Expansion Of Exotic Species Research Articles

Success of an exotic snail Physella acuta in anthropogenically impacted Patagonian streams

The expansion of exotic species is one of the greatest threats to biodiversity and is a significant component of global change that occurs at increasing rates due to the removal of natural barriers and the global transport of species. The snail Physella acuta, has expanded into numerous aquatic environments worldwide, given a set of traits that allows the species to thrive in new and harsh environments. This study documents changes in the composition and structure of the malacofauna and examines the presence of established and expanding populations of P. acuta in the Esquel-Percy basin (Patagonia, Argentina), which has been altered by wastewater treatment plants discharges (WWTPs). The population density of P. acuta in the studied area increased from less than 15 ind/m2 in 2005 to 1800 ind/m2 in 2016-2017. This species was the dominant mollusk at the two post-urban sites, under poor environmental conditions. Understanding the introduction pathways of exotic species to prevent and control their establishment and spread is essential since biological invasions constitute a major threat to freshwater ecosystems.

How the interaction between human settlements and their sociocultural development favored the introduction and expansion of exotic species: The wild boar (Sus scrofa) in the sierras of Córdoba as a case study

En los últimos 300 años, la humanidad ha transformado gran parte de la superficie del planeta, cambiando drásticamente el paisaje. Uno de los factores indirectos de esta modificación es la introducción de manera voluntaria o accidental de especies exóticas invasoras (EEI). Estas producen severos impactos ecológicos y conflictos a las poblaciones humanas tales como destrucción de campos de cultivo, ataques a personas o animales domésticos y transmisión de enfermedades.
 En La provincia de Córdoba una de las EEI más relevante es el jabalí (Sus scrofa). El cual posee varios registros por parte de pobladores rurales y de zonas turísticas del departamento de Calamuchita, Provincia de Córdoba, que han manifestado su preocupación ante las autoridades correspondientes.
 El objetivo de este trabajo es presentar un análisis que reúne los resultados obtenidos en el marco de un diagnóstico ambiental orientado al manejo del jabalí donde interacciona la información bibliográfica del área de estudio, la especie problema y la percepción de la problemática por parte de los habitantes del paraje Villa Berna. Se describe cómo la ubicación geográfica, los procesos geomorfológicos junto con el clima modelaron el relieve y dotaron al área de características particulares para el desarrollo de la biodiversidad autóctona. Estas condiciones junto con la influencia de los primeros asentamientos humanos y los cambios culturales posteriores, sometieron al sistema a prácticas económicas y de uso que favorecieron la introducción de especies exóticas. A lo largo del tiempo estas modificaron el paisaje produciendo características apreciables por parte de los pobladores, pero al mismo tiempo contribuyeron a generar componentes de hábitat favorables para el establecimiento del jabalí.

Conservation status and recovery of Podocarpus angustifolius: a threatened tree of Cuba

AbstractThe recovery of species’ populations is one of the most challenging tasks in conservation, which is why species recovery is most likely to be successful if it involves as many stakeholders as possible. Podocarpus angustifolius, a tree endemic to Cuba, is potentially threatened by overexploitation, deforestation and expansion of exotic species. In December of 2017, in two protected areas containing the only known subpopulations of this species, we recorded the geographical position, height, and diameter at breast height of each individual, and calculated the extent of occurrence (EOO) and area of occupancy (AOO). We recorded a total of 575 individuals, 174 of which were adult (defined as ≥ 6 m height on the basis of the occurrence of reproductive structures), and most of which occurred in Lomas de Banao Ecological Reserve. The EOO and AOO were 125.8 km2 and 6.0 km2, respectively. All P. angustifolius that remain in the wild are within two protected areas, either in rainforest relicts or in coffee plantations. The size structure indicates a growing population. Based on our findings we recommend that P. angustifolius should be recategorized from Vulnerable (on the IUCN Red List) and Critically Endangered (on the national Red List) to Endangered, based on criterion D (small population size). We recommend the continued reinforcement of the population at Topes de Collantes Natural Protected Landscape and the continued engagement of local stakeholders for the long-term conservation of this species.

Freshwater mollusks and environmental assessment of Guandu River, Rio de Janeiro, Brazil

Abstract The Guandu River Basin is extremely important to state of Rio de Janeiro, as a water supplier of several municipalities. However, the malacological knowledge and environmental status is not well known to this basin. The aim of this paper is to present an inventory of freshwater mollusks, as well as an environmental assessment through a Rapid Assessment Protocol, of ten sampling sites at Guandu River basin in six municipalities (Piraí, Paracambi, Japeri, Seropédica, Queimados and Nova Iguaçu). Thirteen species of molusks were found, eight native (Pomacea maculata, Biomphalaria tenagophila, Gundlachia ticaga, Gundlachia radiata, Omalonyx matheroni, Diplodon ellipticus, Anodontites trapesialis and Eupera bahiensis) and five exotics (Melanoides tuberculata, Ferrissia fragilis, Physa acuta, Corbicula fluminea and Corbicula largillierti). The environmental analysis ranked most sites as “modified”. The expansion of exotic species with their associated negative effects, as well the gap in knowledge of native species calls attention to the need of future studies of biology and ecology of the species found.

Density dependent effects of an exotic marine macroalga on native community diversity

The introduction and expansion of exotic species have caused dramatic changes in marine macroalgal assemblages globally. Mechanisms underlying the impacts of macroalgal invaders have been identified for only a few species over small portions of their introduced distribution, and over short time scales. Invasive macroalgae can impact native species through competition for different resources such as light, space or nutrients, as well as modification of abiotic stress and disturbances. We used field experiments to assess the impacts of the invasive macroalga Sargassum muticum (Yendo) Fensholt (Phaeophyceae: Fucales) on native macroalgal communities of the west coast of Vancouver Island, Canada. We manipulated S. muticum in the low intertidal zone to test its effects via both light and space competition at different densities over two consecutive growing seasons. We found non-linear, density-dependent effects of S. muticum on native macroalgal richness. At high cover, S. muticum excludes native species and reduces richness through light competition by shading smaller, understory macroalgae. Light competition was more important than space competition. Native richness was greater when S. muticum cover was reduced to 20% than when it was eliminated entirely, suggesting some facilitation of native species at low cover. The morphology of native macroalgae (canopy, understory, basal) did not predict their response to S. muticum removal, suggesting substantial heterogeneity within functional groups in the types of interactions with S. muticum. The biomass produced by S. muticum failed to compensate for the loss of native biomass due to competition with the exotic, suggesting a negative effect of S. muticum on community productivity. Our results suggest the effects of S. muticum on native macroalgae are largely negative when the invader is abundant, but neutral or positive when the invader is rare.

Landscape disturbance causes small-scale functional homogenization, but limited taxonomic homogenization, in plant communities

Summary 1. Biotic homogenization (BH), a dominant process shaping the response of natural communities to human disturbance, reflects both the expansion of exotic species at large scales and other mechanisms that often operate at smaller scales. 2. Here, we examined the relationship between BH in plant communities and spatio-temporal landscape disturbance (habitat fragmentation and surrounding habitat conversion) at a local scale (1 km²), using data from a standardized monitoring programme in France. We quantified BH using both a spatial partitioning of taxonomic diversity and the average habitat specialization of communities, which informs on functional BH. 3. We observed a positive relationship between local taxonomic diversity and landscape fragmentation or instability. This increase in local taxonomic diversity was, however, paralleled by a decrease in average community specialization in more fragmented landscapes and in more unstable landscapes around forest sites. The decrease in average community specialization suggests that landscape disturbance causes functional BH, but there was limited evidence for concurrent taxonomic BH. 4. Synthesis. Our results show that landscape disturbance is partly responsible for functional BH at small scales via the extirpation of specialist species, with possible consequences for ecosystem functioning. However, this change in community composition is not systematically associated with taxonomic BH. This has direct relevance in designing biodiversity indicators: metrics incorporating species sensitivity to disturbance (such as species specialization to habitat) appear much more reliable than taxonomic diversity for documenting the response of communities to disturbance.

The relative importance of disturbance and exotic‐plant abundance in California coastal sage scrub

Many ecosystems of conservation concern require some level of disturbance to sustain their species composition and ecological function. However, inappropriate disturbance regimes could favor invasion or expansion of exotic species. In southern California coastal sage scrub (CSS) fire is a natural disturbance, but because of human influence, frequencies may now be unnaturally high. Other anthropogenic disturbances such as grazing also occur in reserve areas. Managers charged with imposing or tolerating fire or other disturbance within their reserves are concerned that habitat quality may be degraded by an increasing abundance of exotic plants. We used vegetation monitoring data from Camp Pendleton, California, USA, to assess the correlation between past disturbances (frequent fire, agriculture, or grazing and mechanical disturbances) and current exotic species abundance in CSS. We found that disturbance history was only modestly related to exotic abundance overall, but fire frequency showed the strongest association. We also examined whether cover and richness of various native plant life forms (woody species, perennial herbs, and annual herbs) were more strongly influenced by disturbance history or by exotic-plant abundance. Native plant responses varied among life forms, but woody species and annual herbs were generally more strongly and negatively associated with exotic abundance than with disturbance. Effective CSS conservation will require developing means to curb the negative impacts of exotic plants, which may abound with or without severe or recent disturbance. Additionally, more focus should be given to understory herbs showing sensitivity to invasion. Though understudied, native herbs comprise the greatest portion of plant diversity in CSS and are critical to preservation of the community as a whole.

Biomass dynamics of exotic Sargassum muticum and native Halidrys siliquosa in Limfjorden, Denmark—Implications of species replacements on turnover rates

The expansion of Sargassum muticum in the Danish estuary Limfjorden between 1984 and 1997 was followed by a decrease in abundance of native perennial macroalgae such as Halidrys siliquosa. Although commonly associated with the expansion of exotic species, it is unknown whether such structural changes affect ecosystem properties such as the production and turnover of organic matter and associated nutrients. We hypothesized that S. muticum possesses ‘ephemeral’ traits relative to the species it has replaced, potentially leading to faster and more variable turnover of organic matter. The biomass dynamics of S. muticum and H. siliquosa was therefore compared in order to assess the potential effects of the expansion of Sargassum. The biomass of Sargassum was highly variable among seasons while that of Halidrys remained almost constant over the year. Sargassum grew faster than Halidrys and other perennial algae and the annual productivity was therefore high (P/B = 12 year −1) and exceeded that of Halidrys (P/B = 5 year −1) and most probably also that of other perennial algae in the system. The major grazer on macroalgae in Limfjorden, the sea urchin Psammechinus miliaris, preferred Sargassum to Halidrys, but estimated losses due to grazing were negligible for both species and most of the production may therefore enter the detritus pool. Detritus from Sargassum decomposed faster and more completely than detritus from Halidrys and other slow-growing perennial macrophytes. High productivity and fast decomposition suggest that the increasing dominance of S. muticum have increased turnover of organic matter and associated nutrients in Limfjorden and we suggest that the ecological effects of the invasion to some extent resemble those imposed by increasing dominance of ephemeral algae following eutrophication.

Recent advances in the study of long‐distance dispersal of aquatic invertebrates via birds

ABSTRACTAlthough Darwin pioneered the study of long‐distance dispersal (LDD) of aquatic invertebrates via waterbirds, it remains in its infancy as a modern discipline. A handful of recent studies have quantified internal or external transport in the field, confirming that a variety of long‐distance migrants carry invertebrates both internally and externally. These studies show that variation in the morphology of vectors influences the frequency and size of propagules transported, and suggest that more invertebrate groups disperse via birds than was previously thought. Dispersal limitation has mainly been investigated for zooplankton in small experimental systems from which waterbirds were effectively excluded, and the extent of such limitation for invertebrate populations in wetlands interconnected by waterbird movements remains unclear. We expect that the spatial and temporal scales at which dispersal limitation constrains geographical ranges, species richness and genetic structure of invertebrates depends partly on the density of migratory birds using the area. Birds may have a major role in the expansion of exotic species. We propose several avenues for future research. There is a particular need for more quantitative studies of LDD by birds that will enable modellers to assess its role in maintaining invertebrate biodiversity among increasingly fragmented wetlands and in the face of climate change, as well as in the spread of invasive species.