Showing papers in "Functional Ecology in 1990"

Oxyradical production as a pollution-mediated mechanism of toxicity in the common mussel, Mytilus edulis L., and other molluscs

Abstract: Normal and pollution-enhanced oxy- radical (02-, H202, OH)* production in molluscs have been reviewed and discussed. Additionally, data are presented on the antioxidant enzyme responses and lipid peroxidation effects in diges- tive gland of Mytilus edulis L. exposed to 50p.p.b. benzo(a)pyrene (BaP) or 1 p.p.m. of the model redox cycling compound menadione. Digestive gland microsomes support NADPH- and NADH- dependent oxyradical generation and the rates of production are increased by redox cycling com- pounds (menadione, nitrofurantoin, paraquat). Antioxidant enzymes (superoxide dismutase (SOD), catalase, glutathione peroxidase, NAD(P)H-DT-diaphorase) and free radical scav- engers (glutathione, vitamins A, C and E, ,3-carotene) are present in molluscan tissues.

Fasting endurance and the evolution of mammalian body size

Abstract: The idea that the need for energy reserves may have been important in the evolution of different body sizes can be traced to Lindsey (1966) who recognized that 'the energy reserves may last longer in large rather than in small animals' and suggested that this may be one possible reason for large body sizes among northern poikilotherms. Several subsequent investigators drew similar conclusions based on studies of other taxonomic groups. A number of environmental correlates of body size among mammalian carnivores suggested that 'homeostatic needs' might set a lower limit to body size at higher latitudes (Rosenzweig, 1968). Body size in whales is inversely correlated with the length of the feeding season and suggests that large size reflects the need for energy reserves during the fasting period (Brodie, 1975). Large body size has also been recognized as important in enhancing the survival of terrestrial vertebrates during periods of resource shortage in strongly seasonal environments (Boyce, 1979; Murphy, 1985; Zeveloff & Boyce, 1988). Quantitative models of energy reserves and fasting endurance in relation to body size have been developed (Morrison, 1960; Calder, 1974, 1984; Searcy, 1980, Peters, 1983; Lindstedt & Boyce, 1985). Similar arguments have been used to explain size dimorphism between the sexes (Downhower, 1976; Ralls, 1976; but see Shine, 1988). Despite this diverse support over many years, energy reserves and fasting endurance are not commonly incorporated into models considering the evolution of mammalian body size. Most

Adaptive seasonal variation in the sex ratio of kestrel broods

Abstract: In contrast with the situation in mammals, sex ratio variations of offspring in birds have rarely been documented, and never been shown to be adaptively tuned to systematic differences in the prospects for daughters and sons. The sex ratio (% males) in broods of European kestrels, Falco tinnunculus L., declined with progressive date of birth. This decline enhanced reproductive prospects of the broods since the probability of breeding as yearling declined with birth date for male offspring, but not for females. The sex ratio bias of the brood was produced by non-random sex segregation at meiosis: by altering the within-clutch sequence of sexes (first male then female eggs in early clutches, the reverse in late clutches) laying kestrels assigned the sex with the better long-term reproductive prospects to the initial eggs of their clutch, which suffer least mortality in the nest. file: 1990FunctEcolDijkstraC.pdf Gebruik a.u.b. deze link om te verwijzen naar dit document: http://irs.ub.rug.nl/dbi/4e16b2d622f03

A Physiological Basis of Population Processes: Ecotoxicological Implications

Abstract: Environmental toxicologists often want to use bioassays that can be carried out quickly, easily, and hence inexpensively on individual organisms, to make predictions about long-term impacts of toxicants at an ecological level (Maltby & Calow, 1990). More fundamentally, it is of interest for population dynamicists to understand to what extent processes within individuals, as compared with interactions between them, contribute to population changes (Metz & Diekmann, 1986). Here we explore models that provide the basis of links between physiological and population processes and point out some implications for the application of physiological bioassays in ecotoxicology.

Locomotor Capacity and Social Dominance in Male Lizards

Abstract: Physiological capacities may constrain behavioural options and hence have important ecological consequences. We tested the hypothesis that social dominance is related to capacities for locomotor performance in territorial male lizards (Sceloporus occidentalis Baird & Girard). We first measured the maximal sprint speed and stamina of individual lizards in the laboratory. Pairs of size-matched males were then placed into a novel laboratory arena and allowed to compete for access to a basking site under a heat lamp. The lizard that physically controlled the basking site was judged the 'winner' of a dominance interaction (winner vs loser status was confirmed by quantitative scoring of behaviour). Winners of these dyadic encounters had significantly higher sprint speeds in 14 of 20 cases, with winners averaging 16.5% faster than losers. Stamina, however, did not differ between winners and losers. Key-words: Behaviour, dominance, locomotion, performance, speed, stamina

Allometry of saplings and understorey trees of a Panamanian forest.

Abstract: The dimensional relationships (allometry) of understorey trees were contrasted with those of saplings of subcanopy-canopy trees in a humid tropical forest in Panama. The six selected species were all common, shade-tolerant trees of primary forest and were sampled in shaded understorey

Significance of allometry in tropical saplings.

Abstract: Differences in allometric relationships of understorey saplings (60-300 cm tall) between nine common shade-tolerant species of subcanopy, canopy and emergent trees were examined in an old-growth foothill rain forest in West Sumatra, Indonesia. Interspecific variation was found in the intercept of the regression line between logarithmic dimensions but not in the slope. Detected interspecific differences could be interpreted as a result of a trade-off between height growth (for future exploitation of better-lit conditions at higher levels in the canopy) and leaf area extension (for current exploitation of poor light nearer the base of the canopy). Saplings of emergent Swintonia schwenkii Teijsm. & Binn. ex Hook. f. favoured height growth rather than expansion of assimilative area. Trends of interspecific differences in sapling allometry in tropical rain forest were similar to those in warm-temperate rain forest. Tropical saplings had more slender trunks and greater total leaf area at a given height than warm-temperate saplings, but dry weight proportions among organs were similar. We hypothesize that the advantage of maintaining assimilative area in present height is diminished in a habitat with higher growth rate and/or steeper vertical light gradient such as in

The Adaptive Significance of Cuticular Pigmentation in Daphnia

Abstract: Cuticular pigmentation has been reported in a number of cladoceran crustaceans, but its adaptive significance remains unclear. This study involved an analysis of the distribution and adaptive significance of pigmentation in the Daphnia pulex Leydig group. A survey of more than 1000 ponds in temperate and arctic North America established that pigmented forms predominate in the high arctic, co-occur with unpigmented clones in the low arctic and are absent from the temperate zone except in coastal sand-dune habitats. In the low arctic, pigmented clones dominate clear-water ponds, while unpigmented clones dominate ponds with high concentrations of dissolved humics. Where they co-occur, pigmented clones tend to remain higher in the water column during daytime. Biochemical studies showed that the pigment is melanin, and although it comprised only 0 03% of body weight, it prevented transmission of more than 90% of incident ultraviolet radiation. Melanic clones of both D. pulex and D. middendorffiana Fischer survived exposure to 20W m-2 of near ultraviolet for twice as long as unpigmented clones. Reciprocal transplant experiments confirmed that unpigmented clones were only able to survive in ponds with high concentrations of dissolved organics, while melanic clones survived in both clear and humic water ponds. It is clear that unpigmented clones in the D. pulex group -are restricted to habitats where they are sheltered from ultraviolet exposure by shading or dissolved humics, while melanic clones are restricted to clear-water ponds where u.v. exposure is high. The failure of melanics to colonize other habitats is apparently largely a consequence of the cost of melanin production. Key-words: Arctic, Cladocera, Daphnia, melanin, ultraviolet *Present address: P.D.N. Hebert, Department of Zoology, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Introduction The dark pigmentation of both zooplankton and benthos from arctic and alpine freshwater habitats has been noted for more than 50 years (Brehm, 1938). Studies concerning the adaptive significance of pigmentation have focused on calanoid copepods, which appear to employ carotenoids and carotenoproteins for protection from short wavelength radiation (300-500 nm). Hairston (1976) showed that pale individuals of Diaptomus nevadensis suffered higher mortality than heavily pigmented individuals when exposed to short wavelength light. Comparable mortality differences have been observed between pigmented and unpigmented forms of several other calanoid species (Hairston 1978, 1979ab; Luecke & O'Brien, 1983). Siebeck (1978ab) reported similar differences among cladoceran species which varied in their carotenoid levels. Despite the concordance of these results, there remains some controversy concerning their interpretation (Byron, 1982). Ringelberg (1980, 1981) has argued that the pigments may serve either as a direct energy source or may be correlated with the nutritional status of the organism. If correct, the increased survivorship of pigmented individuals under high light intensity might reflect nothing more than the greater resistance of well-fed individuals to environmental stress. The present study examines the adaptive significance of pigmentation in another group of microcrustaceans the cladocerans. While many cladocerans sequester carotenoids, certain species deposit a tan-brown to black pigment in their cuticle. As the pigmented cuticle is shed at each moult, the need for pigment synthesis is recurrent. This suggests a clear cost to the maintenance of pigmentation, and hence avoids one of the interpretative difficulties associated with studies on carotenoids. Cuticular pigmentation has been reported in several genera of cladocerans, although more detailed investigations have so far been limited to the genus Daphnia. Luecke & O'Brien (1983) have shown that a pigmented form of D. middendorffiana Fischer was less susceptible to light exposure than an unpigmented form. However, Dodson This content downloaded from 157.55.39.178 on Fri, 05 Aug 2016 05:39:47 UTC All use subject to http://about.jstor.org/terms 704 (1984) has suggested that pigmented forms may be P. D. N. more resistent to invertebrate predation as a result Hebert & of their tougher cuticles. The present study has C. J. Einery focused on members of the Daphnia pulex Leydig group, which dominate pond habitats throughout North America. The taxonomy of the group is in flux, but pigmented forms have been recognized in only two species. D. middendorffiana is apparently restricted to low arctic habitats, where it is normally the sole daphniid in ponds occupied by the predatory copepod Heterocope septentrionalis Juday & Muttkowski (Hebert & Loaring, 1980). D. pulex has a broader distribution, being found from the temperate zone to the high arctic. Genetic analysis has shown that populations of both D. pulex and D. rmiddendorffiana are clonally diverse and that individual clones show conspicuous variation in the extent of their pigmentation (Hebert & McWalter, 1983; Weider & Hebert, 1987ab; Weider, Beaton & Hebert, 1987). The present study had two aims. Firstly, to investigate the macroand microgeographical distribution patterns of pigmented clones among members of the D. pulex group. The rationale behind such study was to establish if the distribution of pigmented forms coincided with gradients in predation intensity or with light regimes and secondly, to determine the biochemical nature of the pigment, its role in light interception, and also its effectiveness in providing photoprotec-

Parasites and Host Geographic Range as Illustrated by Waterfowl

Abstract: Several papers have suggested that host species with larger geographic ranges tend to harbour a greater number of parasite species than those with smaller ranges. However, few of these investigations have dealt quantitatively with problems related to host sampling and/or phylogeny. This paper describes a positive relationship between the number of helminth parasite species per host and host species geographic range in Holarctic waterfowl. The analysis controls for the effects of differential sampling of host species and for the effects of taxonomic association. Neither host body size, population size, population density, nor social tendency correlate significantly with the number of parasite species per host corrected for number of hosts examined, and therefore association with these variables is unlikely to confound the relationship between parasites and host geo-

The Influence of Metal and Temperature Stress on the Immune System of Crabs

Abstract: That pollutants render many Crustacea more susceptible to disease implies a stressinduced decrease in immunocompetence. This study examines the effect of heavy metals (20, 50, 500 and 1000 jig 1-1 Cu, 10 and 500 jig 1-1 Cd, and 5 and 50 jig 1-1 Hg) and temperature on the cellular (haemocyte) component of the immune system of the shore crab, Carcinus maenas (L.). Marked fluctuations in circulating haemocyte numbers were observed in control crabs; these appear to correlate with daily changes in tidal height and the spring-neap tidal cycle. No change in haemocyte number was observed in crabs exposed to the metals for up to 30 days. However, Hg (Cu and Cd were not examined) at the highest concentration used, suppressed the tidal influence. A gradual rise in temperature from 10 to 200C significantly increased blood cell numbers although a rapid change initiated no response. In vitro cytotoxicity studies suggest that C. maenas haemocytes are relatively tolerant of metals. Copper had no effect on recognition or phagocytosis of bacteria in vitro although Cd slightly suppressed the latter. It is concluded that the immune system of C. maenas is relatively tolerant of metal stress. Key-words: Carcinus maenas, haemocytes, heavy metals, immunity

A Comparative Study of the Germination Characteristics of Seeds from a Moist Tall Grassland Community

Abstract: To account for observed patterns of emergence in the warm temperate grasslands of Japan the seed germination of several dozen species was tested following various types of thermal pre-treatment. An enormous variety of responses was observed among the species, especially in the capacity for immediate germination and the responses to moist storage with chilling. The extent of chilling requirement for the breakage of primary dormancy was largely correlated with the timing of seed dispersal, spring-summer dispersers tending to have a larger chilling requirement. On the other hand, the seedling emergence phenology of the species was closely related to the temperature dependency of the germination of non-dormant seeds. Key-words: Germination, phenology, seedling emergence, seed dispersal, thermal responses

The allometry of seed weight and seedling relative growth rate.

Abstract: Relative growth rates of plant species are often reported to decrease with increasing seed size. Since a general allometric relationship shows that relative growth rate decreases with increasing body size in animals and unicells, the seed sizerelative growth rate relationship may be a special case of a more general allometric relationship. In this paper, we analysed the allometry of seed weight and seedling relative growth rate in 204 species, based on seven published data sets, and compared our results to the allometric equation of animals. Seedling relative growth rate scaled significantly to seed weight in only three data sets. When points outside of the 95% confidence intervals of the individual regressions were removed, five out of the seven data sets exhibited significant negative correlations. Slopes varied from -0158 to +0 08 among data sets but an analysis of covariance showed that all data sets shared a common slope of -0 038. The amount of variance accounted for by seed weight varied from 68 to less than 1%. Plants and animals differed in their size dependence of growth but all plant relative growth rates closely followed the regression equation based on the animal data and all plant estimates fell well within the 95% confidence intervals of the animal regression. Despite the statistical difference in slopes, there was a general concordance of the plant and animal data, indicating a similarity in the allometry of growth rates. Key-words: Allometry, comparative ecology, relative growth rate, seeds, seed weight

Increase in reproductive effort as explained by body size and resource allocation in the speckled wood butterfly, Pararge aegeria (L.).

Abstract: An investigation of resources allocated to soma vs reproductive reserves at adult eclosion in a satyrine butterfly Pararge aegeria (L.), reveals that heavy females have a higher proportion of both their total carbon and total nitrogen allocated to the abdomen compared to light females. Males allocate differently, with smaller amounts of resources allocated to the abdomen. As among females, heavy males have a higher proportion of their total carbon allocated to the abdomen compared to light males, but abdominal nitrogen is unaffected by body size. These resource allocation patterns are predicted to affect reproductive output, particularly in butterflies with insignificant adult intake of nitrogenous compounds. In accordance with this, heavy females in this study have a proportionately higher lifetime fecundity compared to light females. Females that were deprived of sucrose during their oviposition period have a reduced lifetime fecundity, but the allometric pattern between fecundity and body size remains. Longevity among both males and females is influenced by sucrose feeding. Longevity is also influenced by body weight among unfed females. Key-words: Abdomen, body size, carbon, longevity, nitrogen, Pararge aegeria, resource allocation

Leaf mottling: relation to growth form and leaf phenology and possible role as camouflage.

Abstract: The arguments of Smith (1986) bearing on the adaptive significance of leaf mottling are criticized and an alternative hypothesis is presented. I propose that mottling may serve to camouflage the foliage of certain groups of shortstatured forest herbs, by disrupting their outline as perceived by colour-blind vertebrate herbivores in sun-dappled understoreys. Certain phenological groups are likely to be particularly vulnerable to herbivores, based on their high leaf nitrogen content (spring ephemerals, spring leaves of summeractive species), leaf activity when few other species possess foliage (evergreen species, wintergreen species, winter leaves of dimorphic species) and/or relative cost of replacing consumed foliage (evergreen species on sterile soils). These groups are also exposed to relatively high irradiances and so are less likely to suffer photosynthetic losses as a result of the reduced leaf absorptance that accompanies mottling. A survey of the incidence of leaf mottling in the native flora of the north-eastern USA supports these ideas: mottled leaves occur almost exclusively among forest herbs and are substantially over-represented among evergreen, wintergreen, and spring ephemeral species, and among the winter leaves of dimorphic species and the spring leaves of summer-active species. Mottled leaves are especially common among evergreen forest herbs. Testable extensions of the camouflage hypothesis to account for the relative abundance of mottled leaves among tropical forest herbs are discussed and parallels with other recently proposed mechanisms of vegetative crypsis in angiosperms based on leaf size, shape, texture, colour, and/or movement (i.e. Mimosa pudica) are outlined. Key-words: Anti-herbivore defence, camouflage, forest herbs, leaf mottling, leaf phenology

Preliminary Observations on the Ecological Relevance of the Gammarus `Scope for Growth' Assay: Effect of Zinc on Reproduction

Abstract: 'Gammarus scope for growth' is a 7-day assay that measures the effect of stress on the energy budgets of individuals. Here we use brooding female Gammarus pulex (L.) to directly compare the effect of zinc on scope for growth (SfG) and on reproduction. The reproductive parameters measured were size and number of offspring released from one brood incubated under zinc stress (current brood) and another provisioned under zinc stress (subsequent brood). In both experiments a significant effect was observed at 0 3 mgZn I1. At this concentration, SfG was reduced, as a result of a decrease in energy absorbed, and there was a decrease in the size of offspring released from the subsequent brood. There was no effect on the size or number of offspring released from the current brood nor on the number of offspring in the subsequent brood. Moreover, both present and past zinc stress caused an increase in the number of broods aborted. The consequences of these changes are discussed in relation to changes at the population and community level. Key-words: Gammarus pulex, reproduction, 'scope for growth', zinc

The effects of shade on the gas exchange of seedlings of four tropical trees from Mexico

Abstract: The effects of two light regimes, 'sun' and 'shade', on the gas exchange of four tropical tree species from Mexico were evaluated. Photosynthetic and stomatal responses to light and humidity were studied using a controlled environment cabinet and an infra-red gas analyser. A non-linear model was fitted to the photosynthetic responses and the physiological parameters found were used to compare treatments and species. Species from the secondary forest displayed higher maximal values of photosynthesis than those species normally found in primary forests. These species were also more sensitive to shade, i.e. maximal rates of photosynthesis were reduced to a greater extent when plants were grown in 'shade'. Plants grown under 'sun' conditions displayed enhanced dark respiration, higher values of photosynthesis and their rate of photosynthesis continued to increase above a photon flux density of 400 [Lmol m-2 sol. When plants were raised in 'sun' conditions, their leaves contained more nitrogen (on a leaf area basis) and this was associated with an increased mesophyll conductance. The species differed from each other much more in their growth than in their rates of photosynthesis and it is concluded that assimilate distribution may be more diagnostic of the ecological status of a species than its rate of assimilate production per area of leaf. Key-words: Ecophysiology, gas exchange, models, photosynthesis, shade, stomatal conductance, succession, tropical trees

Estimation of the fracture toughness of leaves

Abstract: A new device for measuring the fracture toughness of leaves is described, based on a 'cutting' system. This has the advantage of producing a measure of toughness that is comparable to that of other materials, biological and nonbiological. Key-words: Ecology, leaf, toughness

Modelling the diffusion component of dispersal during recovery of a population of linyphiid spiders from exposure to an insecticide.

Abstract: This study was designed to describe the spatial and temporal dynamics of an assemblage of linyphiid spiders during recovery from local depletion by an insecticide. A field of winter wheat was partly sprayed with log a.i. ha-' of deltamethrin. Of the linyphiid spiders, Erigone atra (Blackwall) was reduced by 89% and Oedothorax apicatus (Blackwall) females by 82%. Recovery of the populations is described in space and time by comparisons of relative densities of spiders at different distances from an adjacent unsprayed area using multiple-range tests, regression models and a diffusion model. Median estimated recovery times (ERT50) are calculated for species at different distances from the unsprayed area. For 0. apicatus females ERT50 ranged from 1.1 to 15*3 weeks and for E. atra from 3-7 to 6*5 weeks at 15 and 75m from the unsprayed area. Differences in recovery patterns for three spider categories are explained in terms of susceptibility to the pesticide and modes of dispersal. The consequences are discussed with reference to interplot interference in field ecotoxicity trials and commercial practice. Key-words: Deltamethrin, diffusion, dispersal, interplot interference, linyphiid spiders, modelling, spatial dynamics

Analysis of the spatial component of pesticide side effects on non-target invertebrate populations and its relevance to hazard analysis.

Abstract: The relative levels of recovery by populations of Carabidae, Staphylinidae and Linyphiidae were measured, following exposure to dimethoate, in two winter wheat field experiments. Regression analysis of the duration of recovery (the time taken for treatment plot population densities to approach those in control plots) with respect to distance from the plot boundary, revealed differences in the reinvasion potential of the three families. Staphylinidae recovered the most rapidly and Carabidae the most slowly with the Linyphiidae taking an intermediate position. The source of reinvasion differed between the three families with the carabid populations being confined within the field in contrast to the other two families which recolonized treated areas from the field boundary and beyond. The rate at which staphylinid and linyphiid populations dispersed into the plots raised questions concerning the most appropriate scale from which to obtain estimates of the duration of side-effects. More serious interpretative problems arose for the carabids since a large proportion of their apparent recovery may have been an experimental artefact. Regression analysis may provide a simple means of predicting the duration of side-effects on different taxa from field experiments, as long as these interpretative constraints are recognized. This approach incorporates an important feature of life history into predictions of pesticide hazard and may thus be more realistic than predictions based on pesticide toxicity alone. Key-words: Carabidae, dimethoate, dispersal rate, Linyphiidae, modelling, pesticide hazard analysis, Staphylinidae, temporal and spatial metapopulation dynamics

Dynamic Models of Growth and Reproduction of the Mussel Mytilus edulis L.

Abstract: We present two models of growth and reproduction in the mussel Mytilus edulis L. One is a modified version of an existing model developed by Kooijman for general application to ectotherms, the other is a new model specifically formulated for mussels. The models have identical assumptions on energy assimilation and spawning but differ in their a priori assumptions concerning energy partitioning between growth, maintenance and reproduction. Data from three field populations were used: one to estimate model parameters; the others for model testing. Both models were successful in predicting growth and reproduction in the test populations, suggesting that differences between populations can largely be explained by differences in food and seston dynamics. The models yield two contrasting strategies for storing and utilizing assimilate, and with further assumptions yield hypotheses on mortality in fast and slow growing populations. Key-words: Dynamic models, energy budgets, growth, Mytilus, reproduction, spawning

A cheap quantum sensor using a gallium arsenide photodiode

Abstract: A new quantum sensor for measuring photosynthetically active radiation (PAR) was designed using a gallium arsenide photodiode. This sensor is cheap and effectively measures radiation between 400 and 700nm without any filter, which allows both high output level and easy manufacturing. A comparison with two other commercially available quantum sensors (Li-Cor and Macam sensors) was made. The sensor des- cribed here was less sensitive than the two others both in the blue and far-red parts of the spectrum. Its maximum sensitivity is near 600nm. However it was shown, under natural light and several artificial light sources, that the results given by the three sensors were very similar. Nevertheless some problems could arise with monochromatic light sources such as sodium lamps whose spectrum is mainly composed of radiation between 570 and 620nm. This study also shows that gallium arsenide sensors are suitable for PAR measurements under canopies.

Episodic Pollution: Causes, Toxicological Effects and Ecological Significance

Abstract: As pollution control measures have reduced the number of chronic discharges to receiving waters, so the importance of intermittent pollution has increased. The number of pollution incidents reported in England and Wales rose from 12500 in 1981 to 23 253 in 1987 (WAA, 1988) and although this increase may, in part, reflect a greater awareness of pollution problems, these incidents also highlight the importance of peak, compared to mean, pollutant concentration (Edwards, 1987). The causes of episodic pollution incidents are varied but include both the accidental and deliberate release of pollutants to water courses. Farm waste is a cause of growing concern in the UK with an increase in the release of animal slurry and silage liquor, through an inadequate provision of or failure in the containment systems. The unregulated disposal of pesticide washings and surplus pesticides, together with run-off following spraying, also contribute to farm pollution incidents. The inability of sewage works to treat successfully all their effluent and the discharge of storm sewage from combined sewer overflows in urban areas resulted in 4177 incidents of sewage pollution in 1987 (WAA, 1988). Nevertheless, industrial incidents still account for the greatest proportion of episodic pollution events reported in the UK. Releases of oil and chemicals may result from the breakdown of treatment processes, failures in

Biomass and shoot/root allocation of five species from a grassland succession series at different combinations of light and nutrient supply

Abstract: In recent literature the relative importance of interspecific differences in shoot/root allocation patterns and differences in growth rate have been discussed, especially with regard to the mechanisms of succession. We studied growth, leaf area and shoot/root ratio under controlled conditions at various combinations of light and nutrient supply of five species from a grassland successional series. This series was initiated by stopping the application of fertilizers to agricultural grassland but continuing hay-making. Species from the later successional stages (lower nutrient availability, higher level of light at the soil surface) had a higher shoot/root ratio at most treatments, contrary to the predictions of the resource ratio hypothesis. However, a three-way interaction was also found, and thus the combination of light and nutrient level determined whether or not a correspondence between successional position and the sequence of species in shoot/root ratio was found. Some possible explanations are discussed for these results with regard to the mechanisms of succession.

The aerodynamics of plumed seeds.

Abstract: The aerodynamics of plumed seeds are examined using four species of Compositae and Asclepias syriaca. The hairs comprising the plume of the seeds are modelled as a single long cylinder experiencing an ambient wind velocity equivalent to the measured terminal velocity in still air