Demographic back-casting reveals that subtle dimensions of climate change have strong effects on population viability

摘要

The effects of climate change on population viability reflect the net influence of potentially diverse responses of individual-level demographic processes (growth, survival, regeneration) to multiple components of climate. Articulating climate-demography connections can facilitate forecasts of responses to future climate change as well as back-casts that may reveal how populations responded to historical climate change. We studied climate-demography relationships in the cactusCyclindriopuntia imbricata; previous work indicated that our focal population has high abundance but a negative population growth rate, where deaths exceed births, suggesting that it persists under extinction debt. We parameterized a climate-dependent integral projection model with data from a 14-year field study, then back-casted expected population growth rates since 1900 to test the hypothesis that recent climate change has driven this population into extinction debt. We found clear patterns of climate change in our central New Mexico study region but, contrary to our hypothesis,C. imbricatahas most likely benefitted from recent climate change and is on track to reach replacement-level population growth within 37 years, or sooner if climate change accelerates. Furthermore, the strongest feature of climate change (a trend towards years that are overall warmer and drier, captured by the first principal component of inter-annual variation) was not the main driver of population responses. Instead, temporal trends in population growth were dominated by more subtle, seasonal climatic factors with relatively weak signals of recent change (wetter and milder cool seasons, captured by the second and third principal components). Synthesis. Our results highlight the challenges of back-casting or forecasting population dynamics under climate change, since the most apparent features of climate change may not be the most important drivers of ecological responses. Environmentally explicit demographic models can help meet this challenge, but they must consider the magnitudes of different aspects of climate change alongside the magnitudes of demographic responses to those changes.