Population viability analysis (PVA) is used to quantify the risks faced by species under alternative management regimes. Bayesian PVAs allow uncertainty in the parameters of the underlying population model to be incorporated into the predictions. Geoff Heard and colleagues have developed a Bayesian stochastic patch occupancy model (SPOM) and used this model to assess the viability of a metapopulation of the growling grass frog (Litoria raniformis) under different urbanization scenarios.
They fitted a Bayesian model that accounted for imperfect detection to a multi-season occupancy dataset for the growling grass frog (collected from across northern Melbourne). The probability of extinction was modelled as a function of effective wetland area, aquatic vegetation cover and connectivity, using logistic regression. The probability of colonization was modelled as a function of connectivity alone. They then simulated the dynamics of a metapopulation of L. raniformis subject to differing levels of urbanization and compensatory wetland creation.
There was considerable uncertainty in both the probability of quasiextinction and the minimum number of occupied wetlands under most urbanization scenarios. Uncertainty around the change in quasiextinction risk and minimum metapopulation size increased with increasing habitat loss. For their focal metapopulation, the analysis revealed that significant investment in new wetlands may be required to offset the impacts of urbanization.
Geoff explains in his blog why his SPOM is valuable: “The cool thing is that one can explore, using these simulations, how the metapopulation will respond to particular management scenarios. You can take away particular patches to represent habitat loss, you can tweak patch characteristics to represent habitat enhancement or degradation, and you can even add in new patches to see how habitat creation affects metapopulation viability.”
He uses it to explore management options for the endangered growling grass frog but the technique should prove just as useful in the management of any endangered species existing as multiple interacting populations.
Heard GW, MA McCarthy, MP Scroggie, JB Baumgartner & KM Parris (2013). A Bayesian model of metapopulation viability, with application to an endangered amphibian. Diversity and Distributions 19: 555-566. http://onlinelibrary.wiley.com/ doi/10.1111/ddi.12052/full