Overcompensation and adaptive plasticity of apical dominance in Erysimum strictum (Brassicaceae) in response to simulated browsing and resource availability

Abstract

J. 2005. Overcompensation and adaptive plasticity of apical dominance in Erysimum strictum (Brassicaceae) in response to simulated browsing and resource availability. Á/ Oikos 111: 179 Á/191.In the cases where overcompensation has been observed in monocarpic herbs, overcompensation is associated with an apically dominant shoot architecture of intact plants, increased lateral branching following herbivory, and increased reproductive success as a consequence of damage. The compensatory continuum hypothesis expects overcompensation to be more prevalent in resource rich environments compared to poor environments. This is paradoxical since in resource rich conditions the intact plants should branch most vigorously and hence any further increase in branch number should lead to lower seed yield. An explanation could be that apical dominance is rather insensitive to changes in resource availability, and that overcompensation is possible in conditions where plants experience meristem limitation (due to apical dominance) in relation to available resources.We explored the branching patterns and fitness responses of tall wormseed mustard (Erysimum strictum ) to simulated browsing, soil nutrients, and competition in common garden. Competition increased apical dominance and reduced plant fitness whereas fertilization had the reverse effects. Simulated browsing increased lateral branching and had little impact on plant fitness. Fitness overcompensation was observed only among plants grown in competition and in the absence of fertilization Á/ the most resource poor treatment combination in the experiment. The results contradict both with the compensation continuum and the assumption that apical dominance shows no or very little plasticity in relation to growing conditions. Because directional selection gradients on branch number were invariantly positive irrespective of growing conditions, we propose that, in spite of phenotypic plasticity of apical dominance, the plants appear to be meristem rather than resource limited, and that meristem limitation is strongest in conditions where intact plants produce fewest lateral branches. Our results deviate from the compensation continuum because resource availability affected compensation ability more strongly through phenotypic plasticity of shoot architecture rather than via changes in resource availability per se.

Overcompensation in response to simulated herbivory in the perennial herb Sedum maximum

“…For example, Bergelson and Crawley (1992) and Bergelson et al (1996) criticized the suggestion by Paige and Whitham (1987) that the herb Ipomopsis aggregata may benefit from its ungulate herbivores, and attributed their finding of benefits to methodological limitations. However, more recent studies in different experimental designs in this (Paige 1999) and other systems (Lennartsson et al 1998;Rautio et al 2005) provide more solid support for overcompensation. According to Järemo et al (1999), differences in fitness definitions may account for the apparent discrepancy between the existence of overcompensation and the fact that plants cannot benefit directly from their consumers.…”

“…This is the first report of overcompensation in an iteroparous perennial plant in which future costs of herbivore-induced reproduction are explicitly measured. Previously, this phenomenon was known in monocarpic plants such as Ipomopsis aggregata (Paige and Whitham 1987), Sanicula arctopoides (Lowenberg 1994), Gentianella campestris (Lennartsson et al 1997), Raphanus raphanistrum (Agrawal et al 1999) and Erysimum strictum (Rautio et al 2005). Studies on iteroparous perennials that report a positive effect of herbivores on plant reproduction are usually based on the data from a single growing season and overlook future consequences of enhanced reproduction (Hicks and Turkington 2000;Gao et al 2008).…”

“…If herbivory triggers the growth of dormant buds, then the response should be more likely under higher competition and in low-resource environments. Under highresource conditions, plants exhibit more branched architecture by preserving fewer dormant buds, which results in lower herbivory tolerance (Rautio et al 2005). Wise and Abrahamson (2005) attempted to unify these different approaches, proposing a model differentiating between resources that limit plant fitness and those that are affected by herbivores.…”

“…All the above models were constructed for monocarps. The empirical evidence of overcompensation mostly concerns plants with a single bout of seed production (Paige and Whitham 1987;Lowenberg 1994;Lennartsson et al 1997;Agrawal et al 1999;Rautio et al 2005), the reason being that comparing reproductive output of grazed plants with that of non-grazed plants is relatively straightforward in monocarps. The aim of this study was to examine whether overcompensation in terms of current and future performance can be observed in iteroparous perennial plants.…”

Effects of living crown reduction on needle element status of Scots pine

“…Foliar analysis is a widely used method for evaluating nutritional and environmental status of trees, although with some reservations (Morrison 1974, Ballard and Carter 1986, Rautio 2000, Brockley 2001, Luyssaert et al 2004, Mertens et al 2005. Analysis of the elemental composition of foliage can provide additional information as a biomonitoring method in special cases (Manning &Feder 1980, Oliva andMingorance 2006).…”