Fernanda Vieira da Costa

A qualidade do solo afeta a germinação das sementes e o desenvolvimento das plântulas de Dimorphandra mollis Benth. (Leguminosae: Mimosoideae)

Os frutos de Dimorphandra mollis sao coletados de forma indiscriminada para fins comerciais, comprometendo a viabilidade das populacoes naturais. Este estudo teve como objetivo avaliar o efeito da qualidade do solo na germinacao das sementes e no desenvolvimento de plântulas de D. mollis. Solos de tres procedencias (cerrado arenoso, cerrado argiloso e mata seca) foram usados como substratos nos testes de germinacao e desenvolvimento das plântulas. As sementes de D. mollis apresentaram maior germinabilidade em solo de cerrado arenoso (60,5%), seguido por solo de cerrado argiloso (29,7%) e solo de mata seca (13,6%). Alem disto, o indice de velocidade de germinacao (IVG) das sementes de D. mollis foi maior no solo de cerrado arenoso. As raizes das plântulas cultivadas em solo de cerrado arenoso apresentaram maior comprimento do que as cultivadas nos solos de mata seca e cerrado argiloso. Contudo, a massa seca das raizes nao variou entre os tres tratamentos. As plântulas de D. mollis apresentaram maior crescimento e producao de biomassa da parte aerea quando cultivadas em solo de mata seca. Os solos das matas secas normalmente apresentam melhor qualidade nutricional que os solos do cerrado, justificando os resultados observados. Assim, para melhor sucesso da producao de mudas de D. mollis, as sementes devem ser germinadas em substratos que retem pouca agua e as plântulas devem ser cultivadas em solos de melhor qualidade nutricional.

Few Ant Species Play a Central Role Linking Different Plant Resources in a Network in Rupestrian Grasslands

Ant-plant associations are an outstanding model to study the entangled ecological interactions that structure communities. However, most studies of plant-animal networks focus on only one type of resource that mediates these interactions (e.g, nectar or fruits), leading to a biased understanding of community structure. New approaches, however, have made possible to study several interaction types simultaneously through multilayer networks models. Here, we use this approach to ask whether the structural patterns described to date for ant-plant networks hold when multiple interactions with plant-derived food rewards are considered. We tested whether networks characterized by different resource types differ in specialization and resource partitioning among ants, and whether the identity of the core ant species is similar among resource types. We monitored ant interactions with extrafloral nectaries, flowers, and fruits, as well as trophobiont hemipterans feeding on plants, for one year, in seven rupestrian grassland (campo rupestre) sites in southeastern Brazil. We found a highly tangled ant-plant network in which plants offering different resource types are connected by a few central ant species. The multilayer network had low modularity and specialization, but ant specialization and niche overlap differed according to the type of resource used. Beyond detecting structural differences across networks, our study demonstrates empirically that the core of most central ant species is similar across them. We suggest that foraging strategies of ant species, such as massive recruitment, may determine specialization and resource partitioning in ant-plant interactions. As this core of ant species is involved in multiple ecosystem functions, it may drive the diversity and evolution of the entire campo rupestre community.

Mutualistic Interactions Among Free-Living Species in Rupestrian Grasslands

Mutualisms such as animal pollination and seed dispersal, and protection of plants and insects by ants are ubiquitous in terrestrial ecosystems. Currently, mutualistic interactions among plants and animals are recognized for their paramount importance in biodiversity maintenance, especially in tropical ecosystems. In this chapter, we review the literature and present unpublished data on the ecology of mutualistic interactions among free-living species in Brazilian megadiverse montane Rupestrian Grasslands, the Campo Rupestre. We focus on interactions between plants and their pollinators and seed dispersers, and also interactions between ants, myrmecophilous plants and trophobiont insects. We provide basic information on mutualistic interactions, including data on natural history in addition to more advanced studies using network-based approaches. Only in the past decade mutualistic interactions have become intensively studied in Campo Rupestre, but information is still scattered and concentrated for a few localities. Pollination is an important process for reproduction of most plant species studied so far, with bees and hummingbirds acting as the main pollinators. Seemingly, animal pollination is more important than seed dispersal for gene flow across plant populations. Most vertebrate seed dispersal is carried out by non-specialized avian frugivorous, but also by short-distance seed dispersers such as ants and lizards. Moreover, ants are diversified and abundant group that seem to play a major role in these ecosystems, acting as secondary seed dispersers, as nectar thieves, and as bodyguards of plants and insects. We conclude this chapter by pointing out some gaps in our knowledge and proposing avenues for future research.

The role of historical and ecological factors on initial survival of Copaifera langsdorffii Desf. (Fabaceae)

The plant population dynamic is affected by ecological and evolutionary processes that operate at all stages of the plant life cycle. The aim of this study was to characterize the seed and seedling performance of Copaifera langsdorffii by testing four hypotheses: the resource concentration hypothesis; the relationship between seed size and germinability hypothesis; the relationship between seed size and seedling vigor hypothesis; and the intraspecific seedling competition hypothesis. All seeds used in the experiments were collected from 35 C. langsdorffii plants located in a fragment of the Brazilian cerrado (savanna). The number of fruits per plant negatively affected Rhinochenus brevicollis attacks on C. langsdorffii seeds. Therefore, this result does not support the resource concentration hypothesis, and predator satiation was used in order to explain the observed result. In general, seed germinability (percentage and time to emergence) was not influenced by seed size. The homogeneity of the experimental design, together with an abundant water supply, may have masked the effects of seed size on germinability. Seed size positively affected seedling development, corroborating the expected relationship between seed size and seedling vigor. The number of seedling per plastic bags negatively affected the growth of C. langsdorffii. The nutrient-limited soil probably promoted the below-ground competition for nutrients among seedlings. Finally, the role of evolutionary and ecological factors on C. langsdorffii population dynamics is discussed.