Spear-headed by Old Dominion University grad student and seed dispersal aficionado Spencer Schubert, this paper describes an experiment in which we investigated the context-dependence of post-dispersal predation of acorns on microhabitat and annual variation in acorn crops. We show that the probability of surviving post-dispersal predation is lowest in areas with dense rodent populations (chaparral) and that it's risky to be cached below trees that had acorns in a given year. Such context-dependence can thus have a strong effect on oak regeneration, as well as jay caching behavior.
Now out at Acta Oecologica [Link]
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:
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:
Sometimes one gets the nicest surprises from unexpected sources. After receiving a notification that our review paper on scatter-hoarding corvids as seed dispersers was cited, I realized that it was featured in a podcast by the Field Guides, two young New Yorkers that like to discuss botanical and biological topics in a very accessible format. Well, in late October, they recorded a podcast about acorns and the many animals that interact with them. Drawing on our paper, as well as many other sources, the Field Guides provide a compelling story about the many ways in which acorns matter, and even mention that jays could be used to restore oak habitat!
Check out the great podcast here:
I was recently asked to comment on the potential impact of the 2017 solar eclipse on the behavior of birds. Discover magazine wrote this cool article about the topic:
I am proud to present the first product of a collaboration with Michal Bogdziewicz, a colleague based at the Adam Mickiewicz University in Poznan, Poland. Michal got his hands on a neat seed production and pollen monitoring data set for oaks and beech in Poland, and he used it to test several hypotheses about the drivers of mast-seeding in these closely related, yet very different groups of trees. We found that in oaks, flowering synchrony of trees, as measured by the length of pollen availability period, plays a major role in driving seed production, while in beech it was the actual amount of available pollen that correlated most strongly with seed crops the following fall. The results highlight that there are multiple mechanistic pathways that converge to mast-seeding. The study was published in our favorite journal, Ecology!
Read it here: http://onlinelibrary.wiley.com/doi/10.1002/ecy.1951/full
Our recent paper on the habitat preferences by caching island scrub-jays was awarded the cover of the journal Current Zoology. We found that jays preferentially cache acorns in areas of high oak recruitment. They avoid open and grassy areas and put a disproportional amount of caches below coastal sage scrub and chaparral plants. Incidentally, this is also where we find a majority of oak seedlings in the landscape.
Read more here: https://academic.oup.com/cz/issue/63/4academic.oup.com/cz/issue/63/4
Our newest paper just became available in one of my favorite journals, The American Naturalist. Using data from over 1,000 oaks across California, we investigated the predictions of the Terminal Investment Hypothesis, which suggests that organisms should invest disproportionally into reproduction preceding their death. Using annual acorn counts and growth rates of trees, we found no changes in the absolute or relative investments in seed production in California oaks over the last 6 years before their natural death. This is the first study to address this important life-history strategy in long-lived plants.
Read it here: http://www.journals.uchicago.edu/doi/abs/10.1086/691161
In this study, Walt Koenig and I show that avian hoarders - birds that store their seeds for the winter - play an important role in mediating competition among oak species. California scrub-jays (Aphelocoma californica), high-quality seed dispersers of acorns, show up in large numbers on valley oaks (Quercus lobata) when no other acorns are available in the landscape. For the oaks, this means that a majority of their acorns is at least given a chance because jays cache their acorns in the ground. Whenever possible, however, the jays avoid valley oaks because acorn woodpeckers (Melanerpes formicivorus) defend them vigorously and thus attack the foraging jays. Therefore, the seed production by oaks that compete with valley oaks, in this case California blue oaks (Q. douglasii) results in increased predation of acorns by acorn woodpeckers - birds that store their acorns in so-called granary trees which provide no chance for germination or seedling establishment. All together, the blue oaks are thus indirectly competing with valley oaks, a phenomenon termed apparent predation, via the jays and the woodpeckers.
Find the early access version of the article here:
The last of my Ph.D. papers has just been published in the journal Current Zoology. We show that island scrub-jays have strong spatial (habitat) preferences when caching acorns. Because they cache a majority of acorns in areas of oak recruitment - identified by seedling counts - we argue that the jays have contributed to the rapid passive restoration of Santa Cruz Island.
Read the paper here [link]