The succession dynamics of a macroalgal community after a flood disturbance in a tropical stream from São Paulo State, southeastern Brazil

The succession dynamics of a macroalgal community in a tropical stream (20º58' S and 49º25' W) was investigated after disturbance by a sequence of intensive rains. High precipitation levels caused almost complete loss of the macroalgal community attached to the substratum and provided a strong pressure against its immediate re-establishment. After this disturbance, a weekly sampling program from May 1999 to January 2000 was established to investigate macroalgal recolonization. The community changed greatly throughout the succession process. The number of species varied from one to seven per sampling. Global abundance of macroalgal community did not reveal a consistent temporal pattern of variation. In early succession stages, the morphological form of tufts dominated, followed by unbranched filaments. Latter succession stages showed the almost exclusive occurrence of gelatinous forms, including filaments and colonies. The succession trajectory was mediated by phosphorus availability in which community composition followed a scheme of changes in growth forms. However, we believe that deterministic and stochastic processes occur in lotic ecosystems, but they are dependent on the length of time considered in the succession analyses.

Quantitative variables applied to phenological studies of Sargassum vulgare C. Agardh (Phaeophyceae - Fucales) from Ilha Grande Bay, State of Rio de Janeiro

The suitability of quantitative variables for phenological studies was evaluated in a population of the brown seaweed Sargassum vulgare from "Praia das Gordas", Angra dos Reis, Ilha Grande Bay, state of Rio de Janeiro. From June 1998 to May 1999, twenty adult individuals were randomly sampled at bimonthly intervals. Fifteen variables related to the vegetative and reproductive development of perennial and non-perennial parts of the individuals were quantified. Variables related to the non-perennial parts were more useful than those related to the perennial parts, because they showed a clear variation over the year. Vegetative development declined from June to October, and increased from October to February, when maximum median values of thallus height, total dry mass, non-perennial parts dry mass, and degree of branching were reached. This pattern coincided with those described for other species of the genus from warm temperate regions. Thallus height, a usually employed character in other phenological studies of Sargassum, showed lower coefficient of variation (53.2%) than those related to dry mass (72.0% to 182.3%). Peak of reproduction occurred from June to August, according to the following variables: fertile primary lateral branches number and dry mass and receptacles dry mass. Non-perennial parts dry mass and receptacles dry mass are recommended for phenological studies of S. vulgare. This methodological procedure avoids the sampling of the whole individual and warrants its regeneration from the perennial parts.

Patterns of spatial distribution in macroalgal communities from tropical lotic ecosystems

Three sampling sites were analysed in each of the following tropical regions: 1) northwestern São Paulo State, representing a disturbed region; 2) Bonito, Mato Grosso do Sul State, representing a hard water region; and 3) Ubatuba, northern costal region of São Paulo State, a well preserved tropical rainforest region. The hard water region had the highest mean values for macroalgal species richness (6.3) and diversity index (H' = 0.62). Northwest and rainforest regions had the highest percent cover values (22.5% and 17.0%, respectively). All sites in the northwest region had one or two dominant species (percent cover significantly higher than the remaining species), characterizing the niche pre-emption distribution pattern. The same pattern was found in two sites of the Atlantic rainforest. The hard water region had dominance of one species in two out of the three sites, but differently from the northwest region, niche overlap values were lower, evidencing a patch distribution. Competition for space was one of the main factors to explain spatial distribution. Overall, sites characterized by niche pre-emption had lower species richness, higher values for niche width and overlap, dominance index and percent cover of dominant species. In contrast, sites characterized by patch distribution had higher species richness and lower values for niche overlap and width, dominance index and percent cover.

Population structure of Eschweilera coriacea (DC.) S. A. Mori in forest fragments in eastern Brazilian Amazonia

The population structure of a common canopy tree was examined in three sites to investigate the possible effects of forest fragmentation in eastern Amazonia. Evidence for the escape hypothesis of differential seed/seedling survival was evaluated. Two 1 ha plots were established at each site and all individuals of Eschweilera coriacea (DC.) S. A. Mori over 1 m tall were tagged, measured and mapped. Smaller individuals were recorded in the same way within subplots. Mature individuals were abundant at all sites with densities of 32-52 ha-1. The species exhibited substantial regeneration, although total population density varied fourfold among sites (1,256-4,805 individuals ha-1). Overall, juveniles were clumped while adults were randomly distributed. The difference between the dispersion pattern of adults and juveniles supported the escape hypothesis. However, no difference in population structure among sites could be related to the forest fragmentation.

Harvesting of Protium heptaphyllum (Aubl.) March. seeds (Burseraceae) by the leaf-cutting ant Atta sexdens L. promotes seed aggregation and seedling mortality

The role played by leaf-cutting ants as seed dispersers of non-myrmecochorous plants remains poorly understood. Here we document the harvesting of Protium heptaphyllum (Aubl.) March. seeds (Burseraceae) by the leaf-cutting ant Atta sexdens L. and its consequences for (1) seed deposition pattern; (2) seed germination; and (3) seedling mortality. The study was carried out at Dois Irmãos, a 390 ha reserve of Atlantic forest, northeast Brazil. Ant-seed harvesting on the ground was detected in 18.5% of all fruiting trees and ants harvested 41.1% ± 19.7% of the seed crop (mean ± s). In average, ants piled seeds 3.4 ± 2.2 m away from the trunk of parent trees and seed density in these piles reached 128.8 ± 138.8 seeds 0.25 m² during the peak of seed discarding by ants. During a 13 month period, mean seedling mortality varied from 0.54% up to 10.6% in ant-made seed piles vs. 0.05-4.2% in control samples, what resulted in a total seedling mortality of 97.7% vs. 81%. Ants systematically cut seedling epicotyls, accounting for 55% of seedling mortality in seed piles, whereas only 14 seedlings (4.2%) were cut by ants in the control samples. Our results suggest that seed harvesting by A. sexdens (1) affects approximately 20% of fruiting P. heptaphyllum trees and their seed crops; (2) promotes short-distance seed dispersal and high levels of seed aggregation; and (3) reduces seedling survival beneath parents.

Reproductive phenology of Melocactus (Cactaceae) species from Chapada Diamantina, Bahia, Brazil

This paper discusses the phenological strategies of Melocactus glaucescens Buining & Brederoo, M. paucispinus G. Heimen & R. Paul, M. ernestii Vaupel and M. ×albicephalus Buining & Brederoo, species from Chapada Diamantina, northeastern Brazil. Melocactus glaucescens, M. ernestii and M. ×albicephalus occur sympatrically in an area of "caatinga"/"cerrado" vegetation, and M. paucispinus in an area of "cerrado"/"campo rupestre". The superposition of flowering in these sympatric taxa was compared and analyzed. The phenology of M. paucispinus was correlated with both abiotic and biotic factors. Flowering of M. glaucescens and M. ×albicephalus were observed to be continuous (though with moderate peaks of activity), while fruiting was sub-annual. Melocactus ernestii exhibited an annual pattern of both flowering and fruiting; while in M. paucispinus the same patterns were sub-annual. These sympatric taxa showed 40% overlap of flowering periods, reaching to more than 50% in paired combinations of taxa, considering both the number of specimens flowering, as well as the quantity of resources being offered. Available information indicates that these taxa share pollinators, but phenological data rejects the hypothesis of shared pollinators and supports the hypothesis of hybridization in the study area. Rainfall was negatively correlated with flowering in M. paucispinus, but positively correlated with fruiting. Flowering of M. paucispinus in dry periods of the year avoids that erect flowers positioned in terminal cephalium, exposed in open areas of the vegetation, be damaged for the rains, while fruiting in rainy periods can be favorable to the dispersion and germination of this species.

Floral resources used by insects in a grassland community in Southern Brazil

The goal of the present study was to identify plant species used as food source, the floral resources utilized, and the insects that visit flowers in a grassland community in southern Brazil. The study was carried out in an area of one hectare, located in a grassland formation in the Parque Estadual de Itapuã, State of Rio Grande do Sul, Brazil. The flowering pattern was seasonal, and richness and abundance of insects was higher during the period of high resource availability. Flowers of 106 species of angiosperms (73 genera and 34 families) were used as source of floral resources for 219 species (2,767 specimens) of insects. A total of 91.5% of plant species were visited by bees, 53.8% by flies, 34.9% by wasps, 22.6% by butterflies, and 12.3% by beetles. Nectar was the main resource consumed by the visitors (41.1%). Asteraceae was the richest (38 spp.) and most visited family, with 63.1% of the species and 49.5% of all specimens of recorded insects. Bees were the most representative insects (33.2% spp., 65% indiv.), followed by flies (26.9% spp., 16.5% indiv.), wasps, butterflies and beetles. 40 plant species were considered important resources for the floral visitors' community, due to high number of, both, species and individuals recorded in their flowers. The family Asteraceae as a species set was the main floral resource used by insect visitors through the year and has great importance for the maintenance of populations of many species of bees, flies, wasps and butterflies in the studied area.

Cyanoaggregatum brasiliense gen. et sp. nov., a new chroococcal Cyanobacteria from Southern Brazil

The paper proposed Cyanoaggregatum brasiliense, a new genus and species from the plankton of a subtropical brackish coastal lagoon from Rio Grande do Sul State, South Brazil. It differs from all other members of Chroococcales by its characteristic arrangement of cells in irregular groups distributed in a single, flat or slightly curved layer, on irregular rows, slightly distant from each other, forming a mosaic-like pattern slightly below the surface of the mucilaginous colonial envelope. The cell division in one plane perpendicular to the long axis and the lack of pseudo-filaments indicate its classification in the family Synechococcaceae, sub-family Aphanothecoideae. The general characteristics, the diagnostic criteria and the taxonomic position are discussed, and a comparison between Cyanoaggregatum and its most closely related genera is presented. Physical and chemical data on the studied lagoon and geographical distribution are presented.

Biomass and chemical composition of Nitella furcata subsp. mucronata var. mucronata f. oligospira (A. Braun) R. D. Wood (Chlorophyta, Characeae) in the littoral region of Ninféias Pond, São Paulo, Southeast Brazil

Temporal variation of Nitella furcata (Roxburgh ex Bruzelius) C. Agardh emend. R. D. Wood subsp. mucronata (A. Braun) R. D. Wood var. mucronata f. oligospira (A. Braun) R. D. Wood biomass and chemical composition were studied at the Ninféias Pond (23°38'18.9" S, 46°37'16.3" W), a mesotrophic reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, Municipality of São Paulo, Southeast Brazil. Plants were collected monthly from October 1996 to October 1997 at three fixed stations of reservoir's littoral region. Charophyte biomass spatial distribution pattern did not vary significantly throughout the study period at all sampling stations. As to seasonal variation, the highest average values of the total alga biomass (98.35-266.06 g m-2 DW) were registered during the rainy season, whereas lowest values (48.86-170.56 g m-2 DW) were in the dry season. P values varied from 23.8 to 225.2 mg m-2 and C from 139 to 353 mg m-2. During the rainy season, greatest air and water temperature, rain precipitation, turbidity and dissolved inorganic nitrogen values were measured, constituting the best conditions for charophyte growth. Water temperature and nutrient availability in the reservoir played a decisive role towards growth and accumulation of algal biomass.

Pollination biology in Jacaranda copaia (Aubl.) D. Don. (Bignoniaceae) at the "Floresta Nacional do Tapajós", Central Amazon, Brazil

Jacaranda copaia (Aubl.) D. Don is a pioneer tree widespread in the Brazilian Amazon, usually found colonizing forest gaps and altered areas, and the forest fragment edges. This study investigated aspects of the floral biology, breeding system and pollinators of J. copaia trees. Flowering lasts from August to November, during the low rainfall period extending up to four weeks per tree and 3-4 months for the population as a whole, characterizing a cornucopia flowering pattern. The fruit set ends in the beginning of the rainy season, with wind dispersed winged seeds. Fruit set from open pollination was 1.06% (n = 6,932). Hand pollination using self-pollen (n = 2,099) did not set fruits. Cross-pollination resulted in 6.54% fruit set (n = 2,524), representing six times more than the natural pollination rate (1.06%, n = 6,932). Flowers excluded from insect visitation (automatic self-pollination) did not set fruits (n = 5,372). Pollen tube growth down to ovary was detected under fluorescence microcoscopy in cross-pollinated and selfed pistils. The species is an obligate allogamous plant, with late-acting self-incompatibility system. Approximately 40 species of native bees visited the flowers, but the main pollinators were medium-sized solitary bees as Euglossa and Centris species due to the compatibility between their body sizes with the corolla tube, direct contact with the reproductive structures and high frequency of visits.

Patterns of litter production in a secondary alluvial Atlantic Rain Forest in southern Brazil

Above-ground litter production is one of the most accessible ways to estimate ecosystem productivity, nutrient fluxes and carbon transfers. Phenological patterns and climatic conditions are still not fully explained well for tropical and subtropical forests under less pronounced dry season and non-seasonal climates, as well as the interaction of these patterns with successional dynamics. Monthly litterfall was estimated for two years in a 9 to 10 year old secondary alluvial Atlantic Rain forest. Total litterfall was higher in the site with more developed vegetation (6.4 ± 1.2 ton ha-1 year-1; 95% confidence interval) as compared to the site with less developed vegetation (3.0 ± 1.0 ton ha-1 year-1). The monthly production of 11 litter fractions (eight fractions comprising the leaf litter of the seven main species of the community and other species; reproductive parts, twigs £ 2 cm diameter, and miscellaneous material) were correlated with meteorological variables making possible to identify three patterns of deposition. The main pattern, dominated by leaf-exchanging species, consisted of a cycle with the highest litterfall at the beginning of the rainy season, preceding by basically three months the peaks of the annual cycles of rainfall and temperatures. Other two patterns, dominated by brevi-deciduous species, peaked at the end of the rainy season and at the end of the non-rainy season. Tropical and subtropical dry forests that present the highest leaf fall gradually earlier than rain forests (as the studied sites) are possibly related to the start of senescence process. It seems that such process is triggered earlier by a more severe hydric stress, besides other factors linked to a minor physiological activity of plants that result in abscission.

Pollen morphology of species of Hortia (Rutaceae)

A palinological study covering all 10 species of the Neotropical genus Hortia Vand. (Rutaceae) was conducted. Pollen grains were collected from herbarium exsiccates, acetolysed and mounted in glycerine jelly on glass slides. The grains were studied under light and scanning electron microscopy, including measurements of polar and equatorial diameters, shape of the grains, number and shape of apertures, and thickness of the exine. The results demonstrated that the genus is stenopalynous, with pollen grains in monads, subprolate to prolate, 3-colporate, with very thick exine and a psilate-perforate pattern of ornamentation. Pollen grains of all species revealed a great similarity, with few variations in the pattern of ornamentation of exine, number and form of apertures and measurements. Although well-characterized palinologycally, pollen features did not furnish relevant information on the position of Hortia into an intrafamilial phylogeny.

The coastal restinga vegetation of Pará, Brazilian Amazon: a synthesis

The present article reviews studies (some unpublished) of the vegetation of coastal sandy soils (restinga) along the coast of Pará State, northern Brazil. A total of 411 higher plant species are reported; Fabaceae, Poaceae, Cyperaceae, Rubiaceae and Myrtaceae are the most species-rich families. Nearly half of the restinga species (48%) are terrestrial herbs; palms, trees and shrubs account for 39% of the species, the remainder being lianas and epiphytes. Species are frequently wide-spread and occur in coastal areas of Southeastern Brazil as well as at inland sites in the Amazon region. Only two species appear to be exclusively coastal; whereas other species appear to exhibit a preference for sandy soils. Plant assemblages are commonly classified by means of "formations" associated with certain habitats but current data do not allow the description of well-defined plant associations. The species composition at different sites along the Pará coast does not show any clear regional grouping pattern. Seasonal changes in the composition of restinga vegetation are most probably linked to variation in ground water level. Restinga forest is mostly low and open; among the dominant tree species are Humiria balsamifera Aubl., Pouteria ramiflora (Mart.) Radlk., Anacardium occidentale L., Byrsonima crassifolia (L.) Kunth, and Tapirira guianensis Aubl.

Test of hypotheses about herbivory and chemical defences of Qualea parviflora (Vochysiaceae) in Brazilian Cerrado

(Test of hypotheses about herbivory and chemical defences of Qualea parviflora (Vochysiaceae) in Brazilian Cerrado). Qualea parviflora Mart. (Vochysiaceae), a widely distributed tree found in different habitats in Brazilian Cerrado (savanna), provides resources for a great variety of insects. In this study, we tested two hypotheses about plant investment in anti-herbivore defences along a fertility gradient in Cerrado: the carbon/nitrogen balance (CNBH) and resource availability (RAH). We also investigated how the pattern of herbivory varies through the year and among three types of vegetation in Brazilian Cerrado - campo sujo, cerrado sensu strictu and cerradão. Sampling was conducted in three types of vegetation and in rainy (January and November) and dry months (April and July). Damage on 20 completely expanded leaves, leaf nutrients, sclerophlylly, total phenols and tannins were recorded for each plant (n = 30). When leaves were young, less sclerophyllous, and with higher concentration of nutrients and tannins, damage by herbivores was about 7% in cerrado sensu stricto and 3% in campo sujo. Mature leaves did not show any significant difference on herbivory among habitats, that varied from 6 to 9%. Nutrient availability to plants is an important factor determining production of secondary metabolites in Q. parviflora, corroborating the CNBH. The absence of correlation between damaged leaf area and tannin concentration did not corroborate the RAH, suggesting that tannin production is not strongly influenced by herbivores on Q. parviflora.

One-winged Drosophila subobscura: a phenotype with an obscure genetic basis

A line of one-winged Drosophila subobscura was studied. The absent wing is substituted by a bulky structure with macro and microchaetes, showing a thoracic appearance. Genetic crosses showed that there is no way to select for the trait by simple crossing. The number of one-winged flies in the various generations was always low. In one case a wingless fly was also obtained. The trait presents an unknown genetic pattern.