Ontogenetic shifts in plant ecological strategies

Abstract

Ontogenetic shifts in plants are ubiquitous, but their ecological and evolutionary significance remain largely unknown. Juveniles have few opportunities to accumulate sufficient biomass to withstand damage, whereas adults allocate resources to reproduction. Thus, age‐specific environmental filters are expected to drive selection towards specific resource‐investment strategies for each developmental stage. We tested whether species exhibited strategies that favour faster rates of biomass accumulation during early developmental stages to cope with vulnerability, shifting towards habitat‐dependent strategies to optimise resource acquisition and use later on. We also hypothesised that juveniles exhibit greater intraspecific variability of strategies than adults, as a result of continuous filtering of traits throughout the plant’s development towards adulthood. We measured key leaf traits—leaf area (LA), leaf dry matter content (LDMC) and specific leaf area (SLA)—and calculated scores for competitor (C), stress‐tolerator (S), ruderal (R) strategies of the CSR system for juveniles of 54 species and conspecific adults of 27 species naturally occurring either in unproductive (grassland) or productive (forest) habitats. Juveniles exhibited higher SLA and LA and lower LDMC, and thus a more R‐strategy in both habitats when compared with adults, but were not necessarily “R” in absolute terms. We also found smaller intraspecific variation for the R‐strategy in adults compared with juveniles in both habitats, whereas the variation of the other strategies was habitat dependent. Ontogenetic shifts in ecological strategies appear to have been selected as a response to ontogeny‐dependent filters. Thus, strategies that favour less costly leaves and faster growth rates (relatively R‐selected) in juveniles shift towards C and/or S strategies in adulthood, depending on habitat productivity. Nevertheless, habitat‐dependent specialisation seems to be a major driver of ecological strategy selection in juveniles. Our study reveals ontogeny‐dependent strategies, offering a new approach to integrate plant development and functional specialisation. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13221/suppinfo is available for this article.

Short gradient, but distinct plant strategies: The CSR scheme applied to subtropical forests

“…Overall, forest communities in this region are characterized by a strong C and S component, with only a small contribution of component R. This is in accordance with another study performed in the Atlantic Forest (located in a transition with Cerrado vegetation) that showed a more important contribution (over 80%) of components C and S (Dayrell et al, 2018). The low contribution of component R caused a strong (negative) correlation between C and S in the forests studied here.…”

“…The stress‐tolerant component was very important for the subtropical forests studied here, especially for Araucaria and Pampean forests, which face lower minimum temperatures and/or larger ranges of annual temperature. Other studies have shown the relation of this component to colder environments (Vasseur et al., 2018) or, in more general terms, to harsher environments such as in coastal Restinga ecosystems (Silva, Souza, Caliman, Voigt, & Lichston, 2018) and in ecotones between savanna and forest ecosystems (Dayrell et al., 2018; Maracahipes et al., 2018). Components C and S performed better in differentiating regional forest types, whereas component R showed not only less importance (as can be expected, to some extent, for tree species and tree communities in general: Pierce et al., 2013), but also less differences between forest types.…”

“…This is because pioneer species are mostly adapted to environmental conditions typical of these stages, such as high light irradiance and space availability, often as a result of severe disturbances. Adult trees seem to be filtered against the R‐strategy, towards more conservative and/or competitive strategies (Dayrell et al., 2018), like strategies S and C.…”

“…R-selected species mostly include small, fast-growing annuals and aquatic plants (Li & Shipley, 2017;Pierce et al, 2013), and communities with higher importance of component R are usually from early successional stages (Caccianiga, Luzzaro, Pierce, Ceriani, & Cerabolini, 2006 and space availability, often as a result of severe disturbances. Adult trees seem to be filtered against the R-strategy, towards more conservative and/or competitive strategies (Dayrell et al, 2018), like strategies S and C.…”

“…(2017). This calculation generates a three‐way trade‐off between LA, SLA and LDMC (Pierce et al., 2017), that results, for each species, in a value of components C, S and R. Although the CSR calculation considers only three leaf traits, it represents a range of ecological strategies and plant functioning, and represents variation in other leaf, reproductive and whole plant functional traits (Dayrell et al., 2018; Pierce et al., 2017). We used the CSR value for each species to calculate the mean CSR value for each site, based on data of presence/absence.…”