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Chen, S., Z. Fan, D.D. Roby, Y. Lu, C. Chen, Q. Huang, L. Cheng, and J. Zhu. 2015. Human harvest, climate change and their synergistic effects drove the Chinese Crested Tern to the brink of extinction. Global Ecology and Conservation 4:137-145.


Synergistic effect refers to simultaneous actions of separate factors which have a greater
total effect than the sum of the individual factor effects. However, there has been a
limited knowledge on how synergistic effects occur and individual roles of different drivers
are not often considered. Therefore, it becomes quite challenging to manage multiple
threatening processes simultaneously in order to mitigate biodiversity loss. In this regard,
our hypothesis is, if the traits actually play different roles in the synergistic interaction,
conservation efforts could be made more effectively. To understand the synergistic effect
and test our hypothesis, we examined the processes associated with the endangerment of
critically endangered Chinese Crested Tern (Thalasseus bernsteini), whose total population
number was estimated no more than 50. Through monitoring of breeding colonies and
investigations into causative factors, combined with other data on human activities,
we found that widespread human harvest of seabird eggs and increasing frequency of
typhoons are the major factors that threatened the Chinese Crested Tern. Furthermore,
28 percent of breeding failures were due to the synergistic effects in which egg harvestinduced
renestings suffered the higher frequent typhoons. In such combined interactions,
the egg harvest has clearly served as a proximal factor for the population decline, and
the superimposition of enhanced typhoon activity further accelerated the species toward
imminent extinction. Our findings suggest that species endangerment, on one hand, should
be treated as a synergistic process, while conservation efforts, on the other hand, should
focus principally on combatting the threat that triggers synergistic effects.


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July (3rd Quarter/Summer) 2015

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  1. U.S. Geological Survey