Lake Tahoe vs. Lake Kinneret phytoplankton: comparison of long-term taxonomic size structure consistency

Abstract

Both theoretical ecology and lake management practices acutely need quantitative assessment tools for the analysis of structural changes taking place in the plankton community. Size spectrum, a tool allowing such assessment, is usually based on size distributions of organisms irrespective of their taxonomy. The size-frequency distribution of taxonomic units in an assemblage, named by us traditional taxonomic size spectrum (TTSS), has been applied for over 70 years, but seldom in aquatic ecology. Longterm consistency of phytoplankton TTSS, evidenced even during pronounced ecosystem changes, was described for the subtropical and eutrophic Lake Kinneret, Israel. In the present study, we examine whether consistent TTSS patterns prevail across ecosystems, and apply the TTSS to the phytoplankton of the temperate and oligotrophic Lake Tahoe, USA.A typical annual TTSS pattern was revealed, and its details were analyzed quantitatively by hierarchical cluster analysis. The Tahoe TTSS similarity level during 4 years (Pearson r = 0.92 to 0.99) is comparable to that of the Kinneret during its stable period; even for pairs divided by >20 years, r > 0.8. While the Tahoe TTSS general pattern resembles that of Lake Kinneret, the two lakes are distinguishable by means of cluster analysis. A high similarity (r = 0.91) was found between the eight-year averaged TTSSs of the two lakes. The above results let us suppose that the longterm consistency of the aquatic assemblage taxonomic size structure pattern is a general phenomenon. This pattern deserves special attention at times of accelerated global climate change, acerbated by burgeoning anthropogenic impacts.

Lago Maggiore oligotrophication as seen from the long-term evolution of its phytoplankton taxonomic size structure

“…1) was close to the respective estimates found for other lakes (Kamenir et al 2006(Kamenir et al , 2008). Concomitantly, its minimal level (r=0.669), describing a pair of the years (1989 and 2003) at the beginning and the end of the studied process, was found previously only for pairs taken from two different ecosystems (meso-eutrophic Lake Kinneret and oligotrophic Lake Tahoe; Kamenir et al 2008). Both these years look abnormal in their year-groups ( Fig.…”

“…While the two lakes are so different, the stability of their phytoplankton taxonomic size structure is characterized by a comparable level of the applied similarity index (Pearson r here). A close level of similarity was also demonstrated by oligotrophic Lake Tahoe, USA (Kamenir et al 2008). In all three lakes, we can see 'more-or-less' the same size distribution resembling a bell symmetrical in LogV scale.…”

“…The interesting and valuable phenomenon (for many theoretical and applied applications) of long-term consistency of the general pattern of phytoplankton TTSS was initially established for one lake (Kinneret; Kamenir et al 2006). The following studies (Kamenir et al 2008) have supported its more general nature, including oligotrophic lake condi-tions. Thus, it seems that the phytoplankton TTSS pattern is likely to be supported by some ecological mechanisms of a very general nature and demands further studies considering specific objects and situations of general ecological interest (Kamenir et al 2008).…”

“…The following studies (Kamenir et al 2008) have supported its more general nature, including oligotrophic lake condi-tions. Thus, it seems that the phytoplankton TTSS pattern is likely to be supported by some ecological mechanisms of a very general nature and demands further studies considering specific objects and situations of general ecological interest (Kamenir et al 2008). The high self-similarity of the TTSS general pattern during long-term (>20 years) periods can be interpreted as the strength of the ecological community self-maintenance.…”

“…If very close general patterns (a lognormal distribution dissected by deep troughs to 2-4 main peaks) can be observed across long time intervals (>20 years) in very distant regions, one should look for very general mechanisms producing and supporting such distribution patterns (Havlicek & Carpenter 2001;Kamenir et al 2008). Even a short analysis produces a number of such intertwined mechanisms (Kamenir et al 2008). Therefore, specific studies are needed to select one possible factor and produce a pattern difference sufficiently big and consistent to be estimated quantitatively and compared with the change in the impact factors involved.…”