Abundance Of Native Species Research Articles

Variations in soil properties and native woody plant species abundance under Prosopis juliflora invasion in Afar grazing lands, Ethiopia

IntroductionPastoralism and agro-pastoralism are the major modes of life in arid and semi-arid rangelands. However, rangeland quality and quantity are rapidly deteriorating due to a number of natural and human-induced factors, one of which is bush encroachment. Little is known on how bush encroachment affects the ecosystem functions and services expressed in terms of the native vegetation composition and structure, status of the soil seed bank, soil chemical and physical properties, and the abundance of mycorrhiza spores.MethodsWe assessed woody species in 64 plots distributed across four levels of Prosopis juliflora invasion (high, medium, low, and none) at two sites, Amibara and Gewane, in the Afar Region, Ethiopia. We collected composite soil samples to investigate the soil seed bank, mycorrhizal associations, and spore abundance.ResultsPlant biodiversity was generally low, with eight and four woody species in Gewane and Amibara, respectively. Prosopis juliflora was dominant in highly, moderately, and lowly invaded areas while Acacia senegal dominated the non-invaded areas. The average number of P. juliflora individuals ranged from 3/ha at non-invaded areas in Gewane to 4200/ha at highly invaded areas in Amibara while the total individual number of native woody species ranged from 0 to 88/ha at highly and lowly invaded areas, respectively. The population structure of trees/shrubs in all invasion areas showed an inverted J-shaped distribution, characterized by a high abundance of small individuals. Prosopis juliflora invasion was associated with high soil OC, Na, Ca, P, bulk density, and moisture content. Herbaceous seed numbers and species richness were highest in the moderately and highly invaded areas. All sampled tree species were associated with mycorrhiza but the percentage of root length colonization by different arbuscular mycorrhizal fungus structures varied significantly (p < 0.05) across invasion categories and sites.ConclusionsOur results revealed that although P. juliflora invasion negatively impacted the availability of native woody livestock forage species, it had a positive effect on most soil physical and chemical properties. Such variable effects call out for sustainable management practices when invaded areas are restored.

Scientists' warning on invasive alien species.

ABSTRACTBiological invasions are a global consequence of an increasingly connected world and the rise in human population size. The numbers of invasive alien species – the subset of alien species that spread widely in areas where they are not native, affecting the environment or human livelihoods – are increasing. Synergies with other global changes are exacerbating current invasions and facilitating new ones, thereby escalating the extent and impacts of invaders. Invasions have complex and often immense long‐term direct and indirect impacts. In many cases, such impacts become apparent or problematic only when invaders are well established and have large ranges. Invasive alien species break down biogeographic realms, affect native species richness and abundance, increase the risk of native species extinction, affect the genetic composition of native populations, change native animal behaviour, alter phylogenetic diversity across communities, and modify trophic networks. Many invasive alien species also change ecosystem functioning and the delivery of ecosystem services by altering nutrient and contaminant cycling, hydrology, habitat structure, and disturbance regimes. These biodiversity and ecosystem impacts are accelerating and will increase further in the future. Scientific evidence has identified policy strategies to reduce future invasions, but these strategies are often insufficiently implemented. For some nations, notably Australia and New Zealand, biosecurity has become a national priority. There have been long‐term successes, such as eradication of rats and cats on increasingly large islands and biological control of weeds across continental areas. However, in many countries, invasions receive little attention. Improved international cooperation is crucial to reduce the impacts of invasive alien species on biodiversity, ecosystem services, and human livelihoods. Countries can strengthen their biosecurity regulations to implement and enforce more effective management strategies that should also address other global changes that interact with invasions.

Native and invasive zooplankton show differing responses to decadal‐scale increases in maximum temperatures in a large temperate river

AbstractIt has been widely proposed that increasing global temperatures will promote the geographic spread of invasive species, yet few studies have examined the effects of increasing temperatures on existing populations of invaders. Here, we examine temperature trends across a 70‐year series of daily records from the lower Columbia River (Washington and Oregon), and assess the correlation between interannual water temperature variability and the abundance of several native and invasive zooplankton species using a 12‐year series of monthly zooplankton samples from a nearby station. Our results show a clear pattern of increasing temperatures in the river, with a negative correlation between elevated late summer temperatures and the abundance of all examined native taxa, but none of the examined invasive taxa. Our study supports the hypothesis that anthropogenic climate change may promote conditions more favorable to previously established populations of invasive zooplankton species.

Impact of Invasive Tree Species on Natural Regeneration Species Composition, Diversity, and Density

Invasive tree species decrease ecosystem resilience with negative impacts on natural regeneration. The influence of alien tree species on ecosystems is unevenly recognized and does not always account for different habitat specificity. We assessed the impacts of the three most frequent invasive tree species in European forests: Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on natural regeneration diversity, species composition, and density. We hypothesized that invaded forest types, in comparison with non-invaded, will differ in terms of species composition, will have lower taxonomic, functional, and phylogenetic diversity of natural regeneration, and will have lower densities of native tree species. We used a set of 189 study plots (200 m2) in a systematic design, established in various forest types in Wielkopolski National Park (West Poland). We analyzed impacts of forest type, accounting for soil C:N ratio, soil pH, and light availability on natural regeneration (woody species up to 0.5 m height) species composition, diversity, and density. We found an overlap of species composition among invaded and non-invaded forests and low impacts of invasive species on taxonomic diversity and functional richness. We found no impacts on phylogenetic diversity and other functional diversity components. In contrast, we found that the natural regeneration of forest-forming tree species reached lower densities in invaded than non-invaded forest types. However, sub-canopy and shrub species reached higher densities in invaded than non-invaded forest types. We confirmed that invasive tree species affect natural regeneration by decreasing the regeneration density of native tree species (in eight of nine tree species studied), species composition homogenization, and supporting natural regeneration of sub-canopy and shrub species. Therefore, the restoration of invaded forests requires eradication of invasive tree species to decrease propagule pressure and to stop decreases in the abundance of native tree species’ natural regeneration.

The role of native and introduced birds in transmission of avian malaria in Hawaii.

The introduction of nonnative species and reductions in native biodiversity have resulted in substantial changes in vector and host communities globally, but the consequences for pathogen transmission are poorly understood. In lowland Hawaii, bird communities are composed of primarily introduced species, with scattered populations of abundant native species. We examined the influence of avian host community composition, specifically the role of native and introduced species, as well as host diversity, on the prevalence of avian malaria (Plasmodium relictum) in the southern house mosquito (Culex quinquefasciatus). We also explored the reciprocal effect of malaria transmission on native host populationsand demography. Avian malaria infection prevalence in mosquitoes increased with the density and relative abundance of native birds, as well as host community competence, but was uncorrelated with host diversity. Avian malaria transmission was estimated to reduce population growth rates of Hawai'i 'amakihi (Chlorodrepanis virens) by 7-14%, but mortality from malaria could not explain gaps in this species' distribution at our sites. Our results suggest that, in Hawaii, native host species increase pathogen transmission to mosquitoes, but introduced species can also support malaria transmission alone. The increase in pathogen transmission with native bird abundance leads to additional disease mortality in native birds, further increasing disease impacts in an ecological feedback cycle. In addition, vector abundance was higher at sites without native birds and this overwhelmed the effects of host community composition on transmission such that infected mosquito abundance was highest at sites without native birds. Higher disease risk at these sites due to higher vector abundance could inhibit recolonization and recovery of native species to these areas. More broadly, this work shows how differences in host competence for a pathogen among native and introduced taxa can influence transmission and highlights the need to examine this question in other systems to determine the generality of this result.

Evaluating Native Bee Communities and Nutrition in Managed Grasslands.

Native pollinators are important for providing vital services in agroecosystems; however, their numbers are declining globally. Bees are the most efficient and diverse members of the pollinator community; therefore, it is imperative that management strategies be implemented that positively affect bee community composition and health. Here, we test responses of the bee and flowering plant communities to land management treatments in the context of grasslands in the upper Midwestern United States, a critical area with respect to bee declines. Twelve sites were selected to examine floral resources and wild bee communities based on three different types of grasslands: tallgrass prairie remnants, ungrazed restorations, and grazed restorations. Total bee abundance was significantly higher in ungrazed restorations than remnants, but there were no significant differences among grasslands in community composition or Shannon diversity. Across the three grassland types we also examined mass and lipid stores as nutritional health indicators in three sweat bees (Halictidae), Augochlora pura, Agapostemon virescens, and Halictus ligatus. Although there were no differences in lipid content, total average bee mass was significantly higher in Ag. virescens collected from ungrazed restorations as compared to remnants. Floral abundance of native and non-native species combined was significantly higher in grazed restorations compared to remnants and ungrazed restorations. However, ungrazed restorations had higher abundance and richness of native flowering ramets. These data suggest that bee abundance and nutrition are driven by high abundance of native flowering plant species, rather than total flowering plants.

Spatial and temporal variation of potential resource availability provided by street trees in southeastern Brazil

Street trees provide several ecosystem services in urban areas, including food for fauna. Tree species richness, composition and the relative abundance of native vs. non-native species can affect the populations of pollinators and dispersers. This work aims to evaluate the potential availability of food resources provided by street trees, in space and time, considering different pollination and seed dispersal syndromes at Santo Andre city (Southeastern Brazil). The georeferenced data for all catalogued tree individuals in the Urban Macrozone constituted our sampling domain. The species were categorized according to its geographical origin, pollination and seed dispersal syndromes, flowering and fruiting season. We divided the study area into cells and calculated: number of individuals, species richness, species diversity; richness and diversity of potentially flowering and fruiting individuals in each season of the year. 38,379 trees were catalogued, representing 578 trees/km2, totalizing 230 species. Most individuals (73%) were non-native. The number of individuals, species richness and diversity varied spatially. The pollination syndrome with higher potential resources availability was melittophily (pollination by bees and wasps) has during spring whereas ornithochory (seed dispersal by birds) was the dispersal syndrome with higher potential resources availability which occurred in summer. Despite the dominance of exotic individuals, the most common syndromes are in accordance with what is expected for tropical Atlantic rainforest regions. However, some pollination and dispersal syndromes presented very low potential resource availability in different seasons and no availability in some regions. These results should be taken into account by stakeholders for a better planning of planting efforts, considering the distribution, in space and time, of the potential availability of resources provided by street trees to fauna in order to improve connectivity.

Synergistic impacts of co‐occurring invasive grasses cause persistent effects in the soil‐plant system after selective removal

AbstractHuman influence on the environment is so extensive that virtually all ecosystems on the planet are now affected by biological invasions. And, often, ecosystems are invaded by multiple co‐occurring non‐native species. Hence, it is important to understand the impacts these invasions are producing on biodiversity and ecosystem processes.Here, we present results of a 2‐year long field experiment where we tested the effects of co‐occurring invasive C4African grasses in a Cerrado area in central Brazil. We compared plant and arthropod communities, plant biomass, and soil nitrogen dynamics and soil chemical characteristics across five experimental treatments:Urochloa decumbensremoval;Melinis minutifloraremoval; bothU.decumbensandM.minutifloraremoval;U.decumbensandM.minutiflorainvaded plots; and uninvaded Cerrado. We hypothesized that selective removal of invasive grasses would have distinct effects on the native ecosystem structure and functioning. We expected that each invasive grass would produce a different type of impact on the native ecosystem and that their impacts would be synergistic when co‐occurring.Removal ofM.minutifloradoubled native plant diversity and biomass when compared to invaded plots, whereas removal ofU.decumbensdid not alter these parameters. Cerrado plots had four times more plant species than plots cleared of invasives. Removal of invasive grasses did not affect the species richness or community composition of soil epigeal fauna. Cerrado soils had lower fertility, organic matter content and pH than invaded soils. The effects were generally higher when both invasive grasses were removed, suggesting impacts were synergistic, butM.minutiflorahad greater effects on plants and soils thanU.decumbens. Both invasive species produced negative impacts, but a single species was the main driver. We also detected persistent effects of the invasive grass species on the ecosystem after 2 years of removal.We conclude that invasive species of the same functional group have similar types of effects in native ecosystems, but the magnitude of impact was largely dependent on invasive species biomass and cover. Where multiple invasive species are present, research and management of invaded ecosystems should tackle the interacting effects of co‐occurring invaders.

Trace element leaf accumulation in native trees from the remaining Semideciduous Atlantic Forest in Brazil

Remnants of Semideciduous Atlantic Forest surrounded by numerous industries, intense road traffic and agricultural lands in Southeast Brazil have been affected by trace elements. We implemented a passive biomonitoring with the three most abundant native tree species (Astronium graveolens, Croton floribundus and Piptadenia gonoacantha) to answer these questions: 1) which species has the greatest potential to accumulate trace elements?; 2) does the leaf accumulation level of trace elements vary between the edge and interior of the forest remnants, between dry and wet periods or due to the distance from the industrial area?; 3) which species, among the most abundant in the forest remnants, would better indicate the spatial variations in trace elements pollution and which elements would be the most relevant for such spatial discrimination? Leaf samples were collected during the dry and wet seasons, at the edge and interior of four forest remnants. Trace elements were determined using inductively coupled plasma mass spectrometry (ICP MS). Few edge effects were evidenced in the leaf concentrations in all species. Higher concentrations of most trace elements were measured during dry season. Although C. floribundus showed the most accumulating capacity, A. graveolens was the most appropriate species to discriminate spatial variations. The forest closer to the industrial area was distinguished from the others by Mn and Ni from oil burning, but the metal pollution from the industrial area did not interfere on the leaf concentrations in A. graveolens sampled in the urban and rural forests.

Development of a fish-based index for the assessment of the ecological status of Lake Balaton in the absence of present day reference condition

A fish-based index is proposed to indicate the ecological status of Lake Balaton, Hungary in accordance with the standard of the European Water Framework Directive (WFD). The Balaton fish index (BFI) synthetises information of 13 lake-specific fish metrics including gillnetting and electric fishing data of species richness of native assemblages, relative abundance, biomass and age structure of native key species, representation of non-native species and general health status. The main anthropogenic pressures considered were the degradation of littoral habitats, invasion of non-native fish species, eutrophication and fishing/angling including stocking. Ecological quality ratio (EQR) is assessed by relating actual fish assemblage metrics to the supposed undisturbed reference status of Lake Balaton reconstructed by expert judgement based on recent and historic information on the fish fauna and its changes. Values of BFI were consistent and indicated good ecological status of Lake Balaton in the period of 2005–2018. This study provides an example on how an EQR assessment methodology might be established in unique habitats with no possibilities for statistical evaluation of pressure-respond relationships and exact determination of the reference status.

First study of food webs in a large glacial river: the trophic role of invasive trout

Abstract The aim of this study was to determine the food webs structure of a large Patagonian river in two river sections (Upstream and Midstream) and to evaluate isotopic overlap between native and introduced species. We used stable isotope analyses of δ15N and δ13C and stomach content. The Upstream section had a more complex food webs structure with a greater richness of macroinvertebrates and fish species than Midstream. Upstream basal resources were dominated by filamentous algae. Lake Trout were found to have a higher trophic position than all other fish species in that area although, the most abundant fish species, were Rainbow Trout. Depending on the life stage, Rainbow Trout shifted from prey to competitor/predator. In the Midstream section, the base of the food webs was dominated by coarse particulate organic matter, and adult Rainbow Trout had the highest trophic level. Isotopic values changed among macroinvertebrates and fish for both areas. The two most abundant native and invasive species — Puyen and Rainbow Trout — showed an isotopic separation in Midstream but did not in Upstream areas. The presence of invasive fish that occupy top trophic levels can have a significant impact on native fish populations that have great ecological importance in the region.

Spread of Caulerpa cylindracea impacts: The colonization of Atlantic intertidal communities

The occurrence of the invasive macroalga Caulerpa cylindracea in the intertidal macroalgal communities of the Atlantic Ocean is evaluated here for the first time. The Canary Islands (28.36N, 16.07W) are the only distribution area known in the Atlantic for this species, and the presence of this species has currently only been reported in subtidal environments. The objectives of this study were to determine the variables influencing the species’ abundance in the intertidal zone, to delimit the colonized habitats and to assess its impact on invaded communities. The distance to the lower tidal limit, the sediments abundance and substrate type were the main variables related to the abundance of C. cylindracea. The results show that populations of C. cylindracea are restricted to certain habitats, and the existence of synergies between sedimentation and communities invaded by C. cylindracea, i.e., articulated coralline algae (Corallina caespitosa, Jania adhaerens) on platforms of the lower eulittoral and filamentous algae (Melanothamnus sphaerocarpa) in rocky pools of the middle and upper eulittoral. In these habitats the comparison of the communities impacted and not impacted by C. cylindracea (based on a data set of all species and functional groups) showed changes in the structure of the communities via replacement and a reduction in the native species abundance. However, in terms of the total macrophyte cover, species richness and diversity, no significant changes were detected.

Cultural tree preference and its influence on tree biodiversity in urban public spaces in Nanjing city, China

Worldwide, various tree species have been worshiped and praised because they are culturally significant in many nations. To address the questions of whether and how the preference for cultural trees influences the plant diversity in urban ecosystems characterized by human-created vegetation, we surveyed the plant composition in 239 designed landscape units (DLUs). We compared the tree diversity in the DLUs with that in all public green spaces, including both natural remnants and cultivated vegetation, in the built-up area of Nanjing city, China. We found that the species richness proportion of native species decreased from 58.01 % (192/311) in all public spaces to 39.71 % (81/204) in the DLUs, largely due to the low species resource utilization ratio of native noncultural species, which accounted for 75 % of all native tree species. In detail, 77.08 % (37/48 species) of native cultural species and all introduced cultural species (57/57) were recorded in the DLUs; however, only 30.56 % (44/144 species) of native noncultural and 80.49 % (66/82) of introduced noncultural species in all public spaces were recorded in the DLUs. For the native trees that were recorded in the DLUs, the total frequency, total abundance, median abundance and median frequency of native noncultural species were much lower than those of the native cultural tree species, although the species richness of noncultural trees (44 species) was higher than that of cultural trees (37 species). Furthermore, the relative richness and abundance per DLU of native noncultural tree species were significantly lower than those of native cultural tree species (p < 0.05). The results indicated that the preference for cultural trees contributed to the low diversity of native trees in the DLUs. We suggest that the difference between ‘national’ plants in the cultural sense and ‘native’ plants in terms of their natural distributions should be discerned, especially in regions with unified cultures. Promoting regional cultural diversity and accepting the value of ‘localized tree species’ can help us coordinate the cultural value and native biodiversity value of landscaping trees in urban greening.

Conservación en la ciudad: ¿Cómo influye la estructura del hábitat sobre la abundancia de especies de aves en una metrópoli latinoamericana?

A paucity of ecological research in urban ecosystems in Latin America limits the management of urban areas for biodiversity conservation. In addition, the majority of previous ecological studies in cities have focused on parks, ignoring most part of urban ecosystems. To provide robust scientific evidence for the management of urban areas for bird conservation, we investigate the influence of habitat variables on the abundance of native and exotic bird species in Santiago, Chile. During the reproductive season of 2017-2018, we surveyed birds and habitat variables at 455 points distributed throughout the city. We fit generalized linear models to evaluate the influence of habitat variables on individual bird species abundance. In 905 bird counts, we recorded 35 bird species (31 native and 4 exotic). The abundance of native birds (Zenaida auriculata, Elaenia albiceps, Troglodytes aedon, Turdus falcklandii, Zonotrichia capensis and Molothrus bonariensis) increased with woody vegetation cover. Points with greater shrub cover in the microhabitat exhibited a greater abundance of T. falcklandii, Z. capensis and E. albiceps. In contrast to the response of native birds, the abundance of exotic species (Columba livia and Passer domesticus) decreased with vegetation cover. Our results demonstrate the importance of woody vegetation to conserve native bird species in Santiago. Management of habitat that (1) avoids the loss of woody vegetation and (2) aims to increase trees and shrubs in urban areas with low vegetation cover will promote a greater abundance of native birds.

Oithona davisae: Naturalization in the Black Sea, Interannual and Seasonal Dynamics, and Effect on the Structure of the Planktonic Copepod Community

Naturalization of the invasive copepod Oithona davisae is examined based on long-term (2003–2014) routine observations of zooplankton in Sevastopol Bay (the Black Sea). The study analyzes inter-annual and seasonal variability of the species and their impact on the native copepod community. The invasion of O. davisae and their undoubted dominance in terms of abundance have been shown to alter the community structure, while not causing a decline in abundance of native species, except the earlier Black Sea invader Acartia tonsa. A significant decline in A. tonsa numbers over the phases of establishment and naturalization of O. davisae indicates competition between the species. It has been demonstrated that O. davisae have gained a competitive advantage over A. tonsa, which ensured the rapid spread of the former across the Black Sea, acclimatization to the new habitat, and successful competition over native species.

Ecophysiological traits of invasive alien Acacia cyclops compared to co‐occuring native species in Strandveld vegetation of the Cape Floristic Region

AbstractTree invasions of Mediterranean‐climate ecosystems pose a significant threat to both biodiversity and functioning, by excluding native species, altering soil nutrient status and depleting water resources. In order to attain greater relative biomass associated with successful invasion in these characteristically resource‐poor environments, invasive species must have novel traits that enable better acquisition (e.g. deep roots) or exploitation of different resources (e.g. N2 fixation) and/or more efficient use of available resources than native species. We compared the ecophysiological and morphological traits of three abundant native species to those of the invasive Australian tree species, Acacia cyclops. This species is widely invasive in the Mediterranean‐climate coastal vegetation of South Africa that includes the Strandveld vegetation type. A. cyclops had 30–50% greater foliar N concentrations (P &lt; 0.001) in comparison with the native species and lower foliar δ15N values that may indicate N2 fixation. Additionally, A. cyclops maintained higher photosynthetic rates over the dry summer season (ca. 15 μmol m−2 s−1) than the native species. These higher photosynthetic rates may result from sustained access to water due to deeper rooting abilities as indicated by the more negative δD values (P &lt; 0.001) of A. cyclops (−43‰) in comparison with the some native species (−29 to −37‰). Acacia cyclops did not, however, exhibit greater water use efficiencies or photosynthetic nitrogen use efficiencies (P &gt; 0.05) compared to native species. Invasiveness of A. cyclops into this resource‐limited Mediterranean‐climate ecosystem appears to be supported by greater resource acquisition, possibly partially through N2 fixation and greater rooting depth, rather than greater resource use efficiency or conservation.

The exotic species Senecio inaequidens pays the price for arriving late in temperate European grassland communities

The exotic South African ragwort (Senecio inaequidens DC.) rapidly spread across Central Europe after its introduction, but we still do not know to what extent its timing of arrival in a plant community (i.e. before or after natives) and the composition of the native community being invaded affect (1) its capacity to invade a European grassland, (2) the performance of the native species, and (3) the direction and strength of priority effects. In a greenhouse experiment, we manipulated the timing of arrival of the exotic species (Senecio) and the composition of the native community to test the influence of these factors on the productivity and N content of exotic and native species. We also investigated if the plant species origin (native or exotic) and the native community composition affected the benefit of arriving early and the cost of arriving late in the community. The establishment success of Senecio strongly depended on its timing of arrival in a grassland community. Senecio benefited more from arriving early than did the natives. The presence of legumes in the community did not favour invasion by Senecio. When natives arrived later than Senecio, however, priority effects were weaker when legumes were part of the native community. Our results showed that inhibitory priority effects created by natives can lower the risk of invasion by Senecio. An early arrival of this species at a site with low native species abundance is a scenario that could favour invasion.

Biotic and abiotic changes in subtropical seasonal deciduous forest associated with invasion by Hovenia dulcis Thunb. (Rhamnaceae)

Several tree species are found among the most well-know and impacting invasive plants that produce changes in richness, abundance and composition of native plant species as well as in environmental characteristics and ecosystem functioning. Hovenia dulcis Thunb. (Rhamnaceae) is a tree native to East Asia, invasive in southern South America in different forest ecosystems. This study was aimed at assessing the effects of H. dulcis on richness, abundance and composition of regenerating species in seasonal deciduous forest (SDF) by comparing invaded and non-invaded areas. The existence of correlations between abundance and richness of regenerating species with age and density of the invasive species, as well as with characteristics of canopy openness, litter thickness, slope, and soil moisture, was investigated in areas invaded by H. dulcis. Differences observed in canopy openness and litter tickness between areas invaded by H. dulcis and control areas suggest that H. dulcis is able to change environmental conditions on a local scale. Although no difference was observed in species richness between areas with and without H. dulcis, the differences registered in abundance and composition of regenerating species make the impact by H. dulcis on regeneration patterns in SDF fragments evident. The impacts caused by H. dulcis on SDF confirmed by this study highlight the need for its control in legally protected areas and their immediate surroundings, as well as for the adoption of public policies to promote the substitution of H. dulcis for locally native species.

The impact on plant communities of an invasive alien herb, Oenothera drummondii, varies along the beach-coastal dune gradient

One of the major threats to the diversity of coastal dunes is the expansion of invasive species, such as Oenothera drummondii subsp. drummondii (Onagraceae). In southwestern Spain, we studied the impact of this American invasive on community structure and composition along a beach-dune gradient (beach, foredune, and inland dunes). Differences in density, biomass, and the cover of O. drummondii, the cover of perennial and annuals/biennials species, and Shannon diversity index H’ and dominance λ were compared between invaded and uninvaded sectors. We observed that the intensity and impact of the invasion by O. drummondii varies along the beach-dune gradient. The abundance of the invasive plant increased inland and in consequence, its impact on species richness and composition was highest in inland dunes. Here, plant cover of O. drummondii represented 57.9% of total plant cover; species richness was reduced (with 3.3 fewer species per 2 × 2m plot), diversity H’ was lower while dominance λ was higher. At a broader scale, species richness in the invaded sector was 25% larger than in the uninvaded sector, because of the presence of ruderal species. Species composition also was modified after the invasion. The abundance of a keystone native species was largely reduced (Ammophila arenaria), and some natives became locally extinct (Otanthus maritimus, Eryngium maritimum, Medicago marina and Elymus farctus). We conclude that the high environmental severity of the beach and foredunes results in a reduced invasion and impact of O. drummondii, whereas the milder conditions of inland dunes promote its expansion. The shift in community structure and composition can have an increasing domino effect and thus monitoring, and mitigation actions are necessary. When doing so, the environmental heterogeneity of the beach-dune gradient should be considered, given its relevance in the invasion process.

Changes in a Fish Community in a Small River Related to the Appearance of the Invasive Topmouth Gudgeon Pseudorasbora parva (Temminck &amp; Schlegel, 1846)

In recent years, the topmouth gudgeon (Pseudorasbora parva) has been one of the most invasive fishes in Europe. Pseudorasbora parva can potentially affect ecosystems, fish communities, and particular fish species. Electrofishing was carried out over a five-year period at three study sites in the Ciemięga River (eastern Poland) before and after P. parva had been found in the river. Changes in the occurrence, abundance, and density of native fish species after the appearance of the invader were determined. Changes in the species’ richness were calculated, and correlations were estimated between the occurrence and density of P. parva and particular fish species and richness indices. The presence of P. parva has not affected the density of native species but coincides with a significant increase in estimated species richness and the total density of fish. There was a significant relationship between the presence of this invasive species and the fish community’s composition, though the PERMANOVA result was unclear with regards to site-specific effects. Moreover, tench and bleak were associated positively, whereas Eurasian perch and sunbleak were associated negatively with the occurrence of P. parva. Pseudorasbora parva density was highly correlated with Cyprinidae density (excluding P. parva), species richness, and the Margalef diversity index. Thise study has shown that the presence of predatory fish in the river (Salmo trutta L.) may reduce the numbers of invasive P. parva.