Showing papers in "Journal of Applied Ecology in 1994"

Selecting a model to predict the onset of growth of Fagus sylvatica

Abstract: To evaluate the impacts of climate change on the primary production of temperate deciduous tree species, the onset and cessation of the growth must be accurately described. The aim of this study is to find a model which predicts the onset of growth of Fagus sylvatica (European beech) accurately. Several models have been proposed for the prediction of the timing of budburst of woody plants. Most of these models have been evaluated for species other than Fagus sylvatica, and in some cases for flower buds. Six models were fitted to data on leaf unfolding of Fagus sylvatica, collected in the Netherlands over 57 years (1901 -68). All models require only temperature as input. For Fagus sylvatica, however, photoperiod may influence the timing of the onset of growth (...)

Animal Translocation for Conservation: Performance of Dormice in Relation to Release Methods, Origin and Season

Abstract: 1. We suggest that two important hypotheses underlie the translocation of animals for conservation management, namely that performance is higher for: (i) animals acclimated to a novel site before release (soft releases), compared with those not acclimated (hard releases); and (ii) wild-caught animals compared with captive-bred animals. Despite the increased use of translocations, these hypotheses remain largely untested. 2. Before reintroductions of the dormouse Muscardinus avellanarius, experimental translocations were conducted. These examined the performance of released dormice in relation to season, release methods and animal origin (captive-bred or wild-caught). 3. Early releases (May, June) lost body mass at a significantly higher rate than late releases (August, September). This resulted from seasonal food shortage and could be reversed by supplementary feeding. All released dormice appeared not to locate some important food resources. 4. Soft releases continued to nest at their release point and utilized supplementary food. Hard releases often dispersed and ignored food provided. These differences have profound consequences for reintroductions and hypotheses to explain them are proposed. 5. Wild-caught and captive-bred dormice responded differently to pre-release pens. After release, captive-bred animals travelled significantly less far, in total and from nests, each night. This would have reduced their chances of locating natural food sources and suggests that they are slower to establish in novel habitat. 6. The experiments support the hypotheses underlying translocations and imply that there may also be a common mechanism underlying the behaviour of translocated animals.

The effect of selective logging on the primate populations in the Budongo Forest Reserve, Uganda

Abstract: 1. The Budongo Forest Reserve has been logged selectively for over 60 years. Most compartments in the Reserve have records of the volume of timber removed, the date of harvesting, and of treatments carried out to encourage regeneration of valuable timber species. 2. Line transect surveys of the five diurnal primates resident in this forest were carried out in eight of these compartments; two of which had never been logged and six of which had been harvested at approximately 10-year intervals since 1940. 3. Densities were calculated using the computer package DISTANCE. It was found that the 'Hazard Rate Model' fitted the observer-primate distance data better than other models. Densities over the whole forest were as follows: Cercopithecus mitis sthuhlmannii 43 9 km-2; C. ascanius schmidti 33.3km-2; Colobus guereza occidentalis 39.3 km-2; Papio anubis 11-7km-2; Pan troglodytes schweinfurthii 1-3km2. 4. Only C. guereza showed any significant correlation between logging date and animal density, and none of the primates showed any correlation with the volume of timber removed. For three of the primates (C. guereza, C. mitis and C. ascanius) there were significantly higher numbers in the logged compartments when compared with those that were not logged. 5. Cercopithecus mitis and C. ascanius showed significant correlations between the percentage of different forest types and the densities of the primates in each compartment. In particular there was a positive correlation with the 'mixed' forest type that foresters have been encouraging through their management practices. It is concluded that these two primates and C. guereza have benefited from logging in Budongo and that logging has had little effect on the other two primates.

Population structure of the rare, long-lived perennial Gentiana pneumonanthe in relation to vegetation and management in The Netherlands

Abstract: After analysis of population age-state spectra of Gentiana pneumonanthe in a variety of vegetation types, three different population types could be distinguished: (a) «invasive» or «dynamic» populations, characterized by high densities of seedlings and juveniles relative to the adult age states, (b) «normal» or «stable» populations with adult age states prevailing, but with low densities of seedlings and juveniles, and (c) «regressive» or «senile» populations, consisting only of adult flowering and adult vegetative individuals. The structure of the surrounding vegetation appears to be very important in determining the population structure of the marsh gentian. In particular the percentage of bare soil surface and the cover of the litter layer explain most of the variation in the density and proportion of different age states in the populations

The Effects of Car Traffic on Breeding Bird Populations in Woodland. I. Evidence of Reduced Habitat Quality for Willow Warblers (Phylloscopus trochilus) Breeding Close to a Highway

Abstract: This study investigated the effect of a highway with dense traffic on the quality of adjacent habitats for the willow warbler Phylloscopus trochilus. In the zone of 0-200 m from the highway (road zone) the density of territorial males was much lower (2.1 ha −1 ) than in zones with a comparable habitat at a greater distance (3.3 ha −1 ). The lower density in the road zone was due to a low presence of older males. As a consequence, the proportion of yearling males in the road zone was about 50% higher than in the other zones. Yearling males occupied their territories in the road zone later than in the other zones. In the road zone the proportion of successful yearling males was about 50% lower than in the other zones. No difference was observed in the number of nestlings per male

The distribution of Passerine birds in hedgerows during the breeding season in relation to characteristics of the hedgerow and adjacent farmland

Abstract: 1. Passerine birds were surveyed during the breeding season in hedgerows on 46 farms in lowland England. The incidence of each species was recorded in 50-m lengths of hedgerow and various attributes of these hedgerow sections were also recorded. 2. Logistic regression models were fitted to the data to describe the effects on the incidence of 18 bird species of the number of trees, hedge height and width, dominant plant species in the woody hedge, under the hedge and adjacent to the hedge in the uncultivated strip, the number of woody species in a standard length and other hedgerow characteristics. The effects of adjacent land use and cropping, reduced use of pesticides on cereal field edges and the geographical location of the study farms were also included in the models. 3. Most bird species preferred tall hedges with many trees, but there were some (dunnock, willow warbler and lesser whitethroat) which preferred tall hedges with few trees and others (whitethroat, linnet, yellowhammer) which preferred short hedges with few trees. 4. The differences among bird species in response to a sevenfold reduction in the height of hedges estimated from the models showed good agreement with the variation among species in the effects of severe hedge cutting on bird populations at one farm observed in an independent study. 5. The incidence of six bird species was positively influenced by the number of woody species in a standard length of hedgerow. 6. The incidence of two bird species was significantly affected by the identity of the dominant woody plant species in the hedge and one species by the identity of the dominant plant species at the base of the hedge. 7. Land use adjacent to the hedgerow, categorized as grass, tillage and roadside, had a significant influence on the incidence of five species. However, there was no evidence of consistency among species in the direction of effects. 8. The crops grown on tilled land adjacent to the hedgerow had a significant influence on the incidence of the blackbird. There was a significant degree of consistency among bird species in the ranking of crops, with oil-seed rape the most preferred and spring-sown cereal the least preferred. 9. The incidence of greenfinch, robin and song thrush was significantly lower in hedgerows adjacent to autumn-sown cereals which had received reduced levels of spraying of pesticides than in those adjacent to autumn-sown cereals which were fully sprayed. Most of the other species showed non-significant differences in the same direction. Most of the species studied also showed a non-significant tendency towards higher incidence in hedgerows adjacent to spring-sown cereals with reduced spraying than in those adjacent to fully sprayed spring-sown cereals.

An experimental study of the effects of sheep grazing on vegetation change in a species-poor grassland and the role of seedling recruitment into gaps

Abstract: An experiment was set up in 1986 on a species-poor grassland in Oxfordshire to determine the effect of sheep grazing management on vegetation change after cessation of fertilizer applications. Three seasons of grazing (winter, spring and summer) were applied, each with two grazing intensities, in a 2 × 2 × 2 factorial design with two blocks in 16 paddocks. Point quadrat surveys in 1990 showed that the grassland vegetation was dominated by perennial grasses and that the frequency distribution of species was highly skewed. Dicotyledonous species («dicots») were extremely rare, having an overall frequency of only 0.43%

Composition and population responses of an African savanna grassland to rainfall and grazing

Abstract: Summary 1. The influence of inter-annual rainfall variability and cattle grazing on the abundance (density, basal area), population dynamics (recruitment, growth, survival) and population structure of the dominant perennial grasses of an African savanna was investigated from 1984 to 1989. The unpalatable Aristida bipartite and the palatable Heteropogon contortus and Themeda triandra reproduce by seed; Bothriochloa insculpta reproduces mainly by seed, but sometimes by stolons; Digitaria eriantha can be stoloniferous; Setaria incrassata has rhizomatous growth. 2. Species abundance was more responsive to rainfall variability than to grazing. Density increased in all species in response to several successive dry years because of recruitment and tuft fragmentation, but eventually decreased in a severe final drought year because of plant mortality. The response of basal cover differed between species and sites, although all species (except Digitaria) declined in the final drought year. 3. Seedling recruitment, plant basal area, and mortality were likewise more strongly influenced by rainfall variability than by grazing. Differences in the population dynamics of species were related to their life history attributes. Aristida, a prolific seed producer, was favoured by grazing because high levels of seedling recruitment could be maintained. Seedling recruitment of palatable species (Heteropogon, Themeda) and of Bothriochloa was initially increased under heavy grazing because openings were produced within the vegetation, but this was reversed by the end of the study because of a decline in available seed. There was limited seedling recruitment of Digitaria and Setaria, but recruitment of Digitaria from stoloniferous growth increased population size, although there was no expansion of Setaria clones under the conditions of this study. Themeda and Aristida seedlings attained greater size under heavy than under light grazing.

Structural features of field boundaries which influence the overwintering densities of beneficial arthropod predators

Abstract: Vegetation cover was manipulated within enclosures on a field boundary in southern England to test experimentally the effect on the overwintering of Tachyporus hypnorum and Demetrias atricapillus populations, species that use grassy boundaries of arable fields as refugia during winter. Winter survival was lowest for beetles enclosed on bare earth and highest for those enclosed on tussocks of Dactylis glomerata. The contrast in structural complexity of the experimental treatments caused a 44%, 43% and 36% variation in the final densities of beetles during three successive winters. The densities of T. hypnorum on adjacent field boundaries were estimated from the composition of their vegetation cover and the survival rates of the beetles on different treatments

Modelling the Relationship Between Bird Population Variables and Hedgerow and Other Field Margin Attributes. I. Species Richness of Winter, Summer and Breeding Birds

Abstract: 1. An understanding of how farming practices in adjacent fields and the dimensions of the hedge and other components of the boundary affect birds is essential for efficient conservation management of field boundaries. This paper is based upon surveys of field boundary transects at two sites in eastern England. 2. The first study, near Huntingdon (1983-85), was based upon a range of field boundaries, from small ditches to tall hedges. The boundaries were between small pasture, small arable or large arable fields. 3. The second study, at Swavesey (1985-87), covered the various permutations of boundary structure, and adjacent cropping, available within a catchment of a tributary of the River Great Ouse. This study also included a range of drainage regimes. 4. Regression models were used to relate measures of bird species richness, in both winter and summer over several years, to field boundary attributes, including adjacent land use. 5. Bird variables were positively correlated with the physical size of the hedge, the number and height of trees and adjacent permanent pasture. These attributes accounted for most of the observed variation in bird variables. Ditch and verge dimensions played a statistically significant but relatively less important role. 6. Field boundary management options, beneficial for bird conservation with relatively little agricultural cost, are presented.

The effects of grazing management on the vegetation of mesotrophic (meadow) grassland in Northern England

Abstract: Haymeadows in the Yorkshire Dales and the North Pennines in Northern England are grazed with cattle and sheep outside the 2-3-month summer period, when a hay or silage crop is grown. Experimental exclosures were used from August 1987 to June 1991 to prevent this grazing for various periods in the year in a meadow at Ravenstonedale, Cumbria. Vegetation change was investigated using biomass samples taken in June of each year. Experimental treatments were: no grazing at any time of the year; no grazing from the time of the hay cut until 1 January; no grazing from 1 January to the time of the hay cut; control plots in which the normal grazing regime was followed each year. All other management factors were kept constant. All plots showed vegetation changes related to treatment and to time (...)

The introduction of native plant species on industrial waste heaps: a test of immigration and other factors affecting primary succession

Abstract: Industrial waste heaps in north-west England have become colonized by interesting floras which include regionally uncommon species. However, the range of species is restricted and the vegetation remains open even after 100 years. This appears to be due to the chemical and physical characteristics of the sites, and difficulties of immigration for appropriate species. To test these hypotheses and to explore the improvement of such areas for creative conservation and amenity, introduction of further native species was undertaken. Several species from calcareous grassland, were successfully established on alkaline chemical waste and blast furnace slag, and species from acidic heathland on colliery shale (...)

An analytical model of plant virus disease dynamics with roguing and replanting.

Abstract: The dynamics of a virus disease in a perennial plant population are modelled. The population is divided into healthy, latently infected, infectious and post-infectious plants and linked differential equations describe the dynamics of each category. Qualitative analysis of this model shows stable dynamics and threshold conditions for disease persistence. Stable equilibria are reached after several years. The dynamics of the model are highly sensitive to changes in contact rate and infectious period. Disease management by roguing (removal) of infected plants and replanting with healthy ones is investigated. Roguing only in the post-infectious category confers no advantage. At low contact rates, roguing only when plants become infectious is sufficient to eradicate the disease (...)

The Diet of Grey Seals Around Orkney and Other Island and Mainland Sites in North-Eastern Scotland

Abstract: Almost 1000 faeces were collected in February, June, August and November 1985 in order to quantify the diet of grey seals around Orkney; 82% of these contained fish otoliths. Diet composition, by weight, was assessed by identifying and measuring otoliths from the faecal material and correcting for reduction in otolith size as a result of digestion using experimentally derived species-specific digestion coefficients. Sandeels accounted for almost half the fish consumed, by weight. The rest of the diet was composed mostly of gadids (particularly cod), flatfish (particularly plaice), and sculpins

The Effects of Car Traffic on Breeding Bird Populations in Woodland. II. Breeding Dispersal of Male Willow Warblers (Phylloscopus trochilus) in Relation to the Proximity of a Highway

Abstract: 1. In this study the dispersal activity of male willow warblers Phylloscopus trochilus breeding next to a highway carrying heavy traffic was investigated. 2. Breeding dispersal distances of yearling males along the road were larger than at further distances and were in the same order of magnitude as natal dispersal distances (medians being 303 and 515 m, respectively). 3. A simulation of dispersal directions, adjusted for actual landscape features, indicated that breeding dispersal was actively directed away from the road. 4. There appeared to be a relation between dispersal and breeding performance for yearling males, unsuccessful males moving more frequently and further (median 294 m) than successful males (median 120 m)

A food web approach to evaluating the effect of insecticide spraying on insect pest population dynamics in a Philippine irrigated rice ecosystem

Abstract: Summary 1. Data from a 645-taxa Philippines-wide food web and multiple regression models were used to predict population fluctuations of insect pests in a rice field. Independent variables of pest models included the biomass of rice plants in the field, the abundance of each pest, and the abundances of five highly correlated enemies of the pest, all as functions of time. 2. To test the ability of the models to reveal effects of insecticide spraying, a rice field at the International Rice Research Institute (IRRI) in the Philippines was divided into deltamethrin-sprayed and unsprayed plots. Data on the abundance of seven pest species (Nephotettix virescens, Recilia dorsalis, Sogatella furcifera, Nilaparvata lugens, Hydrellia philippina, Ne. nigropictus and Cofana spectra) and their natural enemies (predators and parasitoids) were collected during the dry season of 1990. 3. Spraying insecticide disorganized the population dynamics of insect species feeding in the IRRI field. Multiple regression models were less able in the sprayed plot than in the unsprayed plot to forecast the population fluctuations of pest species on the basis of various numbers and combinations of independent variables. For example, current pest abundance, by itself, was a significant predictor of future pest abundance for four of the seven pests (Ne. virescens, R. dorsalis, S. furcifera, H. philippina) in the unsprayed plot, but significant fits were found for only two pests (R. dorsalis, H. philippina) in the insecticide-sprayed plot. 4. In the unsprayed plot, independent variables were significant predictors of future pest abundance in four of seven initial models compared to one of seven models in the sprayed plot. Step-wise removal of independent variables in the models enhanced their forecasting power in both the sprayed and unsprayed plots, but significant models in the unsprayed plot nearly always outnumbered those in the sprayed plot. 5. In the unsprayed plot, Ne. virescens retained five of seven independent variables as significant predictors, compared to four for S. furcifera, three for C. spectra, and one for the remaining four pests. Classical models that contain one or two species as independent variables may not be sufficient to forecast future abundances of some Philippine rice pests in unsprayed and sprayed plots. 6. In general, models that included interaction terms and either the presence or absence of sprays among the independent variables did not improve the forecasting power of models in either the sprayed or unsprayed plot. 7. The methods developed here for studying the impact of spraying on the organization of arthropod communities in rice fields could be applied to other interventions

Restoration of Endangered Species Conceptual Issues, Planning and Implementation

Abstract: Part I Conceptual Issues in Restoration Ecology: 1 Organizational and managerial guidelines for endangered species restoration programs and recovery teams Tim W Clark and John R Cragun 2 Genetic considerations for plant population restoration and conservation Charles B Fenster and Michelle R Dudash 3 Managing genetic diversity in captive populations of animals Robert C Lacy 4 The relationship of rarity to plant reproductive biology Stephen G Weller 5 Experimental evidence for insect impact on populations of short-lived, perennial plants, and its application in restoration ecology Svata M Louda Part II Restoration Planning: 6 Impacts of biological invasions on the management and recovery of rare plants in Haleakala National Park, Maui, Hawaii Lloyd L Loope and Arthur C Medeiros 7 Disturbance-dependent persistence of rare plants: anthropogenic impacts and restoration implications Noel B Pavlovic 8 A metapopulation approach to Pitcher's thistle recovery in southern Lake Michigan dunes A Kathryn McEachern et al 9 Restoration of woodland caribou to the Lake Superior region Peter J P Gogan and Jean Fitts Cochrane Part III Implemented Restorations: 10 The swift fox reintroduction program in Canada from 1983 to 1992 Ludwig N Carbyn et al 11 Restoration of the endangered black-footed ferret: a twenty-year overview Tim W Clark 12 Development and implementation of a recovery program for the federally threatened Lakeside daisy Marcella M DeMauro 13 Demographic monitoring and the recovery of endangered plant populations Bruce M Pavlik Part IV Synthesis and Future Directions: Biology, Politics and Reality: 14 Restoration ecology: living with the Prime Directive Joel S Brown Taxonomic index Subject index

The Concise Oxford dictionary of ecology

Abstract: From acid rain, CFC's, and the greenhouse effect to the food-chain and the gene bank, The Concise Oxford Dictionary of Ecology provides 5,000 up-to-date entries on all aspects of ecology and the environmental sciences. With many entries derived from the acclaimed Oxford Dictionary of Natural History, it covers a vast range of subjects, from plant and animal physiology, animal behavior, evolution, environmental pollution, and conservation to climatology, meteorology, geomorphology, and oceanography. Also included are biographical notes on eminent ecologists and other scientists, as well as helpful cross-references that make this volume an invaluable reference tool for students, professionals, and anyone with an interest in the natural world and our environment.

Index Numbers for Waterbird Populations. I. Review and Methodology

Abstract: This paper reviews methods used to estimate bird population index numbers and proposes a new method. An index number for a year is defined as the ratio of the population size in the year to the population size in the base year. In the context of waterbird populations, the major problem with generating index numbers is the fact that, owing to missing observations at a subset of localities, the total population size in any year is unknown. We suggest a model-based approach to imputing missing observations so that the total population size at the localities may be estimated and used to produce a series of index numbers of the population sizes each year

The effect of spatial scale of treatment with dimethoate on invertebrate population recovery in winter wheat

Abstract: The influence of plot size in assessing the impact of pesticide treatment on invertebrate populations in cereals was investigated. Within-field experiments were performed in southern England in winter wheat using the broad-spectrum aphicide dimethoate. Post-treatment recovery was monitored using, in separate experimental designs, pitfall traps in the centre of treated plots of different size from 4 × 4 m up to 288 × 288 m, and pitfall traps in transects running from the edge to the centre of large treated plots. Invertebrate population recovery was shown to be dependent on the size of the plot treated. Two contrasting patterns of recovery were identified: (A) recovery progressing from the edge to the centre of treated areas; (B) recovery most rapid in the centre of the large treated areas

Dormouse distribution: survey techniques, insular ecology and selection of sites for conservation

Abstract: A stratified sample of 238 woodlands in Herefordshire was surveyed to determine the incidence of dormice in relation to age, area and isolation of the site. Characteristically gnawed hazel-nut shells were sought as indicators of dormouse presence. Dormice were more frequently found in ancient woodland than in recent woodland, supporting a previous hypothesis that they are an insular species. Both site isolation and area influenced distribution, in accordance with insular ecological theory. Prevalence of woodland and boundaries around a site affected dormouse incidence. The results suggest that isolated woodlands less than about 20 ha in extent are unlikely to support viable dormouse populations

The Effects of Season and Diet Composition on the Radiocaesium Intake by Sheep Grazing on Heather Moorland

Abstract: In north-east Scotland on a mixed heather and grassland pasture grazed by sheep, 2 × 2 m areas of Calluna vulgaris heath and Deschampsia flexuosa grassland were artificially contaminated with 134 Cs by soil injection. Estimates of the 134 Cs intake by sheep were made on the basis of measurements of dry matter intake, diet composition and 134 Cs concentrations in diet components, assuming that the whole pasture had been contaminated. Dry matter intake by sheep was measured using a natural n-alkane of plant waxes and an orally administered n-alkane as markers. Diet composition was determined by a combination of botanical analysis of samples of ingested material and relationships between n-alkane patterns in faeces and ingested material (...)