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State-space model for Svalbard ptarmigan

Citation

Marolla, Filippo et al. (2021), State-space model for Svalbard ptarmigan, Dryad, Dataset, https://doi.org/10.5061/dryad.ngf1vhht0

Abstract

To improve understanding and management of the consequences of current rapid environmental change, ecologists advocate using long-term monitoring data series to generate iterative near-term predictions of ecosystem responses. This approach allows scientific evidence to increase rapidly and management strategies to be tailored simultaneously. Iterative near-term forecasting may therefore be particularly useful for adaptive monitoring of ecosystems subjected to rapid climate change. Here, we show how to implement near-term forecasting in the case of a harvested population of rock ptarmigan in high-arctic Svalbard, a region subjected to the largest and most rapid climate change on Earth. We fitted state-space models to ptarmigan counts from point-transect distance-sampling during 2005-2019 and developed two types of predictions: 1) explanatory predictions to quantify the effect of potential drivers of ptarmigan population dynamics, and 2) anticipatory predictions to assess the ability of candidate models of increasing complexity to forecast next-year population density. Based on the explanatory predictions, we found that a recent increasing trend in the Svalbard rock ptarmigan population can be attributed to major changes in winter climate. Currently, a strong positive effect of increasing average winter temperature on ptarmigan population growth outweighs the negative impacts of other manifestations of climate change such as rain-on-snow events. Moreover, the ptarmigan population may compensate for current harvest levels. Based on the anticipatory predictions, the near-term forecasting ability of the models improved non-linearly with the length of the time series, but yielded good forecasts even based on a short time series. The inclusion of ecological predictors improved forecasts of sharp changes in next-year population density, demonstrating the value of ecosystem-based monitoring. Overall, our study illustrates the power of integrating near-term forecasting in monitoring systems to aid understanding and management of wildlife populations exposed to rapid climate change. We provide recommendations for how to improve this approach.

Methods

The time series of the Svalbard rock ptarmigan population is part of an ecosystem-wide monitoring system that encompasses the period of the most rapid recent climate warming with associated changes in the abiotic and biotic domains of the Svalbard terrestrial ecosystem. Ptarmigan data come from point-transect distance sampling conducted by the Norwegian Polar Institute on calling territorial males during four weeks in April. 

Usage Notes

Please refer to the metadata file for detailed description of the variables and parameters in the RData file. 

Funding

Norwegian Research Council