The ecological consequences of biodiversity loss have aroused considerable interest and controversy during the past decade. Major advances have been made in describing the relationship between species diversity and ecosystem processes, in identifying functionally important species, and in revealing underlying mechanisms. There is, however, uncertainty as to how results obtained in recent experiments scale up to landscape and regional levels and generalize across ecosystem types and processes. Larger numbers of species are probably needed to reduce temporal variability in ecosystem processes in changing environments. A major future challenge is to determine how biodiversity dynamics, ecosystem processes, and abiotic factors interact.

Summary1 The invasion of habitats by non-native plant and animal species is a global phenomenon with potentially grave consequences for ecological, economic, and social systems. Unfortunately, to date, the study of invasions has been primarily anecdotal and resistant to generalization. 2 Here, we use insights from experiments and from long-term monitoring studies of vegetation to propose a new theory in which¯uctuation in resource availability is identi®ed as the key factor controlling invasibility, the susceptibility of an environment to invasion by non-resident species. The theory is mechanistic and quantitative in nature leading to a variety of testable predictions. 3 We conclude that the elusive nature of the invasion process arises from the fact that it depends upon conditions of resource enrichment or release that have a variety of causes but which occur only intermittently and, to result in invasion, must coincide with availability of invading propagules.

Summary0 It is useful to distinguish between the immediate e}ects of species richness on ecosystems and those which become apparent on a longer time scale\ described here as _lter and founder e}ects[ 1 Relationships between plant diversity and ecosystem properties can be explored by classifying component species into three categories Ð dominants\ subordinates and transients[ Dominants recur in particular vegetation types\ are relatively large\ exhibit coarse!grained foraging for resources and\ as individual species\ make a substantial contribution to the plant biomass[ Subordinates also show high _delity of association with particular vegetation types but they are smaller in stature\ forage on a more restricted scale and tend to occupy microhabitats delimited by the architecture and phenology of their associated dominants[ Transients comprise a heterogeneous assort! ment of species of low abundance and persistence^a high proportion are juveniles of species that occur as dominants or subordinates in neighbouring ecosystems[ 2 A {mass ratio| theory proposes that immediate controls are in proportion to inputs to primary production\ are determined to an overwhelming extent by the traits and functional diversity of the dominant plants and are relatively insensitive to the richness of subordinates and transients[ Recent experiments support the mass ratio hypothesis and the conclusion of Huston "0886# that claims of immediate bene_ts of high species richness to ecosystem functions arise from misinterpretation of data[ 3 Attribution of immediate control to dominants does not exclude subordinates and transients from involvement in the determination of ecosystem function and sustainability[ Both are suspected to play a crucial\ if intermittent\ role by in~uencing the recruitment of dominants[ Some subordinates may act as a _lter in~uencing regeneration by dominants following major perturbations[ 4 Transients originate from the seed rain and seed banks and provide an index of the pool of potential dominants and subordinates at speci_c sites[ Where the landscape carousel operates against a background of declining diversity in the reservoir of colonizing transients\ we may predict that a progressive loss of ecosystem functions will arise from the decline in the precision with which dominants can engage in the re!assembly and relocation of ecosystems[ Keywords] biodiversity\ dominance\ ecosystem function\ landscape ecology\ regen! eration Journal of Ecology "0887# 75\ 891Ð809

No abstract

Question: A set of easily-measured ('soft') plant traits has been identified as potentially useful predictors of ecosystem functioning in previous studies. Here we aimed to discover whether the screening techniques remain operational in widely contrasted circumstances, to test for the existence of axes of variation in the particular sets of traits, and to test for their links with 'harder' traits of proven importance to ecosystem functioning. Location: central-western Argentina, central England, northern upland Iran, and northeastern Spain. Recurrent patterns of ecological specialization: Through ordination of a matrix of 640 vascular plant taxa by 12 standardized traits, we detected similar patterns of specialization in the four floras. The first PCA axis was identified as an axis of resource capture, usage and release. PCA axis 2 appeared to be a size-related axis. Individual PCA for each country showed that the same traits remained valuable as predictors of resource capture and utilization in all of them, despite their major differences in climate, biogeography and land-use. The results were not significantly driven by particular taxa: the main traits determining PCA axis 1 were very similar in eudicotyledons and monocotyledons and Asteraceae, Fabaceae and Poaceae. Links between recurrent suites of 'soft' traits and 'hard' traits: The validity of PCA axis 1 as a key predictor of resource capture and utilization was tested by comparisons between this axis and values of more rigorously established predictors ('hard' traits) for the floras of Argentina and England. PCA axis 1 was correlated with variation in relative growth rate, leaf nitrogen content, and litter decomposition rate. It also coincided with palatability to model generalist herbivores. Therefore, location on PCA axis 1 can be linked to major ecosystem processes in those habitats where the plants are dominant. Conclusion: We confirm the existence at the global scale of a major axis of evolutionary specialization, previously recog-nised in several local floras. This axis reflects a fundamental trade-off between rapid acquisition of resources and conservation of resources within well-protected tissues. These major trends of specialization were maintained across different environmental situations (including differences in the proximate causes of low productivity, i.e. drought or mineral nutrient deficiency). The trends were also consistent across floras and major phylogenetic groups, and were linked with traits directly relevant to ecosystem processes.