The demographic effects of functional traits: an integral projection model approach reveals population‐level consequences of reproduction‐defence trade‐offs

Abstract

Quantitatively linking individual variation in functional traits to demography is a necessary step to advance our understanding of trait‐based ecological processes. We constructed a population model for Asclepias syriaca to identify how functional traits affect vital rates and population growth and whether trade‐offs in chemical defence and demography alter population growth. Plants with higher foliar cardenolides had lower fibre, cellulose and lignin levels, as well as decreased sexual and clonal reproduction. Average cardenolide concentrations had the strongest effect on population growth. In both the sexual and clonal pathway, the trade‐off between reproduction and defence affected population growth. We found that both increasing the mean of the distribution of individual plant values for cardenolides and herbivory decreased population growth. However, increasing the variance in both defence and herbivory increased population growth. Functional traits can impact population growth and quantifying individual‐level variation in traits should be included in assessments of population‐level processes.

Range‐wide variations in common milkweed traits and their effect on monarch larvae

“…We found that C:N ratios, both in the field and in a common garden, are driven primarily by nitrogen. The field‐based, range‐wide patterns of trait relationships we observed are similar to those found previously at a more local scale (Struckman et al, 2019), indicating that intraspecific trait relationships are scalable from local to range‐wide settings (Messier et al, 2017). We found support for our hypothesis that LMA would be higher in the south and strongly predicted by temperature, but no support for declining nitrogen in the south.…”

“…to those found previously at a more local scale (Struckman et al, 2019), indicating that intraspecific trait relationships are scalable from local to range-wide settings (Messier et al, 2017). We found support for our hypothesis that LMA would be higher in the south and strongly predicted by temperature, but no support for declining nitrogen in the south.…”

“…Unfortunately, due to the logistics of field collections and limitations of the ability for appropriate sample storage, we were unable to collect tissue for validation of spectral estimates. There is a precedent for transferring models to produce estimates without validation (Couture et al, 2015, 2018; Struckman et al, 2019; Gold et al, 2020). While the spectral trait retrievals used in the current study were within the range of the estimates from the original spectral models, we suggest interpreting the trait data presented here as estimates, and while they may not be absolutely correct, they are likely relatively correct (following Couture et al, 2015, 2018).…”

Severe simulated herbivory constrains Sclerocarya birrea saplings regardless of resource availability

“…Plant responses to herbivory are affected by the availability of resources and the intensity of herbivory (Ballhorn et al 2014;Zhu et al 2014;Maron et al 2014;Scogings et al 2017). Both factors affect the allocation of molecules to vital functions in plants, such as growth, defence, reproduction and storage (Moreira et al 2014;Struckman et al 2019), which then influences the extent of herbivory experienced by plants (Fornara & du Toit 2007;M€ uller & Orians 2018). Given that carbon (C) is the most abundant molecule in plants (McMurtrie & Dewar 2011;Cook et al 2015;Ma et al 2018a), allocation of C to plant growth or defence in response to resource availability or herbivory intensity has been extensively studied and continues to be so.…”

“…2014; Struckman et al . 2019), which then influences the extent of herbivory experienced by plants (Fornara & du Toit 2007; Müller & Orians 2018). Given that carbon (C) is the most abundant molecule in plants (McMurtrie & Dewar 2011; Cook et al .…”