ECOP Subgroup Contributed Talks

Maksim Mazuryn

Technical University of Denmark

"Mean Field Game Model for Diel Vertical Migration"

Diel vertical migration is the largest daily movement of marine species where animals remain in deep, dark water during daylight hours to avoid visual predators and migrate to upper levels at dusk to feed. The migration of each organism can be rationalized as a trade-off between growth and survival with strategies as spatial distributions of the populations. The dynamics driving vertical migration have broad implications for fluxes through the food-web predator-pray interactions; for vertical transport of carbon in ocean with implications for global climate.I will present ongoing work on a framework for expressing diel vertical migration as a game in terms of partial differential equations. In the base model setup we consider a population of animals distributed in the water column. It is assumed that each animal moves optimally, seeking regions with high growth rate and small mortality, avoiding regions with high population density. The Nash equilibrium for this mean field game is characterized by a system of partial differential equations, which governs the population distribution and migration velocities of animals. I will talk about extension of the base model with added diffusion to cover deep water case.

Jasper Croll

IBED, University of Amsterdam

"The effect of growth plasticity on the population dynamics of structured populations"

Population structure is an important aspect of natural populations and has a large impact on population dynamics. In theoretical models, populations are generally structured by age or size. As long as individuals follow a fixed growth curve, age- and size structured models are virtually similar, but if individual growth rates become plastic (e.g. depend on the environment), age- and size structured models start to differ. In nature, individuals of various species differ strongly in the plasticity of their somatic growth rate as well. To explore the effect of plasticity in somatic growth we formulated a physiologically structured population model in which growth plasticity can be varied from entirely plastic to entirely non-plastic. The life history rates in this model were based on a Dynamic energy budget model to ensure closed individual energy dynamics. From the analysis of our model it became clear that changes in growth plasticity provoke a complex trade-off between energy allocation to somatic growth and reproduction. This tradeoff results in two distinct parameter regions which differ in their ecological and evolutionary dynamics. These results can gain insight in the different ways a population can respond to human impact and the different ways population structure can be modelled.

Subekshya Bidari

University of Colorado Boulder

"Evidence accumulation models of social foraging"

Foraging is often modeled as a sequence of patch-leaving decisions. An animal enters a patch of food, harvests resources, and then decides when to leave and search for other patches. Foraging strategies shape experimental observables like patch residence time, inter-patch travel time, as well as rate of energy intake. Models of foraging as an evidence accumulation process accounts for learning processes involved in determining resource availability within and across patches by associating evidence for leaving a patch with a deterministic drift term and the stochasticity of food encounters and memory with diffusive noise (Davidson & El Hady A, 2019). My work extends these individual evidence accumulation models to consider patch foraging decisions of multi-agent systems sharing social information.

Samuel Dijoux

Dept. of Ecosystem Biology, Faculty of Science, University of South Bohemia, České Budejovice, Czech Republic

"Invasions in simple food webs along environmental and size structure gradients: insights on exploitative competition."

Multi-channel food webs are shaped by the ability of apex predators to link asymmetric energy flows in mesohabitats differing in productivity and community traits. While body size is a fundamental trait underlying life histories and demography, its implications for structuring multi-channel food webs are unexplored. To fill this gap, we develop a model that links population responses to predation and resource availability to community-level patterns using a tri-trophic food web model with two populations of intermediate consumers and a size-selective top predator. We show that asymmetries in mesohabitat productivities and consumer body sizes drive food web structure, merging previously separate theory on apparent competition and emergent Allee effects (i.e., abrupt collapses of top predator populations). Our results yield theoretical support for empirically observed stability of asymmetric multi-channel food webs and discover three novel types of emergent Allee effects involving intermediate consumers, multiple populations or multiple alternative stable states.