Gislene Ganade

Asymmetries, compartments and null interactions in an Amazonian ant-plant community

In the tropics, many plants offer housing and food for their specialized ant partners which, in return, offer benefit in the form of defence and/or nutrients, thus forming mutualistic bonds. Such ant-plants, also called myrmecophytes, occur together at a local scale, generating community patterns of mutualistic ant-plant associations. Here, we present the first fully quantitative description of an ant-myrmecophyte community. The study site in Central Amazonian tropical rainforest had a high myrmecophyte density of about 380 ind. ha -1 . Sixteen myrmecophyte and 25 ant species were recorded, the species abundance rank curves being highly uneven. The ant-myrmecophyte matrix was highly compartmentalized, and a Monte Carlo simulation showed that the observed pattern was not a product of chance and sample size (P < 0.0001). Cluster analyses indicated that compartments were partially explained by occurrence of the ants in phylogenetically related host plants, but not by habitat specificity. The connectance of the ant-plant community was 12%. This value seems quite low when compared with published results from other mutualistic systems (pollinator and seed-dispersor), after controlling for the total number of interacting species. The high frequency of null interactions in the ant-myrmecophyte system could not be explained by the phenological non-coincidence hypothesis, since both ant and plant partners occur together throughout the year. Ant-plant interactions were highly asymmetrical: ant species had fewer partners than plant species and ants were more dependent on the plants than the reverse. These asymmetries are in the opposite direction to those recorded for plant-pollinators and plant-dispersors; however, they seem to be the product of the same underlying process: differential fitness benefits between mutualistic partners. The low number of ant and plant partners per compartment, coupled with an apparently high temporal and spatial stability of ant-myrmecophyte interactions, suggests that compartments are the appropriate scale at which to investigate coevolution in ant-myrmecophyte systems.

Changes in plant community diversity and composition across an edge between Araucaria forest and pasture in South Brazil

Neste estudo investigamos como riqueza, abundância, composicao e estrutura da vegetacao lenhosa e herbacea foram alteradas pela proximidade de uma borda entre floresta com araucaria e pastagem no sul do Brasil. Especies lenhosas e herbaceas, incluindo plântulas, foram analisadas em 42 parcelas de 5 × 5 m dispostas aleatoriamente nas seguintes distâncias: 5 e 50 m da borda para dentro do campo e 0, 25, 50, 100 e 250 m da borda para dentro da floresta. Houve um aumento significativo na cobertura da vegetacao, riqueza e abundância de especies lenhosas, plântulas lenhosas e plantas herbaceas na borda (0 m). Essas variaveis, em geral, decresceram nas distâncias 25 a 50 m da borda para dentro da floresta em relacao ao interior da mesma. Poucas plântulas lenhosas foram capazes de estabelecer-se no campo. Houve uma mudanca continua na composicao de especies que ocorreu no gradiente de borda devido a invasao de especies heliofilas e o desaparecimento de alguma especies tolerantes a sombra na borda. Concluimos que a comunidade de plantas encontra-se alterada na borda florestal estudada em uma extensao que vai ate 50 m para dentro da floresta.

Facilitation and competition influence succession in a subtropical old field

The effects of neighboring vegetation and soil fertility on the establishment, survival and growth of tree species were studied in a subtropical old-field area in south Brazil. Seed damage, germination and seedling establishment of four tree species plus growth and survival of two transplanted tree species were monitored under factorial combinations of the following treatments: (1) pioneer vegetation (presence and absence); (2) soil fertility (addition of NPK and control). Facilitation was the main process affecting plant performance. The presence of pioneer vegetation significantly improved germination, establishment, growth and survival of most study species. Around 90% of sown seeds were damaged and the removal of pioneer vegetation significantly increased seed damage for all species studied, decreased germination in three out of four species, and decreased establishment in one species. Moreover a significantly higher seedling growth rate of Ingaxa0virescens was found after the first year of the experiment in plots where vegetation was present. The presence of vegetation significantly increased seedling survival of I.xa0virescens by protecting seedlings from leaf loss due to winter frosts. Competition was detected by the second year when a higher growth of transplanted seedlings of the species Araucariaxa0angustifolia occurred in plots where vegetation was present and fertilizer were applied. A lower growth rate was detected in plots where vegetation was present but fertilizer was not applied. These results indicate a balance between competition for soil nutrients and protection by neighbor vegetation. Damage of seedlings by leaf cutter ants was an important barrier for plant survival. Damage occurred in 80% of the A.xa0angustifolia seedlings and 58% of these damaged seedlings died. The presence of neighboring vegetation tended to protect seedlings from ant damage. Although competition occurred, facilitation seems to be the main process driving early successional changes in this subtropical old field. This was mainly due to the improvement of local microclimatic conditions and protection against herbivores by neighboring vegetation. Facilitation occurred during establishment and growth phases in a subtropical area that is considered a productive, low stress environment. Our results indicate that facilitation may be more frequent in productive environments than previously thought.

Lichen diversity and composition in Araucaria forests and tree monocultures in southern Brazil

Tree plantations for commercial use have been replacing native ecosystems all over the world. We investigated how forest conversion to plantations of exotic and native tree species may influence lichen diversity and composition in a southern Brazilian landscape. The lichen community from the National Forest of São Francisco de Paula was studied using three stands of each of the four vegetation types: native Araucaria forest and plantations of Araucaria, Pine and Eucalyptus trees. All plantation stands were surrounded by native Araucaria forest, were of smaller size and were allowed to endure longer than commercially managed plantations. Lichen species and their cover abundance were recorded on tree trunks from 30 to 150xa0cm above soil level in ten host-trees that were randomly selected in each replication. Seventy-eight lichen species, from 18 genera and 9 families, were registered. Conversion of native forest to plantations of exotic tree species altered species composition by reducing the occurrence of shade tolerant lichens. Plantations of Araucaria angustifolia sustained the highest lichen diversity measured, because this is an excellent host species. These results suggest that a greater diversity of lichens can be preserved in the landscape, if plantations of the exotic Pinus and Eucalyptus genera are replaced by plantations of this native species.

Predação de sementes ao longo de uma borda de Floresta Ombrófila Mista e pastagem

This study aims to evaluate how seed predation of three native tree species (Mimosa scabrella Bentham, Prunus sellowii Koehne, and Myrsine laetevirens Mez.) could be altered along an edge between Araucaria forest and pasture at the National Forest of Sao Francisco de Paula, Rio Grande do Sul, Brazil. Groups of seeds were placed at ten random points in each of the following distances from the forest edge: 0m, 25m, 50m, 100m, and 250m from the edge into the forest, and 5m and 50m from the edge into the pasture. Seeds were monitored until total predation or until their time for germination was over. Seed predation rates decreased from the edge up to 50m inside the forest in relation to the forest interior and open pasture. M. scabrella and M. laetevirens showed a reduction in seed predation rates in pasture points that were located at the vicinities of the forest. The results indicated a decrease in the activity of seed predators near the forest edge, which could enhance plant community regeneration at the edge, and promote the expansion of the forest towards the adjacent pasture.

Using tree population size structures to assess the impacts of cattle grazing and eucalypts plantations in subtropical South America

To evaluate the effects of distinct management of the matrix in which forest fragments are found upon plant populations thriving in forest remnants in south Brazil, we assessed the conservation status of populations of four woody species (Campomanesia rhombea, Diospyros incontans, Myrciaria cuspidata and Sebastiania commersoniana) through analyses of size structure. Analyzes were carried out at two scales. At a local scale, we consider populations in fragments surrounded by pastures or eucalypts forest plantations, and at a regional scale we also consider larger forest tracts taken as reference areas (Rio Grande do Sul Forest Inventory databank). Population size structures were summarized using the symmetry of height distributions. Small individual size classes prevailed at the local scale in fragments surrounded by eucalypts plantations, whereas in areas exposed to cattle ranching, populations of the same species consistently lack small individuals. At the regional scale, populations in fragments surrounded by pastures presented greater skewness (prevalence of small plants) than populations in reference areas, while populations surrounded by eucalypts plantations presented intermediate skewness. These results reinforce the notion that plantations have a higher conservation value for forest ecosystems than other commercial land uses, like cattle ranching.

Effects of different pioneer species on the colonization of Podocarpus lambertii in a restoration area

Interacoes ecologicas entre especies pioneiras e tardias influenciam o arranjo espacial de individuos em comunidades vegetais, resultando em associacoes espaciais positivas ou negativas. Estudos que analisam esses padroes espaciais em areas em processos de regeneracao sao importantes para projetos de restauracao florestal. O objetivo deste trabalho foi investigar a estrutura populacional e a distribuicao espacial de Podocarpus lambertii Klotsch (Podocarpaceae) em uma area em processo de regeneracao, verificando o efeito das especies pioneiras nativas sobre os regenerantes dessa especie. O trabalho foi realizado em uma area degradada de 1 ha em estagio inicial de sucessao na Floresta Nacional (FLONA) de Sao Francisco de Paula, RS, Brasil. Em parcelas contiguas de 10 x 10 m, foram medidos e mapeados todos os individuos de P. lambertii e os individuos das pioneiras nativas Baccharis uncinella e Vernonia discolor . A populacao de P. lambertii manteve-se estavel ao longo do estudo, sendo que o numero de individuos nas classes de tamanho manteve-se razoalvelmente constante. Os regenerantes de P. lambertii apresentaram-se negativamente associados a pioneira B . uncinella, indicando competicao, e positivamente associados a pioneira V. discolor, indicando facilitacao. Esses resultados podem contribuir com o desenvolvimento de tecnicas de manejo para a restauracao de areas degradadas no sul do Brasil. Palavras-chave: associacoes espaciais, competicao, facilitacao, Floresta Ombrofila Mista, regeneracao florestal.