Exploring the `Harperian' paradox: Leaving descendants in a crowded plant world

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Competition between near neighbours is conventionally regarded as one of the most intense forces of natural selection that has shaped the evolution and diversity of functional traits in plants. Most of the traditional theory for evolved strategies of success in plants under resource limitation (competitive ability) is based on a `Size Advantage' hypothesis, where superiority involves generally greater success in uptake/depletion of contested resources, typically associated therefore with greater growth accumulation and larger maximum potential body size (MAX). My recent research however points to an alternative interpretation involving a `Reproductive Economy Advantage' hypothesis, where reproductive success within severely crowded neighbourhoods is generally greater, not for species with larger MAX, but for species with higher `fecundity allocation', i.e. production of a larger number of offspring (sexual or clonal) per unit parent plant size per unit time. The research proposed here will use greenhouse studies, field experiments in natural vegetation, and large scale census surveys of the regional flora in eastern Ontario, Canada to identify the major components of fecundity allocation and hence capacity for reproductive economy in flowering plants. Emphasis will be placed on species at risk and vegetation associated with ecosystem services of marginal lands for agriculture (e.g. old fields). The main predictions are that high fecundity allocation is promoted by four potential size metrics: (i) relatively small MIN (minimum threshold parental body size for producing seed or clonal offspring); (ii) relatively high above-ground body mass density (dry mass per unit of physical space occupancy); (iii) relatively small seed size - i.e. all else being equal, a plant that makes smaller seeds, can make more of them per unit plant body size; and (iv) relatively small leaf size - i.e. a plant that makes smaller leaves can make more leaves for a given body size of supporting vegetative tissue (a higher `leafing intensity'), which enables a larger axillary `bud bank' (per unit body size) available for deployment as clonal and/or sexual reproductive meristems. Having a larger bud bank, we can predict, also means that more meristems are available for strategic deployment in the expression of architectural/growth-form plasticity (e.g. for branching intensity under variable light regimes), or as a `reserve' for survival and compensation following tissue loss to herbivores or disturbance.  These projects, over five years, will involve training for 2 PhD students, 4-5 MSc students, and 10 undergraduate thesis students - with an average of 3-4 graduate students and 2 BSc (Hons) thesis students / summer student technicians working in my lab each year.