Making a Bad Situation Worse: An Invasive Species Altering the Balance of Interactions between Local Species

Biological invasions pose a significant threat to biodiversity, especially on oceanic islands. One of the primary explanations for the success of plant invaders is direct suppression of competitors. However, indirect interactions can also be important, although they are often overlooked in studies on biological invasion. The shrub Leucaena leucocephala is a widespread island invader with putative allelopathic effects on the germination and growth of other species. We quantified the impact of Leucaena on plant communities richness on an oceanic Brazilian island and, through nursery experiments, investigated the potential for allelopathic effects on the germination of Erythrina velutina, a native species that is often absent from stands of Leucaena. Additionally, in a manipulative field experiment, we examined the direct and indirect effects (mediated by the native species Capparis flexuosa) of the invader on the development of Erythrina. The species richness in invaded sites was lower than in uninvaded sites, and Capparis was the only native species that was frequently present in invaded sites. In the nursery experiments, we found no evidence that Leucaena affects the germination of Erythrina. In the field experiments, the odds of Erythrina germination were lower in the presence of Leucaena litter, but higher in the presence of Leucaena trees. However, the survival and growth of Erythrina were considerably inhibited by the presence of Leucaena trees. The isolated effect of native Capparis on the germination and growth of Erythrina varied from positive to neutral. However, when Capparis and Leucaena were both present, their combined negative effects on Erythrina were worse than the effect of Leucaena alone, which may be attributed to indirect effects. This study provides the first empirical evidence that the balance of the interactions between native species can shift from neutral/positive to negative in the presence of an exotic species.     

Prevalence of Different Horticultural Taxa of Ivy (Hederaspp., Araliaceae) in Invading Populations

‘English’ ivy (Hedera spp.) is a complex of invasive plant pests that are separated into several distinct taxa. To better understand the invasion by ivy of Pacific Northwest native forests, we investigated the taxonomic identity of 58 selected invasive populations in the Pacific Northwest. Random amplified polymorphic DNA (RAPD) markers revealed that 83% of the 119 samples from invading populations were derived form H. hibernica (Kirchner) Bean, which has been frequently sold as English ivy, although this apparently is an incorrect common name. It is used widely in urban landscapes in the Northwest. The remaining 20 samples were either H.helix ‘California,’ ‘Pittsburgh,’ ‘Star,’ other cultivars not investigated in the study or possible hybrids.     

The introduced flora of Madagascar

We provide the first comprehensive inventory of the non-native plants on Madagascar since Perrier de la Bathie’s effort 80 years ago, and evaluate the characteristics and importance of this biota. Using botanical databases (especially the Tropicos Catalogue of the Vascular Plants of Madagascar), published plant lists, field observation, and relevant literature, we inventory 546 introduced species that have naturalized, as well as 611 other introduced species that only exist in cultivation. We also list 211 species with unclear status, eight native species that have had different genetic stock introduced, and three endemics that have naturalized outside their native range. Of the naturalized species, 101 display invasive behaviour. Highly represented families include Fabaceae (224 confirmed introduced species), Myrtaceae (143), Poaceae (71), Cactaceae (52), Asteraceae (50), and Solanaceae. (33). Humans have been bringing plants to Madagascar since they colonized the island, mainly for their utility. A number of plants with native varieties but which also have long histories of human use and transport are ripe for further historical biogeographical research (including Eragrostis, Panicum, Sorghum, Dioscorea, Ziziphus, and Adansonia). The introduced flora is similar in composition to other tropical regions; its numerical size appears to confirm that poorer countries experience relatively fewer plant introductions. Madagascar’s introduced species deserve more attention, not just through the rubric of invasion biology, but as plants that build new ecologies and that sustain human communities.     

Invasive trees and shrubs: where do they come from and what we should expect in the future?

The global database of invasive trees and shrubs has been updated, resulting in a total of 751 species (434 trees and 317 shrubs) from 90 families (Rejmánek and Richardson 2013 Divers Distrib 19:1093–1094). This database is used to assess major trends in human-assisted exchanges of dendrofloras among 15 major geographical regions. Areas most invaded by non-native trees are Pacific Islands (136 species), Southern Africa (118), Australia (116), and North America (114). Areas most invaded by non-native shrubs are North America (98), Australia (87), Pacific Islands (71), and Europe (61). The most important sources of invasive trees are Asia (122–146 species, depending on how many Eurasian species are considered to have been introduced only from Europe), Australia (81), and South America (81). The most important sources of invasive shrubs are Asia (103–118), Europe (68), and South America (54). Mean number of native geographical regions for invasive trees is 1.64, while the mean number of invaded regions by trees is 2.51. The difference is smaller for shrubs: 1.60 versus 2.11. Asia is the major source of invasive Rosaceae shrubs, as well as invasive Arecaceae and Oleaceae species. South America and Australia are major sources of invasive Fabaceae trees. North America and Europe are major sources of invasive Pinaceae. Most of the invasive Salicaceae are of Eurasian origin. The identified trends will very likely continue in this century. Because of increasing interactions with many states in Asia, even more invasive woody species will be introduced from this part of the world.     

The role of exotic plants in the invasion of Seychelles by the polyphagous insect <Emphasis Type="Italic">Aleurodicus dispersus</Emphasis>: a phylogenetically controlled analysis

The accidental introduction of the spiralling whitefly, Aleurodicus dispersus Russell (Homoptera: Aleyrodidae) to Seychelles in late 2003 is exploited during early 2005 to study interactions between A. dispersus, native and exotic host plants and their associated arthropod fauna. The numbers of A. dispersus egg spirals and pupae, predator and herbivore taxa were recorded for eight related native/exotic pairs of host plants found on Mahé, the largest island in Seychelles. Our data revealed no significant difference in herbivore density (excluding A. dispersus) between related native and exotic plants, which suggests that the exotic plants do not benefit from ‘enemy release’. There were also no differences in predator density, or combined species richness between native and exotic plants. Together these data suggest that ‘biotic resistance’ to invasion is also unlikely. Despite the apparent lack of differences in community structure significantly fewer A. dispersus egg spirals and pupae were found on the native plants than on the exotic plants. Additional data on A. dispersus density were collected on Cousin Island, a managed nature reserve in which exotic plants are carefully controlled. Significantly higher densities of A. dispersus were observed on Mahé, where exotic plants are abundant, than on Cousin. These data suggest that the rapid invasion of Seychelles by A. dispersus may largely be due to the high proportion of plant species that are both exotic and hosts of A. dispersus; no support was found for either the ‘enemy release’ or the ‘biotic resistance’ hypotheses.     

Genetic variation in the wattle wilt pathogenCeratocystis albofundus

Ceratocystis albofundus is an important wilt pathogen on exoticAcacia mearnsii trees in South Africa. It is known only from this country and has also been reported from nativeProtea spp., but it is not clear if the pathogen is native or introduced to South Africa. This study was conduced to determine the nuclear and mitochondrial gene diversity in a population ofC. albofundus and to compare this diversity with that of otherCeratocystis species. Isolates were collected from a number of geographic regions in South Africa. Total genomic, DNA was extracted from each isolate, digested withPstl and probed with the radioactively labelled oligonucleotide marker (CAT)₅ to determine nulear DNA diversity. For the determination of mitochondrial DNA diversity, the RFLPs ofHaeIII digests were scored directly without probing. Nei’s gene diversity (H) was determined and a distance matrix was developed for each set of markers and analyzed using UPGMA. TheC. albofundus population was found to have a high level of both nuclear and mitochondrial gene diversity when compared with published data of populations of otherCeratocystis spp. This further supports the hypothesis thatC. albofundus is native to South Africa.     

The first report of <Emphasis Type="Italic">Spondias</Emphasis> native to Madagascar: <Emphasis Type="Italic">Spondias tefyi</Emphasis>, sp. nov. (Anacardiaceae)

Spondias represents a genus new to Madagascar’s native flora. Like Campnosperma, it is now known from both American and Asian tropics and Madagascar but not from continental Africa. The new species Spondias tefyi is easily distinguished from all of its Asian congeners by having the stamens shorter than the pistil and fruits brown and lenticellate at maturity (vs. greenish, yellow, orange or red, and relatively smooth). The new species is one of several Anacardiaceae whose fruits are eaten by lemurs in the Analavelona Forest, highlighting the importance of conserving this threatened subhumid forest remnant in southern Madagascar.     

The role of Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island, the Ryukyu Archipelago, Japan

The role of the Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island was investigated by direct observations and radio-tracking from October 2001 until January 2006. We found that Orii’s flying-fox potentially pollinated seven native plant species. Its feeding behavior and plant morphological traits suggested that this species is an important pollinator of Schima wallichii liukiuensis and Mucuna macrocarpa. The flying-fox also dispersed the seeds of 20 native plant species. The seeds of all plants eaten by the flying-fox were usually dropped beneath the parent tree, although large fruits of four plant species were occasionally brought to the feeding roosts in the mouth, with the maximum dispersal distance—for Terminalia catappa—estimated to be 126 m. Small seeds of 11 species (mostly Ficus species) were dispersed around other trees, during the subsequent feeding session, through the digestive tracts, with the mean dispersal distance for ingested seeds estimated at 150 ± 230.3 m (±SD); the maximum dispersal distance was 1833 m. A comparison of the seed dispersal of available fruits according to the size of flying-foxes and other frugivores suggested that the seed dispersal of eight plant species producing large fruits mostly depended on Orii’s flying-fox. On Okinawa-jima Island, the Orii’s flying-fox plays an important role as a pollinator of two native plants and as a long-distance seed disperser of Ficus species, and it functions as a limited agent of seed dispersal for plants producing large fruits on Okinawa-jima Island.     

Floral volatiles, pollinator sharing and diversification in the fig-wasp mutualism: insights from Ficus natalensis, and its two wasp pollinators (South Africa)

Combining biogeographic, ecological, morphological, molecular and chemical data, we document departure from strict specialization in the fig-pollinating wasp mutualism. We show that the pollinating wasps Elisabethiella stuckenbergi and Elisabethiella socotrensis form a species complex of five lineages in East and Southern Africa. Up to two morphologically distinct lineages were found to co-occur locally in the southern African region. Wasps belonging to a single lineage were frequently the main regional pollinators of several Ficus species. In South Africa, two sister lineages, E. stuckenbergi and E. socotrensis, pollinate Ficus natalensis but only E. stuckenbergi also regularly pollinates Ficus burkei. The two wasp species co-occur in individual trees of F. natalensis throughout KwaZulu-Natal. Floral volatile blends emitted by F. natalensis in KwaZulu-Natal were similar to those emitted by F. burkei and different from those produced by other African Ficus species. The fig odour similarity suggests evolutionary convergence to attract particular wasp species. The observed pattern may result from selection for pollinator sharing among Ficus species. Such a process, with one wasp species regionally pollinating several hosts, but several wasp species pollinating a given Ficus species across its geographical range could play an important role in the evolutionary dynamics of the Ficus-pollinating wasp association.     

Geographic and taxonomic distribution of a positive interaction: ant-tended homopterans indirectly benefit figs across southern Africa

Although species pairs and assemblages often occur across geographic regions, ecologists know very little about the outcome of their interactions on such large spatial scales. Here, we assess the geographic distribution and taxonomic diversity of a positive interaction involving ant-tended homopterans and fig trees in the genus Ficus. Previous experimental studies at a few locations in South Africa indicated that Ficus sur indirectly benefited from the presence of a homopteran (Hilda patruelis) because it attracted ants (primarily Pheidole megacephala) that reduced the effects of both pre-dispersal ovule gallers and parasitoids of pollinating wasps. Based on this work, we evaluated three conditions that must be met in order to support the hypothesis that this indirect interaction involves many fig species and occurs throughout much of southern Africa and Madagascar. Data on 429 trees distributed among five countries indicated that 20 of 38 Ficus species, and 46% of all trees sampled, had ants on their figs. Members of the Sycomorus subgenus were significantly more likely to attract ants than those in the Urostigma subgenus, and ant-colonization levels on these species were significantly greater than for Urostigma species. On average, each ant-occupied F.sur tree had 37% of its fig crop colonized by ants, whereas the value was 24% for other Ficus species. H. patruelis was the most common source for attracting ants, although figs were also attacked by a range of other ant-tended homopterans. P. megacephala was significantly more common on figs than other ant species, being present on 58% of sampled trees. Ant densities commonly exceeded 4.5 per fig, which a field experiment indicated was sufficient to provide protection from ovule gallers and parasitoids of pollinators. Forty-nine percent of all colonized F. sur trees sampled had ant densities equal to or greater than 4.5 per fig, whereas this value was 23% for other Ficus species. We conclude that there is considerable evidence to suggest that this indirect interaction occurs across four southern African countries and Madagascar, and involves many Ficus species. Received: 11 December 1997 / Accepted: 6 April 1998     

Fire enhances the ‘competition-free’ space of an invader shrub: <Emphasis Type="Italic">Rosa rubiginosa</Emphasis> in northwestern Patagonia

Fire can influence reproductive phenology of plants, enhancing the reproductive rate of many species. Disturbances such as fire can promote the proliferation of exotic species in native plant communities. In this study we analyze the effect of fire on reproductive phenology in three native species (a shrub: Berberis buxifolia and two small trees: Maytenus boaria and Schinus patagonicus) and in an exotic shrub (Rosa rubiginosa). Flowering and fruiting phenology was monitored in neighbouring burned and unburned forests. The shrubs flowered and fruited in both sites, but the small trees did so only in the unburned site. There is no overlapping in the flowering and fruiting phenophases between the natives and the exotic species. Therefore, they do not compete in resource offering to pollinators and seed dispersers. Consequently, R. rubiginosa has a ‘competition-free’ space enhanced by fire, from the reproductive phenology perspective.     

Plant-based food resources,trophic interactions among alien species,and the abundance of an invasive ant

Recent research on invasive ants suggests that their success may be facilitated by increased resources at introduced locations stemming from the emergence of novel trophic interactions with abundant honeydew-producing Hemiptera. Moreover, those Hemiptera may themselves often be introduced or invasive. To test the importance of mutualisms for invasive species, we conducted a study in the southeastern United States of factors hypothesized to affect the abundance of an invasive ant native to South America, Solenopsis invicta. The study was conducted within grazing pastures, where S. invicta can be extremely abundant while also exhibiting substantial variability in abundance. A path analysis showed that the abundance of S. invicta was strongly and positively affected by the abundance of an invasive honeydew-producing mealybug native to Asia, Antonina graminis, and by the mealybugs’ host grasses because of their strong positive effect on mealybug abundance. Abundance of the mealybug was primarily attributable to an invasive host grass native to Africa, Cynodon dactylon. The abundance of S. invicta was also positively affected by the abundance of other arthropods that they are likely to consume, and those arthropods were positively affected by the abundance of both the A. graminis host grasses and other plants. Thus the study shows that the distribution and abundance of different plant species could have important effects on the abundance of S. invicta through their effect on the ants’ food resources. The results are also consistent with the hypothesis that the emergence of novel trophic interactions among invasive species can promote the abundance of invasive ants.     

Determinants of species richness in southern African fig wasp assemblages

Summary We investigated the species richness of 24 fig wasp (Hymenoptera) assemblages associated with southern African fig trees (Ficus species, Moraceae). Assemblage sizes ranged between 3 and 30 species on different host tree species, with parasitoids slightly outnumbering gall-forming phytophages. Ten potential taxonomic, geographic and ecological determinants of assemblage richness were examined. Galler richness differed significantly between taxonomic sub-groups of Ficus and was significantly correlated with several ecological characteristics of the host trees, but there was no species-area effect. Parasitoid richness was strongly correlated with galler richness. We conclude that both ecological and historical factors have combined to determine the numbers of species that form fig wasp assemblages.     

Genetic diversity and population differentiation of traditional fonio millet (<Emphasis Type="Italic">Digitaria </Emphasis>spp.) landraces from different agro-ecological zones of West Africa

Fonio millets (Digitaria exilis Stapf, D. iburua Stapf) are valuable indigenous staple food crops in West Africa. In order to investigate the genetic diversity and population differentiation in these millets, a total of 122 accessions from five countries (Benin, Burkina Faso, Guinea, Mali and Togo) were analysed by Amplified Fragment Length Polymorphisms (AFLPs). Genetic distance-based UPGMA clustering and principal coordinate analysis revealed a clear-cut differentiation between the two species and a clustering of D. exilis accessions in three major genetic groups fitting to their geographical origins. Shannon’s diversity index detected in D. iburua was low (H = 0.02). In D. exilis, the most widespread cultivated species, moderate levels of genetic diversity (Shannon’s diversity H = 0.267; Nei’s gene diversity H′ = 0.355) were detected. This genetic diversity is unequally distributed with the essential part observed in the Upper Niger River basin while a very low diversity is present in the Atacora mountain zone. Analysis of molecular variance (AMOVA) revealed that a large part of the genetic variation resides among the genetic groups (70%) and the country of origin (56%), indicating a clear genetic differentiation within D. exilis. Influence of mating system (inbreeding or apomixis), agricultural selection and ecological adaptations as well as founding effects in the genetic make-up of the landraces were visible and seemed to jointly contribute to the genetic structure detected in this species. The genetic variability found between the analysed accessions was weakly correlated with their phenotypic attributes. However, the genetic groups identified differed significantly in their mean performance for some agro-morphologic traits. The results obtained are relevant for fonio millets breeding, conservation and management of their genetic resources in West Africa.     

Natural hybridization within seed sources of shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.)

Shortleaf and loblolly pine trees (n = 93 and 102, respectively) from 22 seed sources of the Southwide Southern Pine Seed Source Study plantings or equivalent origin were evaluated for amplified fragment length polymorphism (AFLP) variation. These sampled trees represent shortleaf pine and loblolly pine, as they existed across their native geographic ranges before intensive forest management. Using 17 primer pairs, a total of 96 AFLPs between shortleaf pine and loblolly pine were produced and scored on the sample trees and two control-pollinated F1 interspecies hybrids and their parents. In addition, the well known isocitrate dehydrogenase (IDH) isozyme marker was scored for all trees. IDH detected two putative hybrids among the loblolly pine samples and two among the shortleaf pine samples, while either 13 or 12 putative hybrids were detected using all AFLP markers and IDH and either NewHybrids or Structure software, respectively. Results of this study show that later generation hybrids can be reliably identified using AFLP markers and confirmed that IDH is not a definitive marker for detecting hybrids; that is, at least in some seed sources, the alternative species’ IDH allele resides in the source species. Based on all the markers, hybridization frequency varied geographically, ranging from 30% in an Arkansas seed source to 0% in several other seed sources. The hybridization level was higher in populations west of the Mississippi River than in populations east of the river; the shortleaf pine hybridization rates were 16.3% and 2.4% and the loblolly pine rates were 4.5% and 3.3%, west and east of the river, respectively. The results suggest that hybridization between these two species is significant but varies by seed source and species, and the potential for the unintended creation of hybrids should be considered in forest management decisions regarding both natural and artificial regeneration.     

Aliens or natives: who are the ‘thugs’ in British woods?

The invasion of native habitats by exotic, or alien, plant species has received considerable attention recently from policy, research, and practical conservation management perspectives. However, a new hypothesis for species dynamics in Britain suggests that a small number of aggressive native plant species (termed ‘thugs’) may have an equal, or greater, impact on native species and habitats than exotic species. Here, we examine this hypothesis using multivariate techniques with field-layer cover data collected during a country-wide survey of British woodlands. Multivariate analysis of these data identified a north-south gradient on the first axis, and that 20 of the 25 National Vegetation Classification woodland types were sampled within the study. The most abundant field-layer species included three of the proposed native ‘thugs’, i.e. Rubus fruticosus, Pteridium aquilinum and Hedera helix in addition to the native woodland indicator species Mercurialis perennis. Variation partitioning was used to compare the relative importance of native field-layer ‘thug’ species with invading alien shrub and tree species relative to other environmental drivers. The variation in the field-layer data-set explained by the three native ‘thug’ species was significant, but they explained a relatively small proportion of the variation relative to other environmental variables (climate, soil, management factors etc.). They did, however, explain almost four times as much variation as the three alien species that were significantly correlated with field-layer species composition (Acer pseudoplatanus, Impatiens glandulifera, Rhododendron ponticum). The results of this analysis suggest that the field-layer of British woodlands is impacted as much by native ‘thug’ species, as it is from ‘aliens’. Concern about the impact of these native ‘thug’ species has been reported previously, but their impact has not previously been compared to the impact of invading aliens. It is hoped that this analysis will do two things, first to act as a sound baseline for assessing any changing balance that should occur in the future, and second, to prompt both ecologists and conservationists to develop woodland management policies based on sound science.     

Coevolution of reproductive characteristics in three dioecious fig species and their pollinator wasps

This study investigates dioecious fig species using a pollinator introduction experiment. Our aims were to determine: (1) whether there was a significant difference in foundress distribution between sexes per fig species; (2) whether fig size and foundress number affect reproductive success of dioecious figs; and (3) who is the ‘controlling partner’ in the fig/pollinator mutualism. Three dioecious fig species: Ficus semicordata, Ficus hispida and Ficus tinctoria from Xishuangbanna, China, were selected for this experiment. We found that there was no significant difference of the foundress number in female and male figs of F. semicordata, F. hispida and F. tinctoria. Also, the foundress number did not depend on the fig diameter. The numbers and the proportions of fig seeds and female wasp offspring significantly increased with more foundresses; and fig seed number was significantly higher than female wasp offspring in F. semicordata and F. hispida, but not in F. tinctoria. Our results indicate that figs are generally the ‘controlling partner’ in fig-wasp mutualisms in species with large figs, but not with small figs. Compared with published studies of reproductive success in monoecious figs, the dioecious figs seem to be more efficient in producing both seeds and wasp offspring when there is a high number of foundress.     

Competition between <Emphasis Type="Italic">Lythrum salicaria</Emphasis> and a rare species: combining evidence from experiments and long-term monitoring

The rare endemic plant Sidalcea hendersonii (Henderson’s checker-mallow) occurs in tidal marshes of the Pacific Northwest and may be threatened by Lythrum salicaria (purple loosestrife), a European invader plant. We compared the abundances of Lythrum and Sidalcea in a wetland in British Columbia (Canada) in 1999 to those measured in 1979 to track changes in both species. Although the frequency of Sidalcea decreased by more than 50%, and that of Lythrum increased by almost 20%, there was no significant relationship between the changes of the two species. We assessed the potential effects of competition by Lythrum on Sidalcea in field and patio experiments. In the field, we measured the response of Sidalcea to the removal of Lythrum over a two-year period and compared this to the response of Sidalcea to the removal of native species and in unmanipulated control plots. Removal of Lythrum significantly improved the vegetative performance of Sidalcea compared to the removal of randomly selected native plants and the control treatment in the first year. In the second year, the performance of Sidealcea did not differ significantly with treatment. Removals did not influence the reproductive performance of Sidalcea in either year. A one-year additive experiment, carried out in pots, compared the competitive effect of Lythrum on Sidalcea with that of two native species. Lythrum’s impact on Sidalcea was not consistently stronger than that of the native species. Collectively, these results do not indicate a strong impact of Lythrum on the reproduction or abundance of Sidalcea.     

Assigning birds to wintering and breeding grounds using stable isotopes: lessons from two feather generations among three intercontinental migrants

Geographic origins of populations and migration patterns of several vertebrate and invertebrate species have been inferred from geographically distinct isotopes in their tissues. To test the hypothesis that feathers grown on different continents would reflect continental differences of δD in precipitation and have significantly different stable isotope ratios, we analyzed stable isotopes in two generations of feathers from three bird species (American and Pacific golden-plovers, Pluvialis dominica and P. fulva, and northern wheatears Oenanthe oenanthe) that breed in North America and winter in South America, the South Pacific and Asia, and Africa. We found significant differences in stable isotope signatures between summer- and winter-grown feathers in the plovers, and our use of two generations of feathers provided similar variation to that reported in studies using larger sample sizes. In contrast to plovers, no differences were detected in isotope values between summer- and winter-grown feathers in wheatears. Discriminant analyses separated 80% of summer- and winter-grown feathers for each plover species. Nonetheless, an “assignment with exclusion” method adapted from population genetics to impart a measure of confidence in assigning individuals to groups of origin resulted in an overall accuracy among plovers of only 41%, compared with a 63% assignment accuracy when the exclusion criterion was removed. Thus, we were unable to accurately assign feathers to origin of growth on the continental scale. Moreover, using δD expectations for North America, we were unable to assign summer-grown plover feathers to within better than several thousand kilometers of their true origins. We urge researchers to carefully consider the ecology and physiology of their study organisms, statistical methodology, and the interpretation of results when using stable isotopes to infer the geographic origins of feather growth.     

Are introduced rats (<Emphasis Type="Italic">Rattus rattus</Emphasis>) both seed predators and dispersers in Hawaii?

Invasive rodents are among the most ubiquitous and problematic species introduced to islands; more than 80% of the world’s island groups have been invaded. Introduced rats (black rat, Rattus rattus; Norway rat, R. norvegicus; Pacific rat, R. exulans) are well known as seed predators but are often overlooked as potential seed dispersers despite their common habit of transporting fruits and seeds prior to consumption. The relative likelihood of seed predation and dispersal by the black rat, which is the most common rat in Hawaiian forest, was tested with field and laboratory experiments. In the field, fruits of eight native and four non-native common woody plant species were arranged individually on the forest floor in four treatments that excluded vertebrates of different sizes. Eleven species had a portion (3–100%) of their fruits removed from vertebrate-accessible treatments, and automated cameras photographed only black rats removing fruit. In the laboratory, black rats were offered fruits of all 12 species to assess consumption and seed fate. Seeds of two species (non-native Clidemia hirta and native Kadua affinis) passed intact through the digestive tracts of rats. Most of the remaining larger-seeded species had their seeds chewed and destroyed, but for several of these, some partly damaged or undamaged seeds survived rat exposure. The combined field and laboratory findings indicate that many interactions between black rats and seeds of native and non-native plants may result in dispersal. Rats are likely to be affecting plant communities through both seed predation and dispersal.