Ontogenetic shifts in interactions among annual plants

Abstract

Summary 1Interactions 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 neighbourremoval 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.

Ontogenetic shifts in trait‐mediated mechanisms of plant community assembly

“…Such trait-based ontogenetic trade-offs may equalize overall performance and promote coexistence of functionally diverse competitors. The role of species interactions, such as competition and herbivory, in driving community assembly may also be life-stage specific and thus obscured if ontogeny is overlooked (Werner and Gilliam 1984, Schiffers and Tielbo¨rger 2006, Moll and Brown 2008, Armas and Pugnaire 2009, Piao et al 2013, Baraba´s et al 2014. Niche partitioning along functional trait axes may enable species to coexist, as evidenced by better performance when surrounded by neighbors with divergent trait values (Uriarte et al 2010, Lasky et al 2014a).…”

Biomass explains the intensity of facilitative – not competitive – interactions: three intraspecific tests with annuals

“…We used leaf number as a non-destructive measure for aboveground biomass, because it is highly correlated with biomass (Schiffers and Tielbörger, 2006). We confirmed this and, hence, equations obtained from significant quadratic regressions with intercept zero were used for the estimation of target biomass at each measuring date.…”

“…Holzapfel et al, 2006;Li et al, 2010) and few studies have looked at facilitative interactions within a life form or even species (e.g. Schiffers and Tielbörger, 2006;Leger and Espeland, 2010). Some support for our interpretation about the facilitative mechanism can be found in studies observing lower temperatures and decreased evaporation from the soil surface due to herbaceous plant cover (e.g.…”

“…From previous studies we know that annual plant populations along the gradient differ in morphological and phenological traits as well as in competitive response ability (Petrů et al, 2006;Schiffers and Tielbörger, 2006;Liancourt and Tielbörger, 2009). To ensure natural breaking of summer dormancy, collected seeds were placed in bags of transparent, permeable synthetic fabric and attached to the ground surface at their respective sites of origin (as in Liancourt and Tielbörger, 2009).…”

“…Miriti, 2006;Schiffers and Tielbörger, 2006) and have sometimes been attributed to increasing biomass with age, there are virtually no studies that directly relate such changes to the size of all interacting individuals through time (but see Weigelt et al, 2002). Therefore, we still do not know whether or not biomass determines shifts in competition intensity through a plant's lifetime.…”