight Universal Rice Primers (URPs).Studied populations showed high intra-population variability (I: 0.262–0.419, PPB: 52.08–82.64%). Populations from kurgans showed higher genetic differentiation (Φ_ST = 0.247) than those from loess ravines (Φ_ST = 0.120) and the biosphere reserve (Φ_ST = 0.142). Although the diversity metrics were to a small extent lower for populations from kurgans than from larger refugia we conclude that all studied populations of the species still preserve high genetic variability and are valuable for protection. To what extent this pattern holds true under continuous fragmentation in the future must be carefully monitored.     

Invasions of alien gammarid species and retreat of natives in the Vistula Lagoon (Baltic Sea, Poland)

During the last decades of the twentieth century, the alien gammarid species Gammarus tigrinus, Dikerogammarus haemobaphes, Pontogammarus robustoides and Obesogammarus crassus invaded the lower Vistula River and its deltaic, partly brackish regions. In brackish waters of the Vistula Lagoon the native Atlantic-boreal species Gammarus zaddachi and Gammarus duebeni have been replaced or at least outnumbered by the aliens. As compared to our earlier studies, through the years 1998–2004 we could observe nearly total decline of the native gammarid populations along the coasts of the Lagoon, and overdomination of the North-American G. tigrinus in most places. Possible reasons for the observed phenomena are e.g. increasing pollution and eutrophication of the Lagoon accompanied by competition between the native and the alien species.     

Arundo micrantha,a new reed species for Italy,threatened in the freshwater habitat by the congeneric invasive A. donax

Arundo micrantha Lam., a reed species from southern Mediterranean area, has found in Sardinia. Its presence represents the first record for Italy and the third one for western Europe. Investigations on distribution and ecology of the Sardinian population have been carried out, with special focusing on synecology of the species. A. micrantha has found in 40 localities mainly distributed along temporary streams and permanent rivers in the central and southern part of the island. Most of Sardinian populations occurs on alluvial soils in Thermomediterranean bioclimatic context. The autonomy of Sardinian phytocoenoses was characterized with the definition of exclusive floristic taxa, biological and chorological elements, and syndinamic relationships with other assemblages. Comparing the community with other reed beds from the Mediterranean basin, a marked floristic differentiation arose between the phytocoenoses characterized by autochthonous Arundo species and those dominated by the invasive Arundo donax. Finally, management activities are proposed to ensure the conservation of this threatened autochthonous plant community in freshwater habitat.     

Ecological characterisation of dredge islands for the conservation of salt-marsh beetle fauna. The lagoon of Venice (Italy): a case study

Salt marshes are wet environments at the transition between land and sea, which are inhabited by species that are adapted to stressing environmental factors, such as frequent tidal inundations and highly variable salinity. The rapid and global disappearance of these ecosystems results in the loss of those species that here have their typical habitat. In the lagoon of Venice, a programme for the protection of the surviving salt marshes was initiated by building dredge islands in the framework of more comprehensive restoration work. The ecological characterisation of these man-made habitats was studied through analysing the beetle fauna established on six dredge islands with different topographical traits. Beetle assemblages were evaluated by analysing species richness and abundance. The observed species were arranged in ecological groups and within sub-habitats, delimited according to the zonation of halophytes and ruderal vegetation. Both the composition and distribution of the beetle assemblages were strongly affected by the soil elevation, which determines the salinity gradient and the flooding rate. Hygrophilous and halobious taxa were dominant; however, many generalist taxa were present on some higher islands characterised by areas with a height greater than 60 cm above the mean sea level. Notably, these rarely submerged soils hosted some uncommon halophilous species, as well as thermophilous taxa typical of Mediterranean habitats that were not present on the surrounding mainland. Overall, although the dredge islands possessed some topographical traits that differed significantly from those of the natural salt marsh, they proved to host the biotic communities typical of these latter habitats, as well as other saline soil specialists.     

Localized invasion of the North American Harris mud crab, Rhithropanopeus harrisii, in the Panama Canal: implications for eradication and spread

As the rate of biological invasions continues to increase, a growing number of aquatic introduced species are becoming globally widespread. Despite this ubiquitous phenomenon, rarely do we discover aquatic invaders early enough to allow the possibility of eradication. Recently, the North American Harris mud crab (Rhithropanopeus harrisii) was found in the waters adjacent to the Panama Canal and herein we provide an assessment of the crab’s distribution in Panama to evaluate the possibility of eradication. Using salinity tolerance experiments, we also evaluate the potential for further spread of this crab within the Canal. Our results suggest that populations of R. harrisii are currently limited to two manmade lagoons which are adjacent to the Panama Canal. Our experiments suggest that both juvenile and adult R. harrisii can survive in salinities found outside its current range in Panama. Although it is difficult to predict the potential for future spread and impacts in Panama, current management strategies could reduce the probability for spread locally as well as elsewhere in the world given the intensity of shipping in this region. The current containment of this invader suggests that a localized eradication may be possible.     

Exploring biodiversity in a metropolitan area in the Mediterranean region: The urban and suburban flora of Rome (Italy)

This work provides an overview of plant diversity in the municipality of Rome (Italy) through an assessment of the flora in urban and suburban sectors of the city. It is aimed at providing the knowledge required to support proactive action for plant conservation. On the basis of a literature-derived catalogue and of an extensive survey campaign, the flora was investigated in terms of conservation interest; habitat types and locations that require protection measures were identified according to the occurrence of valuable native plants. Valuable species exclusive of the urban sector are threatened by the compaction trend affecting the urban fabric. Such species occur mainly in ruderal environments and fallows of archaeological sites and urban parks, near river courses and in remnants of natural forests. Valuable species exclusive of the suburban sector are threatened by urban sprawl. They occur prevalently in wet environments of the subcoastal strip and in coastal sands, Mediterranean maquis, tuffaceous gorges, sulphur springs and archaeological sites. The results highlight the need to preserve the complexity of the land mosaic, especially within the urban matrix, and to strengthen the existing environmental protection tools in the suburban area against foreseeable land cover changes.     

North-east Atlantic and Mediterranean species of the genus Buffonellaria (Bryozoa, Cheilostomata): implications for biodiversity and biogeography

In this study we revise the cheilostome bryozoan genus Buffonellaria Canu & Bassler, 1927 and its Mediterranean and north-east Atlantic species, thereby addressing several existing problems. First, a lectotype for the type species, Buffonellaria divergens (Smitt, 1873) from Florida, is chosen, which proves to be distinct from the European species. Second, the two hitherto established north-east Atlantic species [ Buffonellaria nebulosa ( Jullien & Calvet, 1903 ) and Buffonellaria porcellanum Arístegui Ruiz, 1987], are redescribed, which were poorly documented until now. Third, close inspection of material, collected from Spitsbergen to tropical West Africa, using scanning electron microscopy reveals that the actual number of species, all previously referred to either B. divergens or Stephanosella biaperta (Michelin, 1848), is distinctly greater in the north-east Atlantic than has been previously acknowledged. As a result, seven new species are introduced ( Buffonellaria acorensis sp. nov. , Buffonellaria antoniettae sp. nov. , Buffonellaria arctica sp. nov. , Buffonellaria harmelini sp. nov. , Buffonellaria jensi sp. nov. , Buffonellaria muriella sp. nov. , and Buffonellaria ritae sp. nov. ), whereas two are left in open nomenclature. With the increase in number of species, the extremely broad geographical range of distribution assumed for B. divergens breaks down to numerous restricted areas. However, although most species have only been reported from a single location, B. arctica sp. nov. seems to have a fairly wide distribution in the Arctic region.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 537–566.     

Targeted control of widespread exotic species for biodiversity conservation: The Red Fox (Vulpes vulpes) in New South Wales, Australia

Summary   Widespread exotic species provide one of the greatest challenges to biodiversity conservation because they often have devastating impacts on native biota but are near impossible to eradicate. The Red Fox ( Vulpes vulpes ) is established across most of mainland Australia, where it has been linked to severe declines and extinctions of a broad suite of native fauna. A targeted approach to reducing the impacts of Foxes on biodiversity was instigated in New South Wales in 2001 under the New South Wales Fox Threat Abatement Plan. It is based on three simple steps. First, explicit priorities for Fox control are established by identifying which native species are at greatest risk from Fox predation and at which sites Fox control for these species is most critical. Second, high-frequency broad-area Fox-control programmes are established across all land tenures at these priority sites. Third, monitoring programmes are established to measure the response of targeted native fauna and Foxes to Fox control. Monitoring helps refine the priorities for control and the methods used over time. This approach provides a model for the strategic control of widespread exotic pests which threaten biodiversity.     

A test for a cost of opportunism in invasive species in the Commelinaceae

Many invasive species can respond opportunistically to favorable growing conditions. In a previous work, we found that invasive species in the family Commelinaceae were more opportunistic than their noninvasive congeners and could therefore outperform noninvasive relatives in an environment with abundant resources and no competition. Contrary to the expectation that superior performance under favorable conditions comes at the cost of reduced performance under stressful conditions, invasive species did not perform more poorly relative to noninvasive congeners under any conditions we examined. Here we expand our search for potential costs of opportunism in invasive species to additional environmental conditions in which invasive taxa have been shown or predicted to perform poorly. We grew four invasive and four noninvasive species in environments consisting of all possible combinations of high and low soil resources and presence and absence of clipping (removal of aboveground biomass). We also fed leaves of each species to a generalist herbivore to assess resistance to herbivory. We found that the advantage of invasive species is reduced but not eliminated by low soil resources and clipping. At low soil resources, invasive species produced softer leaves than noninvasive species and might therefore be less resistant to generalist herbivory than noninvasive species, although a direct comparison of resistance in a no-choice bioassay revealed no difference. The invasive species outperformed noninvasive species only under the most favorable conditions, and the noninvasive species did not outperform the invasive species in any environment.