The Real History Behind The Palbociclib Accomplishment

The same criterion must also be met for spread of an emerging disease; however, here R0 is a composite of transmission within and between multiple host species. Hence, it is possible for parasites to persist despite R0 in the novel host being up this shortfall. Parallels with invasion are evident when considering deliberate releases of species in attempts to ��force�� them into establishment, such as during ��naturalization�� and biological control projects. For example, exotic species often only persist because of their repeated releases by man (e.g. grass carp Ctenopharyngodon idella in UK), and many biological control agents require multiple releases to be effective (Lockwood, Hoopes & Marchetti 2007). The value of R0 and hence the likelihood of transition to phase III is influenced by demographic factors (e.g. host population structure, propagule pressure), evolutionary factors (on parasite and host traits) and environmental factors, as discussed below. For parasites of a single host species and with density-dependent transmission, theory predicts a threshold host population density below which R0? emerge before human populations reached critical sizes following the agricultural revolution (Wolfe, Dunavan & Diamond 2007). In the United States, successful conservation measures in the Greater Yellowstone Area have led to increasing population densities of elk (Cervus elaphus), with the unintended consequence that elk populations are now of sufficient size to maintain brucellosis, which now spills back into cattle and occasionally humans (Cross et?al. 2010). Stochastic effects also influence extinction probability; outbreaks in the novel host will often stutter to extinction, even if R0?>?1, if successive transmission events fail by chance in small populations (May, Gupta & McLean 2001). Such stochastic extinction depends crucially on the number of individuals infected at the point of spillover (the propagule size). Probabilistic models demonstrate that even when R0 is substantially >1, if the initial propagule of infected individuals is small (