RESUMO
The development of coral reefs results from the interaction between ecological and geological processes in space and time. Their difference in scale, however, makes it difficult to detect the impact of ecological changes on geological reef development. The decline of coral cover over the last 50 years, for example, has dramatically impaired the function of ecological processes on reefs. Yet given the limited-resolution of their Holocene record, it is uncertain how this will impact accretion and structural integrity over longer timescales. In addition, reports of this ecological decline have focused on intrinsic parameters such as coral cover and colony size at the expense of extrinsic ones such as geomorphic and environmental variables. Despite these problems, several attempts have been made to predict the long-term accretion status of reefs based entirely on the contemporary health status of benthic communities. Here we explore how this ecological decline is represented within the reef geomorphic structure, which represents the long-term expression of reef development. Using a detailed geomorphic zonation scheme, we analyze the distribution and biodiversity of reef-building corals in fringing-reef systems of the Mesoamerican Reef tract. We find a depth-related pattern in community structure which shows that the relative species distribution between geomorphic zones is statistically different. Despite these differences, contemporary coral assemblages in all zones are dominated by the same group of pioneer generalist species. These findings imply that first, coral species distribution is still controlled by extrinsic processes that generate the geomorphic zonation; second, that coral biodiversity still reflects species zonation patterns reported by early studies; and third that dominance of pioneer species implies that modern coral assemblages are in a prolonged post-disturbance adjustment stage. In conclusion, any accurate assessment of the future viability of reefs requires a consideration of the geomorphic context or risks miscalculating the impact of ecological changes on long-term reef development.
Assuntos
Antozoários , Animais , Ecossistema , Recifes de Corais , Biodiversidade , Região do CaribeRESUMO
Insect diversity patterns of high mountain ecosystems remain poorly studied in the tropics. Sampling dung beetles of the subfamilies Aphodiinae, Scarabaeinae, and Geotrupinae was carried out at four volcanoes in the Trans-Mexican Volcanic Belt (TMVB) in the Mexican transition zone at 2,700 and 3,400 MASL, and on the windward and leeward sides. Sampling units represented a forest-shrubland-pasture (FSP) mosaic typical of this mountain region. A total of 3,430 individuals of 29 dung beetle species were collected. Diversity, abundance and compositional similarity (CS) displayed a high variability at all scales; elevation, cardinal direction, or FSP mosaics did not show any patterns of higher or lower values of those measures. The four mountains were different regarding dispersion patterns and taxonomic groups, both for species and individuals. Onthophagus chevrolati dominated all four mountains with an overall relative abundance of 63%. CS was not related to distance among mountains, but when O. chevrolati was excluded from the analysis, CS values based on species abundance decreased with increasing distance. Speciation, dispersion, and environmental instability are suggested as the main drivers of high mountain diversity patterns, acting together at different spatial and temporal scales. Three species new to science were collected (>10% of all species sampled). These discoveries may indicate that speciation rate is high among these volcanoes-a hypothesis that is also supported by the elevated number of collected species with a restricted montane distribution. Dispersion is an important factor in driving species composition, although naturally limited between high mountains; horizontal colonization events at different time scales may best explain the observed species composition in the TMVB, complemented by vertical colonization events to a lesser extent. Environmental instability may be the main factor causing the high variability of diversity and abundance patterns found during sampling. Together, we interpret these results as indicating that species richness and composition in the high mountains of the TMVB may be driven by biogeographical history while variability in diversity is determined by ecological factors. We argue that current conservation strategies do not focus sufficiently on protecting high mountain fauna, and that there is a need for developing and applying new conservation concepts that take into account the high spatial and temporal variability of this system.
RESUMO
Abstract Here we examine assemblage structure of coprophagous Scarabaeidae (dung beetles) in the Pantanal of the state of Mato Grosso with respect to flooding regimes, soil texture, leaf litter volume and tree dominance in native and exotic pastures. Samples were collected along 30 transects of 250 m in length in a 5×5 km grid (25 km2). Five pitfalls baited with human feces were placed in each transect. A total of 1692 individuals in 19 species were captured, the majority in the subfamily Scarabaeinae and Aphodiinae. Assemblages were influenced by the duration of flooding and leaf litter volume. None of the other habitat variables was correlated with species richness. Cultivated pastures with exotic grasses were unimportant for composition of the assemblages of beetles. These results indicate that duration of flooding is the most important regulating force in this community.
Resumo Esse estudo avaliou a estrutura espacial de assembleias de Scarabaeidae coprófagos no Pantanal de Mato Grosso, em função do tempo de inundação, textura do solo, volume da serapilheira, dominância de arbóreas, pastagens nativa e exótica. As coletas foram realizadas em 30 transectos de 250 m cada distribuídos sistematicamente em uma área de 25 km2. Cinco armadilhas pitfall iscadas com fezes humanas foram instaladas em cada transecto, e obtidos 1.692 indivíduos distribuídos em 19 espécies pertencentes às subfamílias Scarabaeinae e Aphodiinae. A estrutura e composição das assembleias foram afetadas pelo tempo de inundação e o volume da serapilheira. Todas as variáveis explanatórias foram fracamente correlacionadas e de forma não significativa com a riqueza de espécies. A existência de pastagem exótica não afetou a composição das assembleias de besouros. Esses resultados indicam que o tempo de inundação é a principal força reguladora dessa comunidade no ambiente pantaneiro.
Assuntos
Animais , Biodiversidade , Besouros/fisiologia , Áreas Alagadas , Inundações , Pradaria , Espécies Introduzidas , Folhas de Planta/química , Solo/químicaRESUMO
Abstract Here we examine assemblage structure of coprophagous Scarabaeidae (dung beetles) in the Pantanal of the state of Mato Grosso with respect to flooding regimes, soil texture, leaf litter volume and tree dominance in native and exotic pastures. Samples were collected along 30 transects of 250 m in length in a 5×5 km grid (25 km2). Five pitfalls baited with human feces were placed in each transect. A total of 1692 individuals in 19 species were captured, the majority in the subfamily Scarabaeinae and Aphodiinae. Assemblages were influenced by the duration of flooding and leaf litter volume. None of the other habitat variables was correlated with species richness. Cultivated pastures with exotic grasses were unimportant for composition of the assemblages of beetles. These results indicate that duration of flooding is the most important regulating force in this community.
Resumo Esse estudo avaliou a estrutura espacial de assembleias de Scarabaeidae coprófagos no Pantanal de Mato Grosso, em função do tempo de inundação, textura do solo, volume da serapilheira, dominância de arbóreas, pastagens nativa e exótica. As coletas foram realizadas em 30 transectos de 250 m cada distribuídos sistematicamente em uma área de 25 km2. Cinco armadilhas pitfall iscadas com fezes humanas foram instaladas em cada transecto, e obtidos 1.692 indivíduos distribuídos em 19 espécies pertencentes às subfamílias Scarabaeinae e Aphodiinae. A estrutura e composição das assembleias foram afetadas pelo tempo de inundação e o volume da serapilheira. Todas as variáveis explanatórias foram fracamente correlacionadas e de forma não significativa com a riqueza de espécies. A existência de pastagem exótica não afetou a composição das assembleias de besouros. Esses resultados indicam que o tempo de inundação é a principal força reguladora dessa comunidade no ambiente pantaneiro.
RESUMO
Here we examine assemblage structure of coprophagous Scarabaeidae (dung beetles) in the Pantanal of the state of Mato Grosso with respect to flooding regimes, soil texture, leaf litter volume and tree dominance in native and exotic pastures. Samples were collected along 30 transects of 250 m in length in a 5×5 km grid (25 km2). Five pitfalls baited with human feces were placed in each transect. A total of 1692 individuals in 19 species were captured, the majority in the subfamily Scarabaeinae and Aphodiinae. Assemblages were influenced by the duration of flooding and leaf litter volume. None of the other habitat variables was correlated with species richness. Cultivated pastures with exotic grasses were unimportant for composition of the assemblages of beetles. These results indicate that duration of flooding is the most important regulating force in this community.(AU)
Esse estudo avaliou a estrutura espacial de assembleias de Scarabaeidae coprófagos no Pantanal de Mato Grosso, em função do tempo de inundação, textura do solo, volume da serapilheira, dominância de arbóreas, pastagens nativa e exótica. As coletas foram realizadas em 30 transectos de 250 m cada distribuídos sistematicamente em uma área de 25 km2. Cinco armadilhas pitfall iscadas com fezes humanas foram instaladas em cada transecto, e obtidos 1.692 indivíduos distribuídos em 19 espécies pertencentes às subfamílias Scarabaeinae e Aphodiinae. A estrutura e composição das assembleias foram afetadas pelo tempo de inundação e o volume da serapilheira. Todas as variáveis explanatórias foram fracamente correlacionadas e de forma não significativa com a riqueza de espécies. A existência de pastagem exótica não afetou a composição das assembleias de besouros. Esses resultados indicam que o tempo de inundação é a principal força reguladora dessa comunidade no ambiente pantaneiro.(AU)
Assuntos
Animais , Besouros/fisiologia , Biodiversidade , Áreas Alagadas , Inundações , Pradaria , Espécies Introduzidas , Folhas de Planta/química , Solo/químicaRESUMO
In regularly burned grassland on Morro Santana, Porto Alegre, RS, Brazil, we investigated differences in the floristic composition and their relation to soil properties, aspect and distance from the forest border. In 48 plots of 0.75 m², we identified a total of 201 species from a local species pool of approximately 450 to 500 species. Most species occurred in low frequencies, showing clumpy distribution patterns in the studied area. Multivariate analysis showed that plots close to the forest edge clearly differed from plots in the open grassland concerning composition and structure. Plots exposed to the north differed from plots on the top of the hill both in the composition of species as well as in soil variables, mainly due to shallower soil in the former. No strong relation between soil properties and variation in vegetation composition could be detected at a finer scale. The studied grassland, as all grassland vegetation in southern Brazil, is very rich in species compared to other grassland formations worldwide. However, this high biodiversity and conservational value of Campos vegetation in general has so far not been recognized properly. Disturbance is essential to maintain this open vegetation type and its species richness. Fire should be considered as a management option in the absence of grazing.
Em um campo regularmente queimado no Morro Santana, Porto Alegre, RS, Brasil, foram investigadas diferenças na composição florística e suas relações com as propriedades do solo, a distância da borda florestal e a exposição do relevo. Em 48 parcelas de 0,75 m², foram amostradas 201 espécies identificadas, de um total estimado para o local de aproximadamente 450 a 500 espécies. A maioria das espécies apresentou baixas freqüências e uma distribuição aglomerada na área de estudo. A análise multivariada dos dados indicou que as parcelas adjacentes à borda florestal claramente diferem florística e estruturalmente das parcelas do campo. As parcelas com exposição norte diferiram das do topo do morro, tanto pela composição florística quanto pelas variáveis do solo, principalmente em relação à menor profundidade do solo no norte. Nenhuma relação forte foi detectada entre as propriedades do solo e a variação na composição da comunidade em escala mais fina. A área estudada, assim como a vegetação campestre no sul do Brasil em geral, apresenta-se muito rica em espécies, se comparada a outras formações de campo ou savana no mundo. Apesar disso, a alta biodiversidade e o valor de conservação da vegetação campestre não têm sido reconhecidos. Na ausência do pastejo, o fogo é um imporante fator de manejo para a conservação da vegetação campestre, uma vez que o distúrbio parece ser necessário para manter esse tipo de vegetação aberta, com alta riqueza em espécies.