Exotic Invasive Species Research Articles

Comparative litter decomposability traits of selected native and exotic woody species from an urban environment of north-western Siwalik region, India

Exotic plants can potentially modify ecosystem functions like cycling of nutrients by adjusting their decomposition rates. However, these effects are largely unknown for urban ecosystems, though they act as reservoirs of exotic plants. The present study evaluated the decomposition rates of five native and five exotic (three invasive and two non-invasive) species by conducting the litter bag experiment. Our study, however, did not find any significant differences in overall decomposition rates of native and exotic species but decomposition rates were strongly correlated with initial chemical quality of the litter. Further, litter carbon, lignin to nitrogen ratio and carbon to nitrogen ratio seemed to be good predictors for decomposition rates in this study. Interestingly, invasive exotic species had higher decomposition rate while non-invasive exotic species showed a slower rate as compared to the native species. In conclusion, our study indicates that invasive exotic plants try to maintain a higher chemical quality of litter than native and non-invasive exotic species which promotes their rapid decomposition. Thus, the better chemical quality of litter may facilitate the naturalisation and invasion of exotic plants irrespective of their origin.

The ecological implications of rubber‐based agroforestry: Insect conservation and invasion control

AbstractProtected areas are increasingly threatened by biological invasions, especially in tropical Asia where extensive areas of natural habitats have been converted to monoculture plantations. Such disturbance provides a gateway for exotic species invasions, highlighting an urgent need for cross‐boundary solutions to mitigate invasion impacts.Agroforests, with multi‐storied trees and crops resembling the complex structure of natural forest, are known to promote native species compared to monoculture plantations. Yet, our knowledge on their roles in controlling exotic species is limited to plant invaders, with effects on animal invaders still unknown. Given that protected areas are increasingly threatened by invaders from surrounding plantations, with a majority of them represented by insects, it is important to evaluate the effect of agroforestry practice, and mechanisms of associated management to control invasions.By using both taxonomic and functional trait‐based approaches, we studied leaf litter ant communities in 12 rubber monoculture (mono‐rubber), 9 rubber plantation with understory crops (agro‐rubber), 16 secondary and 12 old‐growth secondary forest plots in and around protected areas in Hainan, China. Sampled ants were further classified into groups based on their invasive potential (tramp vs. non‐tramp) to determine the ecological values of agro‐rubber.We found that despite mono‐rubber and agro‐rubber presenting similar species richness, the latter (a) supports species composition and functional diversity more similar to secondary forests and (b) reduces tramp ant species occurrence, a novel management incentive. Nonetheless, agro‐rubber is not comparable to secondary forest in terms of non‐tramp ant species composition.Synthesis and applications.Against the increasing threat of biological invasions, preserving natural forests in human‐dominated landscapes is crucial. Increasing the area of agro‐rubber at the periphery of protected areas as a proactive mitigation can, however, be perceived as an additional measure to reduce invasive species' establishment and spread across the landscape. Plantation‐based agroforestry has emerged as a potential management avenue and incentive for transforming monoculture plantations into a less ‘harmful’ alternative.

Plant cover restoration to inhibit seedling emergence, growth or survival of an exotic invasive plant species

ABSTRACT We conducted a mesocosm restoration experiment to test the efficacy of early summer sowing of seed mixtures for inhibiting the emergence, growth and/or survival of giant hogweed (Heracleum mantegazzianum) seedlings. H. mantegazzianum is invasive in Europe and North America, where it has a negative effect on plant diversity and represents a serious health hazard, due to the photodermatitis it may cause. We tested five plant mixtures comprising a selection of North American native or naturalized non-invasive plant species. Compared to the unseeded control mesocosm, all plant covers reduced seedling emergence, growth and survival of H. mantegazzianum. There were large differences between mixtures regarding inhibition effects. The nature of the effects depended on species composition, with one mixture more effective in preventing establishment, another essentially affecting seedling growth and survival. Total plant cover, irrespective of seed mixtures, appeared to have a major effect on H. mantegazzianum. Other factors that may have played a role included the litter from the seeded plants and the allelopathic effect of Canada goldenrod (Solidago canadensis). Our study adds to the growing body of evidence promoting the restoration of a plant cover as a means to prevent reinfestation by invasive species following a control operation.

Primer registro de Sceliphron caementarium (Drury, 1773) (Hymenoptera: Sphecidae) en las Islas Baleares, con una clave de identificación para las especies del archipiélago del género Sceliphron Klug, 1801

Díaz-Calafat, J. 2020. First record of Sceliphron caementarium (Drury, 1773) (Hymenoptera: Sphecidae) in the Balearic Islands, with an identification key to the archipelago’s species of the genus Sceliphron Klug, 1801. Ecosistemas 29(1):1939. https://doi.org/10.7818/ECOS.1939 The Black and Yellow Mud Dauber wasp (Sceliphron caementarium (Drury 1773)) is reported for the first time from two distant locations of the island of Mallorca (Balearic Islands, Spain). Possible entry pathways of this potentially invasive species to the archipelago are discussed, as well as potential threats to local biodiversity and ecologically relevant questions raised by the arrival of this new species in the archipelago. The addition of S. caementarium to the Balearic fauna raises the number of species in the genus Sceliphron Klug 1801 to four; with half of them being recent introductions of potentially invasive exotic species. Finally, an illustrated identification key to the Balearic species of the genus Sceliphron is presented in order to ease their identification in the future. Readers are encouraged to use the key and send new records of these species within the Balearic Islands to the author or to online biodiversity recording platforms in order to help studying the dispersion of introduced sphecid wasps and update the distribution data of native and introduced species.

Ecological Plasticity and the Future of the Argentine Giant Tegu (Salvator merianae Dumeril and Bibron, 1839) in the Southeastern US

Salvator merianae (Argentine Giant Tegu) is an invasive exotic species established in 2 as yet unconnected populations in central and southern Florida. Despite intense trapping, this mid-level carnivore remains well-established in a portion of extreme southern mainland Florida where it was first released 20 y ago. High fecundity, nest-guarding, rapid growth to large body size, and broad trophic width by which it negatively impacts wildlife contribute to its success as a colonizing species. Native to more temperate habitat, it experiences a defined winter and summer in South America unlike the wet–dry seasons of southern Florida. We conducted a qualitative comparison of key life-history traits from source areas to those of southern Florida that provided a measure of its ecological plasticity and formed the basis for expectations associated with northward expansion. Our examination of 1168 specimens collected during 2011–2017 revealed an overlap between the sexes in timing of fat storage prior to brumation and late-winter–early-spring peak in gonadal size. Females were ovigerous during March–May and possibly June, and clutch size averaged 28.6 eggs. Hatching was possible during May–August, and both sexes reached sexual maturity by 2 y of age. In this subtropical system, length of seasonal activity, gonadal cycles, and size and age at sexual maturity differed from those of source areas, indicative of the degree of plasticity among these traits over a short period of time. We found that the climate of the Southeast is amenable to the colonization of this vagile species. Our findings are suggestive that a return to the strongly selected seasonal activity and gonadal cycles of central Argentina will accompany the Argentine Giant Tegu in its northward dispersal into more temperate conditions even as it retains a somewhat relaxed cycle in southern Florida.

Vascular epiphyte communities in secondary and mature forests of a subtropical montane area

Vascular epiphytes were traditionally studied in pristine forests, and few studies were performed to understand their colonization in secondary forests, particularly in subtropical areas. Many secondary forests are invaded by exotic tree species that threaten biodiversity, and the impact of invaders on epiphytes remains unknown. The structure, diversity and composition of epiphytes were analyzed along a successional gradient of native forests in a subtropical montane area of Tucuman, Argentina. Changes in epiphyte communities were also analyzed along density gradients of the exotic invaders Ligustrum lucidum and Morus alba in secondary forests. The epiphyte communities of trees with a diameter ≥10 cm were surveyed in 20 × 20 m quadrats in a successional gradient (30-y and 60-y secondary forests, and mature forests) and in 30–45-y secondary forests with different densities of the invaders. In the successional gradient, increasing cover and number of records of epiphytes (i.e. the sum of epiphytes records on all trees) were explained by the pooled basal area of trees, and older patches (60-y secondary forests and mature forests) had higher epiphyte species richness. Epiphyte species richness and the percentage of trees colonized by epiphytes decreased steadily towards higher densities of Ligustrum lucidum and Morus alba in 30–45-y secondary forests. Vascular epiphyte communities were impoverished in secondary forests dominated by Ligustrum lucidum or Morus alba possibly because they represent low quality habitats for these plants. The patterns emerged in this study showed the importance of secondary forests dominated by native trees for epiphyte diversity conservation, and the necessity to control the invasion of exotic tree species.

Resistance to pull-out of Chilean riverine species: Evidence from laboratory experiments

Vegetation growing in river bars and banks determines the morphological processes in river channels. The presence and dynamics of riverine vegetation depend on the magnitude and frequency of floods able to change morphology and uproot plants, and on the plant's resistance to pull-out. A series of pull-out experiments were carried out with the objective to determine the resistance of riverine vegetation to be uprooted and its effects on river-bed dynamics. Nine riverine species were used for the experiment: seven of them are native from Chile, and the other two are exotic and invasive in Chilean environments. A total of 200 specimens were transplanted in a substrate simulating a bar of a gravel-bed river, and after 7 months they were individually pulled-out, and the force and time needed to uproot the plant quantified. Data were analysed by means of generalised linear models (GLM) and linear regressions, and force-time curves were interpreted and related to the root morphology of the species. GLM results showed that resistance values were dependent on root and plant physical characteristics, and by the factor species. Among the species studied, the three species showing higher resistance values were native, while the less resistant was an exotic invasive species. The time needed to uproot the individuals did not seem to be influenced by plant parameters nor by the factor species. Root architecture seemed to have an effect on plant pull-out resistance and uprooting rapidity, being heart-shaped roots the ones that registered higher resistance values. Despite this, when incorporating flow strength on the findings, the exotic invasive ones seemed to be some of the more resistant to uprooting. The findings of this paper contribute to the better understanding of river vegetational and sedimentary dynamics, and are useful for parameterising the modelling of fluvial landscapes evolution and for the design of river restoration projects.

COMPARATIVE NUTRITIVE VALUE OF AN INVASIVE EXOTIC PLANT SPECIES, Prosopis glandulosa TORR. var. glandulosa, AND FIVE INDIGENOUS PLANT SPECIES COMMONLY BROWSED BY SMALL STOCK IN THE BORAVAST AREA, SOUTH-WESTERN BOTSWANA

Nutritive value of an invasive exotic plant species, Prosopis glandulosa Torr. var. glandulosa, and five indigenous plant species commonly browsed by livestock in Bokspits, Rapplespan, Vaalhoek and Struizendam (BORAVAST), southwest Botswana, was determined and compared. These five indigenous plant species were Vachellia hebeclada (DC.) Kyal. & Boatwr. subsp. hebeclada, Vachellia erioloba (E. Mey.) P.J.H. Hurter, Senegalia mellifera (Vahl) Seigler & Ebinger subsp. detinens (Burch.) Kyal. & Boatwr., Boscia albitrunca (Burch.) Gilg & Gilg-Ben. var. albitrunca and Rhigozum trichotomum Burch. The levels of Crude Protein (CP), Phosphorus (P), Calcium (C), Magnesium (Mg), Sodium (Na) and Potassium (K) were determined for the plants foliage and pods (where available). All plant species had a CP value higher than the recommended daily intake. There are however multiple mineral deficiencies in the plant species analysed. Nutritive value of Prosopis glandulosa is comparable to those other species despite the perception that livestock that browse on it are more productive than those that browse on the other plant species.

Is Niagara Falls a barrier to gene flow in riverine fishes? A test using genome-wide SNP data from seven native species.

Since the early Holocene, fish population genetics in the Laurentian Great Lakes have been shaped by the dual influences of habitat structure and post-glacial dispersal. Riverscape genetics theory predicts that longitudinal habitat corridors and unidirectional downstream water-flow drive the downstream accumulation of genetic diversity, whereas post-glacial dispersal theory predicts that fish genetic diversity should decrease with increasing distance from glacial refugia. This study examines populations of seven native fish species codistributed above and below the 58m high Niagara Falls - a hypothesized barrier to gene flow in aquatic species. A better understanding of Niagara Falls' role as a barrier to gene flow and dispersal is needed to identify drivers of Great Lakes genetic diversity and guide strategies to limit exotic species invasions. We used genome-wide SNPs and coalescent models to test whether populations are: (a) genetically distinct, consistent with the Niagara Falls barrier hypothesis; (b) more genetically diverse upstream, consistent with post-glacial expansion theory, or downstream, consistent with the riverscape habitat theory; and (c) have migrated either upstream or downstream past Niagara Falls. We found that genetic diversity is consistently greater below Niagara Falls and the falls are an effective barrier to migration, but two species have probably dispersed upstream past the falls after glacial retreat yet before opening of the Welland Canal. Models restricting migration to after opening of the Welland Canal were generally rejected. These results help explain how river habitat features affect aquatic species' genetic diversity and highlight the need to better understand post-glacial dispersal pathways.

Hydrothermal Carbonization and Pellet Production from Egeria densa and Lemna minor.

Biofuels are seen as a potential option for mitigating the effects of fossil fuel use. On the other hand, nutrient pollution is accelerating eutrophication rates in rivers, lakes, and coastal waters. Harvesting aquatic plants to produce biofuels could mitigate this problem, though it is important to attack the problem at source, mainly as regards the contribution of nutrients. For the first time, solid biofuels were obtained in the forms of carbon and pellets from the aquatic plants Egeria densa, which is classed as an invasive plant under the Spanish Catalogue of Exotic Invasive Species, and Lemna minor, both of which can be found in the Umia River in north-west Spain. The essential oils and macro- and microelements present in both these plants were also extracted and analyzed. The higher heating values (HHVs) of the carbon products obtained ranged from 14.28 to 17.25 MJ/kg. The ash content ranged from 22.69% to 49.57%. The maximum yield obtained for biochar for Egeria densa at 200 °C was 66.89%. Temperature significantly affects solid hydrochar yield. The HHVs of the pellets obtained ranged from 11.38 to 13.49 MJ/kg. The use of these species to obtain biofuels through hydrothermal carbonization (HTC) and pellets is a novel and effective approach that will facilitate the removal of nutrients that cause eutrophication in the Umia River. The elements extracted show that harvesting these plants will help to remove excessive nutrients from the ecosystem.

Niche Complementarity and Resistance to Grazing Promote the Invasion Success of Sargassum horneri in North America

Invasive species are a growing threat to conservation in marine ecosystems, yet we lack a predictive understanding of ecological factors that influence the invasiveness of exotic marine species. We used surveys and manipulative experiments to investigate how an exotic seaweed, Sargassum horneri, interacts with native macroalgae and herbivores off the coast of California. We asked whether the invasion (i.e., the process by which an exotic species exhibits rapid population growth and spread in the novel environment) of S. horneri is influenced by three mechanisms known to affect the invasion of exotic plants on land: competition, niche complementarity and herbivory. We found that the removal of S. horneri over 3.5 years from experimental plots had little effect on the biomass or taxonomic richness of the native algal community. Differences between removal treatments were apparent only in spring at the end of the experiment when S. horneri biomass was substantially higher than in previous sampling periods. Surveys across a depth range of 0–30 m revealed inverse patterns in the biomass of S. horneri and native subcanopy-forming macroalgae, with S. horneri peaking at intermediate depths (5–20 m) while the aggregated biomass of native species was greatest at shallow (<5 m) and deeper (>20 m) depths. The biomass of S. horneri and native algae also displayed different seasonal trends, and removal of S. horneri from experimental plots indicated the seasonality of native algae was largely unaffected by fluctuations in S. horneri. Results from grazing assays and surveys showed that native herbivores favor native kelp over Sargassum as a food source, suggesting that reduced palatability may help promote the invasion of S. horneri. The complementary life histories of S. horneri and native algae suggest that competition between them is generally weak, and that niche complementarity and resistance to grazing are more important in promoting the invasion success of S. horneri.

Short communication: The dissimilarity in plant species composition of savanna ecosystem along the elevation gradient on Flores Island, East Nusa Tenggara, Indonesia

Abstract. Sutomo, Darma IDP, Iryadi R. 2020. Short communication: The dissimilarity in plant species composition of savanna ecosystem along the elevation gradient on Flores Island, East Nusa Tenggara, Indonesia. Biodiversitas 21: 492-496. Savannas in Indonesia are located from west to the east across the archipelago. The objective of this research was to investigate the dissimilarity of floristic composition among savannas at different elevations in Flores. Sixteen sampling plots, each measuring 20 x 20 m were spread over the lowland, midland, and upland savannas. We analyzed the differences in plant community composition among the savannas using NMDS ordination and SIMPER analyses available in PRIMER V.6. As many as 41 species of plants were found in all of the sampling plots. The lowland savanna plant community consisted of Themeda arguens, Zoesya sp., Chromolaena odorata, Crotalaria sp., Adenanthera pavonina, Ocimum sp., Lantana camara in the groundcover layer, and Ziziphus jujube, and Borassus flabellifer at the tree layer. The midland savanna had almost similar composition, except the occurrence of Imperata cylindrica and Leucaena leucocephala, and the upland savanna plant species were Cyperus sp., Polygala paniculata, I. cylindrica, Melastoma malabathricum, C. odorata, Centella asiatica, Vaccinium sp., and Cymbopogon sp. The savannas in Flores were invaded by invasive exotic species, namely L. camara and C. Odorata which may pose serious threat to the existence of savannas.

Demographic characteristics of two freshwater cyclopoid copepods in Mexico, fed a plankton diet: the native Mesocyclops longisetus Thiébaud and the invasive Mesocyclops pehpeinsis Hu

ABSTRACTThe introduction of exotic species often results in a loss of biodiversity. Mexico has 4 invasive species of freshwater cyclopoid copepods: Thermocyclops crassus, Mesocyclops aspericornis, M. thermocyclopoides, and M. pehpeiensis. The Asian cyclopoid M. pehpeiensis is now established in several lakes and rivers in Mexico, but how it might compete with native species and potentially change the structure of plankton communities is unknown. Some insights might be obtained from a study of its demography compared to that of a native species. We compared the life cycle parameters of the native Mesocyclops longisetus and the exotic invasive species M. pehpeiensis in separate cultures. Four treatments were set up with 2 densities of Plationus patulus (Rotifera) individuals (1 and 4 mL−1) and 2 concentrations of Scendesmus acutus (Chlorophyte) cells (0.5 × 106 and 1.5 × 106 mL−1). Both species survived and reproduced in the treatment of 4 mL−1 of P. patulus individuals + 0.5 × 106 mL−1 of S. acutus cells. Mesocyclops pehpeiensis had common characteristics in successful invasive species: short generation time, high reproductive capacity, and a wide dietary range. At low rotifer densities, M. pehpeiensis had a higher population growth rate (0.12 d−1) compared to M. longisetus (0.08–0.10 d−1). M. pehpeiensis is likely to outcompete M. longisetus, especially under food-limited conditions, and most likely expand its range in Mexico.

How influential are squamate reptile traits in explaining population responses to environmental disturbances?

Abstract Context Understanding how organismal attributes influence sensitivity to environmental perturbations is a central theme in ecology and conservation. Certain traits, such as body size, habitat use, dietary preference and reproductive output are considered important determinants of animal species’ responses to the impacts of ecological disturbances. However, the general relationships between functional traits and post-disturbance responses by animals are not fully understood. AimsOur primary aim was to use a meta-analysis to evaluate the influence of species traits on variation in population abundances of squamate reptiles (i.e. lizards and snakes). MethodsWe extracted data from 107 original published studies, from which 1027 mean effect sizes of post-disturbance responses by 298 species were estimated. We examined short-term responses only (i.e. within 3 years since the most recent disturbance). A comprehensive range of disturbances was examined, such as habitat destruction, fragmentation, fire, and exotic-species invasions. We used Bayesian linear mixed-effect modelling (BLMM), utilising the Markov-chain Monte Carlo algorithm (MCMC) for the meta-regression. Specifically, we tested the influence of eight species traits (body size, diet, temporal activity pattern, sociality, reproductive mode, clutch size, habitat selection, and mean body temperature), along with disturbance type, in explaining variation in species-specific abundance responses of squamate reptiles post-disturbance. Key resultsPost-disturbance abundance responses of squamate species were significantly influenced by two parameters, namely, mean body temperature and clutch size. In general, significant positive responses post-disturbance were observed for species with higher mean body temperatures and a greater clutch size. The type of disturbance had no detectable influence on squamate abundances. The influence of random effects (heterogeneity among studies and species, and broad taxonomic identity) accounted for more of the model variation than did the fixed effects (species traits and disturbance type). ConclusionsCertain species traits exerted some influence on the sensitivities of lizards and snakes to ecological disturbances, although the influence of random effects was very strong. Our findings are likely to be a result of the complexity and idiosyncratic nature of natural abundance patterns among animal species, in addition to the potential confounding effect of methodological differences among studies. ImplicationsThe present study is the first major quantitative synthesis of how species traits influence population-level responses of squamate reptiles to ecological disturbances. The findings can be used to guide conservation efforts and ecological management, such as by prioritising the efforts of mitigation on species that reproduce more slowly, and those with lower body temperatures.

New distributional record for two exotic invasive species: Aeschynomene americana L. and Calopogonium mucunoides Desv. in Tripura, North East India

New distributional record for two exotic invasive species: Aeschynomene americana L. and Calopogonium mucunoides Desv. in Tripura, North East India

LISTA DE ESPECIES DE PECES DE LA CUENCA DEL RÍO QUEGUAY, RÍO URUGUAY BAJO

The Queguay river is one of the main tributaries of the lower Uruguay river basin. At the confluencce of its main effluents large wetlands and riparian forest are developed, that according to their biodiversity and ecosystem functions have been included in the National Protected Areas System, under the name “Montes del Queguay”. At a national scale the basin is included in two ecoregions: the Basaltic Slope and the Western Sedimentary Basin. Except for an unsupported listing in scientific collections, there is no documented information about its ichthyofauna. Therefore, the objective of this work was to prepare an updated list of the fish species in the Queguay River basin. Considering all the sources of information, a total of 94 species were registered for the basin, corresponding to 60 genera, 28 families and nine orders. The composition of species found was similar to the largest tributary of the low Uruguay ecoregion, the Rio Negro basin. The main migratory species of the Plata basin stand out, as well as a species of annual fish endemic to the wetlands of the basin, and the presence of an invasive exotic species (Cyprinus carpio).

Partial decoupling between exotic fish and habitat constraints remains evident in late invasion stages

We investigated the relationships between exotic freshwater fish invasions, environmental factors and ecofunctional diversity (i.e. the combination of ecological traits in communities) in streams. We used data from 335 stream sites, belonging to 105 watersheds and 3 basins in Italy, to test whether the exotic species invasion was dominated by species with generalist traits and whether the environment-ecofunctional trait relationships of exotic and native species would differ from each other. We also tested the hypothesis that ecofunctional uniqueness patterns between exotic and native species would be substantially different. We found that generalist traits were widespread in nearly all areas where exotic species occurred, but not all generalist traits were equally abundant in exotic communities. Only temperature tolerant, low oxygen tolerant and eurytopic traits were typically more dominant in exotic communities than native ones, suggesting that not all generalist traits are equally important in the invasion process and that more complex mechanisms of trait selection could take place. Environment-ecofunctional trait relationships of exotic and native species partly differed both in direction and magnitude, suggesting that invasion dynamics could decouple the linkage between environment and biotic communities, but also that this decoupling might decrease at later invasion stages (i.e. > 30 years after major invasions). Finally, site and trait ecofunctional uniqueness differed between exotic and native species. Exotic species ecofunctional diversity hotspots were located in human-disturbed areas, suggesting that human disturbance might play a strong role in invasion patterns. We advocate for a wider use of ecofunctional approaches in conservation studies in the future, as they could be a key to understand complex ecological processes such as exotic invasions.

Tropical dendrochronology applied to invasive tree species in the Brazilian Atlantic Forest

The Atlantic Forest is one of the largest and most biodiverse rainforests of South America but anthropogenic activities are drastically changing these landscapes. The invasion of alien or exotic species is one of the greatest threats to biodiversity. There are few studies of invasive species in tropical Brazilian ecosystems. This research examines growth and ecological aspects of Syzygium cumini and Clitoria fairchildiana, two invasive tree species in the Pedra Branca State Park, an Atlantic Forest remnant in southeastern Brazil. Both species were successfully dated, indicating an average age of 58 and 31 years, respectively. A positive relationship between growth and precipitation of the previous growing season suggests an ecological adaptive strategy, which could be facilitating their invasion into the environment. Cumulative growth diameter curves indicate slow and fast growth rates for S. cumini and C. fairchildiana, respectively. Growth release episodes detected in the tree rings indicate increased anthropogenic disturbances over the last 50 years.

Global change biology: A primer.

Because of human action, the Earth has entered an era where profound changes in the global environment are creating novel conditions that will be discernable far into the future. One consequence may be a large reduction of the Earth's biodiversity, potentially representing a sixth mass extinction. With effective stewardship, the global change drivers that threaten the Earth's biota could be alleviated, but this requires clear understanding of the drivers, their interactions, and how they impact ecological communities. This review identifies 10 anthropogenic global change drivers and discusses how six of the drivers (atmospheric CO2 enrichment, climate change, land transformation, species exploitation, exotic species invasions, eutrophication) impact Earth's biodiversity. Driver impacts on a particular species could be positive or negative. In either case, they initiate secondary responses that cascade along ecological lines of connection and in doing so magnify the initial impact. The unique nature of the threat to the Earth's biodiversity is not simply due to the magnitude of each driver, but due to the speed of change, the novelty of the drivers, and their interactions. Emphasizing one driver, notably climate change, is problematic because the other global change drivers also degrade biodiversity and together threaten the stability of the biosphere. As the main academic journal addressing global change effects on living systems, GCB is well positioned to provide leadership in solving the global change challenge. If humanity cannot meet the challenge, then GCB is positioned to serve as a leading chronicle of the sixth mass extinction to occur on planet Earth.

Phytophthora Species Associated with Plants in Constructed Wetlands and Vegetated Channels at a Commercial Plant Nursery Over Time

Constructed wetlands have been used for decades in agricultural settings to remediate nutrients and other agrichemicals from irrigation runoff and drainage; however, little is known about the presence and distribution of Phytophthora species within irrigation runoff water being treated in constructed wetlands. Therefore, we collected plant samples from within vegetated runoff collection channels and treatment stages of two constructed wetland systems receiving irrigation runoff at a commercial plant nursery in Cairo, GA, to determine if roots of wetland plants were infested by species of Phytophthora. Samples were collected 12 times, at 1- to 2-month intervals, over a 19-month period, from Mar. 2011 through Sept. 2012. The sample period covered all four seasons of the year, so we could determine if the association of Phytophthora species with roots of specific plant species varied with season. Approximately 340 samples from 14 wetland plant species were collected, and 22 isolates of Phytophthora species were recovered. Phytophthora species were typically isolated from plants in channels receiving runoff water directly from plant production areas; Phytophthora species were not detected on plants where water leaves the nursery. No seasonal patterns were observed in plant infestation or presence of species of Phytophthora. In fact, Phytophthora species were rarely found to be associated with the roots of the wetland plants collected; species of Phytophthora were found infesting roots of only 6.5% of the 336 plants sampled. Species of Phytophthora were not found to be associated with the roots of golden canna (Canna flaccida), lamp rush (Juncus effusus var. solutus), duckweed (Lemna valdiviana), or sedges (Carex sp.) during the study period. The exotic invasive plant species marsh dayflower [Murdannia keisak (33% of samples infested)] and alligatorweed [Alternanthera philoxeroides (15% of samples infested)] were found to have the first and third highest, respectively, incidences of infestation, with smooth beggartick (Bidens laevis) having the second highest incidence of samples infested (22%). Management of invasive species in drainage canals and constructed wetland systems may be critical because of their potential propensity toward infestation by Phytophthora species. Plant species recommended for further investigation for use in constructed wetlands to remediate irrigation runoff include golden canna, marsh pennywort (Hydrocotyle umbellata), pickerelweed (Pontederia cordata), and broadleaf cattail (Typha latifolia). The results from this study provide an important first look at the associations between species of Phytophthora and wetland plants in constructed wetland systems treating irrigation runoff and will serve to further optimize the design of constructed wetlands and other vegetation-based treatment technologies for the removal of plant pathogens from irrigation runoff.