Demography of Attalea nucifera: Sustainable management and conservation of a threatened species of Colombia

Attalea nucifera is an acaulescent palm native of Colombia that is in risk of extinction. Between 2016-2017 we evaluated the structure and density of populations in six localities of the Magdalena river valley, and studied the population dynamic in the locality of Guaduas, Cundinamarca (VC). Although the population structure differs among locations (X2 = 1819, gl = 25, P < 0.05), populations tend to group according to the degree of habitat perturbation. In four localities an inverted J population structure was observed. A matrix population model showed a finite growth rate (λ) of 0.979 (CI95 % = 0.962–0.997). The demographic processes of the permanence of seedlings, sub-adults and young adults show more elasticity. A transient dynamic simulation projected to 30 years shows that under the scenarios of paddock and cattle lopping the population size decrease drastically. The extinction threshold calculated for the population in the locality VC is of 145 years, but paddock and cattle lopping activities can reduce it to less than 40 years. Although Attalea nucifera persists in very disturbing locations in the Middle Magdalena Basin, the results of population dynamics in the locality VC suggest that it could be less tolerant of environmental disturbances. Thus, it is necessary to increase our knowledge of its population dynamics, as well as seed germination and seedling establishment in different disturbance conditions.

Bifurcation Analysis for a Food Chain Model with Nonmonotonic Nutrition Conversion Rate of Predator to Top Predator

In this paper, a prey–predator-top predator food chain model with nonmonotonic functional response in the predators is studied. With an emphasis on the nutrition conversion rate of predator to top predator, one can get two important thresholds: the top predator extinction threshold and the coexistence threshold. The top predator will die out if the nutrition conversion rate of predator to top predator is less than the top predator extinction threshold; the prey, predator and top predator will coexist if the rate is larger than the coexistence threshold. While between the two thresholds is a bistable interval. When the nutrition conversion rate of predator to top predator is in the bistable interval, the system will see the emergence of bistability. The bifurcation analysis of the system depending on parameters indicates that it exhibits saddle-node bifurcation and Hopf bifurcation phenomena.

Eradicating Metastatic Cancer and the Evolutionary Dynamics of Extinction

We propose the traditional goal of cancer therapists to develop a single drug or drug combination that can, by itself, eliminate all cancer cells within a host has neglected potential treatments that may achieve curative outcomes by strategically combining agents that are individually effective but non-curative. We derive basic principles for such an approach from the eco-evolutionary dynamics of background extinctions in which a &ldquo;first strike&rdquo; reduces the size and heterogeneity of the initial population and is followed immediately by demographic and ecological &ldquo;second strikes&rdquo; that push the population below an extinction threshold. This proposed strategy appears identical to the empirically-derived curative therapy in childhood Acute Lymphocytic Leukemia.

On the route to extinction in non-adiabatic flames from competitive exothermic reactions

We consider non-adiabatic combustion waves arising from two-step competitive exothermic reaction schemes. A numerical method is employed to study the behaviour of this system and we show that the inclusion of heat loss can lead to a period-doubling route to the termination of the propagating flame front. The nature of oscillations becomes more complex with increasing loss of heat until the system can no longer sustain a propagating front. In other words, beyond some critical value of heat loss, extinction of the combustion reaction would occur. For the non-adiabatic case, particularly close to the extinction threshold, large excursions in temperature and wave speed above those observed for the adiabatic case can occur. Such behaviour close to extinction may have implications for safety or industrial processes.

BISTABILITY AND LONG-TERM CURE IN A WITHIN-HOST MODEL OF HEPATITIS C

Treatment of hepatitis C virus (HCV) is lengthy, expensive and fraught with side-effects, succeeding in only 50% of treated patients. In clinical settings, short-term treatment response (so-called sustained virological response (SVR)) is used to predict prolonged viral suppression. Although ordinary differential equation (ODE) models for within-host HCV infection have illuminated the mechanisms underlying treatment with interferon (IFN) and ribavirin (RBV), they have difficulty producing SVR without the introduction of an external extinction threshold. Here we show that bistability in an existing ODE model of HCV, which occurs when infected hepatocytes proliferate sufficiently faster than uninfected hepatocytes, can produce SVR without an external extinction threshold under biologically relevant conditions. The model can produce all clinically observed patient profiles for realistic parameter values; it can also be used to estimate the efficacy and/or duration of treatment that will ensure permanent cure for a particular patient.