Contrasting Effects of Mean Intensity and Temporal Variation of Disturbance on a Rocky Seashore

Abstract

Understanding the extent to which natural assemblages withstand changes in the regime of disturbance has considerable practical and theoretical interest. In this paper we examine the separate and interactive effects of intensity, temporal variation, and spatial extent of disturbance on temporal variance in assemblages of algae and invertebrates of rocky shores in the northwest Mediterranean. Temporal variation of disturbance is a predictor variable in the experiment, while temporal variance in abundance and number of taxa and in structure of assemblages are response variables. Multivariate analyses detected a positive relationship between intensity of disturbance and temporal variance in the structure of assemblages, while temporal variation of disturbance elicited the opposite effect. Univariate analyses conducted on the most abundant taxa revealed idiosyncratic patterns, while temporal variance in mean number of taxa was greatly reduced by disturbance, with no distinction among levels of intensity, temporal variation, or spatial extent. These outcomes suggest caution in interpreting the results of experiments in which intensity and temporal variation of disturbance cannot be separated. Distinguishing between these traits of disturbance may be key to predicting the ecological consequence of environmental fluctuations, including those expected under modified climate scenarios.

Temporal variance of disturbance did not affect diversity and structure of a marine fouling community in north-eastern New Zealand

“…This type of response has also been observed in studies focused on predation, where enhanced temporal variability of species abundance and fluctuations in community structure occurred in response to variable regimes (Butler 1989;Navarrete 1996). In contrast, Bertocci et al (2005), studying rocky shore assemblages, found the temporal variance of community structure was reduced by increased temporal variability in disturbance regimes.…”

“…To overcome this problem and to create experiments that unambiguously separate the mean (of either frequency or intensity) from the temporal variability of a predictor variable, Benedetti-Cecchi (2003) proposed an experimental design in which intensity and variability are treated as fixed, orthogonal factors. Previous work that has manipulated temporal variation in disturbance has used a single patterned sequence of disturbance events through time as a representative for a given level of variation in disturbance (Robinson and Sandgren 1983;Bertocci et al 2005;Benedetti-Cecchi et al 2006). However, there are many different possible sequences of events that would lead to the same overall level of variance for a given treatment .…”

Benthic assemblages of rock pools in northern Portugal: seasonal and between-pool variability

“…They thus tend to dominate in rocky habitats exposed to severe abiotic stress, including the mechanical impact of waves (e.g. Bertocci et al 2005), and to intense grazing that can remove potential algal competitors (Steneck 1986, Airoldi 2000, Bulleri et al 2002. As stated above, such favourable abiotic conditions, normally occurring at the study site during the winter might have contributed to present findings on L. incrustans.…”

Disturbance effects of kelp thalli on structure and diversity of a coastal Arctic marine soft-bottom assemblage

“…Secondly, timing of manual thallus movements was less regular than that of thalli moved by tidal currents. Irregularly applied disturbances were reported to affect benthic community traits differently than regularly applied disturbances of identical overall intensity (Bertocci et al 2005;Wollgast et al 2008). Thirdly, benthic species may benefit moderately from the continuous presence of a thallus.…”