Resident species with larger size metrics do not recruit more offspring from the soil seed bank in old‐field meadow vegetation

Abstract

1. According to the traditional "Size Advantage" (SA) hypothesis, plant species with larger body size are expected to be more successful when competition is intense, that is, within severely crowded vegetation. Recent studies in old-field habitats, however, have shown that those species with greater numerical abundance as resident plants generally have a relatively small minimum reproductive threshold size (MIN), not a relatively large maximum potential body size (MAX).2. In this study, we test for a size advantage in terms of species abundance representation in the soil seed bank, and we extend the SA hypothesis to include two additional size metrics: leaf size and seed size. Specifically, we ask, for resident species within a crowded old-field meadow: is larger seed size, leaf size, and/or body size associated with greater reproductive / recruitment success (i.e. number of germinable seeds within-and establishing plants emerging from-the soil seed bank)? We collected soil cores for a greenhouse experiment to record relative species abundances of germinable seeds in the seed bank, and we used a field experiment to record local abundances of species emerging from the resident seed bank within denuded plant neighbourhoods over three subsequent field seasons.3. We found no general support for the SA hypothesis involving any of the size metrics, and none of the latter was a strong predictor of the number of germinable seeds emerging from soil cores in the greenhouse experiment. However, for species establishing in the field experiment from the seed bank over the 3-year survey period, more abundant species in years 2 and 3 tended to be those with smaller MIN, and thus smaller MAX. In addition, within more crowded neighbourhoods, representation of reproductive plants was generally greater for species with relatively small MIN (and hence small MAX). Synthesis.Our results extend the support for the "Reproductive Economy Advantage" hypothesis in old-field habitats, to include not just established, largely undisturbed vegetation, but also very early stages of recruitment from seed within locally crowded plant neighbourhoods. Specifically, more successful species here are not those with relatively large potential body size (MAX); they are species capable of producing at least some offspring despite severe body size suppression, K E Y W O R D S body size, competition, leaf size, leafing intensity, reproductive economy, seed bank, seed size, species abundance | 1069 Journal of Ecology TRACEY ET Al.

Smaller species experience mild adversity under shading in an old‐field plant community

“…Inevitably, other factors, like available soil nutrients, can limit the height of the canopy by controlling which species can persist (Borer et al, 2014 ). Large species with large minimum reproductive size thresholds (Tracey & Aarssen, 2019 ) may be less likely to persist in low soil nutrient settings, and self‐thinning among tall plant species may create regular gaps, allowing light to reach smaller species (Schamp & Aarssen, 2014 ). Thus, nutrient limitation and competition among tall species may decrease the abundance of large plant individuals per area, simultaneously increasing light penetration and altering the importance of light as a previously limited resource.…”

“…There is also little evidence of deterministic organization of species according to size in herbaceous communities (Schamp et al, 2008 ). Recent research has shown that species with larger body size in fact do not dominate neighborhood biomass production in old‐field vegetation (Tracey et al, 2017 ), nor do they recruit more offspring from the soil seed bank (Tracey & Aarssen, 2019 ).…”

Smaller species experience mild adversity under shading in an old-field plant community

“…Inevitably, other factors, like the available soil nutrients, can limit the height of the canopy by controlling which species can persist (Borer et al 2014). Large species with large minimum reproductive size thresholds (Tracey and Aarssen 2019) may be less likely to persist in low soil nutrient settings and self-thinning among tall plant species may create regular gaps, allowing light to reach smaller species (Schamp and Aarssen 2014). Thus, nutrient limitation and competition among tall species may decrease the abundance of large plant individuals per area, simultaneously increasing light penetration and altering the importance of light as a previously limited resource.…”

“…There is also little evidence of deterministic organization of species according to size in herbaceous communities (Schamp et al 2008). Recent research has shown that species with larger body size in fact do not dominate neighbourhood biomass production in old-field vegetation (Tracey et al 2017), nor do they recruit more offspring from the soil seed bank (Tracey and Aarssen 2019).…”

Functional traits explain both seedling and adult plant spatial patterns in gypsum annual species

“…Key plant functional traits such as seed mass, maximum plant height, specific leaf area (SLA) and reproductive/vegetative biomass ratio (reproductive ratio, hereinafter) are clearly connected to the main ecological processes that determine community and population assembly. For example, large‐seeded species have competitive (Freckleton & Watkinson, 2001; Rees, 1995) and establishment advantages (Freckleton & Watkinson, 2001; McConnaughay & Bazzaz, 1987; but see Tracey & Aarssen, 2019) compared with small‐seeded species. The initial seedling size is positively correlated with seed size (Leishman et al, 2000), and larger seedlings are usually favoured under competitive or drought conditions (Leishman & Westoby, 1994).…”