Increasing dominance of Brachypodium pinnatum (L.) beauv. in chalk grasslands: A threat to a species-rich ecosystem

Chalk grassland is a semi-natural, species-rich vegetation which was once widespread in West Europe. Due to the high species diversity a number of remnants of this vegetation have been set aside as nature reserves and managed by man to prevent natural succession into woodland.

During the last decade an increase of dominance of the grass Brachypodium pinnatum has been observed in chalk grassland within the greater part of the distribution area. Increasing dominance is strongly negatively correlated with the species diversity. Increase of this species is observed in grassland with different management regimes, e.g. sheep grazing, mowing or burning. Brachypodium can gain 80% or more of the relative above-ground phytomass. In such vegetation the species number decreases to less than 50% of the original number within a few years—the low growing forbs especially disappear almost completely. It is argued that the impact of nutrients by air pollution, especially of nitrogen, causes the increasing dominance of Brachypodium. Further research will focus on the effects of this extra nutrient supply.

The aim of the present research is to formulate management strategies in order to prevent degradation of the species diversity in chalk grasslands.     

Long-term effects of deer browsing and trampling on the vegetation of peatlands

Overabundance of wild ungulates, especially exotic species, is a major threat to several ecosystems worldwide. While the response of forest vegetation to high density of herbivores has been well studied, far less is known about peatland vegetation. In this paper, we assessed the long term impact of white-tailed deer (Odocoileus virginianus) on plant communities of ombrotrophic (bog) and minerotrophic (fen) peatlands in eastern North America. Vegetation of five peatlands that have experienced high deer densities for at least 75 years was compared with that of five peatlands situated at proximity but on deer-free islands. We investigated deer impacts on plant species composition and cover, shrub height and cloudberry (Rubus chamaemorus) fruit/flower production and morphology. In bogs, white-tailed deer had no long-term impact on plant species assemblages, but reduced lichen cover and increased sedges and grasses cover as well as the surface area of bare peat. On the other hand, the floristic composition of fens differed significantly between sites where deer were present or absent. Plant diversity was greater in undisturbed fens than in disturbed fens, especially for shrubs, sedges and liverworts. No detrimental effects of browsing on shrub height were observed. Conversely, deer browsing seemed to have deleterious impacts on cloudberry fruit/flower production as well as on the number of leaves per individual. Overall, our results suggest that white-tailed deer had some important impacts on the vegetation of peatlands that could be harmful for the long-term conservation of peatland plant diversity.     

Effects of hunting with hounds on a non-target species living on the edge of a protected area

The impact of hunting on wildlife is a complex phenomenon which varies in space and across time, and yet limited knowledge is available on it. This is especially the case of the indirect effects of hunting on the behaviour of target as well as non-target species. Here we analyze how hunting affected the spatial behaviour of 62 radiocollared roe deer (Capreolus capreolus) in a protected area adjacent to areas where hunting with hounds (target species: wild boar and hares) and stalking with rifles from high seats without dogs (target species: roe deer) were permitted during the hunting season. Our results showed that hunting caused a significant increase in the home range size of monitored deer, as well as a “reserve effect”, whereby roe deer used the protected area as a refuge from hunters. These behavioural responses were significant only at times when hunting with hounds was conducted, even though roe deer was not the target species of this technique. Reactions to the perceived risk of predation varied among age and sex classes, with yearling being more sensitive and using the protected area more than adults. As shown in our study, hunting harassment provoked by drives with hounds significantly affects the behaviour of non-target species. Therefore, the use of long-legged hounds represents a variable that should be carefully evaluated by wildlife managers in their management plans and conservation policies, especially when endangered or vulnerable species are present.     

Regeneration of mixed deciduous forest in a Dutch forest-heathland, following a reduction of ungulate densities

The conversion of single-species coniferous forest stands into mixed stands by promoting the natural regeneration of indigenous broadleaved tree species was studied in a forest-heathland on the Veluwe, in the central part of the Netherlands. Red deer (Cervus elaphus), roe deer (Capreolus capreolus) and wild boar (Sus scrofa) had a large impact on regeneration dynamics, as was established by comparing 20 pairs of fenced and unfenced plots (40 × 40 m) during a 10-year period. A fivefold reduction of total herbivore biomass to 500 kg per km², resulted in a strong increase of shrub and tree sapling numbers in all vegetation types. However, height growth of the most palatable broadleaved tree species was still strongly impeded. Under the present-day grazing pressure, Scots pine (Pinus sylvestris) and beech (Fagus sylvatica) will become the dominant canopy species in the forests in the near future. It is argued that the most browse-sensitive woody species such as pedunculate and sessile oak (Quercus robur and Q. petraea) will successfully regenerate, only if temporal and spatial variation in browsing pressure is allowed to occur.     

Mortality trends in the African cherry (Prunus africana) and the implications for colobus monkeys (Colobus guereza) in Kakamega Forest, Kenya

Prunus africana (Hook.f.) Kalkm. is a secondary forest canopy tree species that has been declining over much of its geographical range in sub-Saharan Africa during recent decades due to unsustainable harvesting of its bark for the international medicinal plant trade. One of the locations where the species is experiencing rapid mortality is Isecheno study site in the Kakamega Forest, Kenya where this study was conducted. Between 1997 and 2003, 21% of the P. africana (10 cm DBH) at Isecheno died and an additional 9% experienced 50% canopy dieback. However, scars from bark harvesting on P. africana were relatively small and scarred trees were not more likely to be dead or dying than unscarred trees, suggesting that bark exploitation is not causing P. africana mortality at Isecheno. Other possible causes that require further evaluation include disease, insect attack, nutrient deficiency, and/or climatic fluctuation. The poor regeneration of P. africana at Isecheno can likely be explained by the relative lack of recent disturbance coupled with the thick undergrowth layer at this site. P. africana mortality is of concern not only because the species is listed as Vulnerable by IUCN, but also because black and white colobus monkeys [Colobus guereza (Rüppell, 1835)] at Isecheno exploit it as their top food species and are particularly reliant on its leaves during times of ‘preferred' Moraceae fruit scarcity. The anticipated continued decline of P. africana may have adverse effects on C. guereza feeding habits, intergroup relations, and population density at Isecheno. Conservation of P. africana offers a formidable challenge since the species appears to require disturbance for regeneration, yet at sites where disturbance is occurring, P. africana is often a target of bark harvesters engaging in unsustainable levels of exploitation.     

Breeding and post-breeding responses of woodland birds to modification of habitat structure by deer

Birds in woodland can be affected by increasing deer populations through changes to vegetation structure and potential impacts on foraging resources; these effects need to be better understood. Effects of deer browsing are reported from a replicated split-plot exclusion experiment in English coppiced woodland. All stages of growth were examined up to eight years after felling. We used standardised mist-netting (totaling 1920 h) to sample birds in breeding and post-breeding periods. Deer browsing strongly altered vegetation structure by reducing canopy cover and shrub layer foliage density. However deer did not affect invertebrate density per unit of foliage, providing no evidence of an ungulate-mediated plant chemical response affecting forage quality for invertebrate herbivores. At avian guild level, significantly more ground and understorey foraging birds were captured where deer were excluded, and negative responses to browsing were more marked for pooled migrants than pooled residents. At the species level, especially pronounced negative effects were evident for dunnock (Prunella modularis) and garden warbler (Sylvia borin); approximately five times more dunnocks were captured in deer exclosures than in browsed vegetation. We also detected negative responses to browsing by nightingale (Luscinia megarhynchos) and long-tailed tit (Aegithalos caudatus). No significant positive responses to browsing were detected. For some species the use of young re-growth increased post breeding relative to the breeding period, including a marked shift by pooled residents that involved a disproportionate number of juveniles. Previous studies in North America have shown that, through vegetation modification, ungulate activity can alter woodland bird assemblages; as far as we are aware this is the first experimental demonstration of effects in Europe, and at low to moderate browsing intensity typical of the wider landscape scale.     

Evidence for multiple origins of Wolbachia infection in springtails

Bacteria of the genus Wolbachia (Rickettsiae) are endosymbionts found in many species of invertebrates. The traditional division of Wolbachia lines into four supergroups has recently been challenged with the finding of a fifth supergroup. Until now, this E supergroup exists of a single host species of the order Collembola (springtails) and is hypothesized to form a ‘missing link’ between Wolbachia lines in higher arthropods and nematodes. We have sequenced the 16S rDNA, the ftsZ and the wsp genes of a Wolbachia lineage present in the sexually reproducing collembolan Orchesella cincta. We tested the hypothesis on the origin of Wolbachia in Collembola by adding this new Wolbachia lineage and a lineage found in the collembolan Mesophorura macrochaeta to the Wolbachia phylogenetic tree. The addition of these two species clearly shows that Wolbachia is not monophyletic in Collembola. We conclude that the origin of Wolbachia in Collembola is a combination of vertical and horizontal transfer between coexisting species.     

Habitat selection and conservation of an endemic spanish lizard Algyroides marchi (reptilia, lacertidae)

We study the habitat selection of Algyroides marchi, a small lizard endemic to the southeastern mountains of the Iberian Peninsula whose populations are concentrated in a few small localities. Three spatial scales of study were used to analyse the different factors affecting the species distribution patterns: regional scale, local scale and within-habitat use of different substrates. The results obtained at these different spatial scales showed a high consistency, suggesting that the same ecological pressures probably acted at different scales. Localities occupied by A. marchi were characterized by high altitude, high geomorphological complexity, northern aspect, high cover of large rocks, and presence of water. Density of A. marchi in a favourable locality was 213 adult-subadult lizards/ha. Abundance and use of space of A. marchi (at local and individual levels) were directly associated with extent of water (streams and small pools) and the presence of large rocks, and inversely with hours of direct solar radiation and cover of small stones and vegetation. Considering the habitat selection of A. marchi and the management practices within its geographical range, potential risks for the conservation of the species are identified.     

Ovaries of Petrobius brevistylis (Archaeognatha, Machilidae) and Tricholepidion gertschi (Zygentoma, Lepidotrichidae): Morphology, ultrastructure and phylogenetic implications

The ovaries of Petrobius brevistylis (Archaeognatha) and Tricholepidion gertschi (Zygentoma) are composed of seven metamerically arranged panoistic ovarioles that are covered with the external epithelial sheath (=tunica externa) and the basal lamina (=tunica propria). The germaria are small and enclose oogonial cells and somatic prefollicular cells. The vitellaria contain 10–15 linearly arranged oocytes that are surrounded by a one-layered follicular epithelium. Oocyte nuclei (=germinal vesicles) are large and possess giant, compact (P. brevistylis) or lobate (T. gertschi) nucleoli. In both studied species the majority of yolk is incorporated to the oocyte via endocytosis; however, appearance of numerous Golgi complexes and rough endoplasmic reticulum cisternae at the onset of vitellogenesis suggests the involvement of these organelles in synthesis of yolk precursors. The obtained results are discussed in the phylogenetic context and support the idea that Lepidotrichidae are the most basal zygentoman clade.     

Seeing the forest for the deer: Do reductions in deer-disturbance lead to forest recovery?

High levels of deer browsing can prevent canopy tree regeneration, but little is known about changes to forest size-structure following long-term deer herd reductions. We monitored changes in forest stand structure and composition in southwestern Ontario, Canada, over 28-years using permanent plots. Our study site was the largest remaining tract of Carolinian (deciduous) forest in Canada (11 km²), a habitat type that contains up to a fifth of Canada’s species at risk and is under intense anthropogenic pressures. We recorded declines in all tree size classes between 1981 and 1996, during which densities of white-tailed deer (Odocoileus virginianus) reached a peak of 55 deer km⁻². Despite significant and sustained deer herd reductions between 1996 and 2009, which reduced deer densities to 7 deer km⁻², there was limited recruitment of small trees and declines in basal area of tree species that were sensitive to deer browsing. Our results suggest that recovery from herbivory is a protracted process during which canopy tree regeneration may continue to decline despite a reduction in browsing pressure due to deer culling. Large declines in canopy-tree densities in Carolinian forests may lead to forest size-structures and herbaceous plant communities that resemble rare oak savanna habitat, creating difficult decisions for conservation managers aiming to protect rare and endangered species within native ecosystems. We recommend that managers protect Carolinian forest stands and encourage canopy tree regeneration by increasing seed sources of native trees. While deer control is essential in reducing forest damage, our results highlight the need to explore other forms of active management to expedite otherwise slow increases in tree density.     

PCR-RFLP authentication of meats from red deer (Cervus elaphus), fallow deer (Dama dama), roe deer (Capreolus capreolus), cattle (Bos taurus), sheep (Ovis aries), and goat (Capra hircus)

PCR-RFLP analysis has been applied to the identification of meats from red deer (Cervus elaphus), fallow deer (Dama dama), roe deer (Capreolus capreolus), cattle (Bos taurus), sheep (Ovis aries), and goat (Capra hircus). PCR amplification was carried out using a set of primers flanking a conserved region of approximately 712 base pairs from the mitochondrial 12S rRNA gene. Restriction site analysis based on sequence data from this DNA fragment permitted the selection of MseI, MboII, BslI, and ApoI endonucleases for species identification. The restriction profiles obtained when amplicons were digested with the chosen enzymes allowed the unequivocal identification of all domestic and game meat species analyzed in the present work.     

Designing the core zone in a biosphere reserve based on suitable habitats: Yancheng Biosphere Reserve and the red crowned crane (Grus japonensis)

Although much research has been undertaken to design nature reserves, there are few practical methods to determine the interior structure of a reserve. A procedure for design of the core zone in reserves is proposed. As a case study, the core zone in Yancheng Biosphere Reserve, People's Republic of China, which was established to preserve the endangered red crowned crane (Grus japonensis) is designed. A statistical habitat model using geographic information system (GIS) is developed to predict crane presence or absence. Based on predicted suitable habitats, the minimum core zone is defined. More suitable habitats can be contained in the designated core zone, and this will be beneficial to the conservation and restoration for crane habitats.     

Fast and efficient discrimination of the Isotoma viridis group (Insecta: Collembola) by PCR-RFLP

Identification of collembolan species is generally based on specific morphological characters, such as chaetotaxy and pigmentation pattern. However, some specimens do not match to described characters because these refer to adult specimens, often of one specific sex, or the characters are highly variable in adults (e.g. pigmentation, setae or furcal teeth). Isozymes have frequently assisted species discrimination, and also these may vary with developmental stage or environmental conditions. For identification of single species of the Isotoma viridis group, we present both direct sequencing of the cytochrome oxidase subunit II (COII) gene and a simple DNA-based molecular method.

Five PCR primers amplifying the COII region (717 bp) of the mitochondrial DNA were used. The sequences clearly separated the species I. viridis, I. riparia and I. anglicana, irrespective of colour varieties within the first species. DNA amplification products of different species can also be distinguished by digestion with restriction endonucleases, followed by gel electrophoresis for separation of fragments. This restriction fragment length polymorphism (RFLP), obtained after digestion with the endonucleases TaqI, VspI, MvaI and Bsp143I, revealed specific fragments that separated the three species from each other. Since restriction enzymes are sensitive to single base mutations, we suggest to use a combination of enzymes with at least two species-specific restriction sites when using the RFLP technique. For the I. viridis complex, VspI and Bsp143I appear to be an appropriate combination.     

Acari (mite) assemblages under plantations of bluegum, Eucalyptus globulus, in southwestern Australia

Farm forestry, in particular the planting of exotic bluegums Eucalyptus globulus, is a strategy increasingly used in southwestern Australia to mitigate the damaging effects of land clearing and to improve agricultural productivity. At the same time, such agroforestry systems have the potential to at least partially impede the biodiversity decline associated with habitat destruction and agriculture. The soil/litter habitat, an important repository of biodiversity in terrestrial systems, is one of the habitats most affected by clearing and conventional agricultural practices. Within this habitat, free-living mites are one of the most diverse and abundant animal groups contributing significantly to key ecosystem functions. This study compares the soil and litter mite assemblages of 7-year-old E. globulus plantations with those of adjacent native forest and pasture sites. The assemblages associated with E. globulus were substantially more diverse than those of the pasture soils but well below that of the native forest. Particularly low densities of oribatid mites were observed in the plantation sites. We suggest that the young plantation age, the exotic nature of the plantation species, and the homogeneous, mono-specific litter all contributed to limit the potential for these plantations to enhance mite biodiversity.     

Reduced grazing and the decline of Pulsatilla vulgaris Mill. (Ranunculaceae) in England, UK

In England Pulsatilla vulgaris is a threatened herb that declined from 130 to 33 sites between 1750 and the 1960s due to ploughing-up of calcareous grassland. We examined the subsequent fate of these populations using documentary evidence and field survey. Demographic trends were related to changes in grassland composition, structure and management and responses to increased above-ground competition (caused by reduced grazing) were simulated in a 10-year shading experiment. Since 1968 P. vulgaris has been lost from 16 sites and gradually declined on four others. However, the total population size increased by 258% due to the reintroduction of winter grazing on three sites. This produced a significantly shorter, more herb-rich sward, with a lower cover of Bromopsis erecta (c. 10%), than on sites where populations remained stable or declined. Experimental shading had a significant negative effect on plant survival and flowering performance. These results confirmed that reduced grazing is now one of the major threats to species dependent on short swards, especially on isolated sites where livestock farming is no longer economically viable. That many of these declines took place on nature reserves highlights the difficulties of managing isolated grasslands, and the urgent need to re-instate grazing on reserves supporting populations of threatened species in otherwise intensively managed lowland landscapes.     

High levels of genetic differentiation between Wolbachia-infected and non-infected populations of Folsomia candida (Collembola, Isotomidae)

The Gram-negative -Proteobacterium Wolbachia pipientis has been described as an obligate endosymbiont in many arthropod species, where it induces a variety of reproductive alterations, including parthenogenesis. Recently, this microorganism has also been detected in the parthenogenetic collembolan Folsomia candida. Here, we confirm the occurrence of the endosymbiont also in two Italian parthenogenetic populations of F. candida using ultrastructural (electron microscopy) and molecular (PCR screening on two bacterial genes) evidence. The strain isolated in the Italian populations has almost-identical gene sequences compared to that previously isolated in other populations of F. candida. In addition, we discovered a population of Folsomia cf. candida, which showed the presence of both males and females. This population is not infected by Wolbachia. A screening of two mitochondrial genes (COI and COII) showed that the bisexual population has high levels of genetic divergence in comparison with the parthenogenetic ones, even suggesting the possibility that it belongs to a different species. Furthermore, the remarkably high levels of genetic divergence between the two parthenogenetic populations suggests a possible influence of Wolbachia on inducing such differentiation, and, in the long term, speciation.     

Conservation status and causes of decline of musk deer (Moschus spp.) in China

Five species of musk deer (Forest musk deer Moschus berezovskii, Alpine musk deer M. sifanicus, Black musk deer M. fuscus, Himalayan musk deer M. chrysogaster and Siberian musk deer M. moschiferus) occur throughout 17 provinces in China, and all were listed in the second category of the Chinese State Key Protected Wildlife List in 1998. Among these species, the Forest musk deer has the widest distribution, and its population is estimated at about 100,000-200,000 individuals in the wild. Additionally, there are about 100,000 Alpine musk deer and 2000 Siberian musk deer. As for the Black musk deer and Himalayan musk deer, which occur only in parts of Yunnan Province and Tibet, their populations remain unknown but they can be estimated to be rare due to their narrow and limited distribution. Furthermore, there are some 1900 musk deer kept in farms in China. Generally, the musk deer population has been declining due to over-hunting for musk and to loss of habitats. However, the Chinese government is greatly concerned with wildlife protection today. A series of laws and regulations have been launched and many natural reserves and national parks have been established as refuges for this animal, most of which, are within the musk deer's range, and should have positive effects for musk deer conservation.     

Selective consumption and digestion of litter microbes by Porcellio scaber (Isopoda: Oniscidea)

In feeding preference tests with artificial diets consisting of food sources inoculated with different types of litter microbes, Porcellio scaber was capable of discriminating between different microbe species. Generally, microbial colonisation increased the attractiveness of a given food source, in particular, when the food source was of low quality (cellulose) and when food sources were inoculated with single species of actinomycetes (Streptomyces celluloflavus or Pseudonocardia autotrophica). In most cases, actinomycetes (Gram-positive bacteria) were preferred over both Gram-negative bacteria and fungi, whether or not these microbes exhibited cellulolytic activity. Enzymatic in vitro digestion of both the Gram-positive S. celluloflavus and P. autotrophica was significantly greater than that of Gram-negative bacteria (Pseudomonas fluorescens and Myxococcus xanthus) or fungi (Chaetomium globosum and Fusarium ventricosum). S. celluloflavus biomass was more effectively incorporated into isopod biomass than that of fungi and Gram-negative bacteria; P. autotrophica was more effectively incorporated into isopod biomass than that of Gram-negative bacteria. Based on these results, we hypothesise that P. scaber preferentially feeds on those microbes that it can readily digest. Whether this holds true for other Gram-positive bacteria or for other detritivores awaits investigation.     

The Collembola community of pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies) of different age

The idea of establishing mixed forests that are better adapted to site conditions than spruce monocultures has attracted increasing attention of forest owners and governmental institutions over the last decades. Currently, beech is being replanted and an increasing proportion of German forests are mixed stands. Focusing on the reaction of the soil fauna to forest conversion, this study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce. Stands of different age were investigated in a factorial design with the factors stand type (beech, spruce and mixed stands) and stand age (30 and 120 years). Collembola communities did not differ strongly between stand types and stand age and were dominated by Folsomia quadrioculata and Mesaphorura species (e.g. Mesaphorura macrochaeta). Moreover, neither total abundance of Collembola nor densities of the fungal feeding euedaphic Onychiurinae and Tullbergiinae significantly responded to stand type and stand age. The density of the epedaphic and partly herbivorous groups Symphypleona/Neelipleona and Entomobryidae in the 120-year-old stands significantly exceeded that in the 30-year-old stands; presumably, this was due to the well developed herb layer in the 120-year-old stands with more open canopies. Canonical correspondence analysis (CCA) of the Collembola community of the L/F horizon also indicated that most of the epigeic species were associated with the 120-year-old stands. Moreover, the diversity of Collembola significantly increased with forest age which likely reflects increased amount and diversity of food resources in the 120-year-old stands. The density of the hygrophilous species Fo. quadrioculata was significantly higher in the spruce than in the beech stands; probably this was due to the higher water content in litter of the spruce stands. Moreover, the results of the CCAs indicated that soil pH is an important structuring force for the Collembola communities. Overall, the results suggest that stand type and forest age impact Collembola communities, presumably via changes in the amount and quality of food resources, such as living plant and herb litter materials. The pronounced changes which occurred with forest age likely were related to the development of more dense and diverse herb layer in mature forests which provides additional food resources in particular for epedaphic species. On the other hand, dominant species/functional groups of Collembola, such as hemiedaphic species, appear to depend predominantly on abiotic factors, most importantly soil pH and soil water content.     

Responses of root-feeding nematodes (Helicotylenchus spp.) to local and non-local populations of the host plant Ammophila arenaria

The root-feeding nematode community of wild plants may vary throughout their natural range. Little is known about how the variation of wild plants along their range affects their relationship with root-feeding nematodes. In the present study, we examined local and non-local combinations of host plants and root-feeding nematodes to test the hypothesis that nematode reproduction is favoured by local hosts. In two indoor experiments, we exposed populations of the wild dune grass Ammophila arenaria from northern and southern European coastal sand dunes to plant parasitic nematode species (Helicotylenchus spp.) from those same geographical origins. First, we used the southern nematode species to determine whether the effect of a local versus a non-local host may depend on nematode density. Then, in a cross-inoculation experiment we investigated how both nematode species performed with their local, as compared to the non-local hosts.

In both experiments, plant biomass and ontogenetic characteristics were not significantly different between the northern and southern populations. The applied nematode densities did not have a negative impact on plant performance. This allowed us to consider the response of the two different nematode species and their host plants without co-varying differences in plant responses. Reproduction of the nematode species differed according to host origin, but contrary to what we expected, nematode species did not perform better on their local hosts. Helicotylenchus n. sp., the southern species originating from Portugal, performed better on the non-local than on the local host. Male to female ratios were significantly different between the two nematode populations and were lowest in Helicotylenchus pseudorobustus from The Netherlands. Female and juveniles percentages were also quite distinct, with more females in the nematode species from The Netherlands and more juveniles in the nematode species from Portugal.

We concluded that ectoparasitic root-feeding nematodes Helicotylenchus spp. do not necessarily perform best on their local host population of the foredune grass A. arenaria. Our results imply that the natural distribution of Helicotylenchus spp. along the European coast is determined by other factors than host populations. These other factors that could be abiotic, e.g. water availability, or biotic, e.g. local natural enemies adapted to Helicotylenchus spp. Introducing plant genotypes from other parts of the natural range will, therefore, not necessarily lead to reduced abundance of semi-endo or ectoparasitic root-feeding nematodes.