Growth and mortality of introduced fish larvae in a newly restored urban river

The potential of a newly restored river as a nursery for endangered rheophilic fish species was estimated by introducing a population of individually marked larvae of nase Chondrostoma nasus into two river sections differing in river morphology and hydrological conditions. After 12 months, clear differences in fish abundance and fish size were observed: in the braided floodplain section C. nasus were more abundant and larger in size than in the straight river channel section. Total mortality rates over the whole investigation period did not differ between the two sections.     

Unsuitability of introduced tiles for sampling blackfly larvae (Diptera: Simuliidae)*

SUMMARY. 1. Blackfly larvae were collected from twenty-one stations in five lake outlets in Southern Quebec. Tiles (total area=500cm²) were introduced in early March, and collected 4 weeks later: randomly selected rocks (30–500cm) from the surrounding area were collected at the same time. 2. Larval densities on tiles were significantly less variable than on rocks. The variance of density estimates on tiles averaged 36% of the observed variance on natural rocks, or 67% when variance on rocks was corrected for average rock size. 3. Tiles significantly overestimated densities on rocks in some streams, and significantly underestimated them in others. These differences could not be explained by microhabitat differences (distance from the lake, depth, current velocity) between rock and tile samples. The bias that tiles introduce in density estimates precludes their use in comparisons among sites.     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.     

Ability of predatory native Australian fishes to learn to avoid toxic larvae of the introduced toad Bufo marinus

Of two native Australian fishes naïve to the introduced toad Bufo marinus most barramundi Lates calcarifer rapidly learned to avoid B. marinus tadpoles, while sooty grunter Hephaestus fuliginosus exhibited considerable intraspecific variation in their learning ability. Some sooty grunter learned to avoid tadpoles after only a few attacks, while other individuals continued to attack and reject tadpoles throughout the entire laboratory trials. Individuals of both species recognized and avoided tadpoles 1 day after their previous encounter. None of the fishes died during the trials. The observed variation in behavioural responses of fishes to B. marinus may be due to differences in (1) learning ability, (2) fish hunger levels, and or (3) tadpole palatability and toxicity. The results demonstrate that most barramundi and sooty grunter learn to avoid B. marinus tadpoles with minimal trauma. Consequently, it is anticipated that the toads are unlikely to have a significant negative impact on wild populations of these fishes through direct toxic effects.     

Direct and indirect effects of the introduced toad Bufo marinus (Anura: Bufonidae) on populations of native anuran larvae in Australia

Introduced species are frequently believed to have adverse effects on native biota and ecosystems. However, much of our knowledge of the ecological impacts of introduced species is anecdotal, and the mechanisms controlling these effects are often poorly understood. I used replicated artificial pond experiments to investigate the impact of eggs and hatchlings of the introduced toad Bufo marinus on populations of native anuran larvae (Limnodynastes ornatus and Litoria rubella) in Australia. Bufo marinus eggs and hatchlings are highly toxic to predatory native tadpoles. Under naturalistic conditions, populations of predatory L. ornatus tadpoles experienced significantly reduced survival when exposed to Bufo eggs and hatchlings. The impact of Bufo on L. ornatus survival was positively correlated with Bufo density. However, the toxic effects of Bufo on L. ornatus indirectly facilitated the survival of later-breeding L. rubella by altering predator-prey interactions between L. ornatus and L. rubella. Limnodynastes ornatus tadpoles are voracious predators of L. rubella eggs and hatchlings. Consequently, the negative impact of Bufo on populations of L. ornatus tadpoles reduced the intensity of predation by L. ornatus tadpoles on L. rubella eggs and hatchlings, thereby increasing L. rubella survival. The results demonstrate that B. marinus plays an important role in structuring native larval anuran communities via direct and indirect mechanisms, and that Bufo may have both negative and positive effects on populations of native anuran larvae. As far as I am aware, these are the first quantitative data to demonstrate that introduced fauna may affect populations of native biota via toxic effects.     

Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

相似文献   

Nematode larvae (order Spirurida) in gastric tissues of Australian anurans: a comparison between the introduced cane toad and sympatric native frogs

The outcomes of host-parasite interactions depend heavily on the host's immune response, which, in turn, is governed by previous interactions between the host and parasite, both over the host's life time and over evolutionary time. In the case of species introductions, such as the cane toad (Bufo marinus) to Australia, parasites that are benign to native species of the introduced range may present a major challenge to the introduced species. Stomachs of introduced cane toads and seven species of sympatric native frogs were examined for parasites, and their pathology and biology were compared. Cane toads were host to eight species of third-stage spirurid larvae, six of which also occurred in the stomach wall of four native frog species. In general, encysted nematode larvae attained higher prevalence and species richness in introduced cane toads than in sympatric native frogs. This trend was largely explained by differences in body sizes: larger anurans were more likely to possess infections, and cane toads are inherently larger than native frogs. Encysted larvae in cane toad stomachs provoked a marked pathologic response. All larvae (physalopterine and Physocephalus spp.) were surrounded by concentric layers of dense, fibrous tissue, with considerable cellular infiltration characterized by lymphocytes and polymorphs. Many cysts were invaded by cells and exudate, which, in more advanced cases, became calcified. Some larvae appeared viable; most were in various stages of destruction, and some smaller Physocephalus spp. were mummified. Conversely, pathologic response observed in native frogs was minimal, with little fibrotic reaction surrounding the cysts, and no cellular infiltration. Presumably, the contrast in pathology between introduced and native hosts reflects the long evolutionary association between these nematode larvae and native frogs, whereas the recent exposure of introduced toads to these helminths provokes a severe reaction.     

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.     

Determining the effects of introduced species

People have moved species around the world for millenia, sometimes by accident, but often with considerable enthusiasm. English garden birds in New Zealand are merely quaint curiosities introduced by settlers wanting the familiar species of their former homes. Some introductions have been devastating - goats or rabbits on various islands, for example. Other introductions, such as those of genetically engineered organisms, present potential problems yet to be considered in any detail. What should we expect the impact of introduced species to be?     

Man and other introduced organisms

Man's tremendously increased migratory potention, coupled with his ability to transport any material, causes ecological revolutions on most islands of this world–Fernandina and most smaller islands of the Galapagos being fortunate exceptions to that rule. It is proposed to make distinctions between species colonizing the Galapagos We can distinguish between those immigrant species which do not profit from man as a transport medium (independent immigrants) and those who do depend on him (man-dependent immigrants). These immigrants, in turn, may or may not be able to settle and these settlers may either gain a footing with or without depending on man's direct or indirect influence on the habitat (non-settlers, primary resource-using settlers, and secondary resource-using settlers). Introduced species represent a terrible attack on the biotic uniqueness of the Galapagos ecosystems. However, it is proposed to make better use of the scientific value of these introductions. For example, a case of selective impact of an introduced on an indigenous species was investigated: lava lizards of the genus Tropidurus seem to be more wary of moving objects on islands where cats have been introduced by man than on islands free of cats.
Under the peculiar Galapagos conditions it may turn out that science's most difficult and important task is to investigate and interpret man's role in such places.     

Competition between the larvae of the introduced cane toad Bufo marinus (Anura: Bufonidae) and native anurans from the Darling Downs area of southern Queensland

Bufo marinus (L) has been present in the northern edge of the Darling River catchment for more than 25 years and the species currently occupies an area north of Chinchilla on the northern Darling Downs. This paper reports on preliminary findings of competition trials between larvae of B. marinus and native anurans in the Darling Downs area. Trials conducted in artificial ponds (1.4 × 1.2 × 0.2 m) indicated that Bufo reduced the growth of three native species (Limnodynastes tasmaniensis (Gunther), Limnodynastes terraereginae (Fry) and Notaden bennetti (Gunther)), and in some trials reduced the survival of two species (L. tasmaniensis and L. terraereginae). A fourth species (Limnodynastes ornatus (Grey)) showed higher growth rates with Bufo resulting from a non-significant reduction in survival in those treatments. One of two trials conducted in enclosures (1.0 × 0.5 × 0.4 m) placed in a permanent water body indicated that B. marinus had a negative effect on growth of L. tasmaniensis. A survey of 30 breeding sites in the area found that Bufo used only a small number of water bodies in one breeding season and showed little overlap of pool use with most native species. Therefore, although B. marinus may negatively affect growth and survival of native anurans under some circumstances, the potential impact of B. marinus may be minimal if there are always many breeding sites where native anurans can breed in the absence of B. marinus. A more extensive assessment of temporal and spatial overlap of water body use by B. marinus and native anurans is needed to understand the exact impact of B. marinus in this region.     

Ranking introduced into phenological recording

Generally, phenological recording is based on the recognition of separate phases of development in the organism of interest. In the present study samples were ranked with respect to the stage of bud or leaf development reached at the time of sampling. In April 1982 budding and leaf development of all species of trees and shrubs were recorded over 2 km² of the northeastern slope of Nävlingeåsen, a horst in southernmost Sweden. During 3 days, of which the first two were consecutive, the author walked a stretch of 12 km, divided into 107 sections. In each of these the first living twig at about 1.5 m above ground was sampled for each species. At the end of the day all twigs from the same species were ranked by two persons independently. The ranks were normalized, and a mean calculated for each section. To reduce the impact of natural variation within a species, and also the influence of microclimate where species cluster, the ranks of the sections were smoothed by weighted moving averages. Using three localities which were investigated twice as fixed points, the ranking lists of separate days were integrated into a single system. A time lag of 4 or 5 days in the onset of spring was established between different localities.     

Detection of Paenibacillus larvae subspecies larvae spores in naturally infected bee larvae and artificially contaminated honey by PCR

American foulbrood (AFB), a severe bacterial disease of honeybee brood, has recently been found in Uruguayan apiaries. Detection of the causative agent, Paenibacillus larvae subspecies larvae, is a very important concern in order to prevent disease dissemination and decrease of honey production. Since spores are the infective forms of this pathogen, in the present work we report the use of polymerase chain reaction (PCR) to detect P. l. subsp. larvae spores from in vitro cultures, larvae with clinical symptoms and experimentally contaminated honey. The set of primers was designed based on the published P. l. subsp. larvae 16S rRNA gene. Using this approach we could amplify the pathogen DNA and obtain a great sensitivity and a notable specificity. Detection limit for spore suspension was a 10^–2 dilution of template DNA obtained from 32 spores, as determined by plate count. For artificially contaminated honey, we could detect the PCR product at a 10^–3 dilution of template DNA obtained from 170 spores. In addition, when PCR conditions were set to improve specificity, we were able to amplify P. l. subsp. larvae DNA selectively and no cross-reactions were observed with a variety of related bacterial species, including P. l. subsp. pulvifaciens. Since spore detection is very important to confirm the presence of the disease, this method provides a reliable diagnosis of AFB from infected larvae and contaminated honey in a few hours.     

Competitive abilities of introduced and native grasses

Differencesin competitive ability may explain the maintenance of existing plantpopulationsand the invasion of new areas by plant species. We used field experiments toexamine the competitive responses of Agropyron cristatum(L.) Gaertn., an introduced C₃ grass, and Boutelouagracilis (HBK.) Lag., a native C₄ grass, and thecompetitive effects of Agropyron-dominated vegetation andsuccessional prairie. We also tested whether the outcome of competitiveinteractions varied with water availability. In each vegetation type,transplants of each species were grown under two levels of competition(presenceor absence of neighboring vegetation) and three levels of water availability(high, medium, or low). Transplant survival, growth, and biomass allocationpatterns were measured. Water availability had no effect on the measuredvariables, suggesting that both species were limited by another resource.Growthrates were affected more by competition, while survival and root: shoot ratiowere affected more by transplant species identity. In the successional prairie,neighboring vegetation suppressed the growth of Agropyrontransplants less than that of Bouteloua transplants,suggesting that Agropyron has a stronger ability to resistcompetitive suppression in that vegetation type. The spread ofAgropyron into surrounding vegetation may relate to itsability to resist competitive suppression. In theAgropyron-dominated vegetation, neighboring vegetationsuppressed the growth of both species by the same extent. However, competitionaccounted for more variation in transplant growth inAgropyron-dominated vegetation than in successionalprairie, suggesting that Agropyron has strong competitiveeffects which hinder plant growth and prevent other species from establishinginAgropyron fields.     

The difficulty of reducing introduced wasp (

Introduced common wasps (Vespula vulgaris) are widespread, abundant pests in New Zealand. They compete for food with native birds and feed on native invertebrates. We poisoned wasps annually over 4 years to see if it was possible to reduce their abundance in two 30-ha beech forest sites. Two different poisons (sodium monofluoroacetate and sulfluramid) were used, mixed with sardine catfood. There was no evidence that one poison was more effective than the other. Between 82 and 100% of the colonies were killed in the poisoned sites, but reinvasion by foraging workers meant that cumulative wasp biomass (measured using Malaise traps) was reduced by only 55- 70%. Individual wasps were about 16% heavier in the poisoned sites at the Peak of the wasp season (March) than in the non- poisoned sites, although this had a minimal effect on cumulative biomass over the entire season. Conservation gains need to be quantified in order to assess whether the expense of such poisoning operations is warranted.     

Delayed population explosion of an introduced butterfly

1. The causes of lagged population and geographical range expansions after species introductions are poorly understood, and there are relatively few detailed case studies. 2. We document the 29-year history of population dynamics and structure for a population of Euphydryas gillettii Barnes that was introduced to the Colorado Rocky Mountains, USA in 1977. 3. The population size remained low (< 200 individuals) and confined to a single habitat patch (approximately 2.25 ha) to 1998. These values are similar to those of many other populations within the natural geographical range of the species. 4. However, by 2002 the population increased dramatically to > 3000 individuals and covered approximately 70 ha, nearly all to the south of the original site. The direction of population expansion was the same as that of predominant winds. 5. By 2004, the butterfly's local distribution had retracted mainly to three habitat patches. It thus exhibited a 'surge/contraction' form of population growth. Searches within 15 km of the original site yielded no other new populations. 6. In 2005, butterfly numbers crashed, but all three habitat patches remained occupied. The populations within each patch did not decrease in the same proportions, suggesting independent dynamics that are characteristic of metapopulations. 7. We postulate that this behaviour results, in this species, in establishment of satellite populations and, given appropriate habitat structure, may result in lagged or punctuated expansions of introduced populations.     

Estimating the invasion success of introduced plants

We present methods for estimating the base proportion of introduced alien species that will naturalize, and the distribution of time until naturalization occurs. The approach is Bayesian, incorporating prior estimates of the probability of naturalization and the time from introduction to naturalization. A worked example uses data on the introduction and time to recorded naturalization of woody perennials introduced to South Australia. Up until 2007, 188 of 2230 (8.4%) woody perennials listed in nursery catalogues between 1843 and 1985 were recorded as having naturalized. If prior information on naturalization rates from elsewhere is ignored, the available data suggest that the most likely proportion of introduced plants that will naturalize is large (0.93) though uncertain (95% CI 0.51–0.99), with the corresponding mean time to recorded naturalization being protracted (522 years) and similarly uncertain (95% CI 360–678 years). Alternatively, if informative prior estimates of both the naturalization probability and the time to recorded naturalization are incorporated, the most likely probability of naturalization is estimated to be 18.6% (95% CI 15.5–23.4%). For those plants that do naturalize, the most likely value for the mean time from importation to recorded naturalization is 149 years (95% CI 130–174 years). Our results illustrate the potentially long timescale of the naturalization process, and the challenges this presents for obtaining accurate estimates of naturalization parameters.