Blüml, C. | bioRxiv Science

bioRxiv2021

Nonlinear averaging in 2D: intraspecific variation in two interacting species and consequences for population dynamics

Interactions between two species, e.g. between a predator species and a prey species, can often be described as the sum of many individual-by-individual interactions whose outcomes depend on the traits of the interacting individuals. These traits often vary substantially among individuals in each species, and individuals do not always interact randomly, e.g. due to plastic responses to a shared environmental factor in a heterogeneous landscape. Here we investigate the impact of intraspecific trait variation (ITV) and such interspecific trait correlations on species interactions via nonlinear averaging. Building on past models that integrate over an interaction kernel to obtain the impacts of ITV, we develop a modeling framework that allows to model arbitrary species interactions, with interspecific trait correlations as novel feature. Based on two key ingredients, a joint trait distribution and a two-dimensional interaction function, the average interaction parameters (e.g. average predation rate) can be quantified numerically, approximated using an insightful Taylor approximation, and compared to cases without ITV. We highlight two applications of our framework. First, we study the quantitative and qualitative effects of ITV and trait correlations in a simple predator-prey model and show that even in the absence of evolution, variation and trait correlations among interacting individuals can make or break the coexistence between species. Second, we use simulated field data for a predator-prey system to show how the impact of ITV on an ecological interaction can be estimated from empirical data. HighlightsO_LIWe model how intraspecific trait variation in two species affects their interaction. C_LIO_LIOur framework allows correlations between the traits of interacting individuals. C_LIO_LITrait variation and correlations can strongly affect ecological interactions. C_LIO_LITrait variation and correlations can make or break coexistence. C_LIO_LIThe effect of intraspecific trait variation can be estimated from data. C_LI

ecology↗

bioRxiv2020

Waiting for love but not forever: modelling the evolution of waiting time to selfing in hermaphrodites

Although mixed mating systems involving both selfing and outcrossing are fairly common in hermaphrodites, it is unclear how they are maintained. In some species, individuals delay self-fertilization while they have not found a mating partner. The waiting time is subject to two opposing selection pressures: waiting helps to avoid inbreeding depression in offspring by increasing the density-dependent probability to encounter a mate, but also increases the risk of dying before reproduction. In some species waiting time can vary between individuals and be heritable. We therefore used an individual-based model to explore how delayed selfing evolves in response to density and density fluctuations. We find that at high density, when individuals meet often, drift drives waiting time; at intermediate densities, strong inbreeding depression causes waiting time to increase; and at low densities, inbreeding depression is purged, and waiting time approaches zero. Positive feedback loops drive the system to either complete selfing or complete outcrossing. Fluctuating density can slow down convergence to these alternative stable states. However, mixed mating, in the sense of either a stable polymorphism in waiting times, or stable intermediate times, was never observed. Thus, additional factors need to be explored to explain the persistence of delayed selfing.

evolutionary biology↗