Resumo

WILLINER, Verónica  e  COLLINS, Pablo. Spatial and temporal variation in the activity of freshwater prawn Macrobrachium jelskii (Miers, 1877) (Crustacea, Decapoda, Caridea, Palaemonidae). Ecol. austral [online]. 2002, vol.12, n.1, pp.3-10. ISSN 1667-782X.

Exogenous and endogenous factors model different kind of cycles in ecosystems. Organisms reveal the influence of these components upon their activities. The aim of this study was to examine the circadian rhythm of shrimp Macrobrachium jelskii in a pond at Río Pilcomayo National Park and their possible variation along a transect perpendicular to the coast. Samples were taken with traps every four hours during three days. The highest activity was recorded in the macrophyte zone, mainly by adult males. Feeding process was high during the night in the vegetated area, due to resource abundance. The minimum activity level was recorded in the transition between open and vegetated waters during daylight hours. In open water, feeding activity was almost passive during nighttime, as a response to the trophic cycle and to predator activity. The studied population showed some degree of adjustment to environmental conditions, and showed variations related to sex, age, and presence or absence of vegetation (which provides resources and shelter).

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