Recent Replacement of Native Pili Grass (Heteropogon contortus) by Invasive African Grasses in the Hawaiian Islands

We surveyed 41 sites from throughout O'ahu that had been dominated by native pili grass (Heteropogon contortus) in the late 1960s. Pili grass was absent from 14 (35%) of those sites in 1997 and had declined in abundance in most of the 27 remaining sites, relative to the late 1960s. The pili grass communities have been replaced by communities dominated by one of three African grasses: Cenchrus ciliaris (buffel grass), Pennisetum setaceum (fountain grass), or Panicum maximum (Guinea grass). Panicum maximum was often associated with the shrub Leucaena leucocephala, and Cenchrus ciliaris and Pennisetum setaceum communities showed little evidence of succession toward woody vegetation. Communities dominated by the African grasses were significantly less diverse, in terms of number of plant species, than the native pili grass-dominated communities. Observations made on other Hawaiian islands suggest that this rapid pili grass decline and replacement with alien grasses has not been limited to O'ahu. Research is needed to determine how higher-diversity native pili grass communities can be maintained in the Hawaiian Islands as a valuable natural and cultural resource

March of the Green Iguana : Non-native Distribution and Predicted Geographic Range of Iguana iguana in the Greater Caribbean Region

Green Iguanas (Iguana iguana L. 1758) have been introduced outside their native range largely through the pet trade. In many places, exotic populations have invaded and many have become established. Of special concern is the Greater Caribbean Basin, where several exotic populations of Green Iguanas have had a negative impact, and may threaten the conservation of several native species, including possible native and distinct forms of I. iguana in the Lesser Antilles, and the endangered Lesser Antilles Iguana (I. delicatissima Laurenti 1768). We assessed the risk of spread and invasion by Green Iguanas in the Greater Caribbean Basin using the maximum entropy niche-modeling algorithm (MaxEnt) to predict the potential distribution of this reptile. We used a total of 187 location points that represented occurrences from both the native and the invasive range, coupled with environmental data as predictor variables. Our model had average training and test AUC values of 0.90 and 0.87 respectively, indicating a high predictive ability. The model predicts suitable conditions for I. iguana in south and central Florida (mainly along the coast), and in regions of all the islands in the Caribbean. Given the known negative impact of Green Iguanas and their dispersal capabilities, governments in the Greater Caribbean Basin should manage non-native populations to prevent further spread, and revise and enact laws that allow management agencies to respond quickly in the case of new Green Iguana incursions

Short Lag Times for Invasive Tropical Plants: Evidence from Experimental Plantings in Hawai'i

Background: The lag time of an invasion is the delay between arrival of an introduced species and its successful spread in a new area. To date, most estimates of lag times for plants have been indirect or anecdotal, and these estimates suggest that plant invasions are often characterized by lag times of 50 years or more. No general estimates are available of lag times for tropical plant invasions. Historical plantings and documentation were used to directly estimate lag times for tropical plant invasions in Hawai’i. Methodology/Principal Findings: Historical planting records for the Lyon Arboretum dating back to 1920 were examined to identify plants that have since become invasive pests in the Hawaiian Islands. Annual reports describing escape from plantings were then used to determine the lag times between initial plantings and earliest recorded spread of the successful invaders. Among 23 species that eventually became invasive pests, the average lag time between introduction and first evidence of spread was 14 years for woody plants and 5 years for herbaceous plants. Conclusions/Significance: These direct estimates of lag times are as much as an order of magnitude shorter than previous, indirect estimates, which were mainly based on temperate plants. Tropical invaders may have much shorter lag times than temperate species. A lack of direct and deliberate observations may have also inflated many previous lag time estimates. Although there have been documented cases of long lag times due to delayed arrival of a mutualist or environmenta

Drivers of future alien species impacts: an expert‐based assessment

Understanding the likely future impacts of biological invasions is crucial yet highly challenging given the multiple relevant environmental, socio‐economic and societal contexts and drivers. In the absence of quantitative models, methods based on expert knowledge are the best option for assessing future invasion trajectories. Here, we present an expert assessment of the drivers of potential alien species impacts under contrasting scenarios and socioecological contexts through the mid‐21st century. Based on responses from 36 experts in biological invasions, moderate (20%–30%) increases in invasions, compared to the current conditions, are expected to cause major impacts on biodiversity in most socioecological contexts. Three main drivers of biological invasions—transport, climate change and socio‐economic change—were predicted to significantly affect future impacts of alien species on biodiversity even under a best‐case scenario. Other drivers (e.g. human demography and migration in tropical and subtropical regions) were also of high importance in specific global contexts (e.g. for individual taxonomic groups or biomes). We show that some best‐case scenarios can substantially reduce potential future impacts of biological invasions. However, rapid and comprehensive actions are necessary to use this potential and achieve the goals of the Post‐2020 Framework of the Convention on Biological Diversity

Common mullein (Verbascum thapsus): a literature review

Reports were scanned in black and white at a resolution of 600 dots per inch and were converted to text using Adobe Paper Capture Plug-in.Verbascum thapsus, common mullein, is a biennial weed of roadsides, pastures, and open and semi-open natural habitats. This report reviews the autecology of V. thapsus in its native range (Eurasia) as well as in Hawai'i and elsewhere where it has naturalized. V. thapsus exhibits many characteristics of an ideal weed; broad germination conditions, self-compatibility, high seed output and a long-lived seed bank. Populations can vary substantially in life history characters, which may have allowed the species to spread over such a wide geographical range, including most temperate parts of the world. V. thapsus was introduced to the island of Hawai'i about 100 years ago, and it still appears to be spreading. It has invaded sites from sea level to the summit of Mauna Kea, but the densest populations occur in upper montane and subalpine habitats. Outside of Hawai'i, it is a poor competitor in many habitats, relying on continuous disturbance to maintain its populations. In contrast, in Hawai'i common mullein appears to have spread in little-disturbed native habitats, particularly where vegetation is sparse such as on relatively recent lava flows. Little is known about the impact this may have on the native biota. Further studies are needed to determine if the spread of V. thapsus depends on disturbance in Hawai'i. Extreme stem and inflorescence fasciation in V. thapsus appears to be unique to Hawai'i; its cause and how it affects life history characteristics are not known. While certain herbicides are effective in killing common mullein, long-term control is very difficult due to its abundant, long-lived seeds. No biocontrol agents have been introduced to Hawai'i, although a number of insects and pathogens attack it and its seeds elsewhere

Inflorescence Damage by Insects and Fungi in Native Pili Grass (Heteropogon contortus) versus Alien Fountain Grass (Pennisetum setaceum) in Hawai'i

The success of introduced invaders has often been attributed to their release from natural enemies, We compared rates of seed and ovule destruction by insects and fungal pathogens in an alien invader, fountain grass (Pennisetum setaceum), and a declining native competitor, pili grass (Heteropogon contortus), to determine whether the invader experienced less damage from natural enemies. Inflorescences were sampled on O'ahu from three sites on three dates, and seeds and ovules were inspected for insect damage or pathogen infection. Total seed and ovule destruction was significantly lower in alien fountain grass at all times and sites, with the exception of one sample date on Ka'iwa Ridge when very little damage « 1%) was observed in either species. Total seed and ovule destruction ranged from 0.8 to 5% in fountain grass versus 0 to 61% in pili grass. Most seed and ovule loss in pili grass was caused by infection with the smut fungus Sporisorium caledonicum. Between 5 and 35% of pili grass inflorescences showed signs of smut infection. No fungal pathogens were noted on fountain grass. The low impact of natural enemies on seed production in alien fountain grass, relative to native pili grass, could confer a long-term reproductive advantage to the alien

Global and regional nested patterns of non-native invasive floras on tropical islands

Aim: Non-native species are being distributed globally as a result of human actions, but we still know little about emerging biogeographical patterns. We tested whether the distribution of plant invaders across tropical oceanic islands has a nested structure, and identified mechanisms to explain nestedness among invaders and islands. Location: Tropical islands world-wide. Methods: We analysed two datasets: a global one (350 spermatophyte species invading natural areas within 25 archipelagos) and a regional one (145 species within 12 Pacific archipelagos). We quantified island and species nestedness using the NODF metric and evaluated the contributions of each island and species to nestedness. Results: Globally, the distribution of invaders across islands showed a nested pattern related to island area, elevation (a proxy of habitat diversity) and invasive species richness; the pattern was weakly associated with human population density and independent of isolation from the nearest continent. Invader prevalence among islands was the best predictor of species nestedness. Nestedness was more pronounced at a regional than a global scale. Main conclusions: We found novel biogeographical patterns interconnecting non-native invasive floras at a global scale. Both localized and widespread species are important components of island invasive floras. Invader-rich islands host many rare invaders, and many species are invaders in only one island group, suggesting that prevention efforts should pay attention to rare invaders. We have developed a conceptual model to facilitate understanding of nestedness in island invasion. Both habitat and dispersal filtering are potential mechanisms underlying nestedness, whereas idiosyncratic factors of particular islands (e.g. habitat diversity and socio-economic history) or time-lags may explain 'invader endemicity'. Nested regional patterns may be explained by 'hub' islands that serve as early sites of introduction for many invaders, some of which subsequently spread across the region. © 2013 John Wiley & Sons Ltd.During the preparation of this work, A.T. was supported by a project financed by the Spanish Ministry of Science and Innovation (CGL2010-18759BOS)Peer Reviewe

Frequency distribution for time lags between first planting and start of spread in Manoa Valley (Honolulu, Hawai'i) for plant species that became invasive.

<p>Records extend for 89 years.</p

Cecropia obtusifolia (A) and <i>Falcataria moluccana</i> (B) are examples of early plantings in the Manoa Valley that became invasive.

<p>Natural or semi-natural vegetation is visible in the background of both photos, less than 500 m from these plantings. Photos: E. Caum, 31 December 1922.</p