Matrix habitat and plant damage influence colonization of purple loosestrife patches by specialist leaf-beetles

The characteristics of the matrix, that is, the unsuitable habitat connecting host-plant patches may facilitate or limit herbivore movement thus affecting their population dynamics. We evaluated the effect of matrix habitat, distance between patches, and plant damage on movement of two leaf-beetles (Galerucella calmariensis Linnaeus and G. pusilla Duft) introduced to North America as biocontrol agents of the invasive purple loosestrife (Lythrum salicaria Linnaeus). Mark-recapture/resight experiments indicated (1) that leaf-beetles are more likely to colonize purple loosestrife patches surrounded by meadow than forest; (2) that previously attacked purple loosestrife plants are more likely to be colonized by Galerucella spp. than unattacked plants, especially in the forest habitat; and (3) that leaf beetle colonization of purple loosestrife decreased with distance from release point. Low colonization rates of purple loosestrife patches embedded in forests suggest either insufficient detection or active avoidance of such habitats. Biological control programs intend to manage dispersal of specialized insect herbivores for the purpose of sufficient and sustained control of their host plants. Such management needs to be informed by knowledge of interactions of habitat structure, plant damage, and dispersal capabilities of herbivores to facilitate release programs and control at the local and regional level.     

The effects of flooding,plant traits,and predation on purple loosestrife leaf‐beetles

Classical biological weed control is based on the premise that introducing specialized natural enemies from the native range re‐establishes herbivore control of plant invaders, ultimately leading to negative population growth rates. Evidence from past biocontrol programs suggests that herbivores are not solely responsible for shaping plant demography. Diverse environmental conditions in the introduced range may not only affect demography, but also influence top‐down control of target plants. We investigated how flooding affects impacts of predators (top‐down) and plant quality (bottom‐up) on performance of two leaf‐beetles, Galerucella calmariensis L. and Galerucella pusilla Duftschmid (Coleoptera: Chrysomelidae: Galerucini), released in North America as biocontrol agents of purple loosestrife, Lythrum salicaria L. (Lythraceae). Predation and flooding regime have been linked to low leaf‐beetle recruitment at sites where insects failed to attain outbreak populations. Predator exclusion experiments at adjacent flooded and non‐flooded sites indicated a positive effect of flooding on leaf‐beetle survival for all developmental stages, whereas predator exposure had little effect. There was no difference in predation rates at sites with successful or failed purple loosestrife control, questioning the importance of predation in limiting growth and impact of these biocontrol agents’ populations. Effect of flooding on purple loosestrife quality was evaluated in a common garden study where plants were grown under different flooding treatments. Plants grown in flooded soil had higher water content and lower tannic acid concentration than plants grown in well‐drained soil. Consistent with field observations, leaf‐beetle oviposition rate and survival were higher on flooded plants. Results indicate that both bottom‐up and top‐down forces operate on Galerucella populations, yet their relative strength is mediated by flooding regime. Ignoring intricacies of plant‐herbivore and trophic interactions in the introduced range appears to be a major handicap for the improvement of weed biocontrol programs.     

Quantifying the effects of distance and conspecifics on colonization: experiments and models using the loosestrife leaf beetle, Galerucella calmariensis

The ability of an insect to disperse to new habitat patches is difficult to quantify, but key to the establishment and persistence of populations. In this study, we examined dispersal of the phytophagous chrysomelid beetle, Galerucella calmariensis, which is currently being introduced into North America for the biological control of purple loosestrife (Lythrum salicaria), an aggressive wetland weed. We used a mark, release, and recapture approach to determine how rates of colonization of host patches by this beetle are influenced by the distance of the patch from the source of dispersers, and by the presence of conspecifics at the patch. We released color-coded beetles at six distances from a long, linear patch of purple loosestrife that was divided into segments with and without conspecifics. We observed initial flight directions as beetles left the release points and collected all beetles that settled at the target patch. We found a bias in initial flight toward the target for distances up to 50 m. Over the 7 days of the experiment, beetles arrived at the target from all release points, including the farthest release point, 847 m away. G. calmariensis was strongly attracted to conspecifics when settling after dispersal; 86% of the 582 recovered beetles came from the segments inhabited by conspecifics. The probability of an individual arriving at the patch declined steeply with release distance. This relationship fits a model in which beetles move in a random direction and stop if they intercept the target patch, and where beetles are lost at a constant rate with distance travelled. The dispersal and patch-colonizing behavior of G. calmariensis is likely to have important consequences for the biological control program against purple loosestrife. Received: 23 January 1996 / Accepted:30 September 1996     

Impact and management of purple loosestrife (Lythrum salicaria) in North America

The invasion of non-indigenous plants is considered a primary threat to integrity and function of ecosystems. However, there is little quantitative or experimental evidence for ecosystem impacts of invasive species. Justifications for control are often based on potential, but not presently realized, recognized or quantified, negative impacts. Should lack of scientific certainty about impacts of non-indigenous species result in postponing measures to prevent degradation? Recently, management of purple loosestrife (Lythrum salicaria), has been criticized for (1) lack of evidence demonstrating negative impacts of L. salicaria, and (2) management using biocontrol for lack of evidence documenting the failure of conventional control methods. Although little quantitative evidence on negative impacts on native wetland biota and wetland function was available at the onset of the control program in 1985, recent work has demonstrated that the invasion of purple loosestrife into North American freshwater wetlands alters decomposition rates and nutrient cycling, leads to reductions in wetland plant diversity, reduces pollination and seed output of the native Lythrum alatum, and reduces habitat suitability for specialized wetland bird species such as black terns, least bitterns, pied-billed grebes, and marsh wrens. Conventional methods (physical, mechanical or chemical), have continuously failed to curb the spread of purple loosestrife or to provide satisfactory control. Although a number of generalist insect and bird species utilize purple loosestrife, wetland habitat specialists are excluded by encroachment of L. salicaria. We conclude that (1) negative ecosystem impacts of purple loosestrife in North America justify control of the species and that (2) detrimental effects of purple loosestrife on wetland systems and biota and the potential benefits of control outweigh potential risks associated with the introduction of biocontrol agents. Long-term experiments and monitoring programs that are in place will evaluate the impact of these insects on purple loosestrife, on wetland plant succession and other wetland biota.     

Fecundity and feeding of <Emphasis Type="Italic">Galerucella calmariensis</Emphasis> and <Emphasis Type="Italic">G. pusilla</Emphasis> on <Emphasis Type="Italic">Lythrum salicaria</Emphasis>

Fecundity and feeding of two introduced sibling biological control species, Galerucella calmariensis and G. pusilla (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae) were compared at constant temperatures of 12.5, 15, 20, 25, and 27.5 °C. Larval feeding was also carried out at 30 °C, but at this temperature, larvae developed only to the L2 stage and none pupated. Thus, data for this temperature were not used in the analysis. There were significant species × temperature interactions in fecundity. Of the two species, Galerucella pusilla laid more eggs. Although egg production of both species was lowest at 12.5 °C and increased to 20 °C, at higher temperatures, the two species reacted differently. From 25 to 27.5 °C, egg production decreased for G. pusilla, but G. calmariensis fecundity peaked at 27.5 °C. Significant temperature × species × life-stage interactions were also observed in feeding. For each species, the amount of feeding varied with temperature and stage of development. Galerucella pusilla adults consumed more foliage at 15, 20, and 27.5 °C. However, at 12.5 °C G. calmariensis adults fed more than G. pusilla. G. pusilla larvae consumed an average of 25% less foliage than G. calmariensis. The lower larval consumption of G. pusilla suggests that when food is limited, G. pusilla larvae may have a higher survival rate because of its ability to complete larval development with less food and produce more progeny due to its greater fecundity. When food is not limited neither species would have a competitive advantage and both species could coexist temporally and spatially. However, since G. calmariensis larvae consumed more leaf material, the larval stage of this species would have a greater impact on purple loosestrife than G. pusilla.     

Mass rearing the weevil Hylobius transversovittatus (Coleoptera: Curculionidae), biological control agent of Lythrum salicaria, on semiartificial diet

Lythrum salicaria L., purple loosestrife, an invasive Eurasian perennial, is degrading wetlands across temperate North America. Chemical, physical, and mechanical methods failed to provide long-term control. Therefore, four host-specific insect species (two leaf feeders, a root feeder, and a flower feeder) were introduced as biological control agents. To increase the availability of adults of the root feeding weevil Hylobius transversovittatus Goeze for field releases, we developed a semiartificial diet. Suitability of different diet formulations (varying vitamin mixes, salt mixes, antimicrobials, water content, root content) and temperatures for larval development were evaluated. We also monitored how rearing on artificial diet and the number of larvae per container affected larval development time, larval survival, adult weight, and incidences of deformities. Rearing larvae on artificial diet reduced development time from 1-2 yr to 2-3 mo. Larval development was fastest and survival rates highest under constant temperatures of 25 degrees C. Hatch rate and larval survival decreased if eggs were surface sterilized. Using FABCO antimicrobials could not prevent fungal contamination; use of methyl paraben and sorbic acid was successful in suppressing fungal and bacterial growth throughout larval development time to <10%. The moisture content of the diet did not significantly affect larval survival, development, or adult weight. Decreasing the proportion of purple loosestrife roots in the diet reduced adult weight and the proportion of larvae completing development, and increased development time; no larvae were able to complete development in root-free diet. With an increase in the number of larvae per cup, survival rates were reduced. The experiments revealed a female biased sex ratio: females consistently developed faster and were heavier than males. Incidence of adult deformities was consistently below 5%. Increased availability of adults for field release as a result of mass production using the semiartificial diet will accelerate the biocontrol program targeting purple loosestrife. We are able to produce several hundred weevils per week and have adapted the diet to rear other root-feeding weevils.     

Dispersal potential of native and exotic predatory ladybirds as measured by a computer-monitored flight mill

The performance of three species of predatory ladybirds was compared in a flight mill and the effect of diet on their flight parameters was tested. The invasive ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) outperformed Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae) and Adalia bipunctata (L.) (Coleoptera: Coccinellidae) in terms of flight distance, duration and velocity. Harmonia axyridis flew at least two times further, needed three times less breaks and flew two times faster than C. montrouzieri and A. bipunctata fed the same diet. Ladybirds reared on eggs of Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) performed better than their counterparts reared on natural prey (aphids for H. axyridis and A. bipunctata, mealybugs for C. montrouzieri). The findings of this study indicate that comparative flight studies can be useful to identify candidate biocontrol agents with pronounced dispersal abilities and thus can yield significant evidence to be used in an environmental risk assessment. However, it also demonstrates that variability related to mass rearing conditions should not be ignored when standardizing a risk assessment procedure for candidate biocontrol agents.     

Parasitoid dispersal and colonization lag in disturbed habitats: biological control of cereal leaf beetle metapopulations

Natural enemies of insect pests of annual crops have been hypothesized either to lag, or alternatively not to lag, behind their prey in dispersing to and colonizing new habitat. We examined parasitoid dispersal and parasitism of the cereal leaf beetle (Oulema melanopus [L.]; Coleoptera: Chrysomelidae) by the host‐specific wasp Tetrastichus julis [Walker] (Hymenoptera: Eulophidae) in wheat fields of northern Utah to assess whether a colonization lag occurred. Equally high rates of parasitism of beetle larvae (including second instars early in the year) occurred in 2010 and 2011 in fields that were newly planted to wheat vs. in fields where wheat had been grown also the previous year. A caging experiment demonstrated that parasitism in these newly planted wheat fields did not arise from parasitoid adults that had matured within the fields; instead, upon emerging in other fields, parasitoid females dispersed a minimum of 100–250 m to parasitize beetle larvae early in the spring in the newly planted fields. A transect study in 2012 revealed that T. julis females dispersed rapidly at least 600 m into a newly planted wheat field to parasitize most of the early maturing beetle larvae, which occurred at very low density. Thus, the parasitoid has very strong ability to match its host in dispersal over long distances across a highly disturbed agricultural landscape, and colonization lag appears of little importance in affecting biological control associated with this host–parasitoid interaction.     

Establishment and impact of insect agents deployed for the biological control of invasive Asteraceae: prospects for the control of <Emphasis Type="Italic">Senecio madagascariensis</Emphasis>

Several invasive Asteraceae have been targeted for biological control worldwide, with variable success. Senecio madagascariensis Poiret, which invades agricultural lands in Australia and Hawaii, is a recent target. Since several potential insect agents were recorded in the plant’s native range in South Africa, we assessed biocontrol efforts against asteraceous weeds to determine those most likely to deliver success. Some 108 insect species, from five orders and 23 families, were deployed against 38 weed taxa, mostly in the mainland USA, Canada, Australia and New Zealand. Coleoptera (mainly Curculionidae and Chrysomelidae), Diptera (Tephritidae) and Lepidoptera (Tortricidae) featured the most. Despite high establishment success (73% of releases across countries), only 37% of successful releases achieved meaningful impact. Although root-feeding and stem-feeding insects appeared to be the best candidates, neither insect family nor feeding guild significantly influenced the probability of success. This synthesis of the global contribution of different guilds of specialist herbivores to the management of invasive Asteraceae is guiding the selection of candidate agents for the biocontrol of S. madagascariensis in Australia.     

Does Dispersal Limit Beetle Re‐colonization of Restored Fenland? A Case Study Using Direct Measurements of Dispersal and Genetic Analysis

Dispersal ability is known to limit the colonization by many fenland species onto restored habitat but factors determining colonization by wetland invertebrates onto restored fenland have not been previously examined. We used mark‐release‐recapture and harmonic radar tracking coupled with genetic analysis (ISSR‐PCR, inter‐simple sequence repeat—polymerase chain reaction) to assess the population structure and colonization of a brachypterous wetland carabid (Carabus granulatus) onto restored fenland. The first two methods were used to determine the dispersal rate of C. granulatus in the absence of barriers, while the genetic analysis was used to examine whether populations were separated by either distance or the water channels and drainage ditches that intersect fenland landscapes. Mark‐release‐recapture and harmonic radar tracking indicated that the most active 6% of individuals could travel over 25 m in a day and individuals found to be traveling these distances remained atypically active throughout the season. Thus, C. granulatus can disperse at a rate great enough to colonize all areas of restored fenland in the study site within 1 year in the absence of barriers. We found no evidence of genetically distinct sub‐populations of C. granulatus showing that distance and water barriers did not limit the movement of individuals from potential source populations to the restored habitat. This research indicates that where fenland is created with nearby established fenland, colonization opportunities should not be considered a limiting factor to colonization by wetland carabids, even where waterways divide sites.     

The influence of geographical and ecological factors on island beta diversity patterns

Aim To investigate the importance of various island characteristics in determining spatial patterns of variations in beta diversity for various animal groups. Location Analyses are presented for 10 animal groups living on the Aeolian Islands, a volcanic archipelago in the central Mediterranean, near Sicily. Methods Three hypotheses were formulated to explain patterns of beta diversity: the target‐area–distance effect, stepping stone dispersal and island age. Matrices of inter‐island dissimilarities were constructed under each hypothesis and correlated with matrices of faunal dissimilarities using Mantel tests. For the ‘target‐area–distance effect’ hypothesis, inter‐island dissimilarities were calculated using island sizes and distances to nearest mainland areas. For the ‘stepping stone dispersal’ hypothesis, inter‐island distances were measured. Finally, for the ‘island age’ hypothesis, inter‐island dissimilarities were calculated on the basis of the geological age of the islands. Cluster analysis was used to investigate inter‐island faunal relationships. Results Support for a target‐area–distance effect was found only for birds. For these highly mobile animals, inter‐island distances had no significant effects on beta diversity. Birds are known to colonize islands by crossing large sea barriers and thus they can easily reach the Aeolian Islands, which are close to source areas (notably Sicily). Inter‐island distances had a significant role in determining patterns of beta diversity in most invertebrates. For Mollusca, Opiliones, Chilopoda, Heteroptera, coprophagous Scarabaeoidea, and Tenebrionidae, even relatively short distances preclude invertebrates from colonizing an island regularly from the mainland, and most colonization probably results from inter‐island faunal exchanges. Island age was proved to be important only for orthopterans. Main conclusions The origin of most of the Aeolian invertebrate fauna is quite recent, and species appear to have established on the islands predominantly by stepping stone dispersal. Birds, which are highly mobile organisms, follow more direct mainland–island dynamics. As further studies on other islands become available, comparative analyses will confirm whether the factors influencing variations in beta diversity in this study and their relationships with species dispersal ability are consistent across scales and geographical context.     

Effects of local vegetation and plantation age for the parasitoid Asecodes mento– a biocontrol agent in organic strawberry fields

Abstract The parasitoid Asecodes mento (Walker, 1839) (Hymenoptera: Eulophidae) is the most important biocontrol agent of the strawberry leaf beetle Galerucella tenella (L.) (Coleoptera: Chrysomelidae) in northern Europe. Here, I investigated whether natural parasitism in organic strawberry plantations was affected by the presence of the alternative host plant meadowsweet (Filipendula ulmaria), and whether parasitism rates differed between plantations of different ages (6 to 79 years). I also investigated whether parasitoid brood size, body size and sex ratio differed between the two host plants in the field. Parasitism was very low (0%) in newly established plantations and increased to a plateau (～40%) in fields where strawberries had been grown for approximately 20 years or longer. Such an extended colonization process is unacceptable for commercial growers. It would thus be desirable to find a method to catalyze parasitoid population buildup in young plantations. Parasitoid brood sizes were larger in beetles collected from meadowsweet, while body size and sex ratio did not differ between parasitoids collected from the two plants. These findings suggest that meadowsweet can export parasitoids to neighboring strawberry fields. Although this is a possibility, I did not find any significant differences in parasitism rates between isolated strawberry fields and fields adjacent to meadowsweet stands, indicating that effects of local vegetation are small on parasitism rates. Releasing parasitoids in newly established strawberry plantations may be a better strategy for quickly obtaining high parasitism than intercropping with meadowsweet.     

Genetic variation and reproductive patterns in wetland mosses suggest efficient initial colonization of disturbed sites

To understand colonization processes, it is critical to fully assess the role of dispersal in shaping biogeographical patterns at the gene, individual, population, and community levels. We test two alternative hypotheses (H I and H II) for the colonization of disturbed sites by clonal plants, by analyzing intraspecific genetic variation in one and reproductive traits in two typical fen mosses with separate sexes and intermittent spore dispersal, comparing disturbed, early‐succession (limed) fens and late‐successional rich fens. H I suggests initial colonization of disturbed sites by diverse genotypes of which fewer remain in late‐successional fens and an initially balanced sex ratio that develops into a possibly skewed population sex ratio. H II suggests initial colonization by few genotypes and gradual accumulation of additional genotypes and an initially skewed sex ratio that alters into the species‐specific sex ratio, during succession. Under both scenarios, we expect enhanced sexual reproduction in late‐successional fens due to resource gains and decreased intermate distances when clones expand. We show that the intraspecific genetic diversity, assessed by two molecular markers, in Scorpidium cossonii was higher and the genetic variation among sites was smaller in disturbed than late‐successional rich fens. Sex ratio was balanced in S. cossonii and Campylium stellatum in disturbed fens and skewed in C. stellatum in late‐successional fens, thus supporting H I. In line with our prediction, sex expression incidence was higher in, and sporophytes were confined to, late‐succession compared to disturbed rich fens. Late‐successional S. cossonii sites had more within‐site patches with two or more genotypes, and both species displayed higher sex expression levels in late‐successional than in disturbed sites. We conclude that diverse genotypes and both sexes disperse efficiently to, and successfully colonize new sites, while patterns of genetic variation and sexual reproduction in late‐successional rich fens are gradually shaped by local conditions and interactions over extended time periods.     

Potential of aquatic macrophytes and artificial floating island for removing contaminants

Eutrophication is a major environmental issue that mankind is facing today as a result of rapid development. To reduce the eutrophication problem, we are testing an innovative artificial floating islands (AFIs) approach. AFIs include aquatic plants composed of emergent and floating macrophytes. In this experimental approach, two aquatic plants were selected to compare with the control group in order to evaluate the capacity of AFIs. These two emergent macrophytes were evaluated for a 40-day timeframe to examine their ability to purify waste water. The results showed that an AFI with purple loosestrife (Lythrum salicaria Linn.) and one with yellow-flowered iris (Iris wilsonii) have a strong ability to remove nitrogen, phosphorus, and other pollutants from water bodies. The pollutant removal rates of the AFIs with purple loosestrife and yellow-flowered iris were almost over 50%. The chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal rates of the AFI with purple loosestrife were about 75%, 57%, 71%, respectively. At the same time, the COD, TN, and TP removal rates of the AFI with yellow-flowered iris were 60%, 49%, and 68%, respectively. AFIs with aeration are also a good way to remove pollutants. This study reveals that AFIs can be incorporated into wetlands to reduce the effects of water contamination and help strengthen wetland restoration.     

The colonization history of Juniperus brevifolia (Cupressaceae) in the Azores Islands

Background

A central aim of island biogeography is to understand the colonization history of insular species using current distributions, fossil records and genetic diversity. Here, we analyze five plastid DNA regions of the endangered Juniperus brevifolia, which is endemic to the Azores archipelago.

Methodology/Principal Findings

The phylogeny of the section Juniperus and the phylogeographic analyses of J. brevifolia based on the coalescence theory of allele (plastid) diversity suggest that: (1) a single introduction event likely occurred from Europe; (2) genetic diversification and inter-island dispersal postdated the emergence of the oldest island (Santa Maria, 8.12 Ma); (3) the genetic differentiation found in populations on the islands with higher age and smaller distance to the continent is significantly higher than that on the younger, more remote ones; (4) the high number of haplotypes observed (16), and the widespread distribution of the most frequent and ancestral ones across the archipelago, are indicating early diversification, demographic expansion, and recurrent dispersal. In contrast, restriction of six of the seven derived haplotypes to single islands is construed as reflecting significant isolation time prior to colonization.

Conclusions/Significance

Our phylogeographic reconstruction points to the sequence of island emergence as the key factor to explain the distribution of plastid DNA variation. The reproductive traits of this juniper species (anemophily, ornithochory, multi-seeded cones), together with its broad ecological range, appear to be largely responsible for recurrent inter-island colonization of ancestral haplotypes. In contrast, certain delay in colonization of new haplotypes may reflect intraspecific habitat competition on islands where this juniper was already present.     

Specialization to cold‐water upwellings may facilitate gene flow in seabirds: new evidence from the Peruvian pelican Pelecanus thagus (Pelecaniformes: Pelecanidae)

Recent research has shown that tropical seabirds specialized to feed on cold water upwellings exhibit low population genetic differentiation and high gene flow across large geographic distances. This pattern is opposite to the general pattern of differentiation reported for tropical seabirds, and led us to hypothesize that specialization to cold‐water upwellings facilitates gene flow between colonies. As a test of this hypothesis we characterized population differentiation and gene flow across the range of the Peruvian pelican Pelecanus thagus, an upwelling specialist endemic to the Humboldt Current, using an 838 base pair segment of the mitochondrial control region and seven microsatellite loci. In support of our hypothesis we report genetic panmixia across the geographic range of this species and inferred high gene flow between colonies. The high dispersal propensity of upwelling specialist seabirds (adults and/or juveniles) may reduce loss of genetic diversity during population declines, and increase the ability of these species to colonize new islands.     

Implications of individual variation in insect behavior for host specificity testing in weed biocontrol

This study shows that individual behavioral variation is an under-recognised source of error that may affect the outcome of host range tests in a stenophagous species. Original specificity testing of the broom seed beetle, Bruchidius villosus (F.) (Coleoptera: Chrysomelidae: Bruchinae), a biocontrol agent for Scotch broom, Cytisus scoparius (L.) Link (Fabaceae: Genisteae), failed to detect its ability to oviposit in the field on a congeneric non-target plant, the exotic Cytisus proliferus L.f. (Fabaceae: Genisteae). These tests were repeated using individual beetles from the original UK collection sites and from New Zealand, 15 generations post release. In the original tests, low replication of small batches of females masked high levels of individual variation in oviposition preference. Although most beetles showed strong preference for the target weed, there was some indication that New Zealand beetles showed higher preference for the non-target than UK beetles.     

Experimental Invasions Using Biological Control Introductions: The Influence of Release Size on the Chance of Population Establishment

Introductions of biological control organisms offer a unique opportunity to experimentally study the process of invasion by exotic species. I used two chrysomelid beetles, Galerucella calmariensis and Galerucella pusilla, which are currently being introduced into North America for the biological control of purple loosestrife (Lythrum salicaria), to determine how the initial size of a release affects the probability that the introduced population grows and persists. I released both species into stands of their host plant at 36 sites scattered throughout central New York State using four release sizes: 20, 60, 180, and 540. I returned to these sites over the next 3 years to census the populations. For both species, the probability of population establishment increased with release size. Population growth rates also depended positively on release size. The implication from these results is that the demographic factors whose influence depends on population size or density such as demographic stochasticity, Allee effects, and genetics play important roles in the establishment of invading populations. A second set of releases was used to determine if it was at all possible for a single gravid female to found a population. Out of twenty individual females released, one female (a G. calmariensis) founded a population that persisted until the end of the study (3 generations). This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Limited Potential of Azorean Fleshy Fruits for Oceanic Dispersal

How plants arrived to originally sterile oceanic islands has puzzled naturalists for centuries. Dispersal syndromes (i.e., diaspore traits that promote dispersal by long-distance dispersal vectors), are generally considered to play a determinant role in assisting island colonization. However, the association between diaspore traits and the potential vectors by which diaspores are dispersed is not always obvious. Fleshy fruits, in particular, are considered to have evolved to promote the internal dispersal of seeds by frugivores (endozoochory), however some fleshy fruits can also float in saltwater, and thus be potentially transported by oceanic current (thalassochory). We performed saltwater floatation and viability experiments with fruits of the 14 European fleshy-fruited species that naturally colonized the Azores archipelago (North Atlantic Ocean). We show that only Corema album (a berry) and Juniperus oxycedrus (a fleshy cone) floated for as long as 60 days, the estimated minimum time needed to reach the Azores by oceanic currents. Regardless the floatation potential, exposure to saltwater largely reduced the viability of most seeds of the 14 species (46% of viability decline within 15 days and 77% within 60 days of immersion), including those of Corema album (61%) and Juniperus oxycedrus (83%). Floatability and viability trials suggest that while some fleshy-fruited species might have arrived to the Azores by oceanic currents, such would have required extreme meteorological events that could largely reduce the duration of the trip. Thus, the alternative hypothesis that fleshy-fruited species were mostly dependent on animal dispersers (endozoochory) to colonize these remote islands is reinforced.     

Re‐colonization by common eiders Somateria mollissima in the Aleutian Archipelago following removal of introduced arctic foxes Vulpes lagopus

Islands provide refuges for populations of many species where they find safety from predators, but the introduction of predators frequently results in elimination or dramatic reductions in island‐dwelling organisms. When predators are removed, re‐colonization for some species occurs naturally, and inter‐island phylogeographic relationships and current movement patterns can illuminate processes of colonization. We studied a case of re‐colonization of common eiders Somateria mollissima following removal of introduced arctic foxes Vulpes lagopus in the Aleutian Archipelago, Alaska. We expected common eiders to resume nesting on islands cleared of foxes and to re‐colonize from nearby islets, islands, and island groups. We thus expected common eiders to show limited genetic structure indicative of extensive mixing among island populations. Satellite telemetry was used to record current movement patterns of female common eiders from six islands across three island groups. We collected genetic data from these and other nesting common eiders at 14 microsatellite loci and the mitochondrial DNA control region to examine population genetic structure, historical fluctuations in population demography, and gene flow. Our results suggest recent interchange among islands. Analysis of microsatellite data supports satellite telemetry data of increased dispersal of common eiders to nearby areas and little between island groups. Although evidence from mtDNA is suggestive of female dispersal among island groups, gene flow is insufficient to account for recolonization and rapid population growth. Instead, near‐by remnant populations of common eiders contributed substantially to population expansion, without which re‐colonization would have likely occurred at a much lower rate. Genetic and morphometric data of common eiders within one island group two and three decades after re‐colonization suggests reduced movement of eiders among islands and little movement between island groups after populations were re‐established. We predict that re‐colonization of an island group where all common eiders are extirpated could take decades.