4 results
Impact of sedimentary processes on white-sand vegetation in an Amazonian megafan
- Carlos L. O. Cordeiro, Dilce F. Rossetti, Rogério Gribel, Hanna Tuomisto, Hiran Zani, Carlos A. C. Ferreira, Luiz Coelho
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- Journal:
- Journal of Tropical Ecology / Volume 32 / Issue 6 / November 2016
- Published online by Cambridge University Press:
- 04 October 2016, pp. 498-509
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Amazonian white-sand vegetation has unique tree communities tolerant to nutrient-poor soils of interest for interpreting processes of adaptation in neotropical forests. Part of this phytophysionomy is confined to Late Quaternary megafan palaeo-landforms, thus we posit that sedimentary disturbance is the main ecological factor controlling tree distribution and structuring in this environment. In this study, we characterize the topographic trend of one megafan palaeo-landform using a digital elevation model and verify its relationship to the forest by modelling the canopy height with remote sensing data. We also compare the composition and structure (i.e. canopy height and diameter at breast height) of tree groups from the outer and inner megafan environments based on the integration of remote sensing and floristic data. The latter consist of field inventories of trees ≥ 10 cm dbh using six (500 × 20 m) plots in várzea, terra firme and igapó from the outer megafan and 20 (50 × 20 m) plots in woodlands and forests from the inner megafan. The unweighted pair group method with arithmetic mean (UPGMA) and the non-metric multidimensional scaling (NMDS) were applied for clustering and dissimilarity analyses, respectively. The megafan is a sand-dominated triangular wetland with a topographic gradient of < 15 cm km−1, being more elevated along its axis. The outer megafan has a higher number of tree species (367), taller canopy height (mean of 14.1 m) and higher diameter at breast height (mean of 18.2 cm) than the white-sand forest. The latter records 89 tree species, mean canopy height of 8.4 cm and mean diameter at breast height of 15.3 cm. Trees increase in frequency closer to channels and toward the megafan's axis. The flooded and nutrient-poor sandy megafan substrate favoured the establishment of white-sand vegetation according to the overall megafan topography and morphological heterogeneities inherent to megafan sub-environments.
Seed dispersal of the Brazil nut tree (Bertholletia excelsa) by scatter-hoarding rodents in a central Amazonian forest
- Joanne M. Tuck Haugaasen, Torbjørn Haugaasen, Carlos A. Peres, Rogerio Gribel, Per Wegge
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- Journal:
- Journal of Tropical Ecology / Volume 26 / Issue 3 / May 2010
- Published online by Cambridge University Press:
- 30 March 2010, pp. 251-262
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We know surprisingly little about the fate of seeds of the Brazil nut tree (Bertholletia excelsa) under natural conditions. Here we investigate seed removal, predation and caching of Brazil nuts by scatter-hoarding rodents in the wet and dry seasons, based on an experimental approach using 900 thread-marked seeds. We tracked the fate of seeds handled by these animals to examine how seasonal food availability may influence caching rates, dispersal distances and cache longevity. Most seeds exposed to dispersal trials were removed by scatter-hoarders during the first week in both seasons and seeds were generally buried intact in single-seeded caches within 10 m of seed stations. Seeds were removed significantly faster and buried at greater distances during the dry season. The proportion of seeds buried intact was considerably higher in the wet season (74.4%) than in the dry season (38.2%). Most (99.4%) of the 881 primary caches monitored were recovered, but these had a significantly shorter lifetime in the dry season. Our results show that rodents are highly skilled at retrieving buried Brazil nuts and that caching behaviour appears to be affected by seasonal resource abundance. Reduced seed availability due to intensive harvest could potentially create a dry-season scenario where most seeds succumb to pre-dispersal predation, thereby adversely affecting the natural regeneration of Brazil nut trees.
Pollination ecology of Caryocar brasiliense (Caryocaraceae) in Central Brazil cerrado vegetation
- Rogério Gribel, John D. Hay
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- Journal:
- Journal of Tropical Ecology / Volume 9 / Issue 2 / May 1993
- Published online by Cambridge University Press:
- 10 July 2009, pp. 199-211
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The floral biology, breeding system and pollination of Caryocar brasiliense were studied in the cerrado vegetation of Central Brazil. The large, yellowish-cream, brush-like flowers are pollinated mainly by glossophagine bats (Glossophaga soricina and Anoura geoffroyi). Three non-glossophagine bats (Phyllostomus discolor, Vampyrops lineatus and Carollia perspicillata) and two short probosisced hawk moths (Erinyis ello and Pseudosphinx tetrio) may also act as occasional pollinators. Caryocar brasiliense is self-compatible although it sets significantly more fruits when crossed than when selfed. The natural fruit set (fruit/flower ratio) and seed set (seed/ovule ratio) are 3.1% and 1.0% respectively. Most of the fruits and seeds are formed through the action of the flower visitors, despite the fact that about 20% of the non-visited flowers receive self pollen on at least one stigma.
Flowering phenology and pollination biology of Ceiba pentandra (Bombacaceae) in Central Amazonia
- Rogério Gribel, Peter E. Gibbs, Aldenora L. Queiróz
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- Journal:
- Journal of Tropical Ecology / Volume 15 / Issue 3 / May 1999
- Published online by Cambridge University Press:
- 01 May 1999, pp. 247-263
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The flowering and fruiting phenology, floral biology, pollination ecology, and breeding system of the emergent tree Ceiba pentandra were studied in the Brazilian Central Amazon. Of the 21 trees studied, 17 flowered once or twice during the 6-y study period. The mass flowering and relatively high production of nectar per flower (mean of 310 μl) resulted in a high nectar production (over 200 l per tree per season). Flowers were visited by a wide range of nocturnal (bats, marsupials, night monkeys, hawk moths) and diurnal (bees, wasps, hummingbirds) animals, but only phyllostomid bats, especially Phyllostomus hastatus and Phyllostomus discolor, played a relevant role promoting cross-pollination. Pollinations which occurred in the early morning by diurnal floral visitors were ineffective since pollen tubes did not traverse the style and reach the ovary before stylar abscission. Despite the apparently normal growth of the self-pollen tubes, controlled pollinations carried out in one tree revealed no fruit set by selfing and 16.8% fruit set by crossing. Progeny analysis from this ‘self-incompatible’ tree using isozyme markers showed that fruits resulting from mixed-pollination (i.e., 50% self- plus 50% cross-pollen on the stigma) set only 1.6% of selfed seeds. The percentage of outcrossed seeds in fruits resulting from open-pollination in two neighbouring planted trees, which flowered in isolation and concomitantly, was estimated at 91% and 71%. Two isolated trees did not set any fruits despite massive flowering, whereas two others set large quantities of seed, supporting data in the literature stating that variable degrees of self-fertility may occur in this species.
RESUMO. A fenologia de floração e de frutificação, a biologia floral, a ecologia de polinização e o sistema reprodutivo da árvore emergente Ceiba pentandra foram estudados na Amazônia Central Brasileira. Dezessete das 21 árvores estudadas (doze nativas e nove plantadas de sementes de procedência desconhecida) floriram uma ou duas vezes cada uma durante os seis anos do estudo. A maior parte das árvores nativas floriu massivamente somente em 1993 e 1996, enquanto que algumas das árvores plantadas floriram massivamente somente em 1992 e 1997. A floração massiva e a relativamente alta produção de néctar por flor (média de 310 μl de néctar secretado por flor por noite) resultaram em uma alta produção de néctar por árvore (mais
de 200 l de néctar por árvore por estação de floração). As flores de C. pentandra foram visitadas por uma grande variedade de animais noturnos (morcegos, marsupiais, macacos-da-noite, mariposas) e diurnos (abelhas, vespas, beija-flores), mas somente morcegos, especialmente Phyllostomus hastatus e Phyllostomus discolor, parecem exercer papel relevante promovendo a polinização cruzada. Não foram detectadas diferenças na capacidade dos tubos polínicos originados do auto-pólem e do pólem cruzado de se desenvolverem até o ovário e penetrarem nos óvulos. Polinizações que ocorreram no início da manhã foram inefetivas, uma vez que os tubos polínicos não tiveram suficiente tempo para atravessarem o estilete antes da sua abscisão. Apesar do aparente desenvolvimento normal dos tubos polínicos oriundos do auto-pólem, polinizações controladas executadas em uma árvore resultaram em nenhuma produção de frutos em flores auto-polinizadas e em 16,8% de produção de frutos nas flores que sofreram polinização cruzada. A produção natural de frutos (polinização aberta) na mesma árvore foi estimada em 0,7%. O uso de marcadores isoenzimáticos na análise genética da progênie dessa mesma árvore ‘auto-incompatível’ revelou que, em frutos resultantes de polinizações mistas (isto é; uma mistura contendo 50% auto-pólem e 50% pólem cruzado, depositada no estigma), apenas cerca de 1,6% das sementes foram originadas por eventos de auto-fecundação. A proporção de sementes originadas por fecundação cruzada em frutos formados naturalmente em duas árvores plantadas e vizinhas, que floriram isoladamente e concomitantemente em 1992, foi de 91% e 71%, respectivamente. Duas árvores isoladas não produziram frutos, apesar de intensa floração, enquanto que outras duas também isoladas frutificaram em abundância. Essas observações reforçam dados da literatura que indicam a ocorrência de níveis muito variáveis de auto-fertilidade entre as árvores dessa espécie.