The influence of different disturbance frequencies on the species richness, diversity and equitability of phytoplankton in shallow lakes

Abstract

The relationships between the species richness, diversity and equitability of phytoplankton is discussed in the context of Connell's (1978, Science 199: 1304 Intermediate Disturbance Hypothesis (IDH). The records of 759 vertical phytoplankton samples, which were obtained from four shallow central European lakes (Balaton, Neusiedlersee, and two small artificial ponds) at daily to weekly intervals were analysed.1) The Shannon-Weaver function was used to measure diversity of the recorded species composition of the phytoplankton. It is shown on fictitious data that compositional diversity is sensitive to the number of coequilibrating species provided that the suspected interrelationship between diversity and 'complexity' is amenable to the application of this method.2) The disturbance scale that was developed on the basis of the field records fits well to Reynolds' (1988, Verh. int. Ver. Limnol. 23: 683-691) derivation: ~3 days qualifies as high frequency, approximately 3-8 days as intermediate frequency and > 8-9 days as low frequency of disturbance for phytoplankton.3) Arithmetical means of the compositional diversity of phytoplankton under different frequencies of disturbance support the hypothesis that maximal diversity appears at intermediate frequencies.4) There are different reasons for decrease in diversity at higher and lower frequencies. Inequitability diminishes diversity at low disturbance; while species number decreases at high frequencies.5) The case of Neusiedlersee calls attention to the fact that it is difficult, if at all possible, to differentiate between the indices under continuous stress and high frequency of disturbance in lakes in temperate regions. Similar species number-equitability pattern are induced by both and it is also presumable that high frequency disturbance can itself effect a serious stress.6) The striking effects that regular major periodic events (e.g. significant changes in the grazing pressure at the onset of the clear-water phase, autumnal cooling) in the plankton have on its species diversity are evident. Thus, the relative importance of intermediate frequency disturbances has its own seasonality: it is increasingly important in periods (partly in the spring, but mostly in the summer-autumn equilibrium phases), in which competition among phytoplankton species is increasing. This observation suggests a way by which the stochasticity-based IDH can be incorporated into rather more deterministic explanations (e.g. PEG-model;Sommer et al., 1986. Archiv fur Hydrobiologie 106: 433-471) of plankton succession.

Influence of fish farming in net cages on phytoplankton structure: a case study in a subtropical Brazilian reservoir

“…The regimen of mixing water influences directly the phytoplankton structure (Padisák, 1993), as that can affect the availability of nutrients in the water column (Lopes et al, 2005). The decrease in diversity observed in September 2010, May and July 2011 in station N2, and in November 2010 in C1, is a result of the decrease in the number of species and evenness, as observed by Padisák (1993).…”

“…Thus, although evenness has decreased until March 2011, diversity has increased due to an increase in the number of species. However, it is worth emphasizing that the decrease in diversity associated with a high proliferation of Cyanobacteria has been frequently mentioned in literature (Padisák, 1993;Borics et al, 2000;Figueredo and Giani, 2001;Sant'Anna et al, 2006b).…”

“…The variations in the number of species between summer and winter may be a result of the reduced depth of the studied environments, whereas shallow environments are more likely to suffer environmental changes, for example, the changes caused by rain Tundisi, 1990;Padisák, 1993;Straskraba, 1998).…”

Does the intermediate disturbance hypothesis comply with thermodynamics?

“…The data from Keszthely Bay, are particularly well fitted to this theoretical investigation, as offshore samples were taken daily between 1 April and 28 October (Padisak, 1992(Padisak, , 1993 . The data show that an increasing compositional diversity occurs from 1 April to the beginning of June in a period of intermediate frequency of disturbances caused by wind, while a radical change in early July coincided with the clear-water phase .…”

Diversity of phytoplankton community in different urban aquatic ecosystems in metropolitan João Pessoa, state of Paraíba, Brazil

“…According to Padisák (1993), a low degree of diversity in any biological community may be caused by a low number of species or a low degree of evenness, which is related to the occurrence of dominant species. Thus, the lower diversity in the river may be attributed to the smaller number of species in comparison to the other ecosystems.…”