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 […]

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 […]

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). […]

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 […]

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 […]

Stephen Ellner (Cornell), Peter Adler (Utah State), Giles Hooker (Cornell), Robin Snyder (Case Western): An invitation to spatial coexistence theory. Abstract: Previously in this series Sebastian Schreiber reviewed stochastic coexistence theory for infinite population models, based on long-term population growth rates of (infinitesimally) rare invaders. Nadav Shnerb presented progress on the challenges posed by demographic […]

Abstract: Niche Theory has traditionally focused on competitive interactions. In this talk, we propose a general framework that expands the theory to positive interactions, such as facilitation and mutualism, using angular metrics of niche difference. We develop novel niche concepts such as the Allee niche and niche expansion, and illustrate them using a diverse set […]

Abstract: Models of microbial interactions have been developed in recent years, drawing from taxonomic abundances via amplicon sequencing. Many of these models assume that dynamics through time are primarily driven by pairwise interactions between taxa, but with the drawback that how these interaction strengths may change with environmental context is less than clear. Here we […]

Abstract: Why are there so many animals? According an old idea, it is because there are so many different possibilities for life to adapt to. I’ll argue that it is still true, and truer than the suggested alternatives. The challenge is to establish the precise mathematical treatment at this level of generality without losing the […]

NOTE: Because of the asynchronous transition to Summer Time, the usual time of the seminar (9 a.m. Pacific) is one hour earlier in Europe: 4 p.m. London and 5 p.m. Paris. Abstract: Critical transitions whereby small changes in conditions can cause large and irreversible changes in ecosystem states are a cause of increasing concern in […]

Abstract: First, I present a method for calculating how average population densities respond to parameter perturbations when the dynamics are periodic, and show that this practical problem holds a strong connection with basic questions of coexistence. I then generalize this result to stationary nonperiodic density fluctuations. I finish by discussing the connection with existing formalisms […]

Note: The event takes place 3 hours earlier than usual, because of the location of our lecturer. He will speak at midnight, local time, even in this way. Abstract: Previous studies have revealed that microevolution (i.e., temporal changes in allele frequencies) is pervasive in the wild and may be an important factor for understanding various […]

Abstract The Shigesada-Kawasaki-Teramoto model (SKT) was proposed to account for stable inhomogeneous steady states exhibiting spatial segregation, which describes a situation of coexistence of two competing species. Even though the reaction part does not present the activator-inhibitor structure, the cross-diffusion terms are the key ingredient for the appearance of spatial patterns. We provide a deeper […]

Abstract: Ecological networks—how species interactions are organized within ecological communities—are highly structured, which has motivated generations of ecologists to elucidate how these structures affect species coexistence. Unfortunately, we still do not have a clear and consistent answer about the link between network structure and species coexistence. A possible explanation is that most of the studies […]

Abstract: Theoretical ecology has investigated a series of concepts from stability and complexity through biodiversity and ecosystem function to coexistence and tipping points for which empirical data typically plays a less-than-satisfying role. To coax theoretical ecology towards increased empirical relevance and broader scientific synthesis, I propose that environmental biologists focus on predicting key characteristics of […]

Abstract: We investigate the idea that tropical biodiversity is maintained by a combination of niche segregation and niche sharing among species by asking whether tree species in Barro Colorado Island, Panama, fall into groups differing by the local conditions where they typically occur. We first group together species often found near each other, then show […]

Abstract: For decades Lotka-Volterra community models have been used to try to understand how ecological interactions may drive community-scale properties such as species richness, network structure, and species abundance distributions; in short the various dimensions of biodiversity. Here I show how extending the basic community models into spatially and environmentally heterogeneous landscapes can help us […]

Abstract: I’m interested in exploring the degree to which theory on ‘disordered systems’ to community assembly can be linked to statistical methods of pattern analysis. Here, I hope to describe the problem and outline some possible approaches and answers. By doing so, I hope to generate interest and discussion on possible solutions. Zoom link: https://liu-se.zoom.us/j/63158449287 […]