Population (and Habitat) Viability Analysis

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Principle in Ecology and Conservation (LS312)
Population (and Habitat) Viability Analysis

Population viability analysis (PVA) is a process of identifying the threats faced by a species and evaluating the likelihood that it will persist for a given time into the future.         Population viability analysis is often oriented towards the conservation and management of rare and threatened species, with the goal of applying the principles of population ecology to improve their chances of survival. Threatened species management has two broad objectives. The short term objective is to minimize the risk of extinction. The longer term objective is to promote conditions in which species retain their potential for evolutionary change without intensive management. Within this context, PVA may be used to address three aspects of threatened species management: 1. Planning research and data collection. PVA may reveal that population viability is insensitive to particular parameters. Research may be guided by targeting factors that may have an important impact on extinction probabilities or on the rank order of management options. 2. Assessing vulnerability. Together with cultural priorities, economic imperatives and taxonomic uniqueness, PVA may be used to set policy and priorities for allocating scarce conservation resources. 3. Ranking management options. PVA may be used to predict the likely response of species to reintroduction, captive breeding, prescribed burning, weed control, habitat rehabilitation, or different designs for nature reserves or corridor networks. VORTEX :

Vortex is an individual-based simulation model for population viability analysis (PVA). This program will help you understand the effects of deterministic forces as well as demographic, environmental, and genetic stochastic (or random) events on the dynamics of wildlife populations. Vortex models population dynamics as discrete, sequential events (e.g., births, deaths, catastrophes, etc.) that occur according to defined probabilities. The probabilities of events are modeled as constants or as random variables that follow specified distributions. Since the growth or decline of a simulated population is strongly influenced by these random events, separate model iterations or “runs” using the exact same input parameters will produce different results. Consequently, the model is repeated many times to reveal the distribution of fates that the population might experience under a given set of input conditions.

Vortex simulates a population by stepping through a series of events that describe the typical life cycle of sexually reproducing, diploid organisms. The program was written originally to model mammalian and avian populations, but its capabilities have improved so that it can now be used for modeling some reptiles and amphibians and perhaps could be used for fish, invertebrates, or even plants—if they have relatively low fecundity or could be modeled as if they do.

Scenario 1:

Settings :

Monachus monachus (Mediterranean Monk Seal)
Catastrophes : 0
Age of First Offspring for Females : 4 yr
Age of First Offspring for Males : 4 yr
Maximum Age of Reproduction : 20 yr
Maximum Number of Progeny per year : 1
% Adult Females Breeding : 45%
EV in % Breeding : 12.5%
Mortality from Age 0 to 1 : 60%
SD in 0 to 1 Mortality due to EV : 12.5%
% Males in Breeding Pool : 100%
Initial Population Size : 110
Carrying Capacity : 500

Simulation :...
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