Bayesian salamanders: analysing the demography of an underground population of the European plethodontid Speleomantes strinatii with state-space modelling
1 Boyd Orr Centre for Population and Ecosystem Health Division of Ecology and Evolutionary Biology Faculty of Biomedical and Life Sciences University of Glasgow Glasgow G12 8QQ, UK
2 DIPTERIS Università di Genova Corso Europa 26 I-16132 Genova, Italy and Gruppo Speleologico "A. Issel" Villa Comunale ex-Borzino, CP 21I-16012 Busalla (GE), Italy
BMC Ecology 2010, 10:4 doi:10.1186/1472-6785-10-4Published: 2 February 2010
It has been suggested that Plethodontid salamanders are excellent candidates for indicating ecosystem health. However, detailed, long-term data sets of their populations are rare, limiting our understanding of the demographic processes underlying their population fluctuations. Here we present a demographic analysis based on a 1996 - 2008 data set on an underground population of Speleomantes strinatii (Aellen) in NW Italy. We utilised a Bayesian state-space approach allowing us to parameterise a stage-structured Lefkovitch model. We used all the available population data from annual temporary removal experiments to provide us with the baseline data on the numbers of juveniles, subadults and adult males and females present at any given time.
Sampling the posterior chains of the converged state-space model gives us the likelihood distributions of the state-specific demographic rates and the associated uncertainty of these estimates. Analysing the resulting parameterised Lefkovitch matrices shows that the population growth is very close to 1, and that at population equilibrium we expect half of the individuals present to be adults of reproductive age which is what we also observe in the data. Elasticity analysis shows that adult survival is the key determinant for population growth.
This analysis demonstrates how an understanding of population demography can be gained from structured population data even in a case where following marked individuals over their whole lifespan is not practical.