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1.
Andrew P. Norton Amy C. Blair Janet G. Hardin Scott J. Nissen Galen R. Brunk 《Biological invasions》2008,10(1):79-88
Biological control of weeds by arthropod herbivores is thought to work by reducing the competitive ability of the weed relative
to the surrounding vegetation. However, the assumption that herbivory reduces plant competitive ability has not been tested
in most biological control systems, and counter to expectation, recent research on the impact of biological control agents
on invasive Centaurea species suggests that this genus may respond to herbivory by increased competitive ability through enhanced plant re-growth
and/or by inducing increased production of phytotoxic allelochemicals. We examined the impact of two biological control agents
of the invasive plant diffuse knapweed (C. diffusa) to see if feeding by either of these insects would enhance the plant’s competitive ability or allelochemical output. Sub-lethal
herbivory by either of the biological control agents significantly reduced knapweed performance when the plant was grown in
competition with either of two native species. Competition with knapweed significantly reduced the performance of both native
species (Artemisia frigida and Bouteloua gracilis), and herbivory by one of the biocontrol agents resulted in a small but significant increase in both native species’ performance.
Diffuse knapweed’s putative allelochemical 8-hydroxyquinoline was not detected in experimental or field collected soils from
knapweed-infested sites. In contrast to other studies on the impacts of biological control on other Centaurea species, these data support the premise that biological control agents may reduce invading plant competitive ability. We
find no evidence for diffuse knapweed allelopathy mediated by 8-hydroxyquinoline or enhanced allelopathy in response to herbivory
by biological control agents. 相似文献
2.
Soil modification by invasive plants: effects on native and invasive species of mixed-grass prairies 总被引:1,自引:0,他引:1
Invasive plants are capable of modifying attributes of soil to facilitate further invasion by conspecifics and other invasive
species. We assessed this capability in three important plant invaders of grasslands in the Great Plains region of North America:
leafy spurge (Euphorbia esula), smooth brome (Bromus inermis) and crested wheatgrass (Agropyron cristatum). In a glasshouse, these three invasives or a group of native species were grown separately through three cycles of growth
and soil conditioning in both steam-pasteurized and non-pasteurized soils, after which we assessed seedling growth in these
soils. Two of the three invasive species, Bromus and Agropyron, exhibited significant self-facilitation via soil modification. Bromus and Agropyron also had significant facilitative effects on other invasives via soil modification, while Euphorbia had significant antagonistic effects on the other invasives. Both Agropyron and Euphorbia consistently suppressed growth of two of three native forbs, while three native grasses were generally less affected. Almost
all intra- and interspecific effects of invasive soil conditioning were dependent upon presence of soil biota from field sites
where these species were successful invaders. Overall, these results suggest that that invasive modification of soil microbiota
can facilitate plant invasion directly or via ‘cross-facilitation’ of other invasive species, and moreover has potential to
impede restoration of native communities after removal of an invasive species. However, certain native species that are relatively
insensitive to altered soil biota (as we observed in the case of the forb Linum lewisii and the native grasses), may be valuable as ‘nurse’species in restoration efforts. 相似文献
3.
Betsy Von Holle Katherine. A. Joseph Erin F. Largay Rebecca G. Lohnes 《Biodiversity and Conservation》2006,15(7):2197-2215
Robinia pseudoacacia, a nitrogen-fixing, clonal tree species native to the central Appalachian and Ozark Mountains, is considered to be one of
the top 100 worldwide woody plant invaders. We initiated this project to determine the impact of black locust (Robinia pseudoacacia) on an upland coastal ecosystem and to estimate the spread of this species within Cape Cod National Seashore (CCNS). We censused
20 × 20 m plots for vegetation cover and environmental characteristics in the center of twenty randomly-selected Robinia pseudoacacia stands. Additionally, paired plots were surveyed under native overstory stands, comprised largely of pitch pine (Pinus rigida) and mixed pitch pine–oak (Quercus velutina and Quercus alba) communities. These native stands were located 20 m from the edge of the sampled locust stand and had similar land use histories.
To determine the historical distribution of black locust in CCNS, we digitized and georeferenced historical and current aerial
photographs of randomly-selected stands. Ordination analyses revealed striking community-level differences between locust
and pine–oak stands in their immediate vicinity. Understory nonnative species richness and abundance values were significantly
higher under Robinia stands than under the paired native stands. Additionally, animal-dispersed plant species tended to occur in closer stands,
suggesting their spread between locust stands. Robinia stand area significantly decreased from the 1970’s to 2002, prompting us to recommend no management action of black locust
and a monitoring program and possible removal of associated animal-dispersed species. The introduction of a novel functional
type (nitrogen-fixing tree) into this xeric, nutrient-poor, upland forested ecosystem resulted in ‘islands of invasion’ within
this resistant system. 相似文献
4.
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. 相似文献
5.
R. H. Marrs M. G. Le Duc S. M. Smart K. J. Kirby R. G. H. Bunce P. M. Corney 《Kew Bulletin》2010,65(4):583-594
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. 相似文献
6.
Sanon A Martin P Thioulouse J Plenchette C Spichiger R Lepage M Duponnois R 《Mycorrhiza》2006,16(2):125-132
Gmelina arborea Roxb. (Gmelina, Yemane) is a fast growing tree, native from India and considered as a potentially invasive woody plant in
West Africa. Mycorrhizal inoculation of seedlings with Glomus intraradices was performed to study (1) the effect on the growth of G. arborea, (2) the impact on the catabolic diversity of soil microbial communities and (3) the influence on the structure of herbaceous
plant species communities in microcosms. Treatments consisted of control plants, pre-planting fertilizer application and arbuscular
mycorrhizal (AM) inoculation. After 4 months’ culture in autoclaved soil, G. arborea seedlings were either harvested for growth measurement or transferred into containers filled with the same soil but not sterilized.
Other containers were kept without G. arborea seedlings. After 12 months’ further culture, effects of fertilizer amendment and AM inoculation on the growth of G. arborea seedlings were recorded. AM colonization was significantly and positively correlated with plant diversity. The substrate-induced
respiration response to carboxylic acids was significantly higher in the absence of G. arborea and in the presence of G. intraradices as compared to the other treatments. The influence of AM symbiosis on plant coexistence and on allelopathic processes of
invasive plants are discussed. 相似文献
7.
Exotic plant invaders that form monocultures and exclude native plants are often the most detrimental to native diversity
and the hardest to eradicate. To generate a monoculture, the invader must garner more resources than resident natives and,
once established, persist despite high densities of conspecific neighbors. Coincident with expansion and long-term persistence,
successful invaders typically accumulate senesced material, but the role of this litter in mediating the invader’s ability
to establish and maintain monospecific dominance has rarely been investigated. We used stands of the common reed, Phragmites australis, a prolific wetland invader in North America, to explore the impact of litter on interspecific competition with the native
rush, Juncus gerardii, and intraspecific competition among live shoots. In 10 × 10 m areas positioned on Phragmites expansion fronts, we removed litter to isolate its effect from live Phragmites on light availability, aboveground biomass and community composition. Compared to adjacent, unmanipulated fronts, light availability nearly tripled and Juncus biomass increased >170% in litter removal areas after 4 months. Although the positive response of Juncus and native forbs was most pronounced on the leading edge of Phragmites stands, litter removal triggered a 271% increase in native plant biomass even in the interior of stands where Phragmites’ live stem density was highest. Litter treatment did not significantly affect Phragmites biomass, but more, shorter stems emerged in litter removals revealing Phragmites modifies stem phenotype in response to local litter and light conditions. These results suggest that litter plays a central
role in Phragmites’ invasion process, from initial establishment to subsequent monospecific dominance. Thus, prescribed litter removal may be
an effective strategy to enhance coexistence of native plant populations in wetlands where eradication of invasive monocultures
is not an ecologically or economically feasible option. 相似文献
8.
Cameron W. Barrows Edith B. Allen Matthew L. Brooks Michael F. Allen 《Biological invasions》2009,11(3):673-686
Given the abundance of non-native species invading wildland habitats, managers need to employ informed triage to focus control
efforts on weeds with the greatest potential for negative impacts. Our objective here was to determine the level of threat
Sahara mustard, Brassica tournefortii, represents to meeting regional goals for protecting biodiversity. Sahara mustard has spread throughout much of the Mojave
and lower Sonoran Deserts. It has occurred in southern California’s Coachella Valley for nearly 80 years, punctuated by years
of extremely high abundance following high rainfall. In those years the mustard has clear negative impacts on the native flora.
Using mustard removal experiments we identified reductions in native plant reproduction, shifting composition increasingly
toward Sahara mustard while decreasing the fraction of native species. High between-year variance in precipitation may be
a key to maintaining biodiversity as the mustard is less abundant in drier years. Sahara mustard impacts to the native fauna
were much less evident. Of the animal species evaluated, only the Coachella Valley fringe-toed lizard, Uma inornata, demonstrated a negative response to mustard abundance; however the impacts were short-lived, lasting no more than a year
after the mustard’s dominance waned. Without control measures the long-term impacts to desert biodiversity may rest on the
changing climate. Wetter conditions or increased periodicity of high rainfall years will favor Sahara mustard and result in
reduced biodiversity, especially of native annual plants. Drier conditions will keep the mustard from becoming dominant but
may have other negative consequences on the native flora and fauna. 相似文献
9.
Restoration of mangrove plantations and colonisation by native species in Leizhou bay,South China 总被引:1,自引:0,他引:1
Hai Ren Shuguang Jian Hongfang Lu Qianmei Zhang Weijun Shen Weidong Han Zuoyun Yin Qinfeng Guo 《Ecological Research》2008,23(2):401-407
To examine the natural colonisation of native mangrove species into remediated exotic mangrove stands in Leizhou Bay, South
China, we compared soil physical–chemical properties, community structure and recruitments of barren mangrove areas, native
mangrove species plantations, and exotic mangrove species—Sonneratia apetala Buch.Ham—between plantations and natural forest. We found that severely degraded mangrove stands could not regenerate naturally
without human intervention due to severely altered local environments, whereas some native species had been recruited into
the 4–10 year S. apetala plantations. In the first 10 years, the exotic species S. apetala grew better than native species such as Rhizophora stylosa Griff and Kandelia candel (Linn.) Druce. The mangrove plantation gradually affected soil physical and chemical properties during its recovery. The
exotic S. apetala was more competitive than native species and its plantation was able to restore soil organic matter in about 14 years. Thus,
S. apetala can be considered as a pioneer species to improve degraded habitats to facilitate recolonisation by native mangrove species.
However, removal to control proliferation may be needed at late stages to facilitate growth of native species. To ensure sustainability
of mangroves in South China, the existing mangrove wetlands must be managed as an ecosystem, with long-term scientific monitoring
program in place. 相似文献
10.
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. 相似文献
11.
Exotic plants may act as population sinks or evolutionary traps for native herbivores. The native butterfly Pieris oleracea lays eggs on garlic mustard, Alliaria petiolata, but larvae develop very poorly on this exotic invasive plant. We examined oviposition preference of individual females and
larval performance of their offspring for individuals from one area where garlic mustard is well established and one where
it is absent. These data were used to assess whether garlic mustard is being incorporated into or excluded from the diet.
Females from the area without garlic mustard showed a wide range of preference, families had low larval survival on garlic
mustard, and larval survivorship showed no correlation with mothers’ preferences. Females from the area with garlic mustard
preferred it to the native host, and larval survivorship on garlic mustard was positively correlated with the mother’s preference.
Individuals surviving on garlic mustard took longer to pupate and weighed >30% less compared to pupae reared on normal hosts.
Our results suggest that where garlic mustard is well established P. oleracea may be adapting to this plant by both improved larval performance and increased adult female oviposition preference for it. 相似文献
12.
Alien species’ resistance and adjustment to water stress and plant competition might largely determine the success of invasions
in Mediterranean ecosystems because water availability is often limiting biomass production. Two outdoor pot experiments were
conducted to test the hypotheses that at the recruitment stage the invader perennial tussock grass Cortaderia selloana is a superior competitor, and that it is more resistant to water stress than the two coexisting native species of the same
functional group, Festuca arundinacea and Brachypodium phoenicoides. C. selloana reduced aboveground biomass of target native species, but not more than target native species on each other. Moreover, C. selloana did not resist interspecific competition more than target native species. Under control conditions, C. selloana did not have larger specific leaf area (SLA) and root–shoot ratio (R/S) ratio than target native species, contradicting the
general statement that these traits are associated to invasiveness. F. arundinacea was the species which performed best but also the one most affected by water stress. Both C. selloana and B. phoenicoides performed in a similar way under water stress conditions. However, the alien species’ capacity to adjust to water stress,
indicated by the increase in the root–shoot ratio under moderate and severe water stress, was slightly better than that of
B. phoenicoides. Overall, at early recruitment stages, C. selloana is not a better competitor than the coexisting native species. However, it seems to be more resistant to water stress because
as water becomes scarce C. selloana maximizes water uptake and minimizes water losses more than the native species. 相似文献
13.
Frank J. Wessels James P. Cuda M. Tracy Johnson José Henrique Pedrosa-Macedo 《BioControl》2007,52(4):439-449
Strawberry guava, Psidium cattleianum Sabine, is a woody tree or shrub native to coastal southeastern Brazil. Strawberry guava was introduced into Florida in the
late 1800s as an ornamental species. The plant escaped cultivation and is invading natural areas throughout the southern half
of the state. In addition to negative effects on Florida’s native ecosystems, strawberry guava also is a preferred host of
the Caribbean fruit fly, Anastrepha suspensa Loew (Diptera: Tephritidae).
In total, 57 plant species representing 21 families were included in the host range tests. First instar nymphs of Tectococcus ovatus Hempel fed on two closely related guava species, Brazilian guava (Psidium friedrichsthalianum O. Berg), and Costa Rican guava (Psidium guineense Sw.). However, none of the nymphs completed their development on these two non-target species. The results of the host specificity
tests suggest that T. ovatus is a suitable candidate for classical biological control of strawberry guava in Florida. 相似文献
14.
K. Jun Bando 《Biological invasions》2006,8(4):755-763
Two hypotheses for the decline of native species are the superior exploitation of disturbance by exotic species and the competitive displacement of native species by their exotic counterparts. Theory predicts that functional similarity will increase the intensity of competition between native and invasive species. Ecologically important “foundation” species, Zostera marina and other seagrasses have globally declined during the past century. This study used transplant and vegetation removal experiments to test the hypotheses that disturbance and competitive interactions with an invasive congener (Z. japonica) are contributing to the decline of native Z. marina in the northeastern Pacific. Interspecific competition reduced Z. marina and Z. japonica above-ground biomass by 44 and 96%, respectively, relative to intraspecific competition. Disturbance substantially enhanced Z. japonica productivity and fitness, and concomitantly decreased Z. marina performance, effects that persisted two years following substratum disturbance. These results demonstrate that disturbance and competitive interactions with Z. japonica reduce Z. marina performance, and suggest that Z. japonica’s success as an invasive species stems dually from its ability to persist in competition with Z. marina and its positive response to disturbance. These results highlight the importance of understanding the interconnected roles of species interactions and disturbance in the decline of seagrass habitats, and provide a rationale for amending conservation policy in Washington State. In the interest of conserving native eelgrass populations, the current policy of protecting both native and invasive Zostera spp. should be refined to differentiate between native and invader, and to rescind the protection of invasive eelgrass. 相似文献
15.
Ninety isolates of root nodule bacteria from an invasive Mimosa pigra population in Australia were characterized by PCR assays and by sequencing of ribosomal genes. All isolates belonged to the
same bacterial genus (Burkholderia) that predominates on M. pigra in its native geographic range in tropical America. However, the Australian Burkholderia strains represented several divergent lineages, none of which had a close relationship to currently known Burkholderia strains in American M. pigra populations. Inoculation of M. pigra with Australian strains resulted in equal or higher plant growth and nodule nitrogenase activity (measured by acetylene reduction
assays) relative to outcomes with bacteria from M. pigra’s native geographic region. The main difference in symbiotic phenotype for bacteria from the two regions involved responses
to an alternate Mimosa host species: Central American strains failed to fix nitrogen in association with Mimosa pudica, while most Australian Burkholderia isolates tested had high nodule nitrogenase activity in association with both Mimosa species. Invasive M. pigra populations in Australia have therefore acquired a diverse assemblage of nodule bacteria that are effective nitrogen-fixing
symbionts, despite having a broader host range and a distant genetic relationship to bacterial strains found in the plant’s
ancestral region. 相似文献
16.
Samples issued from intensive sampling in the Netherlands (1992–2001) and from extensive sampling carried out in the context
of international campaigns (1998, 2000 and 2001) were revisited. Additional samples from artificial substrates (1992–2003)
and other techniques (various periods) were analysed. The combined data provide a global and dynamic view on the Peracarida
community of the River Meuse, with the focus on the Amphipoda. Among the recent exotic species found, Crangonyx pseudogracilisis regressing, Dikerogammarus haemobaphesis restricted to the Condroz course of the river, Gammarus tigrinusis restricted to the lowlands and seems to regress, Jaera istriis restricted to the ‘tidal’ Meuse, Chelicorophium curvispinumis still migrating upstream into the Lorraine course without any strong impact on the other amphipod species. After a rapid
expansion Dikerogammarus villosushas continued its upstream invasion between 1998 and 2002 at a rate of 30–40 km per year, but no further progression was noticed
in 2003. Locally and temporarily the native species (Gammarus fossarum and G. pulex) and naturalized species (G. roeseliand Echinogammarus berilloni)mayhave been excluded by the most recent invaders (mainly D. villosus), but none of the native and naturalized species has disappeared completely. Therefore, the number of amphipod species found
in the River Meuse has increased. Moreover, the native and naturalized species keep on dominating the tributaries from which
the recent invaders seem to be excluded. A changing Peracarida community structure is observed along the course of the River
Meuse: four native or naturalized species inhabit the upstream (Lorraine) course, three invasive species dominate in the middle
reach (Ardenne-Condroz zone), one exotic species is housed in the Border Meuse and three or four invasive species dominate
the assemblages in the lowlands. 相似文献
17.
Exotic plant invasion may alter underground microbial communities, and invasion-induced changes of soil biota may also affect
the interaction between invasive plants and resident native species. Increasing evidence suggests that feedback of soil biota
to invasive and native plants leads to successful exotic plant invasion. To examine this possible underlying invasion mechanism,
soil microbial communities were studied where Ageratina adenophora was invading a native forest community. The plant–soil biota feedback experiments were designed to assess the effect of invasion-induced
changes of soil biota on plant growth, and interactions between A. adenophora and three native plant species. Soil analysis showed that nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), and available P and K content were significantly higher in a heavily invaded site than in a newly invaded site. The structure
of the soil microbial community was clearly different in all four sites. Ageratina adenophora invasion strongly increased the abundance of soil VAM (vesicular-arbuscular mycorrhizal fungi) and the fungi/bacteria ratio.
A greenhouse experiment indicated that the soil biota in the heavily invaded site had a greater inhibitory effect on native
plant species than on A. adenophora and that soil biota in the native plant site inhibited the growth of native plant species, but not of A. adenophora. Soil biota in all four sites increased A. adenophora relative dominance compared with each of the three native plant species and soil biota in the heavily invaded site had greater
beneficial effects on A. adenophora relative dominance index (20% higher on average) than soil biota in the non-invaded site. Our results suggest that A. adenophora is more positively affected by the soil community associated with native communities than are resident natives, and once
the invader becomes established it further alters the soil community in a way that favors itself and inhibits natives, helping
to promote the invasion. Soil biota alteration after A. adenophora establishment may be an important part of its invasion process to facilitate itself and inhibit native plants. 相似文献
18.
A semi-field experiment was carried out in two peach orchards in northern Italy to assess mortality due to predators and parasitoids
on the exotic coccinellid Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) in comparison with the native coccinellid Adalia bipunctata L. (Coleoptera: Coccinellidae). The experiments were conducted in cages to avoid the possible escape of the exotic ladybird
(not yet established in Italy). Two kinds of cage experiments were included: ‘exclusion cages’ (access by walking predators
impeded) and ‘free cages’ (walking predators free to enter). The cages, containing all the stages of the two ladybird species,
were placed in two localities and left for 24 h. All ladybird stages used for the semi-field experiments came from a laboratory
rearing. The eggs of H. axyridis experienced less mortality than those of A. bipunctata. The ant workers were the most frequent predators in ‘free cages’ but A. bipunctata cannibalism on eggs was also detected. Larvae of both coccinellid species were predated equally but larval predation of L1
and L2 was higher in comparison to predation of L3 and L4. Pupae and adults of both exotic and native ladybirds were never
attacked by predators. Predation on younger larval stages was higher in the ‘free cages’ in comparison with ‘exclusion cages’.
No ladybird parasitisation was observed. The ‘free cage’ technique seems to provide a standardised and realistic estimation
of predation impact but more studies are needed to evaluate ladybird parasitisation in semi-field conditions. 相似文献
19.
Consistent performance of invasive plant species within and among islands of the Mediterranean basin
Anna Traveset Giuseppe Brundu Luisa Carta Irene Mprezetou Philip Lambdon Manuela Manca Frédéric Médail Eva Moragues Javier Rodríguez-Pérez Akis-Stavros D. Siamantziouras Carey M. Suehs Andreas Y. Troumbis Montserrat Vilà Philip E. Hulme 《Biological invasions》2008,10(6):847-858
Since the success of an invasive species depends not only upon its intrinsic traits but also on particular characteristics
of the recipient habitat, assessing the performance of an invader across habitats provides a more realistic analysis of risk.
Such an analysis will not only provide insights into the traits related to invasiveness, but also the habitat characteristics
that underpin vulnerability to invasion that, taken together, will facilitate the selection of management strategies to mitigate
the invader’s effect. In the present study, we considered the Mediterranean basin islands as an excellent study region to
test how the same invasive species perform in different habitats within a single island, and to scale up differences among
islands with similar climate. We tested how the performance of three widespread plant invaders with clonal growth but contrasting
life-history traits, a deciduous tree Ailanthus altissima, a succulent subshrub Carpobrotus spp., and an annual geophyte Oxalis pes-caprae, varied depending upon the species identity, habitat, and invaded island. The environmental parameters considered were habitat
type, elevation, species diversity in the invaded plot, and several soil traits (% C, % N, C/N, pH, and relative humidity).
The study documents that the performance of these three important and widespread plant invaders is dependent mainly on species
identity, and less upon the invaded island’s general features. Likewise, differences in performance among habitats were only
significant in the case of Ailanthus, whereas Carpobrotus and Oxalis appear to perform equally well in different environments. Ailanthus thus appears to have a broader spectrum of invasiveness, being able to invade a larger number of habitat types. On the contrary,
Carpobrotus spp. have not yet invaded habitats different from those where the species have been originally introduced and where they
are still commonly spread by humans. Oxalis distribution is mainly related to agricultural activities and disturbed sites, and the total area infested by this geophyte
may be more reflection of the extent of suitable habitats than of invasiveness or ecological impact. Our results confirm the
potential for these species to significantly alter the functioning of ecosystems in the Mediterranean islands and highlight
the risk to other islands not yet invaded. 相似文献
20.
The success of many alien plant species depends on mutualistic relationships with other species. We describe the assemblage
of seed dispersers on three species of alien Opuntia invading Mediterranean and Macaronesian habitats, and examine the quality of such plant-animal interactions. We identified
vertebrates consuming O. maxima, O. dillenii and O. stricta fruits by direct observation and collecting droppings and pellets. Phenology of the alien species, as well as that of coexisting
native species, was monitored for an entire year. Germination tests of ingested and non-ingested seeds were performed both
in the greenhouse and in the field. Seed coat thickness and viability were also measured for all treatments. A great variety
of taxa, including reptiles, birds and mammals actively participate in the seed dispersal of Opuntia. Phenology of Opuntia fruits in Menorca and Tenerife overlaps with only a few native fleshy-fruited plants present in the study areas, which suggests
an advantage for the invader. Most seeds germinated during the second year of the experiment, independently of the effect
produced by the dispersers’ guts. We found great variation in the germination percentage of Opuntia after gut passage and in the effects of ingestion on seed coat thickness. Seed viability was somewhat reduced after gut passage
compared to manually depulped seeds. Our results show how different Opuntia species are integrated into native communities by means of mutualistic interactions, with both native and alien dispersers.
Although with heterogeneous effects, either type of disperser potentially contributes to the spread of these alien cacti in
the recipient areas. 相似文献