Navegando por Autor "Santos, Renato Vieira dos"
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Item Survival of the scarcer in space.(2013) Santos, Renato Vieira dos; Dickman, RonaldThe dynamics leading to extinction or coexistence of competing species is of great interest in ecology and related elds. Recently a model of intra- and interspeci c competition between two species was proposed by Gabel et al, in which the scarcer species (i.e., with smaller stationary population size) can be more resistant to extinction when it holds a competitive advantage; the latter study considered populations without spatial variation. Here we verify this phenomenon in populations distributed in space. We extend the model of Gabel et al to a d-dimensional lattice, and study its population dynamics both analytically and numerically. Survival of the scarcer in space is veri ed for situations in which the more competitive species is closer to the threshold for extinction than is the less competitive species, when considered in isolation. The conditions for survival of the scarcer species, as obtained applying renormalization group analysis and Monte Carlo simulation, di er in detail from those found in the spatially homogeneous case. Simulations highlight the speed of invasion waves in determining the survival times of the competing species.Item The noise and the KISS in the cancer stem cells niche.(2013) Santos, Renato Vieira dos; Silva, Linaena Méricy daThere is a persistent controversy regarding the frequency of cancer stem cells (CSCs) in solid tumors. Initial studies indicated that these cells had a frequency ranging from 0.0001% to 0.1% of total cells. Recent studies have shown that this does not seem to be always the case. Some of these studies have indicated a frequency of 40%. Through a simple population dynamics model, we studied the effects of stochastic noise and cellular plasticity in the minimal path size of a cancer stem cells population, similar to what is done in what is sometimes called the Kierstead–Skellam–Slobodkin (KISS) Size analysis. We show that the possibility of large variations in the results obtained in the experiments may be a consequence of the different conditions under which the different experiments are submitted, specifically regarding the effective cell niche size where stem cells are transplanted. We also show the possibility of a noise induced transition where the stationary probability distribution of the CSC population can present bimodality.