Gorse Ulex Europaeus Research Articles

Why did specificity testing fail to predict the field host-range of the gorse pod moth in New Zealand?

Contrary to predictions based on host-range testing, the gorse pod moth (GPM) infests pods of several exotic Genisteae and Loteae species, as well as the target weed gorse Ulex europaeus, throughout New Zealand. The original host-range tests were conducted on moths collected in southern England; however, the offspring of Portuguese moths were also released in New Zealand. We investigated whether failure to predict non-target attack was because (a) a cryptic species was accidentally introduced; (b) asynchrony between the oviposition period of GPM and gorse flowering results in deprivation, causing less preferred plants to become more acceptable for oviposition and (c) the Portuguese GPM population has a different host-range to the tested English population. Dissections of genitalia and molecular data collected on COI mtDNA indicated that a cryptic species was not introduced. Specificity tests on moths sourced from England concurred with the original tests and indicated that GPM should be unlikely to exploit the non-target species that are attacked in New Zealand. In contrast, GPM sourced from Portugal were able to exploit a broader range of plants, although choice oviposition tests indicated that gorse is, nevertheless, the preferred host of this population. Adult GPM activity was often poorly synchronized with gorse flowering in New Zealand and non-target attack was most prevalent when gorse flowers and pods were absent. We conclude that the release of untested moths sourced from Portugal, coupled with asynchrony between the flight period of GPM and gorse flowering explains the unanticipated non-target attack in New Zealand.

Genetic divergence and ecological specialisation of seed weevils (Exapion spp.) on gorses (Ulex spp.)

Abstract 1. Reproductive isolation of sympatric populations may result from divergent selection of populations in different environments, and lead to ecological specialisation. In Brittany (France), the gorse Ulex europaeus (Fabaceae, Genisteae), may be encountered in sympatry with one of the two other gorse species present: U. gallii and U. minor. A recent study based on morphological identification of seed predators of gorse has shown that two weevil species (Curculionoidea, Apionidae) infest gorse pods at different seasons and have different host ranges: Exapion ulicis infests U. europaeus in spring, whereas E. lemovicinum infests U. gallii and U. minor in autumn. Weevil populations may thus have diverged in sympatry.2. As morphological identification of weevils is often difficult and some of the characters used may exhibit individual or environmental variation, mitochondrial and nuclear sequences of weevils collected within pods of the three gorse species in 10 populations of Brittany were used to reconstruct their phylogeny.3. The results reveal that species differentiation based on morphological characters is confirmed by the two molecular data sets, showing that E. ulicis and E. lemovicinum are distinct species, and suggesting the absence of host races. Finally, E. ulicis was able to use U. gallii and U. minor pods in spring in some years in some populations, which appeared to depend on the availability of pods present during its reproductive period.4. Divergence between E. ulicis and E. lemovicinum may have resulted from temporal isolation of reproductive periods of weevil populations followed by specialisation of insects to host phenology.

Post-release investigations into the fi eld host range of the gorse pod moth Cydia succedana Denis & Schiffermüller (Lepidoptera: Tortricidae) in New Zealand

The gorse pod moth Cydia succedana was released in New Zealand as a biological control agent against gorse Ulex europaeus L. in 1992 and is now widely established. Post-release evaluations of the host range of C. succedana were undertaken using both laboratory assays and field collections on native and exotic plants related to gorse. Field surveys did not detect any attack on native New Zealand plant species. However, contrary to predictions based on pre-release host-range testing, several species of exotic Genisteae, including Scotch broom Cytisus scoparius, Montpellier broom Teline (Genista) monspessulana, and tree lupin Lupinus arboreus, as well as lotus Lotus pedunculatus (Loteae) growing in the vicinity of infested U. europaeus plants, were shown to be hosts of C. succedana in both the North and South Islands of New Zealand. Hypotheses to explain this unexpected non-target attack include a seasonal asynchrony between C. succedana and gorse fl owering phenology, or that the original biocontrol introduction accidentally consisted of either two cryptic species or two populations with different physiological host range.

How is the invasive gorse Ulex europaeus pollinated during winter? A lesson from its native range

Many examples of plant-insect interac- tions have shown that selection from herbivores can act on flowering and fruiting phenology. In Ulex europaeus (Fabaceae), escaping seed predation resulted in extended, but variable flowering periods, with some plants flowering from autumn until spring and others flowering only in spring. The present study aims at understanding how gorses can have a high reproductive success during winter despite harsh climatic conditions and low number of pollinators. We measured pollen production, flower size and seed production in spring and winter, and compared the different seasons. The pollination success of flowers was high in both seasons. The flowers produced as much pollen, and were of comparable size in spring and winter, but they stayed open twice as long in winter than in spring. The high pollination rate we observed was thus due to the longer opening period of flowers and the high attractiveness of flowers during winter. However, pod abortion was higher in winter, with 43% of the flowers in winter and 75% in spring producing ripe pods. Antagonistic selective pressures exerted by biotic and abiotic interactions may, therefore, have lead to the observed flowering polymorphism, and allow U. europaeus to thrive in various climates, thus, increasing its invasiveness in different countries.

Introduced mammals coexist with seabirds at New Island, Falkland Islands: abundance, habitat preferences, and stable isotope analysis of diet

The largest known colony of Thin-billed prions Pachyptila belcheri has been coexisting with introduced mammals for more than 100 years. Three of the introduced mammals are potential predators of adults, eggs and chicks, namely ship rats Rattus rattus, house mice Mus musculus and feral cats Felis catus. We here determine habitat preferences over three seasons and dietary patterns of the unique set of introduced predators at New Island, Falkland Islands, with emphasis on the ship rats. Our study highlights spatial and temporal differences in the levels of interaction between predators and native seabirds. Rats and mice had a preference for areas providing cover in the form of the native tussac grass Parodiochloa flabellata or introduced gorse Ulex europaeus. Their diet differed markedly between areas, over the season and between age groups in rats. During the incubation period of the prions in November–December, ship rats had mixed diets, composed mainly of plants and mammals, while only 3% of rats had ingested birds. The proportion of ingested birds, including scavenged, increased in the prion chick-rearing period, when 60% of the rats consumed prions. We used δ13C and δ15N to compare the importance of marine-derived food between mammal species and individuals, and found that rats in all but one area took diet of partly marine origin, prions being the most frequently encountered marine food. Most house mice at New Island mainly had terrestrial diet. The stable isotope analysis of tissues with different turnover times indicated that individual rats and mice were consistent in their diet over weeks, but opportunistic in the short term. Some individuals (12% of rats and 7% of mice) were highly specialized in marine-derived food. According to the isotope ratios in a small sample of cat faeces, rodents and rabbits were the chief prey of cats at New Island. Although some individuals of all three predators supplement their terrestrial diet with marine-derived food, the current impact of predation by mammals on the large population of Thin-billed prions at New Island appears small due to a number of factors, including the small size of rodent populations and restriction mainly to small areas providing cover.

Habitat type determines the effects of disturbance on the breeding productivity of the Dartford Warbler Sylvia undata

Numerous studies have examined the causes and impacts of human disturbance on birds, but little is known about how these impacts vary among habitats. This is of applied importance both for predicting bird responses to changes in disturbance and in planning how to reduce disturbance impacts. The Dartford Warbler Sylvia undata, a key heathland breeding species, occupies territories in a range of heathland types. Three territory habitat groups were identified: heather‐dominated territories, heather territories with significant areas of European Gorse Ulex europaeus and territories containing Western Gorse U. gallii. Productivity was significantly affected by the timing of breeding in all habitats, but disturbance only appeared to have a significant impact on the productivity of birds in heather territories. Disturbance events in heather territories delayed breeding pairs for up to 6 weeks. This significantly decreased both the number of successful broods raised and the average number of chicks fledged per pair. Nests situated close to territory boundaries in heather territories, with high numbers of disturbance events, were more likely to fail outright. It was determined that an average of between 13 and 16 people passing through a heather territory each hour would delay breeding pairs sufficiently to prevent multiple broods.

Effects of mixing radiata pine needles and understory litters on decomposition and nutrients release

A microcosm experiment was conducted to understand the impacts of mixing radiata pine (Pinus radiata D. Don) needle litter and understory (gorse—Ulex europaeus L., broom—Cytisus scoparius L., bracken—Pteridium aquilinum L., and lotus—Lotus pedunculatus L.) litter materials on decomposition and nutrient release dynamics. Mixing of pine needle litter with understory litter material had significant impacts on both the rate of decomposition and nutrient release patterns of pine litter as well as that of the understory species. Incubation in microcosms over 10 months resulted in significantly lower mass loss of radiata pine needle litter mixed with broom and lotus litters (35.8±8.4 and 41.3±0.8%, respectively) than pure pine needle litter (63.5±2.3%). Mixing with pine needle litter significantly increased the mass loss of broom (53.1±6.1%) compared to that of pure broom (30.2±1.0%). Significant transfers of nutrients, especially of magnesium and potassium, were observed in litter mixture treatments. Concentration of K in litter materials was found to be the most limiting factor for the decomposing microorganisms in the present study. The findings of this study suggest that management of understory litter composition via weed control could be used to manipulate carbon turnover and nutrient release in the forest floor. Also, initial selection of understory species will be important and could be managed.

Effects of land-use and agricultural management on birds of marginal farmland: a case study in the Llŷn peninsula, Wales

Extensive pastoral farming and marginal land are important for many bird species of conservation concern. This study identified the bird species associated with a range of marginal upland habitats in the Llyn peninsula in Wales and discusses the impact on these species of further land-use change. Bird and habitat surveys of 45 sites were conducted between May and July 2000. The bird species observed at each site were recorded along with the densities of eight species characteristic of marginal farmland. Sites were assigned to land management categories representing different management intensity and land-use options. A binary similarity index was used to quantify species associations with each of these categories and canonical correspondence analysis (CCA) was used to identify associations with individual habitat characteristics. Habitat differences were largely attributable to differences in management. Very few species were recorded on intensively managed sites, although house martin Delichon urbica and swallow Hirundo rustica were significantly associated with improved grassland with scrub or bracken. Sites that were abandoned or under-managed had a high tree density, high cover of bracken Pteridium aquilinium and supported many common scrub or woodland species. Extensively managed sites with unimproved grassland, shrub heath, bracken and scrub (ffridd) were found to be important for several species, including chough Pyrrhocorax pyrrhocorax, wheatear Oenanthe oenanthe, mistle thrush Turdus viscivorus, stonechat Saxicola toquata and meadow pipit Anthus pratensis. High densities of yellowhammer Emberiza citrinella and linnet Carduelis cannabina occurred on sites with improved grassland and gorse Ulex europaeus. This study highlights the need for a diversity of habitats on marginal farmland, which is most likely to be achieved through the distribution of funds to marginal areas through agri-environment and rural development measures.

Large−scale disturbances, biological control and the dynamics of gorse populations

Summary Simulation and analytical models were developed for gorse Ulex europaeus. The simulation model incorporated spatially local density−dependent competition, disturbance, asymmetric competition between seedlings and established plants, a seed bank, local seed dispersal, an age structured established plant population, and temporal variation in the probability of disturbance. The analytical models were simple approximations of the simulation. The models extended our previously published model for Scotch broom Cytisus scoparius to include large−scale disturbances and possible management options, such as the use of fire, herbicides and oversowing with perennial grasses. Fire was assumed to influence established plant mortality, seed survival in the seed bank, and the probability of germination. We reviewed published data on the demography of gorse in New Zealand, the current management techniques, and the ongoing biological control programme. Over a wide range of biologically reasonable parameter values, the analytical models accurately predicted the outcome of the simulations. The analytical models worked well, providing gorse occupied a high proportion of the available sites and large−scale disturbances did not occur too frequently. The potential impact of seed−feeding biological control agents on gorse abundance was assessed, using the models, for several environmental and management scenarios. In particular, we explored how large−scale disturbance, such as fire and herbicide application, influences the outcome of biological control. The success of a biological control programme was found to depend critically on the frequency and intensity of disturbance, whether disturbed sites became suitable for recruitment, and the effects of disturbance on germination and seed mortality. The models highlight the need to manage recruitment opportunities carefully in order to maximize the effect of biological control agents. The models also indicate that details of plant population biology can have a profound effect on the success of any management strategy.

Territory quality and reproductive success in the Dartford warbler Sylvia undata in Dorset, England

The relationship between territory quality and reproductive success was investigated in a population of the Dartford warbler Sylvia undata, breeding at Holt Health National Nature Reserve, Dorset, UK. Reproductive success, as measured by the number of young produced, was high, with most pairs raising two broods of young. Nine separate measurements of territory quality revealed considerable variation and larger territories contained more heather Calluna vulgaris, but not more gorse Ulex europaeus. There was no initial relationship between measures of territory quality and reproductive success, but when adult losses were removed from the analysis, territories containing more gorse produced more young. Territories containing more gorse were also closer to the road where most adult losses occurred, thus initially masking the positive relationship between the amount of gorse and reproductive success. The study suggests that the amount of gorse within a territory, and distance to a road, are the two most important territory quality variables affecting reproductive success in this population. These findings have important implications for the future conservation of Dartford warblers, and in particular for the effective management of nature reserves on the remaining lowland heaths of southern England.

Dartford warblers Sylvia undata, their habitat and conservation in the New Forest, Hampshire, England in 1988

The breeding range of the Dartford warbler Sylvia undata extends over much of maritime western Europe as far north as southern England, where it is more or less confined to lowland heaths. It is vulnerable to extended winter snowlie and periodically its numbers and range have contracted to the distribution centre in Hampshire and Dorset in south-central England. In a census of the species in the New Forest, Hampshire, in 1988, 454 occupied territories were found, 123% more than in a 1984 survey and the largest number recorded since surveys began in 1960. The increase was attributable mainly to four mild winters. In 1988 the New Forest may have held nearly 75% of the national population of Dartford warblers compared with 48% in 1984. In 1984 most pairs were in the south and east but in 1988 there was a more even distribution, reflecting adjustments in the management of the heaths by burning. In 1988, 402 pairs (89%) were in mature dry heath, humid heath, or thickets of gorse Ulex europaeus These vegetation types covered 1830·6 ha, comprising 22% of the ericoid heathland in the New Forest, and had remained unburnt for at least 15 years. We consider that it is probably not possible to increase the amount of Dartford warbler habitat by changing the burning rotation. However, there may be opportunities to restore heathland on some areas planted with conifers. In this event, attempts should be made to create Dartford warbler habitat on the restored heathland.

Heathland management in the New Forest, Hampshire, England

Heathland in the New Forest, Hampshire, England, is subject to systematic controlled burning, the main intention of which is to maintain and enhance the quality of the grazing for commoners' animals. Mature heathland vegetation is richer in bird, reptile and invertebrate life than younger age classes. However, a survey has confirmed that despite a recent reduction in the area burnt annually, burning had produced an imbalance in favour of young age classes of heather Calluna vulgaris and Erica spp., and that intensive browsing after fire was severely inhibiting the regeneration of gorse Ulex europaeus. The data obtained made it possible to recommend management policies which attempted to correct the imbalance in vegetation age structure and also satisfied the requirements of the grazier.

FOOD AND FEEDING HABITS OF THE MOUNTAIN HARE LEPUS TIMIDUS SCOTICUS, HILZHEIMER

The food of the mountain hare Lepus timidus scoticus Hilzheimer was studied by means of stomach analysis, and the use of hare‐proof enclosures on moorland; and grazing habits by regular visits to a study area in Banffshire. The main grazing period is at night, varying seasonally in relation to sunset and sunrise. During the day grazing may occur sporadically, or intensively if before rain or during heavy snow cover. Refection, that is the production of soft faeces which are swallowed directly from the anus, occurs during the period between the end of morning grazing and the start of the next evening's grazing. On ground covered with young ling Calluna vulgaris, mountain hares removed 27 per cent of the vegetation (dry weight) from the control plot, and on cotton grass Eriophorum spp. ground, 20 per cent and 24 per cent from control plots. In three of the eight enclosures used, on various herbage complexes, there was no appreciable difference from the control plots. Analysis of the dried stomach contents of forty‐seven mountain hares, collected at monthly intervals over a period of a year, showed that ling formed 90 per cent of the winter and about half the summer diet. Cotton grass made up about a tenth of the winter and a fifth of the summer diet, while grass species, present as a trace in winter stomachs, increased to a quarter of the total food in summer. Food plants of particular importance during storms and complete snow cover may be missed by the method of sampling or the use of enclosures. The extent to which hares grazed these plants was verified by visits during snow. Gorse Ulex europaeus, juniper Juniperis communis and soft rush Juncus effusus, are among the chief food plants in storms and snow cover.Summary1. The grazing habits of the mountain hare are described. The main grazing period is at night, varying seasonally in relation to sunset and sunrise. Sporadic grazing, or intensive grazing before rain or during snow cover, may occur during the day.2. Refection, the production of soft faeces which are swallowed directly from the anus, occurs during the day, beginning with the end of intensive grazing and ceasing with its resumption.3. The use of hare‐proof enclosures on moorland showed that on ground covered with young ling Calluna vulgaris mountain hares removed 27 per cent of the vegetation (dry weight), and on cotton grass Eriophorum spp. ground 20 per cent and 24 per cent. In three out of eight enclosures used, covering various herbage complexes, there was no appreciable difference from the control plots.4. Analysis of the dried stomach contents of forty‐seven mountain hares, collected at approximately monthly intervals over a period of a year, showed that ling formed almost 90 per cent of the winter and about half the summer diet. Cotton grass made up about a tenth of the winter and a fifth of the summer diet, while grass species present as a trace in winter stomachs, increased to a quarter of the total food in summer.5. Food plants of particular importance during storms and complete snow cover may be missed by the method of sampling or the use of enclosures. The extent to which hares grazed these plants was verified by visits during snow. Gorse Ulex europaeus, juniper Juniperus communis and soft rush Juncus effusus are among the chief food plants in storms and snow cover.