Showing papers in "Journal of Applied Ecology in 1996"

The vegetation N:P ratio: a new tool to detect the nature of nutrient limitation

Abstract: Nutrient limitation (mostly N or P) is a driving force in ecosystem development. Current techniques to determine the nature of nutrient limitation use laborious fertilization experiments. It was hypothesized that the N:P ratio of'the vegetation directly indicates the nature of nutrient limitation on a community level (N vs. P limitation). This hypothesis was tested by reviewing data on fertilization studies in a variety of European freshwater wetland ecosystems (bogs, fens, wet heathlands, dune slacks, wet grasslands). In a subset of the data (dune slacks) between-site intraspecific variation and within-site interspecific variation in nutrient content and N:P ratio was studied in five plant species. A review of 40 fertilization studies reveals that an N:P ratio >16 indicates P limitation on a community level, while an N:P ratio < 14 is indicative of N limitation. At N:P ratios between 14 and 16, either N or P can be limiting or plant growth is colimited by N and P together. In only one out of 40 fertilization studies, the N:P ratio gave a false indication of the nature of nutrient limitation. Measuring the N:P ratio of the vegetation is a simple and cheap alternative to fertilization studies. The method can only be used under conditions where either N or P controls plant growth. The dataset contains a large variety of vegetation types and plant species, and 11 I of the 40 sites were near-monocultures. This suggests that interspecific differences in critical N:P ratios among species may be insignificant. However, a rigorous test of this hypothesis is required. A survey in 18 dune slacks showed large within-site variation in N:P ratio among five species (Calamagrostis epigejos, Phragmites australis, Lycopus europaeus, Mentha aquatica and Eupatorium cannabinum). The N:P ratios of the five species suggested that within plant communities species can be differentially limited by N or P. Moreover, species with an N:P ratio that suggested P-limitation were found at sites where N controlled community biomass production, and vice versa. Between-site intraspecific variation in N and P contents and N:P ratios was also large, and about equal for the five species. This illustrates the plasticity of plant species with respect to N and P contents, probably in response to differences in N and P supply ratios. The vegetation N:P ratio is of diagnostic value and its use may increase our understanding of numerous facets of physiological, population, community and ecosystem ecology.

Global biodiversity assessment

Abstract: Foreword Preface Acknowledgements Executive summary 1. Introduction V. H. Heywood and I. Baste 2. Characterization of biodiversity F. A. Bisby 3. Magnitude and distribution of biodiversity D. L. Hawkesworth and M. T. Kalin-Arroyo 4. Generation, maintenance and loss of biodiversity R. Barbault and S. D. Sastrapradja 5. Biodiversity and ecosystem functioning: basic principles H. A. Mooney, J. Lubchenco, R. Dirzo and O. E. Sala 6. Biodiversity and ecosystem functioning: ecosystem analyses H. A. Mooney, J. Lubchenco, R. Dirzo and O. E. Sala 7. Inventorying and monitoring of biodiversity N. E. Stork and M. J. Samways 8. The resource base for biodiversity assessments D. L. Hawkesworth 9. Data and information management and communication S. Olivieri, J. Harrison and J. R. Busby 10. Biotechnology B. Barlow and G. T. Tzotzos 11. Human influences on biodiversity J. A. McNeely, M Gadgil, C Leveque, C Padoch and K Redford 12. Economic values of biodiversity C. Perrings 13. Measures for conservation of biodiversity and sustainable use of its components K. Miller, M. H. Allegretti, N. Johnson and B. Jonsson Annex 1. Organization of the Global Biodiversity Assessment Annex 2. Institutions and staff involved in the GBA project Annex 3. Venues, dates and participants in GBA meetings and workshops Annex 4. Contributors to the GBA Annex 5. List of peer reviewers of the GBA Annex 6. Glossary Annex 7. List of acronyms.

Ecological census techniques : a handbook

Abstract: Preface 1 Planning a research programme William J Sutherland 2 Principles of sampling Jeremy J D Greenwood and Robert A Robinson 3 General census methods Jeremy J D Greenwood and Robert A Robinson 4 Plants James M Bullock 5 Invertebrates Malcolm Ausden and Martin Drake 6 Fish Isabelle M Cote and Martin R Perrow 7 Amphibians Tim R Halliday 8 Reptiles Simon Blomberg and Richard Shine 9 Birds David W Gibbons and Richard D Gregory 10 Mammals Charles Krebs 11 Environmental variables Jacquelyn C Jones, John D Reynolds and Dave Raffaelli 12 The twenty commonest censusing sins William J Sutherland Index

Species loss in fragments of tropical rain forest: a review of the evidence.

Abstract: A review of the literature shows that in nearly all cases tropical rain forest fragmentation has led to a local loss of species. Isolated fragments suffer reductions in species richness with time after excision from continuous forest, and small fragments often have fewer species recorded for the same effort of observation than large fragments or areas of continuous forest. Birds have been the most frequently studied taxonomic group with respect to the effects of tropical forest fragmentation. The mechanisms of fragmentation-related extinction include the deleterious effects of human disturbance during and after deforestation, the reduction of population sizes, the reduction of immigration rates, forest edge effects, changes in community structure (second- and higher-order effects) and the immigration of exotic species. The relative importance of these mechanisms remains obscure. Animals that are large, sparsely or patchily distributed, or very specialized and intolerant of the vegetation surrounding fragments, are particularly prone to local extinction. The large number of indigenous species that are very sparsely distributed and intolerant of conditions outside the forest make evergreen tropical rain forest particularly susceptible to species loss through fragmentation. Much more research is needed to study what is probably the major threat to global biodiversity.

An autologistic model for the spatial distribution of wildlife

Abstract: 1. A new method for estimating the geographical distribution of plant and animal species from incomplete field survey data is developed. 2. Wildlife surveys are often conducted by dividing a study region into a regular grid and collecting data on abundance or on presence/absence from some or all of the squares in the grid. Generalized linear models (GLMs) can be used to model the spatial distribution of a species within such a grid by relating the response variable (abundance or presence/absence) to spatially referenced covariates. 3. Such models ignore or at best indirectly model dependence on unmeasured covariates, and the intrinsic spatial autocorrelation arising for example in gregarious populations. 4. We describe a procedure for use with presence/absence data in which spatial autocorrelation is modelled explicitly. We achieve this by extending a logistic model to include an extra covariate which is derived from the responses at neighbouring squares. The extended model is known as an autologistic model. 5. To allow fitting of the autologistic model when only a random sample of squares is surveyed, we use the Gibbs sampler to predict presence/absence at unsurveyed squares. 6. We compare the autologistic model with the ordinary logistic model using red deer census data. Both models are fitted to a subsample of 20% of the data and results are compared with the 'true' abundance and spatial distribution indicated by the full census. We conclude that the autologistic model is superior for estimating the spatial distribution of the deer, whereas the ordinary logistic model yields more precise estimates of the overall number of squares occupied by deer at the time of the survey.

Serengeti II : dynamics, management, and conservation of an ecosystem

Abstract: The aim of this text is to provide an up-to-date understanding of the Serengeti-Mara ecosystem in East Africa, home to one of the largest and most diverse populations of animals in the world. Building on the groundwork laid by "Serengeti: Dynamics of an Ecosystem", published in 1979 by the University of Chicago Press, this work integrates studies of the ecosystem at every level, from the plants at the bottom of the visible food chain to the many species of herbivores and predators, as well as the system as a whole. Drawing on data from long-term studies, the contributors examine the processes that have produced the Serengeti's biological diversity, with its species-species and species-environment interactions. The book also discusses computer modelling as a tool for exploring these interactions, employing it to test and anticipate the effects of social, political and economic changes on the entire ecosystem and on particular species, with the aim of assisting the development of future conservation and management strategies.

Low-intensity farming systems in the conservation of the countryside

Abstract: The historical role of agriculture in creating semi-natural vegetation is still not fully appreciated by many ecologists, conservationists, policy-makers or the general public. Nor is the fact that for many European landscapes and biotopes of high nature conservation value, the only practicable, socially acceptable and sustainable management involves the continuation of low-intensity farming. Consequently, too much emphasis is placed on attempting to ameliorate damaging effects of agricultural management rather than supporting ecologically sustainable low-intensity farming practices. More than 50% of Europe's most highly valued biotopes occur on low-intensity farmland. However, most of this farmland has no environmental policy directly affecting it; most management decisions are taken by farm businesses and determined primarily by European and national agricultural officials. As a result, there continues to be intensification or abandonment of traditional practices, changes which are equally damaging to the nature conservation value. However, the nature conservation importance of low-intensity farming systems is gradually being recognized. Reforms and reviews of agriculture policy are providing a variety of potential opportunities for maintaining such systems. Unfortunately, initiating change through policy is a slow process. There is therefore also a pressing need to look for other opportunities to maintain surviving systems and, where poss-. ible, to reinstate those recently lost. Although these systems may be considered low-intensity in terms of chemical inputs and productivity, they are usually high-intensity in terms of human labour. Therefore, the processes that make the low-intensity farmed countryside biologically rich and diverse must be understood, but at the same time mechanisms to make life easier and more rewarding for the people who work such farmland must be found. Ecologists and conservationists should think less of'remnants of habitat being left amongst farmland' and more of a farmland biotope for which optimum management practices need to be developed. At the same time the current emphasis on site-based conservation should be complemented by strategic initiatives that promote wise management of the wider countryside.

Biodiversity : a biology of numbers and difference

Abstract: What is biodiversity? Part 1 Measuring biodiversity: genetics of biological diversity - from varieties to species comparing character diversity among biotas species richness - measure and measurement measuring relations among biodiversity, ecological function and functional diversity diversity and higher-levels of organization. Part 2 Patterns in biodiversity: spatial and temporal patterns of genetic diversity within species spatial patterns in taxonomic diversity temporal changes in biodiversity - detecting patterns and identifying causes spatial and temporal patterns in functional diversity. Part 3 Conservation and management: does biodiversity matter? - evaluating the case for conserving species identifying priorities for the conservation of biodiversity - systematic biological criteria within a socio-political framework managing biodiversity biodiversity and global change.

Experimental studies on the dispersal of plants and animals on sheep in calcareous grasslands

Abstract: 1. In June to September 1993 a transhumant flock of sheep on the Schwabische Alb was examined with respect to which plants and animals are transported on and in the wool of sheep within calcareous grasslands. Several factors possibly influencing the attachment and detachment of diaspores on fleeces were studied, as well as the distribution of diaspores on the various body-parts of a sheep. The effects of different modes of sheep locomotion on dispersal were examined with the help of a sheep dummy. In order to assess the retention time of diaspores and animals on sheep, some experiments with marked diaspores and animals were carried out on two tamed sheep. 2. In 16 intensive examinations of the fleece of a single sheep, over 8500 diaspores of 85 vascular plants species were found. The highest numbers of diaspores were attached at the breast and neck of the sheep. 3. Height of diaspore presentation, surface structure of diaspores and sheep locomotion were found to be the decisive factors for the reception and transport of diaspores in the wool. In addition, plant frequency and the length of the disseminating period are of importance. 4. Marked diaspores with both adhesive and smooth surfaces remained on the sheepskin for up to seven months, and can consequently be dispersed over the entire roaming area of the sheep. 5. Amongst the animals transported by sheep, only grasshoppers (13 species) were observed frequently on the flock of sheep. The period of time marked grasshoppers stayed on sheep ranged from I to 69min, with an average of 14 min. During this period sheep can cover distances of over 100m when grazing and well over 500m when roaming. 6. Our study indicates that the importance of the dispersal of diaspores, and especially animals, by animals has so far been largely underestimated. This is mostly due to the methods previously used to examine dispersal mechanisms. 7. Conservation management of rare and endangered species should consider the importance of sheep for maintaining the species richness of calcareous grasslands. It is likely that transhumant sheep farming is irreplaceable in the restoration of grasslands threatened by fallow and woody successional stages. Moreover, traditional shepherding facilitates the exchange of individuals of both plants and animals between isolated patches. That is, sheep are able to maintain dynamic processes even in our greatly fragmented landscape; this is probably essential to long-term population viability of many species.

Dynamics of Weed Populations.

Abstract: Dynamics of weed populations , Dynamics of weed populations , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

A method to quantify the effects of human disturbance on animal populations

Abstract: 1 The extent and consequences of human disturbance on populations of vertebrates are contentious issues in conservation As recreational and industrial uses of the countryside continue to expand, it is becoming increasingly important that the effects of such disturbance on wildlife are quantified 2 This study describes a method of quantifying the effect of disturbance, based on measuring the trade-off between resource use and risk of disturbance This approach is based on one used by ethologists to study the effects of predation risk on patch use 3 Pink-footed geese, Anser brachyrhynchus, feeding on arable fields, are highly responsive to disturbance from surrounding roads The extent to which these fields are exploited declines linearly with increasing risk of disturbance The reduction in use of these feeding grounds caused by disturbance can be quantified by translating the biomass of food not exploited into the number of birds that this food could have supported 4 This approach allows both quantification of the impact of disturbance on a population, and exploration of the potential consequences of changes in disturbance on the size of populations

Relationships among grizzly bears, roads and habitat in the Swan Mountains, Montana

Abstract: Relationships between grizzly bears, habitat, and roads were investigated between 1990 and 1994 in the Swan Mountains, Montana. Relationships were examined at three levels of resource selection. Differences existed between habitat and road features within, and those outside, the multi-year composite female grizzly bear home range. Using logistic regression, large resource selection probability functions were obtained for the subalpine zone within multiple-use lands having no roads. Selection probability was zero for private lands and declined as total road density increased. Within seasonal ranges, most grizzly bears favoured low temperate and temperate elevation zones over the subalpine zone during all seasons. Relative to forested habitats, avalanche chutes were positively selected for during all seasons, but especially in spring. Shrub lands and cutting units were important to most bears during summer and autumn. Grizzly bears were more closely associated with higher total road densities during spring than during other seasons. When in low temperate habitats, most bears used habitats with lower total road density than occurred randomly. Seasonal use by grizzly bears of areas within a 0.5 km buffer surrounding roads was evaluated. Most grizzly bears exhibited either neutral or positive selection for buffers surrounding closed roads and roads receiving 10 vehicles per day. Between 1988 and 1994, eight grizzly bears were killed by humans. These deaths were directly influenced by road access and unnatural food sources. These deaths, in addition to natural mortality, were too great to promote local population growth.

A review of wolf predation in southern Europe: does the wolf prefer wild prey to livestock?

Abstract: The recent recovery of the wolf in southern Europe has not yet removed the risk of local extinction. Wolf populations are fragmented and often comprise fewer than 500 individuals. In North America, northern and eastern Europe, wolves feed mainly on wild herbivores. In southern Europe, this canid has apparently adapted to feed also on fruit, rubbish, livestock, small and medium-size mammals. The main conservation problem lies with predation on domestic ungulates, which leads to extensive killing of wolves. The reintroduction of wild large herbivores has been advocated as a means of reducing attacks on livestock, but predation on the latter may remain high if domestic ungulates are locally abundant. Our synthesis of 15 studies, published in the last 15 years, on food habits of the wolf in southern Europe, has shown that ungulates have been the main diet component overall. A significant inverse correlation was found between the occurrence (%) of wild and domestic ungulates in the diet. The presence of relatively few wild ungulate species was necessary to reduce predation on livestock. Selection of wild and domestic ungulate prey was influenced mainly by their local abundance, but also by their accessibility. Feeding dependence on rubbish was local and rare. In Italy, the consumption of rubbish/fruit and that of ungulates was significantly negatively correlated. Diet breadth increased as the presence of large prey in the diet decreased. The simultaneous reintroduction of several wild ungulate species is likely to reduce predation on livestock and may prove to be one of the most effective conservation measures.

Invasive plants and water resources in the Western Cape Province, South Africa: modelling the consequences of a lack of management.

Abstract: 1. The invasion of fynbos shrublands by woody weed species can reduce the water yield from catchment areas dramatically. We modelled the consequences of uncontrolled invasion on water yield using a geographical information system (Arc/Info). 2. Five important processes were recognized : the occurrence of fire ; the spread and establishment of alien plants after fire ; rainfall-to-run-off ratios ; growth and changes in biomass between fires ; and effects of these changes on streamflow. 3. The simulations of water yield were modelled with the Arc/Info GRID module using a 200 x 200-m grid. It was assumed that the interval between fires was 15 years and that proliferation and dispersal of alien plants took place only after fires. 4. Between fires, the model simulated the growth of the vegetation and its effects on streamflow, using relationships between rainfall and run-off, and run-off and above-ground biomass. 5. Results for the Kogelberg area in the Western Cape Province showed that alien plants invaded about 40% of the grid cells within 50 years. Cover of alien plants increased from an initial estimate of 2.4% to 62.4% after 100 years. 6. Invasion of catchment areas would result in an average decrease of 347 m 3 of water per hectare per year over 100 years, resulting in average losses of more than 30% of the water supply to the city of Cape Town. In individual years, where large areas would be covered by mature trees, losses would be much greater. 7. In addition, invasion of fynbos by alien plants will cause the extinction of many plant species, increase the intensity of fires, destabilize catchment areas with resultant erosion and diminished water quality, and decrease the aesthetic appeal of mountain areas. 8. Control of alien weed species is necessary to avert the above impacts, and the costs of control operations could be justified by the savings achieved in maintaining adequate water run-off from stable catchments in the long term.

An experimental study of the reproductive behaviour and success of farmed and wild Atlantic salmon (Salmo salar)

Abstract: 1. Escape of cultured organisms into natural ecosystems may threaten wild populations both ecologically and genetically. In the aquaculture industry, farmed Atlantic salmon (Salmo salar L.) often escape and enter the spawning grounds of wild salmon. We report experiments to assess the competitive and reproductive abilities of fifth-generation farmed salmon and their potential impacts upon wild salmon. 2. The farmed and wild females had similar levels of competitive behaviour; however, they differed in reproductive behaviour and success. Farmed females displayed less breeding behaviour, constructed fewer nests, retained a greater weight of eggs unspawned, were less efficient at nest covering, incurred more nest destruction, and suffered greater egg mortality than wild females. As a result, farmed females had less than one-third of the reproductive success of wild females. 3. The farmed males were even less successful than the farmed females in competition with the wild fish. They were less aggressive, courted less, partook in fewer spawnings, and achieved only an estimated one to three percentage of the reproductive success of the wild males. 4. The farmed males exhibited inappropriate mating behaviour, that led to poor fertilization success, even in the absence of competition with wild males. 5. Adult farmed fish are thus likely to be relatively unsuccessful in natural environments due to a competitive and reproductive inferiority apparently resulting from domestication.

Foraging habitat preferences of vespertilionid bats in Britain

Abstract: The selection of foraging habitats by vespertilionid bats in Britain was quantified using a stratified sample of 1030 1-km squares. Quantitative analysis of habitat preference and avoidance on a large scale indicated that bats were flexible, yet consistent in their habitat use across contrasting landscapes. Habitats associated with broadleaved woodland and water were most preferred, while arable land, moorland and improved grassland were strongly avoided. Linear vegetation features were selected in all landscapes, demonstrating the importance of habitat continuity to bats. The availability of preferred habitats was low and patchy in all landscapes, indicating that bats have specialized habitat requirements. Differences in habitat selection between landscape types and possible factors influencing habitat selection are discussed. Habitat selection analysed on a local scale demonstrated the same consistent preference for woodland, riparian and corridor habitats across 19 discrete land classes. Management policies for bats in Britain should endeavour to preserve and enhance the availability of woodland, water margins and linear corridor habitats. Lack of continuity of the landscape, loss and fragmentation of habitat patches plus deterioration of the quality of such patches may pose a threat to bat populations.

The effect of an experimental reduction in predation pressure on the breeding success and population density of grey partridges Perdix perdix

Abstract: 1. A 6-year experiment is described which was designed to test whether or not predation control, as practised by traditional and currently legal methods, increases (i) the breeding success and autumn numbers of partridges, and (ii) the subsequent breeding density. 2. In the experiment, predation control effort was highly seasonal and designed to reduce partridge breeding season losses by killing resident predators of selected species. 3. The predation control significantly reduced the abundance of foxes, carrion crows and magpies during the critical partridge nesting period. 4. After the nesting period, predators re-established themselves each year, during late summer and early autumn. 5. The predation control significantly increased the proportion of partridges that bred successfully and the average size of their broods, thus substantially improving the production of young. Excluding effects of site and year predation control increased August numbers by 75%. Incorporating the effects on breeding stocks in subsequent years this led to an overall 3.5-fold difference between autumn populations with and without predation control. 6. Predation control significantly increased partridge breeding stocks the following year. Breeding stocks in years following predation control were 36% larger than stocks in years that did not follow predation control-excluding the effects of year and site. After 3 years this had produced a 2.6-fold difference in breeding density between the sites with and without predation control. 7. These results suggest that predators play a key role in limiting production and subsequent breeding density of partridges.

Decline of the flora in Danish arable fields

Abstract: Surveys of the weed flora in Danish arable fields were conducted in 1967-70 and 1987-89. Frequencies of 67 common weed species in spring barley, spring rape, winter rye, winter wheat and grass ley were compared. The comparison showed that the occurrence of common weed species has generally decreased during the last 20 years. The frequency of some species such as Anagallis arvensis, Arenaria serpyllifolia, Atriplex patula, Cerastium caespitosum, Galium aparine, Plantago major and Silene noctiflora has decreased remarkably, possibly because of intensive chemical weed control. The dominating weed species in the 1987-89 survey were largely the same as in the 1967-70 survey, namely Capsella bursa-pastoris, Chenopodium album, Elymus repens, Myosotis arvensis, Poa annua, Polygonum aviculare, P. convolvulus, P. persicaria, Stellaria media, Taraxacum, Veronica arvensis, V. persica and Viola arvensis. Some species occurred more frequently in 1987-89 than in 1967-70, but only Stellaria media increased significantly and only in grass ley.

The effects of habitat fragmentation and livestock grazing on animal communities in remnants of gimlet Eucalyptus salubris woodland in the Western Australian wheatbelt. I. Arthropods

Abstract: The effects of habitat fragmentation (remnant biogeographic characteristics) and livestock activity (grazing, trampling) on arthropod communities were examined within 26 remnants of gimlet Eucalyptus salubris woodland in the central wheatbelt of Western Australia. Significant correlations between remnant biogeographic variables were between remnant area and connectivity (+ ve, P < 0001), and between connectivity and distance from the study remnant to the nearest patch of native vegetation (- ve, P < 0.001). Remnant disturbance indices (sheep faecal pellet density, percentage cover of weeds) were significantly correlated with remnant biogeographic characteristics (P < 0.01). Small and poorly connected remnants showed significantly higher intensities of disturbance than larger and better connected remnants. When disturbance indices were used to categorize study remnants into groups with high, moderate or low disturbance, remnants with high intensities of disturbance had significantly less lichen, litter and shrub cover. Highly disturbed remnants were associated with : fewer scorpion species, lower termite and ant diversity (Shannon-Wiener); a lower abundance of scorpions, termites and mygalomorph spiders; more beetle species and higher beetle diversity, and greater abundance of earwigs and beetles. Cockroach, earwig and ant species richness showed no significant response to disturbance. Species richness of termites, and the abundance of lycosid and idiopid (mygalomorph) spiders, isopods, cockroaches and ants, was highest under moderate disturbance. Significant biogeographic covariates were area (abundance of araneaomorph spiders, 'associated subordinate' and 'opportunistic' ants; richness of carabid, scarabid and 'other' beetle species, subordinate and opportunistic ants), connectivity (richness of termites, scarabid beetles) and distance to the nearest native vegetation (richness of 'dominant' ants). When disturbance and biogeographic effects were combined, total termite richness, and the richness of termite functional groups, declined markedly in highly disturbed, small and poorly connected remnants. Termite communities in relatively undisturbed remnants were more similar in species composition to communities in moderately disturbed quadrats than to communities in highly disturbed quadrats. Community similarity values for ants and beetles were similar across the study quadrats with different degrees of disturbance. Arthropod communities were also examined by canonical variate analyses across remnants with different degrees of disturbance, using total abundance and richness, and abundance and richness of predators (scorpions, spiders, carabid beetles, ants) and detritivores/herbivores (termites, isopods, earwigs, cockroaches, weevil and scarab beetles). Effective site separation into the three disturbance categories was found for abundance and richness of all arthropods, and for predators alone. Abundance and richness of detritivores/herbivores separated into two groups of sites: high disturbance sites, and sites with low or moderate disturbance with no separation. In stepwise regression analyses, lichen cover, weed cover and sheep faecal pellet density were the most significant indicators of faunal abundance, richness and diversity. Remnant biogeographic variables explained a low percentage of variation in faunal characteristics. Habitat disturbance was the major influence on the arthropod communities, with remnant biogeographic factors consistently explaining low variations in the abundance or diversity of the fauna. The implications of our findings for the management of remnant vegetation are discussed.

Dragonflies (Odonata) as Indicators of Biotope Quality in the Kruger National Park, South Africa

Abstract: 1. Monitoring programmes that assess ecosystem changes depend on indicator species or assemblages. Indicators should be sensitive and their response easily measured. This study assessed the suitability of adult male Odonata as indicators of biotope quality along the Sabie River in the Kruger National Park (KNP). 2. Odonate diversity was investigated at 25 sites along the Sabie River using univariate statistical procedures. The KNP supports 81 species, 59 recorded during this study (16 for the first time). 3. Sampling sites were classified by Two Way INdicator SPecies Analysis (TWINSPAN) and ordinated by DEtrended CORrespondence ANAlysis (DECORANA), based on the abundance of adult male Odonata. A predictive model relating Odonate species-groups to biotope variables, was formulated. 4. Classification led to the recognition of 10 ecologically meaningful biotope groups, each with an indicator species and a characteristic assemblage of associated species. 5. Multiple Discriminant Analysis (MDA) indicated that shade cover, permanency and flow rate could discriminate between biotope types defined by TWINSPAN. Variation in site membership between MDA and TWINSPAN suggests interaction between variables in determining species membership. 6. Biotope variables were incorporated into a model which predicted the membership of 82% of sites to the TWINSPAN groups; shade cover alone correctly predicted 44% of the sites. 7. The suitability of the Odonata as indicators of biotope quality, and its consequences for management are discussed.

Use of Non-Wildlife Passages Across a High Speed Railway by Terrestrial Vertebrates

Abstract: Seventeen culverts and pathway passages across a high speed railway were monitored for one year in order to determine factors influencing their use by terrestrial vertebrates. Carnivores, lagomorphs, small mammals and reptiles used the passages. Crossing rates generally reflected the spatiotemporal variation in vertebrate abundance and activity, suggesting that the passages could be valuable in allowing movement across the railway. Wild ungulates known to be present did not use the passages, probably due to a combination of unsuitable dimensions and placement, a lack of cover near their entrances and human disturbance. Ungulates probably need specifically designed passages. The presence of cover in the passage entrances favoured their use by carnivores, while small mammals preferred narrow passages where, presumably, predation risk was lower. Reptiles preferred passages of intermediate size, in which they moved between sun-warmed and shaded vertical surfaces for thermoregulation. The main factor determining the use of passages by vertebrates was their location with respect to habitat. Minor modifications to non-wildlife passages and to the management of surrounding areas may further improve the efficacy of these passages for allowing wildlife to cross linear barriers and, therefore, potentially reduce the effects of habitat fragmentation.

The effects on butterfly abundance of the management of uncropped edges of arable fields

Abstract: 1. The abundance and species richness of butterflies on expanded-width uncropped arable field edges, which were subject to 10 contrasting, experimental management regimes, were measured using transects in 1989, 1990 and 1991. The effects of the management regimes on a number of botanical variables, likely to be of importance to butterflies, were measured. 2. On the experimental field edges, butterfly abundance and species richness fluctuated between years and peaked at different times each year. 3. Butterfly abundance and species richness differed between experimental treatments. Plots which were either cut in the spring and autumn, or not cut at all, attracted more individuals and species of butterfly than did plots cut in the summer. Sowing with a grass and wild flower seed mixture increased butterfly abundance. Butterfly abundance declined on swards sprayed once annually with herbicide. 4. Mowing, sowing and spraying had significant effects on mean flower abundance, on the annual and perennial components flowering in the sward, and on the abundance of commonly used nectar sources and larval host-plants. 5. Stepwise multiple regression analyses on butterfly and plant data showed that the abundance of adults of most butterfly species was most closely associated with the abundance of flowers of key nectar source species. 6. The results are discussed in relation to resource provision for larval and adult butterfly stages. Recommendations (emboldened in the text) are made for the conservation management of butterflies on arable farmland.

Effects of fishing effort and catch rate upon the structure and biomass of Fijian reef fish communities

Abstract: An improved understanding of fishing effects is required to assess the sustainability of existing fishing practices and to determine the ecological implications of offering fishing concessions in marine reserves. The effects of fishing were investigated in six Fijian fishing grounds (qoliqoli) subject to different fishing intensities. A visual census technique was used to determine the structure and biomass of the shallow-water reef fish communities targeted by the fishers. A supervised voluntary logbook scheme was used to assess the size and composition of yield from the qoliqoli. The fish communities in the least intensively fished qoliqoli were significantly different from fish communities elsewhere. The significance of these differences was attributable to the greater biomass of invertebrate feeding and piscivorous fishes in the least intensively fished qoliqoli. Annual yields of herbivorous fishes ranged from 0.3 to 5.2% of the biomass estimated by visual census. There were no significant differences in herbivore biomass among qoliqoli subject to different fishing intensities. The biomass of invertebrate feeding fishes was significantly higher in the least intensively fished qoliqoli. The biomass of invertebrate feeding/piscivorous fishes was significantly higher in the two least intensively fished qoliqoli. In the two least intensively fished qoliqoli the estimated annual yields of invertebrate feeding and invertebrate feeding/piscivorous fishes did not exceed 4% of the biomass estimated by visual census. However, yields of these trophic groups approached 20% of biomass in the intensively fished qoliqoli where biomass was significantly lower. The fishing effects observed were primarily attributed to significant differences between the fish communities in the least intensively fished qoliqoli and all others. Thus, at higher fishing intensities, the biomass of target species provided a poor index of relative fishing pressure. The results suggest that the annual removal of 5% of fish biomass may cause significant structural changes in reef fish communities. Thus, it is important to ensure that fishing concessions and poaching activities are carefully regulated in marine reserves.

Studies on the feasibility of re-creating chalk grassland vegetation on ex-arable land. I. The potential roles of the seed bank and the seed rain

Abstract: 1. This study is an investigation of the potential of the seed bank and the seed rain to promote the re-establishment of chalk grassland vegetation on an ex-arable site which had not been cultivated for 10 years. Comparisons are drawn with the composition of the seed bank as recorded in a study undertaken close to the current site 6 years alter cultivation ceased. 2. The seed bank had the following composition: 46.6% grass seeds, 38.6% perennial forbs, 8.4% biennial forbs and 6.3% annual forbs. In comparison, annual forbs had accounted for 49.5% of the seed bank 6 years after cultivation ceased. The seed bank was concentrated near the top of the soil profile and grass seeds showed a more marked decline in abundance with depth than forb species. However, common annual forb species mostly germinated from the lower soil strata. The common grasses and perennial forbs were species with wide ecological amplitudes, characteristic of fertilized, neutral grassland. 3. Only 20 of the 68 forb species recorded in the seed bank were characteristic components of adjacent ancient chalk grassland. These species accounted for less than 20% of the total forb seed bank. Only two out of 11 recorded grass species were characteristic of the ancient chalk grassland, and these accounted for only 0.3% of all grass seedlings. The grass component of the seed bank was dominated by Agrostis stolonifera. 4. The species richness of the seed bunk has increased in recent years due mainly to acquisition of seeds of non-annuals. However, species characteristic of the ancient chalk grassland have made little contribution either to the seed bank or to the vegetation growing on the site. Those chalk grassland species which were most abundant in the seed bank tended to be short-lived species and they occurred mainly at the margins of the ex-arable site, close to the adjacent chalk grassland. Even here they rarely accounted for more than 20% of the germinable seed bank. They were strongly concentrated at the soil surface, indicating their deposition since cultivation ceased. 5. Agrostis spp., Phleum pratense and Holcus lanatus accounted for over 50% of the recorded seed rain. Of the commonly trapped species, analyses of mean dispersal breadths indicated that forb species characteristic of the adjacent chalk grassland would be comparatively slow invaders of ex-arable habitats. 6. The vegetation on transects across the ex-arable site contained few of the species which occurred in the adjacent old chalk grassland. Chalk grassland species were more abundant in vegetation at the margins of the ex-arable site, but even here similarity indices between the ex-arable vegetation and the chalk grassland vegetation were normally below 25%. 7. The slow invasion of species from the adjacent chalk grassland into this ex-arable site, which is ideally placed for their colonization, suggests that seeds of such species will often need to be artificially introduced to prevent ex-arable sites becoming dominated by fast-growing more weedy species. Further management would also be necessary to prevent more weedy species subsequently invading and eliminating the chalk grassland species.

Spatial Relationships Between Iberian Lynx and Other Carnivores in an Area of South-Western Spain

Abstract: 1. Spatial relationships between Iberian lynx and other carnivores were studied by radio-tracking and/or track censusing in two adjacent areas of Donana (south-western Spain). 2. Both radio-tracking and track censusing showed that lynx were restricted to an undisturbed area of Pistacia lentiscus shrubs called Matasgordas. Minimum and maximum lynx density in Matasgordas were estimated as 0.55 and 0.75 ind. km -2 . 3. Egyptian mongoose tracks were mainly detected outside Matasgordas (83% of tracks), European badger tracks were detected most often inside Matasgordas (76% of tracks), and red fox tracks were frequently detected both outside (54%) and inside (46%) Matasgordas. Surveys of tracks and faeces undertaken in other 14 areas where P. lentiscus shrubs also dominated corroborated the census data obtained inside and outside Matasgordas. 4. Trapping and radio-tracking of mongooses and common genets indicated that both species avoided use of Matasgordas. They were almost exclusively trapped (24 out of 25 mongooses and all of 11 genets) and mainly radio-located (94.5% and 95.4% of times, for mongooses and genets, respectively) in the areas of P. lentiscus shrubs situated outside Matasgordas. Their densities were estimated as 0.2 and 0.03 ind. km -2 inside, and as 2.0 and 0.7 ind. km -2 outside Matasgordas for mongooses and genets, respectively. 5. Lynx may kill mongooses, genets, and foxes ; thus, the avoidance of Matasgordas by smaller carnivores (mongooses and genets) could be related to the risk of lynx predation. It is suggested that the decline of the lynx in the Donana area may have caused the increase in the population size of smaller, previously rarer carnivores. 6. The true relationship between lynx and foxes remains unclear, and badgers were apparently indifferent to lynx presence or absence.

Seasonal movements and behaviour of adult barbel (Barbus barbus), a riverine cyprinid fish: Implications for river management

Abstract: To provide information on the movements and localized activity of barbel Barbus barbus (Cyprinidae) in a river containing potentially obstructing weirs, 31 adult barbel were radio-tracked in the River Nidd, a tributary of the Yorkshire Ouse, North East England between June 1993 and September 1994. Barbel exhibited substantial movements, ranging from 2 to nearly 20 km. Four fish are known to have moved between the Nidd and the Ouse, demonstrating that at least a part of the barbel population utilize the Nidd and Ouse at different times of the year. Range of upstream movement was restricted by the presence and nature of several weirs, including Skip Bridge flow-gauging weir. Low levels of spawning downstream of Skip Bridge weir appear to have been due to a lack of suitable spawning habitat. Movements followed a seasonal pattern, with males and females migrating upstream in spring to spawn on gravel beds. Females moved downstream more quickly than males over the summer months. Both sexes moved downstream in autumn and winter. Day length and water temperature were the best predictors in relation to distance moved up the River Nidd. Descriptive models, relating movement to water temperature and day length, are provided. For both sexes, localized activity varied greatly on both diel and seasonal scales, and was mainly associated with foraging. During summer there was typically a bimodal pattern of diel activity with peaks usually in early morning and late evening. In winter, mean daily activity was less than 20% of peak summer levels and fish were relatively dormant. In winter, diel activity patterns exhibited a single peak towards dusk. Mean daily activity levels for each month were linearly correlated with mean monthly water temperatures, even during the months where movement to and on the spawning sites occurred. The importance of natural migrations and seasonal activity patterns for barbel, and likewise many other riverine cyprinids, has probably been underestimated for a wide variety of river systems. As major components of riverine fish communities, the importance of seasonal movements of mobile cyprinid species should be considered when constructing weirs and other obstructions. Greater consideration should be given to ways of mitigating effects of existing barriers to movement of non-salmonid species.

Progressive restoration of a shallow lake : a 12-year experiment in isolation, sediment removal and biomanipulation

Abstract: 1. Cockshoot Broad (mean depth 1 m, area of open water 3.3 ha) was isolated from the sewage-effluent contaminated River Bure in 1982. About 70 cm of sediment were pumped out at the same time and settled in a remote lagoon. The total phosphorus and phytoplankton chlorophyll a concentrations rapidly fell and large numbers of large-bodied Daphnia were present. The zooplanktivorous fish stock was probably then very low. Submerged macrophytes colonized one area (the Dyke) heavily but more slowly over the main basin. 2. These conditions lasted until 1985 by which time the fish stocks had increased, the Daphnia declined, and plants disappeared from the main basin. Plant communities remained stable in the Dyke. Chlorophyll a increased in the main basin and remained at a high value until 1988. 3. In early 1989, virtually all of the fish community was manually removed. Daphnia numbers recovered, chlorophyll a concentrations fell and plants began to recolonize the main basin. Recolonizing fish were removed in successive winters and chlorophyll has remained low and Daphnia high except in 1992. In that year, an estuarine mysid, Neomysis integer, colonized the Broad when the dams separating it from the river were overtopped. This was a consequence of low fluvial flows in a drought period and was apparently only a temporary set-back. There was also a loss of macrophytes from the dyke in 1991/92. This is thought to have resulted from bird damage to the overwintering inocula in a cold spring. 4. In 'low Daphnia-high fish' years, there was a significant positive correlation between total P and chlorophyll, but not in 'high Daphnia-low fish' years. Overall, however, there was no correlation between chlorophyll and nutrients but a strong inverse correlation with Daphnia numbers. The nutrient conditions supporting phytoplankton and macrophyte dominance overlapped and the two conditions are seen as alternative stable states. The results are discussed in the context of a general hypothesis of change with eutrophication in shallow lakes.

Factors determining the abundance of vespertilionid bats in Britain: geographical, land class and local habitat relationships

Abstract: 1. Transect surveys of foraging bats in a stratified sample of 1030 1-km squares in Britain were used to compare bat abundance in different land classes. 2. Bat abundance remained constant from early to late summer but varied significantly between land classes. Increased ambient temperatures caused increased local abundance of bats. High abundance occurred within arable and pastural land class groups in the south, while low abundance occurred in arable, marginal upland and upland land class groups in the north. 3. Regression analyses identified a significant negative gradient in bat abundance on a south-north axis in Britain and also on a west-east gradient within a transect across North Wales and the English Midlands. 4. Regression analyses further outlined significant relationships between bat abundance and habitat availability within seven land class groups. Habitats included in the models were similar for each land class group. In general, bat abundance was positively related to the availability of woodland, vegetation corridors, lacustrine and riverine habitats and negatively related to the availability of arable land. 5. The models quantifying the relationship between bat abundance and habitat availability presented in this paper provide a basis for predicting the suitability of sites for foraging bats and a tool for further research to test the hypotheses relating the impact of past and future large-scale land-use change on vespertilionid bat populations in Britain.