Showing papers in "Journal of Ecology in 1978"

Plant Root Systems. Their Function and Interaction with the Soil.

Abstract: his book is concerned with the growth and function of the root systems of plants in the soil and is divided into 3 parts : physiological background (5 chapters); response to soil conditions (4 chapters); and tillage of the soil (2 chapters). The 1st part covers the physiological control of growth throughout the plant, the growth and form of roots, the absorption and transport of nutrients, water relations and root/rhizosphere flora interactions. The 2nd part covers the soil environment, mechanical impedance of root growth, effects of anaerobic soil conditions and the root/soil interface. The 3rd part covers traditional and modern methods of tillage and effects of reduced cultivation on soil conditions and crop growth. The book is aimed at 3rd yr undergraduates and research workers.ADDITIONAL ABSTRACT:The book is written for advanced students and research workers. Its first six chapters are concerned with root physiology (root/shoot relationships, growth substances, root growth and form, nutrient uptake and transport, water relations, and rhizosphere effects). The next four chapters deal with responses to soil conditions (physical and chemical environment, mechanical impedance, anaerobic conditions and the soil/root interface). The two concluding chapters are on tillage methods and reduced cultivation.ADDITIONAL ABSTRACT:The topics considered are: physiological relationships between roots and shoots; the growth and form of root systems; the absorption and transport of nutrients; the water relations of root systems; relationships between roots and the rhizosphere flora; the soil environment; mechanical impedance of root growth; effects of anaerobic soil conditions; the soil/root interface;traditional and modern methods of tillage; reduced cultivation, soil conditions and crop growth.

Stand structure and allometry of trees during self-thinning of pure stands

Abstract: SUMMARY (1) Stand structure and mean weight-density relations of nearly pure, dense, even-aged, natural stands of Prunus pensylvanica and Abies balsamea in the north-eastern U.S.A. were examined and related to allometric growth. Values for the exponents of allometric and mean weight-density equations were estimated by principal components analysis of logarithmically transformed data. (2) It is proposed that soon after a stand of woody plants becomes established the sizefrequency distribution is a negatively skewed, bell-shaped curve; the distribution subsequently becomes positively skewed, and eventually approaches normality after substantial thinning. Maximum positive skewness occurs at the tiine self-thinning begins. (3) The weight-frequency distribution undergoes a parallel series of stages: roughly normal at first, but quickly changing to lognormal, with maximum skewness attained at the tiine thinning begins. These curve-forins are proposed only as approximations to empirically observed distributions. A consistent tendency toward bimodality is one commonly-observed departure from the idealized distributions. (4) The calculated exponents of the inean weight-density equations for Prunus pensylvanica and Abies balsamea were - 1 46 and - 1 22, as compared to the proposed value of - 15 (- 3/2 power 'law' of self-thinning). In general, weight changes in plant parts during self-thinning did not parallel those for whole plants; in particular, the mean weight-density exponent for foliage was approxiinately - 1 0. The exponents of inean weight-density equations for total roots and total shoots, however, approximately equalled the exponent for whole plants. (5) It is concluded that observed patterns of alloinetric growth are incompatible with inean weight-density equations for whole plants, unless a mutual adjustment between allometry and stand structure is assumed.

The structure and function of ten Western North American grasslands: III. Net primary production, turnover and efficiencies of energy capture and water use

Abstract: (1) Levels of net primary production and the efficiencies of energy capture and water use were investigated in six grassland types encompassing ten western North American grasslands. Emphasis was placed on between-site analysis to show the importance of abiotic variables in the functioning of the ecosystem at the producer level. (2) Above-ground primary production (ANP) ranged from 54 to 523 g m -2 yr -1 . Average ANP for grazed grasslands was 212 compared to 236 g m -2 yr -1 for ungrazed grasslands (P ≤ 0.05). (3) There was an apparent linear increase in ANP with increasing precipitation up to approximately 500 mm yr-1. Likewise, ANP increased linearly with increases in both growing-season and annual actual evapotranspiration. (4) Net root production (RP) ranged from 148 to 641 g m -2 yr -1 . The RP was significantly higher on grazed treatments compared to ungrazed grasslands. In general, RP increased with decreasing levels of long-term mean annual temperature. (5) Total net primary productivity (TNP) ranged from 225 to 1425 g m -2 yr -1 . Approximately 46% and 58% of the variability in TNP were explained by annual precipitation in ungrazed and grazed grasslands, respectively. (6) Generally, the warmer grasslands had higher rates of turnover of crown material than did cooler grasslands. As annual usable incident solar radiation and annual actual evapotranspiration increased, so the rate of crown-turnover increased. (7) The average rate of turnover of root material was 0.18, 0.30 and 0.49 for the mixed-grass, tallgrass and shortgrass prairies, respectively. There was a positive curvilinear relationship between root turnover and total annual usable incident solar radiation. (8) Efficiency of energy capture in TNP ranged from 0.12% to more than 1.4% for both ungrazed and grazed grasslands. It appears that plant communities dominated by cool-season species were comparable to or more efficient in energy capture than the communities dominated by warm-season plants. Grasslands having higher efficiencies of water use for TNP also had greater efficiency of energy capture. Consequently, these two important functional properties of the producer system are positively related.

An investigation of the biotic factors determining the rates of plant decomposition on blanket bog

Abstract: (1) The microbial and animal contributions to plant decomposition in peat and mineral soils in the northern Pennines were assessed by exposing litter of seven different plant species in nylon bags of two mesh sizes, one of which excluded all soil animals. (2) The average rate of microbial decomposition of the same substrates was similar at the peat and at the mineral sites, but the rates of decomposition of litter from different plant species showed large differences. (3) The role of animals in the decomposition of the plant materials differed markedly according both to the soil type and to the plant species of the substrate. Little of the decomposition of Eriophorum vaginatum and Sphagnum recurvum on peat soils was attributable to animal activity, whereas Calluna vulgaris and Rubus chamaemorus owed an appreciable part of their decomposition to the activity of soil animals. (4) The decomposition losses attributed to micro-organisms and to animals were not significantly correlated. (5) Significantly greater densities of soil animals were found on R. chamaemorus leaves that had been exposed on peat as compared with mineral soils, despite the much lower overall density of soil animals in peat soils. (6) The rates of microbial decomposition of the plant substrates were highly correlated with their P or N concentrations on both peat and mineral soils. When the animal contribution to decomposition was included, the high correlation with N or P was maintained on the mineral soils, but the correlation was lower and not significant on the peat. (7) The concentrations of N and P in the plants used were highly correlated. Their effects were separated by comparison between decomposition rates of litter derived from plants growing on areas fertilized with either N or P, and of litter of control material from the same plant species. The material enriched with N, but not that enriched with P, showed increased decomposition rates. (8) The addition of nitrogen fertilizer to blanket bog produced an increase in the density of soil invertebrates. It also caused increased larval growth in Tipula subnodicornis and Lasiocampa quercus, and increased fecundity in the former. Addition of a phosphorus fertilizer had less marked effects, but where these were significant they usually took the form of a decrease in density or in growth rate. (9) It is concluded that the chemical composition of a plant species is of paramount importance in determining the rate of its decomposition on blanket bog. Peat accumulation on blanket bog is primarily the result of the intrinsic slow decay rate of some of the species in the plant communities on such areas.

The structure and function of ten Western North American grasslands: I. Abiotic and vegetational characteristics

Abstract: (1) Data collected from coordinated comparative studies on the structure and function of ten central and western United States grasslands are presented and analysed. The ten study areas encompassed six major grassland types: mountain grassland, northwest bunchgrass, mixed-grass prairie, shortgrass prairie, tallgrass prairie and desert grassland. Experimental design at each location included two replications of ungrazed (i.e. long-term absence of grazing by large domestic herbivores) and grazed treatments. (2) Structural characteristics studied included quantities of cool- and warm-season plants at each site, and magnitude and seasonality of primary producer compartments. (3) The environmental variables measured at each site were precipitation, temperature and solar radiation. These variables were calculated as both annual and growing-season values, along with annual and growing-season potential and actual evapotranspiration. (4) The seasonal mean live biomass averaged 94 g m -2 for the ten grasslands, with a mean of 98 g m -2 on ungrazed grasslands and 89 g m -2 for grazed grasslands. Ungrazed grasslands averaged about 160 g m -2 of recent and old dead plant material, compared to approximately 70 g m -2 on grazed grasslands. Ungrazed grasslands had about 50 and 150% more recent and old dead material, respectively, than grazed grasslands. Generally, grazing in previous seasons decreased the standing crop of dead material across the grasslands. (5) The mean total shoot standing crop averaged 203 g m -2 for all grasslands across all treatments; ungrazed grasslands averaged 245 g m -2 , compared to 161 g m -2 for grazed grasslands. The magnitude of litter corresponded in general to the amount of total shoot standing crop. (6) Generally, the shortgrass prairie had the maximum amount of crown material, followed by the mixed-grass prairie, with the tallgrass prairie least. Crown material averaged c. 275 g m -2 for the mixed- and shortgrass prairie, compared to c. 200 g m -2 for the tallgrass prairie. Although grazing did not significantly influence the amount of crown material, crown material tended to increase under grazing in mixed-grass and shortgrass prairies. (7) Root biomass ranged from 156 g m -2 in the desert grassland to as much as 2000 g m -2 in the mixed-grass prairie, while other grasslands were intermediate between these two extremes. (8) There was an inverse relationship between root biomass and dynamics and mean annual temperature. Grazing generally resulted in an increase in the root/shoot ratios, particularly on the cooler grasslands.

Myrmecochory in viola: dynamics of seed-ant interactions in some west virginia species

Abstract: SUMMARY (1) The interactions of ants and diplochorous Viola seeds were studied at four forest and forest-edge sites in Monongahela National Forest, West Virginia. Of the nine Viola species studied, seeds of six (V. blanda, V. papilionacea, V. pedata, V. pensylvanica, V. rostrata and V. triloba) were readily taken. (2) The most important seed transporters were Aphaenogaster spp., but Formica subsericea, Lasius alienus, Leptothorax spp., Myrmica punctiventris and Tapinoma sessile also took seeds. Unlike the situation in Europe, ants of the Formica rufa group displayed little interest in Viola seeds. There was no evidence of specialization of particular ant species on particular Viola species. (3) Cleistogamous seeds were taken much less frequently than chasmogamous seeds, even though cleistogamous seeds had larger elaiosomes. This difference is apparently due to diet shifts of the ants in summer. (4) Most seeds picked up by ants were carried to the nest. The distances seeds were moved averaged about 75 cm, which is less than the average ballistic dispersal distance. (5) The advantage of ant dispersal is relocation to a 'safe site' for germination, thus reducing predation, increasing germination stimuli, and increasing the available supply of nutrients.

The adaptive significance of stomatal occurrence on one or both surfaces of leaves

Abstract: SUMMARY (1) The relationship of stomatal occurrence (on one or both sides of leaves to environment was studied by literature search, mathematical modelling and investigation of herbarium specimens. The starting hypothesis, that hypostomatous leaves (with stomata only on the underside) should occur in dry habitats, was contradicted by all three sources. (2) The models, based on mass-transfer physics, produced three major results; (a) mesophyll thickness is the chief variable determining stomatal distribution, with thick leaves tending to be amphistomatous (with pores on both sides); (b) stomatal distribution does not depend much on environmental variables, but the dependence is strongest under conditions of low water stress; (c) within the limits of the models, amphistomatous leaves appeared nearly always to be better adapted than hypostomatous leaves, indicating that the models are not yet complete. (3) Leaf thickness and stomatal distribution were determined from herbarium specimens of the Indiana species of Compositae, Liliaceae, Salicaceae and Scrophulariaceae. These measurements were then compared with a simple habitat rating derived for each species from published habitat descriptions. Hypostomatous leaves occurred least often in xeric habitats, most often in mesic ones, and again less often in hydric habitats. However, the data suggest that this relationship is secondary, with leaf thickness being the intervening variable. (4) Finally, explanations are considered for the predominance of hypostomatous leaves over hyperstomatous ones.

The Demography of a Sand Dune Annual: Vulpia Fasciculata: I. The Natural Regulation of Populations

Abstract: (1) The population dynamics of the winter annual grass Vulpia fasciculata on two dune systems in North Wales is described. Permanent quadrats were mapped frequently to obtain data on the fates of seedlings and the reproductive performance of each individual. The role of density in the regulation of populations was assessed by the manipulation of natural densities in the field. (2) The behaviour of populations of V. fasciculata on the fixed dunes of the two dune systems studied was remarkably similar. The probability of a seedling surviving to maturity was high, but the potential seed rain on some plots was considerably reduced by rabbit grazing at or just before flowering. There was a peak of mortality during inflorescence development. The causes of mortality during the life cycle were various. (3) There was no evidence for any density-dependent mortality, but above a density of 100 flowering plants per 0 25 m2 it was found that there was a significant negatively density-dependent relationship between the number of spikelets per plant and the density of flowering plants. A simple model which describes the population dynamics of V. fasciculata in terms of the density-dependent regulation of spikelet number and the density-independent mortality is presented. (4) The reasons for the stabilization of the density of V. fasciculata at different levels in different areas on the two dune systems and the reasons for the annual fluctuations in population density within these areas are discussed.

A comparison of the abilities of colonizers and closed-turf species to establish from seed in artificial swards

Abstract: (1) The seeds of a range of ruderals and closed-turf species were sown into 2 5-cm-wide gaps in short turf (1 cm tall) and tall turf (8 cm tall) of Festuca rubra. Germination and seedling growth in these swards were compared with those on bare soil. (2) Germination was not appreciably reduced in either group of species in short turf, but that of the ruderals was greatly reduced in tall turf. (3) In short turf, seedlings of the ruderals were generally much less able than those of the closed-turf species to withstand the competition, which appeared to be effective mainly at the roots in this treatment. Seed weight was found to have no significant effect on competitive ability. (4) In tall turf, seedlings of both groups of species grew hardly at all. There was some indication that a potentially high relative growth rate may be a disadvantage to seedlings establishing in tall turf. (5) The importance of tolerance of competition in young seedlings is discussed.

The ecology of the seas

Abstract: The Ecology of the seas , The Ecology of the seas , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

A study of the dynamic ecology of zambian vegetation

Abstract: (1) Traditionally three broad vegetation types have been recognized in northern Zambia: chipya, an open woodland subjected to intense dry-season fires; miombo, a light closedcanopy woodland dominated by species of Brachystegia and Julbernardia; and mateshi, a dry evergreen forest now reduced to remnant patches. (2) The present study formed part of an integrated land-appraisal survey of north-eastern Zambia; 398 quantitative samples (each 20 x 20 m) were recorded, and the majority were found to contain species from two or three of the above vegetation types. (3) It is suggested that there is a dynamic relation between the three vegetation types, with a trend in the absence of fire from chipya via miombo to mateshi; and that, specifically, certain chipya species form patches of low canopy which provide a suitable habitat for the establishment of a number of Uapaca spp. that are unable to grow in the open chipya. Under the protection of Uapaca the miombo and mateshi canopy species regenerate. (4) The component species have been sorted into four ecological groups-chipya, Uapaca, Brachystegia-Julbernardia woodland, and dry evergreen forest and the dynamic relationships between the groups discussed by reference to an ordination of 206 samples. (5) Topography has been shown to play a minor role in the determination of vegetative patterns. Fire is the major factor, and the dynamic vegetative patterns have been described in terms of the development of successive tree canopies that control the effects of fire.

Factors Influencing the Spatial Distribution of Phytoplankton in a Small Productive Lake

Abstract: (I) A study of the horizontal and vertical distribution of the phytoplankton in a small productive lake, Esthwaite Water in the Lake District, was made during thermal stratification. Distribution patterns of the phytoplankton were related to horizontal variations in specific conductance and pH and to the vertical distribution of temperature and oxygen. (2) A diel study of the changes in the vertical distribution of the dominant algal species, chlorophyll a, temperature and oxygen was also made at the time of maximum phytoplankton density. (3) Appreciable non-uniform horizontal distribution of the phytoplankton was observed only when buoyant blue-green algae or the dinoflagellate Ceratium hirundinella were present. (4) On most occasions horizontal variations of phytoplankton density showed clear systematic patterns related to wind-induced water movements. These patterns were particularly pronounced when individual species formed well-defined vertical aggregations in regions of upwelling or downwelling water. (5) Observations on the vertical distribution of Ceratium showed that this alga underwent diel vertical migrations, with a proportion of the population aggregating at the metalimnion at night. During calm weather large daytime sub-surface accumulations of the alga were found. Vertical perturbations of such small-scale, vertical aggregations may have produced the extreme small-scale horizontal variations of algal concentration noted on two occasions. (6) Daily mean wind speeds above 100 km day 1 were normally sufficient to break down patches of phytoplankton, whereas values below 50 km day-' allowed the formation of dense, small-scale, near-surface aggregations of Ceratium. (7) Lateral transport of algal cells at the metalimnion by water currents could assist in maintaining high nutrient gradients at the cell surface, and contribute to the sustained growth of the phytoplankton.

The structure and function of ten Western North American grasslands: II. Intra-Seasonal dynamics in primary producer compartments

Abstract: (1) Intra-seasonal dynamics of the various above-ground and below-ground primary producer compartments for ten central and western North American grassland sites are presented. (2) The seasonal peak values of the primary producer compartments are examined, as indicative of the net accumulation of organic material, and the relationships of these peak values to various abiotic regimes at the sites are investigated. (3) Seasonal live biomass followed either a unimodal or a bimodal growth pattern. In general, grasslands with only cool-season or only warm-season plants showed a unimodal pattern, while grasslands dominated by both cool- and warm-season species had a bimodal seasonal growth pattern. There were no significant differences between grazed and ungrazed treatments in seasonal live biomass, although there was a significant site × treatment interaction. (4) Peak live biomass ranged from 84 to 336 g m -2 , and showed a linear increase with increasing amounts of growing-season precipitation up to 450 mm; at higher values of precipitation increases in live biomass tended to level out. (5) Maximum rates of accumulation of live biomass ranged from 0.4 to 6.5 g m -2 day -1 . Ungrazed grasslands had a peak rate of 4.2 g m -2 day -1 compared with 3.2 g m -2 day -1 for grazed grasslands. (6) Generally the recent-dead compartment showed maximum values soon after the peak in the live compartment. Material in the old-dead compartment, however, was at a maximum early in the growing season, and a general decline in the standing crop of old dead material followed as material was transferred to the litter compartment. (7) Litter dynamics responded closely to precipitation events, and showed a rather erratic pattern. (8) Root biomass generally reached a maximum about midway through the growing season. On the cooler grasslands, grazed treatments typically had a larger peak in root biomass; in contrast, the warmer grasslands did not show a marked response in root biomass to grazing.

Dynamics and succession of the phytoplankton in a tropical lake: lake lanao, philippines

Abstract: SUMMARY (1) Phytoplankton dynamics in Lake Lanao, Philippines, were studied over a 16-month period on the basis of weekly abundance measurements for seventy species and a number of physical and chemical variables. (2) An analysis of growth pulses and growth correlations in the major classes of phytoplankton provides evidence that the niche space is divided temporally on the basis of nutrient and light availability. Growth maxima of diatoms and cryptomonads occur during periods of relatively low light availability and high nutrient availability; pulses of green algae, blue-green algae and finally dinoflagellates occur successively towards the high light and low nutrient end of the spectrum. (3) Variations in total autotroph biomass over the 16-month period were more closely related to factors affecting growth than to factors affecting loss of biomass. Loss control factors nevertheless influenced succession by their differential effects on individual species. (4) Major factors controlling phytoplankton growth include light availability (computed from measurements of incident light, mixing depth and transparency) and nutrient availability (computed from measurements of nutrient concentrations, turbulence and change in depth of mixing). Individual species were arranged by statistical methods according to their growth patterns along gradients of these two factors. There is an identifiable taxonomic trend in the separation similar to that observed in the class-level analysis of succession, but a number of species showed divergent behaviour from others of their taxonomic group. (5) Measurable factors governing loss of autotroph biomass include grazing rate (analysed

The effect of pollen recruitment processes on pollen distribution over the sediment surface of a small lake in cumbria

Abstract: SUMMARY (1) Pollen recruitment was studied at a small Cumbrian lake (area 10 2 ha) into which two experimental tubes, each isolating a water column 45 m diameter x 12 m deep, had been introduced. (2) Pollen deposition per unit area per unit time was measured at 4-6-weekly intervals in traps floating inside the tube rims, and in other traps submerged inside and outside the tubes and at two points on the mid-lake mud surface. Additional pollen counts were made on water and suspended sediment samples from inflow streams, and on surface sediment samples from thirty-six locations in the lake. (3) Floating traps apparently underestimated, by a factor of x 2, the actual flux of airborne pollen deposition on the water surface. (4) Catches in the traps submerged inside the tubes varied seasonally with the relative recruitment of fresh airborne pollen and of pollen resuspended by turbulence during destratification from the mud surface within the tubes. (5) The traps submerged in the open lake caught seasonal components of airborne and resuspended pollen, and also a streamborne pollen component. This streamborne component changed seasonally in composition and its magnitude varied with runoff. (6) Annual pollen catches in traps submerged inside the tubes were equivalent to only 15% of the catches outside, indicating that a high proportion of all pollen supplied to mid-lake must be streamborne. (7) Annual underwater pollen catches inside the tubes were dominated by pollen taxa which are apparently dispersed efficiently in air, whereas the open lake catches included high proportions of streamborne pollen and also a large component of indeterminable (degraded) pollen, which was probably recruited from catchment soils. (8) A closer correspondence between the pollen composition of material trapped in mid-lake and the composition of vegetation on the catchment area of the lake was found for the catches in the traps submerged in the open lake (where a substantial streamborne pollen component was present) than for catches inside the tubes. (9) Two different multivariate methods (principal components analysis and minimumvariance cluster analysis) were used to analyse percentage pollen counts from thirty-six surface sediment samples. Both analyses showed that pollen spectra from within the 8-m water-depth contour were closely similar, but that spectra from shallower water differed considerably from place to place (apparently as a result of high and localized pollen input from marginal vegetation), despite the effects of littoral resuspension, which might be expected to obliterate such spatial differences. (10) Pollen per cm3 sediment (adjusted for water content) was found to be approximately uniform in samples from 0-1 cm depth along a transect through the lake, and also in a 0-8 cm

Ecological genetics : the interface

Abstract: 1. Theory.- On the Evolution of Ecological Parameters.- Coevolution in Ecological Systems III. Coadaptation and Equilibrium Population Size.- 2. Physiology, Biochemistry, and Adaptation.- Physiology and Biochemistry of Enzyme Variation: The Interface of Ecology and Population Genetics.- Genes, Enzymes, and Hypoxia.- 3. Drosophila.- Speciation and Sexual Selection in Hawaiian Drosophila.- Ecology and Genetics of Sonoran Desert Drosophila.- Microspatial Genetic Differentiation in Natural Populations of Drosophila.- 4. Other Animals.- Ecological Parameters and Speciation in Field Crickets.- Some Contributions of Snails to the Development of Ecological Genetics.- 5. Plants.- Genetic Demography of Plant Populations.- Some Genetic Consequences of Being a Plant.- 6. Coda.- Population Differentiation: Something New or More of the Same?.

The Demography of a Sand Dune Annual: Vulpia Fasciculata: III. The Dispersal of Seeds

Abstract: (1) On dispersal the caryopses of the winter annual grass, Vulpiafasciculata, remain within the spikelet, forming a seed-dispersal unit. The dispersal of these units, which was studied on two dune systems in North Wales, has two distinct phases. Firstly, dispersal units fall onto the soil surface from the infructescences (Phase I), and, secondly, they may be moved along the ground surface by various inorganic or organic agencies (Phase II). (2) The release of seed-dispersal units began immediately after they had ripened at the end of June and continued over 3 months, although 94% were dispersed in July. The rapid shedding of seed maximizes the time available for Phase II dispersal. (3) The distance of Phase I and Phase II dispersal was in general restricted to a few centimetres. The mean distance of Phase I dispersal was density-dependent and strongly correlated with the height of the infructescence, and the distance of Phase II dispersal was strongly dependent upon the percentage cover of the vegetation. The greatest proportion of dispersal units moved in the direction of the local prevailing winds. Few units were buried on the fixed dunes, but most were buried on the one yellow dune site studied. (4) The distance of dispersal is discussed in relation to the population dynamics of V. fasciculata, and in relation to the colonization of new areas of habitat. The curves relating the logarithm of seed density to the logarithm of distance from seed source indicate that the species will spread more as isolated colonists from tall infructescences and as an advancing front from short ones. On the ground the species will spread as a colonizing front where the vegetation cover is less than 50%, and more as isolated colonists where it is greater than this.

Mortality and initial propagule size in mangrove seedlings in panama

Abstract: SUMMARY (1) Cohorts of seedlings of Avicennia bicolor+A. germinans, Laguncularia racemosa, Pelliciera rhizophorae and Rhizophora mangle were studied for 1 year, the Avicennia and Pelliciera on the Pacific side of the Isthmus of Panama, and the Laguncularia and Rhizophora on the Caribbean side. The seedlings were in almost pure stands of the mangroves concerned. (2) There was an exponential decay of numbers in three species, the half-lives being 85, 338 and 604 days in Avicennia, Rhizophora and Pelliciera respectively. (3) The rate of decay of the Laguncularia cohort increased with time; 50% were lost in

Spectral analysis and the analysis of pattern in plant communities

Abstract: SUMMARY (1) Spectral analysis is a relatively untried method for the analysis of data from a line of contiguous quadrats. Conventional block-size analyses are shown to be related to square waves. In spectral analysis square waves are replaced by sine waves. (2) These methods and Mead's test are compared with conventional methods, using artificial and field data. Spectral analysis performed reliably and gave a good indication of the type of departure from a random pattern. Mead's test proved sensitive but hard to interpret, often contradicting other methods. (3) It is argued that standardization should not be used with methods based on variances.

The ordination of incidence data

Abstract: SUMMARY (1) Principal components analysis of incidence (presence and absence) data produces a horseshoe effect. A new method, called step-across, is described which removes this effect. (2) From a matrix of joint occurrences, distances are found directly for all positive values. Distances for zero joint occurrences are found from the shortest network distance. The complete distance matrix is then analysed by Gower's principal coordinates technique. (3) The method can be used on both the rows and columns of an incidence matrix. It is illustrated with artificial data and with data on euphausiids from the Indian Ocean.

Regulation of seed yield in plantago

Abstract: SUMMARY (1) The correlation and variation of four yield-components are important in regulating seed yield in the genus Plantago. (2) Negative correlations between weight per seed and seed number per capsule, and between the capsule number per inflorescence and the inflorescence number per plant, are evident among thirty species in the genus Plantago. These compromises have limited the variation in total seed yield per plant during speciation. (3) In contrast, investigations of variation within populations using random samples, and within species using herbarium material, reveal that correlations between yield-components are positive or neutral, suggesting that phenotypic plasticity in yield-components is important in allowing plants to regulate their seed production in relation to the immediate environment. (4) In order of increasing importance in the regulation of seed production, both within populations and wi, hin species, are seed number per capsule, weight per seed, capsule number per inflorescence, and inflorescence number per plant.