https://repositorio.utem.cl/handle/30081993/1168 2026-04-04T12:55:16Z https://repositorio.utem.cl/handle/30081993/1177 The Big Ifs in The Outcomes of Species Interactions: Review and Insights from the Interaction Function (IF) Model Hernandez, Maria-Josefina The conceptual framework for species interactions calls for a new perspective: conditional outcomes are not rare; but, rather, closer to the norm. Interactions may shift or switch between beneficial and detrimental following variations in the (context-dependent) balance of costs and benefits involved for each species. A classic (simple) model such as a Lotka-Volterra can be adjusted to represent these (complex) dynamics by introducing the appropriate nonlinearities in the interspecific terms. The Interaction Function (IF) model introduces a density-dependent function that takes values along the negative to positive continuum; a change in sign denotes a shift in the effect of one species on the other. In this paper I discuss the foundations and development of the IF model, along with other models and conceptual bodies that have emerged on the topic. A brief advance on the central results: (i) the systems present multiple stable equilibria where species may coexist at any combination of interaction outcomes (+ , – , 0), or one be excluded, (ii) transitions between outcomes occur either gradually (environmental conditions vary) or abruptly (drastic change in population abundances leads to another domain of attraction); catastrophic jumps are also possibilities, (iii) fragmentation of space and dispersal trigger source-sink dynamics that cause further variation in the outcomes at local and regional levels, and, remarkably, dynamic variations in the sink or source roles of localities and populations also occur. The fundamental conclusion is that the beneficial or detrimental role of a species in an association is a spatiotemporal dynamic quality, determined by the balance of many concurrent density-dependent effects, some reinforcing, some counteracting, one another. Páginas: 73-90 2021-01-01T00:00:00Z https://repositorio.utem.cl/handle/30081993/1176 Sobre el conjunto de umbrales sostenibles Gajardo, Pedro Hacer operativo el concepto de sostenibilidad es un desafío importante en la gestión de recursos naturales, problemas de conservación de la biodiversidad, el cambio climático y la epidemiología, entre otros. Diferentes enfoques se han propuesto, basados en restricciones y umbrales que consideran no sobrepasar indicadores biológicos, ecológicos, económicos o sociales como metas para los objetivos de una gestión sostenible. Cuando las restricciones inducidas por umbrales deben satisfacerse a lo largo del tiempo, estos problemas pueden formularse en el marco matemático de la teoría de la viabilidad, como han propuesto numerosos autores durante las últimas décadas. El eje central de estos enfoques ha sido principalmente el cálculo del núcleo de viabilidad, concepto clave en la mencionada teoría, que consiste en el conjunto de estados iniciales del sistema a partir del cual es posible satisfacer las restricciones prescritas a lo largo del tiempo. Nuestro enfoque en los últimos años ha sido en el sentido inverso, consistente en determinar los umbrales para los que existe una trayectoria que satisface las restricciones parametrizadas por dichos umbrales, a partir del estado actual de un sistema. El conjunto de todos estos umbrales se denomina conjunto de umbrales sostenibles, que corresponde al operador inverso del núcleo de viabilidad. Este nuevo concepto, y su cálculo, proporciona una herramienta para la gestión y visualización de múltiples objetivos relacionados con la sostenibilidad que se puede alcanzar, permitiendo observar la (in)compatibilidad y compensaciones entre ellos. En este trabajo revisamos la definición del conjunto de umbrales sostenibles, presentando algunas interpretaciones y un método para calcularlo, resumiendo trabajos recientes desarrollados con varios coautores. Páginas: 37-47 2021-01-01T00:00:00Z https://repositorio.utem.cl/handle/30081993/1175 Growth and Extinction in Randomly Varying Environments: Modelling and Optimization Using Stochastic Differential Equations Braumann, Carlos A. This paper presents a brief overview of a range of applications of stochastic differential equations (SDE) in describing the growth of wildlife populations living in randomly varying environments and the associated risks of extinction, including profit optimization issues in the particular case of fish or other populations subjected to harvesting. The same basic ideas apply also to the growth of individual animals and how to optimize the profit of the farmers that raise such animals. Páginas: 25-36 2021-01-01T00:00:00Z https://repositorio.utem.cl/handle/30081993/1174 Elucidating the Role Played by Cancer Stem Cells in Cancer Growth Barberis, Lucas; Benítez, Lucia; Condat, Carlos A. The cancer stem cell hypothesis states that cancer growth is propelled by a relatively small number of cancer stem cells (CSCs). These CSCs have been shown to play a crucial role in the growth and recurrence of many tumor types. The possibility that their elimination becomes an efficient cancer control procedure has even led to new therapeutic paradigms. On the other hand, from their early stages, most solid tumors grow in stressed environments. The stress field impacts on tumor evolution, and it is likely to affect different cancer cell populations in different ways. It is therefore of great interest to determine the nature and strength of the interactions between CSCs and differentiated tumor cells and how these interactions are affected by the mechanical properties of the environment. We have developed a two-population mathematical model suitable to describe the initial stages of cancer growth and applied it to extract information from three different experiments. Two of these experiments involve tumorspheres (spheroids resulting from the proliferation of a single CSC). In these cases, the model validates the concept of CSC niche (the microenvironment responsible for signals that stimulate or inhibit CSC growth), shows that interspecific interactions stimulate growth, while intraspecific interactions are generally inhibitory, and indicates how substrate hardness modifies growth. In the third experiment analyzed, where stress-induced growth suppression was measured in multicellular tumor spheroids, we were able to reconstruct the (unobserved) CSC fraction and found that medium rigidity eventually forces all cell interactions to be competitive. We find that, under adverse environmental conditions the CSC fraction always remains nonzero. This lends support to the hypothesis of the existence of the niche as a regulatory maintenance mechanism whose understanding will be crucial to the development of a successful therapy based on CSC elimination. Páginas: 48-54 2021-01-01T00:00:00Z