International Initiative for Theoretical Ecology

Nadav Shnerb (Bar-Ilan University): Quantifying coexistence
2020-12-08 09:00 - 10:00 (America/Los_Angeles)
Abstract.
Modern coexistence theory employs mutual invasibility as a coexistence criterion and mean growth rate when rare as an invasibility criterion. When implemented as quantitative metrics, both criteria have shortcomings: persistence time may decline when the chance of invasion grows, and invasibility may decrease as the mean growth rate increases in magnitude. I will discuss an alternative framework and introduce a new metric for invasibility under both demographic and environmental stochasticity.
Zoom link: https://liu-se.zoom.us/j/63158449287
eventbrite link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805

Stefano Allesina (University of Chicago): A metapopulation model in which patches have memory
2020-11-24 09:00 - 10:00 (America/Los_Angeles)
Levins’ metapopulation model has been extended in numerous ways. Here we analyze a model in which species have distinct colonization rates that depend on which species previously occupied the patch. We connect this model to the Janzen-Connell hypothesis and show some surprising behavior for a simplified version of the model.
Zoom link: https://liu-se.zoom.us/j/63158449287
eventbrite link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805

Sebastian Schreiber (UC Davis): Towards a general theory of coexistence: Lyapunov exponents, auxiliary variables, and Hofbauer's criterion
2020-11-09 09:00 - 10:00 (America/Los_Angeles)
Warning: this is a Monday!
Abstract: In the 1980s, Josef Hofbauer introduced a criterion for mathematically verifying coexistence using per-capita growth rates of species when rare i.e. Lyapunov exponents. This criterion ensures coexistence is robust to large perturbations of the community state (i.e. permanence) and small structural perturbations of the governing equations (i.e. robust permanence). Originally developed for deterministic models without population structure, Hofbauer’s criterion has been extended in the past decade to models allowing for auxiliary variables and environmental stochasticity. In this talk, I review the key ingredients of this theory and illustrate its use in multi-species models with intransitivities, eco-evolutionary feedbacks, sexual dimorphisms, autocorrelated environmental fluctuations, or spatial structure.
Zoom link: https://liu-se.zoom.us/j/63158449287
eventbrite link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805

André M. de Roos (University of Amsterdam): Dynamics of within-population structure stabilise complex ecological communities
2020-10-27 09:00 - 10:00 (America/Los_Angeles)
Warning!
During this week the time difference between America and Europe is one hour less, than usual. The seminar will begin at 9 am Pacific, as always, but now it will correspond to 4 pm in London and 5 pm in Paris.
Abstract:
Dynamic models of ecological communities that neglect within-population structure predict that stability depends on substantial self-limitation of species. Using a stage-structured food web model I show that differences between juveniles and adults result in diverse ecological communities that are stable or exhibit limited-amplitude fluctuations, despite that only a single basal species is self-regulated. Eigenvalue analysis reveals that community stability results from dynamic changes in within-population stage-structure that override destabilising effects induced by the species interaction network.
Zoom link: https://liu-se.zoom.us/j/63158449287
eventbrite link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805

Vadim Karatayev (University of Guelph): Species heterogeneity can reduce the potential for alternative stable states in food webs
2020-10-13 17:00 - 18:00 (Europe/London)
Abstract. Can alternative stable states arise when food webs dissipate feedbacks across many species in diverse systems like coral reefs? Although consumer loss often characterizes degraded ecological states, food web resilience theory predominantly focuses on specific systems and few-species models. After developing a generalized model of consumer collapse, we show that alternative stable states dominated by either consumer or resource guilds can arise when consumer species improve conditions in the same way, for instance when different herbivore species promote habitat-forming corals by limiting the total cover of macroalgae. Conversely, specialized feedbacks where size refugia or group defense make individual resource species inedible are less likely to drive many-species alternative stable states because losing the most vulnerable consumers cascades into a guild-wide collapse.
Vadim Karatayev, Marissa Baskett, Egbert van Nes, Marten Scheffer
Zoom link: https://liu-se.zoom.us/j/63158449287
eventbrite link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805
Video: https://www.youtube.com/watch?v=2bZfsRBXJX4

Éva Kisdi (University of Helsinki): The evolution of habitat choice facilitates niche expansion
2020-09-29 17:00 - 18:00 (Europe/London)
Abstract: Matching habitat choice and local adaptation are two key factors that control the distribution and diversification of species. We study their joint evolution in a structured metapopulation model with a continuous distribution of habitats. Habitat choice follows from dispersal with non-random immigration, a process always acknowledged yet rarely incorporated into theoretical models. For fixed local adaptation, we find the evolutionarily stable habitat choice as a function linking the probability of settlement to the local environment. When the local adaptation trait co-evolves, the metapopulation can become polymorphic. Our main result shows that coexisting strains with only slightly different local adaptation traits evolve substantially different habitat choice. In turn, different habitat use selects for divergent local adaptations. We thus propose that under wide conditions, the joint evolution of habitat choice and local adaptation can facilitate niche expansion via diversification.
Zoom link: https://liu-se.zoom.us/j/63158449287
EventBrite Link (for reminders): https://www.eventbrite.co.uk/e/theoretical-ecology-seminar-series-tickets-119884512805
Video: https://www.youtube.com/watch?v=qMpR1mNLkq4&t=293s

Guy Bunin: Phase-transitions as signatures of complex communities
2020-09-15 17:00 - 18:00 (Europe/London)
Abstract: What characterizes species-rich communities with complex species interactions–for example, competing over many niches? Models predict sharp transitions, as conditions are changed, between qualitatively different dynamical behaviors. These include the abrupt appearance of a vast number of alternative steady-states; and the onset of persistent abundance fluctuations, nearly uncorrelated between species. We discuss these phenomena, and how they differ from related low-dimensional behavior.
Video: https://www.youtube.com/watch?v=Dw3Gsa8FI18
