Reintroduction affects demographic rates but not their interannual correlations in an endangered shrub

Abstract

Reintroducing endangered species constitutes an important conservation tool. The performance of reintroduced populations is commonly assessed through mean demographic rates (survival, growth, reproduction and fecundity), but rate correlations are less studied despite their role in extinction risk and trait evolution.

In our study, we reintroduced the endangered shrub Vella pseudocytisus subsp. paui in two locations in Spain and compared its demographic performance to that of two natural populations to assess reintroduction success. In both natural and reintroduced sites, we selected sub-locations with presumably more favourable (clay) vs. more stressful (gypsum) soil conditions. We monitored a total of 1269 individuals in natural (12 years) and reintroduced populations (6 years) and compared their mean demographic rates and the within-individual rate correlations between years.

In clay substrate, mean demographic rates of the natural and the reintroduced population were similar, suggesting a successful reintroduction. In contrast, the reintroduced population in gypsum showed higher reproduction and fecundity than the natural population, but lower survival and growth.

Contrary to mean demographic performance, interannual correlations among demographic rates did not vary between natural and reintroduced populations. While reproduction in a given year was positively correlated with later growth and later reproduction, growth in a given year had some negative consequences in subsequent plant performance, especially in gypsum substrate.

Synthesis and applications. Our study shows that stressful conditions may trigger individual-level trade-offs in resource allocation and population-level compensation among demographic rates. Demographic shifts arising from reintroductions in different environmental conditions may be considered by managers as a potential mechanism of resilience against environmental change. Finally, the similarity in rate correlations among sites suggests that information about correlations, which can be relevant when focusing conservation efforts, may be extrapolated from natural to reintroduced populations. This might be particularly reliable for species where rate correlations are demographically influential, such as those living under generally stressful conditions, or lacking buffering mechanisms for demographic variation.