Impact Of Exotic Species Research Articles

Anthropogenic activities explained the difference in exotic plants invasion between protected and non-protected areas at a northern subtropics biodiversity hotspot

Biological invasion poses a major threat to biodiversity and conservation efforts in protected areas. The Greater Shennongjia Area (GSA) is one of China's 16 key areas for biodiversity, as stated in the China National Biodiversity Conservation Strategy and Action Plan. However, the local authorities lack appropriate data on the extent and impact of exotic species in protected areas, as well as lack the capacity and motivation to properly plan for exotic species strategy and action plan to support both prevention, control as well as management of exotic plants in their jurisdiction. In addition, while most previous studies have focused on exotic species in protected areas, little effort has been devoted to specifying which environmental factors contribute to the difference between protected and non-protected areas. Here, we explored the current distribution pattern of the richness and abundance of exotic species in relation to environmental variables within the GSA. In total, we found 84 exotic plant species, of which 41 exotic species within the protected areas, in 64 genera and 27 families, predominately from Asteraceae, Fabaceae, and Poaceae. The generalized linear mixed models (GLMMs) revealed that the protection status and the distance to human settlements were the most important predictors of exotic plant richness and abundance in the GSA. Our results showed that the average exotic plant richness and coverage in the protected areas were 22% and 31% lower than outside the protected areas, respectively. Such differences were probably the result of anthropogenic activities (e.g., proximity to human settlements and the proportion of cropland). Although protected areas provide an important barrier against plant invasions, invasion may be a tricky issue for protected area management in the future. The Alliance of Protected areas in Western Hubei and Eastern Chongqing will need to further consider stringent control and management strategies for the entry of exotic species into protected areas to effectively maintain the continuity and integrity of the GSA's biodiversity and ecosystems. Our results provided guidance and support to enhance the capacity of scientific and effective management and sustainable development of the Shennongjia World Natural Heritage Site and other protected areas.

How exotic Sonneratia species affect the spatiotemporal dynamics of mangroves in Shenzhen Bay, China: A remote sensing perspective

Mangroves are essential forest communities in tropical and subtropical coastal zones, providing unique ecological functions and significant social and economic value. Accurate and efficient monitoring of mangroves is crucial for their protection and management. The impact of exotic species on native species is still debated, especially for mangroves, the spatiotemporal dynamics of introduced species and native mangrove species need to be closely monitored. This study aimed to investigate how exotic mangrove species affects the spatial dynamics of mangroves in Shenzhen Bay, China. Yearly Landsat images from 2000 to 2011 and Chinese high spatial resolution images during 2012–2022 were obtained and the pixel-based and multiscale object-based methods were used to obtain mangrove distribution. The results showed that: (1) Overall, mangroves in the study area increased from 281.51 ha to 526.43 ha from 2000 to 2022, with different spatiotemporal patterns in Shenzhen (+5.14%) and Hong Kong (+2.38%); (2) rapid spread of Sonneratia species was one of the main contributions to the growth of mangrove hotspots, and growth hotspots were mainly concentrated in the estuary delta; and (3) Sonneratia mangrove species was dominant in interspecific competition, not only invading the habitat of local mangroves, but also preventing the expansion of native mangrove growth. The results provide a reference for fine-scale and accurate mangrove mapping with high spatial and temporal resolutions, and highlight the need to pay more attentions to the spread and invasive potential of exotic mangrove species in the study area, as well as cooperation in adjacent reserves.

Climate‐driven impacts of exotic species on marine ecosystems

AbstractAimTemperature is fundamental to the physiological and ecological performance of marine organisms, but its role in modulating the magnitude of ecological impacts by exotic species remains unresolved. Here, we examine the relationship between thermal regimes in the range of origin of marine exotic species and sites of measured impact, after human‐induced introduction. We compare this relationship with the magnitude of impact exerted by exotic species on native ecosystems.LocationGlobal.Time period1977–2017 (meta‐analysis).Major taxa studiedMarine exotic species.MethodsQuantitative impacts of exotic species in marine ecosystems were obtained from a global database. The native range of origin of exotic species was used to estimate the realized thermal niche for each species and compared with the latitude and climatic conditions in recipient sites of recorded impact of exotic species. The difference in median temperatures between recipient sites and the thermal range of origin (i.e., thermal midpoint anomaly) was compared with the magnitude of effect sizes by exotic species on native species, communities and ecosystems.ResultsRecorded impacts occurred predominantly within the thermal niche of origin of exotic species, albeit with a tendency toward higher latitudes and slightly cooler conditions. The severity of impacts by exotic species on abundance of native taxa displayed a hump‐shaped relationship with temperature. Peak impacts were recorded in recipient sites that were 2.2°C cooler than the thermal midpoint of the range of origin of exotic species, and impacts decreased in magnitude toward higher and lower thermal anomalies.Main conclusionsOur findings highlight how temperature and climatic context influence ecological impacts by exotic species in marine ecosystems and the implications for existing and novel species interactions under climate change.

Landscape-level determinants of the spread and impact of invasive grasses in protected areas

Anthropogenic disturbances play an important role in invasibility, and the traits of exotic species act as mediators of invasion success. The impact of exotic species can be evaluated through an association with invasion potential. The magnitude and potential severity of exotic species impacts can aid in decision making regarding the best conservation, restoration, management and control actions. In this sense, our objectives were to (1) evaluate the potential invasion risk of naturalized graminoid species in the Cerrado biome using risk analysis; (2) understand the magnitude of the impact of these species on protected areas by analysing the relationships between invasiveness, invasion potential and proximity to strictly protected areas, as well as to the biome as a whole; and (3) identify the drivers of spread contributing to species richness and abundance in the Cerrado. Our results showed that naturalized graminoid species in the Cerrado biome present invasion risks and potential impacts varying from medium to high. Additionally, these landscapes were vulnerable due to their proximity to protected areas, which act as filters against these species and against anthropogenic agents (human population and road density) that may increase the richness and population sizes of these plants. Based on our results, we recommend developing and prioritizing management and control strategies in strictly protected areas and in their surrounding areas to avoid the dispersal and establishment of aggressive species (African grasses) in their interiors, homogenization risks and the consequent loss of native biodiversity.

Consequences of removal of exotic species (eucalyptus) on carbon and nitrogen cycles in the soil-plant system in a secondary tropical Atlantic forest in Brazil with a dual-isotope approach.

The impact of exotic species on heterogeneous native tropical forest requires the understanding on which temporal and spatial scales these processes take place. Functional tracers such as carbon (δ13C) and nitrogen (δ15N) isotopic composition in the soil-plant system might help track the alterations induced by the exotic species. Thus, we assess the effects from the removal of the exotic species eucalyptus (Corymbia cytriodora) in an Atlantic forest Reserve, and eucalyptus removal on the alteration of the nutrient dynamics (carbon and nitrogen). The hypotheses were: (1) the eucalyptus permanence time altered δ13C and δ15N in leaves, soils and litter fractions (leaves, wood, flowers + fruits, and rest); and (2) eucalyptus removal furthered decomposition process of the soil organic matter. Hence, we determined the soil granulometry, the δ13C and δ15N in leaves, in the superficial soil layer, and litter in three sites: a secondary forest in the Atlantic forest, and other two sites where eucalyptus had been removed in different times: 12 and 3 months ago (M12 and M3, respectively). Litter samples presented intermediate δ13C and δ15N values in comparison with leaves and soil. In the M3, the greater δ13C values in both litter rest fraction and soil indicate the presence, cycling and soil incorporation of C, coming from the C4 photosynthesis of grassy species (Poaceae). In the secondary forest, the soil δ15N values were twice higher, compared with the eucalyptus removal sites, revealing the negative influence from these exotic species upon the ecosystem N dynamics. In the M12, the leaves presented higher δ13C mean value and lower δ15N values, compared with those from the other sites. The difference of δ13C values in the litter fractions regarding the soil led to a greater fractioning of 13C in all sites, except the flower + fruit fractions in the secondary forest, and the rest fraction in the M3 site. We conclude that the permanence of this exotic species and the eucalyptus removal have altered the C and N isotopic and elemental compositions in the soil-plant system. Our results suggest there was organic matter decomposition in all litter fractions and in all sites. However, a greater organic matter decomposition process was observed in the M3 soil, possibly because of a more intense recent input of vegetal material, as well as the presence of grassy, easily-decomposing herbaceous species, only in this site. Therefore, the dual-isotope approach generated a more integrated picture of the impact on the ecosystem after removing eucalyptus in this secondary Atlantic forest, and could be regarded as an option for future eucalyptus removal studies.

Analysis of Pond Fisheries in Climate Change Scenario in the Haor Region of Bangladesh

Aims: To identify the potential environmental impacts and influence of climate change on the pond fishery in haor region and impact of exotic species on the indigenous species through aquaculture.
 Study Design: An investigation on the influence of the pond fishery approach to determine whether the approach is successful with respect to the climate change impacts in the haor area.
 Place and Duration of Study: The study sites are located in five haor districts in Bangladesh for a period of one-year (May 2018 – April 2019) covering HILIP working area.
 Methodology: The study includes collection and analyses of both quantitative and qualitative data. For quantitative study, 92 sample households in 58 unions of 28 upazilas (sub-districts) in five project districts were randomly selected. Fish catch data, including information on species composition, production and sale were collected from perennial and seasonal ponds. The qualitative primary data obtained through in-depth interviews, key informants interviews and focus group discussions have been used in this paper.
 Results: Fish production was found to be better at perennial ponds, but not significantly more than that in the seasonal ponds. However, biodiversity was found to be better in seasonal ponds and greater than that in the perennial ponds. The findings clearly support the observation that pond fish culture is an attractive activity for haor people, especially those who are able to run both perennial and seasonal ponds and manage minimum feeding requirements, maintain those and market the outputs effectively. The present study fills gaps in existing knowledge of fish pond culture diffusion in haor region of Bangladesh.
 Conclusions: Pond fishery appears to perform better so, aquaculture production would mitigate some lost capture fisheries in the haor area of Bangladesh. Existing cultural practices could support experimentation and learning under future initiatives in the haor area. Pond fishery in the haor area mainly has an income-generating feature and less probability of being affected by climate change impacts. However, future initiatives should emphasize on culturing fish, which has the potential of balancing the haor ecosystem.
 Aims: To identify the potential environmental impacts and influence of climate change on the pond fishery in haor region and impact of exotic species on the indigenous species through aquaculture.
 Study Design: An investigation on the influence of the pond fishery approach to determine whether the approach is successful with respect to the climate change impacts in the haor area.
 Place and Duration of Study: The study sites are located in five haor districts in Bangladesh for a period of one-year (May 2018 – April 2019) covering HILIP working area.
 Methodology: The study includes collection and analyses of both quantitative and qualitative data. For quantitative study, 92 sample households in 58 unions of 28 upazilas (sub-districts) in five project districts were randomly selected. Fish catch data, including information on species composition, production and sale were collected from perennial and seasonal ponds. The qualitative primary data obtained through in-depth interviews, key informants interviews and focus group discussions have been used in this paper.
 Results: Fish production was found to be better at perennial ponds, but not significantly more than that in the seasonal ponds. However, biodiversity was found to be better in seasonal ponds and greater than that in the perennial ponds. The findings clearly support the observation that pond fish culture is an attractive activity for haor people, especially those who are able to run both perennial and seasonal ponds and manage minimum feeding requirements, maintain those and market the outputs effectively. The present study fills gaps in existing knowledge of fish pond culture diffusion in haor region of Bangladesh.
 Conclusions: Pond fishery appears to perform better so, aquaculture production would mitigate some lost capture fisheries in the haor area of Bangladesh. Existing cultural practices could support experimentation and learning under future initiatives in the haor area. Pond fishery in the haor area mainly has an income-generating feature and less probability of being affected by climate change impacts. However, future initiatives should emphasize on culturing fish, which has the potential of balancing the haor ecosystem.

Habitat restoration opportunities, climatic niche contraction, and conservation biogeography in California's San Joaquin Desert.

A recent global trend toward retirement of farmland presents opportunities to reclaim habitat for threatened and endangered species. We examine habitat restoration opportunities in one of the world’s most converted landscapes, California’s San Joaquin Desert (SJD). Despite the presence of 35 threatened and endangered species, agricultural expansion continues to drive habitat loss in the SJD, even as marginal farmland is retired. Over the next decades a combination of factors, including salinization, climate change, and historical groundwater overdraft, are projected to lead to the retirement of more than 2,000 km2 of farmland in the SJD. To promote strategic habitat protection and restoration, we conducted a quantitative assessment of habitat loss and fragmentation, habitat suitability, climatic niche stability, climate change impacts, habitat protection, and reintroduction opportunities for an umbrella species of the SJD, the endangered blunt-nosed leopard lizard (Gambelia sila). We use our suitability models, in conjunction with modern and historical land use maps, to estimate the historical and modern rate of habitat loss to development. The estimated amount of habitat lost since the species became protected under endangered species law in 1967 is greater than the total amount of habitat currently protected through public ownership and conservation easement. We document climatic niche contraction and associated range contraction away from the more mesic margins of the species’ historical distribution, driven by the anthropogenic introduction of exotic grasses and forbs. The impact of exotic species on G. sila range dynamics appears to be still unfolding. Finally, we use NASA fallowed area maps to identify 610 km2 of fallowed or retired agricultural land with high potential to again serve as habitat. We discuss conservation strategies in light of the potential for habitat restoration and multiple drivers of ongoing and historical habitat loss.

Invasive alien plant species, fragmentation and scale effects on urban forest community composition in Durban, South Africa

BackgroundUrban forests are under increased pressure from invasion by exotic (alien) species. The vegetation present in the matrix of urban sites is a rich source of alien invasive propagules, which increases the risk of alien invasion in forests within an urban space, leading to a decline in indigenous species. Therefore, determining the distribution patterns of native and exotic species as influenced by environmental factors can assist in quantifying the impact of exotic species at broad scales based on responses on a finer scale. Quantifying the effects of multiple environmental factors on the distribution patterns of both indigenous and alien species in the ecosystem may help in prescribing suitable management efforts.MethodsFifteen forest patches were sampled in the eThekwini (Durban) Municipality and data collected from 74 100-m2 plots with different degrees of invasion. Indigenous and alien species of trees, shrubs and climbers occurring in ten and more plots were considered for analysis and the CANOCO 5.1 package was used to run various constrained ordination analyses. Variation partitioning analysis was used to assess the impact of environmental variables at different spatial scales, namely the plot and patch scales.ResultsCanopy gaps are the major controlling factor for invasive alien plants (IAPs) occurrence at fine scale. At patch level, residential and industry areas outside the boundaries (buffer area) of forest patches have a high influence on the distribution of IAPs. Communities dominated by the invasive Chromolaena odorata (L.) R.M. King are most common on the lowland coastal forests while communities dominated by either Litsea glutinosa (Lour.) C.B.Rob. or Cardiospermum grandiflorum Sw. can prevail in both lowland coastal and scarp forests.ConclusionsCanopy gaps in lowland forests can facilitate the transition of native forests to novel communities containing a variety of alien plant species. Communities of shrub, climber and tree IAPs occur in lowland coastal forests while climber and tree IAPs dominate the high-elevation scarp forests. The resilience shown by some native species to the tree, shrub and climber IAPs by remaining when IAPs establish makes these species very suitable for restoration projects. Forest patches surrounded by a high incidence of residential and industrial areas in the buffer matrix are likely to have a high diversity of IAPs. Larger patch size and high connectivity to nearby native forests are key in reducing invasion by IAPs.

Textbook of Limnology

Textbook of Limnology

Biodiversity investigation on forest communities in lantau, HongKong

Biodiversity investigation on forest community structures were conducted under different gradients of human disturbance in Lantau, Hong Kong. The results show that species diversity of forest community decreases along the disturbance gradient of different intensity, diversity of forest community of natural growing vegetation (hill) diversity of light disturbed (Ngong Ping) diversity of heavy disturbed (Tung Chung). The species compositions and dominance also vary with the intensity of human-induced disturbance. Exotic species are introduced into the communities purposedly by human activities, and therefore build up new community structures. The ecolgical impact of exotic species should be investigated from several respects in more details.

Meta-analysis reveals asymmetric reduction in the genetic diversity of introduced populations of exotic insects

Factors promoting the invasion success of introduced populations have been receiving increased attention in studies of biological invasions. Previous reports have indicated that successful invasions may be attributable to reduced genetic diversity in the invasive species. However, there is large variation in the magnitude and direction of the impact of exotic species that have remained unexplained. Here, we present a structured meta-analysis of papers investigating the genetic diversity of native and introduced populations of exotic insects using nuclear microsatellites and mitochondrial DNA sequences. The results indicate that invasion by exotic insects had an overall reducing effect on the genetic diversity of the invading population, with nonzero effect sizes for the number of alleles (NA), observed heterozygosity (Ho), expected heterozygosity (He) and nucleotide diversity (Nd). However, when analyzing different orders (e.g., Lepidoptera, Hemiptera), the effect sizes of NA, Ho and Nd in Lepidoptera were found to bracket zero, as did the effect size of He in Hemiptera. These results suggest an asymmetric reduction in the genetic diversity of introduced populations of exotic insects, indicating diverse mechanisms underlying their successful invasion.

The role of exotic ladybeetles in the decline of native ladybeetle populations: evidence from long-term monitoring

Ladybeetles (Coleoptera: Coccinellidae) are ubiquitous predators which play an important role in suppressing pest insects. In North America, the coccinellid community is increasingly dominated by exotic species, and the abundance of some native species has declined dramatically since the 1980s. Several hypotheses have been proposed to describe the mechanism of invasion coupled with native species declines, e.g. vacant niche exploitation, intraguild predation, competitive exploitation and habitat compression. We analyze a 24-year dataset of coccinellid community structure in southwestern Michigan to elucidate the most likely mechanism(s) of native coccinellid decline and implications for their conservation. Correlation analyses indicated that impact of exotic species on native coccinellids varies with their degree of interaction. Although several native species were observed to be in numerical decline, only Adalia bipunctata and Coleomegilla maculata had declines that were statistically significant. The magnitude of decline in these two species varied with the degree of dietary overlap with invaders, thus their decline is most likely driven by competitive exploitation. Habitat use patterns by some native species (A. bipunctata and Coccinella trifasciata) changed during years when the exotic Harmonia axyridis reached high numbers, lending support to the habitat compression hypothesis, where native species survive in ancestral (i.e. natural or semi-natural) habitats when invaders dominate cultivated habitats. Coccinellid communities occurring in semi-natural forested habitats were unique in both composition and variability from those occurring in cultivated habitats. Such semi-natural habitats can act as refuges for native coccinellids and may play a role in maintaining the functional resilience of coccinellid communities.

Allelopathy: a tool for weed management in forest restoration

Forest restoration uses active management to re-establish natural forest habitat after disturbance. However, competition from early successional species, often aggressively invasive exotic plant species, can inhibit tree establishment and forest regeneration. Ideally, restoration ecologists can plant native tree species that not only establish and grow rapidly, but also suppress exotic competitors. Allelopathy may be a key mechanism by which some native trees could reduce the abundance and impact of exotic species. Allelopathy is a recognized tool for weed management in agriculture and agroforestry, but few studies have considered how allelopathic interactions may aid restoration. Here we introduce the “Homeland Security” hypothesis, which posits that some naive exotic species may be particularly sensitive to allelochemicals produced by native species, providing a tool to reduce the growth and impacts of invasive exotic species on reforestation. This article explores how exploiting allelopathy in native species could improve restoration success and the re-establishment of natural successional dynamics. We review the evidence for allelopathy in agroforestry systems, and consider its relevance for reforestation. We then illustrate the potential for this approach with a case study of tropical forest restoration in Panama. C4 grasses heavily invade deforested areas in the Panama Canal watershed, especially Saccharum spontaneum L. We measured the effect of leaf litter from 17 potential restoration tree species on the growth of invasive C4 grasses. We found that leaf litter from legume trees had a greater inhibitory effect on performance of S. spontaneum than did litter from non-legume trees. However, allelopathic effects varied greatly among species within tree functional groups. Further evaluation of intra- and inter-specific interactions will help to improve our selection of restoration species.

Digenean species diversity in teleost fishes from the Gulf of Gabes, Tunisia (Western Mediterranean)

This study is the first attempt to survey the diversity of fish digeneans in the Gulf of Gabes (southern coast of Tunisia). A total of 779 fishes belonging to 32 species were sampled. 53 species of Digenea belonging to 15 families were recorded. Among these species, 24 are reported for the first time from the coast of Tunisia. We report one new host record, Lecithochirium sp. from Sardinella aurita. The Hemiuridae is the dominant family. A host-parasite list is presented with the information on the prevalence, abundance and mean intensity of each species collected. The diversity of Digenea is compared with other localities in the Mediterranean Sea and the northern east of Tunisia. The Gulf of Gabes shows the lowest diversity linked to the anthropogenic activities and impact of exotic species. The use of Digenea as indicators of the state of the ecosystem is discussed.

Effects of an invasive grass on the demography of the Caribbean cactus Harrisia portoricensis: Implications for cacti conservation

The impact of exotic species around the world is among the primary threats to the conservation and management of rare and endangered species. In this work we asked whether or not the presence of the African grass Megathyrsus maximus on Mona Island was associated with negative impacts on the demography of the endangered Caribbean cactus Harrisia portoricensis. To address this question we performed field observations where we compared demographic data collected at un-manipulated areas invaded by Megathyrsus with un-manipulated areas non-invaded by this exotic grass. Additionally, demographic data were also collected in areas in which we removed the exotic grass biomass using two alternative treatments: complete and partial grass removal. Results demonstrated that the presence of Megathyrsus has negative effects on demographic parameters of Harrisia at various stages throughout its life cycle. In general, the survival, growth, and reproduction of Harrisia plants were depressed under the presence of Megathyrsus. Growth and survival of seedlings and juveniles of Harrisia were more impacted by the presence of Megathyrsus than adult performance and seedling recruitment only occurred in areas with grass absence. Our combined results suggest that modifications of the micro-environment by the presence of Megathyrsus may add an additional level of vulnerability to the persistence of Harrisia, and as such this factor must be considered when designing conservation strategies for this endangered species. This study highlights the need for a greater emphasis on understanding the interactions between invasive grass species and native cacti, and the importance of such information in designing conservation strategies for cacti species elsewhere.

Long-term changes in fish community and the impact of exotic fish, between the Nakdong River and Upo Wetlands

To evaluate fish community changes and the impact of exotic fish between the Nakdong River (lotic) and Upo Wetlands (lentic) using long-term ecological monitoring results, we conducted seasonal surveys of the fish community from 2005 to 2010. A fixed shore net (mesh <TEX>$15{\times}15\;mm$</TEX>), cast net (<TEX>$7{\times}7\;mm$</TEX>), and scoop-net (<TEX>$5{\times}5\;mm$</TEX>) were used to collect fish specimens. Changes in the fish community were not significantly different in the Nakdong River and Upo Wetlands, respectively (<TEX>$R_s$</TEX> > 0.322, N = 44, P < 0.05). Changes in the fish community between the Nakdong River and Upo Wetlands were identified as significant according to the results of cluster analysis. The relative abundance of exotic species increased steadily during the study period, and reached 34.2% and 89.7% in the Nakdong River and Upo Wetlands, respectively, in 2010. The bluegill (Lepomis macrochirus) was used to evaluate the level of health according to prevalence around all study sites. The length-weight relationship for bluegill in the Upo Wetlands was shown to have the highest values, via the formula (W = <TEX>$aL^b$</TEX>), with an average of 3.26 for the 'b' variable. According to the results of this study, lentic and lotic systems differed significantly; exotic species had an impact on both the lentic and lotic systems, but the impact of exotic species in lentic systems was greater than in the lotic systems. Additionally, the exotic species tested herein (bluegill) adapted well in the lentic system.

How are the North American Great Lakes coping with multiple stressors? Comparison of Lakes Ontario and Superior

The North American Great Lakes continue to be impacted by multiple stressors including: eutrophication and phosphorus abatement, invasive species, synergistic food web disruptions, degradation of fisheries and fish habitat, and climate change. The Great Lakes are an enormous global aquatic resource, spanning 245 000 km and containing 20% of the world’s supply of fresh water. Stressors affecting the health of the lakes have implications for the entire planet. In previous studies, we have considered the impact of exotic species on the complete food web of Lake Erie (Munawar et al. 2005) and the lower trophic levels of Lake Ontario (Munawar et al. 2006). Since these studies were published, more invasive species have been observed in the Great Lakes, including Hemimysis anomala in the summer of 2007 (J. Gerlofsma, Fisheries and Oceans Canada, pers. comm.). Lake Superior, perhaps due to its size (12 100 km) and relatively sparse population density along its shores, has not been subject to the same eutrophication pressure as Lake Ontario (1640 km; Vollenweider et al. 1974); however, both have been subject to ecosystemic disruption as a result of invasive species. In this study, we consider long-term changes in species composition at the top (fishes) and at the bottom (phytoplankton) of the food web of Lakes Ontario and Superior and consider the long term implications in terms for ecosystem health and resilience. We discuss how these synergistic changes reverberate through the food web to provide insights into the impact of multiple stressors for large lakes management.

Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms.

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Introduction of exotic fish into a Mediterranean lake over a 90-year period

The impact of exotic species is a neglected, worldwide ecological problem, particularly for freshwater fish. Examples of historical changes in southern Europe due to fish introduction are rare. Lake Banyoles, the second largest lake of the Iberian Peninsula, has suffered a long history of fish introductions. We reviewed the historical changes in the fish assemblage and assessed its current state in a field study. Before 1910, only five or six native species were present. During this century up to 12 exotic species were introduced, leading to the apparent loss of two native species (three-spined stickleback Gasterosteus aculeatus and, possibly introduced several centuries ago, tench Tinca tinca) and the decline of three others (eel Anguilla anguilla, chub Leuciscus cephalus, and barbel Barbus meridionalis). The current fish assemblage is dominated by exotic species, particularly the largemouth bass (Micropterus salmoides) and the pumpkinseed sunfish (Lepomis gibbosus) in the littoral zone and roach (Rutilus rutilus) in the pelagic zone. The only native species still common nowadays is the freshwater blenny (Salaria (= Blennius)fluviatilis).

Importance of population data in forest management planning

Recent shifts in emphasis to preservation of biological diversity and establishment of large nature reserves have resulted in downgrading of the perceived importance of data at the population level. These shifts in emphasis, while laudable, should not result in loss of focus on the fundamental importance of population information. Suitable habitat, although a prime necessity, is not sufficient for wildlife preservation. Species may not occupy otherwise suitable habitat because of internal (predation, interspecific competition, disease) or external (adverse climate, exploitation, disturbance, impact of exotic species, pollution and toxicants) factors. Historical impacts may persist for many years, and may require active restoration. Forest management plans must consider population data on a metapopulation scale. Data for common species can be at the reconnaissance level whereas for threatened or sensitive species they need to be more detailed. To evaluate sustainability, population data must be integrated with forest stand data in projection models to predict habitat-population mosaics at various times in the future. These models must be developed and improved over time in an adaptive management approach.