SummaryBased on empirical evidence from the literature we propose that, in nature, phenotypic plasticity in plants is usually expressed at a subindividual level. While reaction norms (i.e. the type and the degree of plant responses to environmental variation) are a property of genotypes, they are expressed at the level of modular subunits in most plants. We thus contend that phenotypic plasticity is not a whole-plant response, but a property of individual meristems, leaves, branches and roots, triggered by local environmental conditions. Communication and behavioural integration of interconnected modules can change the local responses in different ways: it may enhance or diminish local plastic effects, thereby increasing or decreasing the differences between integrated modules exposed to different conditions. Modular integration can also induce qualitatively different responses, which are not expressed if all modules experience the same conditions. We propose that the response of a plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to integration. The local response rules to environmental variation, and the modular interaction rules may be seen as evolving traits targeted by natural selection. Following this notion, whole-plant reaction norms are an integrative by-product of modular plasticity, which has far-reaching methodological, ecological and evolutionary implications.

Summary1 Long-distance dispersal events are biologically very important for plants because they aect colonization probabilities, the probabilities of population persistence in a fragmented habitat, and metapopulation structure. They are, however, very dicult to investigate because of their low frequency. We reviewed the use of molecular markers in the population genetics approach to studying dispersal. With these methods the consequences of long-distance dispersal are studied, rather than the frequency of the dispersal events themselves. 2 Molecular markers vary, displaying dierent amounts of variation and dierent modes of inheritance: they may be either dominant or codominant, and may or may not be subjected to genetic recombination. Use of markers has inspired the development of maximum likelihood techniques that take the evolutionary history of alleles into account while estimating gene¯ow. 3 Inferring seed dispersal rates from indirect measurements of gene¯ow involves three steps: (i) quantifying genetic dierentiation among populations and using this to estimate the rate of gene¯ow; (ii) producing a genetic dispersal curve by regressing geographical distance among populations against the amount of gene¯ow; and (iii) separating seed-mediated from pollen-mediated gene¯ow, by comparing dierentiation in nuclear vs. cytoplasmic molecular markers. In this way, potentially very low levels of gene¯ow can be detected. 4 The indirect approach is based on a number of assumptions. The validity of each assumption should be assessed by independent methods or the estimates of genē ow and dispersal should be mainly used in a comparative context. In metapopulations, with frequent extinction and colonization, the relationship between genetic dierentiation and gene¯ow is not straightforward, and other methods should be used. 5 Highly variable molecular markers, especially microsatellites, have facilitated a direct genetic approach to measuring gene¯ow, based on parental analyses. 6 The population genetic approach provides dierent information about dispersal than ecological methods. Thus population genetic and ecological methods may supplement each other, and together lead to a better insight into the dispersal process than either of the methods on its own.

Elasticity is a perturbation measure in matrix projection models that quantifies the proportional change in population growth rate as a function of a proportional change in a demographic transition (growth, survival, reproduction, etc.). Elasticities thus indicate the relative “importance” of life cycle transitions for population growth and maintenance. In this paper, we discuss the applications of elasticity analysis, and its extension, loop analysis, in life history studies and conservation. Elasticity can be interpreted as the relative contribution of a demographic parameter to population growth rate. Loop analysis reveals the underlying pathway structure of the life cycle graph. The different kinds of results of the two analyses in studies of life histories are emphasized. Because elasticities quantify the relative importance of life cycle transitions to population growth rate, it is generally inferred that management should focus on the transitions with the largest elasticities. Such predictions based on elasticities seem robust, but we do identify three situations where problems may arise. The mathematical properties and biological constraints that underlie these pitfalls are explained. Examples illustrate the additional information that needs to be taken into account for a sensible use of elasticities in population management. We conclude by indicating topics that are in need of research.

Summary 1The diversity and abundance of viable diaspores trapped at the downstream end of a 15-km lowland stream were quantified and related to five potentially predicting variables: species' occurrence in the species pool, distance to the nearest stand and the life-history traits seed buoyancy, seed production and plant height. 2 From 126 samples, 106 614 individuals of vascular plants developed, 95.8% from vegetative diaspores and 4.2% from seeds. Among these plants, three free-floating, 12 submerged, 22 emergent (aquatic) and 70 riparian (semi-aquatic and terrestrial) species were recorded, respectively, accounting for 24.3%, 71.9%, 1.2% and 2.6% of the total number of viable diaspores trapped. 3 Of the free-floating, submerged and emergent species, 100%, 98.9% and 23.7% of the diaspores were vegetative, respectively, whereas it was 2.9% for riparian species. 4 Diaspores of 79% of the total number of aquatic species and 40% of riparian species observed in the established vegetation were trapped. Minimal dispersal distances ranged from 0 to 6 km. 5 Multiple regression analysis conducted for submerged species, showed that 71% of the variation in the diaspore pool could be predicted by occurrence of species in the vegetation. For emergent species, seed production and occurrence of species explained 54% of the variation, seed production being most important. Mean seed buoyancy of emergent species was higher than that of the other groups. For riparian species, seed production, occurrence and buoyancy explained 48% of the variation in the diaspore pool. Seed production per plant was the most important variable. Linear regression revealed a negative relationship between distance and abundance of the diaspore pool for submerged and riparian species. 6 We conclude that the occurrence of species in the species pool is a significant predictor for the dispersal of free-floating and submerged aquatics that rely on vegetative propagation. Seed production and buoyancy are of additional importance with regard to emergent aquatics. Riparian species with a limited terrestrial dispersal capacity may largely extend their range by hydrochory. That is, if they produce large amounts of (small) seeds and provided that these can reach the water body. Buoyancy and high frequency and abundance in the established vegetation promote this dispersal capacity as well.

Summary1 Restored floodplains and backwaters lacking a viable propagule bank, may need flood pulses to facilitate inward dispersal of diaspores. Temporal patterns of hydrochorous plant dispersal are, however, not well known. 2 Diversity and abundance of diaspores dispersed in a water body over 12 months were quantified using a 200 µ m net in order to: (i) test for a relationship between discharge and the number of species and diaspores dispersed; (ii) examine the effect of seed buoyancy and seed release period on the length of the dispersal period; and (iii) test whether diaspores of species that disperse during a similar period of the year are characterized by similar dispersal and dormancy traits. 3 A total 359 188 individuals of 174 vascular species developed from 144 samples, with most (90%) from vegetative diaspores and only 10% from seeds. Mean number of species and diaspores varied between months in parallel with discharge levels. Stepwise multiple regression analysis showed that both seed buoyancy and seed release influenced dispersal periods. 4 In general, species that dispersed most diaspores in spring and summer had nondormant seeds, a shorter seed release period and a shorter seed dispersal period than species whose dormant seeds dispersed in autumn and winter. Vegetative diaspores were dispersed on average over 8 months, indicating their importance to long-distance dispersal. Several species dispersed both generative and vegetative diaspores, often in different seasons. 5 Our results may assist the planning of regenerative processes in riverine wetlands at landscape scales, as dispersal phenology, and discharge rates must be taken into consideration. Vegetative diaspores may be more important than seeds, although the latter may extend the species dispersal period into other seasons. Temporal heterogeneity in diaspore dispersal influences the identity of diaspores reaching restored habitats.