Population hazard analysis
Population hazard analysis (translated from English Population Viability Analysis, then often abbreviated as PVA) is a method to calculate the probability of a population becoming extinct under defined framework conditions.
The PVA is based on an ecological model in which the population size with its essential (demographic) influencing factors, in particular the birth rate ( natality ), death rate ( mortality ), immigration (immigration) and emigration (emigration) is mathematically modeled. Environmental factors are included as influencing factors on these factors that are essential for the population size. The population is extinct if at any point in time the population size reaches zero. Since the environmental factors cannot be predicted precisely, and in addition, in the case of small populations, only integer values for the population size are possible (a population size of 0.75 individuals would be meaningless), in practice these are not deterministic but stochastic models , d. H. only the probability of extinction in relation to a certain period is calculated. Which probability is assessed as acceptable is based on a value decision and is ultimately not scientifically justifiable. Often, a probability of extinction of 1 or 5 percent is expected. The period under consideration is also chosen conventionally; an estimate of 100 years is common.
Typically, realistically modeled populations result in a population size that fluctuates strongly from year to year, mainly due to climatic and weather influences, which can be favorable or unfavorable for the species under consideration. Other, more deterministic mortality factors, such as possible hunting or a change in the size of the habitat, must of course be taken into account. If, however, this results in a negative size for the growth of the population under all circumstances, its extinction is inevitable, and the analysis can then no longer contribute anything to its rescue. Normally, therefore, rather small, but principally viable populations are considered. The size of the population does not increase proportionally, even under favorable environmental conditions, but will slow down at higher population densities due to density-limiting factors such as competition and ultimately fall to zero when the environmental capacity is reached. This maximum possible population size is often modeled instead of the real population size. Determining the density dependence of the population size is difficult in practice; most population models are based on the logistic equation (cf. for example the Lotka-Volterra equations in predator-prey systems). The modeling of the weather data is based on the extrapolation of existing data, which, with short data series, can lead to an underestimation of the risk of extinction due to rare catastrophe years (hurricanes or other rare weather phenomena). An important variable of the PVA is the concept of the smallest viable population (MVP, after the English minimally viable population).
With the help of a PVA, questions that are essential for species protection can be better assessed, for example whether a system of protected areas is large enough to maintain the population or needs to be enlarged, whether the conservation of the population can be sufficiently improved if the habitat is changed (important for example for management plans of protected areas), how changes in population sizes of other species (e.g. of predators ) affect the population of the species and whether a use, e.g. B. by hunting or fishing, is viable for the survival of the population. PVA must be created separately for each population, and in many cases the data required for modeling is lacking. In practice, they are usually only set up for a few populations and species.
literature
- Beissinger, Steven R. and McCullough, Dale R. (2002). Population Viability Analysis, Chicago: University of Chicago Press.
- Manlik, Oliver, Robert C. Lacy and Sherwin WB (2018). Applicability and limitations of sensitivity analyzes for wildlife management. Journal of Applied Ecology 55, 1430-1440. doi: 10.1111 / 1365-2664.13044
- Volker Grimm: Population Risk Analysis (PVA): an overview of concepts, methods and areas of application. Laufener seminar papers 3/2000, pp. 67-77.
- Paquita Hoeck, Ursina Tobler, Rolf Holderegger, Kurt Bollmann, Lukas Keller: Population ecology. Technical report as the basis for supplementing the overall nature conservation concept of the Canton of Zurich, published by the Institute for Evolutionary Biology and Environmental Sciences, University of Zurich on behalf of the Nature Conservation Department. Zurich 2016. PDF .
Individual evidence
- ↑ Entry population hazard analysis . in: Theodor CH Cole: Dictionary of Biology / Dictionary of Biology: German / English / English / German. Springer Verlag, 2014. ISBN 978-3-642-55328-8