Andrew Cherrill

Soil, vegetation and space: an analysis of their effects on the invertebrate communities of a moorland in north-east England

1. The role of spatial factors in determining the structure and function of plant and invertebrate communities on a 117 ha upland moor in north-east England was investigated using ordination and Mantel tests. 2. The vegetation species composition was spatially autocorrelated and associated with the soil conditions. The species composition of Auchenorrhyncha (Hemiptera) communities appeared to be determined by both the soil conditions and vegetation species composition, whereas Heteroptera (Hemiptera) were associated primarily with the vegetation. Araneae were not found to be directly related with either the soil conditions or vegetation, but were linked to the spatial location of the sample. Carabidae (Coleoptera) were associated with variation in soil conditions, but not directly to spatial location or vegetation. 3. The implications of these results for the management of vegetation in upland landscapes are discussed.

Predicting the distributions of plant species at the regional scale: a hierarchical matrix model.

This paper describes a model which links four levels in an ecological hierarchy using a series of matrices. The four levels are landscape, land cover type, community and species. Each matrix quantifies the probabilistic associations between entities in two adjacent levels in the hierarchy. A landscape classification (1 km resolution) provides a spatial element to the model enabling the distributions of species to be predicted and presented as maps within a geographical information system (GIS). Implementation of the model in Northern England is described. The distributions of 579 species of plants were predicted and compared with data from independent field surveys. The predicted distributions were found to be accurate for 59 % of species. The distributions of rare and non-native (introduced) species of plant were relatively poorly predicted. The potential of this approach to model plant species distributions is discussed.

A comparison of land cover types in an ecological field survey in Northern England and a remotely sensed land cover map of Great Britain

Earth-orbiting remote sensing satellites have important roles to play in resource assessment and monitoring changes in land cover. However, there will often be a need to relate the land cover types identified from the classification of satellite imagery to other classifications of land cover, and particularly those familiar to practical conservationists working in the field. This paper compares the land cover types recognised in the first remotely sensed land cover map of Great Britain with those of a widely used ecological field survey method (the Phase-1 survey technique of the former Nature Conservancy Council of Great Britain) within a sample area of 188 km2 in Northern England. Digitised field maps were combined with the remotely sensed land cover map within a geographical information system (GIS) to produce a matrix of correspondence linking the two classifications. The results are discussed with an emphasis on the factors underlying the observed differences between the two sets of map data. Two potential applications of the land cover map are investigated — first in the mapping of dwarf shrub vegetation (a habitat which has declined over the last 50 years), and second in the detection of coniferous afforestation (a significant cause of semi-natural habitat loss in upland Britain).

Seed dormancy, nitrogen nutrition and shade acclimation of Impatiens glandulifera: implications for successful invasion of deciduous woodland

Background : Non-native invasive plants capable of fast growth may establish and develop rapidly under the high soil nitrogen (N) and increased irradiance levels that occur in gaps at disturbed sites within deciduous woodland. However, if disturbance is transitory, then the long-term success of an invasive species within deciduous woodland will be dependent on its ability to compete with native species and acclimate to the typical conditions of low N availability and irradiance. Aims: To gain greater understanding of the ecophysiological reasons for the success of Impatiens glandulifera as a weed species in deciduous woodland. Methods: We examined N form, N concentration and irradiance effects on seed dormancy, N nutrition and shade acclimation of Impatiens. Results: Under controlled conditions, Impatiens seed required a period of wet chilling to overcome dormancy. High nitrate ( ) concentration and light gave substantial increases in germination over 8–12 weeks chilling and decreased time to 50% emergence over a full winters chilling. Under high irradiance in a glasshouse, Impatiens showed N nutrition characteristics similar to those of fast growing crop and weed species. Within woodland and on high and relatively low supply in a glasshouse, Impatiens showed a range of mechanisms of acclimation to low irradiance, in particular, increases in height, dry matter partitioning to the shoot, use of as osmoticum in stems, specific leaf area (SLA) and leaf chlorophyll concentration. Conclusions: High soil concentrations and light may be factors in the synchronisation of emergence of Impatiens in disturbed sites producing a high-density and competitively strong cohort of seedlings within a short period of time. Rapid growth under high irradiance and N supply will allow Impatiens seedlings to establish quickly in disturbed woodland sites. Acclimation to low irradiance, in particular, maintenance of height and development of an exceptionally high SLA at relatively low supply, as demonstrated could allow Impatiens to shade out competing field layer species at the low levels of N and irradiance typical of woodland.

Character displacement in Hydrobia

SummaryFenchels study of size variation in Hydrobiid snails in the Limfjord, Denmark, provides one of the most convincing cases of ecological character displacement available. In order to assess the generality of the phenomena within the Hydrobia genus, allopatric and sympatric Hydrobia ventrosa, H. neglecta and H. ulvae were collected from 24 coastal sites around Eastern England in July and October, 1982. Shell heights of 5,850 snails from 55 samples were recorded. These data were analysed for intraspecific allopatric-sympatric, and interspecific height differences. Such differences were not significant for H. ventrosa/H. neglecta, but the species exhibited parallel variation at sympatric sites. H. ventrosa/H. ulvae showed only significant interspecific differences, but in both allopatry and sympatry. The pattern of mean size variation for these species resembles that in the Limfjord. However the statistical analyses fail to provide support for character displacement. Differences in character states attributed to the process of character displacement may result from a number of other causes. Environmental conditions at sympatric and allopatric sites may act differentially on the heights of H. ulvae and H. ventrosa. The conditions that prevail at sympatric H. ulvae sites appear to lead to increased size in this species irrespective of the presence of H. ventrosa.

The reliability of ‘Phase 1’ habitat mapping in the UK: the extent and types of observer bias

Abstract The recording of broad vegetation types in habitat or land cover maps is often the starting point of ecological investigations of sites and landscapes. Habitat maps inform wildlife evaluations and management decisions, and can aid in the identification of areas requiring further investigation. Little data are currently available on the reliability of maps recorded by field surveyors, or the types of error that they contain. In this study, maps of the same upland area in northern England produced by six experienced ecologists are compared. The surveyors used a standard method applied widely within the United Kingdom, but agreement between pairs of maps averaged only 25.6% of the study site’s area. The majority of differences were due to differing interpretations of the types of vegetation present, rather than spatial errors – although the latter were also detected. The range of vegetation types which were confused with each other was great, but ecologically related vegetation types were most often confused. The causes and consequences of differences between maps are discussed, and quality control and quality assurance are identified as important, but neglected issues in ecological survey.

Timing of life cycles in a seasonal environment: the temperature-dependence of embryogenesis and diapause in a grasshopper (Chorthippus brunneus Thunberg)

SummaryThe durations of the stages in the embryonic development of Chorthippus brunneus (Thunberg) have been estimated at constant temperatures of 20° C and 30° C. There was stage-dependent variation in the temperaturedependence of morphogenesis-a pattern apparently not previously described. The earliest and latest stages of morphogenesis proceeded relatively rapidly at higher temperatures. But intermediate stages, which would tend to occur around the diapause stage in a temperate winter, proceeded relatively rapidly at lower temperatures, as did diapause development. At a given temperature, there was individual variation between eggs such that some developed consistently faster than others. However, these intrinsic differences could be altered by exposure to diapause-breaking conditions at different morphological stages. The results are discussed in terms of their adaptive significance, their effect on population dynamics in a seasonal environment, and their implications for the nature of diapause in insects generally.

Relationships between oviposition date, hatch date and offspring size in the grasshopper Chorthippus brunneus

Abstract 1. The grasshopper Chorthippus brunneus has been shown to increase egg size with maternal age under constant laboratory conditions, such that late‐laid eggs are larger than early laid eggs. In this study, an increase in the size of eggs (and hatchlings from those eggs) was recorded with date of oviposition in a field cage population. This suggests that the relationship between maternal age and egg size, observed previously in the laboratory, also occurs in the field. There was, however, some evidence that the behaviour of the maternal females in field cages was modified by the onset of autumnal weather at the end of the breeding season. Only a small number of eggs was laid in the last 3 weeks of the summer but these yielded relatively small hatchlings.

Assessing the Floristic Diversity of Hedge Networks: A landscape perspective

The type of land cover adjacent to hedges has been shown to influence the species composition of the ground flora. An assessment of the contribution of hedge networks to the biodiversity of landscapes therefore requires information on the relative lengths of hedge associated with different land covers. In the River Tyne catchment, Northern England, the association between hedges and land cover types differed between four landscapes. Overall, the greatest length of hedge was adjacent to arable crops, improved grasslands and roads. Hedges next to improved grassland and roads were the most species-rich, while those adjacent to arable crops were the least species-rich. Species which were common adjacent to arable crops were also common adjacent to other land covers. Hedges adjacent to improved grassland, roads and semi-natural broadleaved woodland supported species which were not common elsewhere in the hedge network. It was also found that hedges with different land cover on each side supported different floras on each side. When planning landscape-scale surveys of hedge biodiversity, it is important to survey both sides of hedges, and sampling should be stratified to include hedges adjacent to the different types of land cover present.

The survey and prediction of land cover using an environmental land classification: A case study in northern England

Abstract The formulation of policies influencing land cover requires accurate information on the distributions of competing land cover types. This paper investigates the use of a numerical land classification (derived by the Institute of Terrestrial Ecology, Merlewood, UK) in the survey and prediction of land cover. The classification groups 1-km grid squares with similar environmental characteristics into distinct landscape types (ITE land classes). The ITE land classes were used to stratify sampling effort in a field survey of land cover within the catchment of the River Tyne in northeast England in 1991. Variation in land cover within and between land classes is analysed and the principal patterns of land cover within the catchment are described. The use of the land classes in the prediction of land cover within unsurveyed 1-km grid squares is discussed in light of the observed variation in land cover. It is concluded that stratification of field surveys using land classification can aid the identification and interpretation of broad patterns of variation in land cover, but that intra- and inter-land class variation in land cover is too great to allow the use of ITE land classes in the prediction of land cover within individual unsurveyed grid squares.