The role of seabirds and seals in the survival of coastal plants: lessons from New Zealand Lepidium (Brassicaceae)

Six of the eight indigenous New Zealand Lepidium species are coastal, and have restricted or reduced distributions. One is extinct and the remainder are considered threatened with extinction. This limited distribution is in marked contrast to their apparent abundance in the eighteenth and early nineteenth centuries (1760s–1830s). Accounts from the voyages of Cook, Surville and d'Urville describe L. oleraceum as an abundant coastal plant which was collected extensively for use as an antiscorbutic. However, by the late 19th century, resident botanists were expressing concern about the marked decline in coastal species of Lepidium, a decline which has continued to the present. Ecologically, coastal species of Lepidium are similar, being restricted to open sites often close to the high tide mark. They are commonly associated with bird colonies, and occasionally with fur seal colonies. Traditionally their decline has been attributed to introduced herbivores. However, wild grazing animals were not common until the end of the 19th century, well after the initial decline had occurred. Other possible reasons for their decline include herbivory and predation by rats, and by fungal and invertebrate pests of cultivated Brassicaceae, overcollecting and coastal development. However, we suggest that a major factor in the decline of coastal Lepidium species was a decline in coastal seabirds through predation and seals through culling. Seabirds and seals are critical for the survival of Lepidium species by keeping sites open through disturbance, dispersing seed, and providing nutrient enrichment for plant growth, and their loss has resulted in decline of habitat for Lepidium.     

Distribution and forage use of exotic bumblebees in South Island, New Zealand

The rapid decline in bumblebee populations within Europe has been linked to habitat loss through agricultural intensification, and a consequential reduction in the availability of preferred forage plants. The successful introduction of four European Bombus species to the South Island of New Zealand from England (in 1885 and 1906) provides an opportunity to determine how important different forage plants (also introduced from the U.K.) are to two severely threatened European bumblebee species (Bombus ruderatus and B. subterraneus). In January 2003 we conducted a survey of bumblebee populations across 70 sites in the central and southern South Island, recording which plant species were being used as pollen and nectar sources for each Bombus species. All four bumblebee species showed a clear preference for plants of European origin. Only B. terrestris, the most polylectic species, was recorded feeding on native plant species. The longer-tongued bumblebees, B. hortorum, B. ruderatus, and B. subterraneus, foraged predominantly on just two plant species; Trifolium pratense for both nectar and pollen, and Echium vulgare for nectar. These plant species are now declining in abundance in the U.K. Our results provide support for the hypothesis that the loss of flower-rich meadows, particularly those containing populations of Fabaceae species with long corollae, is responsible for the decline of bumblebee species across Europe. Comparison with earlier bumblebee surveys suggests that long-tongued bumblebees may also be in decline in New Zealand, particularly B. subterraneus which is now very localised and scarce.     

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.     

Effects of plant invasions on the species richness of abandoned agricultural land

While exotic plant invasions are thought to lead to declines in native species, the long-term impacts of such invasions on community structure are poorly known. Furthermore, it is unknown how exotic plant invasions compare to invasions by native species. We present data from 40 yr of continuous vegetation sampling of 10 fields released from agriculture to examine the effects of invasions on species richness. The effects of both exotic and native species invasions on species richness were largely driven by variations among fields with most species not significantly affecting species richness. However, invasion and dominance by the exotics Agropyron repens, Lonicera japonica. Rosa multiflora. Trifolium pratense and the native Solidago canadensis were associated with declines in richness. Invasions by exotic and native species during old field succession have similar effects on species richness with dominance by species of either group being associated with loss of species richness. Exotic species invasions tended to have stronger effects on richness than native invasions. No evidence was found of residual effects of invasions because the impact of the invasion disappeared with the decline of the invading population. When pooled across species, heavy invasion by exotic species resulted in greater loss o species richness than invasion by native species. Studies of invasion that utilize multiple sites must account for variability among sites. In our study, had we no included field as a factor we would have incorrectly concluded that invasion consistently resulted in changes in species richness.     

Relationships between plant diversity,vegetation cover,and site conditions: implications for grassland conservation in the Greater Caucasus

Overgrazing, land use abandonment and increasing recreational activities have altered the vegetation of high-montane and subalpine grassland of the Caucasus. The failure of previous restoration efforts with unsuitable and exotic plant species indicates the need for information on the present vegetation and in which way it might change. Within the Greater Caucasus, we have described and quantified the mountain grassland which develops under characteristic overgrazed and eroded site conditions. Further, we have proposed potential native plant species for revegetation to restore and conserve valuable mountain grassland habitats. We used non-metric dimensional scaling ordination and cluster comparison of functional plant groups to describe a gradient of grassland vegetation cover. For our study region, we identified four major vegetation types with increasing occurrence of ruderal pasture weeds and tall herb vegetation on abandoned hay meadows within the subalpine zone. Within high-montane grassland a decline of plant diversity can be observed on sites of reduced vegetation cover. Due to a low potential of the grassland ecosystem to balance further vegetation cover damage, the long-term loss of diverse habitats can be expected. We conclude with management recommendations to prevent erosion and habitat loss of precious mountain grasslands.     

从有意引入到外来入侵--以意大利蜂Apis mellifera L.为例

原产于欧洲、非洲等地的意大利蜜蜂几个世纪以来被人类频繁地有意引入到其它国家和地区,然而其在带来经济利益的同时,意大利蜂凭借其在诸多方面的竞争优势对当地物种和生态系统产生不利影响。本文主要阐述了意大利蜜蜂引入后对我国本地种——中华蜜蜂造成的负面效应：①中华蜜蜂种群数量急剧下降,甚至在某些地区已到了灭绝的边缘;②影响了以中华蜜蜂作为主要传粉媒介的早花乔木、灌木和草本植物的正常繁育,从而降低了物种多样性,破坏了群落结构及其稳定性。     

Abundance of introduced species at home predicts abundance away in herbaceous communities

Many ecosystems worldwide are dominated by introduced plant species, leading to loss of biodiversity and ecosystem function. A common but rarely tested assumption is that these plants are more abundant in introduced vs. native communities, because ecological or evolutionary-based shifts in populations underlie invasion success. Here, data for 26 herbaceous species at 39 sites, within eight countries, revealed that species abundances were similar at native (home) and introduced (away) sites - grass species were generally abundant home and away, while forbs were low in abundance, but more abundant at home. Sites with six or more of these species had similar community abundance hierarchies, suggesting that suites of introduced species are assembling similarly on different continents. Overall, we found that substantial changes to populations are not necessarily a pre-condition for invasion success and that increases in species abundance are unusual. Instead, abundance at home predicts abundance away, a potentially useful additional criterion for biosecurity programmes.     

Aboveground plant community and seed bank composition along an invasion gradient

Invasive plants can reduce plant diversity and abundance in native grassland communities; however, the effect on the native seed bank is less clear. The objective of this study was to assess the effects of invasion by the exotic grass old world bluestem (OWB; Bothriochloa spp.) on native aboveground plant species composition and seed bank diversity and abundance (i.e., cover, density). In this central Great Plains grassland, OWB invasion had differential effects on native diversity and abundance of both aboveground and seed bank plant communities. Native plant species diversity and cover showed a steep decline as OWB cover increased. No change in native seed density or richness was observed in response to OWB invasion, however, OWB seed density increased with increasing invasion, thus increasing total seed density. Our results indicate that as OWB invasion increases, the native plant community decreases in diversity and abundance. Although, no effect on native seed bank diversity and density was observed in this study, as native seeds are lost through a loss of native species in the plant communities, native seed bank diversity and density is expected to decline.     

Soil moisture dynamics and restoration of self‐sustaining native vegetation ecosystem on an open‐cut coal mine

Post‐mining landscape reconstruction on open‐cut coal mines aims to support restoration of self‐sustaining native vegetation ecosystems that in perpetuity require no extra inputs relative to unmined analogs. Little is known about the soil moisture retention capacity of the limited layer of topsoil replaced (often <30 cm deep), impacts of deep ripping of the profile, and the combined impacts of these on plant available water during the mine restoration process. We examined changes in soil moisture parameters (soil water potential, Ψ, and soil water content, Θ) daily using automated soil sensors installed at 30 and 45–65 cm depths on mine restoration sites aged between 3 and 22 years and on adjacent remnant vegetation sites following heavy rainfall events at Meandu mine, southeast Queensland, Australia. Consistent patterns in soil moisture attributes were observed among rehabilitated sites with generally marked differences from remnant sites. Remnant site soil profiles had generally higher Θ after drying than rehabilitated sites and maintained high Ψ for extended periods after rain events. There was a relatively rapid decline of Ψ on reconstructed soil profiles compared with remnant sites although the times of decline onset varied. This response indicated that vegetation restoration sites released soil moisture more rapidly than remnant sites but the rate of drying decreased with increasing rehabilitation age and increased with increasing tree stem density. The rapid drying of mine rehabilitated sites may threaten the survival of some remnant forest species, limit tree growth, and delay restoration of self‐sustaining native ecosystem.     

Relationships between Scotch broom (Cytisus scoparius), soil nutrients, and plant diversity in the Garry oak savannah ecosystem

Scotch broom (Cytisus scoparius), is a leguminous shrub, native to the Mediterranean, which has invaded most of the remaining Garry oak savannah ecosystems in Oregon, Washington, and British Columbia. Here, it is considered to be a threat to the native plant community. We tested the hypothesis that broom would increase available soil nitrogen by comparing soil nutrients in contiguous broom-invaded and non-invaded sites. We then looked for changes in patterns of diversity in the herbaceous community that might indicate a role of Scotch broom in changing conditions following its invasion. Finally we carried out greenhouse assays to test whether broom had a greater impact on the growth of a native and an introduced grass compared to that of a native shrub. Broom was associated with only a weak trend in increased soil nitrogen, but a significant decrease in soil phosphorus was observed. Patterns of plant diversity differed between two sites. At one site, 60% of the plants whose abundances increased in the broom-invaded plots were introduced species while native species abundances decreased in the broom-invaded plots compared to broom-free plots. At the other site, 60% of the plants that caused the differences between broom-invaded and un-invaded plots were native species that were less abundant in the broom-invaded plots. Finally, in greenhouse assays grass growth was not affected as a result of being grown with broom; however, grasses appeared to produce more flowers when grown with broom. We conclude that broom does not necessarily modify soil nitrogen availability but may deplete soil phosphorus availability and that broom invasion can be associated with increase of exotic species and/or the decline of native species.     

Predation and other factors currently limiting New Zealand forest birds

Holdaway (1989) described three phases of historical extinctions and declines in New Zealand avifauna, the last of which (Group III, declining 1780?1986) was associated with European hunting, habitat clearance, and predation and competition from introduced European mammals. Some forest bird species have continued to decline since 1986, while others have increased, usually after intensive species-specific research and management programmes. In this paper, we review what is known about major causes of current declines or population limitation, including predation, competition for food or another resource, disease, forest loss, and genetic problems such as inbreeding depression and reduced genetic variation. Much experimental and circumstantial evidence suggests or demonstrates that predation by introduced mammals remains the primary cause of declines and limitation in remaining large native forest tracts. Predation alone is generally sufficient to explain the observed declines, but complex interactions between factors that vary between species and sites are likely to be the norm and are difficult to study. Currently, the rather limited evidence for food shortage is mostly circumstantial and may be obscured by interactions with predation. Climate and food supply determine the number of breeding attempts made by herbivorous species, but predation by introduced mammals ultimately determines the outcome of those attempts. After removal of pest mammals, populations are apparently limited by other factors, including habitat area, food supply, disease or avian predators. Management of these, and of inbreeding depression in bottlenecked populations, is likely to assist the effectiveness and resilience of management programmes. At the local or regional scale, however, forest area itself may be limiting in deforested parts of New Zealand. Without predator management, the number of native forest birds on the New Zealand mainland is predicted to continue to decline.     

Community structure of pollination webs of Mauritian heathland habitats

Pollination webs have recently deepened our understanding of complex ecosystem functions and the susceptibility of biotic networks to anthropogenic disturbances. Extensive mutualistic networks from tropical species-rich communities, however, are extremely scarce. We present fully quantitative pollination webs of two plant–pollinator communities of natural heathland sites, one of which was in the process of being restored, on the oceanic island of Mauritius. The web interaction data cover a full flowering season from September 2003 to March 2004 and include all flowering plant and their pollinator species. Pollination webs at both sites were dominated by a few super-abundant, disproportionately well-connected species, and many rare and specialised species. The webs differed greatly in size, reflecting higher plant and pollinator species richness and abundance at the restored site. About one fifth of plant species at the smaller community received <3 visits. The main pollinators were insects from diverse taxonomic groups, while the few vertebrate pollinator species were abundant and highly linked. The difference in plant community composition between sites appeared to strongly affect the associated pollinator community and interactions with native plant species. Low visitation rate to introduced plant species suggested little indirect competition for pollinators with native plant species. Overall, our results indicated that the community structure was highly complex in comparison to temperate heathland communities. We discuss the observed differences in plant linkage and pollinator diversity and abundance between the sites with respect to habitat restoration management and its influence on pollination web structure and complexity. For habitat restoration to be successful in the long term, practitioners should aim to maintain structural diversity to support a species-rich and abundant pollinator assemblage which ensures native plant reproduction.     

Home and away: biogeographical comparison of species diversity in <Emphasis Type="Italic">Thymus vulgaris</Emphasis> communities

We examined the effects of Thymus vulgaris (common thyme) on associated vegetation in both its native and introduced range. We compared local (within-community) and landscape (among-community) species richness and community composition between thyme-dominated communities in France (native range) and New Zealand (introduced range). From 7 native sites (France) and 10 introduced sites (New Zealand), all plant species present in 20 (New Zealand, 25 in France) randomly placed 100 cm × 50 cm quadrats were recorded. Local species richness was determined by calculating mean species richness/quadrat inside and outside thyme-dominated plant communities and tested for significance with the factors of range and across sites. Landscape scale differences were determined by comparing total species richness inside and outside thyme communities across all sites from both ranges. Species differences between native and introduced thyme communities were analysed using similarity percentages. We found native range microenvironments with thyme harbour more species than microenvironments without thyme and this pattern was reversed in the introduced range with thyme decreasing local species richness. A higher percentage of shared species occurred both with and without thyme in the native range compared to the introduced range. In both ranges and across all sites (except for one) species composition of thyme-associated plant communities differed from communities without thyme. Native plant communities with thyme were more similar in species composition than plant communities without thyme, but in the introduced range species composition was most similar in plant communities without thyme. These results suggest thyme’s ecosystem engineering consequences are context-dependent. Thyme may filter out competitive species that could negatively impact local species richness in its native range, but when introduced to a disturbed landscape in a novel biogeographic region, thyme reduces local species richness.     

Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa.

High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the bivoltine European parasite Peristenus digoneutis Loan became well established, average parasitism of the first and second generations increased to 64%, and tarnished plant bug numbers dropped by 65%. This reduced host density eventually caused a decline in total parasitism by both parasite species to 22%. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest or increase its parasitism rate. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs, an adventive (accidently introduced) pest, was increased to 21% by the introduced univoltine parasite, Peristenus conradi Marsh, and a slight reduction in the pest may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), an adventive pest of forage grasses, so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the native tachinid parasite [Phasia robertsoni (Towns.)] of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.     

Plant community changes after the reduction of an invasive rangeland weed, diffuse knapweed, Centaurea diffusa

The expected outcome of weed control in natural systems is that the decline of a dominant weed will result in an increase in diversity of the plant community but this has seldom been tested. Here we evaluate the response of the plant community following the decline of diffuse knapweed (Centaurea diffusa) in six different pastures at White Lake, BC, Canada over five years. This period followed the establishment, spread and high levels of attack by the introduced European weevil, Larinus minutus, as part of a biological control program. Knapweed declined immediately before and during the study period, but, contrary to expectations, the species richness and diversity of the rangeland plant community did not increase. The absolute cover of native and introduced forbs and grasses increased following knapweed decline, but only the introduced grasses showed a consistent increase in cover relative to the other life-forms. However, unlike in other studies, the native plants dominated the study site. We conclude that the changes in plant communities following successful biological control are variable among programs and that the impact of replacement species must be evaluated in assessing the success of ecological restoration programs that use biological control to manage an undesirable weed.     

Establishment of woody species across 26 years of revegetation on a Queensland coal mine

The establishment success of woody plant species at 56 revegetation sites, four to 26 years old, across the Meandu open‐cut coal mine in south‐east Queensland was assessed. The revegetation process involved returning stockpiled topsoil, deep ripping and mechanical sowing of a mix of native seeds. Blakes Wattle (Acacia blakei) and less often Black Wattle (A. leiocalyx), both primarily derived from respread topsoil seed, dominate the vegetation canopy at 59% and 20% of revegetation sites, respectively. The additional sowing of seeds of many tree and shrub species within the sites has had limited success with most failing to persist or grow well. Revegetation management, for example selective thinning of acacias (Acacia spp.) saplings within the first 5 years is recommended to release the competition pressure on the poorly performing tree species. This will also allow opportunities for other less well represented shrub and herb species to persist. This study has shown that a range of tree and shrub species, including Eucalyptus spp., are performing poorly under the current revegetation regime, suggesting adjustments to revegetation species selection and/or methodologies are needed. The natural colonization of woody native species within the sites from nearby remnant vegetation is shown to be limited to only four species, and therefore is unlikely to significantly supplement the species diversity of the revegetation.     

Population ecology of the endangered aquatic carnivorous macrophyte Aldrovanda vesiculosa at a naturalised site in North America

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Palatability and tolerance to simulated herbivory in native and introduced populations of Alliaria petiolata (Brassicaceae)

The European herb garlic mustard (Alliaria petiolata) is a serious invader of North American deciduous forests. One explanation for its success could be that in the absence of specialized herbivores, selection has favored less defended but more vigorous genotypes. This idea was addressed by comparing offspring from several native and introduced Alliaria populations with respect to their palatability to insect herbivores and their tolerance to simulated herbivory. Feeding rates of a specialist weevil from the native range were significantly greater on American plants, suggesting a loss of resistance in the introduced range. In contrast, there was significant population variation but no continent effect in the feeding rates of a generalist caterpillar. After simulated herbivory, A. petiolata showed a substantial regrowth capacity that involved changes in plant growth, architecture, and allocation. Removal of 75% leaf area or of all bolting stems reduced plant fitness to 81% and 58%, respectively, of the fitness of controls. There was no indication of a difference in tolerance between native and introduced Alliaria populations or of a trade-off between tolerance and resistance.     

Potential impacts of climate change on patterns of insect herbivory on understorey plant species: A transplant experiment

Species‐specific responses to climate change will lead to changes in species interactions across multiple trophic levels. Interactions between plants and their insect herbivores, in particular, may become increasingly disrupted if mobile herbivores respond more rapidly to climatic change than their associated host plants. We present a multispecies transplant experiment aimed at assessing potential climatic impacts on patterns of leaf herbivory. Four shrubby understorey plant species were transplanted outside their native range into a climate 2.5°C warmer in annual mean temperature. After 12 months, we assessed the types and amount of herbivore leaf damage, compared with plants transplanted to a control site within their native range. The overall amount of foliage loss to herbivores ranged from approximately 3–10% across species and sites, a range consistent with most estimates of leaf loss in other studies. The most common types of leaf damage were sucking and chewing and this pattern was consistent for all four plant species at all sites. There were no significant differences in levels and patterns of herbivory between control and warm sites for three out of four plant species. This suggests that with moderate climate warming, most herbivory will continue to be dominated by chewers and suckers, and that the overall level of foliage loss will be similar to that experienced presently.     

Status of mammals on Groote Eylandt: Safe haven or slow burn?

Native mammals across northern Australia have suffered severe decline, with feral cats (Felis catus), introduced herbivores and changed fire regimes being implicated as drivers. However, uncertainty surrounding the relative contribution of each of these threats, and the interactions between them, is limiting the development of effective management strategies. The absence of introduced herbivores and cane toads (Rhinella marina) on Groote Eylandt, Northern Territory, provides an opportunity to evaluate some hypothesised threats in isolation of others. We used camera traps to investigate the correlates of native mammal distribution and abundance at 112 lowland savanna sites across Groote Eylandt. Two large grids of camera traps were also deployed to obtain estimates of feral cat density. We hypothesised that native mammal populations would be negatively associated with feral cat occupancy as well as frequent, large fires. Native mammal site‐occupancy on Groote Eylandt was generally higher compared to mainland Northern Territory. Feral cats were infrequently detected, precluding both an estimate of feral cat density and an evaluation of the relationship between feral cats and native mammals. We found no evidence that native mammal site‐occupancy or relative abundance is negatively associated with frequent, large fires. The relatively healthy state of native mammal populations on Groote Eylandt is likely due to the low density of feral cats, the benign fire regime and the absence of large introduced herbivores and cane toads. However, due to a lack of historical data, the current state of mammals should not be taken as evidence that these populations are safe from decline. This study highlights that the apparent resilience of mammal populations is a result of complex interactions between factors that vary substantially across the landscape. Caution is therefore required when making broad inferences about the drivers of mammal decline from studies that are spatially and temporally limited.