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In exploring the relationship between multivariate abundance data and environmental variables, a rarely used approach is to graph raw data separately for each different taxon. It is proposed that such raw data graphs become part of the standard toolset for graphing and analysing multivariate abundances. The key advantage of this approach is that axis scales have quantitative interpretations, enabling quantitative interpretation of patterns in abundance. In contrast, ordinations only present qualitative information. Ordinations are useful for inferring overall, qualitative patterns and raw data graphing is a complementary tool of greater use for answering more specific questions, aimed at a deeper understanding the ecology of a community. It is demonstrated using some well-known examples that our understanding of the nature of associations can be considerably improved by using raw data graphs, even when only plotting a subset of variables. One example describes how an often-cited dataset has been misinterpreted in key methodological papers, because data were interpreted from ordinations alone, with no consideration of plots of the raw data. [ABSTRACT FROM AUTHOR]

This paper explores the effect of spatial processes in a heterogeneous environment on the dynamics of a host-parasitoid interaction. The environment consists of a lattice of favourable (habitat) and hostile (matrix) hexagonal cells, whose spatial distribution is measured by habitat proportion and spatial autocorrelation (inverse of fragmentation). At each time step, a fixed fraction of both populations disperses to the adjacent cells where it reproduces following the Nicholson-Bailey model. Aspects of the dynamics analysed include extinction, stability, cycle period and amplitude, and the spatial patterns emerging from the dynamics. We find that, depending primarily on the fraction of the host population that disperses in each generation and on the landscape geometry, five classes of spatio-temporal dynamics can be objectively distinguished: spatial chaos, spirals, metapopulation, mainland-island and spiral fragments. The first two are commonly found in theoretical studies of homogeneous landscapes. The other three are direct consequences of the heterogeneity and have strong similarities to dynamic patterns observed in real systems (e.g. extinction-recolonisation, source-sink, outbreaks, spreading waves). We discuss the processes that generate these patterns and allow the system to persist. The importance of these results is threefold: first, our model merges into a same theoretical framework dynamics commonly observed in the field that are usually modelled independently. Second, these dynamics and patterns are explained by dispersal rate and common landscape statistics, thus linking in a practical way population ecology to landscape ecology. Third, we show that the landscape geometry has a qualitative effect on the length of the cycles and, in particular, we demonstrate how very long periods can be produced by spatial processes. [ABSTRACT FROM AUTHOR]

The article studies the ecology of shingle beach plants. The author mentions some of the relevant papers on shingle beaches as a plant habitat, or on their vegetation. Each of the two principal factors, beach composition and shingle mobility, is continuously variable in itself as well as interacting with other factors such as local topography, climate and water supply, and the whole is influenced by time and by past history, according to the author. The author says that the material of shingle beaches consists of two components, the shingle or coarse fraction and the matrix or fine fraction.

The article reports on the acquisition of the journal "The Plant World" by the Ecological Society of America in the U.S. It says that the acquired journal bears the title "Ecology". The acquisition made the journal as the organ of the Society and will publish papers both on plant and animal ecology. Furthermore, the Plant World journal has always published several ecological papers, and its successor, the Ecology journal may now be expected to become one of the main outlets for American ecological work.

Data are often collected for a single species within an ecological community, so quantitative tools for drawing inferences about the unobserved portions of the community from single-species data are valuable. In this paper, we present and examine a method for estimating community dimension (the number of strongly interacting species or groups) from time series data on a single species. The dynamics of one species can be strongly affected by environmental stochasticity acting not only on itself, but also on other species with which it interacts. By fully accounting for the effects of stochasticity on populations embedded in a community, our approach gives better estimates of community dimension than commonly used methods. Using a combination of time series data and simulations, we show that failing to properly account for stochasticity when attempting to relate population dynamics to attributes of the community can give misleading information about community dimension. [ABSTRACT FROM AUTHOR]

1. Linking the movement and behaviour of animals to their environment is a central problem in ecology. Through the use of electronic tagging and tracking (ETT), collection of in situ data from free-roaming animals is now commonplace, yet statistical approaches enabling direct relation of movement observations to environmental conditions are still in development. 2. In this study, we examine the hidden Markov model (HMM) for behavioural analysis of tracking data. HMMs allow for prediction of latent behavioural states while directly accounting for the serial dependence prevalent in ETT data. Updating the probability of behavioural switches with tag or remote-sensing data provides a statistical method that links environmental data to behaviour in a direct and integrated manner. 3. It is important to assess the reliability of state categorization over the range of time-series lengths typically collected from field instruments and when movement behaviours are similar between movement states. Simulation with varying lengths of times series data and contrast between average movements within each state was used to test the HMMs ability to estimate movement parameters. 4. To demonstrate the methods in a realistic setting, the HMMs were used to categorize resident and migratory phases and the relationship between movement behaviour and ocean temperature using electronic tagging data from southern bluefin tuna ( Thunnus maccoyii). Diagnostic tools to evaluate the suitability of different models and inferential methods for investigating differences in behaviour between individuals are also demonstrated. [ABSTRACT FROM AUTHOR]

• To better understand invasion dynamics, it is essential to determine the influence of genetics and ecology in species persistence in both native and nonnative habitats. One approach is to assess patterns of selection on floral and growth traits of individuals in both habitats. • Mimulus guttatus (Phrymaceae) has a mixed mating system and grows under variable water conditions across its native and nonnative range in North America. Field investigations of patterns of selection of floral and plant size traits were conducted in two native and two nonnative populations. Field-collected seed was grown and crossed in the glasshouse using a paternal half-sib design. The resulting offspring were grown in saturated and dry-down low-water conditions and the same traits were measured in both environments. • Patterns of selection varied across years in the native range. Nonnative populations exhibited selection for increased floral size, consistent with the hypothesis that selection favors larger size in nonnative habitats. In the glasshouse, we detected genetic variation for traits across population/treatment combinations. However, size hierarchy in the glasshouse was dependent on water conditions. • Our results suggest that both variable selection pressures and local adaptation probably influence the persistence of both native and nonnative populations. [ABSTRACT FROM AUTHOR]

Aim To explore variation in the number of vertebrae in fishes in the context of Jordan’s rule and other ecogeographical rules. Location Global. Methods The study is based on literature review. Results The number of vertebrae varies very widely across the diversity of fishes. Jordan’s rule states that vertebral number increases with latitude, and this is widely attributed to ambient temperatures during ontogeny of individual fishes. However, the number of vertebrae may depend on both the ontogenetic environment and inheritance. Diverse other aspects of fish development and ecology are suggested as influencing vertebral number, including fish size, phyletic position, body shape and swimming mode. Main conclusions The number of different factors that influence the number of vertebrae in fishes makes for highly complex patterns of variation, and means that unravelling causes is difficult. The question needs to be addressed at the population/species/species group scale; moreover, the lack of discrimination between environmental and inherited causes of variation adds to the complexity. [ABSTRACT FROM AUTHOR]

The article addresses criticisms of the BIODEPTH project, a biodiversity and ecosystem functioning research in Great Britain. It shows that patterns for legume species are not generally consistent with the multispecies sampling effect for legumes proposed by Huston & McBride in 2002. The BIODEPTH results are not also consistent with transient biodiversity effects. Researchers propose that the conflict in the results of biodiversity experiments and observational biodiversity studies arises because they use different approaches to address different questions.

Plant phenotypes often differ in their resistance to natural enemies, but the mechanism for this has seldom been identified. The aim of this study was to determine if the spatial patterns of phenotype use of a highly specialized insect herbivore (the galling sawfly Pontania triandrae) in a natural willow population can be related to phenotypic variation in plant secondary chemistry. Furthermore, we tested if traits that confer resistance to one type of natural enemy, i.e. the galling sawfly, also confer resistance to others, in our case a leaf beetle Gonioctena linnaeana and the rust fungus Melampsora amygdalinae. We identified 18 phenotypes with high and 18 phenotypes with low gall density in our field population and determined gall densities, the degree of leaf damage and rust infection on each phenotype and collected leaves for chemical analyses. The concentration of phenolics was higher in phenotypes with high density of galls suggesting that this galling sawfly may use phenolics as oviposition cues. Rust infection showed the opposite pattern, with lower levels on clones with high concentration of phenolics, while leaf damage by G. linnaeana did not differ between clone types. This indicates that these important natural enemies may assert divergent selection on willow phenotypes and that this might provide a mechanism for maintaining phenotypic variation within willow populations. [ABSTRACT FROM AUTHOR]

Individual traits are often assumed to be linked in a straightforward manner to plant performance and processes such as population growth, competition and community dynamics. However, because no trait functions in isolation in an organism, the effect of any one trait is likely to be at least somewhat contingent on other trait values. Thus, to the extent that the suite of trait values differs among species, the magnitude and even direction of correlation between values of any particular trait and performance is likely to differ among species. Working with a group of clonal plant species, we assessed the degree of this contingency and therefore the extent to which the assumption of simple and general linkages between traits and performance is valid. To do this, we parameterized a highly calibrated, spatially explicit, individual-based model of clonal plant population dynamics and then manipulated one trait at a time in the context of realistic values of other traits for each species. The model includes traits describing growth, resource allocation, response to competition, as well as architectural traits that determine spatial spread. The model was parameterized from a short-term (3 month) experiment and then validated with a separate, longer term (two year) experiment for six clonal wetland sedges, Carex lasiocarpa, Carex sterilis, Carex stricta, Cladium mariscoides, Scirpus acutus and Scirpus americanus. These plants all co-occur in fens in southeastern Michigan and represent a spectrum of clonal growth forms from strong clumpers to runners with long rhizomes. Varying growth, allocation and competition traits produced the largest and most uniform responses in population growth among species, while variation in architectural traits produced responses that were smaller and more variable among species. This is likely due to the fact that growth and competition traits directly affect mean ramet size and number of ramets, which are direct components of population biomass. In contrast, architectural and allocation traits determine spatial distribution of biomass; in the long run, this also affects population size, but its net effect is more likely to be mediated by other traits. Such differences in how traits affect plant performance are likely to have implications for interspecific interactions and community structure, as well as on the interpretation and usefulness of single trait optimality models. [ABSTRACT FROM AUTHOR]

The article presents a discussion on alternative stable states (ASS) in ecology. It argues the theories of R. K. Didham and colleagues regarding ASS of ecological communities. It also cites the three major criteria for ASS such as it must be shown to occur in the same environment, the perturbation which causes the change in species composition must be applied as a pulse and must not cause a prolonged change in the environment, and it must be self sustaining. ASS has been discussed mainly for semi-arid rangelands.

Hubbell's neutral theory of biodiversity has generated much debate over the need for niches to explain biodiversity patterns. Discussion of the theory has focused on its neutrality assumption, i.e. the functional equivalence of species in competition and dispersal. Almost no attention has been paid to another critical aspect of the theory, the assumptions on the nature of the speciation process. In the standard version of the neutral theory each individual has a fixed probability to speciate. Hence, the speciation rate of a species is directly proportional to its abundance in the metacommunity. We argue that this assumption is not realistic for most speciation modes because speciation is an emergent property of complex processes at larger spatial and temporal scales and, consequently, speciation rate can either increase or decrease with abundance. Accordingly, the assumption that speciation rate is independent of abundance (each species has a fixed probability to speciate) is a more natural starting point in a neutral theory of biodiversity. Here we present a neutral model based on this assumption and we confront this new model to 20 large data sets of tree communities, expecting the new model to fit the data better than Hubbell's original model. We find, however, that the data sets are much better fitted by Hubbell's original model. This implies that species abundance data can discriminate between different modes of speciation, or, stated otherwise, that the mode of speciation has a large impact on the species abundance distribution. Our model analysis points out new ways to study how biodiversity patterns are shaped by the interplay between evolutionary processes (speciation, extinction) and ecological processes (competition, dispersal). [ABSTRACT FROM AUTHOR]

Allee effects can play a critical role in slowing or preventing the establishment of low density founder populations of non-indigenous species. Similarly, the spread of established invaders into new habitats can be influenced by the degree to which small founder populations ahead of the invasion front are suppressed through Allee effects. We develop an approach to use empirical data on the gypsy moth, a non-indigenous invader in North America, to quantify the Allee threshold across geographical regions, and we report that the strength of the Allee effect is subject to spatial and temporal variability. Moreover, we present what is to our knowledge the first empirical evidence that geographical regions with higher Allee thresholds are associated with slower speeds of invasion. [ABSTRACT FROM AUTHOR]

Short-term, transient population dynamics can differ in important ways from long-term asymptotic dynamics. Just as perturbation analysis (sensitivity and elasticity) of the asymptotic growth rate reveals the effects of the vital rates on long-term growth, the perturbation analysis of transient dynamics can reveal the determinants of short-term patterns. In this article, I present a completely new approach to transient sensitivity and elasticity analysis, using methods from matrix calculus. Unlike previous methods, this approach applies not only to linear time-invariant models but also to time-varying, subsidized, stochastic, nonlinear and spatial models. It is computationally simple, and does not require calculation of eigenvalues or eigenvectors. The method is presented along with applications to plant and animal populations. [ABSTRACT FROM AUTHOR]

Despite the importance of community-structuring processes operating at both local and regional scales, there is relatively little work examining both forces within a single system. I used a combination of observational and experimental approaches to examine the processes structuring larval dragonfly distributions in lentic habitats that encompass a gradient of both permanence and top predator type. I compared the relative vulnerability of species to predators from different portions of this gradient to assess the role of predation as a local force structuring communities. I also assessed the role of regional processes on species’ distributions by examining species’ propensity to disperse to and colonize artificial ponds distributed across a landscape. In both studies I contrasted habitat specialist species, which had larvae restricted to permanent lakes, with habitat generalist species, which had larvae that occur broadly across the habitat permanence and top predator transition. Results from this work suggest that dispersal and colonization behavior were critical mechanisms restricting the distributions of habitat specialist species, but that predation may act to reinforce this pattern. The habitat specialists dispersed less frequently, colonized artificial ponds less often when they did reach them, and most moved shorter distances than the habitat generalist species. Habitat specialists were also more vulnerable than habitat generalists to an invertebrate top predator with which they do not co-exist. Results from these studies suggest that species distributions can be shaped by processes operating at both regional and local spatial scales. The role of dispersal and recruitment limitation may be generally underestimated as a force shaping species distributions and community structure across habitat gradients in which there is a transition in both the biotic interactions and the disturbance interval across that gradient. [ABSTRACT FROM AUTHOR]

The article discusses the effects of precipitation change on ecosystems. Almost all terrestrial biomes is influenced by the availability of water influences ecosystem structure and function in almost all terrestrial biomes. Precipitation is the main input of this limiting resource, which drives both biotic and abiotic processes. The inherent variability in precipitation is one of the grand challenges associated with studies of precipitation change. An increasing number of experiments are focusing on the interaction of precipitation change with other potential abiotic or biotic driving variables becuase many global changes are occuring simultaneously.

Range edges are of particular interest to ecology because they hold key insights into the limits of the realized niche and associated population dynamics. A recent feature of Oikos summarized the state of the art on range edge ecology. While the typical question is what causes range edges, another important question is how range edges influence the distribution of abundances across a species geographic range when dispersal is present. We used a single species population dynamics model on a coupled-lattice to determine the effects of dispersal on peripheral populations as compared to populations at the core of the range. In the absence of resource gradients, the reduced neighborhood and thus lower connectivity or higher isolation among populations at the range edge alone led to significantly lower population sizes in the periphery of the range than in the core. Lower population sizes mean higher extinction risks and lower adaptability at the range edge, which could inhibit or slow range expansions, and thus effectively stabilize range edges. The strength of this effect depended on the potential population growth rate and the maximum dispersal distance. Lower potential population growth rates led to a stronger effect of dispersal resulting in a higher difference in population sizes between the two areas. The differential effect of dispersal on population sizes at the core and periphery of the range in the absence of resource gradients implies that traditional, habitat-based distribution models could result in misleading conclusions about the habitat quality in the periphery. Lower population sizes at the periphery are also relevant to conservation, because habitat removal not only eliminates populations but also creates new edges. Populations bordering these new edges may experience declines, due to their increased isolation. [ABSTRACT FROM AUTHOR]

We investigated if dragonfly larvae community composition and species abundance curves are sensitive to variation in predation intensity, and whether the fit to a particular niche partitioning model could be used to make inferences about mechanisms structuring communities. The approach taken was to compare communities in lakes either having or lacking fish predation. Dragonfly species classified as active, strongly dominated the dragonfly communities in fishless lakes, and low active species dominated fishless lakes. As activity level is known to correlate with susceptibility to fish predation this indicates that these communities are structured by fish predation. Fitting relative abundance data to five niche partitioning models showed that the same model fitted data from both types of habitats (fish/no fish). This means that the observed differences in relative abundances were substitutive, i.e. the relative abundance of a rank stayed constant, even though the identity of the species having this rank changed. The best fit to data from both types of lakes was found for the random assortment model, which is usually interpreted as an indication that the community is not structured by within-guild interactions. This interpretation for fishless lakes did not seem to agree with other community measures (i.e. lowered diversity and evenness and no relationship between species richness and dragonfly biomass), which indicate that the community is structured by within-guild interactions. Moreover, a detail in the fitting procedure, the number of species included in the analysis, affected which model that fitted data best. Thus, we question if fitting niche partitioning models to data can provide mechanistic understanding of how resources are partitioned in natural communities. [ABSTRACT FROM AUTHOR]

Prediction of species’ distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species’ distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species’ occurrence data. Presence-only data were effective for modelling species’ distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve. [ABSTRACT FROM AUTHOR]

We explore the issues relevant to those types of ecosystems containing new combinations of species that arise through human action, environmental change, and the impacts of the deliberate and inadvertent introduction of species from other regions. Novel ecosystems (also termed ‘emerging ecosystems’) result when species occur in combinations and relative abundances that have not occurred previously within a given biome. Key characteristics are novelty, in the form of new species combinations and the potential for changes in ecosystem functioning, and human agency, in that these ecosystems are the result of deliberate or inadvertent human action. As more of the Earth becomes transformed by human actions, novel ecosystems increase in importance, but are relatively little studied. Either the degradation or invasion of native or ‘wild’ ecosystems or the abandonment of intensively managed systems can result in the formation of these novel systems. Important considerations are whether these new systems are persistent and what values they may have. It is likely that it may be very difficult or costly to return such systems to their previous state, and hence consideration needs to be given to developing appropriate management goals and approaches. [ABSTRACT FROM AUTHOR]

1. A central question in ecology is to separate the relative contribution of density dependence and stochastic influences to annual fluctuations in population size. Here we estimate the deterministic and stochastic components of the dynamics of different European populations of white stork Ciconia ciconia. We then examined whether annual changes in population size was related to the climate during the breeding period (the ‘tap hypothesis’ sensu Sæther, Sutherland & Engen (2004, Advances in Ecological Research, 35, 185–209) or during the nonbreeding period, especially in the winter areas in Africa (the ‘tube hypothesis’). 2. A general characteristic of the population dynamics of this long-distance migrant is small environmental stochasticity and strong density regulation around the carrying capacity with short return times to equilibrium. 3. Annual changes in the size of the eastern European populations were correlated by rainfall in the wintering areas in Africa as well as local weather in the breeding areas just before arrival and in the later part of the breeding season and regional climate variation (North Atlantic Oscillation). This indicates that weather influences the population fluctuations of white storks through losses of sexually mature individuals as well as through an effect on the number of individuals that manages to establish themselves in the breeding population. Thus, both the tap and tube hypothesis explains climate influences on white stork population dynamics. 4. The spatial scale of environmental noise after accounting for the local dynamics was 67 km, suggesting that the strong density dependence reduces the synchronizing effects of climate variation on the population dynamics of white stork. 5. Several climate variables reduced the synchrony of the residual variation in population size after accounting for density dependence and demographic stochasticity, indicating that these climate variables had a synchronizing effect on the population fluctuations. In contrast, other climatic variables acted as desynchronizing agents. 6. Our results illustrate that evaluating the effects of common environmental variables on the spatio-temporal variation in population dynamics require estimates and modelling of their influence on the local dynamics. [ABSTRACT FROM AUTHOR]

Determining the factors that influence migratory population abundance has been constrained by the inability to connect events in different periods of the annual cycle. Carry-over effects are events that occur in one season but influence individual success the following season and recent empirical evidence suggests that they may play an important role in migratory population dynamics. Using a long distance migratory shorebird as an example, I incorporate carry-over effects and changes in the relative amount of habitat quality into a density-dependent equilibrium population model. The model uses the example where the quality of habitat on the wintering grounds (nonbreeding season) influences breeding output the following summer (breeding season). Carry-over effects, however, may be manifested in a number of other ways that could influence population dynamics. In the simulations, population declines occur when habitat is lost on the wintering grounds. However, results show that carry-over effects can magnify these declines when a disproportionate amount of high quality habitat is lost the previous winter. Simulations also show that carry-over effects can have a relative, positive impact on population size when the majority of habitat that is lost in the previous season is low quality. In this case, the carry-over interacts with density-dependence the following season producing an additive and positive effect, buffering the population from severe declines. To predict changes in population size of migratory animals, it will be important to determine (i) which demographic factors in which season produce strong carry-over effects and, (ii) not just the amount, but the relative quality of habitat that is lost. If carry-over effects are significant, they could potentially mitigate‘seasonal compensation effects’ from density-dependence, leading to exacerbated population declines. [ABSTRACT FROM AUTHOR]

Conventional theories of population and community dynamics are based on a single currency such as number of individuals, biomass, carbon or energy. However, organisms are constructed of multiple elements and often require them (in particular carbon, phosphorus and nitrogen) in different ratios than provided by their resources; this mismatch may constrain the net transfer of energy and elements through trophic levels. Ecological stoichiometry, the study of the balance of elements in ecological processes, offers a framework for exploring ecological effects of such constraints. We review recent theoretical and empirical studies that have considered how stoichiometry may affect population and community dynamics. These studies show that stoichiometric constraints can affect several properties of populations (e.g. stability, oscillations, consumer extinction) and communities (e.g. coexistence of competitors, competitive interactions between different guilds). We highlight gaps in general knowledge and focus on areas of population and community ecology where incorporation of stoichiometric constraints may be particularly fruitful, such as studies of demographic bottlenecks, spatial processes, and multi-species interactions. Finally, we suggest promising directions for new research by recommending potential study systems (terrestrial insects, detritivory-based webs, soil communities) to improve our understanding of populations and communities. Our conclusion is that a better integration of stoichiometric principles and other theoretical approaches in ecology may allow for a richer understanding of both population and community structure and dynamics. [ABSTRACT FROM AUTHOR]

Copyright of Conservation Biology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Conservation Biology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Species composition, population structure and the seed banks of the perennial grasses Aristida bipartita, Bothriochloa insculpta, Heteropogon contortus, Themeda triandra and Urochloa mosambicensis, were described for nine sites in mesic savanna grasslands (seed banks for five) on a similar soil type ranging in grazing history, from sustained heavy grazing (>20 years) to light grazing. The influence of two seasons of grazing on the seed production and the seed bank of Themeda, Setaria incrassata, Heteropogon, Aristida. Bothriochloa and Digitaria eriantha, was estimated at two other sites. Compositional variation reflected grazing history. Lightly grazed sites were characterized by the longer-lived, palatable perennials Themeda, Bothriochloa. Heteropogon and Digitaria, and heavily grazed sites by the shorter-lived perennials Urochloa, Sporobolus nitens, Chloris virgata, the unpalatable Aristida, and some forb species. Grass tuft size declined with increasing grazing pressure. Sustained heavy grazing reduced or eliminated Themeda. Bothriochloa and Heteropogon from the seed bank, but increased the abundance of Aristida and Urochloa spp. Rainfall influenced the seasonal pattern of seed production, which decreased with intra-seasonal drought. The number of seeds produced m−² of tuft basal area varied from 21000 for Setaria to 1,9 million for Aristida. Annual seed production m −² of ground with light grazing was <400 for Themeda. for Heteropogon, 13004000 for Setaria, >10000 for Aristida, and 300 for Bothriochloa. Seed viability varied from zero for Digitaria to 68% for Setaria, and varied within a season for Themeda (24–49%) and Setaria (26–68%). The seeds of all species tested possessed a period of innate dormancy of < 1 year. Seven to ten grass and six to seven forb species were found in the seed banks at two sites. Perennial grasses constituted 85–95% of the seed bank. with >90% of all seeds occurring in the top 2 cm of soil. Seed density differed markedly between sites and grazing treatments. A simple model of the seed bank dynamics of the perennial grasses showed that because their seeds germinate readily and have a limited survival when in secondary, dormancy, the seed bank size is determined primarily by the abundance of the species in the vegetation. Thus, the seed banks of Themeda and Heteropogon, which produce small numbers of seeds, can easily be eliminated by sustained grazing. This was also indicated by the distribution of these two species along the gradient of grazing history. [ABSTRACT FROM AUTHOR]

The article offers information on the multivariate methods in plant ecology. Association-analysis in plant communities was conducted using the method developed by D. W. Goodall in 1953. Goodall developed the utility of interspecific associations for sorting quadrants into groups is based on definition of a homogeneous unit of vegetation as one in which all species-associations are indeterminate or non-significant. Details related to the ecological information obtained from two heathland communities are presented, followed by discussion on the conclusion that a method by Goodall is likely to prove a very useful tool in primary survey.

The article talks about the concepts and criteria used for the recognition of biotic communities. These concepts describe the fundamental use of the ecological units established by Clements and Shelford, which are used by many American and British authors. The definitions of the concepts, including association abstract, abstract communities and associes abstract, are offered. The subdivisions of the biotic formation (biome), which includes the perennial nucleus, seasonal societies of communities, and intradiel communities, are discussed.

The article describes the relict method in dynamic ecology. It discusses ecological methods for the field and the indicator method and its applications. A relict is defined as a community or fragment of one that has survived some change, often to become an integral part of the existing vegetation. It offers information on the nature of relicts, shrinkage of climaxes and utilisation and interpretation. The two kinds of relict communities re those due to climatic pulsations and those produced by human coactions. It stresses the importance when applying the relict method to the interpretation of a particular climax to realise that the structure of the latter is a mosaic of climatic, seral and coactive effects.

The article discusses the ecology of lichen. It says that fungus is one component of lichen thallus, usually lived during its vegetative stages inside dead or living organic matter and thus away from the light. It also says that lichen is hydrophilous, hygrophilous and saprophytic. The article noted that lichen is composed of algae and fungus and can live in the driest, coolest and most exposed localities, where no organic matter can be detected in the substratum. Moreover, lichen have been enabled to adapt themselves very closely to the new conditions by which they are surrounded and, more than other plants, they can alter their structure and mode of living directly and individually to suit their new life.

The article presents a reply to the comments of J. M. Jeschke, M. Kopp and R. Tollrian regarding time and energy constraints in ecology. It acknowledges the classifications in handling-limited and digestion-limited predators was not meant to apply to typical field conditions. It mentions that seven out of fourteen mammal and bird examples cited to demonstrate that digestion-limitation of the wide majority of predators were based on field studies. It calls for research in the time of demanding conditions to determine what constrains time-energy budgets in wild animals.