Composition and seasonality of an Amphipod community assoiated to the algae Bryocladia trysigera

Abstract

The monthly fluctuations of amphipods associated to the algae Bryocladia trysigera was described from March 1997 to February 1998 at the rocky shore known as Poço de Anchieta in the Peruíbe Beach, Itanhaém, Southeastern Brazil. A total of 75,344 individuals were sampled, belonging to 10 species and 9 families. Three species dominated the phytal in number: Hyale nigra, Caprella danileviskii and Caprella penantis. Despite the alternation in dominance of the 3 most abundant species, the amphipod species composition remained generally unchanged, so that the majority of the species were observed in all sampling months. The temporally changing pattern of the community structure, with a decline in amphipod abundance in winter followed by an increase in spring, was probably due to a higher predation pressure in winter period.

Ecological model of competitive interaction among three species of amphipods associated to Bryocladia thrysigera (J. Agardh) and extreme environmental stress effects

“…Based on data sampled by Valério-Berardo and Flynn (2002), natural population rates of the three dominant species (Hyale nigra, Caprella danileviskii and Caprella penantis) were calculated.…”

“…The cosine term for the first equation was replaced by the term sin (inverse of cosine) as H. nigra carrying capacity varies in opposite direction from that of the two other species (Valério-Berardo and Flynn, 2002) (see Fig. 1).…”

“…The parameters c i (cycle frequency) and k i (cycle amplitude) were considered based on the biennial cycle verified by Valério-Berardo and Flynn (2002), imposing a 180 days cycle adaptation with alternating dominance. Amplitudes were considered by the average density of each population (data from Valério-Berardo and Flynn, 2002).…”

“…Amplitudes were considered by the average density of each population (data from Valério-Berardo and Flynn, 2002). Population peaks were recorded and the ratio (mean population/population peak) calculated and then applied to the adjusted theoretical carrying capacity values.…”

“…Valério-Berardo and Flynn (2002) suggested that numerical fluctuation of dominant species indicates an attempt to distinguish ecological niche by means of reproductive strategies such as life cycles, incubation periods and fecundity. Attempts to explain this temporal pattern ended in failure when data on physical-chemical elements (e.g., salinity, water temperature, etc.)…”