Browsing by Author "NAVARRETE, SA"

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    BARNACLE WALLS AS MEDIATORS OF INTERTIDAL MUSSEL RECRUITMENT - EFFECTS OF PATCH SIZE ON THE UTILIZATION OF SPACE
    (1990) NAVARRETE, SA; CASTILLA, JC
    Recruitment of the competitively dominant mussel Perumytilus purpuratus to the mid rocky intertidal zone in central Chile depends upon the presence of recruitment-mediators such as mussel clumps, filamentous algae or barnacle shells. The relationship between the lateral walls of adult barnacles and the recruitment of P. purpuratus was investigated in a semi-sheltered rocky habitat at Las Cruces, central Chile. Changes in number of individuals and percent cover of sessile species were recorded for 8 mo (January to September 1988) in different sized patches of bare rock. All patches were surrounded by barnacle beds. Throughout the study, P. purpuratus recruited only on the walls of adult barnacles that formed the patch borders, and never on bare rock. Conversely barnacles recruited directly on the bare surface of cleared patches. Regressions of numbers of individuals in relation to patch area showed that mussel recruits outnumbered those of barnacles in patches smaller than 35.5 cm2. Above this critical patch area, the number of barnacle recruits was progressively larger than that of mussels. The area of barnacle walls suitable for mussel recruitment increases linearly with increasing patch perimeter, while the area suitable for barnacle recruitment is a function of patch area. The number of recruits was related to the substratum availability in different patch sizes, suggesting that recruitment of barnacles and mussels is not limited by larval abundance. The probability of mussels monopolarizing the patches was higher in small than in large patches; the chance for barnacles to monopolize large patches increased with increasing size of patch. Consequently a barnacle-dominated substratum may change to a mussel-dominated one depending upon the relative abundances of small and large patches. A barnacle bed disrupted in several small patches will provide more substratum for mussel recruitment than if only few large patches are produced. Possible effects of patch and predator sizes on intertidal community structure are discussed.
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    BODY-SIZE, POPULATION-DENSITY, AND THE ENERGETIC EQUIVALENCE RULE
    (1995) MARQUET, PA; NAVARRETE, SA; CASTILLA, JC
    1. We critically evaluated the Energetic Equivalence Rule (EER) with regard to its underlying theoretical framework, its dependence of a particular relationship between population density and body size, and the way it is calculated.
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    FORAGING ACTIVITIES OF CHILEAN INTERTIDAL CRABS ACANTHOCYCLUS-GAYI MILNE-EDWARDS ET LUCAS AND ACANTHOCYCLUS-HASSLERI RATHBUN
    (1988) NAVARRETE, SA; CASTILLA, JC
    Foraging activities of the Chilean intertidal carnivorous crabs Acanthocyclus gayi Milne-Edwards et Lucas and A. hassleri Rathbun were studied in the laboratory. These crabs are morphologically similar and coexist in the intertidal zone, feeding mainly on mussels, barnacles, and gastropods. The consumption rates of A. gayi were generally higher than those of A. hassleri, when feeding on mussels and limpets, but similar, when feeding on barnacles. Both species foraged more actively underwater. Out of water, foraging activity was greater at night than during the day. Both crab species preferred the smallest sizes of the mussel Perumytilus purpuratus Lamarck, well below the maximum size they can handle. In both species, the critical size of mussels increased linearly with crab size. A. hassleri was able to handle larger mussels than its congenergic species, but when > 15 mm carapace width both crabs could handle even the largest mussels found in the field. A. gayi strongly preferred the mussel Semimytilus algosus (Gould), which is much less abundant in the intertidal than P. purpuratus, and the least preferred item was the barnacle Jehlius cirratus (Darwin), one of the most abundant organisms in the field. In paired experiments, A. hassleri showed the same preference order as A. gayi, and when all prey species were available, A. hassleri preferred J. cirratus over any other prey. Both crabs used similar techniques to handle, open, and eat their prey. Crabs adopted any of six different techniques to handle mussels, depending largely on the crab-prey size ratio. For handling limpets and barnacles, the crabs used two different techniques, which also depended on crab and prey sizes. In conclusion, the two crab species are similar, not only morphologically, but also in their trophic behaviour. Factors enabling the coexistence of both species in the intertidal zone need further study. The results are compared with those obtained for other crab species and the possible ecological role of Chilean crabs in the community is discussed.
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    GALLERIES OF THE CRABS ACANTHOCYCLUS UNDER INTERTIDAL MUSSEL BEDS - THEIR EFFECTS ON THE USE OF PRIMARY SUBSTRATUM
    (1989) CASTILLA, JC; LUXORO, C; NAVARRETE, SA
    The mid rocky intertidal of Cachagua, like many other rocky sites in central Chile, is dominated by beds of the mussel Perumytilus purpuratus. Under these mussel beds the predatory crabs Acanthocyclus gayi and A. hassleri build separated bind-ending galleries whose floor is the rock and the roof is the mussel bed. Samples of 1 m2 of Perumytilus beds (100% cover) showed that the surface area of crab galleries ranged between 17.4% and 34.7% of the total area, and that 80% of the crabs were A. hassleri. In 130 of the 157 galleries analyzed, one or two conspecific crabs were found. In the remainder, up to six crabs were found together. Comparisons between the floor of crab galleries and similar rocky areas under the mussel bed, but without galleries (controls), showed that both density and cover of Balanus flosculus, Phymactis clematis and bryozoans were significantly higher in galleries. Similarly, the total number of species was greater on the floor of the galleries than in the controls. Although from outward appearances the cover of P. purpuratus remained at 100%, crab galleries allowed more sessile species to occupy the mid intertidal fringe. This occurs because of the introduction of species typical of the lower intertidal, which would otherwise be excluded by mussels.
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    RESOURCE PARTITIONING BETWEEN INTERTIDAL PREDATORY CRABS - INTERFERENCE AND REFUGE UTILIZATION
    (1990) NAVARRETE, SA; CASTILLA, JC
    Acanthocyclus gayi Milne-Edwards et Lucas and A. hassleri Rathbun are two intertidal predatory crabs that coexist along the rocky coast of Chile. The two species are morphologically similar and remain hidden inside refuges during diurnal low tide periods. Their microhabitat distributions and diets were studied at two sites in central Chile. Juveniles of each species were found coexisting in three microhabitats (mussel beds, rock crevices and kelp holdfasts), although most lived amongst mid intertidal mussels. Most recruits were observed in mussel beds. In contrast to juveniles, adults were segregated by microhabitat. Most adults of A. hassleri were in galleries built through mussel beds, while adults of A. gayi were found only in rock crevices and holdfasts of the kelp Lessonia nigrescens Bory. Diets of both species were similar, even between adults. Because of the large dietary overlap observed between juveniles and adults of the two species, and the apparent abundance of food in the field, segregation between adult crabs did not seem to result from competition for food. Because thickness of the mussel bed was positively correlated with the density and size of crabs, ther may be a paucity of suitable living spaces for adult crabs. In contrast to juvenile crabs, which shared refuges during low tides, adults aggressively defended refuges, both intra- and interspecifically. Laboratory and field experiments showed strong asymmetry in interspecific contests. Adults of A. hassleri, which have a proportionally larger master chela, were able to aggressively exclude adults of A. gayi from refuges provided in the laboratory, and from galleries in mussel beds in the field. Segregation between adult crabs seem to be the outcome of interference competition for refuges. Refuges are readily available for small crabs and hence they coexist in the same microhabitats. Refuges are hypothesized to provide protection for Acanthocyclus crabs from visual predators, such as the kelp gull Laru dominicanus. Analysis of relative predation pressure on crabs by gulls indicates that galleries in mussel beds constitute an effective refuge against this kind of predator.
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    SCALING POPULATION-DENSITY TO BODY SIZE IN ROCKY INTERTIDAL COMMUNITIES
    (1990) MARQUET, PA; NAVARRETE, SA; CASTILLA, JC
    Interspecific comparisons of animal population density to body size has been the subject of active research in the last decade, especially for terrestrial animals when considering particular taxa or taxonomic assemblages. Studies of rocky intertidal communities showed that animal population density scales with body size to the -0.77 power. This relation held within local communities representing a broad array of animal taxa and was not affected by a dramatic alteration in the network of between-species interactions, as revealed by two long-term human exclusion experiments.