Spring 2020 Schedule

The seminar meets on Thursdays at 2:30 pm in Avery 119.

If you would like to speak at the seminar, please contact Richard Rebarber at rebarber@unl.edu

Thursday, January 30, 2020
  • Lyndsie Wszola, UNL School of Biological Sciences, UNL

Title: Evolving regulations for a changing world

Abstract: It has become increasingly clear that harvest from fish and wildlife populations can induce ecological and evolutionary changes in population stage and size structure, especially in fisheries. Harvest-induced evolution tends to reduce fish age and size at maturity regardless of regulation because intensive fish harvest favors early reproduction even without intentional size selection. We built a stage-structured eco-evolutionary model of harvest-induced changes in size and stage structure to assess how size-specific harvest regulations affect population stability, extinction risk, and recovery potential under ecologically and evolutionarily-induced changes in population stage structure. Our approach incorporates emerging evolutionary theory with the wealth of available fisheries data to provide a framework for evaluating regulations in the context of a changing world.

Thursday, February 13, 2020
  • Matt Reichenbach, UNL

Title: Asymptotic Convergence to a Stable Stage Distribution

Abstract: One of the consequences of the Perron-Frobenius theorem is that powers of a positive irreducible matrix (normalized by its spectral radius) converge to a projection onto the eigenspace of the leading eigenvector. In particular, this fact guarantees that population models with a Leslie matrix approach a stable stage distribution. In this talk, I will first go over the generalization of this result to integral projection models with a compact operator, and also my recent result that the result is true in the case of a non-compact operator..

Thursday, February 27, 2020
  • Amanda Laubmeier, UNL

Title: TBA

Abstract: TBA.

Thursday, March 19, 2020
  • Aminur Rahman, Texas Tech Department of Statistics, UNL

Title: Physics-based models and simulations of cancer drug response in solid tumors

Abstract: Over the past few decades, cancer related deaths have fallen significantly as noted by the National Cancer Institute. However, assessing cancer treatments is still predominantly a trial and error process. This approach may result in delays to administer the correct treatment, the use of more invasive procedures than necessary, or an increase in toxicity due to superfluous treatments. Although these procedures may end up saving the patient, the treatment may also have an adverse effect on their quality of life. Reliable mechanistic models of drug response can potentially be used to aid oncologists and doctors in deciding on an optimal treatment strategy for the patient. We develop a modeling framework for tumor ablation, and present coupled transport - population models of varying complexity. First, we present a radially symmetric drug diffusion and binary cell death model, which produces a theoretical dose for optimal efficacy to toxicity ratios. Further, we investigate inhomogeneous - anisotropic drug diffusion, and develop an algorithm to locate the optimal injection points. Importantly, we show that this modeling framework has the potential to be employed in computer-aided treatment strategies.

Here are the talks we had last semester (Fall 2019)

Thursday, September 5
  • Amanda Laubmeier, UNL

Title: Towards understanding factors influencing the benefit of diversity in predator communities for prey suppression

Thursday, September 12
  • Glenn Ledder, UNL

Title: A discrete/continuous time consumer-resource model and it’s implications

Abstract: Most population models use either discrete time or continuous time. But what do we do in the case of a resource that grows continuously paired with a consumer that has a synchronized life history with annual birth pulses? Answer: We use a mixed time model consisting of differential equations on fixed time intervals and jump conditions. For analysis, it is better to think of it as a discrete model in which the continuous component is used to identify the discrete map. In this talk, I will show the simplest reasonable model for this scenario, and we will see that its dynamics can be even a little more complicated than a standard discrete model.

Thursday, September 19
  • Richard Rebarber, UNL

Title: A discrete/continuous time Resource Competition Model and it’s implications

Abstract: Many ecological settings feature consumers that reproduce in annual birth pulses and feed on a resource that grows continuously, so that an appropriate model consists of a time-limited continuous model embedded in a discrete model. Last week Glenn Ledder discussed such a model with a single consumer species. This week I consider a similar model with two consumer species, with competition only in resource collection. For most parameter regimes corresponding to the stable and overcompensation cases for one consumer, the two consumers cannot coexist. In these cases, we show that the successful consumer is the one whose consumer-resource equilibrium point is at a lower level of the resource. We then consider a hypothetical situation where the two consumers have different timing of their birth pulses, and consider what happens when a stressor (say, a toxin) is introduced with it’s own release pulses; we show that under some circumstances, the stressor can change which consumer is successful. This is joint work with Amanda Laubmeir, Glenn Ledder, Terrence Pendleton and Jonathan Weisbrod.

Thursday, September 26
  • Yu Jin, UNL

Title: We present a novel model that considers the longitudinal variation as introduced by the sinuosity of a meandering river where a main channel is laterally extended to point bars in bends. These regions offer different habitat conditions for aquatic populations and therefore may enhance population persistence. Our model is a nonstandard reaction– advection–diffusion model where the domain of definition consists of the real line (representing the main channel) with periodically added intervals (representing the point bars). We give an existence and uniqueness proof for solutions of the equations. We then study population persistence as the (in-) stability of the trivial solution and population spread as the minimal wave speed of traveling periodic waves. We conduct a sensitivity analysis to highlight the importance of each parameter on the model outcome. We find that sinuosity can enhance species persistence.

Thursday, October 3
  • Matt Reichenbach, UNL

Thursday, November 7
  • Amanda Laubmeier, UNL

Title: Integrating mathematical models and data to understand ecological processes

Abstract: Mathematical models for ecological populations can lead to an improved understanding of the factors driving population change. However, ecological data is equally informative in determining current and future population behaviors. The presentation will begin with a brief summary of my approach to studying ecological populations, which involves a balance of mathematical modelling, empirical data, and biological input. I will discuss model development for a particular project concerning interactions between an agricultural pest and its natural insect predators. Highlights of the project include designing experiments to test the model and using simulations to determine the qualities of an optimal predator community for pest suppression. As time allows, I will also discuss ongoing work in different ecological applications, including a theoretical project concerning competition between native and invasive trout species and a data-driven project concerning long-term monitoring of a perennial wildflower.

Thursday, November 21
  • Drew Tyre, UNL School of Natural Resources, UNL

Thursday, December 3
  • Peter Wagner, Dept. of Earth and Atmospheric Sciences & School of Biological Sciences, UNL