COMPENSATORY DYNAMICS IN PLANKTONIC COMMUNITY RESPONSES TO pH PERTURBATIONS

Abstract

Compensatory population dynamics, in which species that decline in response to an environmental perturbation are replaced by similar species, may be crucial in maintaining processes performed by functional groups of species. Compensatory dynamics may be produced by negative interactions among species, such that the decrease in abundance of a species releases the suppression of another species and allows it to increase. We conducted a mesocosm experiment in Trout Lake, Wisconsin, USA, to test the hypothesis that compensatory shifts in species abundances play a role in overall planktonic community response to pH perturbation. In 2000‐L mesocosms over a period of six weeks, we contrasted a control treatment with two acidified treatments (press, sustained pH = 4.7; and pulse, alternating pH = 4.7 and ambient pH). In the acidified treatments, we saw changes in abundance of the major zooplankton and phytoplankton species, but we observed few cases of compensatory dynamics. Nonetheless, when present, compensatory dynamics could be strong. Analyses using autoregressive models revealed negative interactions among species that could potentially lead to compensatory dynamics. However, this potential for compensatory dynamics was not realized in cases where all species were sensitive to the pH perturbations. Therefore, compensatory dynamics that buffer community responses to perturbations may be limited in communities in which many species are sensitive to the perturbation.

Compensatory Dynamics in Zooplankton Community Responses to Acidification: Measurement and Mechanisms

“…Our results are consistent with other studies indicating that compensatory dynamics among species within a functional group can reduce more aggregate responses to perturbation (Frost et al 1995, Tilman 1996, Havens and Carlson 1998, Micheli et al 1999, Klug et al 2000. To predict ecosystem responses to environmental change, however, ecologists must understand the mechanisms controlling functional group responses to perturbations like acidification.…”

“…We quantified the extent of compensatory dynamics among species within functional groups using a variance ratio (Schluter 1984, McCulloch 1985, Frost et al 1995, Klug et al 2000. For each aggregated group of species (G), variance is a function of the variance of individual species (S) and the covariance among species (Box et al 1978 This approach provides a measure of the magnitude of covariation among species in a functional group, relative to the variation of the constituent species.…”

“…4 diatoms and chrysophytes in an acidification experiment conducted in mesocosms (Klug et al 2000). 1 1, No.…”

Rapid eco-evolutionary responses in perturbed phytoplankton communities

“…Compensatory dynamics have previously been shown to play an important role in community recovery [34,53], although on longer timescales (inter-annual variation) synchronous dynamics may be more prevalent [54]. Among phytoplankton morpho-taxa specifically, as we also observed, compensatory dynamics can regulate community biomass in response to acid perturbation via opposing interactions of diatoms (or cryptophytes), with chlorophytes [15]; with larger-bodied chlorophytes being more acid tolerant. In the Pulse treatment in particular, wherein recovery of initial environmental conditions were permitted, such compensatory dynamics were most prevalent.…”

“…These ecological interactions can buffer density, total biomass and functional fluctuations potentially arising following species extinction [12][13][14]. Compensatory dynamics occur when two species covary negatively, with species being asymmetrically affected by the perturbation [15]. Compensation occurs via the insurance effect when competing taxa are functionally redundant [16][17][18].…”