ACTITUD HACIA EL CAMBIO DE USO DE SUELO EN LA REGIÓN GOLFO CENTRO DE VERACRUZ, MÉXICO

El objetivo de esta investigación fue conocer la actitud de los productores del mango y caña de azúcar hacia el cambio de uso de suelo, en la región Golfo centro de Veracruz, México. La metodología fue propuesta para analizar la actitud con la técnica de Likert, combinando aspectos sociales y agro-ecológicos, a través de enunciados sociales, ambientales y económicos. Los productores (n=90) de siete ejidos se estratificaron en tres grupos: mango, caña reciente y caña persistente. Los resultados demuestran actitud positiva alta (3.95) hacia el cambio de uso del suelo, significativamente mayor (ANDEVA F=3.69; p=0.03) para los productores de caña reciente comparados con los productores del mango (3.79). En contraste, los productores de caña persistente presentaron actitud similar (3.85) comparada con los productores de mango. Usando el análisis multivariado basado en las dimensiones sociales, ambientales, económicas y autoevaluación prospectiva - retrospectiva, se identificaron tres grupos: rechazo-rechazo, aceptación-rechazo y aceptación-aceptación

RECRUITMENT, GROWTH AND SURVIVAL OF LESSONIA-NIGRESCENS (PHAEOPHYTA) AT VARIOUS TIDAL LEVELS IN EXPOSED HABITATS OF CENTRAL CHILE

Mortality effects of ecological factors were not generally tested in field population studies of benthic algae. Recruitment, growth and survival of the low-intertidal/shallow-subtidal L. nigrescens were measured at 4 tidal levels in exposed rocky habitats in central Chile. Through experimental manipulation the effects of the abiotic environment, small-size grazers and mid-littoral algae on the survival of the juveniles of L. nigrescens recruited in the upper part of its vertical range were evaluated. Disturbance effects of adult plants and grazing effects of large-sized subtidal herbivores on juvenile recruitment, and effects of interspecific interference on the survival of newly settled juveniles were also evaluated. Interference by adult plants and grazing by large-sized subtidal herbivores completely inhibit recruitment. In their absence, the abiotic environment limits recruitment and growth of L. nigrescens at the uppermost tidal level while inter-specific interference owing to over-shading by the fastest growing individuals limits the lower-most extent of the belt. Interference by adult plants and grazing are patchy and often mutually exclusive in the field. Recruitment within the band of L. nigrescens is maximal in patchy vegetational openings which are large enough to experience reduced disturbance by adult plants and small enough for reduced grazing pressure. In mature, consolidated belts of L. nigrescens on vertical walls these openings correspond to roughly triangular areas with the hypotenuse formed by interholdfast distances of 1-2 m. Such patchy vegetation openings can be produced normally by dislodgement of old, eroded plants

CEPHALIC ANATOMY OF THE HERBIVOROUS FISH GIRELLA-LAEVIFRONS (OSTEICHTHYES, KYPHOSIDAE) - MECHANICAL CONSIDERATIONS OF ITS TROPHIC FUNCTION

Structural and functional restrictions hindering the development of efficient mechanism for cropping and ingestion of algal material could constitute an explanatory hypothesis for the observed low diversity of herbivorous fishes. In this study, the cephalic structures of the herbivorous kyphosid fish Girella laevifrons (Tschudi 1844) are described, including a functional analysis of its alimentary apparatus. This species can be characterized by having: (i) a great freedom of movement between the dentary and articular-angular, (ii) a double insertion of the muscle adductor mandibulae Al in both faces of the maxilla, (iii) specialized teeth, long and flexible with a peculiar articular condyle at their anterior base, (iv) a mobile articulation between ceratohyal and dorsal hypohyal, and (v) a well developed branchiostegal system. A mechanism based on a mandibular manipulation associated with a slow suction of a large volume of water is proposed. This mechanism would allow the ingestion of large amounts of algae (as long stripes) in a continuous fashion. The combined activity of both an oral manipulation and buccal suction systems are possible by the existence of a decoupling of the anterior and posterior regions of the buccal cavity involving the jaw and the hyoid arch. The adaptive value of this mechanism is discussed in relation of the feeding strategies utilized by this species

ECOLOGICAL DOMINANCE OF LESSONIA-NIGRESCENS (PHAEOPHYTA) IN CENTRAL CHILE

Experimental removal of various types of dominant canopies has resulted in predictable patterns of competitive hierarchies among algae in intertidal and subtidal communities. Few attempts were made to distinguish functionally different groups of algae in these communities. The intertidal/subtidal boundary of exposed rocky habitats in central Chile is numerically dominated by the kelp L. nigrescens. When the kelp is absent, 2 other algal formations can be found at this intertidal level. In vegetational openings surrounded by individuals of L. nigrescens and in the absence of large grazers, large patches of Geldium chilense occur. In vegetational openings with abundance of grazers, patches of calcareous algae and bare rock are normally found. Through experimental manipulation the ecological changes of the understory algal assemblages following removal of the numerically dominant L. nigrescens were evaluated and with minor differences, the 3 functional groups of algae distinguished elsewhere (canopy forming, fugitive and obligated understory) also occur here. By experimental removal at different seasons and in presence or absence of sea urchins the occurrence of the 2 algal formations found in areas devoid of kelp is explained

Feeding selectivity of the herbivorous fish <i>Scartichthys viridis</i>

The ecological importance of fish herbivory was examined in a temperate rocky intertidal zone along the central Chilean coast. In this system, the blenny Scartichthys viridis is the most abundant and only herbivorous fish. We describe its diet, determine its field food selectivity (gut contents vs macroalgal field availability comparison), and report on its laboratory dietary preferences in a multiple-choice feeding experiment. Finally, we evaluate the relative effects of fish herbivory and grazing invertebrates on macroalgal abundance, distribution and diversity patterns in the field, using replicated exclusion cages to manipulate grazing intensity. S. viridis was found to be a selective grazer; its diet was dominated by 2 macroalgae: the green Ulva and the red Gelidium, representing 32.6 and 41.4% of its total gut content biomass, respectively. Ulva was consumed much above its field availability while Gelidium was selected only during fall-winter. In the laboratory, S. viridis selected the green macroalgae Ulva rigida and Codium dimorphum and avoided Gelidium chilense. We suggest that Gelidium may be included in its diet due to the limited availability of Ulva in the field. Experimental exclusion of this fish from rocky surfaces resulted in increased abundance of green foliose macroalgae (U. rigida and Enteromorpha linza), and, to a much lesser extent, of the red foliose macroalgae G. chilense, Porphyra columbina, and Mazzaella laminarioides, and of the brown macroalgae Colpomenia phaeodactyla and Petalonia fascia, as well as an extension of the distribution of P. columbina from the high intertidal to the mid intertidal zone, where it normally does not occur. Exclusion of grazing invertebrates resulted in a decrease in foliose macroalgal species richness, but had no effect on biomass. To our knowledge, this is the first experimental demonstration of the effect of an herbivorous fish on macroalgal community structure in a temperate rocky intertidal area. The selective feeding displayed by S, viridis, its high numerical abundance, and the results of the herbivore exclusion experiment suggest its importance in maintaining the low abundance of foliose macroalgae and the high relative cover of brown and red crustose macroalgae, characteristic of many low to mid rocky intertidal areas along the coast of central Chile

COMPARATIVE-ANALYSIS OF THE HEAD MORPHOLOGY OF PACIFIC TEMPERATE KYPHOSID FISHES - A MORPHOFUNCTIONAL APPROACH TO PREY-CAPTURE MECHANISMS

Vial & Ojeda (1990) proposed that the low diversity of herbivorous fishes observed among Percoids might be owing to the existence of morpho-functional restrictions of the feeding apparatus that hinder the acquisition of efficient mechanisms for cropping and ingesting plant material. The morphological and functional evidence presented therein for the herbivorous kyphoid Girella laevifrons indicates that its morphological specializations are related to structural decouplings of the anterior and posterior regions of the buccal cavity involving the jaw and the hyoid arch. Functionally, these decouplings allow the ingestion of algae in a continuous fashion at low energetic cost. In this study, we evaluate the general validity of the proposed model by means of a morphological and functional comparative analysis of the cephalic structures of the four most abundant Kyphosid species of the Chilean coast: the girellids Girella laevifrons (Tschudi), Girella albostriata Steindachner, and Graus nigra Philippi, and the scorpid Scorpis chilensis Guichenot. We found great osteological and myological similarities between the two strict herbivores, G. albostriata and G. laevifrons, thus suggesting that the mechanism previously described for the latter species corresponds very closely to that of the former. This mechanism provides for mandibular manipulation carried out independently by the upper jaw and for a decoupling of the lower jaw into two mechanical units. Graus and Scorpis display a somewhat different morphological design. Although both maintain the intrahyoid decoupling shared by all kyphosid species, they do not present mechanical independence between the upper and lower jaw, nor a capacity for intramandibular movements. In Graus, teeth are well developed, conical, and slightly curved toward the interior. These characteristics make possible a trophic mechanism primarily based on a strong biting especially well suited for carnivory. The structural plan of Scorpis appears more distant from species in the other two genera, althoug it shares with them characters such as the double tendon of the A1 muscle in the maxilla, the intrahyoid articulation, the type of teeth, their replacement system, and the general design of the suspensorium. The particular morphology of the adductor muscles, and the mandibular design of Scorpis suggest a trophic mechanism mainly based on a rapid suction. From a functional viewpoint, the structural differences encountered in the four species analyzed may be understood as modifications related to their different mechanisms of prey capture