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Community closure: species fail to re-establish following local extinctions.
KAUNZINGER, CHRISTINA*,1, LONG, ZACHARY1, STEVENS, M. HENRY2, MORIN, PETER1, 1 Rutgers University, New Brunswick, NJ2 Miami University, Oxford, OH
ABSTRACT- Recent theory predicts that species lost during local extinctions may not be able to re-invade the remaining community, a phenomenon described as community closure. We investigated whether aquatic microbial communities become closed to re-invasion of their original members after local extinctions. We also asked if resource heterogeneity influenced re-invasion success. Communities consisted of 11 species of bacterivorous and herbivorous protozoans with bacterial, microflagellate, and algal resources. A 2 x 2 factorial experiment manipulated the perturbation (constant vs. elevated temperature) and resource base (bacteria, microflagellates and Chlamydomonas (a highly edible alga) vs. bacteria, microflagellates and Chrysapsis (a less edible alga)). Three protozoan species went extinct during the perturbation in both resource treatments. Re-invasion success was variable, and successful re-invaders did not attain pre-perturbation densities. Communities with Chlamydomonas were more resistant to re-invasion than communities with Chrysapsis. These results suggest that species may be unable to re-establish following local extinctions and that re-establishment may be more difficult where resource heterogeneity is higher. Similar local extinctions caused by anthropogenic changes to natural systems may be difficult to reverse.
KEY WORDS: community closure, community assembly, conservation, protists