Guilds and assembly rules in lawn communities

Abstract. The community structure of 11 lawn sites in New Zealand and Fiji was examined in terms of guilds, seeking assembly rules based on guild proportionality. First, associations were analysed, using a new patch model which examined the mean of associations within patches of about 4 cm x 4 cm. As expected from the previously-demonstrated existence of niche limitation at this scale in lawns, the majority of associations between individual species were negative. Even in a lawn only four months old there were significant associations (mostly negative, and one positive). At some sites those species with the most negative associations were those whose morphology might be expected to restrict co-existence with other species. Much ecological theory is based on the assumption that there are limitations to coexistence, related to the resource usage of the species, such that species that are too similar in resource use are less likely to coexist. This theory was tested by looking for evidence of guild proportionality. We defined two guilds, graminoids and forbs. Using these guilds, three of the sites showed significant evenness in proportional representation from the two guilds in quadrats containing four species, i.e. there was less variation in the graminoid:forb ratio than expected on a random basis. Inclusion of species-poor quadrats in a joint analysis over all richness categories overwhelmed this effect, though there was still a strong trend for two of the New Zealand sites: the two species-rich grass lawns. Preliminary analyses of alternative guild delimitations gave no indication that other guild delimitations would have revealed stronger community structure. There was a strong and significant tendency in most sites for the graminoid guild to be more strongly represented in species-poor quadrats, an effect caused by species frequencies.     

Pattern of species dominance and factors affecting community composition in areas deforested due to air pollution

Vegetation of mountain areas affected by SO₂ pollution (Kruné hory Mts., Czech Republic) was analysed using multivariate methods. Communities with prevailing species Calamagrostis villosa, a rhizomatous grass expanding into deforested sites, were sampled by Braun-Blanquet relevé method. Canonical correspondence analysis was used to assess the effect of environmental variables (soil removal, deforestation, and shading). To test the effects of light, moisture, soil acidity and nitrogen, mean sample indicator values were correlated a posteriori with sample axes on ordination scores. Light, soil acidity, moisture, and site history (in terms of past deforestation and soil removal applied in reclamation procedures) were found to be the main factors responsible for the community composition. Nitrogen level had not a significant effect on the community composition. When analyzing the whole data set, i.e. including also remnants of natural spruce forests, light was the factor affecting at most the composition of communities. Within the bare spot vegetation, if treated separately, the highest variation was found along the soil acidity/moisture gradient. The effect of soil removal was only obvious at early successional stages. Species diversity increased with moisture and decreased with soil acidity. Species exhibiting S- and/or R-strategy are successful on extremely acid soils whereas forbs present in bare spots appear to be supported by disturbances.     

Effects of Quercus emoryi on herbaceous vegetation in a semi-arid savanna

Ten trees (5–70 m² canopy area) were selected to determine effects of tree size (crown area) on herbaceous species composition and biomass in a Quercus emoryi savanna in southeastern Arizona. Consistent with most studies in temperate savannas, herbaceous biomass was reduced beneath the canopy relative to grassland areas. However, tree size appeared to exert no influence over herbaceous biomass. In contrast to most temperate savannas, Q. emoryi trees did not affect distribution of herbaceous species.     

New approaches to direct gradient analysis using environmental scalars and statistical curve-fitting procedures

The conceptual framework of direct gradient analysis (DGA) is discussed in relation to the functional, factorial approach to vegetation. Both approaches use abstract simplified environment gradients with which to correlate vegetation response. Environmental scalars based on physical process models of environment and/or known biological growth processes can be incorporated to make analyses less location specific. An example of an environmental scalar (radiation index) for converting aspect and slope measurements to the more biologically relevant radiation input at a site is given. The problem of the shape of species response curves to environmental gradients is examined using a sample of 1 286 plots from eucalypt forest in southern New South Wales. An important conclusion is that skewed or bimodal response curves may be due to unsatisfactory distribution of observations and/or unrecognized environmental factors. The use of Generalized Linear Modelling (GLM) as a method for providing a statistical basis for DGA is presented. Analyses using GLM, and presence/absence data are presented for a range of eucalypt species (Eucalyptus rossii, E. dalrympleana, E. fastigata etc.). Successful prediction of species distributions (realized niches) can be achieved with mean annual temperature, mean annual rainfall, radiation index and geology. Quadratic terms are required in many cases, indicating bell-shaped response curves. The major variability associated with species niches is shown to be related to a limited number (4) of environmental factors. DGA with biologically relevant scalars and appropriate statistical methods is suitable for studying many problems of species' realized niches and plant community composition.     

Ranking species based on the components of equivocation information

Summary The results presented in this paper suggest that for species to be weighted according to their suitability to characterize isolated groups of relevés in a phytosociological table, the equivocation information may serve as a suitable weight. The appropriate formulations are derived and computed for some data from a salt marsh community.Contribution from the Working Group for Data-Processing in Phytosociology, International Society for Vegetation Science.The author thanks the National Research Council of Canada for support given.     

Study of interrelationship among A-genome species of the genus Oryza through isoenzyme variation

Summary The interrelationships among ten different A-genome species of the genus Oryza were studied based on variations in the electrophoretic pattern of isoenzymes of two non-specific enzymes, esterase and peroxidase. There were 16 isoenzymes of esterase and 14 of peroxidase. The esterase pattern could be classified into 3 different Zymograms 1e, 2e & 3e based on the presence and/or absence of bands at particular Rf values. The pattern le was found exclusively among the species and varietal groups of sativa complex, whereas 2e and 3e were distributed exclusively among the species of the glaberrima complex and related wild forms. The peroxidase pattern also fell into 3 different zymograms viz. 1p, 2p and 3p. Unlike esterase, all three zymograms were present in both the sativa and glaberrima complexes.The similarity indices (S) between the different pairs of entries were computed taking into account the presence as well as the relative intensity of the corresponding isoenzyme bands. The varieties and sub-species of 0.sativa showed very high similarity values with the Asian perennis (O.perennis sub sp. balunga), lending evidence for the probable differentiation of the former from the latter. The African cultivated species O.glaberrima showed very high similarity to the African perennis form O.pevennis sub sp. barthii, O.breviligulata and O.stapfii. The only cubensis form studied had the same esterase and peroxidase pattern as that of the species of the glaberrima complex and also a very high similarity with this group. Thus, the entire A-genome species could be broadly grouped into the sativa and glaberrima complexes, and within the group there was a lot of overlapping in similarity values making it difficult to identify and pin-point species or subspecies based on their isoenzyme patterns and similarity values.     

Drought and biodiversity in Grasslands

Summary The local species richness of four different grassland fields fell an average of 37% during a 1988 drought that decreased above-ground living plant mass by an average of 47%. Despite the return to more normal plant mass and precipitation during the next two years, there was no significant recovery in species richness in the 46 permanent plots, suggesting that local species richness became recruitment limited. The drought led to the loss of annual species independent of their abundance. For perennial grasses, perennial forbs, legumes and woody species, the probability of a species being lost from a plot was significantly negatively correlated with its predrought abundance. These results demonstrate that environmentally extreme conditions can limit species richness by causing the local extinction of rare species. Because droughts of this intensity occur about every 50 years in the prairie, periodic drought may have limited prairie diversity. Moreover, if the accumulation of greenhouse gases leads to a more variable or extreme climate, it could cause increased rates of species extinctions.     

Robert H. Whittaker (1920–1980): The man and his work

R. H. Whittaker enlivened many fields within ecology, systematics and evolution with his insights. Perhaps his most significant contributions to ecology lie in the development of the theories and methods of gradient analysis. Through the verification of the individualistic hypothesis with field data from many regions, and the subsequent development and dissemination of methods for studying species distributions along continua, he helped replace the Clementsian paradigm with a Gleasonian one. His extensive field data on primary production, nutrient cycling patterns and species diversity established new standards for documentation in synecology and helped clarify the basis for site-to-site variation in these variables. Through his broad command of the ecological literature, his writings and his contact with ecologists throughout the world he fostered international understanding of the diversity of approaches to vegetation study.     

How mosquitoes fly to man

1. A model is presented to estimate the mosquito density and radius (r) of the attraction range of man as the bait.
2. Man walked to a spot in the woods and sampled mosquitoes flying to him with a net continuously. The arrival pattern was constant in each mosquito species, and in all species, the number of mosquitoes sampled per five min became constant after ten minutes sampling.
3. The mosquitoes gathered to man were composed of D: those waiting alight, I: those intruding the attraction range and F: those following man to the spot. They were estimated by means of continuous sampling sets and densities of D and I were calculated.
4. r s of female and male of A. albopictus and A. japonicus were 4.0, 5.6 and 9.0 m respectively. In these species, most individuals were D, although, in T. bambusa all individuals were I, flying to search for hosts.
5. How mosquitoes and hosts encounter, is discussed.