A metapopulation approach to Examining the effect of restorations on population viability in the Indiana Dunes

Background/Question/Methods

In order to increase metapopulation viability, new populations of Cirsium pitcheri, a federal threatened dune plant with metapopulation dynamics, was introduced to the Indiana Dunes National Lakeshore in 1994.  To determine the degree to which addition of populations affect Cirsium pitcheri metapopulation viability at Indiana Dunes, we use 23 years of demographic data, to quantitatively predict persistence rates through the use of matrix models to simulate the progression of the metapopulation with and without the addition of reintroduced populations. We also use simulations to project how many populations are needed for the metapopulation to persist for a 50 years.  Through the comparison of the vital rates between natural and reintroduced populations within the metapopulation via life-table response experiments (LTRE), we assess demographic responses on population growth rate (λ).  Lastly, we use elasticity analysis to determine whether natural or reintroduced populations have a greater contribution to the metapopulation growth rate. We expect that Indiana Dunes’ Cirsium pitcherimetapopulation viability will improve with the addition of reintroduced populations as compared to without the addition of reintroductions.  These analyses aid management decisions through the determination of the number of reintroductions required and how each population improves the metapopulation viability.

Results/Conclusions

Reintroductions decreased the probability of extinction of the Indiana Dunes C. pitcheri  Metapopulation though only by a few years; however, the addition of more populations would not yield a significant increase in population viability. LTRE analyses suggest that population type; native or reintroduced has no significant bearing on the contribution on the growth rate with each individual populations dynamics influenced by differences in their life histories and habitat. Positive contributions of growth transitions to larger plants and negative contributions of fecundity are the driving factors that that have the greatest impacts on the overall metapopulation growth rate. Elasticity analysis of the contributions of the different vital rates to λ shows strong linear relationships between growth and fecundity with population growth rates. In contrast stasis has an inverse relationship with population growth. Overall, the addition of two Cirsium pitcheri populations to Indiana Dunes Metapopulation has improved the viability of the species from a metapopulation perspective.