BIOL 4255 Lab: Module 3 – Extinction

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Many species are on the verge of extinction, as we have entered what is frequently referred to as Earth’s sixth mass extinction event (Ceballos et al. 2015). In light of this, the ability to model and predict population extinction events is of considerable importance to conservation biologists. This is most often done using computer programs written to model the effects of various parameters of the survival probability of populations. In this lab, we will use the program Vortex to model population extinction (


The Extinction Vortex When a declining population reaches a small enough size, it becomes susceptible to mutual negative reinforcement from environmental, demographic, and genetic processes, which together rapidly drive population size downward to extinction. This negatively-reinforced decline is commonly referred to as an extinction vortex. Large populations are relatively robust to impacts from environmental and demographic stochasticity1 , but these same stochastic events can represent major reductions for already small populations. Small populations are also at risk from genetic processes, since individuals in small populations are more likely to express one or more recessive, deleterious alleles (normally masked by dominant alleles). Increased expression of these deleterious alleles results in reduced fecundity and survival of individuals in the population, further reducing population size. In other words: as a population’s size decreases, it becomes susceptible to a number of processes, all of which further reduce population size, making the population even more susceptible, increasing its risk of extinction at a logarithmic rate. This is the basis of the vortex. You will be performing several sets of analyses using the program Vortex, which is named for this phenomenon. While you may not explicitly model an extinction vortex per se, you will have the opportunity to observe the mutually-reinforcing effects of different processes that contribute to extinction. In Part 1, you will investigate the influences of demographic parameters upon the mean time to extinction for a population. In Part 2, you will investigate the effects of environmental catastrophes upon the time to extinction. Finally, in Part 3, you will investigate the effect of variation in genetic parameters upon the time to extinction.

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