Can assessing microsite and regeneration niche preferences when introducing endangered species help mitigate extinction debt?

Background/Question/Methods

Rare species introductions and/or assisted migrations are being considered as possible solutions to help mitigate extinction debt in an era of development and climate change. Lessons learned from invasion ecology show the importance of introduced individuals surviving long enough to reproduce and for the resulting recruits to establish and reproduce themselves for population persistence. Therefore, understanding target species’ specific microsite and regeneration requirements is essential yet often unknown when introducing a population. We used an experimental introduction approach and long-term monitoring to asses which microsite characteristics best supported a persistent population of the Florida State endangered Tephrosia angustissima var. corallicola.

Specifically, we asked which of three microsites, light, and soil moisture conditions support optimal transplant survival, growth, and reproduction and recruit germination, growth, reproduction, and survival for T. angustissima var. corallicola?

Three microsites in T. angustissima var. corallicola’s native habitat were designated based on soil moisture, light, and amount of rock exposure. A total of 141 transplants were planted across the three microsites. Measurements were taken on transplant growth, reproduction, and survival and on recruit germination, growth, reproduction, and survival over a 6 year period.

Results/Conclusions

The highest transplant and recruit growth, flowering, and survival occurred in shady, dry microsites; recruits germinated in shadier locations than where adults were planted. Over 1,700 recruits germinated within seven months of initial planting.  Recruits totaled more than 3,000 over the study period. As of September 2009, a population of 160 T. angustissima var. corallicola individuals in all life-stages was being monitored at the introduction site.

As climate changes and species become threatened, introductions and/or assisted migration may become one of our most important tools in the conservation of biodiversity.  Introducing propagules into microsites containing environmental characteristics needed to support propagule survival, growth, and reproduction is essential for introduction success.  Our results showed that recruited seedlings tended to germinate and survive in locations that were dry and shadier than the locations where transplants were planted. Through this study, we learned valuable demographic and microsite and regeneration requirements while mitigating development induced extinction debt.