RESUMO

UNLABELLED: • PREMISE OF THE STUDY: For tropical forest understory plants, the ability to grow, survive, and reproduce is limited by the availability of light. The extent to which reproduction incurs a survival or growth cost may change with light availability, plant size, and adaptation to shade, and may vary among similar species.• METHODS: We estimated size-specific rates of growth, survival, and reproduction (vital rates), for two neotropical understory herbs (order Zingiberales) in a premontane tropical rainforest in Costa Rica. During three annual censuses we monitored 1278 plants, measuring leaf area, number of inflorescences, and canopy openness. We fit regression models of all vital rates and evaluated them over a range of light levels. The best fitting models were selected using Akaike's Information Criterion.• KEY RESULTS: All vital rates were significantly influenced by size in both species, but not always by light. Increasing light resulted in higher growth and a higher probability of reproduction in both species, but lower survival in one species. Both species grew at small sizes but shrank at larger sizes. The size at which shrinkage began differed among species and light environments. Vital rates of large individuals were more sensitive to changes in light than small individuals.• CONCLUSIONS: Increasing light does not always positively influence vital rates; the extent to which light affects vital rates depends on plant size. Differences among species in their abilities to thrive under different light conditions and thus occupy distinct niches may contribute to the maintenance of species diversity.

Assuntos

RESUMO

UNLABELLED: • PREMISE OF THE STUDY: Sexual reproduction is often associated with a cost in terms of reduced survival, growth, or future reproduction. It has been proposed that plant size and the environment (availability of key resources) can sometimes lower or even nullify the cost of reproduction.• METHODS: We address this issue experimentally with the Neotropical herb Goeppertia marantifolia, by manipulating sexual reproductive effort and measuring the demographic performance of plants and of their clonal offspring, in the context of natural variation in light availability.• KEY RESULTS: Plants in the high-reproductive-effort treatment grew less between seasons but did not differ in their probability of flowering the second season or in inflorescence size compared with plants in the low-effort treatment. Reproductive effort of parent plants influenced the leaf area of their clonal offspring. Plants that invested less in sexual reproduction produced clonal offspring that were initially larger than those produced by plants that invested more in reproduction. The magnitude of this effect was greater in parent plants that received two seasons of the manipulated reproductive effort than in those that received a single season. The trade-off between reproductive modes dampened with time, leading to smaller differences in clonal offspring leaf area between treatments over time.• CONCLUSIONS: We found evidence of a cost of reproduction and trade-offs between reproductive modes, although the magnitude of these costs was small. However, we found no evidence of lower costs of reproduction for larger plants or for plants in higher-light environments over our 2-yr study period.

Assuntos

RESUMO

O presente estudo investigou a fenologia de floração, a biologia floral e os visitantes florais de Calathe acrocata. Os dados foram coletados no sub-bosque de um fragmento de Mata Atlântica no município de Igrapiúna, Bahia. Expedições mensais ocorreram de julho de 2009 a agosto de 2011. Mensalmente foram registrados dados da fenologia de floração de C. crocata. Foram obtidos dados de morfometria floral, de volume e concentração de néctar, além de registrado os atributos florais de C. crocata. As espécies de beija-flores visitantes florais foram registradas durante observações indivíduo-focal em plantas floridas, da aurora ao crepúsculo, determinando a frequência e o comportamento de forrageio. Testes de polinização natural e autopolinização foram realizados, além da eficiência na liberação do estilete. A floração desta espécie é anual e tem duração intermediária, possuindo correlação negativa com a temperatura. Calatheacrocata é uma espécie ornitófila; suas flores são tubulosas, com corola amarela, com comprimento médio de 24,3mm e abertura de 2,6mm. O néctar tem concentração média de 21% de açúcares, com volume médio produzido de 9,4µl. As flores foram visitadas legitimamente por quatro espécies de beija-flores, com frequência de 0,69 visitas por inflorescência/hora, sendo Phaethornis ruber eficiente no disparo do gatilho. O principal vetor de pólen de C. crocata foi Phaethornis ruber. Calathea crocata é uma espécie alógama e não se autopoliniza espontaneamente: somente houve produção de frutos no teste de polinização natural. Características mais pontuais, como a redução do gatilho, presentes nessa espécie, podem ser um indício da evolução da melitofilia para a ornitofilia, já observada na família Marantaceae, porém ainda pouco evidenciada no gênero.

The study goals were to investigate the flowering phenology, the floral biology, and the floral visitors of Calathea crocata. The data was collected in an understory fragment of Atlantic Forest at Igrapiúna city, state of Bahia. Field expeditions were conducted by month from July 2009 to August 2011. Every month flowering phenology data was documented. Besides floral morphometry, volume and concentration of nectar data, the floral attributes of C. crocata were collected. Hummingbird species that visited the plant was registered by focal observations in breeding plants from sunrise to sunrise, establishing the frequency and forage behavior. Natural pollination and self-pollination tests were conducted, in addition to trigger efficiency. The breeding season is annual, and has intermediate duration, being negatively correlated with the temperature. Calathea crocata is an ornithophilous species; its flowers are tubular, with yellow corollas of 24,3mm of length average, and 2,6mm of aperture average. The nectar has a sugar's concentration average of 21%, and a volume's average production of 9,4 µl. The flowers were visited legitimately by four hummingbird species. The visits frequency was 0,69 visits per inflorescence/hour, all of them were able to release the trigger. Phaethornis ruber was the mainly pollen vector of C. crocata. Calathea crocata is an allogamous species, and is not capable of spontaneous selfpollination: just the natural pollination test produced fruits. More specific features, as the trigger reduction, visible in this species, can be an evolutionary evidence from melitophily to ornithophily already seen in Marantaceae family, but not too noted on the genre.

Assuntos

RESUMO

This study aimed to characterize the structure of the herb stratum in relation to light availability in the Submontane Atlantic Rain Forest at the Carlos Botelho State Park, SP, Brazil. Fortyone 10 x10 m plots were established under the closed canopy (18 plots), small and medium canopy gaps (11) and large canopy gaps dominated by Guadua tagoara (Ness) Kunth (12). Inside each plot, the line intercept method was applied to assess soil coverage as an estimate of density of herb stratum vegetation. Hemispherical photographs were taken at the centre of the plots to evaluate the annual light regime. Overall, Calathea communis Wanderley and S. Vieira had the greater mean coverage, followed by woody seedlings, ground ferns and other herbs (mainly, Araceae, Acanthaceae, Amaranthaceae and Cyperaceae). There were strong correlations among several groups of the herb stratum, such as the negative correlations between woody seedlings with the coverage of C. communis and with rocks. The analysis of the hemispherical photographs confirmed the difference among environments that led to significant differences in the soil coverage of the herb stratum vegetation but woody seedlings. For instance, C. communis showed great coverage in large gaps while ferns were more abundant in small and medium gaps and in the understorey. Other herbs, in turn, demonstrated bigger soil coverage in small and medium gaps. Although this study represents a rough assessment of the structure and composition of the herb stratum, the results found here illustrated the evident relation between herb species density and the environmental variation promoted by changes on canopy structure and topography.

O objetivo deste estudo foi caracterizar a estrutura do estrato herbáceo em relação à disponibilidade de luz na Floresta Pluvial Atlântica Submontana do Parque Estadual Carlos Botelho, SP, Brasil. Para tanto, foram instaladas 41 parcelas de 10 x 10 m em ambientes sob o dossel fechado (18 parcelas), em clareiras pequenas e médias (11), e em clareiras grandes com dominância de Guadua tagoara (Ness) Kunth (12). Em cada parcela a percentagem de cobertura de solo, avaliada através do método de interceptação em linha, foi usada como estimativa da densidade da vegetação do estrato herbáceo. Fotografias hemisféricas foram tomadas ao centro de cada uma das parcelas para avaliar o regime anual de luz nos ambientes. No geral, a maior média obtida foi para Calathea communis Wanderley e S. Vieira, seguida por plântulas de regenerantes lenhosos, pteridófitas terrestres e outras ervas (principalmente Araceae, Acanthaceae, Amaranthaceae e Cyperaceae). Houve ainda fortes correlações entre vários grupos do estrato herbáceo, como as correlações negativas entre plântulas de regenerantes com a cobertura de C. communis e de rochas. A análise das fotografias hemisféricas confirmou a existência de ambientes com diferentes regimes de luz, que promoveram diferenças significativas na cobertura do solo de todos os grupos do estrato herbáceo, exceto para plântulas de regenerantes. Por exemplo, C. communis apresentou grande cobertura nas grandes clareiras, enquanto que as pteridófitas terrestres foram mais abundantes no subbosque e nas clareiras pequenas e médias. O grupo Outras Ervas, por sua vez, apresentou maiores coberturas nas clareiras pequenas e médias. Apesar de representar uma análise grosseira da estrutura e composição, os resultados encontrados aqui ilustraram uma evidente relação entre a densidade de formas de vida herbácea e as variações ambientais promovidas por mudanças na estrutura do dossel da floresta e na topografia.

Assuntos

RESUMO

This study aimed to characterize the structure of the herb stratum in relation to light availability in the Submontane Atlantic Rain Forest at the Carlos Botelho State Park, SP, Brazil. Fortyone 10 x10 m plots were established under the closed canopy (18 plots), small and medium canopy gaps (11) and large canopy gaps dominated by Guadua tagoara (Ness) Kunth (12). Inside each plot, the line intercept method was applied to assess soil coverage as an estimate of density of herb stratum vegetation. Hemispherical photographs were taken at the centre of the plots to evaluate the annual light regime. Overall, Calathea communis Wanderley and S. Vieira had the greater mean coverage, followed by woody seedlings, ground ferns and other herbs (mainly, Araceae, Acanthaceae, Amaranthaceae and Cyperaceae). There were strong correlations among several groups of the herb stratum, such as the negative correlations between woody seedlings with the coverage of C. communis and with rocks. The analysis of the hemispherical photographs confirmed the difference among environments that led to significant differences in the soil coverage of the herb stratum vegetation but woody seedlings. For instance, C. communis showed great coverage in large gaps while ferns were more abundant in small and medium gaps and in the understorey. Other herbs, in turn, demonstrated bigger soil coverage in small and medium gaps. Although this study represents a rough assessment of the structure and composition of the herb stratum, the results found here illustrated the evident relation between herb species density and the environmental variation promoted by changes on canopy structure and topography.

O objetivo deste estudo foi caracterizar a estrutura do estrato herbáceo em relação à disponibilidade de luz na Floresta Pluvial Atlântica Submontana do Parque Estadual Carlos Botelho, SP, Brasil. Para tanto, foram instaladas 41 parcelas de 10 x 10 m em ambientes sob o dossel fechado (18 parcelas), em clareiras pequenas e médias (11), e em clareiras grandes com dominância de Guadua tagoara (Ness) Kunth (12). Em cada parcela a percentagem de cobertura de solo, avaliada através do método de interceptação em linha, foi usada como estimativa da densidade da vegetação do estrato herbáceo. Fotografias hemisféricas foram tomadas ao centro de cada uma das parcelas para avaliar o regime anual de luz nos ambientes. No geral, a maior média obtida foi para Calathea communis Wanderley e S. Vieira, seguida por plântulas de regenerantes lenhosos, pteridófitas terrestres e outras ervas (principalmente Araceae, Acanthaceae, Amaranthaceae e Cyperaceae). Houve ainda fortes correlações entre vários grupos do estrato herbáceo, como as correlações negativas entre plântulas de regenerantes com a cobertura de C. communis e de rochas. A análise das fotografias hemisféricas confirmou a existência de ambientes com diferentes regimes de luz, que promoveram diferenças significativas na cobertura do solo de todos os grupos do estrato herbáceo, exceto para plântulas de regenerantes. Por exemplo, C. communis apresentou grande cobertura nas grandes clareiras, enquanto que as pteridófitas terrestres foram mais abundantes no subbosque e nas clareiras pequenas e médias. O grupo Outras Ervas, por sua vez, apresentou maiores coberturas nas clareiras pequenas e médias. Apesar de representar uma análise grosseira da estrutura e composição, os resultados encontrados aqui ilustraram uma evidente relação entre a densidade de formas de vida herbácea e as variações ambientais promovidas por mudanças na estrutura do dossel da floresta e na topografia.