Are invasive species the drivers of ecological change?

Invasive species are widely accepted as one of the leading direct causes of biodiversity loss. However, much of the evidence for this contention is based on simple correlations between exotic dominance and native species decline in degraded systems. Although appealing, direct causality is not the only possible interpretation. A plausible alternative hypothesis is that exotic dominance could be the indirect consequence of habitat modification driving native species loss. In a new paper, MacDougall and Turkington now provide the first direct test of whether invasive species are the drivers of community change, or merely 'passengers' along for the environmental ride.     

‘One Health' for the people of Hong Kong and the world

正Translational medicine refers to the conversion of scientific discoveries into improvements in medical practice.‘From bench to bedside and back’is a phrase that is often used to describe the two-way information flow in translational medicine.On one hand,scientists working at the bench make new discoveries that enable clinicians to revolutionize     

Are legislative frameworks in Canada and Ontario up to the task of addressing invasive alien species?

As a signatory to the international Convention on Biological Diversity (CBD), Canada has committed to prevent, control, and eradicate invasive alien species (IAS). Yet, despite developing policy on biodiversity and IAS, the federal government has been criticized for its inaction on biological invasions over the past decade. In Canada’s most populous province, Ontario, similar concerns have been raised about the provincial government’s approach to dealing with IAS. The ongoing criticism of government response suggests that an effective legislative framework to guide and coordinate action on IAS may be lacking in Canada. In this paper, we examined how well existing legislation at the federal and Ontario levels addresses IAS threats, and thus contributes to CBD commitments. We reviewed a total of 98 pieces of legislation, comprised of 55 federal acts, two federal omnibus bills, and 41 Ontario acts. Of these, 20 federal and 12 Ontario acts were found to cover IAS either intentionally or incidentally, but IAS was not the central focus of most legislation. No consistent terminology existed across legislation referring to IAS, further highlighting a lack of focus on the issue. Legislation on IAS was administered by several different ministries both federally and in Ontario, but coordination of action among agencies was not explicitly addressed in laws and regulations. While many acts provided broad powers of enforcement, most provisions were not directly linked to IAS prevention and management. In general, Canada’s legislative framework on IAS is fragmented, and this complicates the development of a coordinated approach to the problem.     

Are invasive species a major cause of extinctions?

The link between species invasions and the extinction of natives is widely accepted by scientists as well as conservationists, but available data supporting invasion as a cause of extinctions are, in many cases, anecdotal, speculative and based upon limited observation. We pose the question, are aliens generally responsible for widespread extinctions? Our goal is to prompt a more critical synthesis and evaluation of the available data, and to suggest ways to take a more scientific, evidence-based approach to understanding the impact of invasive species on extinctions. Greater clarity in our understanding of these patterns will help us to focus on the most effective ways to reduce or mitigate extinction threats from invasive species.     

Are the “100 of the world’s worst” invasive species also the costliest?

Biological Invasions - Biological invasions are increasing worldwide, damaging ecosystems and socioeconomic sectors. Two decades ago, the “100 of the world’s worst” invasive alien...     

Are long‐unburnt eucalypt forest patches important for the conservation of plant species diversity?

Question: Are long‐unburnt patches of eucalypt forest important for maintaining floristic diversity? Location: Eucalyptus forests of southeastern New South Wales, Australia. Methods: Data from 976 sites representing a range of fire history from three major vegetation formations – shrubby dry sclerophyll forest (SF), grassy dry SF and wet SF – were analysed. Generalized linear models were used to examine changes in species richness with increasing time since wildfire and analysis of similarities to examine changes in community composition. Chi‐squared tests were conducted to examine the distribution of individual species across four time since fire categories. Results: Plant species relationships to fire varied between the three formations. Shrubby dry SF supported lower plant species richness with increasing time since wildfire and this was associated with shifts in community composition. Grassy dry SF showed significant shifts in community composition and species richness in relation to time, with a peak in plant species richness 20–30 yr post fire (either prescribed fire or wildfire). Wet SF increased in species richness until 10–20 yr post wildfire then displayed a general declining trend. Species richness in each vegetation type was not related to the fire frequencies and fire intervals observed in this study. Conclusions: Long‐unburnt (30–50 yr post wildfire) forests appeared to play a minor role in the maintenance of plant species diversity in dry forest systems, although this was more significant in wet forests. Maintenance of a range of fire ages within each vegetation formation will assist in maintaining floristic diversity within regions.     

Are rare species useful species? Obstacles to the conservation of tree diversity in the dry forest zone agro‐ecosystems of Mesoamerica

Aim To test the potential to conserve rare dry forest tree and shrub species circa situm. Location Oaxaca, Mexico and Southern Honduras. Methods Local uses (timber, posts and firewood) of species were determined principally through semistructured interviews with 20 rural householders in each of four communities in Honduras and four in Oaxaca. Tree and shrub diversity inventories were carried out in a total of 227 forest patches and parcels of farmland in those eight communities. Species’ conservation priorities were determined using the star system of Hawthorne (1996) and IUCN listings. Results Despite a large number of useful species, remarkably few were also conservation priorities. Useful species were found to be substitutable as is illustrated by Bombacopsis quinata, Cordia alliodora, Guaiacum sanctum and G. coulteri. Conclusions In these areas, circa situm conservation is inhibited by the lack of species that are both rare and useful. Usefulness must be interpreted as a function of substitutability. Natural regeneration provides an abundance of diversity, farmers are unlikely to invest in the management of a species when suitable substitutes are freely available. The key to conserving rare species may be in maintaining or enhancing the value of the landscape elements in which they are found.     

What’s for dinner? Assessing the value of an edible invasive species and outreach actions to promote its consumption

Biological Invasions - The consumption of edible aquatic invasive species has gained popularity as a means to minimize their impacts while easing pressure on native resources and ecosystems....     

Preadapted for invasiveness: do species traits or their plastic response to shading differ between invasive and non‐invasive plant species in their native range?

Aim Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non‐invasive species differ in presumably adaptive plasticity. Location Europe (for native species); the rest of the world and North America in particular (for alien species). Methods We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non‐shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance. Results Invasive species had higher shoot–root ratios, tended to have longer leaf‐blades, and produced more biomass than congeneric non‐invasive species both under shaded and non‐shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade‐induced responses, which are widely considered to be adaptive, did not differ between invasive and non‐invasive species. Main conclusions We conclude that high biomass production across different light environments pre‐adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured.     

Molecular and quantitative trait variation across the native range of the invasive species Hypericum canariense: evidence for ancient patterns of colonization via pre‐adaptation?

To understand the success of invasive species, it is important to know whether colonization events are facilitated by adaptive evolution or are limited to sites where a species is pre-adapted to thrive. Studies of the ancient colonization patterns of an invader in its native range provide an opportunity to examine its natural history of adaptation and colonization. This study uses molecular (internal transcribed spacer sequence and amplified fragment length polymorphism) and common garden approaches to assess the ancient patterns of establishment and quantitative trait evolution in the invasive shrub Hypericum canariense. This species has an unusually small and discrete native range in the Canary Islands. Our data reveal two genetic varieties with divergent life histories and different colonization patterns across the islands. Although molecular divergence within each variety is large (pairwise FST from 0.18 to 0.32 between islands) and nearly as great as divergence between them, life-history traits show striking uniformity within varieties. The discrepancy between molecular and life-history trait divergence points to the action of stabilizing selection within varieties and the influence of pre-adaptation on patterns of colonization. The colonization history of H. canariense reflects how the relationship between selective environments in founding and source populations can dictate establishment by particular lineages and their subsequent evolutionary stasis or change.     

Is fungal species richness and composition related to the occurrence of the old‐growth associated wood‐decaying Amylocystis lapponica?

Amylocystis lapponica (Romell) Singer is a widely distributed wood‐decaying polypore fungus found throughout the Northern Hemisphere. Despite its huge distribution range it occurs rather patchily and seems narrowly associated with old‐growth forest stands. Notably, it has been used as an ‘indicator species’, believed to reflect the long‐term presence of dead wood, naturalness of forest stands, and indirectly, species richness and possibly composition. In this study we focused on the last issue – whether or not there is a link between the occurrence of A. lapponica and the species richness and composition of other wood‐decaying fungi. Selecting log characteristics and microclimate as similar as possible, we compared 12 logs with and 12 logs without visible fruit bodies of A. lapponica to examine: 1) if visible fruit bodies corresponded with molecular identification of the mycelia, 2) if fungal species richness and composition of the substrate were related to A. lapponica occurrence, and 3) if A. lapponica was restricted to certain parts of the log. Fungal species were recorded by inspecting visible fruit bodies and by culture isolation and ITS sequencing from wood disc samples. Laboratory and field identification of A. lapponica had 71% correspondence, and mycelia were identified in two logs without visible fruit bodies. Twice as many fungal species were detected using ITS sequencing compared to fruit body identification. Total species richness was similar between the two log categories, but number of species per log was slightly higher in A. lapponica logs. Antrodia serialis (Fr.) Donk, and possibly also Fomitopsis pinicola (Sw.:Fr.) P. Karst. and Phellinus nigrolimitatus (Romell) Bourdot & Galzin, occurred more frequently in A. lapponica logs. Mycelia of A. lapponica were restricted to less decayed parts of the wood in the centre of the middle part of the logs.     

Are high densities of fishes and shrimp associated with top‐down control of tropical benthic communities? A test in three Hong Kong streams

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How do invasive species travel to and through urban environments?

Globalisation has resulted in the movement of organisms outside their natural range, often with negative ecological and economic consequences. As cities are hubs of anthropogenic activities, with both highly transformed and disturbed environments, these areas are often the first point of entry for alien species. We compiled a global database of cities with more than one million inhabitants that data had on alien species occurrence. We then identified the most prominent pathways of introduction and vectors of spread of alien species in these cities. Most species were intentionally introduced to cities and were released or escaped from confinement. The majority of alien species then spread within cities through natural means (primarily unaided dispersal). Pathway prominence varied across the taxonomic groups of alien species: the most prominent pathway for plants and vertebrates was the escape pathway; for invertebrates the stowaway and contaminant pathways were most likely to facilitate introductions. For some organisms, pathway prominence varied with the geographical and climatic characteristics of the city. The characteristics of the cities also influenced the prominence of vectors of spread for alien species. Preventing the natural spread of alien species within cities, and into adjacent natural environments will be, at best, difficult. To prevent invasions, both the intentional and unintentional introduction of potentially harmful alien species to cities must be prevented. The pathways of introduction and vectors of spread identified here should be prioritised for management.     

Are the metabolomic responses to folivory of closely related plant species linked to macroevolutionary and plant–folivore coevolutionary processes?

The debate whether the coevolution of plants and insects or macroevolutionary processes (phylogeny) is the main driver determining the arsenal of molecular defensive compounds of plants remains unresolved. Attacks by herbivorous insects affect not only the composition of defensive compounds in plants but also the entire metabolome. Metabolomes are the final products of genotypes and are constrained by macroevolutionary processes, so closely related species should have similar metabolomic compositions and may respond in similar ways to attacks by folivores. We analyzed the elemental compositions and metabolomes of needles from three closely related Pinus species with distant coevolutionary histories with the caterpillar of the processionary moth respond similarly to its attack. All pines had different metabolomes and metabolic responses to herbivorous attack. The metabolomic variation among the species and the responses to folivory reflected their macroevolutionary relationships, with P. pinaster having the most divergent metabolome. The concentrations of terpenes were in the attacked trees supporting the hypothesis that herbivores avoid plant individuals with higher concentrations. Our results suggest that macroevolutionary history plays important roles in the metabolomic responses of these pine species to folivory, but plant–insect coevolution probably constrains those responses. Combinations of different evolutionary factors and trade‐offs are likely responsible for the different responses of each species to folivory, which is not necessarily exclusively linked to plant–insect coevolution.     

Are the mitochondrial cox1 and cob genes suitable markers for species of Dinophysis Ehrenberg?

The identification of Dinophysis species with similar morphology but different toxic (Diarrhetic Shellfish Poisoning, DSP) potential is a crucial task in harmful algae monitoring programmes. The taxonomic assignment of Dinophysis species using molecular markers is a difficult task due to extremely low interspecific variability within their nuclear ribosomal genes and intergenic regions. Mitochondrial cox1 gene has been proposed as a better specific marker for Dinophysis species based on its higher resolution for two morphologically related species (Dinophysis acuminata and Dinophysis ovum) of the “Dinophysis acuminata complex”. In this study, the potential of two mitochondrial genes (mt cox1 and cob) to discriminate among six Dinophysis species (field isolates and cultures) associated with DSP events was explored. Neither mt cox1 nor cob genes provided enough resolution for all species of Dinophysis. The cob gene showed very poor resolution and grouped all Dinophysis spp. in a common clade. In contrast, the cox1 phylogeny distinguished 5 clades in the Dinophysiales – the “acuminata complex”, the “caudata group”, “acuta + norvegica” and Phalacromaspp. However, within the “D. acuminata complex” mtcox1 is so far the unique marker that differentiates D. acuminata from other species: isolates of D. ovum and Dinophysis sacculus had almost identical sequences (only four mismatches), but they were well separated from D. acuminata. D. acuminata and Dinophysis skagii (considered a life cycle stage of the former) showed identical cox1 sequences. Probes towards this gene can be useful in Mediterranean and Western Iberia sites where the co-occurrence of close morphotypes of D. acuminata and D. sacculus pose a problem for monitoring analyses. This is the first report on cultures of D. sacculus and its phylogenetic relation with other species of the D. acuminata complex.     

Sonneratia apetala Buch.Ham in the mangrove ecosystems of China: An invasive species or restoration species?

By the end of 1990s when China initiated a 10-year mangrove reforestation project, the mangrove forest area had decreased from 250,000 to 15,000 ha. Over 80% of current Chinese mangroves are degraded secondary forests or plantations. As an initial restoration and reforestation effort, Sonneratia apetala, a native of India, Bengal and Sri Lanka, was introduced in 1985 to Dong Zhaigang Mangrove Nature Reserve in Hainan Island from Bengal. It has then been introduced into other places since 1991. However, the further use of the species is becoming increasingly controversial as there are emerging signs that it may become invasive in certain locations. A comprehensive evaluation of the species’ condition in China regarding benefits and risks is critically needed. Here, we map the introduction and dispersal routes and monitor the growth of S. apetala in China from 1985 to 2006. S. apetala grows fast and performs well in the introduced 2300 ha muddy beaches area. It greatly improves the soil fertility and shows a suite of suitable characteristics as a pioneer restoration species. Currently, no natural invasion of S. apetala has been observed in the northern mangrove area. However, invasion into natural forests does occur in southerly locations such as Shenzhen, Zhanjiang and Dong Zhaigang. In these locations, S. apetala exhibits invasive characteristics such as overgrowth and high spreading ability that evidently affects local mangrove ecosystem structure and function. While the species clearly offers some benefits at some locations where it cannot naturally invade, it appears harmful to other native mangrove species, posing a major practical problem to both ecologists and land managers. This situation will be similar to previously imported non-native and invasive intertidal wetland species, Spartina alterniflora (smooth cordgrass), with similar results and problems.     

Are reward polymorphisms subject to frequency‐ and density‐dependent selection? Evidence from a monoecious species pollinated by deceit

Abstract Most deceit‐pollinated species involve floral dimorphisms characterized by the presence of rewarding male flowers and nonrewarding female flowers. It has been proposed that this polymorphism establishes the conditions for the action of frequency dependent selection (FDS). The tendency of foraging animals to aggregate in areas of high resource density suggests that pollination efficiency and fruit production may be positively influenced by flower density (density dependent selection, DDS). In this paper we offer a graphical model describing the effects of FDS and DDS on a monoecious species pollinated by deceit. We test the FDS and DDS assumptions and the predictions of the model using field observations and experimental populations of Begonia gracilis in which population sex ratio and flower density were controlled. We found a marked effect of both FDS and DDS on pollinator visitation, fruit‐set, and on the probability of female flowers to setting fruits. We conclude that these two types of selection have had a strong influence on the evolution of deceit‐pollinated species.     

Can the functional response to prey predict invasiveness? A comparison of native fishes and alien poeciliids in Hong Kong

Biological invasion is globally pervasive and an increasing threat to biodiversity. We need to be able to predict the ecological impacts of alien species, in order to prioritize management of those expected to be most damaging. Comparisons of functional response (FR) between invaders and trophically similar natives has been proposed as useful for predicting invader impacts, as interaction intensity tends to be reflected in higher FRs. We undertook feeding trials comparing FRs of four invasive poeciliids (mosquitofish [Gambusia affinis], guppy [Poecilia reticulata], liberty molly [P. salvatoris] and swordtail [Xiphophorus hellerii]) in Hong Kong with three similar-sized native fishes (ricefish [Oryzias curvinotus: Adrianichthyidae]; predaceous chub [Parazacco spilurus] and half-banded barb [Puntius semifasciolatus: Cyprinidae]). We tested whether FRs correctly reflected known impacts of the mosquitofish and guppy locally, and used FRs to forecast potential impacts of the molly and swordtail. Overall, the swordtail and molly consumed more prey and had higher FRs than the other five fishes, owing to their shorter prey handling time and/or higher attack rate. Mosquitofish and guppy had similar FRs to native fishes. All fishes showed type-II FRs, and had some potential to destabilize prey populations. Such results predict that the molly and swordtail could have strong ecological effects in Hong Kong freshwaters. However, FR alone was not highly predictive of known impacts of mosquitofish and guppy. It is suggested a more holistic approach incorporating estimates of field abundance and parameterization of other niche dimensions of the invader will be needed.