Impact Of Invaders Research Articles

Distinctiveness magnifies the impact of biological invaders in aquatic ecosystems

AbstractThere exist few empirical rules for the effects of introduced species, reflecting the context‐dependent nature of biological invasions. A promising approach toward developing generalizations is to explore hypotheses that incorporate characteristics of both the invader and the recipient system. We present the first general test of the hypothesis that an invader's impact is determined by the system's evolutionary experience with similar species. Through a meta‐analysis, we compared the taxonomic distinctiveness of high‐ and low‐impact invaders in several aquatic systems. We find that high‐impact invaders (i.e. those that displace native species) are more likely to belong to genera not already present in the system.

Predicting the impacts of an introduced species from its invasion history: an empirical approach applied to zebra mussel invasions

SUMMARY1. Quantitative models of impact are lacking for the vast majority of known invasive species, particularly in aquatic ecosystems. Consequently, managers lack predictive tools to help them prioritise invasion threats and decide where they can most effectively allocate limited resources. Predictive tools would also enhance the accuracy of water quality assessments, so that impacts caused by an invader are not erroneously attributed to other anthropogenic stressors.2. The invasion history of a species is a valuable guide for predicting the consequences of its introduction into a new environment. Regression analysis of data from multiple invaded sites can generate empirical models of impact, as is shown here for the zebra mussel Dreissena polymorpha. Dreissena's impacts on benthic invertebrate abundance and diversity follow predictable patterns that are robust across a range of habitat types and geographic regions. Similar empirical models could be developed for other invaders with a documented invasion history.3. Because an invader's impact is correlated with its abundance, a surrogate model may be generated (when impact data are unavailable) by relating the invader's abundance to environmental variables. Such a model could help anticipate which habitats will be most affected by invasion. Lack of precision should not be a deterrent to developing predictive models where none exist. Crude predictions can be refined as additional data become available. Empirical modelling is a highly informative and inexpensive, but underused, approach in the management of aquatic invasive species.

Impacts of freshwater invaders at different levels of ecological organisation, with emphasis on salmonids and ecosystem consequences

SUMMARY1. Invaders can influence freshwater systems at the individual, population, community and ecosystem levels. Some of these impacts may be subtle or not easily predicted but they may be critical to understanding more obvious changes. Despite this, studies of impacts of freshwater invaders at several levels of ecological organisation are rare. Most commonly reported are changes in the distribution or abundance of populations after invasion, whereas documentation of impacts on ecosystem functioning, such as energy and nutrient flux, is rare.2. Unlike most invaders, salmonids have been studied at multiple ecological levels. These fish can cause trophic cascades that result in increased algal biomass and production and are responsible for changes to energy and nutrient flux in both streams and lakes. The mechanisms behind these changes are different in the two systems and only become evident when information at the individual and population levels are considered. In streams, salmonids can alter invertebrate behaviour that suppresses grazing of periphyton. In lakes, salmonid feeding behaviour can stimulate phytoplankton by shunting nutrients from the littoral to the pelagic zone.3. Simultaneous study at several ecological levels should yield a fuller understanding of the mechanisms underlying impacts of invading animals and plants, providing a sounder basis for predicting the impacts of freshwater invasive species. Species traits of the invaders that may be associated with particularly profound impacts include: a method of resource acquisition formerly lacking in the invaded system, a broad feeding niche that links previously unlinked ecosystem compartments, a feeding relationship with negative consequences for native strong interactors, physiological traits that enhance resource transformation and lead to high biomass, and behavioural or demographic traits that provide high resistance or resilience in the face of natural disturbances.

Biological invaders in a greenhouse world: will elevated CO2fuel plant invasions?

Climate change and biological invasions, two of the hottest topics in ecology, both have ecological and societal implications, but they have developed on separate and parallel paths. Both are likely to have global impacts, yet researchers seldom explicitly consider their interaction. We argue that changes in atmospheric concentrations of carbon dioxide (CO2) and subsequent climate change may facilitate biological invasions, both directly and indirectly, and that our research agenda to date has left us poorly prepared to predict the consequences for communities and ecosystems. Forecasting the impact of biological invaders or elevated CO2 is a challenge for ecologists, and it is therefore prudent and timely to investigate the greater challenge, namely predicting the combined effects of invaders and elevated CO2 on native ecological systems.

Potential invasion of China by exotic insect pests associated with tree seeds

A total of 39 insect species, mostly seed chalcids in the genus Megastigmus (Hymenoptera), but also midges (Diptera), are listed as potential seed-borne invaders of Chinese conifers. Although the number of native seed insects per conifer genus does not differ between China and other biogeographical regions, there are significantly fewer seed insects associated with each conifer genus in China than potential invaders. The eventual success of the invaders is likely to depend on the presence of native Chinese conifers that are congeneric with the original host, or on the presence of the original host as an exotic. When a substantial entomofauna is already associated with cones, competition for seed resources may limit the potential impact of invaders because seed insects are usually the last organisms to colonize the cone. A survey of 26 fir species, both native and introduced to Europe, showed that overall seed infestation by five species of exotic chalcids is negatively correlated to levels of damage by native insects, except on the original hosts of the chalcids. Similar patterns are hypothesized for native firs, spruces, Douglas firs, and larches in China. Uncontrolled importation of seeds and nuts of broad-leaved trees could also facilitate the introduction of seed chalcids, seed bruchids, tortricid moths and nut weevils into China. Only six species of seed chalcids are present in China, out of the 72 known to attack broad-leaved seeds over the world.

Dispersal and emerging ecological impacts of Ponto-Caspian species in the Laurentian Great Lakes

We describe, explain, and "predict" dispersal and ecosystem impacts of six Ponto-Caspian endemic species that recently invaded the Great Lakes via ballast water. The zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena bugensis, continue to colonize hard and soft substrates of the Great Lakes and are changing ecosystem function through mechanisms of ecosystem engineering (increased water clarity and reef building), fouling native mussels, high particle filtration rate with selective rejection of colonial cyanobacteria in pseudofeces, alteration of nutrient ratios, and facilitation of the rapid spread of their Ponto-Caspian associates, the benthic amphipod Echinogammarus ischnus and the round goby, Neogobius melanostomus, which feeds on zebra mussels. The tubenose goby,Proterorhinus marmoratus, which does not feed on zebra mussels, has not spread rapidly. Impacts of these benthic invaders vary with site: in some shallow areas, habitat changes and the Dreissena [Formula: see text] round goby [Formula: see text] piscivore food chain have improved conditions for certain native game fishes and waterfowl; in offshore waters, Dreissena is competing for settling algae with the native amphipod Diporeia spp., which are disappearing to the detriment of the native deep-water fish community. The predatory cladoceran Cercopagis pengoi may compete with small fishes for zooplankton and increase food-chain length.

Potential Impact of Filter-feeding Invaders on Temperate Inland Freshwater Environments

Since the 1990s, biological invasions have captured the attention of the scientific community as an important element of global change and a major threat to biodiversity. The inland waters of South America provide two examples of biological invasions. This review examines bivalve invasions in South America, summarizes the research results for two species, the Asian clam (Corbicula fluminea) and the golden mussel (Limnoperna fortunei), and suggests further studies. The rapid expansion of invasive bivalves into these environments involves significant changes. Until now, C. fluminea, the Asian clam, did not produce generalized macrofouling in the Neotropical region, as is common in the Holarctic region. However, the first specific cases of macrofouling by C. fluminea were recently detected in heat interchangers of power stations in Brazil. On the other hand, L. fortunei is provoking new economic impacts in South American freshwaters through macrofouling. Before the invasion by the golden mussel, macrofouling was recorded only in the marine and estuarine environments of the Neotropical region. The impact caused by invasive bivalves in this region is not only economic, however. Rapid changes in the benthic community, favoring the presence of Oligochaeta and Hirudinea, as well as the displacement of native species of mollusks, are among the problems related to the presence of the golden mussel. Another issue is the settlement of golden mussels on native bivalves. This bivalve is now a new element in the diet of some native fish species, being the main food item in some cases.

Facilitative interactions among aquatic invaders: is an "invasional meltdown" occurring in the Great Lakes?

A widely cited hypothesis in ecology is that species-rich communities are less vulnerable to invasion than species-poor ones, owing to competition for limiting resources (the "biotic resistance" model). However, evidence for biotic resistance in aquatic ecosystems is equivocal. Contrary to the view that communities become more resistant to invasion as they accumulate species, the rate of invasion has increased over the past century in areas that have received frequent shipping traffic. Furthermore, introduced species may facilitate, rather than compete with, one another. A review of invasions in the Great Lakes indicates that direct positive (mutualistic and commensal) interactions among introduced species are more common than purely negative (competitive and amensal) interactions. In addition, many exploitative (e.g., predator–prey) interactions appear to be strongly asymmetric in benefiting one invading species at a negligible cost to another. These observations, combined with an increasing invasion rate in the Great Lakes, tentatively support the Simberloff – Von Holle "invasional meltdown" model. The model posits that ecosystems become more easily invaded as the cumulative number of species introductions increases, and that facilitative interactions can exacerbate the impact of invaders. It provides a theoretical argument for substantially reducing the rate of species introductions to the Great Lakes.

Facilitative interactions among aquatic invaders: is an "invasional meltdown" occurring in the Great Lakes?

A widely cited hypothesis in ecology is that species-rich communities are less vulnerable to invasion than species-poor ones, owing to competition for limiting resources (the "biotic resistance" model). However, evidence for biotic resistance in aquatic ecosystems is equivocal. Contrary to the view that communities become more resistant to invasion as they accumulate species, the rate of invasion has increased over the past century in areas that have received frequent shipping traffic. Furthermore, introduced species may facilitate, rather than compete with, one another. A review of invasions in the Great Lakes indicates that direct positive (mutualistic and commensal) interactions among introduced species are more common than purely negative (competitive and amensal) interactions. In addition, many exploitative (e.g., predator–prey) interactions appear to be strongly asymmetric in benefiting one invading species at a negligible cost to another. These observations, combined with an increasing invasion rate in the Great Lakes, tentatively support the Simberloff – Von Holle "invasional meltdown" model. The model posits that ecosystems become more easily invaded as the cumulative number of species introductions increases, and that facilitative interactions can exacerbate the impact of invaders. It provides a theoretical argument for substantially reducing the rate of species introductions to the Great Lakes.

Measuring and mapping endemism and species richness: a new methodological approach and its application on the flora of Africa

The adjustment of an existing index which combines endemism and species richness (Williams 1993) is proposed so that it requires markedly less data on the study area and its flora or fauna than was necessary with the conventional calculation method. Using this adjusted method, the resulting scores are calculated and mapped for the seed plant flora of the 20 African regions as delineated by White (1983). We argue that this index, here referred to as a measure of ‘endemism richness’, can be regarded as the specific contribution of an area to global biodiversity. We demonstrate that at a given sampling scale it shows a linear relation with area. We further demonstrate that, within certain limits, this linearity can also be observed in many cases when sampling scales vary which makes the comparison of differently sized geographic units easier than is the case for species richness. The two most important advantages over species richness are that this index is more suitable to measure both the conservation value of an area and the negative impact of invaders. The latter quality is due to the fact that it yields scores which usually do not rise substantially but can rather be expected to drop in many cases when an area is invaded by alien species.

Predicting the identity and impact of future biological invaders: a priority for aquatic resource management

The identification and risk assessment of potential biological invaders would provide valuable criteria for the allocation of resources toward the detection and control of invasion threats. Yet, freshwater biologists have made few attempts at predicting potential invaders, apparently because such efforts are perceived to be costly and futile. We describe some simple, low-cost empirical approaches that would facilitate prediction and demonstrate their use in identifying high-risk species from an important donor region: the Ponto-Caspian (Black, Caspian, and Azov seas) basin. This region is the source of several freshwater organisms already invading North America, including the zebra mussel (Dreissena polymorpha), quagga mussel (Dreissena bugensis), ruffe (Gymnocephalus cernuus), and round goby (Neogobius melanostomus). Based on a thorough literature review, we identify 17 additional Ponto-Caspian animals that have recent invasion histories and are likely to be transported overseas in ship ballast water; moreover, their broad salinity tolerance could allow them to survive an incomplete ballast-water exchange. These results suggest that, unless current vectors are more effectively controlled, the Great Lakes - St. Lawrence River system and other North American inland waterways will continue to receive and be impacted by invasive Eurasian species.

Mohammed and Charlemagne: A Revision

IT is not my purpose to challenge the core of Pirenne's conclusions. Mahomet et Charlemagne, and Dopsch's Grundlagen however much one may disagree on point of details and on range of implications have helped historians to realize that their traditional division of ages was wrong: Germanic invasions did not mark the beginning of a new era; Arab invasions did.' This is undoubtedly true in so far as history of culture is concerned. The great push of the Germans had been preceded by long interpenetration, and was followed by thorough fusion of the newcomers into the mass of the conquered people. The followers of Alaric, Theodoric and Clovis neither wanted to nor could break the moral unity of the Western Empire, and its connections with the East. They only gave a political expression to those particularisms which were already cracking the surface of the old Roman edifice without breaking its deep foundations. The Latin language and Latin literature, however much their already advanced barbarization may have been precipitated by the impact of rude invaders, remained as the common background of European culture. The greatest achievements of the mediaeval 'Germanized' world, the Church and the Empire, were either a heritage or an imitation of Roman institutions. As soon as Europe was again able to produce something great and original, Roman peoples again took the lead. Niebelungennot and the wooden buildings of the Germans were forgotten for Romanesque and French ('Gothic') architecture, and for the Italian Divina Commedia. On the other hand, wherever the Arabs stepped on Romanic soil (except in Spain and in Sicily, outposts which they held for too short a time), they eradicated the classic roots forever. A slow but sweeping revolution won over the masses in Syria, Egypt, and North Africa to a new civilization, whose language and religion (these typical expressions of a people's soul) were the language and the religion of the conquerors. There was no Arab Romanesque architecture, and no Arab Imperium.2 Even where there was imitation, an original blend was formed out of three cultures Graeco-Roman, Persian, and Semitic.