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Use of a Relative Physiological Performance Value in the Prediction of Performance in Multispecies Mixtures from Monoculture Performance
Journal of Ecology
Abstract
(1) A relative physiological performance value is defined as: RiJ = YiJ/YmJ where YiJ is the shoot dry weight yield of a monoculture of species i at a factor level J and YmJ is the yield for a monoculture of the most productive species, m, at that factor level. (2) The RiJ values are used to determine relative physiological performance curves for species in relation to a nutrient gradient, using data from a published experiment where performance in monoculture and in five- and ten-species mixtures was recorded. (3) A normalized ecological performance value (EiJ) was defined for multispecies mixtures: $E_{\mathrm{iJ}} = \frac{Y'_{\mathrm{iJ}}}{Y'_{\mathrm{mJ}}$ where Y'iJ is the shoot dry weight yield of species i in mixture at factor level J and Y'mJ is the yield of the most productive species in the mixture at that factor level. (4) For a regression equation of the form log EiJ = a + bRiJ the relative physiological performance accounted for a large part of the observed variation in performance in multispecies mixtures. For three different multispecies mixtures, r2 values greater than 0.6 were found at almost all levels. (5) Examination of the residuals from the regressions, particularly for the ten-species mixture, indicates that specific effects associated with particular species at particular positions along the gradient are important. In particular, Holcus lanatus performance was not well predicted due to its exploitation of a niche (horizontal growth over the sides of the pots) not available to erect growing species. (6) Species ecological maxima, i.e. maximum EiJ value, in these multispecies mixtures correspond in position along the gradient with the species maximum values for the relative physiological performance (RiJ) but do not correspond with the physiological optima measured using absolute yield. This contradicts both Ernst's and Ellenberg's views of the relationship between ecological and physiological optima.
... Unfortunately, the population fitness homoeostasis is not a readily quantifiable variable. Quantities like mean "relative physiological performance" or mean "relative ecological performance" across environmental gradients (Austin 1982;Austin et al. 1985) can be used as surrogates for population fitness homoeostasis (Fig. 4). A more direct measure would be the geometric mean of population growth rates ( ) across realistic ranges of environments (Venette 1997). ...
... Performance of introduced taxa in the presence of other species can be elucidated in classic two-or few species competition experiments (Jolliffe 2000 or, perhaps more realistically, in diffusion competition experiments (Austin 1982, Austin et al. 1985, Wilson and Keddy 1986) and individual-based, spatially-explicit experiments (Silvertown and Wilson 2000). ...
... Relationship between the number of regions in Australia (out of 97) invaded by eight European grass species (after Hnatiuk 1990) in dependence on their mean relative physiological performance over 15 nutrient concentrations. Calculated from results ofAustin's (1982) experiments conducted in Bangor, UK (from Rejmánek 2000a, reproduced with permission). ...
... Grime 1979) have proposed that there exists a correlation between relative growth rate and competitive ability for plants of similar life history. Recently, Austin (1982) and Austin et al. (1985) have proposed that the performance of species in multispecific mixtures along an environmental gradient can be predicted from the relative monoculture performance if the appropriate measures of performance are used. In this paper I evaluate the method of Austin using data from experiments of Typha spp. ...
... Monocultures and 50:50 mixtures were used, and experiments extended over a 2 5-year period. Austin (1982) and Austin et al. (1985) proposed the following indices to predict mixture performance from monoculture performance: 'Relative Physiological Performance' has been defined as ...
... P. Austin, personal communication). In the case of two species, the method of Austin (1982) reduces to the expectation that the species with the greater Rij at any water depth should have the greater Ei. Since the species with the greater Rij or Eij is automatically assigned a value of 1 0, then the expectation is that Rij = Eij = 1 0 for the species with the more abundant monoculture growth at each depth. ...
(1) Austin (1982) has proposed a method for predicting relative mixture performance from relative monoculture performance. In this paper I evaluate the method of Austin using data from experiments on Typha spp. competing along gradients in water depth. (2) The data used to evaluate Austin's method are from two studies; one of competition between Typha latifolia and Typha domingensis seedlings along a miniature water-depth gradient; and the second of competition between adult plants of both species in a large, experimental pond. The seedling experiment compared species over a fourteen-level gradient that ranged from 18 cm above the water to 21 cm deep. The adult experiment included eleven levels ranging from 5 cm above water to 115 cm deep, and extended over a 2.5 year period. Both experiments included monocultures as well as 50:50 mixtures. (3) The ability to predict relative mixture performance from relative monoculture performance using Austin's method varied, depending upon the age of the plants. The correlation between mixture and monoculture results was greatest for one-year-old adults and declined strongly with increasing age. Relative monoculture performance at 12 months was significantly correlated with mixture performance at 12, 13, 14, 15 and 24 months, but not beyond. Except for the oldest plants (28 months old), mixture performance at any point in time correlated significantly with the monoculture performance at some earlier time. For plants older than 24 months, their mixture performance correlated with the monoculture performance 11-12 months before. (4) The results show that the ability to predict mixture performance from monoculture performance in Typha depends upon the age of the plants. Monoculture growth early in the life of the plant predicts subsequent mixture performance for a substantial period (in this study, up to one year later). As plants grow older, their mixture performance becomes more difficult to predict from monoculture growth.
... In the present paper, we experimentally examine the relative growth and competitiveness of five grasses chosen to represent different stages in the sequence of botanical change described by Moore (1970), together with two introduced perennial grasses commonly sown with fertilizer in south-eastern Australia. The grasses were grown alone in monocultures and in multispecies mixtures over a wide range of total nutrient levels using the approach of Austin and Austin (1980) as modified subsequently (Austin 1982; Austin et al . 1985). ...
... In order to make comparisons of species' behaviour along the nutrient gradient where total biomass changes dramatically it was necessary to standardize the data. Austin (1982) defined the relative physiological performance (RPP) of a species i in monoculture at nutrient level j as RPP ij = Bm ij /Mm ij , where Bm ij is the biomass of species i per area unit of monoculture at nutrient level j and Mm ij is the biomass of the most productive species per area unit of monoculture at nutrient level j. Relative ecol ...
... , native species; (), introduced species. experimental conditions was examined by regressing REP on RPP (Austin 1982). A linear regression of the form: log10 (REP + 0.001) = a + bRPP was fitted for each nutrient level (Austin 1982). ...
Abstract Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16× the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia (Themeda triandra, Poa labillardieri and Danthonia carphoides); (ii) two introduced annuals (Vulpia bromoides and Hordeum leporinum); and (iii) two introduced perennials (Lolium perenne and Dactylis glomerata). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south-eastern Australian grasslands after 150 years of continuous grazing by sheep.
... Unfortunately, the population fitness homoeostasis is not a readily quantifiable variable. Quantities such as mean 'relative physiological performance' or mean 'relative ecological performance' across environmental gradients (Austin 1982;Austin et al. 1985) can be used as surrogates for population fitness homoeostasis (Fig. 3). ...
... Currently, larger and larger volumes of soil are moved around (topsoil, mud on cars, horticultural stock). Species with numerous, relatively small, seedbank-forming seeds are preadapted for this type of Austin's (1982) experiments which were conducted in Bangor, UK). dispersal (UCPE 1996;Hodkinson & Thompson 1997). ...
... Austin & Austin 1980) and a substitutive design is used with constant density and one plant per species in the mixture, then the full range of response shown in Fig. 1 could occur. In two recent multispecies studies (Austin & Austin 1980;Austin 1982;Austin et al. 1985), different designs have been used. In the first experiment, Austin & Austin (1980) used an additive design in which mixtures of five and ten species were multiples of the monoculture density. ...
... The design used here is insufficient. In the multispecies design used by Austin and collaborators (Austin & Austin 1980;Austin 1982;Austin et al. 1985), this knowledge is lacking as it is in most competition experiments. The RYwas not used as such in those experiments, but the influence of the yield-density relationship will have been present. ...
(1) The role of the yield-density relationship in determining the choice of an additive or substitutive experimental design for competition experiments is examined, with particular reference to the design of multispecies experiments. A competition experiment between two thistle species Silybum marianum and Cirsium vulgaris at five density levels and six nutrient concentrations is described. (2) The design allows the influence of density and nutrient concentration on the relative yield in mixture compared with monoculture (RY) of the two species (as estimated from a substitutive design of N/2 plants in mixture) to be examined, and compared with that estimated from an additive design of N plants in mixture, where N is number of plants in monoculture. (3) Yields of the two species in monoculture show similar significant responses to both nutrient concentration and density: maximum yield occurs at a nutrient concentration four times standard Hoagland, and response to density is asymptotic. S. marianum has similar performance in mixture while C. vulgare yields are markedly reduced. Nutrient concentration has a significant influence on the RY of both species. A clear influence of density is only apparent at extremely high nutrient concentrations. (4) Acceptance of an asymptotic yield-density function implies that RY values between 0.5 and 1.0 cannot be interpreted unambiguously as being due to competition in substitutive experiments. Analysis of the substitutive design for S. marianum gives RY between 0.5 and 1.0, which cannot be interpreted as due to competition from C. vulgare. The additive design provides no evidence for such a competitive effect. RY values for C. vulgare are less than 0.5 in both designs indicating a competitive effect by S. marianum. (5) Choice of substitutive or additive design depends on knowledge of the yield-density function. Unequivocal results require a range of density combinations to be included in the design.
... Most textbooks (Giller 1984) assume that the realised niche is a much restricted version of the fundamental niche (Fig. 4), representing the optimal conditions for the species. Smith (1989, see also Austin 1980) have summarised a series of studies for plants showing a great diversity of ideas on response shapes, environmental gradients and resources (Table 1, see also Eilenberg 1953;Muller-Dombois and Ellenberg 1974;Austin 1982). They indicate that the realised niche response may be very different from the textbook representation of resource competition and may even be bimodal (Fig. 4). ...
... These propositions allow the recognition of different functional types of trees (Smith and Huston 1989). Simulations using a FORET type model (Smith and Huston 1989) reproduce many of the features of different types of succession and of species patterns along environmental gradients found in direct gradient studies (Austin 1987) and in multispecies experiments (Austin 1982;Austin et al. 1985). The statement that plants able to grow rapidly under high light conditions could not also be shade-tolerant cannot be justified. ...
Physiologists, vegetation modellers of climate change and community ecologists assume very different temperature responses for plants. Physiologists often assume a skewed non-monotonic curve with a tail towards low temperatures; forest modellers using FORET type models, a symmetric curve; and community ecologists a skewed response with a tail towards high temperatures. These assumptions are reviewed in relation to niche theory, and recent propositions concerning the continuum concept. Distinctions need to be made between responses due to growth (physiological response), potential fitness (fundamental niche) and observed performance (realised niche). An example of a statistical method for quantifying the realised environmental niche response of a species to temperature is based on generalised linear modelling (GLM) of presence/absence data on Eucalyptus fastigata for 8377 sites in S New South Wales, Australia. Seven environmental variables or factors are considered: mean annual temperature, mean annual rainfall, mean monthly solar radiation, topographic position, rainfall seasonality, lithology, and soil nutrient status. The probability of occurrence is a skewed function of mean annual temperature. Any process-models of climate change for vegetation incorporating temperature changes due to elevated CO2 must be capable of generating such realised environmental niche responses for species. -from Author
... The tolerances of species to ecological factors may differ when a species grows in a monoculture or in a mixture with other species (Ellenberg 1952(Ellenberg , 1954Austin & Austin 1980;Austin 1982;Aarsen & Epp 1990;Keddy et al. 1994). This phenomenon has been given a theoretical basis in association with terms such as fundamental vs. realized niche (Hutchinson 1957;Miller 1967) or physiological vs. ecological response (Mueller-Dombois & Ellenberg 1974). ...
... Both explanations are likely to be true. The higher species richness in the Peene valley is discussed above but the growth forms and, therefore, competitive ability (see Keddy et al. 1994) That realized niches of plants become narrower due to competitive pressure of other species was reported from experimental studies of Austin and colleagues (Austin & Austin 1980;Austin 1982). However, shifts in the ecological optima along the nutrient gradient in comparison to those measured in a monoculture occurred only for a few species. ...
The realized habitat of a species can be considered as the product of its physiological requirements and competitive interactions with other species. One may, therefore, expect that the realized habitat differs between areas when a species has to coexist (and hence - compete) with different species. To test this hypothesis, we compared the responses of wetland plants to hydrological conditions in two European lowland river valleys: the Drentse A valley (The Netherlands) and the Peene valley (eastern Germany). We used mean water level and water level amplitude as hydrological parameters to analyse differentiation in realized habitats within species. Concerning the groundwater regime, most species appeared to have narrower realized habitats indicating for slightly wetter conditions with wider water level amplitude in the German site than in the Dutch site. We suggest that the narrower tolerances in the first may result from higher intensity of competition for light in this area, possibly caused by a larger local species pool and/or presence of more dominant species with a high competitive ability. The consequences for practical applications - such as parameter estimation for predictive models - are discussed.
... Unfortunately, population fitness homoeostasis is not a readily quantifiable variable. Quantities such as mean relative physiological performance and mean relative ecological performance across environmental gradients (Austin 1982;Austin et al. 1985) can be used as surrogates for population fitness homoeostasis ( Figure 6.4). A more direct measure would be the geometric mean of population growth rates (h) across realistic ranges of environments (Venette 1997). ...
... More sophisticated models such as those of Tilman (1982Tilman ( , 1988 have predicted competitive success using specific assumptions about the mechanisms of resource use. In some cases, statistical approaches have been used to predict competitive ability (Austin, 1982;Grace, 1988a). At the most detailed level, complex simulation models have, at times, been used to predict the relationships between plant traits and competitive ability (Baldwin, 1976). ...
... We used population biomass of monocultures as a measure of population performance (Austin 1982; Grace 1988). Monocultures were part of the Jena Experiment (Roscher et al. 2004). ...
Traits are powerful predictors of ecosystem functions pointing to underlying physiological and ecological processes. Plant individual performance results from the coordinated operation of many processes, ranging from nutrient uptake over organ turnover to photosynthesis, thus requiring a large set of traits for its prediction. For plant performance on higher hierarchical levels, e.g. populations, additional traits important for plant‐plant and trophic interactions may be required which should even enlarge the spectrum of relevant predictor traits.
The goal of this study was to assess the importance of plant functional traits to predict individual and population performance of grassland species with particular focus on the significance of root traits. We tested this for 59 grassland species using 35 traits divided into three trait clusters: leaf traits (16), stature traits (8) and root traits (11), using individual biomass of mesocosm plants as a measure of individual performance and population biomass of monocultures as a measure of population performance. We applied structural equation models to disentangle direct effects of single traits on population biomass and indirect effects via individual plant biomass or shoot density.We tested multivariate trait effects on individual and population biomass to analyse whether the importance of different trait clusters shifts with increasing hierarchical integration from individuals to populations.
Traits of all three clusters significantly correlated with individual and population biomass. However, in spite of a number of significant correlations, above‐below‐ground linkages were generally weak, with few exceptions like N content.
Stature traits exclusively affected population biomass indirectly via their effect on individual biomass, whereas root and leaf traits showed also direct effects and partly indirect effects via density.
The inclusion of root traits in multiple regression models improved the prediction of individual biomass when compared with models with only above‐ground information only slightly (95% vs. 93% of variance prediction with and without root traits, respectively) but was crucial for the prediction of population biomass (77% and 49%, respectively). Root traits were more important for plant performance than leaf traits and were even the most important predictors at the population level
Synthesis . Upscaling from the individual to the population level reflects an increasing number of processes requiring traits from different trait clusters for their prediction. Our results emphasize the importance of root traits for trait‐based studies especially at higher organizational levels. Our approach provides a comprehensive framework acknowledging the hierarchical nature of trait influences. This is one step towards a more process‐oriented assessment of trait‐based approaches.
... Several authors have examined competitive relations and niche characteristics of plant species using controlled environmental gradients (Parrish and Bazzaz 1976, b, Pickett and Bazzaz 1976, 1978a, b, Austin and Austin 1980, Austin 1982. Comparisons between the niche responses of fugitive and persistent species have found fugitives to be weaker competitors and to have broader niches (e.g., Parrish 1982b), though this general relationship between niche breadth and competitive ability does not always hold (Pickett and Bazzaz 1976). ...
In monoculture, T. latifolia germinated and grew better at slightly higher elevations than T. domingensis. In mixture, T. latifolia was the better competitor above the water table, T. domingensis below the water table. Summed over the entire gradient, the 2 species did not differ significantly in their overall competitive abilities despite the fact that T. latifolia has larger seeds. Relative competitive ability in Typha is size dependent. The factors most likely to cause the observed shift in relative competitive abilities are 1) onset of flowering, 2) changes in morphology and physiology associated with growth and development, and 3) changes in factors limiting growth as plants increase in size. Type of initial propagules used in competition experiments can affect the outcome. In some cases, the outcome of competition may be dependent upon the initial density of propagules.-from Author
... The lower ground cover in the Chrysopogon and Sporobolus also affected the ground cover of their mixed stands were poorest among the mixed grass species. This corroborates Austin's (1982) report that performance of species in mixed stands can be modelled from their individual performance in monoculture. Table 2. F-statistics to determine the effect of treatment and their interactions on ground cover (%) in grasses and their mixtures weeks after clipping (WAC). ...
The study assessed the performance of Axonopus compressus, Chysopogon aciculatus, Sporobolus pyramidalis, Eleusine indica and Dactyloctenium aegyptium in turf establishment. The five grass species planted in sole and mixed stands were varied with the legume - Desmodium triflorum. Ground cover differed significantly among grass species and their mixtures from 4 - 11 weeks after planting (WAP) but ground cover in the legume and no legume subplots were not significantly different from 4 – 6 WAP. Eleusine, Axonopus and Dactyloctenium and their mixtures had higher ground cover than those of Sporobolus and Chrysopogon. There were significant differences in ground cover among grasses and mixtures at 3 and 6 weeks after clipping (WAC), and grass-legume subplots and subplots without the legume were different at 3 and 4 WAC. Recovery weeks after trampling was faster in sole stands and mixtures with Axonopus and Eleusine, indicating they are better adapted to trampling.
... In its approach, our study is similar to earlier approaches to predict overall performance of 'null' mixtures from abundance data of the monocultures assuming that there is no difference between intra-and interspecific interactions (Austin, 1982;Goldberg, 1994;Goldberg et al., 1995;Goldberg and Estabrook, 1998;Zamfir and Goldberg, 2000;Rajaniemi et al., 2003). In contrast to these earlier approaches our approach is less phenomenological and mechanistically models processes of stand development (Weiner, 1982;Weiner et al., 2001;Damgaard and Weiner, 2008). ...
Understanding the behavior of mixtures of species based solely on knowledge of the individual (component) species remains a big challenge for plant ecology. We used the observed outcome of two-species mixtures from a garden competition experiment with five clonal sedge species (two runners and three clumpers), and compared the data with predictions from a highly parameterized simulation model based only on monoculture data of these species. After two growing seasons (i.e., 300 growing days), overall performance of the mixtures (total biomass and ramet number of the mixtures, proportion of the biomass and ramet number of each species) was predicted rather well by the simulation model and the simulated variables were all within the 50% fit of observed values. Therefore, the single-species parameterization can capture most of the important processes that determine species behavior in the mixture and there is strong equivalence of species and a weak species-specific effect. This study demonstrates the power of modeling studies to perform virtual experiments for explicit hypothesis testing. Using this approach, we show that performance of mixtures can be realistically predicted by models parameterized and calibrated based on single species information.
... By illustrating the losses in growth that would occur if each population actually inhabited the ecologic optima, Fig. 13 also shows why optimal productivity occurs under the null transfer. As applied to populations within species, Fig. 13 reconciles the philosophical arguments among Ellenberg (1953), Ernst (1978), and Austin (1982) pertaining to possible discrepancies between ecological and physiological optima of plant species: populations do indeed occupy suboptimal environments. Our results and their interpretation thus support the belief of Harper (1964) that the reaction of plants to their neighbors is one of the most critical elements of autecology. ...
Fundamental plant-environment relationships were revealed by analyses of 20-yr height and survival of 118 populations representing two subspecies of Pinus contorta growing in common gardens at 60 environmentally disparate test sites in British Columbia. The approach involved (1) preparing models that described the general climate of British Columbia, (2) developing population-specific response functions driven by predicted climate variables, (3) developing general transfer functions that predict performance from the climatic distances over which populations were transferred, and (4) interpreting the results in terms of niche breadth, effects of climate change on adaptedness of populations, and reforestation in a changing environment. Polynomial regression models used physiographic descriptors to predict seven climate variables from normalized records of 513 weather stations. Values of R-2 ranged over 0.80-0.97 for thermal variables and 0.54-0.61 for precipitation variables. Validations with independent data from 45 stations were strong and suggested that the models were generally free of bias within the limits of the original data. Response functions describing the height or survival of each population were developed from quadratic regressions using predicted climate variables for each test site. Mean annual temperature and mean temperature in the coldest month were the most effective variables for predicting population height, while the ratio of summer temperature to summer moisture was the best predictor of survival. Validation of the response functions with independent data from two additional test sites produced values of R-2 between actual and predicted values that were as high as 0.93 for height and 0.73 for survival. The results demonstrated that natural populations have different climatic optima but tend to occupy suboptimal environments. Nevertheless, the general transfer functions showed that optimal growth and survival of the species as a whole is associated with the null transfer distance. These seemingly anomalous results suggest that the same processes thought to determine the distribution of species control the distribution of genotypes within species: (1) environmental selection to produce a broad fundamental niche, and (2) density-dependent selection to produce a relatively narrow realized niche within which most populations are relegated to suboptimal environments. Consequently, the steep geographic dines typical of P. contorta seem to be driven more by density-dependent selection than by environmental selection. Asymmetric gene flow from the center of distribution toward the periphery is viewed as a primary regulator that provides the fuel for both environmental and density dependent selection and thereby indirectly perpetuates suboptimality. The response functions predict that small changes in climate will greatly affect growth and survival of forest tree populations and, therefore, that maintaining contemporary forest productivities during global warming will require a wholesale redistribution of genotypes across the landscape. The response functions also provide the climatic bases to current reforestation guidelines and quantify the adjustments necessary for maintaining adaptedness in planted trees during periods of small (similar to 1 degrees C) temporal temperature shifts.
... There is little experimental evidence for the shape or position of species response curves on environmental gradients under multi-species competition (Ellenberg 1953(Ellenberg , 1954Austin 1982Austin , 1990). The need for predictive models based on fundamental responses rather than realized responses has been reviewed by Austin (1992), where he suggested that the impact of temperature increases on vegetation as a consequence of global CO2 increase requires fundamental niche models. ...
. Comparisons of the positions of species on Grimes'C-S-R triangular ordination model with their responses to individual environmental gradients indicates that the C-S-R model does not necessarily predict species ecological behaviour. The importance of the stress, productivity and disturbance gradients relative to other environmental gradients needs to be determined. In studies of species behaviour along a biomass/productivity gradient the collective vegetation property, biomass, has been confused with the environmental factor, fertility. Patterns of responses to biomass gradients e.g. Keddy's centrifugal model, should be examined in a two-dimensional environmental space to avoid such confounding effects. Assumptions regarding the shapes of species responses to environmental gradients remain untested. A recent model of species response functions to environmental gradients suggested that skewed responses curves show a pattern in the direction of the skew, always with the tail towards the presumed most mesic position on the gradient. Further evidence is presented to support this model for a temperature gradient in eucalypt forest in south-eastern Australia. 21 out of 24 species tested conform to the model.
... In addition, several environmental factors known to influence eucalypt distribution were not incorporated into the equations, raising the possibility of bias and also, it cannot be assumed that polynomial functions accurately reflect the response function. Some experimental glasshouse studies indicate that species response curves are context-sensitive and vary depending on the other species present (Austin 1982;Austin & Smith 1989;Austin et al. 1985). If these experimental results are indicative of natural conditions, then complex response curves could be the norm. ...
The importance of the shape of a species response curve to an environmental gradient is reviewed. The implications for vegetation theory, ordination methods, species as indicators of environmental conditions, predicting species distribution from surveys and simulation models of climatic impact on vegetation are examined. A beta-function V = k (x - a)alpha . (b - x)gamma is used to model species response curves using generalized linear modelling (GLM). Two hypotheses are tested; (1) that response curves differ significantly from a unimodal symmetric (Gaussian) shape and (2) that the direction of skew is a function of species position along the gradient. Nine eucalypt species are modelled using GLM with a beta-function fitted for mean annual temperature. Six other environmental variables and factors are considered in fitting the statistical models; mean annual rainfall, mean monthly solar radiation, topographic position, lithological type, nutrient index and rainfall seasonality. All nine species are significantly skewed in response to temperature. The direction of skew is positive when a species optimum temperature falls below 11.5-degrees-C and negative for species with optimum above. These results indicate that current vegetation analyses which require the modelling of species response curves, or assumptions about the shape of the response, require reassessment.
... This has been high-lighted by the different response observed in field studies as compared to monoculture field, glasshouse and laboratory studies. The manner in which abundances of particular species vary in relation to environmental gradients, in the absence of interference from other species, has created concepts and terms like physiological response function (Ellenberg, 1953;Austin and Austin, 1980), fundamental environmental niche (Austin, 1985), or relative physiological performance (Austin, 1982). The corresponding terms for observed response in the presence of other species are ecological response function, realised environmental niche, or normalised ecological performance. ...
A simulation model, using the often observed log-linear relationship between the relative abundance and rank of species, shows that vegetation will tend to form a series of communities of constant composition along an environmental gradient even if the constituent species are initially responding independently to those environmental changes. The discreteness of these communities increases with increasing conformity to the log-linear relationship. An index quantifying this conformity (range 0 -1.0) is defined and a method for estimating it from field vegetation data devised. In three vegetation data sets tested the conformity index was 0.0, 0.32 and 0.37.
... Ellenberg 1954;Austin & Austin 1980;Tilman 1984). The results obtained are used to analyse the effects of interspecific competition and to explain the spatio-temporal structure of plant communities (Austin 1982, Walter & Breckle 1985. ...
The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/1 Cl ⁻¹ ). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/1 Cl ⁻¹ : (1) glycophytes (non‐salt‐tolerant species), (2) salt‐tolerant species and (3) halo‐phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments.
The species differ in their capacity to reproduce in the autumn; only Zannichelliapedunculata and Tolypella hispánica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia marítima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range.
Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations.
... Ellenberg 1954;Austin & Austin 1980;Tilman 1984). The results obtained are used to analyse the effects of interspecific competition and to explain the spatio-temporal structure of plant communities (Austin 1982, Walter & Breckle 1985. ...
The effects of salinity on the reproduction of coastal submerged macrophyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/l Cl –). In a companion paper (Grillas, van Wijck & Bonis 1993) three groups of species were distinguished on the basis of their biomass production over the salinity range 0 to 6 g/l Cl – : (1) glycophytes (non-salt-tolerant species), (2) salt-tolerant species and (3) halo-phytes. This part of the study describes the impact of salinity on the reproduction of the individual species during the two experiments. The species differ in their capacity to reproduce in the autumn; only Zannichellia pedunculata and Tolypella hispanica were able to produce fruits in that season. For all species reproduction was greater in spring and strongly correlated with biomass, except for Chara canescens. Differences in reproductive effort over the salinity range amplified the halophytic nature of Ruppia maritima and Chara canescens and the intolerance of Callitriche truncata and Chara contraria. For the other species, reproductive effort did not differ significantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were large differences in the total weight of propagules produced at the community level and in the relative contribution of individual species. The resulting quantitative changes in the species composition of the seed bank could affect the structure of the communities by their effects on the establishment and survival of species populations.
... 3) If environment is instead the sole determinant of observed spatial patterns of abundance in conifer and broad-leaved trees, then the addition to environmental regressions of terms describing Nothofagus abundance should produce only a negligible improvement in model fit. 4) Based on the known influence of environment on competitive interactions in experiments (e.g., Ellenberg 1954, Connell 1961, Harper 1977, Austin 1982, Austin et al. 1985, we expect competitive effects of Nothofagus to be dependent on environment, an effect that should be detectable by the addition of appropriate statistical interaction terms. ...
New Zealand's four broad-leaved evergreen tree species from the genus Nothofagus all show pronounced distributional disjunctions, independent of environmental factors known to influence tree distributions. Here, we use these disjunctions as the basis for a natural removal experiment to investigate competitive interactions between Nothofagus and a range of other widespread conifer and broad-leaved tree species. We first model the abundance of non-Nothofagus species as a function of environment, using Generalized Additive Models (GAMs) and an extensive data set sampling much of New Zealand's remaining old-growth forests. We then assess the effects of competitive interaction with Nothofagus by adding statistical terms describing (1) Nothofagus abundance, and (2) interactions between Nothofagus abundance and annual temperature, the dominant environmental gradient. Results indicate substantial reductions in the abundance of many species as Nothofagus abundance increases. The magnitude of this reduction varies with position along the dominant environmental gradient; species overlapping most strongly with Nothofagus are generally most sensitive to increases in Nothofagus abundance. In addition, both the shapes of species responses to mean annual temperature and the positions of their optima change as Nothofagus abundance increases. This demonstration of competition using community compositional data has implications both for vegetation theory and for prediction of the likely impacts of global warming on New Zealand's forest pattern.
... The gradient approach with numerous treatment levels used here (cf. Austin & Austin 1980;Tilman 1986) has been successful, enabling the detection of small changes in relative performance, which are likely to be critical in determining the outcome of competition (Austin 1982;Austin et al. 1985). ...
Our objectives were as follows: (i) to quantify the realized environmental niche of two co‐occurring species and their differences and (ii) to examine whether differences in the species niches relate to differences in water and light use efficiency and growth responses to light and water.
Statistical models of the environmental niches of two Eucalyptus species were derived from presence/absence records and from environmental variables (mean annual temperature, mean summer rainfall, mean summer daily radiation) and three factors (topographic position, lithology and a nutrient index) for 10 577 plots from south‐eastern New South Wales, Australia. Generalized additive models (GAM) were fitted in a backwards stepwise procedure using Aikake's Information Criterion (AIC) for model selection.
Seedlings were used in two experiments: (i) a water supply gradient with 20 treatments from 10 mL per day to 1000 mL per day and (ii) a light gradient with five treatments from 3% to 100% (full) sunlight.
After controlling for lithology and nutrients, the principal differences in niche between species were as follows: (i) Eucalyptus mannifera was insensitive to mean summer daily radiation, (ii) it had a higher probability of occurrence in gullies and (iii) the two species differed in response shape and breadth of response to temperature, and temperature of maximum occurrence. Both species had a similar response to mean summer rainfall.
Eucalyptus mannifera showed a monotonic increase in total biomass along the water supply gradient, consistently outperforming Eucalyptus dives, which showed little further increase above 440 mL per day. Consistent differences between species were found for leaf area, specific leaf area and allocation to leaves and stems.
Diurnal measurements of conductance, transpiration, carbon dioxide assimilation and water use efficiency (WUE) showed differences between species along both the water and light gradients. Eucalyptus dives exhibits conservative responses to increasing resources and relatively higher WUE while E . mannifera has lower WUE.
Synthesis . Species differences in ecophysiological strategies are consistent with their co‐occurrence and with their realized environmental niche responses except for their temperature responses. The combination of statistical niche models and ecophysiological gradient experiments focuses attention on important unresolved environmental processes controlling distributions.
Richly illustrated and packed with numerous examples, this unique global perspective introduces wetland ecology from basic principles to advanced applications. Thoroughly revised and reorganised, this new edition of this prize-winning textbook begins with underlying causal factors, before moving on to more advanced concepts that add depth and context. Each chapter begins with an explanation of the basic principles covered, illustrated with clear examples. More difficult concepts and exceptions are introduced only once the general principle is well-established. Key principles are now discussed at the beginning of the book, and in order of relative importance, enabling students to understand the most important material without wading through complex theory. New chapters on wetland restoration and wetland services draw upon practical examples from around the world, providing a global context, and a new chapter on research will be particularly relevant to the advanced student planning their own studies.
Richly illustrated and packed with numerous examples, this unique global perspective introduces wetland ecology from basic principles to advanced applications. Thoroughly revised and reorganised, this new edition of this prize-winning textbook begins with underlying causal factors, before moving on to more advanced concepts that add depth and context. Each chapter begins with an explanation of the basic principles covered, illustrated with clear examples. More difficult concepts and exceptions are introduced only once the general principle is well-established. Key principles are now discussed at the beginning of the book, and in order of relative importance, enabling students to understand the most important material without wading through complex theory. New chapters on wetland restoration and wetland services draw upon practical examples from around the world, providing a global context, and a new chapter on research will be particularly relevant to the advanced student planning their own studies.
Growth characteristics and competitive relationships of cotton and three perennial weeds (johnsongrass, purple nutsedge, and yellow nutsedge) were investigated at the USDA Cotton Research Station in Shafter, CA. In growth analysis experiments, yellow nutsedge and johnsongrass had highest values for height, biomass, leaf area production, growth rate, and photosynthetic efficiency. The weeds exhibited greater overall resource use and production efficiency than cotton, while cotton attained greater leafiness and canopy closure than weeds over the 10-wk experiment. Linear correlation indicated that most growth variables were significantly correlated with aggressivity (competitiveness); however, all correlation coefficients were less than 0.80. Stepwise multiple regression, using aggressivity as the dependent variable, defined 4 growth variables out of 12 that best described competitiveness. These were unit leaf rate (ULR), height, relative growth rate (RGR), and initial propagule weight (PWT). Thus, parameters of light utilization (ULR, height) and early establishment (RGR, PWT) were best predictors of competitive success in this system.
Most people can readily identify a forest, or a grassland, or a wetland - these are the simple labels we give different plant communities. The aim of this book is to move beyond these simple descriptions to investigate the 'hidden' structure of vegetation, asking questions such as how do species in a community persist over time? What prevents the strongest species from taking over? And, are there rules that confer stability and produce repeatable patterns? Answers to these questions are fundamental to community ecology, and for the successful management of the world's varied ecosystems, many of which are currently under threat. In addition to reviewing and synthesising our current knowledge of species interactions and community assembly, this book also seeks to offer a different viewpoint - to challenge the reader, and to stimulate ecologists to think differently about plant communities and the processes that shape them. © J. Bastow Wilson, Andrew D. Q. Agnew and Stephen H. Roxburgh 2019.
This study assessed the geospatial variability and ecological amplitudes of plants along nutrient gradients in Imo River Wetland. Systematic sampling was employed for the vegetation and soil using ten 10 m x 10 m quadrat spaced at 20 m interval along established belt transects. Soil samples were obtained using a soil auger at two rooting depths (0 – 15 cm and 15 – 30 cm) and were analyzed using standardized methods. Eight (8) species belonging to six (6) families were found. Nypa fruticans was the most dominant (541.78±155.90 st/ha) and frequent (75%) species while Phoenix reclinata, Rhizophora mangle, Laguncularia racemosa and Pandanus candelabrum were the species with the least frequency of 25%, respectively. Laguncularia racemosa also had the least density value of 25.00±0.00 st/ha. The ecological amplitudes showed that species responded differently to nutrients and environmental gradients. Nypa fruticans showed peak density values at pH and available phosphorus values of log 1.64 and log 0.77 mg/kg respectively. Phoenix reclinata and Rhizophora mangle showed a strong affinity for organic carbon and total nitrogen reaching peak density values at log 2.69% and log – 0.99%, respectively. Nypa fruticans recorded wide adaptability with increasing Ca concentration reaching a peak density value at log 2.44 cmol/kg. Generally, Nypa fruticans was the most successful of all species having recorded the highest density values at different nutrient gradients. By and large, this study showed overlapping occurrences of species in response to varying levels of nutrients across the plots and lends credence to wetland conservation and appropriate environmental monitoring against invasive species.
Agropyron smithii and Bouteloua gracilis plants from intensively grazed prairie dog colonies and from a grazing exclosure in Wind Cave National Park, South Dakota, were used to compare responses of conspecific populations with different histories of exposure to grazing and to competition for light. In separate experiments for each species, plants grown in monocultures and two‐population replacement‐series mixtures were used to examine effects of defoliation, frequency‐dependent competition, and population on biomass and morphology.
Colony and exclosure plants frequently responded differently. Defoliation more often adversely affected exclosure plants than colony plants, while interpopulation competition more often adversely affected colony plants. Defoliation frequently negated the competitive advantage of exclosure plants. Intrapopulation competition appeared to be greater among exclosure than colony plants. Our results indicate that conclusions based on studies of plants in long‐term exclosures may not apply to plant populations having long histories of intensive grazing. While there were differences between species, in both, these experiments provide evidence of population differentiation, resulting in morphologically dissimilar populations which responded differently to defoliation and to inter‐ and intrapopulation competition.
Vegetation science started as descriptive, geographically orientated phytosociology, with an emphasis on the floristic composition of plant communities and the correlation of community patterns with variations in climate and soil. It is now rapidly broadening to include structural and functional characteristics of plant communities integrated with operational factors from the dynamic environment. Parallel to this development, there has been a shift in related disciplines: from floristic plant geography, soil science, climatology, and nature conservation to population ecology, ecophysiology, paleoecology, mathematics, natural resource ecology, and landscape ecology.
Environmental gradients are a powerful and largely overlooked research tool. They exist only because of heterogeneity. The objective of this chapter is to provide an overview of techniques for using environmental gradients to explore heterogeneous systems. The chapter begins by noting that any tool is helpful only if it is used with a well-defined goal. The goal of “assembly rules” and “response rules” for communities is suggested and briefly described. Because not all habitats have obvious gradients, techniques for finding gradients where they are not obvious are then introduced. Eight guidelines for using gradients as research tools are explored. These guidelines deal with the following topics: (1) choosing gradients to maximize generality; (2) selecting independent variables; (3) selecting dependent variables and the value of screening to create “trait matrices”; (4) importance of inferential statistics for detecting patterns; (5) incorporating experiments into natural gradients; (6) merits of locating two orthogonal gradients; (7) making gradients if they cannot be found; and (8) considerations of scale. The chapter concludes by discussing centrifugal organization, a model of community organization at the landscape scale that is built around species’ responses to gradients.
Competition is important for both natural and agricultural plant communities, and being investigated in many settings and for many purposes. Plant competition has several attributes, and can be examined from different perspectives, including importance, intensity, effect, response, and outcome. The selection and use of related indices has an important bearing in the assessment of plant competition, which in turn may condition the inferences drawn from plant competition experiments. Here, three fundamental components of plant competition ability were summarized, and related indices were classified as: 1 indices for quantifying the intensity and importance of competition, 2 indices for quantifying the effects of competition, and 3 indices for quantifying the outcome of competition. Moreover, the functions and applications of different indices were discussed. We hope this essay will make researchers aware of the diversity of the indices that are available, and help them to choose those indices that are suitable to their needs.
Plants make up 99.9 percent of the world's living matter, provide food and shelter, and control the Earth's climate. The study of plant ecology is therefore essential to understanding the biological functions and processes of the biosphere. This vibrant new introductory textbook integrates important classical themes with recent ideas, models and data. The book begins with the origin of plants and their role in creating the biosphere as the context for discussing plant functional types and evolutionary patterns. The coverage continues logically through the exploration of causation with chapters, amongst others, on resources, stress, competition, predation, and mutualism. The book concludes with a chapter on conservation, addressing the concern that as many as one-third of all plant species are at risk of extinction. Each chapter is enriched with striking and unusual examples of plants (e.g., stone plants, carnivorous plants) and plant habitats (e.g., isolated tropical tepui, arctic cliffs). Paul Keddy - winner of the 2007 National Wetlands Award for Research- writes in a lively and thought-provoking style will appeal to students at all levels.
Density and spatial arrangement (rectangularity) effects on the competitive relationships, yield performance, and dynamics in canopy dominance of winter wheat and Italian ryegrass were evaluated using two addition series experiments. In experiment 1, combinations of six densities of each species formed the treatment matrix of addition series. In experiment 2, each species was tested at four densities and three rectangularities (RE) of winter wheat. In monocultures, crop density (plants per square meter) explained 82 to 85% of the total variation in the per-plant biomass of winter wheat in experiment 1. In mixtures of crop and weed, initial wheat density (N1) and initial ryegrass density (N2) and interaction of N1 and N2 explained 74 to 80% of the total variation in the per-plant biomass of winter wheat and 68 to 79% of Italian ryegrass in experiment 1. Intraspecific competition was apparent between 15 and 90 days after emergence (DAE) in winter wheat and between 90 and 170 DAE in Italian ryegrass. In mixtures, RE influenced plant size of Italian ryegrass up to 50 DAE only. Maximum winter wheat intraspecific competition occurred at 170 DAE, but maximum interspecific competition occurred during reproductive stages in mixtures. High RE increased seed yield, seed size, and harvest index of winter wheat and reduced biomass of Italian ryegrass. Grain yield of winter wheat was reduced up to 92% by competition from ryegrass. Even nine ryegrass plants in 100 winter wheat plants m-2 reduced winter wheat grain yield by 33%. However, the extent of loss in winter wheat grain yield was less in RE 16 (wider spacing) than in RE 1 (square planting) or 4 (close row spacing). Winter wheat was the stronger competitor during vegetative stages, but Italian ryegrass became the stronger competitor during the reproductive stages of development. Winter wheat leaves dominated at the top canopy during the vegetative stage, but ryegrass dominated at the top canopy during the reproductive stages. In the top canopy of mixtures at 200 DAE, the leaf area indices (LAI) of ryegrass was 6.6 times greater than winter wheat at RE 1 compared to only 1.6 times at RE 16. Greater LAI of Italian ryegrass in the top canopy reduced photosynthetically active radiation available to winter wheat by 68% at booting stage.
Richly illustrated and packed with numerous examples, this unique global perspective introduces wetland ecology from basic principles to advanced applications. Thoroughly revised and reorganised, this new edition of this prize-winning textbook begins with underlying causal factors, before moving on to more advanced concepts that add depth and context. Each chapterbegins with an explanation of the basic principles covered, illustrated with clear examples. More difficult concepts and exceptions are introduced only once the general principle is well-established. Key principles are now discussed at the beginning of the book, and in order of relative importance, enabling students to understand the most important material without wadingthrough complex theory. New chapters on wetland restoration and wetland services draw upon practical examples from around the world, providing a global context, and a new chapter on research will be particularly relevant to theadvanced student planning their own studies.
Title: Limits of a game - assembly rules in ecological communities (in Hungarian)
1. A variety of autecological attributes of seeds and seedlings (seed weight, germination rate, germination percentage, absolute and relative growth rate, variations in growth form) were determined for 15 wetland species by means of (i) germination tests under conditions of constant temperature and mositure and natural daylight, (ii) 3 weeks' growth in monoculture in a controlled environment, and (iii) 3 months' growth in monoculture in a glasshouse in special root chambers having a fixed water table. 2. A mesocosm experiment was conducted in which the same collection of wetland species was sown into cylindrical soil containers of volume 0.14 m3 and grown under highly competitive conditions. Factorial combinations were applied in respect of amount of sown seed (5 g m-2 or 15 g m-2), composition of sown seed (with or without adjustment of the mixture according to C-S-R plant strategy theory (sensu J.P. Grime), and amount of flooding (none or 4 days of flooding per 3-week period). 3. A predictor/response investigation, employing correlation and multiple regression analysis, estimated the relative value of each autecological attribute for predicting the establishment and composition of vegetation under the various conditions used in the mesocosm experiment. Across all species, germination rate over the first 4 days of the germination test, leaf weight ratio in the growth-room experiment and total shoot length after 61 days in the root-chamber experiment were clearly correlated with biomass production in the mesocosm experiment, most strongly so at the sown density of 15 g m-2, in the seed mixture without C-S-R adjustment, and in the non-flooded treatments. In the multiple regression analysis, the combination of germination rate in the first 4 days and total shoot length after 61 days explained 83% of variance in biomass production in the treatment of the mesocosm experiment without C-S-R adjustment; and presented the most significant regression of all (F = 29.42, P
We tested the prediction that plant species that grow in undisturbed, nutrient-rich habitats tend to have higher competitive abilities than those found in disturbed or nutrient-poor habitats. The distributions of seven species (Eriocaulon septangulare, Rhynchospora fusca, Hypericum ellipticum, Juncus pelocarpus, Lysimachia terrestris, Dulichium arundinaceum, and Drosera intermedia) were measured along a gradient of exposure to wave action on the shore of Axe Lake, Ontario. The exposure gradient incorporates disturbance, through the removal of plant biomass, and stress, through the creation of a gradient in sediment organic content, nutrient concentrations, and fine particle sizes. Species distributions on the exposure gradient were quantified by determining the mean sediment organic content of the quadrats containing each species. Competitive abilities were measured as relative increase in dry mass per plant, in a field experiment in which species were grown together in all pairwise combinations (N = 10 replicates). Species had significantly heterogeneous competitive abilities (P < .01). Species found on exposed, nutrient-poor shores (e.g., E. septangulare) had low competitive abilities, while those growing on sheltered, nutrient-rich shores (e.g., D. arundinaceum) had high competitive abilities. Competitive ability was significantly correlated with mean position on the exposure gradient.
Species diversity is generally considered to have a unimodal relationship with productivity where diversity reaches a maximum at intermediate productivity due to abiotic limitation at low productivity and competitive exclusion at high productivity. Various patterns in this relationship have been detected in understory communities of U.S. eastern deciduous forests, raising questions about the effects of abiotic limitation and competition in these communities. We examined vegetation structure and species distribution patterns in the forest understory community of two topographically similar watersheds to evaluate the predicted roles of abiotic limitation and competition along a productivity gradient. Canonical correspondence analysis identified a dominant compositional gradient that was strongly correlated with moisture, light, and herbaceous-layer cover. Given these relationships, the first axis of the ordination was taken as a reliable index of productivity. Contrary to expectation, species richness increased monotonically along the gradient rather than reaching a maximum and then declining which suggests that species are not excluded by light competition at the high-productivity end of the gradient. Other vegetation patterns, however, indicated both abiotic limitation in regions of low productivity and competition at high productivity. Patterns in species' distributions also suggested resource limitation at low productivity, but they showed mixed evidence of competition at high productivity. Taken together, these patterns in vegetation structure and species' distributions imply that while competition may occur among herbaceous-layer species, particularly at high productivity, competitive exclusion remains low. This may be because the traits that permit survival under tree canopy shading reduce the effects of light competition with other understory species, or because understory productivity is not high enough to induce intense light competition among herbaceous-layer species.
(1) Populations of Poa pratensis and Agrostis tenuis were collected from high fertility and low fertility plots of long-term fertilizer experiments at Rothamsted (England) and Samsstadir (Iceland). (2) The populations were grown in the field, in pure stands and in all possible two-species mixtures at Reading (England) and Korpa (Iceland) for 2 years. Two levels of nitrogen fertilizer (25 and 200 kg N ha-1 year-1) were applied. (3) Agrostis tenuis was the more competitive at Reading, whereas P. pratensis was the more competitive at Korpa. N fertilizer increased the competitive ability of P. pratensis, relative to A. tenuis, at both locations. (4) In pure stands, populations generally performed best in their native country, but populations rarely differed in response to fertilizer. In mixtures, populations of contrasting climatic origin were more competitive in their native country. Populations from soils of contrasting fertility were also more competitive at N inputs similar to those of their native site. (5) The yield advantage of mixtures, as measured by the relative yield total (RYT), was greater when populations were grown in fertility conditions resembling those of their native habitat.
Two of the central hypotheses of the triangular model of primary plant strategies were tested by a movel technique involving seven grasses of contrasted ecology grown in pure stands and an additive mixture on an experimental matrix of crossed gradients of mineral nutrient stress and vegetation disturbance. The experimental design allowed reductions in vegetative and reproductive vigor resulting from interspecific competition to be distinguished from those arising from direct effects of nutrient stress and vegetation disturbance. It was also possible to determine the extent to which competitive suppression of each species was affected by stress and disturbance. In isolation, all species showed maximum vegetative and reproductive vigor at high soil fertility and low disturbance. In the mixture, absolute reductions in biomass and flowering due to competition were greatest at high soil fertility and low disturbance, and the species of most extreme strategy became restricted to areas of the matrix broadly consistent with those predicted by strategy classification. When standardized for differences in biomass in pure stands, the effect of competition remained relatively constant across the stress-disturbance matrix for all species except Poa annua, which was less restricted by competition at high intensities of stress. There were marked and consistent differences between species in their susceptibility to competition. At both high and low soil fertility, two species of natural occurrence on infertile soils (Festuca ovina, Bromus erectus) were poor competitors relative to Arrhenatherum elatius, a widespread dominant of productive grasslands. The effect of competition was least severe on flowering of annuals in low-stress portions of the matrix. If competition is assessed simply as the percentage of reduction in biomass between pure and mixed stands it appears that competition intensity is constant across different intensities of stress and disturbances. However, observations that maximum reductions in biomass coincided with low stress and low disturbance, that competition decreased in importance as a factor reducing yield and flowering (relative to stress and disturbance) as stress and disturbance intensities increased, and that there was a consistently inferior competitive ability of plants from infertile soils at all positions on the matrix all support the hypothesis that competition declines in importance as a vegetation determinant in the vegetation of infertile soils.
Two methods for estimating climatic response functions by measuring realized climatic niche spaces are compared. The first, direct gradient analysis, utilizes measures of abundance of the species at sites spanning the climatic range of the species' occurrence. The second, geographic distribution analysis, quantifies the proportion of the species' total areal occurrence that is found within each climatic zone. A geographic information system is used to digitize species distribution maps and climatic isoline maps, and to compute areas of coincidence. The methods are compared, using independent data sets, on eight species of Californian coastal sage scrub. The position of species maxima along climatic gradients coincided for 75% of the 24 cases in which climatic response from the two methods was compared. This result suggests that the quicker and less expensive geographic distribution analysis method may have value in generating first approximations to climatic response functions. The geographic distribution analysis method is also used to characterize the realized climatic niche space for an additional eight species of Californian hard chaparral. Most species' response surfaces from data throughout the species' range were approximately bell shaped along climatic axes, providing some confirmation of theoretical expectation. The smoothness of such curve shapes will, however, be somewhat sensitive to the scale of sample resolution.
In the last decade, we have seen the emergence and consolidation of a conceptual framework that recognizes the landscape as an ecological unit of interest. Plant ecologists have long emphasized landscape-scale issues, but there has been no recent attempt to define how landscape concepts are now integrated in vegetation studies. To help define common research paradigms in both landscape and plant ecology, we discuss issues related to three main landscape concepts in vegetation researches, reviewing theoretical influences and emphasizing recent developments. We first focus on environmental relationships, documenting how vegetation patterns emerge from the influence of local abiotic conditions. The landscape is the physical environment. Disturbances are then considered, with a particular attention to human-driven processes that often overrule natural dynamics. The landscape is a dynamic space. As environmental and historical processes generate heterogeneous patterns, we finally move on to stress current evidence relating spatial structure and vegetation dynamics. This relates to the concept of a landscape as a patch-corridor-matrix mosaic. Future challenges involve: 1) the capacity to evaluate the relative importance of multiple controlling processes at broad spatial scale; 2) better assessment of the real importance of the spatial configuration of landscape elements for plant species and finally; 3) the integration of natural and cultural processes and the recognition of their interdependence in relation to vegetation management issues in human landscapes.
The study of the relationship between species richness of a plant
community and its productivity has received much attention, recently
renewed by the concern on the loss of biological diversity at a global
scale. Here, we briefly review some indices widely used in agronomic and
competition experiments to compare monocultures and mixtures, and
compare them to other, more recently designed ones. These various
indices are then calculated for two experiments. In the first
experiment, two grass and two legume species were grown at six levels of
nitrogen availability, either in monocultures or in mixtures of the four
species in a substitutive design; in the second experiment, five grass
species were grown at 16 levels of total nutrient availability, either
in monocultures or in mixtures of the five species in an additive
design. These data clearly show that the conclusions drawn from the
experiments depend on the index used to compare the experimental
communities. We argue that a clear test of whether the productivity of
communities increases with species richness requires that: (1) all
species present in the multispecies assemblages also be grown in
monocultures under the same environmental conditions, and (2) the
productivity of these assemblages be compared to the most productive
monoculture. We conclude that there are as yet very few cases where
superior productivity of multispecies assemblages as compared to
monocultures has been clearly shown.
Agropyron smithii and Bouteloua gracilis from intensively grazed prairie dog colonies and from a grazing exclosure in Wind Cave National Park, South Dakota, were used to compare responses of conspecific populations with different histories of exposure to grazing and to competition for light. Defoliation more often adversely affected exclosure plants than colony plants; interpopulation competition more often adversely affected colony plants. Defoliation frequently negated the competitive advantage of exclosure plants. Intrapopulation competition appeared to be greater among exclosure plants. -from Authors
Salinity and water regime have previously been recognised as the main environmental factors controlling the abundance of coastal submerged macrophytes in temporarily-flooded marshes in the Camargue. The effects of these environmental variables, which are considered interrelated, are tested experimentally by subjecting experimental macrophyte communities from six temporarily flooded marshes to different levels of salinity (from 0 to 6 g/1 Cl−). Communities subjected to high salinity levels (4 and 6 g/1 Cl~) showed a decrease in species richness and in biomass of all species involved. The species that most frequently dominate these communities, Chara áspera and Zannichellia pedunculata, are tolerant of salt and dominate over the entire salinity range. Three species groups can be distinguished based on the distribution of their biomass and centre of gravity of distribution over the salinity range: (1) non-salt-tolerant species, ‘glyco-phytes’, (2) moderately salt-tolerant species and (3) very tolerant species (‘halophytes’). A species ordination based on the experiments appeared to give results close to those previously obtained from field data.
The concept of centrifugal organization integrates community ecology's two main conceptual approaches: description of gradients and study of process. Centrifugal organization describes distributional patterns of species and vegetation types along standing crop gradients that are caused by different combinations of environmental constraints. Gradients radiate outwards from a single core habitat to many different peripheral habitats. The assumed mechanism is a competitive hierarchy where weaker competitors are restricted to the peripheral end of the gradient as a result of a trade‐off between competitive ability and tolerance limits. The benign ends of the gradients comprise a core habitat which is dominated by the same species. At the peripheral end of each axis, species with specific adaptations to particular sources of adversity occur.
In wetlands, the core habitat has low disturbance and high fertility, and is dominated by large leafy species capable of forming dense canopies. Peripheral habitats are formed by different kinds and combinations of infertility and disturbance and support distinctive floras. The centrifugal organization model therefore allows us to predict the distribution of particular organisms (rare species) and to predict how changes to the conditions creating peripheral habitats will alter community composition.
This study examined the relationship between vegetation patterns at three spatial scales and five plant-growth attributes that were suspected to affect competitive ability in 10 species collected from two hay field plots of different ages (cultivated in 1974 and 1984). Relative abundance of species at the plot scale (30 × 100 m) showed no relationship with any of the attributes. Species diversity within 1 × 1 m quadrats, however, had a significant negative relationship with mean seed weight in the 1984 plot and a significant negative relationship with mean plant height, mean lateral spread, mean growth rate, and "potential growth index" (combining all five attributes) in the 1974 plot. Multiple regression analysis indicated that the relationship between the five plant attributes and species diversity within the 1 × 1 m quadrats was stronger for the older (1974) (r2 = 0.67) than for the younger plot (r2 = 0.32). These data suggest that (i) the role of "competitive ability" attributes in affecting community structure becomes more evident in later stages of community development, (ii) different attributes may affect competitive ability at different stages of grassland community development, and (iii) the consequences of attribute differences among species may be revealed only in patterns at the local neighbourhood scale within vegetation. Key words: competitive ability, diversity, grassland, vegetation patterns.
Abstract An area of dry grassland in New Zealand, comprising an equal mixture of native and exotic species, was subject to perturbations of irrigation, fertilization and cessation of grazing. The vegetation response was recorded for 3 years. Total cover, and the contribution of native species to that cover, fluctuated between years even in the control plots. Irrigation increased total cover, but decreased the cover of native species. Fertilization produced the same effects, only less strongly, and also reduced species richness, the loss being in native species. In spite of overall effects of treatments on native and exotic cover, when individual species’ responses to irrigation, fertilization or exclosure were calculated, there was no significant difference between the native and exotic plant guilds. Species differed in their responses, but the native and exotic guilds overlapped. When grouped by morphology, the only significant difference between the responses to perturbation was that forbs and graminoids responded more positively to irrigation than woody and cryptogamic species. The realized responses of the species to the perturbations described here showed little correlation with their physiological responses as determined in previous greenhouse experiments. It is suggested that the realized responses are strongly, and currently unpredictably, influenced by competition from the other species present. Soil nutrients and soil water were both important controls on the community. The relative similarity in the nature of the response to these two factors – nutrients and water – suggests that they affect species in similar ways, possibly because the greater growth rate of the exotic species mediates the short-term response to both. Grazing has less effect on the current community than either nutrients or water, although it may have been historically important in shaping the species pool. From the poor predictability of field responses from morphological guilds or from ecophysiological responses, it is suggested that the ‘functional types’ approach, although conceptually attractive, lacks experimental support in these grasslands. It is concluded that the exotic species have invaded by being pre-adapted to the environment with the same environmental responses as the natives, but with the advantage of generally higher growth rates.
Indirect gradient analysis methods require an explicit vegetation model which must be based on direct gradient analysis studies. Various vegetation models are reviewed. Field evidence for the models is discussed. Experimental studies of species response to environmental gradients are reviewed and discussed. Three types of gradient are recognized as important for development of models: indirect environmental gradients where the environmental factor has no direct physiological influence on plant growth e.g. elevation; direct environmental gradients where the factor has a direct physiological effect on growth but is not an essential resource, e.g. pH; resource gradients where the factor is an essential resource for plant growth. The behaviour of the ecological carrying capacity and the role of competition along such gradients are shown to be important for developing vegetation models.
Plant species diversity patterns of the Rocky Mountain forests were found to be at variance with patterns reported from other regions. The most centrally located forests in terms of elevation, site moisture and successional status were found to have the lowest diversity. In contrast, the peripheral and environmentally more severe sites were found to have relatively high diversity. In particular, the forest-grassland transition and the low elevation riparian forests have species diversity values as high as any yet reported from western North America.When diversity was examined in terms of variation across elevation or moisture gradients, varying results were obtained due to the interaction of these factors. The failure of previous studies to converge on generalizations about plant diversity reflects, in part, the failure of most investigators to view diversity in a regional context of variation across several interacting gradients.Diversity was seen to vary inversely with the degree of development of the forest canopy. The interaction of different components of the forest community is one reason for the failure of general patterns of plant species diversity to emerge from previous studies. A potentially rich herb community can be greatly suppressed by a single species tree stratum.Among the most successful work to date on species diversity is that on birds, a distinct albeit large and functional group. It is unlikely that similar success could have been achieved through work on all animal species simultaneously. This suggests the need to examine plant species diversity, not in terms of total diversity, but in terms of component functional groups, perhaps guilds, growing under similar microclimatic conditions and subject to similar competitive pressures.
Eucalyptus is one of the most distinctive botanical features of Australia, and since most of the species are trees and occur mainly in the non-arid quarter of the Continent with a rainfall of more than about 15 inches, they are a very prominent feature of the natural landscape of most of the more closely settled areas and a major component of the plant communities of this zone.
Pryor's rule that mixed stands of eucalypt forest consist of species from different subgeneric groups was tested statistically using data from a vegetation survey of part of the South Coast of New South Wales. The plot data were stratified by environmental regions, and expressed in terms of the subgeneric combinations of the two most abundant tree species. The categories recognized were the eucalypt subgenera Monocalyptus, Symphyomyrtus and Corymbia, plus Angophora and others. The results suggest that: (a) subgenera are characteristic of certain environmental regions; (b) combinations of subgenera are not random; (c) a modification of Pryor's rule is applicable to three of the four regions studied; and (d) in addition, certain combinations of subgenera occur more frequently than expected by chance, e.g. Monocalyptus occurs as the most abundant species, with Symphomyrtus as subordinate, more frequently than the reverse situation. The results accord with recent reviews of eucalypt forest ecology but there are many plots with a composition of three species from the same subgenus. Biological explanations for Pryor's rule must also take account of these exceptions and the tendency for Symphyomyrtus species to be subdominant to Monocalyptus in the coastal region.
Parasitic damage to the leading shoot of young regrowth eucalypts was found to vary considerably
between trees and between different stands but it averaged greater than 20 % 'effective leaf area loss'
overall. Many fungal parasites and some of the phytophagous insects responsible for this damage
exhibited host specificity or host preference towards trees of a particular subgenus of Eucalyptus.
These findings are discussed in relation to the hypothesis that parasites play an important role in
the maintenance of stable associations between codominant species of Eucalyptus.
Evidence from competition experiments in pots suggests that pairs of eucalypt species from the same
association make almost the same use of the physical and chemical resources of the environment
during the seedling stage. These results are discussed in relation to present theories concerning the
coexistence of eucalypts in mixed associations.
An outline of the nature and aims of trend-surface analysis is given. A method for calculating trends by fitting polynomial surfaces to observed values of mapped variables and for evaluating the fitted trends and their components is described. Two applications of the procedure to ecological situations are discussed with the object of assessing its potential value in studies of vegetation. A limitation of the present study is that the interpretation of results has rested on unaided visual inspection of fitted surfaces. These preliminary ecological analyses suggest that in certain circumstances trend-surface analysis may: (i) Provide a convenient means of testing predictions and generalizations arising from previous analyses of vegetation. (ii) Enable abstract features of analyses such as factor or components analysis to be related back to and evaluated against conditions in the field. (iii) Form an excellent means for mapping vegetation and for describing and predicting the occurrence of other variables of ecological interest. A number of generalizations of the basic techniques employed are referred to, and the possible ecological significance of deviations on the trends is briefly considered. It is concluded that trend-surface analysis should prove to be a useful tool in ecological studies of vegetation.
Species richness was studied in the understorey of natural Pinus sylvestris forest in the eastern Pyrenees. Understorey plant species were grouped in three structural groups as woody species, herbs and mosses. The response curves of total species richness and species richness of each structural group were fitted against environmental and stand-structural parameters, using Generalized Linear Models. The results suggested that, to predict species richness, environmental parameters were more important than tree-canopy structural parameters, in particular incoming radiation and soil nutrient concentration. The species richness, response curve was often humped in relation to soil nutrient concentration. Different patterns of species richness were found for each structural group.
The aim of the study is to define homogeneous rainfall regions in order to improve methods for meso-scale extrapolation of isohyets. Two multivariate approaches are used, agglomerative classification and a modification of principal coordinates analysis. The median, mean, upper and lower quartiles and deciles for each month for a 30-year period were used as the attributes for 109 rainfall stations. Several data standardizations and classification methods are examined. Classification results were robust with respect to changes of method. Standardization based on proportions was preferred to that based on standard deviates. Fourteen groups of rainfall stations are recognized arranged in four regions. Use of mean data for groups clearly shows the spatial pattern of seasonal changes in rainfall. Differences in the relationship of rainfall to altitude are shown to be marked between geographically adjacent groups of rainfall stations.
In 1959, in his seminal paper "Homage to Santa Rosalia," G. E. Hutchinson asked, Why are there so many kinds of organisms? This paper focused attention on problems of species diversity and community organization that have occupied many theoretical and empirical ecologists for the last two decades. In the present paper I evaluate the attempt to answer Hutchinson's question by considering three topics. First, I reexamine the main themes which Hutchinson developed in "The Homage" and call attention to the central importance of energetic relationships in his view of ecological communities. Second, I examine the development of theoretical community ecology over the last two decades in an attempt to determine why some avenues of investigation, such as competition theory, have proven disappointing, whereas others, such as the theory of island biogeography, have enjoyed at least modest success. Finally, I suggest that future attempts to understand patterns of species diversity might focus on developing two kinds of theoretical constructs: capacity rules, which describe how characteristics of the physical environment determine its capacity to support life, and allocation rules, which describe how limited energetic resources are subdivided among species.
A maximum likelihood fit of a logistic regression model (and other similar models) is extremely sensitive to outlying responses and extreme points in the design space. We develop diagnostic measures to aid the analyst in detecting such observations and in quantifying their effect on various aspects of the maximum likelihood fit. The elements of the fitting process which constitute the usual output (parameter estimates, standard errors, residuals, etc.) will be used for this purpose. With a properly designed computing package for fitting the usual maximum-likelihood model, the diagnostics are essentially "free for the asking." In particular, good data analysis for logistic regression models need not be expensive or time-consuming.
- M P Austin
Austin M. P. (1978) Vegetation. In: Land Use on the South Coast of
New South Wales. Vol. 2 Biophysical Background Studies (eds
M. P. Austin & K. D, Cocks) pp. 44-67. CSIRO, Melbourne,
Australia.
Vegetation pattern in east coast forests
- R G Florence
Florence R. G. (1963) Vegetation pattern in east coast forests. Proc.
Linn. Soc. NSW SS, 164 79.
The biology of the eucalypt forest
- R G Florence
Florence R. G. (1981) The biology of the eucalypt forest. In:
Biology of Native Australian Plants (eds J. Pate & A. McComb)
pp. 147-80. University of Western Australia Press, Nedlands,
Western Australia.
Inventory Analysis of Southern New South Wales Rainforest Vegetation. MSc thesis
- C Helman
Helman C. (1983) Inventory Analysis of Southern New South
Wales Rainforest Vegetation. MSc thesis. University of New
England.
Genetic control in Eucatyptus distribution
- L Pryor
Pryor L. (1953) Genetic control in Eucatyptus distribution. Proc.
Linn. Soc. NSW1S,S'\S.