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Showing papers in "Journal of Ecology in 1981"


Journal ArticleDOI
TL;DR: Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles.
Abstract: seeds for immediate germination. Of the 403 species examined, 158 failed to exceed 10% germination but 128 attained values greater than 80%. Germination was high in the majority of grasses and low in many annual forbs and woody species. With respect to initial germinability, major families could be arranged in the series Gramineae > Compositae > Leguminosae = Cyperaceae > Umbelliferae. Many small-seeded species were able to germinate immediately after collection and seeds of these species were often elongated or conical and had antrorse hairs or teeth on the dispersule. High initial germinability was conspicuous among the species of greatest abundance in the Sheffield flora. (4) In the majority of species, germination percentage increased during dry storage; this effect was most marked in small-seeded species. Among the seventy-five species which responded to chilling, some germinated at low temperature in darkness whilst others were dependent upon subsequent exposure to light or to higher temperature or to both. Responses to chilling were characteristic of the Umbelliferae. In all of the legumes examined, rapid germination to a high percentage was brought about by scarification. (5) Under the experimental conditions, all of the annual grasses showed the potential for rapid germination. High rates were also observed in many of the annual forbs and perennial grasses. Low rates of germination occurred in the majority of sedges, shrubs and trees, and were particularly common in species of northern distribution in Britain. Rapid germination was characteristic of the species of greatest abundance in the Sheffield flora. Rate of germination showed a progressive decline with increasing seed weight, and, with some exceptions, there was a positive correlation between rate of germination and the relative growth rate of the seedling. (6) In sixteen species, germination in the light was found to be dependent upon exposure to diurnal fluctuations in temperature. Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles. A requirement for relatively high temperature was apparent in sedges, in plants of northern distribution and in a majority of the marsh plants. The range of constant temperatures conducive to germination tended to be wider in grassland plants than in woodland species. Rapid germination over a wide range of temperature occurred in many of the species which attain greatest abundance in the Sheffield flora. 0022-0477/81/1100-1017 $02.00 (?1981 Blackwell Scientific Publications

962 citations


Journal ArticleDOI
TL;DR: In this paper, a model based on the two-layer hypothesis is proposed to compare the resilience of grass and woody vegetation in the presence of heavy or over-grazing.
Abstract: SUMMARY (2) The model is based on Walter's two layer hypothesis. Woody vegetation and grasses compete for water in the surface layers of the soil, but woody vegetation has exclusive access to a source of water relatively deep underground. Where there is only a small biomass of grass the soil surface tends to become impermeable and, in these conditions, the model shows that two different steady states may develop: with a lot of woody vegetation alone, or with a relatively large biomass of grass and rather little woody vegetation. (3) The results are discussed in terms of the concept of resilience. The continued existence of both stable states under ranching conditions seems to depend on periodic heavy, or over-, grazing which allows for the maintenance of unpalatable or unstable grass species, which thus set a minimum to grass biomass-a minimum which cannot be reduced by herbivores. (4) Comparison of the dynamics of various savanna and other natural systems leads to the conclusion that the resilience of the systems decreases as their stability (usually induced) increases.

775 citations


Journal ArticleDOI
TL;DR: Two adjacent populations of the clonal perennial Ranunculus repens in park grassland and in mixed deciduous woodland in North Wales are evaluated, and the terms 'phalanx' and 'guerilla' are introduced to describe patterns of clonal growth and death.
Abstract: SUMMARY (1) Demographic investigations were made over a period of 18 months in two adjacent populations of the clonal perennial Ranunculus repens in park grassland and in mixed deciduous woodland in North Wales. Ramets were treated as units of population. (2) The carrying capacity of the woodland site for Ranunculus repens (inferred from the peak summer density of ramets) was twice as high as that of the grassland site (264 and 112 ramets m-2, respectively, in 1977). (3) Despite the presence of a large and viable seed bank in the grassland soil (>1000 seeds m-2), germination and establishment of new genets was rare in both sites. (4) The birth rate of ramets per rosette was apparently density-independent, but death rates per rosette were density-dependent, particularly in summer. (5) Clonal growth and the death of ramets were in phase throughout the study. The average production of new ramets by each rosette was similar at both sites (4.6 daughter ramets in woodlands, 4.0 daughter ramets in grassland). (6) Demographic treatment assumes that the units enumerated may validly be compared. This assumption was tested and daughter ramets were found to have the same biomass at both sites, but daughter ramets were differently constructed at the two sites; those in grassland had proportionately more dry matter in caudex and root tissue than those in the woodland, which had more biomass in stolons. (7) The terms 'phalanx' and 'guerilla' are introduced to describe patterns of clonal growth, and the two populations of Ranunculus repens are evaluated in these terms.

706 citations


BookDOI
TL;DR: In this article, the importance of edge in the structure and dynamics of forest islands was discussed and a preliminary survey of urban island spatial patterns was conducted in order to understand the relationship between edge edges and forest islands.
Abstract: 1. Introduction.- Dissected Landscapes of the Deciduous Forest Biome.- Problems for This Volume.- 2. The Minimum Critical Size of Ecosystems.- 3. Woodlots as Biogeographic Islands in Southeastern Wisconsin.- Description of the Study Area.- Methods.- Results and Discussion.- Conclusions.- 4. The Groundlayer Vegetation of Forest Islands in an Urban-Suburban Matrix.- Description of the Study Area.- Methods.- Results and Discussion.- Conclusions.- 5. Mammals in Forest Islands in Southeastern Wisconsin.- Description of the Study Area.- Methods.- Results and Discussion.- Conclusions.- 6. The Importance of Edge in the Structure and Dynamics of Forest Islands.- Concepts of Forest Edge.- Description of the Study Area.- Methods.- Results.- Conclusions.- 7. Biogeography of Forest Plants in the Prairie-Forest Ecotone of Western Minnesota.- Description of the Study Area.- Methods.- Results.- Discussion and Conclusions.- 8. Effects of Forest Fragmentation on Avifauna of the Eastern Deciduous Forest.- Methods.- Results.- Discussion.- Conclusions.- Appendices.- A. Computation of Detectability Coefficients.- B. Forest Interior Bird Species Pool.- C. Habitat Utilization by Bird Species Groups.- D. Habitat Utilization in the Beltsville Forest.- E. The Regional Species Pool.- F. Regression Analyses for Tolerance to Fragmentation.- 9. Modeling Recolonization by Neotropical Migrants in Habitats with Changing Patch Structure, with Notes on the Age Structure of Populations.- A Simple Model without Age Structure.- A Model with Age Structure.- 10. Modeling Seed Dispersal and Forest Island Dynamics.- The Wind Dispersal Model.- The Animal Dispersal Model.- Vegetation Dynamics Model.- Conclusions.- 11. Optimization of Forest Island Spatial Patterns: Methodology for Analysis of Landscape Pattern.- Objectives.- Background.- Discussion.- 12. Artificial Succession-A Feeding Strategy for the Megazoo.- The Geography of Dominance.- The Ecology of Dominance.- A Preliminary Survey of Urban Islands.- Discussion.- 13. Summary and Conclusions.- Landscape Patterns.- Species Richness of Forest Islands.- Implications for Environmental Management.- Conclusions.- References.

592 citations


BookDOI
TL;DR: In the field of ecology, there are two long-standing ways to study large ecosystems such as lakes, forests, and salt-marsh estuaries: the holo-logic approach and the merological approach as mentioned in this paper.
Abstract: Ecologists have two long-standing ways to study large ecosystems such as lakes, forests, and salt-marsh estuaries. In the first, which G. E. Hutchinson has called the holological approach, the whole ecosystem is first studied as a "black box," and its components are investigated as needed. In the second, which Hutchinson has called the merological approach, the parts of the system are studied first, and an attempt is then made to build up the whole from them. For long-term studies, the holological approach has special advantages, since the general patterns and tentative hypotheses that are first worked out help direct attention to the components of the system which need to be studied in greater detail. In this approach, teams of investigators focus on major func tions and hypotheses and thereby coordinate their independent study efforts. Thus, although there have been waves, as it were, of investigators and graduate students working on different aspects of the Georgia salt-marsh estuaries (personnel at the Marine Institute on Sapelo Island changes every few years), the emphasis on the holo logical approach has resulted in a highly differentiated and well-coordinated long-term study. Very briefly, the history of the salt-marsh studies can be outlined as follows. First, the general patterns of food chains and other energy flows in the marshes and creeks were worked out, and the nature of imports and exports to and from the system and its subsystems were delimited."

328 citations



Journal ArticleDOI
TL;DR: Changes in vegetation structure, species composition, and species dominance were studied over the first twenty-two months of succession after the cutting and burning of several mature tierra firme forest sites in south Venezuela in the upper Rio Negro region of the Amazon Basin.
Abstract: (1) Changes in vegetation structure, species composition, and species dominance were studied over the first twenty-two months of succession after the cutting and burning of several mature tierra firme (i.e. non-flooded) forest sites in south Venezuela in the upper Rio Negro region of the Amazon Basin. To explain the observed succession, additional field investigations were undertaken. (2) Four months after burning the density of plants was less than 1 m-2. The density of successional woody plants, forbs, and grasses increased rapidly from the fourth to the tenth month of succession. There was little change in plant density between the tenth and twenty-second month, but a large change in vegetation height occurred during this time. By the twenty-second month a loose canopy of Cecropia spp. was present at 5 m height. (3) Many of the forest tree species sprouted from the stump when cut, but burning killed sprouts and significantly reduced the size of the seed bank. Nevertheless, the first successional woody colonizers established from seed which survived the burn. The first forb and grass colonizers established from seeds dispersed onto the site after the burn. (4) The common successional woody species had bator bird-dispersed seeds. Many forbs and grasses had wind-dispersed seeds. (5) Population densities were low during the first months of succession because of the low density of propagules and because the low rainfall during this time was not favourable for seedling germination or establishment. The rapid increase in plant density after about the fourth month occurred because the early colonizers had then begun to produce, and disperse locally, large numbers of seeds. (6) There were six distinct microhabitat types present on the sites after burning. Most species tested showed distinct microhabitat preferences.

317 citations




Journal ArticleDOI
TL;DR: The basis, scope and development of plant taxonomy, the process of classification ways and means taxonomy in the service of man and the sources of taxonomic information are explained.
Abstract: Part 1: the basis, scope and development of plant taxonomy. Part 2: sources of taxonomic information - structural, chemical, chromosomal, from breeding systems, from plant geography and plant ecology. Part 3: taxonomy in practice the process of classification ways and means taxonomy in the service of man.

263 citations



Journal ArticleDOI
TL;DR: Spacing patterns of shrubs were studied on a series of sites in the Mojave and Sonoran Deserts, suggesting the increasing importance of competition as the plants grow.
Abstract: SUMMARY (1) Spacing patterns of shrubs were studied on a series of sites in the Mojave and Sonoran Deserts. Both aggregation and regularity in dispersion of individual shrubs were fairly common. Aggregation may result from vegetative reproduction or environmental heterogeneity, and regularity from competition among plants. (2) Small shrubs tend to be clumped, medium-sized ones tend to a random arrangement, and large shrubs tend to a regular pattern. This suggests the increasing importance of competition as the plants grow. (3) Further evidence of interference between plants was provided by the correlations of plant size with the distance to their neighbours. (4) Root systems were extensive enough to abut or overlap each other in the interplant spaces. (5) Most plants tended to have neighbours of the same species rather than other species. (6) None of these results depended on position along the considerable climatic gradients across the Mojave and Sonoran Deserts.


Journal ArticleDOI
TL;DR: The correlations between pollen and basal-area data were significant for all tree taxa except Fraxinus, Fagus and Salix; the correlations for these taxa were higher when the data were expressed as percentages.
Abstract: (1) An analysis of the relationship between pollen frequency and plant numbers in a given area is an essential step if pollen diagrams are to be used as records of past tree populations. This relationship was studied by comparing the pollen content of moss samples with the vegetation within 20-m radius of each sample site, at seventy-eight sites in the New Forest, Hampshire, The Mens and the Cut, Sussex, and Bradfield Woods, Suffolk. (2) Linear regression analysis was used to analyse the relationship between the intensity of pollen deposition and tree basal area, and between pollen percentages and percentages of total basal area per plot for the major tree species. (3) The rank-order of taxa for number of pollen grains deposited per unit of tree basal area for all sites was Betula > Pinus > Taxus > Alnus > Quercus > Fraxinus - Fagus Salix. The correlations between pollen and basal-area data were significant for all tree taxa except Fraxinus, Fagus and Salix; the correlations for these taxa were higher when the data were expressed as percentages. There was a wide range of pollen representation for different shrub and herb taxa. (4) With the exception of Quercus, a consistent order of pollen representation for the major forest trees of northern Europe can be recognized. Senescent Quercus populations are a contributory factor to the low pollen representation of this taxon in south-east England. (5) The regression coefficients derived in this study can be used to convert fossil pollen counts into estimates of tree basal area for areas of 20-m radius around very small sedimentary basins. An example is given for a small woodland pond in Suffolk.


Journal ArticleDOI
TL;DR: In this article, the effects of physical variables on freshwater production were analyzed based on models M. Straskraba and F. Koonce, A. Park and J. Winberg.
Abstract: 1. Introduction L. Tonolli 2. History and development of the freshwater production section of IBP J. Rzoska 3. The effects of physical variables on freshwater production: analyses based on models M. Straskraba 4. Chemical budgets and nutrient pathways H. L. Golterman and F.A. Kouwe 5. Primary production D. F. Westlake, M. S. Adams, M. E. Bindloss, G. G. Ganj, G. C. Gerloff, U. T. Hammer, P. Javornicky, J. F. Koonce, A. F. H. Marker, M. D. McCracken, B. Moss, A. Nauwerck, I. L. Pyrina, J. A. P. Steel, M. Tilzer and C. J. Walters 6. Secondary production N. C. Morgan, T. Backiel, G. Bretschko, A. Duncan, A. Hillbricht-Ilkowska, Z. Kajak, J. F. Kitchell, P. Larsson, C. Leveque, A. Nauwerck, F. Schiemer and J. E. Thorpe 7. Organic matter and decomposers G. W. Saunders, K. C. Cummins, D.Z. Gak, E. Pieczyhska, V. Straskrabova and R.G. Wetzel 8. Trophic relationships and efficiencies P. Blafka, T. Backiel and F.B. Taub 9. Estimating the productivity of lakes and reservoirs M. Brvlinskv 10. Dynamic models of lake ecosystems C.J. Walters, R. A. Park and J. F. Koonce 11. General characteristics of freshwater ecosystems based on Soviet IBP studies G. G. Winberg.


Journal ArticleDOI
TL;DR: The phenological behaviour of annuals, geophytes and some perennial herbs suggests that they may have been derived from the lower mediterranean matorral flora.
Abstract: (1) Vegetative activity and flowering and fruiting records are given for ninety-seven species from three vegetational belts in the andean (alpine) zone of the Cordon del Cepo (33017'S, 70016'W), Cordillera de los Andes, central Chile. Comparisons of phenological behaviour and overall phenological patterns were made at six altitudes between 2320 and 3550 m, including both northand south-facing slopes. (2) Nine categories of phenological behaviour and their altitudinal distribution are described. The percentage of summer-dormant species (dying back before the onset of winter) reaches a maximum at 2320 m (>75% of all species), and generally decreases with altitude. More summer-dormant species are present on north-facing (equatorial) slopes than on south-facing slopes. (3) The maximum growing season within the andean zone was 8 months at 2320 m altitude; the minimum growing season was 5 months on south-facing slopes at 3410 m. Shrubs and cushion plants had the longest period of vegetative activity, followed by perennial herbs and sub-shrubs, and then by geophytes and annuals. (4) Flowering in some species began before snowmelt, and continued until autumn, reaching a maximum in the austral summer between late December and late February at the altitudinal extremes. Peak flowering corresponded with the period of maximum temperature at lower altitudes, but was displaced after this period at higher altitudes and on south-facing slopes. (5) The average length of the flowering period for each species increased with altitude, approximately doubling over 1200 m altitude. Fruits of some species failed to mature both on some of the north-facing slopes and on most south-facing slopes in 1979. (6) Slower floral development at higher altitudes accounted for about two-thirds of the difference in the lengths of the flowering periods at the altitudinal extremes. (7) Checks in 1979-80 indicated that the phenological patterns detected in 1978-79 remained constant from one year to another. (8) The phenological behaviour of annuals, geophytes and some perennial herbs suggests that they may have been derived from the lower mediterranean matorral flora.


Journal ArticleDOI
TL;DR: The results of a controlled removal experiment showed that water-related interference does occur at this site when water availability is low, and that at present, interference between species is usually more intense than that within a species.
Abstract: (3) The results of a controlled removal experiment showed that water-related interference does occur at this site when water availability is low, and that at present, interference between species is usually more intense than that within a species. These results, together with nearest-neighbour analyses, revealed that regular distributions may not necessarily indicate present interference among individuals of the same species, but rather past interference. (4) The importance of episodic seedling establishment and longevity in horizontal pattern development are also discussed.

Journal ArticleDOI
TL;DR: Viable seed in soils of forest plantations was studied by spreading samples of soil in seed trays and recording the number of seedlings that germinated; it was concluded that many seeds had survived in the soil for at least 30 yr, and in one case probably for about 45 yr.
Abstract: (1) Viable seed in soils of forest plantations was studied by spreading samples of soil in seed trays and recording the number of seedlings that germinated. (2) Numerous seedlings emerged from most samples; it was concluded that many seeds had survived in the soil for at least 30 yr, and in one case probably for about 45 yr. (3) In 30-40-year-old plantations, seed density was typically 1000-5000 seeds m-2 on brown earths, 500-2500 on peaty gleys and 50-250 on deep peat. In younger plantations the seed density was higher, especially on deep peat. (4) Calluna vulgaris was much the most abundant species. Carex spp. (mostly C. binervis and C. pilulifera), Erica tetralix, Galium saxatile, Juncus effusus and J. squarrosus were also frequent in soils of older plantations, together with Agrostis canina and A. tenuis on brown earths. (5) There was apparently no long-term survival of seeds of Betula spp., Deschampsia flexuosa or conifers. Agrostis canina and A. tenuis survived for several decades but perhaps not for the full length of a normal rotation (50 yr). (6) Development of the vegetation following clear-felling depends mainly on seeds and established plants already present. Immigration is largely confined to species with wind-borne propagules.

Journal ArticleDOI
TL;DR: The results of this experiment do not support the hypothesis that this community is divided into well-defined groups of competing species (guilds), and the spatial patterning of the community showed no relationship to the responses to removals.
Abstract: (1) Species were removed singly (by hand) or in groups (by herbicide or soil sterilization) in a mown field. The vegetation of treated and control quadrats was assessed before and after the removals by measuring the cover of each species. (2) In all cases total cover returned to its original value within a year, although the species composition remained different. (3) The effects of the removals of single species upon the abundance of the other species were small, accounting for an average of only 7% of the variance. Fourteen of the seventy-two pairwise effects tested were significant. Interactions between the different pairs of species did not differ greatly in magnitude. The results of this experiment do not support the hypothesis that this community is divided into well-defined groups of competing species (guilds). A previous study provided evidence for the division of the community into temporal guilds. But within each temporal guild the species are characterized by diffuse competition. (4) Interactions between pairs of species were in general non-reciprocal. (5) Some interactions were found among three or more species that were not predictable from interactions of pairs of the constituent species. Two species with vigorous vegetative spread pre-empted space from competitors, and there were several significant negative responses to species removals. (6) No divisions of the community along taxonomic or morphological lines were found. However, the temporal guilds correspond to the distribution of the C3 and C4 photosynthetic pathway in the grass species. (7) The spatial patterning of the community showed no relationship to the responses to removals.

Journal ArticleDOI
TL;DR: The behaviour of two populations of Salicornia europaea agg.
Abstract: SUMMARY tion to the adverse effects of hypersalinity in the upper marsh. (3) The demography of the two populations was examined. Permanent quadrats were mapped or photographed to follow the fate of seedlings; the reproductive and growth performances of individuals in relation to plant density were measured. (4) Overall, demographic trends in the two populations were similar. The probability of a seed giving rise to an adult plant was very low; most seeds died without germinating. Mortality of plants appeared to be density-independent, but there was a significant negative density-dependent relationship between number of seeds per plant and the density of Salicornia plants. (5) By midsummer the seed bank in the sediments was exhausted, so each generation of Salicornia at both sites appears to be distinct. (6) A model is given which describes the population dynamics of Salicornia in terms of density-dependent regulation of seed number and density-independent mortality. The reasons for the prevailing densities are discussed. In this study the behaviour of two populations of Salicornia europaea agg., from the upper marsh and from the open sandy mudflats of the lower marsh, respectively, has been examined in relation to environmental heterogeneity at Stiffkey salt marsh on the north Norfolk coast, England. In cultivation, plants from the two populations exhibit different


Journal ArticleDOI
TL;DR: The results presented are consistent with a bell-shaped model of species response to environmental gradients, and with an error function relationship between sample similarity and ecological separation.
Abstract: (1) Several nonmetric multidimensional scaling programs (PARAMAP, POLYCON, ALSCAL and SIBSON) were applied to simulated and real plant community data in order to test their effectiveness as ordination techniques in comparison to reciprocal averaging (RA) and an improved version of RA: detrended correspondence analysis (DCA). (2) Nonmetric ordination gave better results than did RA for data having three to four dimensions, whereas RA was superior to nonmetric ordination for one dimension. For two dimensions there was little difference. Experimental variation of the sample-set (beta) diversity and of noise showed that neither method had consistent advantages over the other. For most ecological uses RA is preferable because it requires much less computation than do nonmetric methods. DCA was superior to RA and to nonmetric ordination, and needs exceptionally little computer time and storage. (3) The programs PARAMAP, POLYCON, ALSCAL and SIBSON differ little in the solutions produced, but they differ considerably in computing speed, quality of the initial configuration (and hence ability to avoid local minima), and convenience of output. Dissimilarities can be weighted by POLYCON, and SIBSON can use local scaling, but neither of these features improved results. In general ALSCAL was best. (4) Because its assumptions are unusually simple and general, nonmetric ordination results are of special interest for models of vegetation structure. The results presented are consistent with a bell-shaped model of species response to environmental gradients, and with an error function relationship between sample similarity and ecological separation.


Journal ArticleDOI
TL;DR: Rhododendron ponticum was introduced into the Killarney area of S.W. Ireland during the 19th century, and has subsequently spread by means of large numbers of very small, easily dispersed seeds, throughout the semi-natural oakwoods, now a serious threat to these woods by shading the ground flora and preventing regeneration of native woody species.
Abstract: SUMMARY (1) Rhododendron ponticum was introduced into the Killarney area of S.W. Ireland during the 19th century, and has subsequently spread by means of large numbers of very small, easily dispersed seeds, throughout the semi-natural oakwoods (BlechnoQuercetum association). It is now a serious threat to these woods by shading the ground flora and preventing regeneration of native woody species. (2) The woods have been subject to almost continuous human disturbance and to grazing for at least four centuries, and they are currently severely overgrazed by the introduced sika deer (Cervus nippon). This disturbance and grazing is a major factor in aiding the spread of Rhododendron ponticum. (3) Seedlings of R. ponticum are closely associated with bryophyte communities on slopes. Successful germination appears to occur almost exclusively in bryophyte communities of less than 1-cm depth. These 'safe sites' seem to provide the necessary humidity and light for germination, as well as offering some protection from adverse factors.

Journal ArticleDOI
TL;DR: A method of analysis is proposed to test whether differences in survivorship of a given species among two or more habitats are the result of variation among the habitats in environmental factors (density-independent effects), or in species density (densitydependent effects).
Abstract: (1) A method of analysis is proposed to test whether differences in survivorship of a given species among two or more habitats are the result of variation among the habitats in environmental factors (density-independent effects), or in species density (densitydependent effects). (2) The method requires that a range of seed densities of the species be sown in a given habitat, and survivorship and reproductive output measured for each sowing density. If a straight line with negative slope can be fitted to the survivorship v. sowing density relationship, then the survivorship y-intercept of the line is an estimate of densityindependent mortality, and the slope is an estimate of the density dependence of mortality. (3) If this analysis is carried out for the species growing in several habitats, it is possible to test whether intercepts or slopes (and consequently density-independent or density-dependent effects) differ among habitats. A similar analysis can be carried out for reproductive output. (4) The annual plant Cakile edentula, a common species on sand dunes in eastern North America, is used as an example. Three experimental sites along a sand-dune gradient were each sown with seeds at a range of densities and survivorship and reproductive output measured for each density at each site. (5) The density dependence of survivorship changed significantly (P < 0.001) along the gradient (among habitats), whereas density-independent mortality stayed constant. (6) Significant differences (P < 0.001) were observed for both density-independent and density-dependent effects on reproductive output. (7) The effects of density on survivorship were greatest at the landward end of the gradient, whereas the effects of density on reproductive output were greatest at the seaward end.

Journal ArticleDOI
TL;DR: This work focuses on coastal lagoonal ecology and methods for the study of coastal lagoons, and investigates the role of man-made and natural barriers to access, as well as their effects on species and habitats.
Abstract: Preface Acknowledgements 1. Introduction 2. Formation and fate of lagoons 3. The lagoonal environment 4. Lagoonal ecology 5. Strategies for lagoonal species 6. Human use of lagoons 7. Methods for the study of coastal lagoons 8. Other coastal lagoon-like systems Further reading References Indexes.

Journal ArticleDOI
TL;DR: Decomposition rates differed between the two years of study, probably due to differences in the weather, but leaching was an important component of weight loss.
Abstract: (1) A study of litter fall, litter standing crop and leaf-litter decomposition was carried out over a 20-month period in 5to 8-year-old regenerating secondary rain-forest at Ibadan, Nigeria. (2) The dry season (December to March) was characterized by a high rate of litter fall, negligible decomposition and the accumulation of a reservoir of Ca, Mg, N, P and K in the litter layer. (3) The onset of rain in March to April led to rapid decomposition of leaf litter. Most of the nutrient reservoir was released from the leaf litter during the first 8 weeks of the rainy season. (4) During the initial period of decomposition, leaching was an important component of weight loss. During subsequent decomposition, leaf litter breakdown by microorganisms and by animals was in the approximate ratio of 1:2. (5) Decomposition rates differed between the two years of study, probably due to differences in the weather.