Browsing by Author "Pacheco, C"

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    Distribution, population structure, population biomass and morphological characteristics of the tunicate Pyura stolonifera in the Bay of Antofagasta, Chile
    (2000) Castilla, JC; Guiñez, R; Alvarado, JL; Pacheco, C; Varas, M
    The present study analyzes the distribution, population structure, population biomass and morphological characteristics of the intertidal tunicate Pyura stolonifera (Heller, 1878) in the Bay of Antofagasta, Chile, where the species shows a reduced geographical range extending around 60-70 km. Three sites along its distribution were studied. At the central site the tunicate presents the widest intertidal belts, reaching nearly 11 m (the mid-intertidal-Pyura-zone shows the higher percent cover). Population dry biomass here averaged up to 20.45 kg.m(-2), representing one of the highest intertidal specific biomasses reported in the literature. Lower values occur towards the borders of its distribution. Population densities were over 1800 indiv..m(-2) at mid-intertidal-Pyura-belts. Crowding and competition potentially affect morphological characteristics and the energy/tissue allocation along the intertidal and geographical gradient of P. stolonifera.
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    Patch recolonization by the tunicate Pyura praeputialis in the rocky intertidal of the Bay of Antofagasta, Chile
    (2001) Alvarado, JL; Pinto, R; Marquet, P; Pacheco, C; Guiñez, R; Castilla, JC
    Patch dynamics of intertidal Pyura praeputialis (Heller, 1838) were studied in experimentally cleared plots at 3 vertical levels (upper, mid arid lower P, praeputialis levels) and 3 sites within the Bay of Antofagasta, Chile. The sites corresponded approximately to the northern limit (Las Conchillas), the center (EL Way), and the southern limit (El Lenguado) of the species geographic distribution in Chile. Replicated 40 x 60 cm quadrats were photographed periodically to follow patch re-colonization. Patch recolonization (recolonized area) followed a sigmoid curve and could be fitted at most sites and levels by applying maximum likelihood techniques to the asymptotic model: y = a/{1 + exp[-(x - b)/c]} where Parameters a and b are asymptotic percentage cover and time for 50 % recovery respectively, and Parameter c defines the shape of the curve (growing phase). Among sites, the highest asymptotic values and fastest recovery times were observed at El Way, in the center of the species distribution. Among levels, the highest asymptotic values were observed in the mid P. praeputialis level quadrats. The perimeter of the patches increased and subsequently decreased as a function of recolonized area. Recruitment observations showed the process of recolonization to be related to the perimeter of the patch to be colonized rather than to the area available. Further more, the recolonization patterns could be predicted using the patch perimeter scaled by a linear coefficient. We believe that the mechanism of recolonization is most probably related to the settlement of recruits to the border of previously settled individuals, possibly mediated by intraspecific self-facilitation mechanisms.