By OCAdmin in Research highlights on

Aspecies-rich ecological community is composed of few abundant species and a large number of rare species. This universal phenomenon,known as species abundance distribution (SAD), hasintrigued a century of research to understand the underlying mechanism for a general law of community, yet remains controversial.In past, most of studies have treated SAD as a static pattern. It is believed that changes of biodiversity and community structure through time are regulated by compensatory dynamics in a species-rich ecosystem. That is, community is compensated by constituent species: some species become rare, while the others turn to dominance through time. This turnover of species abundances and maintenance of rare part of SAD keep the ecosystem resilient to environmental changes.As such, the shape of SAD remains static even though species are constantly changing. However, in reality, SAD may not be static over time.Specifically, when an ecosystem ispushed by environmental changes over a critical threshold, the balance of rare and dominant species may fail and rare species may not recover from disturbances.

To understand dynamic nature of SAD, a research team led by professors Chih-hao Hsieh and Takeshi Miki and their students, Cheng-Han Tsai and Chun-Wei Chang, of the Institute of Oceanography, National Taiwan University, with collaborative effortsof scientists from Japan studied long-term variation of phytoplankton in Lake Biwa (Figure 1), the third oldest lake in the world and the largest in Japan (water reservoir for Kyoto and Osaka). This study discoveredthe recovery failure of rare species and changes of SAD and biodiversity of phytoplankton community in response to a directionally changing environment in Lake Biwa. This study is published in Ecology andwas recently highlighted by NHK and Asahi News, Japan. Using a unique >30 year-long phytoplankton time series data of Lake Biwa, the study found those rare species that adapt to littoral (coastal macrophyte, sandy and rocky shore) habitats have disappeared in late 1980’s in response to lake warming,decreased water level variation,and re-oligotrophication (i.e., reduced nutrient supply) (Figure 2).According to the study, the disappearance of specific rare species is also correlated with the shifting climatic conditions in late 1980’s, and these species have yet been recovered.Stabilizing water level variation by lake management could further obstruct the recovery of rare species. The study showed that the changes of specific functional response group (littoral species) explain the dynamic cause of SAD. That is, rare and common species in a community can result from their specific responses to environmental changes.The rise and fall of rare species from functional groups provides a species trait-based and dynamical explanation for why some species are rare and others are common in nature.

References

Tsai,C. H., T. Miki, C. W. Chang, K. Ishikawa, S. Ichise, M. Kumagai, and C. H. Hsieh (2014) Phytoplankton functional group dynamics explain species abundance distribution in a directionally changing environment. Ecology. DOI: 10.1890/13-1946.1

Hsieh, C. H., K. Ishikawa, Y. Sakai, T. Ishikawa, S. Ichise, Y. Yamamoto, T. C. Kuo, H. D. Park, N. Yamamura, and M. Kumagai (2010) Phytoplankton community reorganization driven by eutrophication and warming in Lake Biwa. Aquatic Sciences. 72: 467-483.

Figure 1. Images of phytoplankton taken from Lake Biwa. (Photo by Keiichiro Watanabe)

Figure 2. Decadal change in species abundance distribution of phytoplankton in Lake Biwa. The rare species that adapt to littoral habitats (green) have disappeared in late 1980’s in response to lake warming, decreased water level variation, and re-oligotrophication, and have not yet recovered.