Search

1 Interactions among plants strongly influence the structure and dynamics of plant populations and communities. However, most empirical studies of plant–plant interactions failed to make repeated measures of responses to neighbouring individuals and thereby neglected possible changes in interactions throughout the life history of the plants. 2 We tested the hypothesis that competition between annual species intensifies from early to late life-history stages, by sequentially measuring interactions in neighbour-removal experiments at three study sites located along a rainfall gradient in Israel. 3 Two annual species, Biscutella didyma and Hymenocarpos circinnatus, grew with and without neighbours in their natural habitats. Five response variables representing consecutive life-history stages (seedling survival, juvenile biomass, adult survival, number of seeds and final biomass) were recorded throughout the whole growing season. 4 The direction and intensity of interactions varied considerably between environments and life stages. On average, growth-related response variables indicated higher competition intensity at the productive end of the climatic gradient, while survival indicated either facilitation at the dry end or no trend along the gradient. 5 Temporal changes occurred, with moderate facilitation soon after germination shifting to strong competition at the end of the growing season. 6 Our results demonstrate that the outcome of experimental studies on plant–plant interactions may depend not only on the environmental productivity but more so on the life stage at which the target plant is studied. [ABSTRACT FROM AUTHOR]

Parental effects ( PE) can be adaptive and improve offspring performance when parents and offspring experience similar environmental conditions. However, it is unknown whether adaptive PE exist also in habitats where such similarity is unlikely due to strong temporal variation. In particular, we do not know whether PE can adapt offspring to fluctuating levels of neighbour competition in such habitats., Here, we tested for adaptive PE in terms of two key environmental factors in a semi-arid annual system, competition and drought. While rainfall was stochastic in the study site, the competitive environment was partly predictable: higher plant densities followed after favourable (rainy) years due to high seed production. We therefore expected PE to adapt the offspring's competitive ability to these (predictable) fluctuations in plant densities, rather than to adapt the offspring's drought tolerance to the (unpredictable) occurrence of intensified drought., Parental plants of Biscutella didyma, an annual Brassicaceae, were raised under favourable watering and under drought conditions. Offspring performance was then tested under a full-factorial combination of two neighbour regimes and six watering levels in the glasshouse., Offspring of parents grown under favourable conditions were stronger competitors. This was associated with a small shift in phenology but not with higher parental seed provisioning. Offspring from parents grown under drought showed no improved drought tolerance. Moreover, no PE were detectable when offspring were grown without neighbours., Our results suggest a novel path of adaptive PE: higher competitive ability was induced in offspring that were more likely to experience high neighbour densities. Together with the lack of adaptive PE towards drought tolerance, this emphasizes that a correlation between parental and offspring environment is crucial for adaptive PE to evolve. Our results also call for the inclusion of competitive effects in future PE studies., Synthesis. This study demonstrates the important role of adaptive PE for plant fitness (regarding competition) but also their limits (regarding drought) in temporally variable environments, based on the predictability of the respective environmental factor. [ABSTRACT FROM AUTHOR]

1. Interactions among neighbouring plants are often mediated by foraging choices of pollinators. For example, the presence of a conspicuous species may increase the number of pollinators attracted to its vicinity, indirectly increasing visitation rates also to neighbouring plants. Because pollinator choices are frequently density-dependent, the presence of a conspicuous species at high densities may also increase competition for pollination services. Additionally, models predict that plant density will interact with spatial distribution in manipulating the pollinator behaviour, yet experimental evidence for this effect is missing. 2. We performed a field experiment in which we introduced a highly conspicuous species in different densities and spatial configurations in a full-factorial manner into a species-rich meadow and studied its effect on neighbouring plants. 3. We showed that the highly conspicuous species strongly contributed to the attractiveness of its local patch and thus benefited its neighbours. However, because of the strong density effect, the conspicuous species changed its role and became a competitor for pollinators when its density increased. 4. We supported our theoretical assumptions and showed that when the introduced conspicuous species was regularly distributed among other plants in the patch, it increased visitation rate, and in some cases also seed set, to conspicuous neighbours relative to when it was aggregated, at least at low densities. 5. Synthesis. We suggest that complex interactions between density and spatial distribution of plant species at the patch scale are highly relevant for the interpretation of pollinator behaviour and therefore should be treated as factors of floral attractiveness in future studies. [ABSTRACT FROM AUTHOR]