South Africa is one of the world's most biologically invaded countries and has spent billions of rands on efforts to eradicate alien invasive plants. Chemical and mechanical control methods have varied in success and the need for integrated management strategies has been realised. This requires a better understanding of all aspects of the invasion process. Some of the most invasive plant species rely on vertebrate dispersers which facilitate long-distance seed dispersal. Frugivory is based on a mutualism in which the frugivores gain a resource and the plants benefit from seed dispersal away from the parent plant. Seed germination itself may either be enhanced, reduced or not affected at all after gut passage. The first aim of this study was to determine if generalist avian frugivores and a fruit bat species (Epomophorus wahlbergi) enhance or decrease seed germination of invasive alien plants in South Africa, by either pulp removal or seed coat abrasion, or if they serve as dispersers only. The second aim was to determine if avian frugivores are able to meet their energetic demands by feeding on a specific alien fruit diet. Finally, we also quantified the nutritional content and morphological characteristics of fleshy fruits of various invasive alien and exotic plant species. Avian frugivores: Red-winged Starlings (Onychognathus morio), Speckled Mousebirds (Colius striatus), and Dark-capped Bulbuls (Pycnonotus tricolor), varied in their effects on the germination success of seeds of four invasive alien species, namely: Lantana camara, Solanum mauritianum, Cinnamomum camphora, and Psidium guajava. However, this was not associated with differences in seed retention times. Similar germination success was observed for avian ingested and de-pulped seeds. This was also observed for fruit bat spat and depulped seeds of Psidium guajava, Melia azedarach, Eriobotrya japonica, and Morus alba. Therefore seed coat abrasion was not important for the germination of these fleshy-fruited invasive alien plants. Pulp removal resulted in significantly earlier seed germination as well as higher seed germination percentages than in the case of whole fruit controls for some of these invasive species. Gut passage is thus important for long-distance dispersal, and in some cases, for enhanced germination of seeds. The invasive Solanum mauritianum and indigenous congener S. giganteum showed similar germination responses, with both ingested and depulped seeds germinating profusely. However, S. giganteum benefited from pulp removal as seeds from whole fruits had less germination. Avian frugivores varied significantly in most energetic parameters calculated when given diets of invasive alien fruit. Speckled Mousebirds and Dark-capped Bulbuls were able to maintain body mass and efficiently process fruits of all four alien invasive plants, while Red-winged Starlings were only able to do so on lipid-rich C. camphora and sugar-rich S. mauritianum. Furthermore, frugivores also adjusted their feeding behavior by eating more nutritionally poor fruit and less energetically rewarding fruit. Fruit bats consumed more fruit per gram body mass than avian frugivores did. They therefore process proportionately more seeds than avian dispersers and thus their role in invasive seed dispersal, which has previously been underestimated particularly in South Africa, is highlighted. Fruits of invasive plant species were similar in morphology, but greater in nutritional content, than fruits of indigenous species. These fruits also contained small, light seeds with approximately only 30% having more than 10 seeds per fruit. The ability of frugivores to efficiently process these fruits and the greater nutritional rewards offered by these provide new insights into why these invasive fruits are preferred by frugivores. In addition, invasive alien plants may have a competitive edge over indigenous species because of their larger reproductive outputs and not necessarily because of greater germination success. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

The Amazon rainforest harbors the planet's highest biodiversity among terrestrial ecosystems; however, the biology and ecology of most of its species are unknown. Niche partitioning is considered a key factor allowing species co-existence, especially for morphological similar species such as spiny rats of the genus Proechimys. I examined the extent to which habitat differentiation, species body mass, and diet could explain the community composition of small mammals at a site in the southeastern Amazon. Moreover, I radio-tagged sympatric species of Proechimys spp. and Mesomys stimulax (an arboreal spiny rat) to obtain detailed autoecology information, including habitat use and use of space. I found support for niche partitioning among species and associated small mammal species with distinct successional phases of gap dynamics. I also observed among Proechimys spp. a typical polygynous organization: females appeared to be territorial against females of any species of their genus; but male territories overlapped with those of several females. Mesomys stimulax showed evidence of monogamy and possible sociality, although sample sizes were small. To identify the importance of small mammals as seed disperser of Brazil nut seeds, I conduct experiments using a combination of fluorescent powder, seed exclosures, and track plates in forests with and without Brazil nut groves, and in forests with and without Brazil nut harvesting. Among small mammals, only Proechimys spp. removed, dispersed, and preyed upon Brazil nut seeds. Proechimys spp. sometimes scatterhoarded these seeds, and hence have the potential to play a significant role in recruiting new Brazil nut trees. I also trapped small mammals and measured forest structures on the same sites used for the seed dispersal experiment, to determine the ecological effects of Brazil nut harvest on small mammal communities; however, my results showed little evidence of changes associated with the seed exploitation. My results highlight the importance of habitat heterogeneity in structuring small mammal communities, and indicate that forest management practices that alter habitats, such as partial logging, also can be expected to alter small mammal composition and diversity. Proechimys spp. have the potential to play an important role in the ecological restoration of intensive exploited Brazil nut groves.

Made available in DSpace on 2014-06-11T19:35:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-26Bitstream added on 2014-06-13T19:25:11Z : No. of bitstreams: 1 bianconi_gv_dr_rcla.pdf: 2615245 bytes, checksum: e626d43cffce5b3b04c96086c87decdf (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Filostomídeos frugívoros são considerados elementos-chave na conservação e restauração florestal dado à sua representatividade numérica (espécies e indivíduos), alto potencial de deslocamento e eficiência na dispersão de sementes. Técnicas que potencializem esse papel ecológico podem ter grande aplicação na recuperação de hábitats degradados, comuns à Mata Atlântica brasileira. Estudos com óleos essenciais isolados de frutos quiropterocóricos maduros sugeriram que eles podem ser utilizados para atrair e capturar morcegos frugívoros no interior de áreas florestais. Assim, a presente tese foi desenvolvida para fundamentar o caráter prático-funcional desta nova ferramenta, na medida em que se propôs a investigar os movimentos e o uso do hábitat fragmentado por espécies frugívoras, bem como as suas respostas a atrativos odoríferos instalados na matriz agropecuária de uma paisagem intensamente fragmentada no sul do Brasil (municípios de Fênix e São Pedro do Ivaí, estado do Paraná). Seus resultados indicaram uma atração altamente significativa dos morcegos aos óleos, um elevado potencial de dispersão de um grande número e diversidade de propágulos, e a possibilidade de manter os indivíduos por algum tempo sobrevoando pontos específicos da matriz, o que incrementaria, sobremaneira, a chuva-de-sementes no local. Os métodos de marcação/recaptura e radiotelemetria demonstraram existir uma alta mobilidade de Artibeus lituratus (Olfers, 1818) e Carollia perspicillata (Linnaeus, 1758), morcegos frugívoros mais comuns na região, dentro e entre os remanescentes florestais, com a utilização conjunta de diferentes elementos da paisagem (fragmentos, matriz agropecuária, pomares, rios, etc.). A matriz agropecuária da região parece não inibir os deslocamentos das espécies, padrão este relevante para o processo de dispersão de sementes e para a eficácia... / Frugivorous phyllostomids are considered key elements to forest conservation and restoration due to their representative number (species and individuals), high mobility, and efficiency as seed dispersers. Techniques to improve this ecological role can find great application in the recovery of degraded habitats, usually found in the Brazilian Atlantic Forest. Previous tests with essential oils from ripe chiropterochoric fruits suggested they can be used to attract and capture fruit-eating bats inside forest remnants. The present thesis was conducted to provide the basis to functional and practical characteristics of this new tool. Thus, we investigated the movements and use of a fragmented habitat by frugivorous species, as well as bats’ response to odor attractives installed in the agropecuary matrix of an extremely fragmented field at South Brazil (city of Fênix and São Pedro do Ivaí, State of Paraná). The results indicate a significant bat attraction to the essential oils, a great potential for dispersion of a large number and diversified seeds, the possibility of keeping bats flying for some time over specific locations of the matrix, which can increase significantly seeds dispersion in specific spots. By using mark/recapture and radiotelemetry techniques we observed high mobility of Artibeus lituratus (Olfers, 1818) and Carollia perspicillata (Linnaeus, 1758), the most common frugivorous bats in the study region , inside and between forests remnants with the combined use of different habitat attributes (fragments, agropecuary matrix, orchards, rivers, etc.). So, the regional agropecuary matrix does not seem to inhibit the movement of the species, which is an important behavior for seed dispersal and for the efficacy of the tool used for restoration of degraded areas.

Various aspects of myrmecochory were investigated. Effect of different storage methods on atractiveness of seeds with elaiosomes for ants was examined. Viable seed bank of refuse piles (places where ants deposit unused objects from ant nests, e.g. seeds after the elaiosome was eaten) and places outside them were compared. Chemical content of five major chemical groups, specifically amino acids, free fatty acids, organic acids, polyols and sugars, of elaiosomes and seeds of selected species was determined, and compared with respect to their taxonomic relatedness.

Various aspects of myrmecochory were investigated. Effect of different storage methods on atractiveness of seeds with elaiosomes for ants was examined. Viable seed bank of refuse piles (places where ants deposit unused objects from ant nests, e.g. seeds after the elaiosome was eaten) and places outside them were compared. Chemical content of five major chemical groups, specifically amino acids, free fatty acids, organic acids, polyols and sugars, of elaiosomes and seeds of selected species was determined, and compared with respect to their taxonomic relatedness.

Uma questão que ainda instiga discussões na literatura ecológica é como explicar a coocorrência dinâmica e milenar de formações florestais e campestres sob um mesmo regime climático que tende a favorecer as primeiras, como ocorre atualmente com mosaicos florestacampo no sul do Brasil. A partir de meados do século XX, têm-se evidenciado um fenômeno mundial de avanço de elementos lenhosos sobre áreas abertas. Neste sentido, a modelagem dos processos ecológicos envolvidos na manutenção de ambas as formações numa escala de paisagem permite o esclarecimento dos mecanismos que atuam na manutenção dessa coexistência até o presente e permite prever estados futuros diante dos prognósticos de drásticas alterações climáticas globais já nas próximas décadas. Para tanto, desenvolveu-se um modelo espacialmente explícito (2D-aDGVM) que agrega um Modelo Adaptativo Global de Dinâmica de Vegetação (aDGVM) e ainda inclui heterogeneidades topográficas, propagação do fogo e dispersão de sementes. Este modelo busca satisfazer a necessidade de modelagem mais realista de processos biofísicos, fisiológicos e demográficos na escala de indivíduos e relacionados de forma adaptativa às variações ambientais e aos regimes de distúrbios, ao mesmo tempo que agrega importantes processos ecológicos espaciais, até então pouco ou nada abordados por esse grupo de modelos numa escala de paisagem. Com este modelo, avaliaram-se os efeitos das variações topográficas da radiação solar incidente e destas nos mecanismos de interação (feedbacks) positiva e negativa que surgem daqueles processos na escala de indivíduos e que definem localmente os limites da coexistência entre elementos arbóreos e herbáceos. Ainda, foram analisados os efeitos do aumento da temperatura, precipitação e CO2 atmosférico, desde o período pré-industrial até projeções futuras para as próximas décadas, na performance das diferentes fisiologias envolvidas, bem como no balanço daquelas interações entre as mesmas e, finalmente, na sensibilidade da dinâmica dos mosaicos floresta-campo. Os resultados evidenciaram que, sob o regime climático vigente, uma coexistência relativamente estável entre floresta e campo numa mesma paisagem é mantida por uma alta freqüência de distúrbios, que por sua vez, resulta do forte feedback positivo do acúmulo de biomassa inflamável da vegetação campestre na intensidade do fogo, proporcionado pela condição altamente produtiva do atual clima mesotérmico. Por outro lado, intensificadas pela declividade do terreno, as heterogeneidades espaciais afetaram o balanço dessas interações, interferindo nos padrões espaço-temporais relacionados ao comportamento do fogo e dependentes da densidade de elementos arbóreos. Ainda, tanto esses efeitos observados na escala das manchas de vegetação, como o arranjo espacial inicial das mesmas na paisagem, afetaram as taxas de expansão florestal. Em outras palavras, a manutenção da coexistência de duas formações vegetais constituídas por elementos de inerente assimetria competitiva é possível pela manutenção de uma maior conectividade daquela que propicia o distúrbio, superando a vantagem da outra, que por sua vez é dependente da densidade dos indivíduos. Numa escala de paisagem, isto causa a manutenção de uma baixa conectividade entre as manchas florestais, propiciando sua relativa estabilidade num contexto de dispersão predominante a curtas distâncias. Contudo, embora ambos os sistemas tenham apresentado incremento no crescimento, produtividade e fecundidade, observou-se uma sensibilidade maior no sentido de aumento das taxas de avanço florestal em resposta às projeções climáticas futuras, principalmente nos próximos 90 anos, mesmo na presença do fogo. Isto seria proporcionado pela vantagem fotossintética das árvores-C3 sobre gramíneas-C4 na presença do fogo sob altas concentrações de CO2 atmosférico. Por fim, uma abordagem mais sistêmica dos mosaicos como estados alternativos mostrou ser adequada para o entendimento dos mecanismos que propiciam essa coexistência dinâmica na paisagem. / A longstanding problem in ecology is how to explain the coexistence over thousands of years of forests and natural grasslands under the same climatic regime, which favors the first, such as in forest-grasslands mosaics in South Brazil. Since the middle of the 20th century, a worldwide bush encroachment phenomenon of woody invasion in open vegetation has been threatening this relatively stable coexistence. In this sense, modelling ecological processes that arbitrate the maintenance of both vegetation formations at the landscape scale allows a better understanding of the mechanisms behind the maintenance of this coexistence, as well as predictions of future states under projections of drastic climate change over the next decades. For this, we developed a bidimensional spatial explicit model (2D-aDGVM) that aggregates an adaptive Global Vegetation Model (aDGVM), which includes topographic heterogeneity, fire spread and seed dispersal. The model aims at fulfilling the need for a more realistic representation of biophysical, physiological and demographical processes using an individualbased approach as it adapts these processes to environmental variations and disturbance regimes. In addition, the model includes important spatial ecological processes that have gained less attention by such models adopting a landscape-scale approach. Therefore, we evaluated the effect of topographic variations in incoming solar radiation on positive and on negative feedbacks that rise from those individual-based processes, and which in turns define the limiting thresholds upon which woody and grassy forms coexist. Additionally, the effects of increasing temperature, rainfall and atmospheric CO2 levels on the performance of distinct physiologies (C3-tree and C4-grass) were analyzed, as well as the sensitivity of forestgrassland mosaics to changes in climate from the preindustrial period to the next decades. Results showed that a relatively stable coexistence of forests and grasslands in the same landscape was observed with more frequent fires under the present climatic conditions. This was due to strong positive feedbacks of the huge accumulation of flammable grass biomass on fire intensity promoted by the high productivity of the present mesic conditions. On the other hand, spatio-temporal density dependent processes linked to fire and enhanced by slope at the patch scale, as well as the initial spatial arrangement of vegetation patches affected the rate of forest expansion at the landscape scale. The persistence of coexisting vegetation formations with an inherent asymmetry of competitive interactions was possible when the higher connectivity of the fire-prone patches (grassland) affected negatively the performance of the entire fire-sensitive system (forest). This was possible by overcoming its local densitydependent advantage, or by maintaining it with a low connectivity, which is expected to reduce the rate of coalescence of forest patches in a scenario of predominantly short distance dispersal. Despite the increments in biomass production, stem growth and fecundity that were observed in both grassland and forest, climate change increased the rates of forest expansion over grasslands even in presence of fire, and mainly over the next 90 years. This was attributed to a high photosynthetic advantage of C3-trees over C4-grasses in presence of fire under higher atmospheric CO2 levels. Finally, in the face of the general observed tendency of forest expansion over grasslands, the ancient grasslands have persisted as alternative ecosystem states in forest-grassland mosaics. In this sense, exploring this dynamic coexistence under the concept of alternative stable states have showed to be the most appropriate approach, and the outcomes of this novel perspective may highlight the understanding of the mechanisms behind the long-term coexistence.

Woody plant encroachment is one of the major problems worldwide because it affects negatively the herbaceous layer, which provide forage for livestock production. However, the role of ruminants particularly browsers in the dispersal of woody plant seeds still remains a concern for farmers interested in grass production. Seedpods of various woody plant species constitute a crucial part of the diet of herbivores during the dry season because of their high nutritional quality compared to herbaceous material. The interaction of associated diet quality, seed characteristics and animal species among other factors play a pivotal part in the success of livestock faecal seeds dispersion. Furthermore, dispersed seeds that successfully grow into mature woody plants become an important source of protein for herbivores. The use of woody plants as a source forage is known to be limited by plant secondary metabolites (PSMs) such as condensed tannins. The objectives of this study were to determine 1) the effects of condensed tannins and crude protein of Vachellia tortilis and Dichrostachys cinerea pods in seed recovery and germination fed to goats, and 2) the effects of diet mixing on the feed intake of plant species by goats. In the first experiment, a total of 12 female indigenous goats and 12 female Pedi sheep were utilised in this study, with the average body weights of 29.50 kg ± 1.60 (S.E) and 28.70 kg ± 1.60, respectively. Twelve goats were grouped into two groups of six goats per group, one group was fed D. cinerea pods and the other group was fed V. tortilis pods. The group of 12 sheep were divided similarly, the one group was fed D. cinerea pods and the other group was fed V. tortilis pods. Each animal was given V. tortilis and D. cinerea pods at 2.50% of their body weight. All animals were allowed to consume D. cinerea or V. tortilis pods within 24 h, after which the remaining pods were collected and weighed. Faecal collection commenced immediately after the 24 h pods feeding and was carried on until no seeds were discovered in faeces. All faeces extracted from sheep and goats were collected daily in the morning from the faecal bags. In the second experiment, a total of 24 indigenous goats with average body weight of 26.6 kg ± 0.51 were utilised. Goats were arbitrarily selected and grouped into four groups of six goats per group (goats were placed individually in 2 m2 pens). Each group was fed one of the following diets: diet one - Searsia lancea, diet two - S. pyroides, diet three - Euclea crispa and diet four - was a combination of the three plant species (Searsia lancea, S. pyroides and Euclea crispa). Searsia lancea, S. pyroides and E. crispa branches were collected every morning prior to feeding, and were weighed before offering the animals. Refusals were gathered and weighed, and intake was calculated as distinction between weight in and refusals. Plant species foliage were analysed for crude protein, condensed tannin, acid detergent lignin, acid detergent fibre and neutral detergent fibre. During the first experiment, the cumulative percentage seed recovery of V. tortilis from goats (46.00 % ± 1.90) and sheep (52.00 % ± 2.93) was significantly higher than D. cinerea from goats (13 % ± 1.47) and sheep (24.00 % ± 1.16). Germination percentage of D. cinerea seeds that passed through the gastro-intestinal tract of goats (33.12 % ± 2.94) and sheep (36.00 % ± 2.68) was significantly higher than V. tortilis seeds that passed through the gastro-intestinal tract of goats (28.98 % ± 2.68) and sheep (23.04 % ± 2.81). Average D. cinerea (34.56 % ± 1.99) and V. tortilis (26.02 %± 2.10) seeds that went through the gastro-intestinal of goats and sheep had a significantly higher germination rate than the control (i.e. no passage through the gut; D. cinerea = 2.31 % ± 1.55, V. tortilis = 5.07 % ± 2.68). The high mean cumulative percentage seed recovery of V. tortilis (18.80 %) may be attributed to the relatively higher crude protein than D. cinerea (12.20 %). This may encourage animal seed dispersal and germination of woody plant species with relatively high crude protein content. In the second experiment, Searsia lancea contained 8.50 % CP, 21.46 % acid detergent fibre (ADF), 12.50 % ADL and 39.37 % NDF. Searsia pyroides had 9.03 % CP, 27.07 % ADF, 10.89 % ADL and 40.30 % NDF. Euclea crispa had 6.19 % CP, 26.20 % ADF, 16.63 % ADL and 30.02 % NDF. Mixed diet (combination of the three plant species) had 8.96 % CP, 23.72 % ADF, 11.13 % ADL and 38.28 % NDF. Searsia lancea had 2.70 % of CTs while S. pyroides had 5.20 % CT, E. crispa had 6.44 % CT and mixed diet had 7.20 % CT. The mean dry matter intake varied significantly among dietary groups (P < 0.001). Similarly, goats offered a mixed diet consumed more CTs (P < 0.01) than those offered individual forage species. The high mean cumulative percentage seed recovery of V. tortilis may be attributed to the higher crude protein of V. tortilis (18.80 %) than D. cinerea (12.20 %). Higher passage rate may encourage animal seed dispersal and germination of plant species. The results from experiment two support the postulation that animals foraging in mixed diet systems consume more PSMs and achieve higher dry matter intake than animals confined to monocultures or single species feeding systems. Given that woody plant encroachment is already reducing farm-grazing capacities in African savannas and this problem is predicted to double by 2050, strategies that improve herbivore ability to consume woody plants will increase forage availability and inform bush control programmes and policies. Moreover, the concomitant increase in CTs by goats exposed to diets with diverse species also has positive implications for animal / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)

Les bords de route constituent un des principaux habitats herbacés et linéaires des paysages agricoles, ils jouent le rôle de refuge pour différentes espèces et constituent aussi un habitat favorable pour des espèces adventices jugées problématiques. L’objectif de cette thèse est de mesurer les effets de la structure du paysage et des pratiques de gestion sur la flore de l’interface route – champ cultivé. Nos résultats suggèrent que les communautés végétales de l’interface ont une réponse temporellement décalée vis-à-vis des changements paysagers. L’étude de la végétation exprimée et de la dispersion des graines montre que la fauche tardive n’est pas le levier de gestion optimal pour favoriser la diversité végétale du bord de route, et que les pratiques de fauche influencent aussi la flore de la bordure intérieure du champ. Afin de limiter les influences croisées des pratiques de gestion, nous suggérons des stratégies réfléchies à l’échelle de l’interface route – champ. / Road verges constitute the main herbaceous and linear habitats of arable landscapes. They represent a refuge for different species, but also constitute a habitat for weeds considered problematic. The aim of this thesis was to measure the effects of landscape structure and management practices on the flora of the road-field boundary. Our results suggest that plant communities of road-field boundary have a time lagged response to landscape changes. The study of the vegetation and of seed dispersal showed that late mowing was not the optimal method to promote plant diversity on road verges and that mowing practices also influenced the flora of the inner field margin. To limit the cross-influence of management practices, we recommend well thought out strategies at the scale of the road-field boundary.

Uma questão que ainda instiga discussões na literatura ecológica é como explicar a coocorrência dinâmica e milenar de formações florestais e campestres sob um mesmo regime climático que tende a favorecer as primeiras, como ocorre atualmente com mosaicos florestacampo no sul do Brasil. A partir de meados do século XX, têm-se evidenciado um fenômeno mundial de avanço de elementos lenhosos sobre áreas abertas. Neste sentido, a modelagem dos processos ecológicos envolvidos na manutenção de ambas as formações numa escala de paisagem permite o esclarecimento dos mecanismos que atuam na manutenção dessa coexistência até o presente e permite prever estados futuros diante dos prognósticos de drásticas alterações climáticas globais já nas próximas décadas. Para tanto, desenvolveu-se um modelo espacialmente explícito (2D-aDGVM) que agrega um Modelo Adaptativo Global de Dinâmica de Vegetação (aDGVM) e ainda inclui heterogeneidades topográficas, propagação do fogo e dispersão de sementes. Este modelo busca satisfazer a necessidade de modelagem mais realista de processos biofísicos, fisiológicos e demográficos na escala de indivíduos e relacionados de forma adaptativa às variações ambientais e aos regimes de distúrbios, ao mesmo tempo que agrega importantes processos ecológicos espaciais, até então pouco ou nada abordados por esse grupo de modelos numa escala de paisagem. Com este modelo, avaliaram-se os efeitos das variações topográficas da radiação solar incidente e destas nos mecanismos de interação (feedbacks) positiva e negativa que surgem daqueles processos na escala de indivíduos e que definem localmente os limites da coexistência entre elementos arbóreos e herbáceos. Ainda, foram analisados os efeitos do aumento da temperatura, precipitação e CO2 atmosférico, desde o período pré-industrial até projeções futuras para as próximas décadas, na performance das diferentes fisiologias envolvidas, bem como no balanço daquelas interações entre as mesmas e, finalmente, na sensibilidade da dinâmica dos mosaicos floresta-campo. Os resultados evidenciaram que, sob o regime climático vigente, uma coexistência relativamente estável entre floresta e campo numa mesma paisagem é mantida por uma alta freqüência de distúrbios, que por sua vez, resulta do forte feedback positivo do acúmulo de biomassa inflamável da vegetação campestre na intensidade do fogo, proporcionado pela condição altamente produtiva do atual clima mesotérmico. Por outro lado, intensificadas pela declividade do terreno, as heterogeneidades espaciais afetaram o balanço dessas interações, interferindo nos padrões espaço-temporais relacionados ao comportamento do fogo e dependentes da densidade de elementos arbóreos. Ainda, tanto esses efeitos observados na escala das manchas de vegetação, como o arranjo espacial inicial das mesmas na paisagem, afetaram as taxas de expansão florestal. Em outras palavras, a manutenção da coexistência de duas formações vegetais constituídas por elementos de inerente assimetria competitiva é possível pela manutenção de uma maior conectividade daquela que propicia o distúrbio, superando a vantagem da outra, que por sua vez é dependente da densidade dos indivíduos. Numa escala de paisagem, isto causa a manutenção de uma baixa conectividade entre as manchas florestais, propiciando sua relativa estabilidade num contexto de dispersão predominante a curtas distâncias. Contudo, embora ambos os sistemas tenham apresentado incremento no crescimento, produtividade e fecundidade, observou-se uma sensibilidade maior no sentido de aumento das taxas de avanço florestal em resposta às projeções climáticas futuras, principalmente nos próximos 90 anos, mesmo na presença do fogo. Isto seria proporcionado pela vantagem fotossintética das árvores-C3 sobre gramíneas-C4 na presença do fogo sob altas concentrações de CO2 atmosférico. Por fim, uma abordagem mais sistêmica dos mosaicos como estados alternativos mostrou ser adequada para o entendimento dos mecanismos que propiciam essa coexistência dinâmica na paisagem. / A longstanding problem in ecology is how to explain the coexistence over thousands of years of forests and natural grasslands under the same climatic regime, which favors the first, such as in forest-grasslands mosaics in South Brazil. Since the middle of the 20th century, a worldwide bush encroachment phenomenon of woody invasion in open vegetation has been threatening this relatively stable coexistence. In this sense, modelling ecological processes that arbitrate the maintenance of both vegetation formations at the landscape scale allows a better understanding of the mechanisms behind the maintenance of this coexistence, as well as predictions of future states under projections of drastic climate change over the next decades. For this, we developed a bidimensional spatial explicit model (2D-aDGVM) that aggregates an adaptive Global Vegetation Model (aDGVM), which includes topographic heterogeneity, fire spread and seed dispersal. The model aims at fulfilling the need for a more realistic representation of biophysical, physiological and demographical processes using an individualbased approach as it adapts these processes to environmental variations and disturbance regimes. In addition, the model includes important spatial ecological processes that have gained less attention by such models adopting a landscape-scale approach. Therefore, we evaluated the effect of topographic variations in incoming solar radiation on positive and on negative feedbacks that rise from those individual-based processes, and which in turns define the limiting thresholds upon which woody and grassy forms coexist. Additionally, the effects of increasing temperature, rainfall and atmospheric CO2 levels on the performance of distinct physiologies (C3-tree and C4-grass) were analyzed, as well as the sensitivity of forestgrassland mosaics to changes in climate from the preindustrial period to the next decades. Results showed that a relatively stable coexistence of forests and grasslands in the same landscape was observed with more frequent fires under the present climatic conditions. This was due to strong positive feedbacks of the huge accumulation of flammable grass biomass on fire intensity promoted by the high productivity of the present mesic conditions. On the other hand, spatio-temporal density dependent processes linked to fire and enhanced by slope at the patch scale, as well as the initial spatial arrangement of vegetation patches affected the rate of forest expansion at the landscape scale. The persistence of coexisting vegetation formations with an inherent asymmetry of competitive interactions was possible when the higher connectivity of the fire-prone patches (grassland) affected negatively the performance of the entire fire-sensitive system (forest). This was possible by overcoming its local densitydependent advantage, or by maintaining it with a low connectivity, which is expected to reduce the rate of coalescence of forest patches in a scenario of predominantly short distance dispersal. Despite the increments in biomass production, stem growth and fecundity that were observed in both grassland and forest, climate change increased the rates of forest expansion over grasslands even in presence of fire, and mainly over the next 90 years. This was attributed to a high photosynthetic advantage of C3-trees over C4-grasses in presence of fire under higher atmospheric CO2 levels. Finally, in the face of the general observed tendency of forest expansion over grasslands, the ancient grasslands have persisted as alternative ecosystem states in forest-grassland mosaics. In this sense, exploring this dynamic coexistence under the concept of alternative stable states have showed to be the most appropriate approach, and the outcomes of this novel perspective may highlight the understanding of the mechanisms behind the long-term coexistence.

Uma questão que ainda instiga discussões na literatura ecológica é como explicar a coocorrência dinâmica e milenar de formações florestais e campestres sob um mesmo regime climático que tende a favorecer as primeiras, como ocorre atualmente com mosaicos florestacampo no sul do Brasil. A partir de meados do século XX, têm-se evidenciado um fenômeno mundial de avanço de elementos lenhosos sobre áreas abertas. Neste sentido, a modelagem dos processos ecológicos envolvidos na manutenção de ambas as formações numa escala de paisagem permite o esclarecimento dos mecanismos que atuam na manutenção dessa coexistência até o presente e permite prever estados futuros diante dos prognósticos de drásticas alterações climáticas globais já nas próximas décadas. Para tanto, desenvolveu-se um modelo espacialmente explícito (2D-aDGVM) que agrega um Modelo Adaptativo Global de Dinâmica de Vegetação (aDGVM) e ainda inclui heterogeneidades topográficas, propagação do fogo e dispersão de sementes. Este modelo busca satisfazer a necessidade de modelagem mais realista de processos biofísicos, fisiológicos e demográficos na escala de indivíduos e relacionados de forma adaptativa às variações ambientais e aos regimes de distúrbios, ao mesmo tempo que agrega importantes processos ecológicos espaciais, até então pouco ou nada abordados por esse grupo de modelos numa escala de paisagem. Com este modelo, avaliaram-se os efeitos das variações topográficas da radiação solar incidente e destas nos mecanismos de interação (feedbacks) positiva e negativa que surgem daqueles processos na escala de indivíduos e que definem localmente os limites da coexistência entre elementos arbóreos e herbáceos. Ainda, foram analisados os efeitos do aumento da temperatura, precipitação e CO2 atmosférico, desde o período pré-industrial até projeções futuras para as próximas décadas, na performance das diferentes fisiologias envolvidas, bem como no balanço daquelas interações entre as mesmas e, finalmente, na sensibilidade da dinâmica dos mosaicos floresta-campo. Os resultados evidenciaram que, sob o regime climático vigente, uma coexistência relativamente estável entre floresta e campo numa mesma paisagem é mantida por uma alta freqüência de distúrbios, que por sua vez, resulta do forte feedback positivo do acúmulo de biomassa inflamável da vegetação campestre na intensidade do fogo, proporcionado pela condição altamente produtiva do atual clima mesotérmico. Por outro lado, intensificadas pela declividade do terreno, as heterogeneidades espaciais afetaram o balanço dessas interações, interferindo nos padrões espaço-temporais relacionados ao comportamento do fogo e dependentes da densidade de elementos arbóreos. Ainda, tanto esses efeitos observados na escala das manchas de vegetação, como o arranjo espacial inicial das mesmas na paisagem, afetaram as taxas de expansão florestal. Em outras palavras, a manutenção da coexistência de duas formações vegetais constituídas por elementos de inerente assimetria competitiva é possível pela manutenção de uma maior conectividade daquela que propicia o distúrbio, superando a vantagem da outra, que por sua vez é dependente da densidade dos indivíduos. Numa escala de paisagem, isto causa a manutenção de uma baixa conectividade entre as manchas florestais, propiciando sua relativa estabilidade num contexto de dispersão predominante a curtas distâncias. Contudo, embora ambos os sistemas tenham apresentado incremento no crescimento, produtividade e fecundidade, observou-se uma sensibilidade maior no sentido de aumento das taxas de avanço florestal em resposta às projeções climáticas futuras, principalmente nos próximos 90 anos, mesmo na presença do fogo. Isto seria proporcionado pela vantagem fotossintética das árvores-C3 sobre gramíneas-C4 na presença do fogo sob altas concentrações de CO2 atmosférico. Por fim, uma abordagem mais sistêmica dos mosaicos como estados alternativos mostrou ser adequada para o entendimento dos mecanismos que propiciam essa coexistência dinâmica na paisagem. / A longstanding problem in ecology is how to explain the coexistence over thousands of years of forests and natural grasslands under the same climatic regime, which favors the first, such as in forest-grasslands mosaics in South Brazil. Since the middle of the 20th century, a worldwide bush encroachment phenomenon of woody invasion in open vegetation has been threatening this relatively stable coexistence. In this sense, modelling ecological processes that arbitrate the maintenance of both vegetation formations at the landscape scale allows a better understanding of the mechanisms behind the maintenance of this coexistence, as well as predictions of future states under projections of drastic climate change over the next decades. For this, we developed a bidimensional spatial explicit model (2D-aDGVM) that aggregates an adaptive Global Vegetation Model (aDGVM), which includes topographic heterogeneity, fire spread and seed dispersal. The model aims at fulfilling the need for a more realistic representation of biophysical, physiological and demographical processes using an individualbased approach as it adapts these processes to environmental variations and disturbance regimes. In addition, the model includes important spatial ecological processes that have gained less attention by such models adopting a landscape-scale approach. Therefore, we evaluated the effect of topographic variations in incoming solar radiation on positive and on negative feedbacks that rise from those individual-based processes, and which in turns define the limiting thresholds upon which woody and grassy forms coexist. Additionally, the effects of increasing temperature, rainfall and atmospheric CO2 levels on the performance of distinct physiologies (C3-tree and C4-grass) were analyzed, as well as the sensitivity of forestgrassland mosaics to changes in climate from the preindustrial period to the next decades. Results showed that a relatively stable coexistence of forests and grasslands in the same landscape was observed with more frequent fires under the present climatic conditions. This was due to strong positive feedbacks of the huge accumulation of flammable grass biomass on fire intensity promoted by the high productivity of the present mesic conditions. On the other hand, spatio-temporal density dependent processes linked to fire and enhanced by slope at the patch scale, as well as the initial spatial arrangement of vegetation patches affected the rate of forest expansion at the landscape scale. The persistence of coexisting vegetation formations with an inherent asymmetry of competitive interactions was possible when the higher connectivity of the fire-prone patches (grassland) affected negatively the performance of the entire fire-sensitive system (forest). This was possible by overcoming its local densitydependent advantage, or by maintaining it with a low connectivity, which is expected to reduce the rate of coalescence of forest patches in a scenario of predominantly short distance dispersal. Despite the increments in biomass production, stem growth and fecundity that were observed in both grassland and forest, climate change increased the rates of forest expansion over grasslands even in presence of fire, and mainly over the next 90 years. This was attributed to a high photosynthetic advantage of C3-trees over C4-grasses in presence of fire under higher atmospheric CO2 levels. Finally, in the face of the general observed tendency of forest expansion over grasslands, the ancient grasslands have persisted as alternative ecosystem states in forest-grassland mosaics. In this sense, exploring this dynamic coexistence under the concept of alternative stable states have showed to be the most appropriate approach, and the outcomes of this novel perspective may highlight the understanding of the mechanisms behind the long-term coexistence.