Showing papers in "Journal of Ecology in 1983"

Seed dispersal of the tropical tree, Platypodium elegans, and the escape of its seedlings from fungal pathogens

Abstract: On recherche l'importance relative des causes de la mortalite des jeunes plantes; on etudie l'effet de la distance de dispersion sur la probabilite de survie des jeunes plantes et sur l'importance relative des causes differentes de mortalite; enfin on precise l'effet de la lumiere sur la mortalite

The Demography of Bromus Tectorum: Variation in Time and Space

Abstract: (1) Amplitude in the variation of recruitment, survivorship and fecundity was examined for the introduced annual grass Bromus tectorum in three habitat types in eastern Washington (U.S.A.) for three consecutive generations. A total of 18 143 individuals in populations varying from 364 to 5322 members per site were mapped repeatedly from emergence to death with sufficient frequency to detect multiple constituent cohorts varying in age from fewer than 16 to more than 200 days. (2) Recruitment was usually concentrated in late summer and autumn, but occurred at any time until mid-May of the following year. (3) Most of any population experienced low death risk until June, although some cohorts emerging in late summer were devastated (Deevey Type III curve) during periods of drought or extended snow cover. (4) Most plants survived to produce seed. Loss of seed production from devastated autumn-emergent plants was off-set by the reproduction of late winter-spring recruits. Even individuals less than 45 days old often produced at least one viable seed by June. (5) B. tectorum persists under the vagaries of steppe environments by its ability to behave simultaneously on the same site as an ephemeral monocarpic, annual monocarpic and winter annual monocarpic species. (6) Year-to-year variation in environment (weather, predator activity) overrode the intrinsic differences among the three habitat types along a 200 km transect of varying moisture availability often producing considerable amplitude in population attributes (recruitment, survivorship and fecundity). Characterization of any species as a colonizer, etc. on the basis of life history traits alone may be erroneous; knowledge of the variation in such population attributes is also necessary.

Photosynthetic inorganic carbon use by freshwater plants

Abstract: SUMMARY (1) A pH-drift technique was used to calculate free CO2 (CO2) and bicarbonate (HCO ) compensation points for a range of freshwater macrophytes and phytoplankters. Some half-saturation constants for CO2 uptake were also estimated. The validity of the technique and interpretation is discussed and generally confirmed. (2) Variation in the CO* compensation point of Hippuris vulgaris was related to the oxygen concentration of the bathing medium, and seasonal changes in HCOcompensation point were found in Potamogeton filiformis and in HCOI and CO* compensation points in Elodea canadensis. The performance of these two macrophytes is probably affected more by seasonal changes in HCOI compensation points than by CO* compensation points. (3) The quotient of total carbon remaining at the end of a pH-drift experiment to the constant alkalinity of the solution (CT/Alk) was used as a measure of the uptake ability of a species. Ranked by this criterion, species showed a fairly continuous range in uptake ability with a nearly fifteen-fold difference between the most efficient (low quotient) and least efficient (high quotient) species. (4) Although the uptake abilities of macrophytes and phytoplankters overlapped, the four most efficient carbon extractors were phytoplankters, and the nine least efficient were macrophytes. Anabaena cylindrica, Microcystis aeruginosa and Scenedesmus quadricauda removed more than 90% of the available carbon compared with 70% for the most efficient macrophytes tested (Myriophyllum spicatum and Potamogeton perfoliatus). (5) Those species which remove 5% or less of the available carbon are taken to be unable or poorly able to use HCOi. Such 'macrophytes may benefit from: (i) growing in unproductive lakes that do not experience carbon depletion; (ii) seasonal access to aerial C02; (iii) high CO* concentrations in and close to the sediment. (6) Competition for inorganic carbon may be an important factor determining the outcome of seasonal and longer-term changes in the species composition of productive freshwaters. The reduction or loss of submerged macrophytes in certain recently enriched lakes may result partly from carbon competition with phytoplankton.

Effects of organic matter additions to sediment on the growth of aquatic plants

Abstract: Etude de la croissance de 3 especes completement submergees (Elodea canadensis, Hydrilla verticillata et Myriophyllum spicatum) et de 3 especes partiellement emergees (Myriophyllum aquaticum, Potamogeton nodosus et Sagittaria latifolia

Ecological studies in four contrasting lowland rain forests in gunung mulu national park, sarawak iii. decomposition processes and nutrient losses from leaf

Abstract: SUMMARY (1) Measurements of soil respiration, leaf litter decomposition and litterfall-standing crop quotients were made during one year in three rain forest types in Gunung Mulu National Park, Sarawak: alluvial forest (AF), dipterocarp forest (DF) and heath forest (HF). Comparative studies were also made in forest over limestone (LF) over a 6-month period. (2) At the three main sites soil respiration rates showed considerable variation which was not attributable to changes of soil temperature or moisture. Mean annual soil temperatures in the litter layers on the four sites fell within the range 24.3-25.6 IC and mean values for sampling occasions varied less than 1 OC over the year. Mean soil moisture values (wet wt) at 0-5 cm depth, of 60% (AF), 63% (DF) and 73% (HF) varied within 10%. The mean soil moisture of the limestone site was 71%. There was some evidence of a seasonal relationship between rainfall and soil respiration rates in the DF and HF. It is concluded on other evidence that soil respiration mainly represents CO2 efflux from the surface litter layers and the root mat. (3) Chemical analysis of freshly fallen, mixed leaf litter from each site showed the following ranges of element concentration (mg g-1): N, 4.4-11.0; P, 0.06-0-41; K, 0.9-3.8; Na, 0.03-0.11; Ca, 3.7-35.0; and Mg, 1 1-2.7. Concentrations inFicus and Parashorea from the AF were at the upper limits of these ranges except for Na (0.02) and P in Ficus (0. 72). Lignin concentration varied between 31% and 40% for the mixed leaves and between 27% and 28% for Parashorea and Ficus. The highest concentration of polyphenols was in the leaves from HF and the lowest in leaves from the LF, but Parashorea had the highest overall concentration and Ficus the lowest. (4) Weight losses after 10 months from mixed leaves in fine-mesh (40,um) litter bags were 41% (AF), 44% (DF) and 55% (HF). Mixed leaves in the LF showed lower weight losses over 6 months than leaves in the other sites over the same period. Weight losses were 67-75% for Ficus and 49-61% from Parashorea in the three main sites. Weight losses from coarse-mesh (20-40 mm) bags were ranked LF > DF > HF > AF and were not related to total population of litter feeding invertebrates or to the population of individual groups. (5) Litterfall-standing crop quotients (kL values) for leaves ranged from 1 . 7 (AF, DF and LF) to 1.4 (HF) and, for total small litter, were 1.7 (AF), 1.5 (LF), 1.3 (DF) and 1.3 (HF). The kL values for total litter, including wood 2-10 cm, ranged from 0.8 to 1.2 The litter kL values show no obvious relationship to estimated organic matter standing crop in the top 30 cm of soil of 320 t ha-' (HF), 240 t ha-' (AF), 200 t ha-' (DF), and 160 t ha-' in the top 11 cm of the LF. (6) Losses of K, Mg and Ca from litter bags were rapid while N and P were conserved; Na concentration increased in mixed leaves. There was evidence of the fauna increasing mineral losses from the leaves. Accession-standing crop quotients for elements confirmed the rapid flux of K and Mg at all sites; Ca had the highest quotient in the AF,

The evolutionary biology of colonizing species

Abstract: Professor Parsons uses the colonizing species as a case study in the dynamics of microevolution at work in living systems. The colonizing species, a lie, and potentially disruptive force in a 'naive' habitat, is studied primarily as an ecological phenotype and more generally as an ecological behavioural phenotype. Conventional life-history traits and components of fitness, can be incorporated into these phenotypes. Integrating genetic change, natural selection, and the interaction of the species with its environment and other living systems therein, the colonizing species is transformed into a sophisticated and complex source of data for understanding evolutionary biology. Throughout the book it is emphasized that using the organism as the unit of selection is the most direct way of understanding the nature of successful colonizing phenotypes, and, by using specific phenotypic criteria, the prediction of likely successful colonists can be made. Such criteria include tolerance of extreme environments, resource utilization, reproductive capacity, and relative abundance.

Ecological studies in four contrasting lowland rain forests in gunung mulu national park, sarawak ii. litterfall, litter standing crop and preliminary observations on herbivory

Abstract: SUMMARY (1) Small litterfall (leaves, wood ?2 cm diameter, renroductive parts, and trash) was compared on sites of 1 ha in each of four types of lowland forest in Gunung Mulu National Park, Sarawak, for quantity, seasonal distribution and the concentrations of nitrogen, phosphorus, potassium, sodium, calcium, magnesium and total phenols. The sampling period was 50 weeks for the sites in alluvial forest (AF), dipterocarp forest (DF) and heath forest (HF) and 42 weeks for the forest over limestone site (LF). (2) The total small litterfall was (t ha-' year-' ? 95% confidence limits): for the AF, 11.5 ? 1.9; DF, 8.8 ? 0.6; HF, 9.2 ? 1.2; and LF, 12.0 ? 1.3. A peak of litterfall occurred on all four sites during a May-June period of high rainfall before the driest time of the year. (3) The element concentrations in the litterfall differed greatly between each forest type. The concentrations of all elements (except calcium in samples from the LF) were below or within the ranges reported for other tropical forests and there was no consistent seasonal variation. The low calcium concentration in the DF litterfall and low nitrogen in the KF litterfall were notable. (4) Total polyphenol concentrations in the leaf litterfall were ranked HF > LF > DF > AP. (5) Large-wood litterfall was measured over a shorter period than the small litterfall. Virtually no wood over 10 cm diameter fell in the collection quadrats and the results for

Phenological patterns of chihuahuan desert plants in relation to the timing of water availability

Abstract: SUMMARY (1) Phenology, density, and cover of plant species occurring in a single Chihuahuan desert habitat were studied for 2 years as a function of habitat moisture with the objective of relating plant species diversity to water partitioning. (2) Much of the temporal variation in growth and phenology between species was correlated with differences in life form and photosynthetic pathway. (3) The annual plant species consisted of a winter-spring group containing only species with the C3 photosynthetic pathway which utilize the moisture from frontal storms of winter, and a summer group containing a large majority of species with the C4 photosynthetic pathway which utilize the moisture from convectional storms of late summer. (4) The perennial plant species consisted of C3 and C4 forbs, C4 grasses, C3 shrubs and CAM shrubs. The C3 forbs showed greatest activity in spring or autumn while the C4 forbs and grasses were most active in the summer and autumn. The C3 shrubs and CAM shrubs were active at various times from spring to autumn and not as dependent as the other groups on available soil moisture. (5) There was above average precipitation in late summer and autumn during the first year of study and an early and prolonged drought in autumn of the second year. Some species of perennial C3 forbs and C4 grasses responded to the abundant precipitation of the first autumn with increased density or cover in the second year, but there was little change in the shrub species. The drought in the second year caused a reduction in the number of species and individuals of both C3 and C4 annual plants. (6) The results suggest that the high species diversity in this habitat is partly a result of the different life form and photosynthetic pathway groups, each being adapted for utilizing a particular phase of the seasonally and yearly variable water.

Use of visual cover assessments as quantitative estimators of some british woodland taxa

Abstract: SUMMARY (1) Ten observers made visual estimates of plant cover on a series of 4 m2, 50 m2 and 200 m2 quadrats in a woodland. (2) Mean cover values from the ten observers corresponded reasonably closely with point quadrat estimates of cover for most species in the 4 m2 quadrats. (3) For all taxa, significant differences occurred between the estimates of different observers at all quadrat sizes. Using an observer drawn at random, 90% confidence intervals were in the range + 10-20% cover. The corresponding range for an individual repeating an estimate on the same quadrat was + 5-15% cover. (4) Variability between observers was usually lowest when estimating broad-leaved species and highest with fine-leaved species and bryophytes. (5) Observers differed in the consistency with which they tended to under- or over-estimate cover in relation both to species and to quadrat size; this consistency was not correlated with experience. (6) The biases of different observers for a particular species and quadrat size were sufficiently consistent that the use of mean bias correction factors brought about clear gains in the precision of cover estimates for most species.

Experimental ecology of Dryas octopetala ecotypes. I. Ecotypic differentiation and life-cycle stages of selection.

Abstract: SUMMARY (1) Natural populations of Dryas octopetala show large site-specific variations in phenotype. The genetic and environmental basis for this variation was examined in common-garden and reciprocal-transplant experiments. Morphological characters were examined in seedlings grown from seed in a 'common garden' in controlled growth chambers at the Duke University Phytotron. Adult plants of three D. octopetala populations were transplanted reciprocally at three sites along a snowbank gradient in mountains of interior Alaska. (2) Several factors capable of maintaining genetic differentiation between adjacent snowbed and fellfield populations were studied. Restrictions on pollen flow by phenological and spatial isolation were determined. Barriers to gene flow, selection between ecotypes, and site effects within an ecotype were investigated experimentally by measuring survival of reciprocal transplants at the pollination, seed, seedling, and adult stages. (3) Seedlings raised under common conditions showed differences in leaf size parallel to those observed in the field. Differences in leaf pubescence, used to distinguish two D. octopetala subspecies, were also maintained. The two most prevalent forms were therefore termed ecotypes. (4) Leaf morphology was measured to assess phenotypic effects of reciprocal transplants of adults. Analysis of leaf traits suggested that greater morphological plasticity in the snowbed ecotype accounts for the bulk of the observed phenotypic differences between populations. (5) Pollen flow was greatly reduced by separation of flowering times of the two ecotypes. More than 99% of pollen movement was between flowers of the same ecotype. Neither ecotype was apomictic or auto-fertile; both were self-incompatible. There were apparently no breeding system barriers to gene flow. (6) Selection, measured as survival, favoured seedlings of the snowbed ecotype over those of the fellfield ecotype at the snowbed site (selection coefficient 0 55). At the fellfield site, selection favoured the fellfield ecotype at the adult stage (selection coefficient 0.50). No significant selection was demonstrated at any other life-cycle stage, although 10 of 11 stage-specific selection coefficients indicated a trend toward selection against an alien ecotype at both sites. (7) Seed germination was higher and seedling survival lower at the fellfield site than at the snowbed site for both ecotypes. Therefore, the 'home' site was not always the 'better' site at all life-cycle stages; ecotypes were not perfectly matched with the environment. Therefore, selection at present acts only to give a relative advantage to native ecotypes.

The growth of spha gnum: experiments on, and simulation of, some effects of light flux and water-table depth

Abstract: SUMMARY (1) Experiments were made to determine the effects of both shading and of water-table depth on the growth of three species of Sphagnum. The species (and their usual habitats) were: S. capillifolium (hummocks); S. papillosum (lawns); and S. recurvum (pools and flushed lawns). (2) Water-table depth had little effect on growth measured as increase of dry matter; shading reduced growth and there were specific differences associated with plant size. There were no significant interactions between water-table depth and shading. (3) For growth measured as growth in length, there were highly significant interactions, individual species behaving differently in response to shade and, to a lesser extent, in response to water-table depth. (4) In Sphagnum lawns in two natural habitats there was a negative correlation between depth of the water-table and surface-roughness. In experimental conditions surface-roughness increased both as the water-table was raised and as shade increased. (5) A computer simulation of growth of Sphagnum in a lawn was able to reproduce the observed variations in surface roughness. In mixed lawns of two species, the one in its 'natural' habitat out-grew the other.

Trifolium Repens L.

Abstract: A glabrous or glabrescent creeping perennial of indeterminate size, rooting at the nodes. Roots adventitious except for the tap root developed from the primary root of the seedling. Stolons up to 50 cm long, 1.9-4.0 mm in diameter; internodes up to 6 cm long. Leaves palmately trifoliate; leaflets 10-35 mm long, obovate or obcordate, minutely denticulate, usually with a whitish angled band towardsthe base, pinnately nerved with the lateral veins thin and nearly straight. Petioles erect, commonly up to 7 cm long and sometimes longer; stipules ovate to oblong, shortly subulate at the apex, striate. Inflorescence an axillary racemose head, 15-20 mm in diameter, globular, usually bearing 20-40 flowers; peduncles usually longer than the petioles. Flowers white or pink, scented; pedicels up to 6 mm long; erect at first, reflexing after anthesis. Calyx tube 2-4 mm long; campanulate, white with green veins; teeth narrowly triangular, approximately half as long as the tube. Flower zygomorphic, with five petals. The standard, erect, oblong, 8-16 mm long, persistent, folding over the pod; the wings, shorter than the standard each with blade and claw; the two petals of the keel are more or less fused along their adjoining margins and slightly adherent to the wings. The keel encloses nine fused stamens and one free one. Pod sessile, 4-5 mm long, oblong, usually 3-6 seeded, compressed between seeds. Seeds heart-shaped, 1 0 x 1 .1 x 0 6 mm, with a mean 1000-seed weight of 0 5-0.8 g.

Some relationships between environmental reliability and seed dormancy in desert annual plants

Abstract: Etude des reponses de germination de 3 especes annuelles du desert de Chihuahua en fonction de la saison pluvieuse d'ete et de la saison d'hiver: Pectis angustifolia, Lepidium lasiocarpum et Lappula redowskii

Interspecific Competition and Niche Differentiation between Plantago-Lanceolata and Anthoxanthum-Odoratum in a Natural Hayfield

Abstract: (1) A removal experiment was carried out to investigate whether intraspecific competition, interspecific competition and niche differentiation occurred within and between populations of Anthoxanthum odoratum and Plantago lanceolata in a natural hayfield By removal of other plant species, plots were created in which each species occurred alone at different densities or with the second species (2) There was strong intraspecific competition within the populations of both species at the densities in which they occurred In mixed plots Anthoxanthum odoratum was less negatively influenced by interspecific competition than by competition with other A odoratum individuals, and Plantago lanceolata was not affected by interspecific competition with Anthoxanthum odoratum (3) The relative yield total (the sum of yields per species in mixed culture divided by yields in monoculture) reached values of about 15, which indicated a high degree of niche differentiation During the 2 years of observation an equilibrium between the two species was established (4) In undisturbed vegetation, the biomass of Plantago lanceolata decreased greatly after the addition of nutrients In plots from which other plant species had been removed, fertilization led to an increase in P lanceolata biomass Decline of P lanceolata (and probably of other dicotyledons) after fertilizer application may be caused by an increase in the intensity of interspecific competition

Ground water and the evolution of patterned mires, Glacial Lake Agassiz Peatlands, northern Minnesota

Abstract: (1) The hydrogeological setting of the Glacial Lake Agassiz Peatlands in Minnesota was investigated by measuring ground-water levels in observation wells, by studies of soil types and thicknesses, and by computer model experiments to simulate ground-water flow. (2) Most ground water circulates along flow paths several kilometers long that pass through the peat column and into the underlying mineral soil. (3) Most ground-water flow is probably caused by the development and persistence of large raised bogs, and occurs because of ground-water mounds (elevated water tables) under the bogs. (4) Lateral bog growth may be limited by the neutralizing of bog water acidity by ground-water discharge ('artesian' flow) at raised bog margins.

Limiting nutrients for plant growth in coastal sand dune soils

Abstract: (1) A pot-culture experiment and a field experiment were carried out to examine the relative importance of nitrogen, phosphorus and potassium supplies for plant growth on coastal dune soils, using Oenothera erythrosepala as a test plant. (2) The plants grown in pot culture were deficient in phosphorus rather than nitrogen and potassium, while the plants grown in the field were deficient in nitrogen rather than phosphorus and potassium. (3) Dune sands were incubated to examine the differences in nutrient availabilities between pot and field conditions. The incubation resulted in an increased availability of nitrogen and a decreased availability of phosphorus. (4) It is suggested that the low supply of inorganic nitrogen in the field is attributable to restriction of mineralization and nitrification and to leaching of nitrate.

Nutrient use by evergreen and deciduous shrubs in southern California. I. Community nutrient cycling and nutrient-use efficiency

Abstract: Etude du cycle des elements mineraux dans des peuplements d'arbustes de chaparral et de scrub cotier du Sud de la Californie, au cours de deux annees

Plant geometry and self-thinning

Abstract: SUMMARY (1) Monocultures of Agrostemma githago, Cichorium endivium and Festuca pratensis were grown at high densities to investigate the effects of plant geometry on self-thinning. Whilst populations of all three species followed the -3/2 power law when weight was plotted against density on logarithmic scales the intercepts were different and fell in the order Festuca > Agrostemma > Cichorium. These differences are related to plant geometry. (2) Published reports show that coniferous trees generally have higher intercepts than deciduous trees and that grasses have higher intercepts than dicotyledons. (3) The mean volume of canopy available to each plant was also found to be related to density by the -3/2 power law. However, the intercepts for a number of species on a volume-density plot on logarithmic scales all fell within one order of magnitude in comparison with two orders of magnitude on a weight-density plot. (4) The biomass which could be packed into a given volume of space generally increased with canopy height, but the range was nevertheless relatively narrow (1 .5-5.2 kg m-3) for the three species. Only part of the variation in intercept between species on a weight-density plot could be related to differences in biomass packing. (5) Variation in the biomass per unit volume through time means that the gradient of the thinning line on a weight-density plot may be different to that on a volume plot. It is suggested that the -3/2 power law might be better stated in terms of canopy volume rather than weight.