Exotic Populations Research Articles

Propagule pressure as a driver of establishment success in deliberately introduced exotic species: fact or artefact?

A central paradigm in invasion biology is that more releases of higher numbers of individuals increase the likelihood that an exotic population successfully establishes and persists. Recently, however, it has been suggested that, in cases where the data are sourced from historical records of purposefully released species, the direction of causality is reversed, and that initial success leads to higher numbers being released. Here, we explore the implications of this alternative hypothesis, and derive six a priori predictions from it. We test these predictions using data on Acclimatization Society introductions of passerine bird species to New Zealand, which have previously been used to support both hypotheses for the direction of causality. All our predictions are falsified. This study reaffirms that the conventional paradigm in invasion biology is indeed the correct one for New Zealand passerine bird introductions, for which numbers released determine establishment success. Our predictions are not restricted to this fauna, however, and we keenly anticipate their application to other suitable datasets.

A comparative study of the reproductive fitness and pathogenicity of a population of Radopholus similis from Davao, Philippines, on banana (Musa spp.)

The in vitro reproductive fitness on carrot discs and the in vivo pathogenicity on selected FHIA (Fundación Hondureña de Investigaciónes Agrícola) banana hybrids of a population of Radopholus similis isolated from banana in Davao, Philippines, were investigated at the Bureau of Plant Industry, Davao City, Philippines. It was shown that on carrot discs following inoculation with 25 females, the Davao population had the highest population density and multiplication rate compared with two other R. similis populations from the Philippines (Los Baños and Quezon) and two exotic populations of R. similis (from Uganda and Indonesia). According to the Gompertz model, the Davao population also had a short lag phase and a high maximum specific growth. Following inoculation with one single female, the Davao population also had the highest multiplication rate and the highest proportion of juveniles and females compared with the other four populations included in the experiments. Nine weeks after inoculation with 1000 vermiforms, the R. similis population from Davao had reduced the plant height of the FHIA hybrids included in the experiment (FHIA-3, FHIA-4, FHIA-5, FHIA-18 and FHIA-23) on average by 37%, plant girth by 5.3–40.9%, shoot weight by 20.1–65.8% and root weight by 31.7–69.7%, indicating the high pathogenicity of this population on banana. FHIA-4 was tolerant to R. similis infection.

Intrinsic time dependence in the diversity–invasibility relationship

Contrasting patterns in the diversity-invasibility relationship have intrigued ecologists for many years, and are now known as the "invasion paradox." Experiments usually detect negative relationships, while field surveys find them to be positive. It is widely believed that the paradox is driven by differences in spatial scale, but this is challenged by field surveys that find positive relationships at all spatial scales. If factors that determine invasion dynamics change during the invasion process, the paradox may be partially driven by differences in temporal scale. Here we used simulation (cellular automata) models to explore the generality of temporal change in the diversity-invasibility relationship. The probability of invaders colonizing an area was inversely related to the density of natives, creating a negative native-exotic correlation when invaders first arrived. Over time, native and exotic populations were both shaped by the same post-introduction processes (disturbance, dispersal, and recolonization), shifting their correlation to positive. The rate of temporal change in the diversity-invasibility relationship was mainly dependent upon the fecundity of invaders. Greater fecundity meant that invaders spread through the landscape faster and were subject to post-introduction processes sooner. We propose a unified conceptual model where the diversity-invasiblity relationship is a function of both spatial and temporal scales.

Developing the next generation of diverse and healthier maize cultivars tolerant to climate changes

Maize (Zea mays L.) average yields per hectare have significantly increased in the past 80 years. However, the variability of these yields across years has also significantly increased in the past 40 years making newer and genetically narrow-based hybrids, on average, less stable and more susceptible to climate changes. The objective of this research was to develop new sources of short-season inbred lines carrying unique alleles to grow maize hybrids under challenging environments. The North Dakota State University (NDSU) maize germplasm enhancement program has recently developed 10 new and unique exotic short-season populations partially derived from Argentina, Brazil, Chile, Cuba, Mexico, Saint Croix, and the USA. These germplasm sources were created recombining top early-generation NDSU EarlyGEM lines that were extensively tested in hybrid trials for general combining ability of several traits. Results have shown that germplasm carrying unique alleles can break environmental margins for maize production. Unfortunately, maize breeding programs tend to be located in ideal crop production areas instead of exploiting marginal environments for the development of more stable products. The NDSU EarlyGEM program is a successful example of tropical and late-temperate maize germplasm adaptation into short-season environments in order to increase the genetic diversity on farms. However, public sector applied maize breeding programs continue to disappear across the USA and abroad because of changes in research emphasis. Long-term germplasm adaptation and improvement programs carrying unique alleles will be essential in the development of the next generation of healthier cultivars tolerant to climate changes.

Enemy damage of exotic plant species is similar to that of natives and increases with productivity

Summary In their colonized ranges, exotic plants may be released from some of the herbivores or pathogens of their home ranges but these can be replaced by novel enemies. It is of basic and practical interest to understand which characteristics of invaded communities control accumulation of the new pests. Key questions are whether enemy load on exotic species is smaller than on native competitors as suggested by the enemy release hypothesis (ERH) and whether this difference is most pronounced in resource‐rich habitats as predicted by the resource–enemy release hypothesis (R‐ERH). In 72 populations of 12 exotic invasive species, we scored all visible above‐ground damage morphotypes caused by herbivores and fungal pathogens. In addition, we quantified levels of leaf herbivory and fruit damage. We then assessed whether variation in damage diversity and levels was explained by habitat fertility, by relatedness between exotic species and the native community or rather by native species diversity. In a second part of the study, we also tested the ERH and the R‐ERH by comparing damage of plants in 28 pairs of co‐occurring native and exotic populations, representing nine congeneric pairs of native and exotic species. In the first part of the study, diversity of damage morphotypes and damage levels of exotic populations were greater in resource‐rich habitats. Co‐occurrence of closely related, native species in the community significantly increased the probability of fruit damage. Herbivory on exotics was less likely in communities with high phylogenetic diversity. In the second part of the study, exotic and native congeneric populations incurred similar damage diversity and levels, irrespective of whether they co‐occurred in nutrient‐poor or nutrient‐rich habitats. Synthesis. We identified habitat productivity as a major community factor affecting accumulation of enemy damage by exotic populations. Similar damage levels in exotic and native congeneric populations, even in species pairs from fertile habitats, suggest that the enemy release hypothesis or the R‐ERH cannot always explain the invasiveness of introduced species.

Dietary flexibility despite behavioral stereotypy contributes to successful invasion of the pike killifish, Belonesox belizanus, in Florida, USA

It is well known that the establishment of invasive-fish populations depends on the ability of introduced individuals to adapt to environmental conditions in the invaded ecosystem, including the ability to feed on diverse, locally available prey resources. Furthermore, the current invasive-biology paradigm postulates that having a generalist-food habit is key to the successful invasion of a novel community by exotic species. This study investigated how the invasive pike killifish, Belonesox belizanus, has succeeded in establishing exotic populations in Florida, USA despite having a feeding apparatus that is characteristic of a specialized piscivore (i.e., fish-eating fish). Pike killifish collected from their point of introduction in south Florida were (1) filmed using high speed video while feeding on live fishand shrimp-prey to determine whether prey type affects prey-capture kinematics and then (2) subjected to a prey-selectivity experiment to determine which prey type (live fish or shrimp) the invasive pike killifish eats when both prey are available in the environment. Results indicated that (1) prey-capture kinematics were not affected by prey type, indicating that consumption of fish and shrimp prey was accomplished using a stereotypical feeding repertoire, and (2) pike killifish consumed fish and shrimp when both prey were available in the feeding environment. It is concluded that the invasive pike killifish has the ability to feed on alternative, locally available prey using its piscivorous feeding functional morphology and prey-capture kinematics. This study contributes a new perspective to our understanding of the mechanisms that underlie success of exotic fishes in invaded communities. That is, the ability of a functional-morphological specialist to utilize stereotypical prey-capture kinematics (= behavior) in consuming alternative, locally available prey types (= dietary flexibility) contributes to the establishment of invasive populations. It is evident that these functional specialists are not constrained in their diet, thus, enabling them dietary flexibility and enhancing their invasive potential.

When invasive exotic populations are threatened with extinction

An important question that arises is what to do when an invasive exotic is a species threatened with extinction within its original distribution and there are few cases in the world illustrating this situation. These species potentially compete with local species for resources and may displace native species or, may in some cases, weaken the gene pool of the native species. The simple eradication of the invasive population could reduce the species′ gene pool, and the eradication process might affect local sympatric species. We recommend a program including identification of areas within the natural range where the species is extinct, removal of the causes of extinction in those areas, then gradual removal of the species from its introduced range and release in the relocation areas following proper guidelines for reintroduction of species.

Riparian Forest Restoration: Conflicting Goals, Trade-Offs, and Measures of Success

Restoration projects can have varying goals, depending on the specific focus, rationale, and aims for restoration. When restoration projects use project-specific goals to define activities and gauge success without considering broader ecological context, determination of project implications and success can be confounding. We used case studies from the Middle Rio Grande (MRG), southwest USA, to demonstrate how restoration outcomes can rank inconsistently when narrowly-based goals are used. Resource managers have chosen MRG for restoration due to impacts to the natural flood regime, reduced native tree recruitment, and establishment of non-native plants. We show restoration “success” ranks differently based upon three goals: increasing biodiversity, increasing specific ecosystem functions, or restoring native communities. We monitored 12 restored and control sites for seven years. Treatments ranked higher in reducing exotic woody populations, and increasing proportions of native plants and groundwater salvage, but generally worse at removing fuels, and increasing species and habitat structural diversity. Managers cannot rely on the term “restoration” to sufficiently describe a project’s aim. Specific desired outcomes must be defined and monitored. Long-term planning should include flexibility to incorporate provisions for adaptive management to refine treatments to avoid unintended ecological consequences.

March of the Green Iguana

Green Iguanas (Iguana iguana L. 1758) have been introduced outside their native range largely through the pet trade. In many places, exotic populations have invaded and many have become established. Of special concern is the Greater Caribbean Basin, where several exotic populations of Green Iguanas have had a negative impact, and may threaten the conservation of several native species, including possible native and distinct forms of I. iguana in the Lesser Antilles, and the endangered Lesser Antilles Iguana (I. delicatissima Laurenti 1768). We assessed the risk of spread and invasion by Green Iguanas in the Greater Caribbean Basin using the maximum entropy niche-modeling algorithm (MaxEnt) to predict the potential distribution of this reptile. We used a total of 187 location points that represented occurrences from both the native and the invasive range, coupled with environmental data as predictor variables. Our model had average training and test AUC values of 0.90 and 0.87 respectively, indicating a high predictive ability. The model predicts suitable conditions for I. iguana in south and central Florida (mainly along the coast), and in regions of all the islands in the Caribbean. Given the known negative impact of Green Iguanas and their dispersal capabilities, governments in the Greater Caribbean Basin should manage non-native populations to prevent further spread, and revise and enact laws that allow management agencies to respond quickly in the case of new Green Iguana incursions.

Low genetic and morphological differentiation between an introduced population of dunnocks in New Zealand and an ancestral population in England

Species invasions and exotic species introductions can be considered as ‘unplanned experiments’, which help us to understand the evolution of organisms. In this study, we investigated whether an exotic bird species, the dunnock (Prunella modularis), has diverged genetically and morphologically from its native source population (Cambridge, England) after introduction into a new environment (Dunedin, South Island of New Zealand; exotic population). We used a set of microsatellite markers and three morphological traits to quantify the divergence between these two populations. We quantified neutral genotypic differentiation between the populations, and also used an individual-based Bayesian clustering method to assess genetic structure. We compared morphological divergence using univariate and principal components analyses. We found that individuals from the Dunedin population are genetically distinct from the Cambridge population, but levels of differentiation are very low. Overall within-population levels of genetic diversity are low compared to other bird species, and effective population sizes are small; indicating that the native population probably has a historically low level of genetic diversity, and that the introduced population retained most of that diversity after its introduction into New Zealand. We found little evidence of morphological divergence, and the evolutionary rate of change in these traits is below the average for other taxa. Our study adds support to the growing literature showing that invasive species maintain most of their initial genetic diversity after multiple founder events, even when population size is severely reduced. Moreover, our morphological data indicate slow evolutionary rates in species introduced to similar habitats.

Quantifying how fine-grained environmental heterogeneity and genetic variation affect demography in an annual plant population

The ability of plant species to colonize new habitats and persist in changing environments depends on their ability to respond plastically to environmental variation and on the presence of genetic variation, thus allowing adaptation to new conditions. For invasive species in particular, the relationship between phenotypic trait expression, demography, and the quantitative genetic variation that is available to respond to selection are likely to be important determinants of the successful establishment and persistence of populations. However, the magnitude and sources of individual demographic variation in exotic plant populations remain poorly understood. How important is plasticity versus adaptability in populations of invasive species? Among environmental factors, is temperature, soil nutrients, or competition most influential, and at what scales and life stages do they affect the plants? To investigate these questions we planted seeds of the exotic annual plant Erodium brachycarpum into typical pasture habitat in a spatially nested design. Seeds were drawn from 30 inbred lines to enable quantification of genetic effects. Despite a positive population growth rate, a few plants (0.1 %) produced >50 % of the seeds, suggesting a low effective population size. Emergence and early growth varied by genotype, but as in previous studies on native plants, environmental effects greatly exceeded genetic effects, and survival was unrelated to genotype. Environmental influences shifted from microscale soil compaction and litter depth at emergence through to larger-scale soil nutrient gradients during growth and to competition during later survival and seed production. Temperature had no effect. Most demographic rates were positively correlated, but emergence was negatively correlated with other rates.

Commentary: Geographic patterns of establishment success among exotic bird populations

ISSN 1948-6596 the capacity to deal with numerous statistical models, ranges of initial conditions, different cli- mate projections, and many more effects. Person- ally, I never liked the idea of automatically proc- essing hundreds of species without careful consid- eration of predictor sets with regard to a specific species. However, I will now use BIOMOD even for single species projections, simply because the general framework makes ensemble forecasting so easy for us. And if one chooses to use only a few carefully chosen predictors, then BIOMOD can successfully process many species simultane- ously. news and update Thuiller, W., Lafourcade, B., Engler, R., & Araujo, M.B. (2009) BIOMOD – a platform for ensemble fore- casting of species distributions. Ecography, 32, Niklaus E. Zimmermann Swiss Federal Research Institute WSL e-mail: niklaus.zimmermann@wsl.ch http://www.wsl.ch/staff/ niklaus.zimmermann/ Edited by Thiago F. Rangel commentary Geographic patterns of establishment success among exotic bird populations Human-mediated species invasions are a major component of global environmental change and there remains a pressing need to understand the mechanisms by which a species becomes invasive. With this in mind, the key stage in the invasion pathway (sensu Williamson and Brown 1986) is species establishment. It is at this stage, when a species has been transported outside its native geographic range and released in a novel recipient environment, that a species either fails or suc- ceeds to establish an exotic population. However, while much attention has been focussed on what species-level traits determine establishment suc- cess in exotic bird populations (Blackburn et al. 2009), relatively less research has concerned the role of location-level variables. The most obvious reason for this relative ‘lack of research’ is that in most cases, compara- tive analyses have consisted of large datasets of good quality records of different species to single specific locations (e.g. Hawaii, Moulton et al. 2001; Australia, Duncan et al. 2001; New Zealand, Duncan et al. 2006) rather than repeated intro- ductions of the same species to multiple locations. Bird species are conspicuous elements of the envi- ronment and their distribution and abundance have attracted considerable research attention in the discipline of biogeography (e.g. Gaston and Blackburn 2000). It is therefore somewhat surpris- ing that autecological studies of exotic birds have received disproportionately limited research at- tention within invasion biology (Pysek et al. 2008). A recent article in the Journal of Biogeography (Strubbe and Matthysen 2009), provides a timely example of a study that addresses this bias. Diederik Strubbe and Erik Matthysen com- piled data on the introductions and establishment success of two parakeet species (ring-necked Psit- tacula krameri and monk Myiopsitta monachus parakeets) across their exotic European distribu- tion. In doing so, the authors provide one of the first comparative biogeographic studies to test environment-level features of establishment suc- cess among exotic birds. In total, 181 introduction events were used for their analysis in the exotic range. In their native ranges, parakeet occurrence was estimated using the presence-only method MAXENT (Phillips et al. 2006). For both parakeet species, individually, their establishment success in Europe was 53%. Data from environmental and climatological variables were used to test the rela- tive influence of alternative 'climate-matching' and 'human-activity' hypotheses. The authors found that parakeet establishment success was greater in areas of more dense human population settlement and, both in the native and exotic ranges, their distribution was associated with a smaller number of annual frost days. Further ex- amination revealed that both species were equally sensitive to frost in their exotic range, the major- ity of failed introductions occurring in regions with more than 50 frost days per year. Human activity can influence establishment success both indi- rectly, through habitat modification and provision frontiers of biogeography 1.2, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society

Bemisia tabaci Phylogenetic Groups in India and the Relative Transmission Efficacy of Tomato leaf curl Bangalore virus by an Indigenous and an Exotic Population

Bemisia tabaci adults from various host-plant species were collected from 31 regions across India. 266 B. tabaci samples were first screened by RAPD-PCR to examine molecular variability and to select individuals with different fingerprints. Host-plant and region of collection were then used to select 25 individuals for PCR amplification and sequencing of their partial mitochondrial cytochrome oxidase subunit one (mtCOI) genes. Pairwise comparisons with mtCOI consensus sequences showed that the majority of these samples had <3.5% sequence divergence from groups currently termed Asia I, Asia II-5, Asia II-7, and Asia II-8. The biotype-B B. tabaci from India clustered into the Middle East-Asia Minor 1 group. A new group of B. tabaci from Coimbatore, collected from pumpkin, was related most closely to the Asia I group (6.2% sequence divergence from the consensus Asia I sequence). To increase our understanding of the epidemiology of tomato leaf curl disease (ToLCD) and the key B. tabaci genetic groups involved in virus spread, the indigenous Asia I and the exotic biotype-B population from South India were used to carry out transmission experiments using Tomato leaf curl Bangalore virus (ToLCBV). The acquisition access periods (AAP), inoculation access periods (IAP), latent periods (LP), and ToLCBV transmission efficiencies of the two populations were compared and the biotype-B had the more efficient transmission characteristics. These results are discussed in relation to recent changes in the epidemiology of tomato leaf curl disease in South India.

First record of the invasive alien species Axis axis (Erxleben, 1777) (Artiodactyla: Cervidae) in Brazil

The exotic alien species Axis axis was introduced in the Americas at the beginning of last century and since then has established itself, expanding its distribution. This is the first record of this species in Brazil. In the extreme south of the country, an individual of A. axis was recorded with a camera trap in the Espinilho State Park. The area is close to the border of Uruguay and Argentina, countries where the species is established and from where this individual presumably originated. The Pampas biome is strongly disturbed by human activity in Brazil and since many native mammal species such as the Pampas deer Ozotoceros bezoarticus are threatened regionally. It is alarming that exotic populations can potentially rapidly expand their ranges in the region, as A. axis deer has done in Uruguay and Argentina. Possible consequences for this invasion are discussed.

Population dynamics and reproductive output of the non-indigenous crab Charybdis hellerii in the south-eastern Caribbean Sea

Charybdis hellerii is one of several poorly known non-indigenous crabs in the Caribbean. In this study we report on the reproductive dynamic of a shallow subtidal population that invaded Isla Margarita, Venezuela, south-eastern Caribbean Sea &gt; 15 years ago and has persisted in the region up to date. Male and female crabs, both large and small, were found year-round at the study site. The size–frequency distribution indicated a lifespan of 2–3 years. Charybdis hellerii reproduces continuously but with very low intensity during the year. Small individuals (&lt;25 mm carapace length) were uncommon and intermittently found during the study period. Sex-ratio varied between 0.1 and 0.65 (mean ± SD = of 0.46 ± 0.14) and did not differ significantly from 1:1 ratio during most of the year. The size of the smallest brooding female was 36.81 mm carapace width (CW). Behavioural size at first maturity (movable abdomen) in males and females was estimated to be 22.39 mm CW (confidence limits: 18.35–24.72) and 37.43 mm CW (35.55–39.09), respectively. Reproductive output, estimated as the ratio of embryo to female body dry mass, varied between 0.052 and 0.084 (0.07 ± 0.008). Also, reproductive output was size-dependent with large females allocating proportionally less resources to egg production than small females. The reproductive schedule here reported for C. hellerii disagrees with the generalized idea of exotic populations ‘thriving’ in an environment free of natural enemies (e.g. predators, competitors and diseases).

Biotic resistance on the increase: native predators structure invasive zebra mussel populations

SUMMARY 1. Abundant native predators, parasites and pathogens that switch to consuming a hypersuccessful exotic species may be able to control the invasive population. Native predators may, however, need time to adapt to feed effectively on an exotic resource. In this case, mortality on an exotic population from native predators could increase over time even without a numerical increase in the predator population. 2. We measured mortality of zebra mussels (Dreissena polymorpha) in the Hudson River both in controls open to predation and in exclosures that excluded large predators to estimate mortality of zebra mussels from large predators and other causes. 3. We found that predation by the blue crab (Callinectes sapidus), and perhaps other predators, causes high mortality on zebra mussels in the Hudson River estuary. This predation apparently led to increased mortality and altered population structure in the invader over time. 4. Long-term data from the Hudson River suggest that components of the invaded ecosystem, like rotifers, are recovering through predator-caused release from zebra mussel grazing. Increased mortality on hyper-successful exotic populations over time may be a common phenomenon with both ecological and management implications.

Microsatellite loci for dreissenid mussels (Mollusca: Bivalvia: Dreissenidae) and relatives: markers for assessing exotic and native populations

We developed and tested 14 new polymorphic microsatellite loci for dreissenid mussels, including the two species that have invaded many freshwater habitats in Eurasia and North America, where they cause serious industrial fouling damage and ecological alterations. These new loci will aid our understanding of their genetic patterns in invasive populations as well as throughout their native Ponto-Caspian distributions. Eight new loci for the zebra mussel Dreissena polymorpha polymorpha and six for the quagga mussel D. rostriformis bugensis were compared with new results from six previously published loci to generate a robust molecular toolkit for dreissenid mussels and their relatives. Taxa tested include D. p. polymorpha, D. r. bugensis, D. r. grimmi, D. presbensis, the 'living fossil'Congeria kusceri, and the dark false mussel Mytilopsis leucophaeata (the latter also is invasive). Overall, most of the 24 zebra mussel (N = 583) and 13 quagga mussel (N = 269) population samples conformed to Hardy-Weinberg equilibrium expectations for the new loci following sequential Bonferroni correction. The 11 loci (eight new, three previously published) evaluated for D. p. polymorpha averaged 35.1 alleles and 0.72 mean observed heterozygosity per locus, and 25.3 and 0.75 for the nine loci (six new, three previously published) developed for D. r. bugensis. All but three of these loci successfully amplified the other species of Dreissena, and all but one also amplified Congeria and Mytilopsis. All species and populations tested were significantly divergent using the microsatellite data, with neighbour-joining trees reflecting their evolutionary relationships; our results reveal broad utility for resolving their biogeographic, evolutionary, population and ecological patterns.

Heterozygosity and Fixation Index for ABO Gene in Barak Valley Populations vis-a-vis a Few Exotic Populations

In a genetic study of 26 human populations including 2 major endogamous populations (Hindus and Muslims) of Barak Valley in Assam and 24 exotic populations, observed heterozygosity (Ho), fixation index (F) and Panmictic index (P) for ABO gene were estimated from gene frequency data to reveal the extent of inbreeding that has taken place in each population during evolution. Observed heterozygosity, a measure of genetic variation, ranged from 0.3254 to 0.6086 in these populations. Expected Hardy-Weinberg heterozygosity of ABO gene was estimated as 0.6666 assuming the occurrence of all the three alleles in equal frequency. Fixation index was the highest in the population of Sudan (51.18%) followed by Australia (48.51%) and Iceland (38.28%) indicating the occurrence of high inbreeding and the presence of more homozygosity in these populations during evolution. But the fixation index was the lowest in the population of South China (8.70%) followed by Central Asia (11.82%) and Russia (12.96%). It suggested the occurrence of low inbreeding and hence more outbreeding in these populations resulting in the existence of more heterozygosity (high genetic variation) in these populations. Panmictic index, a measure of outbreeding, is the opposite of fixation index and it varied from 48.82 (Sudan) to 91.30% (South China). The population showing the highest fixation index recorded the lowest panmictic index and vice-versa. In evolutionary context, outbreeding in human populations would be more desirable to reduce the incidence of genetic diseases caused by recessive genes and to enhance heterozygosity for those loci for better adaptation of future generations, possibly at the cost of gradually increasing genetic load in the population.

Forecasting the distribution of Marmorkrebs, a parthenogenetic crayfish with high invasive potential, in Madagascar, Europe, and North America

The parthenogenetic marbled crayfish, Marmorkrebs, has high potential to become an invasive species because single individuals can establish a population. Marmorkrebs have already been introduced in several countries, have successfully established populations in at least two of them, and are rapidly expanding in one case (Madagascar). To assess the potential ecological threat arising from further Marmorkrebs introductions, we developed four species distribution models using the distribution of Procambarus fallax (the sexual form of Marmorkrebs) and exotic populations of Marmorkrebs in Madagascar and Europe. The models were applied to three regions where Marmorkrebs pose a conservation concern: Madagascar, where Marmorkrebs populations are growing; Europe, where individuals have been found repeatedly, and where some Marmorkrebs populations are becoming established, and; North America, where Marmorkrebs are sold as pets, which presents a risk of introduction into North American ecosystems. All models predicted that eastern Madagascar provides suitable habitat for Marmorkrebs. Most models suggested that relatively small areas of Europe are suitable habitat, although a model that includes locations of Marmorkrebs introductions in Europe predicts much of Europe could be suitable, which is supported by recent discoveries of populations in Germany. All models predicted that the south eastern United States, Cuba, and much of Mexico are also potential habitats. The climatic variable with the greatest predictive power was precipitation in the warmest quarter, which may reflect a susceptibility to drought that has been documented for P. fallax.

Contemporary morphological diversification of passerine birds introduced to the Hawaiian archipelago

Species that have been introduced to islands experience novel and strong selection pressures after establishment. There is evidence that exotic species diverge from their native source populations; further, a few studies have demonstrated adaptive divergence across multiple exotic populations of a single species. Exotic birds provide a good study system, as they have been introduced to many locations worldwide, and we often know details concerning the propagule origin, time of introduction, and dynamics of establishment and dispersal within the introduced range. These data make them especially conducive to the examination of contemporary evolution. Island faunas have received intense scrutiny, therefore we have expectations concerning the patterns of diversification for exotic species. We examine six passerine bird species that were introduced to the Hawaiian archipelago less than 150 years ago. We find that five of these show morphological divergence among islands from the time since they were established. We demonstrate that some of this divergence cannot be accounted for by genetic drift, and therefore we must consider adaptive evolution to explain it. We also evaluate evolutionary divergence rates and find that these species are diverging at similar rates to those found in published studies of contemporary evolution in native species.