Our new paper in the Journal of Applied Ecology: "Oak habitat recovery on California's largest islands: scenarios for the role of corvid dispersal"

One of the most rewarding aspects of science is to put the data and insights gained from research projects to use in conservation and management efforts. Our newest paper, a large collaboration between scientists from the University of Melbourne, University of Queensland, James Cook University, as well as the Cornell Lab of Ornithology and the Smithsonian Institution, but also land managers from the U.S. Geological Survey and The Nature Conservancy, does just that. We used a novel modeling technique, ensemble modeling, to simulate the population dynamics of oaks, as well as the seed dispersal and predation by gravity and animals, with the goal of creating scenarios of oak expansion under different seed dispersal dynamics.

​Specifically, we wanted to answer two questions:

• i) was seed dispersal by scatter-hoarding island scrub-jays necessary for the pace of oak recovery that was observed on Santa Cruz Island?
• ii) What would the potential impact of an island scrub-jay population of Santa Rosa be on the pace and extent of oak recovery if they were reintroduced to the island from which they have gone extinct?

First, we built a simulation model of the species dynamics and interactions, and parameterized it with lots of field data and published estimates for growth rates, expansion rates, seed predation and dispersal. Then, we applied the model to Santa Cruz Island, and trained the model to keep only the parameter constellations and settings that were able to best retrace the known recovery from 1985 to 2005.

The best model that included jay dispersal was able to recreate 92%, while the best model without jays could only reach 43% of the recovered areas. This is strong evidence for the role of island scrub-jay seed dispersal in the extent and pace of oak habitat recovery on Santa Cruz Island.

To create scenarios of potential oak recovery on neighboring Santa Rosa Island, from which jays have gone extinct, we used the top models to predict the extent of oak recovery over the next 200 years, either under current conditions or in the presence of jays. Elsewhere, managers have suggested that reintroducing the jay could be an effective way to prevent the extinction of the birds, who are not only North America's most range-restricted species, but also vulnerable to West Nile virus or a catastrophic fire.

Our simulation shows that oak habitat would recover more quickly and to a much broader area with the help of jay seed dispersal than under current conditions. In addition to a predicted 500% increase of oak cover, the oaks would also move up the hillsides, where they would help precipitate fog and generally improve ecosystem health.

The model structure can easily be modified for other scenarios where seed dispersal may help habitat recovery. Both the plant and animal aspects can be parameterized with data from other ecosystems and provide managers with a cost-effective and powerful way to create scenarios for the potential outcome of management actions.

The paper is dedicated to our friend Cause Hanna, the late director of the Santa Rosa Island Field Station, who left us way too early. His passion, energy, and love for the islands was unmatched. 

Find the full article here:
http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.13041/full