Estimating lacustrine zooplankton species richness and complementarity

Literature and original information reveals that lakes at any latitude may be expected to lodge + 50 spp. of cladocerans, against + 150 spp. of rotifers in the temperate, and + 210 spp. in the tropical zone. Collector's curves can be used to estimate the number of species present at any point in time in a lake. Hyperbolic regression and Chao's non-parametric estimator were used to extrapolate from species numbers observed to true numbers present. Estimates for rotifers were better (had lower variances) than for cladocerans, and both were better in the temperate than in the tropical zone, where more species co-exist than in the temperate zone but where many more species are rare. Approximate numbers of samples required to approach true instantaneous species richness were calculated. However, a test in a (sub)tropical lake in Brasil where such an asymptotic number of samples was collected and examined failed to reduce the variance, while recording a number of species higher than predicted. We conclude that seasonal succession was still significant here, and that more research is needed to determine the minimum number of sampling repeats needed for a full census.Lakes with an ATBI (All Taxa Biological Inventory) for rotifers and cladocerans were compared by a complementarity index. This revealed geographic gradients between lakes, strong for cladocerans, but less so for rotifers. It is argued that this mainly reflects a difference in the state of taxonomic advancement between these two groups, and that the theory of cosmopolitanism must be abandoned for both.     

Niche use patterns among some Stenodemini (Heteroptera: Miridae) of limestone grassland,and an investigation of the possibility of interspecific competition between Notostira elongata Geoffroy and Megaloceraea recticornis Geoffroy

Summary It was suggested in a previous paper that mortality patterns in two species of Stenodemini (M. recticornis and N. elongata) could be explained by interspecific competition (Gibson 1976a)Such competition would have been generated by seasonal changes in the foodplants used by the two species resulting in both species using virtually the same range of plants at one time of year.As with a number of phytophagous insects (McNeill and Southwood 1978) many changes in foodplant use could be explained by differential seasonal changes in nitrogen content of the plant part (leaves) that the bugs were using in different plant species. Each bug had an ideal food nitrogen range which it used whenever possible. Lack of fit to this mechanism could often be explained by defensive chemistry and physical properties of some grass species.Although the total bug population was taking under 1% of the area's primary production, a potential refuge foodplant for one bug species was very heavily eaten where it was rare, and behavioural interference between bug species suggested that space to feed in was a limiting resource.Laboratory and semi-field culture experiments showed that the presence of one bug species adversely affected the growth and/or survival of the other, although the outcome of competition was different to that in the field, probably due to the different relative and absolute densities used.Although one cannot be completely certain without field manipulation experiments, it is extremely likely that interspecific competition was occurring and could be stabilised by the losing species (N. elongata) having a refuge generation.Competition between stenodemine species on the study area could usually be avoided by separation along a number of resource axes e.g. foodplant species, plant part, nitrogen level of food or emergence timing. In the present circumstance, a particular combination of bug and plant species in the area has forced one species pair into overlap. It should be possible to predict the guild structure and competition relations in other areas from this.     

Comparing plant life histories using elasticity analysis: the importance of life span and the number of life-cycle stages

Recent studies have used transition matrix elasticity analysis to investigate the relative role of survival (L), growth (G) and fecundity (F) in determining the estimated rate of population increase for perennial plants. The relative importance of these three variables has then been used as a framework for comparing patterns of plant life history in a triangular parameter space. Here we analyse the ways in which the number of life-cycle stages chosen to describe a species (transition matrix dimensionality) might influence the interpretation of such comparisons. Because transition matrix elements describing survival (stasis) and growth are not independent, the number of stages used to describe a species influences their relative contribution to the population growth rate. Reduction in the number of stages increases the apparent importance of stasis relative to growth, since each becomes broader and fewer individuals make the transition to the next stage per unit time period. Analysis of a test matrix for a hypothetical tree species divided into 4–32 life-cycle stages confirms this. If the number of stages were defined in relation to species longevity so that mean residence time in each stage were approximately constant, then the elasticity of G would reflect the importance of relative growth rate to . An alternative, and simpler, approach to ensure comparability of results between species may be to use the same number of stages regardless of species longevity. Published studies for both herbaceous and woody species have tended to use relatively few stages to describe life cycles (herbs: n=45, ; woody plants: n=21, ) and so approximate this approach. By using the same number of stages regardless of longevities, the position of species along the G-L side of the triangular parameter space largely reflects differences in longevity. The extent of variation in elasticity for L, G and F within and between species may also be related to factors such as successional status and habitat. For example, the shade-tolerant woody species, Araucaria cunninghamii, shows greater importance for stasis (L), while the gap-phase congener species, Araucaria hunsteinii, shows higher values for G (although values are likely to vary with the stage of stand development).     

Habitat Partitioning Among Primates in Maracá Island, Roraima, Northern Brazilian Amazonia

I studied a primate community on a tropical rainforest island, in the northernmost area of the Brazilian Amazonia. While walking through six distinct habitats along a 12-km trail, running toward the center of the island—a remote undisturbed area—I collected data on the use of the different forest types and forest strata by the primate community and the formation of either mixed groups or species assemblages. Five species are present: Cebus olivaceus, C. apella, Saimiri sciureus, Ateles belzubuth, and Alouatta seniculus. They seemed to be habitat generalists, using most habitat types. The five species used the higher strata more significantly, probably because Maracá does not present well-defined forest floors, which could be a result of being located in the transition between the great areas of savannah and the Amazonian seasonally dry forests. The five species all formed some polyspecific associations, which involved sharing the available food resource. Mixed groups were significantly more frequent and therefore possibly more important to Saimiri, which was not the case in relation to the other four species. Assemblages, defined as the presence in the same clumped resource, without coordinated activity, of 3 primate species, were recorded primarily in fruiting fig trees. I suggest that assemblages are impelled by food constraints, forcing cofeeding in large seasonal resources, highlighting the ecological importance of figs to these primates. Linear regression models show that the number of feeding bouts in each habitat type is positively related to the number of fruiting trees exploited, but the density of these fruit trees, diversity of plant species, tree height, and total basal area of each habitat type have no relationship to feeding.     

Additions to the rotifer fauna of south-east Asia: new and rare species from north-east Thailand

Ninety-three freshwater habitats in the north-eastern part of Thailand were surveyed for rotifers during March–October 1993. Two hundred species were identified, 120 of which are new to Thailand. Brachionus africanuss Segers, B. lyratus Shephard and Trichocerca hollaerti De Smet are new to Asia. Brachionus niwati n.sp. is described and figured. Brachionus donneri Brehm, Keratella edmondsoni (Ahlstrom) and Lecane blachei Berzi, endemic to south and southeast Asia, were found also.Comments are presented on some insufficiently known taxa. Of special zoogeographic interest is the record of several species previously considered endemic to Australia. An attempt is made to characterise the Thai rotifer fauna in the light of recent developments in rotifer zoogeography.     

Simultaneous transformation of Escherichia coli by pairs of compatible and incompatible plasmid DNA molecules.

Summary This paper describes experiments involving simultaneous transformation of Escherichia coli by DNA of two species of multicopy plasmid in order to study competence and DNA uptake in this organism. In transformation mixtures where separate species of plasmid DNA were present in equal amounts, selection for a single plasmid gave doseresponse curves with slopes of 1. These results indicate that uptake of a single molecule of plasmid DNA is sufficient to produce one transformant. Simultaneous selection for markers on both plamsids gave a dose-response curve with a slope of 2. The total numbers of transformants obtained in single or double transformation experiments at saturating DNA concentrations were the same, and represented the maximum number of transformable cells. However, the absolute frequency of double transformants was reduced 4–6 fold relative to frequencies obtained with single markers. Similar results were obtained using pairs of compatible or incompatible plasmids in rec ⁺ or recA strains. These findings may be explained either on the basis of interference between competing plasmid molecules for uptake or establishment or by assuming that competent cells of Escherichia coli vary in their ability to incorporate more than one plasmid DNA molecule. Our results are consistent with an interpretation where more than 80% of the transformable cells are only capable of establishing one plasmid moiecule.     

Biodiversity of marine nematodes in Australian sandy beaches from tropical and temperate regions

The universal occurrence and abundance of nematodes provides opportunities to investigate ecological factors that may influence biodiversity. Clarke and Warwick (2001) have proposed diversity indices average taxonomic distance(AvTD), variation in taxonomic distinctness (VarTD) for computing marine nematode biodiversity based on classification trees. Faith [Biological Conservation 61 (1992) 1] had previously proposed a diversity index based on phylogenetic trees, though not applied to nematodes. Clarke and Warwick (2001) also considered an index AvPD analogous to AvTD. These indices have been applied to five very large collections of free-living nematodes from three exposed sandy beaches in Australia. Two were from a beach close to Darwin in northern Australia, two from the temperate southeast coast of Australia and one from the south of the Australian mainland. The collections extend over a considerable range of latitude, from 12°26S to 38°33S and the controversial hypothesis that latitudinal gradients per se influence the biodiversity of marine nematode assemblages is examined. AvTD did not vary among collections and its value for any collection was indistinguishable from that of random samples of the same size drawn from the total species pool. VarTD showed no variation for three of the collections, but was slightly higher than expected for the mid-latitude beach, attributed to unevenness in the classification trees. AvTD and VarTD were not greatly affected by differences in sampling intensity. PD varied directly with the number of species found but observed PD did not differ from the PD of random samples of the same number of species taken from the total species pool. Thus, the observed variation in PD is wholly accounted for by variations in species richness. The number of species found increased with decreasing latitude. It appears that species richness by itself is an adequate index of biodiversity for the free-living nematodes of these sandy beaches, and more complex indices such as AvTD, VarTD and PD are unnecessary.     

Temporal infectivity and specificity of vesicular-arbuscular mycorrhizas in co-existing grassland species

Specificity in vesicular-arbuscular mycorrhizas (VAM), arising from selection favouring host plant/mycorrhizal fungus associations in which both organisms receive benefit, might have a significant influence on interactions between co-existing plant species. In an attempt to detect such specificity root inoculum of four tempt to detect such specificity root inoculum of four plant species, harvested from a species-rich grassland on three dates during the plant growth season, was used to infect the same plant species grown in pots. The rate and overall level of infection was different according to inoculum source and the time of year in which the inoculum was harvested, i.e. temporal variation in VAM infectivity occurs. However, there was no evidence for either specificity or mycorrhizal benefit. Inoculum produced during this experiment was used to infect bait Trifolium pratense plants and protein patterns of these roots indicated that a number of biochemically different endophytes were present, both within the inoculum of the four plant species but also within inoculum from one plant species. Temporal variation in mycorrhizal infectivity could be important for mycorrhizal propagation in the field. However, the lack of evidence, in this study, for specificity of VAM or an obvious nutritional benefit to plants with mycorrhizas make the role of mycorrhizas in this community difficult to interpret.     

Difference in response by two cyprinid species to predatory threat from the nocturnal catfish Silurus asotus

Response to predators may not be identical between different prey species with different life histories and body sizes, particularly when the threat of predation is not great. To clarify this hypothesis, we introduced two prey species (10 Japanese dace, Tribolodon hakonensis, and 10 pale chub, Zacco platypus) into each experimental pond (in total, 8 ponds×4 trials) in which benthic algae had been allowed to grow. The presence or absence of Far Eastern catfish, Silurus asotus, and a refuge for prey fish was used to produce four treatments. The presence of catfish and/or a refuge did not affect either the feeding behavior or growth rate of Japanese dace. In contrast, when catfish were present and no refuge was available, the incidence of bottom feeding for pale chub greatly decreased. Pale chub growth rate was low when catfish were present and a refuge was available, indicating that pale chub spent more of their time in the refuge and lost opportunities of acquiring food. Japanese dace can reach a threshold size at which the prey are safe from predation, but pale chub cannot, and this may explain the differences in response to predators of the two species.     

The effect of plant size on vegetative reproduction in a pseudo-annual

The relationship between plant size and vegetative reproduction in clonal plants appears complex because vegetative expansion, growth, and reproduction are not clearly separable in such plants. In pseudo-annuals, which are clonal plants surviving the winter only as seeds and hibernacles produced by the rhizome apices, vegetative growth and reproduction are clearly separate processes so that the relationship between vegetative reproduction and plant size can be studied. We used the pseudo-annual Helianthus x laetiflorus Pers. to study the relationship between plant size and total rhizome biomass, rhizome (hibernacle) biomass, and number of hibernacles. We manipulated resource acquisition of the plants by reducing leaf area (leaf-clipping) and by fertilization, thus affecting plant size. Furthermore, we studied the success of thin and thick hibernacles in terms of future growth and reproduction in a separate experiment. The results showed that vegetative reproduction was positively related to plant size. The ratio between the number of hibernacles and mean hibernacle weight was affected by plant size in such a way that in small plants both number of hibernacles and mean hibernacle weight were reduced to the same extent as compared to those in large plants.However, the size distributions of plants of the next generation growing from thin and thick hibernacles did not differ. It remains unclear therefore why this pseudo-annual species produces thick hibernacles at all.     

The spectrum of β-thalassemia mutations in northern and northeastern Thailand

Summary A total of 123 -thalassemia genes from northern (n = 113) and northeastern (n = 10) Thailand were examined. Using five oligonucleotide probes, the mutation in 108 genes (88%) was identified: 50 nonsense 17, 49 frameshift 41-42, 4-28(AG), 2IVS1 nt5(GC), 2IVS2 nt654, and 1 deletion removing the entire -globin gene. The nonsense 17 mutation (n = 39) was linked to a single haplotype, whereas the frameshift 41-42 mutation occurred with several haplotypes. The results of the present study indicate that prenatal diagnosis of clinically important -thalassemia syndromes using a limited set of oligonucleotides is feasible in approximately 80% of affected families in northern Thailand and most of the families with -thalassemia-Hb E disease in northeastern Thailand.     

Medicinal plants in the southern region of the State of Nuevo León,México

Background

Although the flora of the State of Nuevo León is well known, there are few records of ethnobotancial information. An ethnobotanical study was undertaken in order to know the medicinal plants used by people living at the scrublands and oak-pine forest areas in the southern Nuevo León. Collection of plants specimens and interviews were carried out among the people of the municipalities of Aramberri, Galeana, and Zaragoza. Since former studies in the region are scarce, the aim of this work was to record the medicinal species and their uses in the scrublands and oak-pine forest areas, of southern Nuevo León, Mexico, and also to know if there are differences in the number of species and number of uses knowledge by people.

Methods

Field work was carried out over a 2 years period; useful plants were collected and a total of 105 people from 46 different villages were interviewed. A database was compiled using data collected by means of semi structured interviews. The data were analyzed by means of non-parametric statistics, using goodness-of-fit test (Chi-squared) (number of species known by people of each municipality, number of uses known by people of each municipality), Chi-squared modified to incorporate the Yates Correction (number of species known by people living at scrublands and oak-pine forest); the Kruskall-Wallis test (number of species known by women and men of the three municipalities), and the Spearman’s rank correlation coefficient (age and number of species known, and age and number of uses).

Results

A total of 163 medicinal plant species were recorded in the study area, comprising 108 wild and 55 cultivated plants. A total of 117 species were recorded in the oak-pine forest, and 111 in the scrublands area, a total of 68 were recorded in both areas; 68 medicinal species are used in all three municipalities, 40 wild and 28 cultivated. We documented 235 different medicinal uses. The most common plant parts used for medicinal purposes were found to be leaves (123 species), stems (55), fruits (28), roots (17), and bark (14). No differences were noted in the number of medicinal plant species identified among people, but differences were significant in their knowledge with respect to the number of uses among people of the three municipalities studied; people from both, scrublands and oak-pine forest know similar number of species and number of uses. Men and women of the three different municipalities knew statistically the same number of species and number of uses. There was no correlation between resident’s age and number of species known and resident’s age and number of uses either in Galeana or in Aramberri, but, there was high correlation among these variables in Zaragoza.

Conclusion

In southern Nuevo León people use at least 5% of the total State flora as medicinal plants, and most of these species are included in few plant families. Most of medicinal species are wild and indigenous to the region. The two most important major plant communities, scrublands and oak-pine forest provide almost the same number of medicinal species. A third of the medicinal flora recorded are used in all three municipalities, most of them are wild. Leaves, stems and fruits are the plant parts most commonly used for healing, and boiling is the most common method used for this purpose. Men and women from the three municipalities are familiar with nearly the same number of species; however, their knowledge of the number of uses varies significantly. In Galeana and Aramberri there was no correlation between a person’s age and number of species recognized, however, in Zaragoza, there existed a high correlation between these two factors.

     

Taxonomic studies on the 0-group eel larvae (Anguilla sp.) caught in the Sargasso Sea in 1979

More than 2000 0-group larvae (5.0–30.0 mm long) of both AtlanticAnguilla species were examined taxonomically. With regard to the total number of myomeres inA. rostrata andA. anguilla, an average difference between the two species of 6 to 8 myomeres was found in all size groups. 31 specimens (i.e. 1.76 %) exhibited 111 myomeres. The position of the last vertical blood vessel and the number of preanal myomeres turned out to be statistically different in both species; however, these differences cannot be used for species identification. The regression line for the position of the last vertical blood vessel according to the total number of myomeres indicates that individuals with a total of 111 myomeres may beA. anguilla. Measurements of total lengths revealed highly significant differences between the larvae of both eel species. It can be concluded that, on the average,A. rostrata ( ) hatched about two weeks beforeA anguilla ( ). On the other hand, results obtained from the biggestA. rostrata larvae (29.5 mm) andA. anguilla larvae (23.5 mm) make a spawning ofA. rostrata likely two months beforeA. anguilla, when findings from hatching experiments withA. japonica are taken as a basis. There is no difference in the relative length of the intestine in eitherAnguilla species.     

Cytogenetics of the parthenogenetic grasshopper Warramaba (formerly Moraba) virgo and its bisexual relatives

The karyotypes of Warramaba virgo and the two bisexual species which gave rise to it, by hybridization, have been studied by the C- and G-banding techniques. W. virgo consists of a number of clones which differ by a limited number of inversions, translocations and fusions and also in C-banding pattern. In general, each local population consists of a single clone, although instances are known where two clones exist at the same locality. A total of fifteen cytological clones are here recognised and described. Some of these are known from single localities, while others have been found at several collecting sites in the same general area. The differences between them in banding pattern are relatively minor, i.e. the architecture of the karyotype has been highly conserved. A total of 50 C-bands have been recognised in W. virgo, but some of these are only present in a single clone and most clones have 39–40 bands. Most of these are centromeric or interstitial; a few are terminal (telomeric) in the short arms. There are three types of bands, dark-staining centromeric ones, intermediate ones that are somewhat less densely staining, and lighter ones that appear grey even after successful C-banding. The C-banding pattern of W. virgo provides additional evidence for its origin by hybridization between the bisexual species P196 and P169. It is possible that W. virgo arose only once (i.e. from one or more matings between P196 and P169 individuals in the same deme, within a few generations). However, two clones (Zanthus and Boulder), which are themselves closely similar, differ so much in banding pattern from all others that they may have arisen independently.     

The relationship between nested subsets,habitat subdivision,and species diversity

Biotic assemblages are said to be nested when the species making up relatively species-poor biotas comprise subsets of the species present at richer sites. Because species number and site area are often correlated, previous studies have suggested that nestedness may be relevant to questions of how habitat subdivision affects species diversity, particularly with respect to the question of whether a single large, contiguous patch of habitat will generally contain more species than collections of smaller patches having the same total combined area. However, inferences from analyses of nestedness are complicated by (1) variability in degrees of nestedness measured in natural communities, (2) variability in species-area relationships, and (3) the fact that nestedness statistics do not account for the size of habitat patches, only in the degree of overlap among sites with different numbers of species. By comparing various indices of nestedness with a saturation index that more directly measures the effect of habitat subdivision, it is shown that the first two of these factors are not as important as the third. Whether a single large site or several smaller ones having the same total combined area maximizes species diversity is dependent on (1) overlap in species composition among sites and (2) the number of species per unit area in the different sites. Because nestedness indices do not account for species number at a site, they cannot accurately predict how habitat subdivision affects species diversity patterns. Still, nestedness analyses are important in that they indicate the degree to which rare species tend to be found in the largest, or the most species-rich, sites, patterns not revealed by the saturation index. Both types of analysis are important in order to obtain a more complete picture of how species richness and compositional patterns are influenced by habitat subdivision.     

Patterns of floristic diversity in semi-natural coastal vegetation of Lebanon and implications for conservation

The current understanding of the status of the vegetation in Lebanon is largely derived from herbarium data and associated floristic studies produced by early 20th century field botanists. In common with other areas in the Mediterranean, the Lebanese coastline is highly threatened by unregulated development, yet current patterns of species richness along the Lebanese coastal zone are little studied. The objective of this study was to assess the floristic richness of the Lebanese coastal zone and to provide baseline information for conservation planning. For this purpose, permanent sample plots (6m×100m) were established in 26 selected vegetation communities in coastal habitats. Monthly field collections of plant specimens were undertaken between October 1999 and July 2000. A total of 441 species were collected and identified. None of the recorded species are currently considered globally threatened, but two are Lebanese endemics (Matthiola crassifolia Boiss. & Gaill., Origanum ehrenbergii Boiss.). Species richness varied between communities, ranging from six species in a littoral limestone pavement community to 113 in an abandoned terrace community. The similarity between communities, based on Sorensen indices, was low and a large number of species were recorded only once. Cluster analysis showed a grouping of different communities within locations in some instances and the clustering of similar community types regardless of location in others. Species richness in riparian and littoral communities consisted mostly of habitat non-specific species. The low community similarity, patchy species distribution, and predominance of habitat non-specific species all point to the need to complement in situ conservation measures with ex situ conservation.     

Physiologic and environmental factors influencing the calcium-to-tissue ratio in populations of three species of freshwater pulmonate snails

Summary A study of three species of freshwater pulmonate snails, Physa gyrina (11 populations), Physa integra (17 populations), and Helisoma anceps (18 populations) was carried out from 1973 to 1976, primarily in Michigan.The ratio of whole animal calcium content to tissue dry weight (Ca: tissue ratio) changes with age, but these changes are largely restricted to early growth and do not significantly affect individuals over 40 mg total dry weight, regardless of species.Parasitization by larval trematodes was found to have no significant effect on the Ca: tissue ratio in the populations examined regardless of species.Ca: tissue ratio of P. gyrina did not vary greatly between populations and showed a narrow range over a wide range of environmental calcium concentrations. Shell mass in P. gyrina is therefore either physiologically regulated in all populations (at a species specific constant level) or interpopulation variation is minimized by moderately high levels of gene flow between populations.There was no relationship between Ca: tissue ratio and environmental calcium for either P. integra or H. anceps over a wide range of snail and environmental calcium values. In both of the foregoing species, shell calcium content varied greatly between populations. This variation did not conform to any apparent geographic cline.In 7 of the population sites studied, P. integra and H. anceps coexist, and when these sites are listed from highest to lowest Ca: tissue ratios, the rank orders for the two species are nearly identical. This suggests that there is some environmental factor (possibly trophic conditions) at these localities that influences shell mass.In 8 other species of pulmonates briefly examined, differences in Ca: tissue ratio between populations of the same species were often as great as or greater than differences between species.While the patterns of shell mass and environmental calcium for these species are not unlike those previously reported, the proposed causal factors for these patterns are clearly distinct from those suggested for other freshwater pulmonates.     

Karyotype studies in thirteen species of fishes

The karyotypes of thirteen species of fishes belonging to nine families, studied in spermatogonial cells and in primary and secondary spermatocytes are reported. All these fishes were collected from the river Jumna near Delhi (India). The diploid number of chromosomes of these species ranges between 86 (Wallago attu) and 40 (Ompak bimaculatus). The karyotypes of seven species are characterized by exclusively possessing acrocentric chromosomes, while the remaining six species have varying numbers of metacentric chromosomes in addition to acrocentric chromosomes. Species belonging to the same family, and even the same genus, have been found to differ in chromosome number and morphology.On the basis of the data available, the author has endeavoured to discuss the relationship between cytologically known fish species and the various complications involved in their classification. The validity of the nombre fondamental hypothesis of Matthey in fish karyotypes has also been discussed.     

The influence of coppicing on vegetation

In the Netherlands and adjacent countries on old (non-holocene) soils the relation was studied between high forest dominated by Fagus sylvatica, and coppice derived from it, with Quercus spp. and Betula spp. or Carpinus betulus. From place-names a shift Fagus > Quercus > Betula is found, caused by cutting and coppicing. An analysis of relevés of the vegetation yielded more detailed information.The occurrence and rejuvenation of Fagus and other climax tree species decrease, while most other trees and shrubs show an increase. The mean total number of species in 1396 relevés increases from 22.0 to 24.4. Decreasing species include widely distributed species as well as character species. Increasing species include shrubs, woodedge species of heathland or limestone grassland, and nitrophilous species.The light-indication according to Ellenberg increases considerably, most of all in the types on poor soils. Moisture seems hardly involved, but pH-indication is divergent: decreasing in acid types, increasing in alkaline types. For the latter erosion is held responsible. N-indication follows the same trend. All ecological shifts remain within the framework of each association concerned.The Sørensen index for floristic composition shows a mean of 68% correlation, of the same order as variants within one association. The ecological correlation is even higher. So coppice can be considered as management variants, not deserving an association status, as often was given in the past.     

Components of relative growth rate and sensitivity to nitrogen availability in annual and perennial species of Bromus

Summary Two grass species, the annual Bromus sterilis and the perennial Bromus erectus, were grown from seeds for 28 days in a hydroponic culture system at 1 and 100 M NO₃ ^- in the nutrient solution. At 100 M NO₃ ^-, the relative growth rate (RGR) of the perennial was 30% lower than that of the annual. This was only the consequence of the higher specific mass of its leaves, since its leaf mass ratio was higher than that of the annual and the unit leaf rates (ULR), calculated on an area basis, were similar for the two species. At 1 M, the RGR of the annual was 50% lower than at 100 M, while that of the perennial was not significantly lower. This was due mainly to a lower ULR for the annual. while for the perennial ULR was the same in both treatments. These differences between the two species were all the more striking in that the differences in total nitrogen concentrations and nitrate reductase activities between the two treatments were very similar for both species. These different responses together with differences in the nitrogen productivity of the two species suggest that the level of nutrient availability may play an important role in the distribution of these Bromus species in natural habitats. Scope: Components of growth and response to nitrate availability in annual and perennial grasses