Os bandos mistos de aves são agregações sociais complexas estáveis durante o tempo e espaço. Até hoje, a estrutura social dessas espécies foi descrita a partir de estudos subjetivos de campo ou a partir de compilações do número e intensidade das interações a nível de todo o grupo, sem considerar as interações par-a-par individualmente. Nossos objetivos foram buscar evidências de associações não-randômicas entre pares de espécies de aves, delimitar os grupos a partir das espécies com as associações mais fortes e verificar se há diferenças na estrutura social entre os habitat de floresta primária e secundária. Utilizamos dados de ocorrência das espécies coletados a partir de redes de neblina e gravação de vocalizações para identificar pares de espécies que foram co-detectadas mais frequentemente do que o esperado a partir do modelo nulo e compararamos a força dessa interação entre as florestas tropicais primária e secundária Amazônicas. Nós também utilizamos as associações par-a-par para construir as redes de interação social e suas mudanças entre os tipos de habitat. Nós encontramos muitas interações positivas fortes entre as espécies, mas nenhuma evidência de repulsão. As análises das redes de interação revelaram vários grupos de espécies que corroboram com grupos ecológios descritos na literatura. Além disso, tanto a estrutura da rede de interação como a força da interação se alteraram drasticamente com a perturbação do habitat, com formação de algumas associações novas, mas uma tendência geral para quebra de associações entre as espécies. Nossos resultados mostram que as interações sociais entre essas aves podem ser fortemente afetados pela degradação do habitat, sugerindo que a estabilidade das interações desenvolvida entre espécies é ameaçada pelos distúrbios causados pelo homem. / Inter-specific associations of birds are complex social phenomena, frequently detected and often stable over time and space. So far, the social structure of these associations has been largely deduced from subjective assessments in the field or by counting the number of inter-specific encounters at the whole-group level, without considering changes to individual pairwise interactions. Here, we look for evidence of non-random association between pairs of bird species, delimit groups of more strongly associated species and examine differences in social structure between old growth and secondary forest habitat. We used records of bird species detection from mist-netting capture and from acoustic recordings to identify pairwise associations that were detected more frequently than expected under a null distribution, and compared the strength of these associations between old-growth and secondary forest Amazonian tropical forest. We also used the pairwise strength associations to visualize the social network structure and its changes between habitat types. We found many strongly positive interactions between species, but no evidence of repulsion. Network analyses revealed several modules of species that broadly agree with the subjective groupings described in the ornithological literature. Furthermore, both network structure and association strength changed drastically with habitat disturbance, with the formation of a few new associations but a general trend towards the breaking of associations between species. Our results show that social grouping in birds is real and may be strongly affected by habitat degradation, suggesting that the stability of the associations is threatened by anthropogenic disturbance.

Os bandos mistos de aves são agregações sociais complexas estáveis durante o tempo e espaço. Até hoje, a estrutura social dessas espécies foi descrita a partir de estudos subjetivos de campo ou a partir de compilações do número e intensidade das interações a nível de todo o grupo, sem considerar as interações par-a-par individualmente. Nossos objetivos foram buscar evidências de associações não-randômicas entre pares de espécies de aves, delimitar os grupos a partir das espécies com as associações mais fortes e verificar se há diferenças na estrutura social entre os habitat de floresta primária e secundária. Utilizamos dados de ocorrência das espécies coletados a partir de redes de neblina e gravação de vocalizações para identificar pares de espécies que foram co-detectadas mais frequentemente do que o esperado a partir do modelo nulo e compararamos a força dessa interação entre as florestas tropicais primária e secundária Amazônicas. Nós também utilizamos as associações par-a-par para construir as redes de interação social e suas mudanças entre os tipos de habitat. Nós encontramos muitas interações positivas fortes entre as espécies, mas nenhuma evidência de repulsão. As análises das redes de interação revelaram vários grupos de espécies que corroboram com grupos ecológios descritos na literatura. Além disso, tanto a estrutura da rede de interação como a força da interação se alteraram drasticamente com a perturbação do habitat, com formação de algumas associações novas, mas uma tendência geral para quebra de associações entre as espécies. Nossos resultados mostram que as interações sociais entre essas aves podem ser fortemente afetados pela degradação do habitat, sugerindo que a estabilidade das interações desenvolvida entre espécies é ameaçada pelos distúrbios causados pelo homem. / Inter-specific associations of birds are complex social phenomena, frequently detected and often stable over time and space. So far, the social structure of these associations has been largely deduced from subjective assessments in the field or by counting the number of inter-specific encounters at the whole-group level, without considering changes to individual pairwise interactions. Here, we look for evidence of non-random association between pairs of bird species, delimit groups of more strongly associated species and examine differences in social structure between old growth and secondary forest habitat. We used records of bird species detection from mist-netting capture and from acoustic recordings to identify pairwise associations that were detected more frequently than expected under a null distribution, and compared the strength of these associations between old-growth and secondary forest Amazonian tropical forest. We also used the pairwise strength associations to visualize the social network structure and its changes between habitat types. We found many strongly positive interactions between species, but no evidence of repulsion. Network analyses revealed several modules of species that broadly agree with the subjective groupings described in the ornithological literature. Furthermore, both network structure and association strength changed drastically with habitat disturbance, with the formation of a few new associations but a general trend towards the breaking of associations between species. Our results show that social grouping in birds is real and may be strongly affected by habitat degradation, suggesting that the stability of the associations is threatened by anthropogenic disturbance.

Os bandos mistos de aves são agregações sociais complexas estáveis durante o tempo e espaço. Até hoje, a estrutura social dessas espécies foi descrita a partir de estudos subjetivos de campo ou a partir de compilações do número e intensidade das interações a nível de todo o grupo, sem considerar as interações par-a-par individualmente. Nossos objetivos foram buscar evidências de associações não-randômicas entre pares de espécies de aves, delimitar os grupos a partir das espécies com as associações mais fortes e verificar se há diferenças na estrutura social entre os habitat de floresta primária e secundária. Utilizamos dados de ocorrência das espécies coletados a partir de redes de neblina e gravação de vocalizações para identificar pares de espécies que foram co-detectadas mais frequentemente do que o esperado a partir do modelo nulo e compararamos a força dessa interação entre as florestas tropicais primária e secundária Amazônicas. Nós também utilizamos as associações par-a-par para construir as redes de interação social e suas mudanças entre os tipos de habitat. Nós encontramos muitas interações positivas fortes entre as espécies, mas nenhuma evidência de repulsão. As análises das redes de interação revelaram vários grupos de espécies que corroboram com grupos ecológios descritos na literatura. Além disso, tanto a estrutura da rede de interação como a força da interação se alteraram drasticamente com a perturbação do habitat, com formação de algumas associações novas, mas uma tendência geral para quebra de associações entre as espécies. Nossos resultados mostram que as interações sociais entre essas aves podem ser fortemente afetados pela degradação do habitat, sugerindo que a estabilidade das interações desenvolvida entre espécies é ameaçada pelos distúrbios causados pelo homem. / Inter-specific associations of birds are complex social phenomena, frequently detected and often stable over time and space. So far, the social structure of these associations has been largely deduced from subjective assessments in the field or by counting the number of inter-specific encounters at the whole-group level, without considering changes to individual pairwise interactions. Here, we look for evidence of non-random association between pairs of bird species, delimit groups of more strongly associated species and examine differences in social structure between old growth and secondary forest habitat. We used records of bird species detection from mist-netting capture and from acoustic recordings to identify pairwise associations that were detected more frequently than expected under a null distribution, and compared the strength of these associations between old-growth and secondary forest Amazonian tropical forest. We also used the pairwise strength associations to visualize the social network structure and its changes between habitat types. We found many strongly positive interactions between species, but no evidence of repulsion. Network analyses revealed several modules of species that broadly agree with the subjective groupings described in the ornithological literature. Furthermore, both network structure and association strength changed drastically with habitat disturbance, with the formation of a few new associations but a general trend towards the breaking of associations between species. Our results show that social grouping in birds is real and may be strongly affected by habitat degradation, suggesting that the stability of the associations is threatened by anthropogenic disturbance.

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Bare-root Nuttall oak, Shumard oak, and swamp chestnut oak seedlings were planted on former agricultural fields in Mississippi to evaluate growth and survival following treatment by different combinations of mechanical site preparation and pre-emergent Oust XP® applications. Mechanical treatments included: (1) controls, (2) subsoiling treatment, (3) bedding treatment, and (4) combination plowing. Pre-emergent Oust XP® treatments included: (1) one-year Oust XP® applications and (2) two-year Oust XP® applications. Evaluations and measurements were performed over the course of three years. Results within this dissertation should be considered in the context of high quality former agricultural sites with silt loam soils. Seedling height and GLD increased each growing season. Height and GLD of seedlings were greater in bedded and combination plowed areas compared to control and subsoiled areas. Height and GLD were not different by Oust XP® application. However, seedling survival in two-year Oust XP® application areas was reduced compared to one-year Oust XP® application areas. Nuttall oak seedlings planted in bedded and combination plowed areas exhibited greater stem biomass compared to those planted in control or subsoiled areas. Seedlings planted in two-year Oust XP® areas exhibited greater stem and root biomass compared to those planted in areas receiving the one-year treatment. Better growth and biomass production in bedded and combination plowed areas would promote their use for site preparation on similar sites. While survival was lower in two-year Oust XP® treatment areas compared to one-year treatment areas, the difference would not warrant change in management strategy. Additionally, woody biomass was much greater in two-year Oust XP® areas. Thus, if cost is not prohibitive, treatment with two years of Oust XP® is recommended. The objective of the mixed species study was to establish baseline growth and survival data for mixed Nuttall oak and green ash plantations on former agricultural areas. Height and GLD for both species increased each growing season. Third-year survival was excellent at 96.0 percent. In conclusion, the mixture performed satisfactorily. Growth and survival were excellent, which indicates this mixture would be useful in afforesting similar former agriculture sites.

The increasing frequency and intensity of droughts threaten forests and their climate change mitigation potential. Mixed-species forests are promoted to increase forest productivity and stability compared to monospecific forests, but we still lack a mechanistic understanding of the strength, nature and drivers of tree diversity effects on productivity and stability under drought. Here, I studied the stress hotter droughts inflict on trees and examined whether diversification in tree species, structures and drought-tolerance traits is a potential solution to this threat. In study 1, I found that the hotter drought years 2018–2019, the severest droughts since records, induced unprecedented tree productivity and physiological stress responses (reduced growth and increased δ13C) in a Central European floodplain forest. Hotter droughts thus constitute a novel threat. In studies 2–4, I examined diversity-productivity and diversity-stability relationships across spatiotemporal scales in a tropical (study 2) and a subtropical (studies 3, 4) tree diversity experiment specifically designed to examine biodiversity-ecosystem functioning relationships. Tree species richness consistently increased productivity and stability, and this effect was strongest at the highest levels of diversity. Structural diversity increased productivity but was unrelated to stability, while diversity in drought-tolerance traits increased stability but not productivity. Assessing drought-tolerance traits was essential for understanding the role of tree diversity during drought. Positive diversity effects on productivity scaled up from the tree neighbourhood to the community level, but effects on stability emerged only at the community level. Community stability increased with species richness due to asynchronous species responses to dry and wet years driven by species’ drought-tolerance traits. I showed that diversity but not identity in drought-tolerance traits increases community stability. Overall, promoting structurally and functionally diverse mixed-species forests may enable high productivity and stability under intensifying climate change.:1. General introduction 1.1. Mixed-species forests 1.2. Diversity-productivity relationships 1.3. Diversity-productivity relationships during drought 1.4. Diversity-stability relationships 1.5. Diversity facets 1.6. Drought-tolerance traits 1.7. Linkages between the four studies 2. Methodological features 2.1. Study sites and approaches 2.2. Productivity, stability and physiological water stress 2.3. The quantification of diversity 2.4. Spatiotemporal analyses 3. Original contributions Study 1: Cumulative growth and stress responses to the 2018–2019 drought in a European floodplain forest Study 2: Drivers of productivity and its temporal stability in a tropical tree diversity experiment Study 3: Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13C responses to drought Study 4: Species richness stabilizes productivity via asynchrony and drought- tolerance diversity in a large-scale tree biodiversity experiment 4. General discussion 4.1. Summary of main findings 4.2. Hotter droughts and forest functioning 4.3. Diversity signals across spatial scales 4.4. Diversity signals across temporal scales 4.5. Diversity facets 4.6. Context dependency and transferability 4.7. Implications for forest management in the 21st century 5. Outlook and future research 5.1. Observation and experimentation under hotter droughts 5.2. Response variables 5.3. Diversity facets 5.4. Drought-tolerance traits 5.5. Zooming in 5.6. Zooming out 5.7. From understanding to use of BEF relationships 6. Conclusion 7. Summary 8. Zusammenfassung 9. References Acknowledgements Author contribution statements Curriculum vitae List of publications Selbstständigkeitserklärung

With shifting preferences of consumers towards healthier food, organic food demand has been on the rise for the past two decades. This increased demand has created an opportunity for farmers to shift from conventional to organic production. However, there are risks and uncertainties associated with organic farming. The management of an organic farm in the absence of organic-based disease and pest suppressing strategies constrains farmers from adopting organic vegetable production. The use of cover crops to control soil-borne diseases and suppress weeds and other pests has increased because of its sustainable and environmental friendly nature. This study of the economic impact of the cover crops on organic tomato production in the three states Ohio, New York, and Maryland showed mixed results. In Maryland, mixed forage radish and hairy vetch was projected to have a net present value over 15 years that was $1.53 million higher than single species hairy vetch, assuming maximum adoption level of 50 percent. In New York, mixed rye and turnip gave the higher return with a net present value of $2.61 million. In Ohio, the highest projected return was from mixed hay compared to hairy vetch with a net present value of $3.12 million when used without adding compost amendments. In Maryland and New York when bare ground was also used as a control, only mixed forage radish and hairy vetch in Maryland produced better returns compared to bare ground. A probit regression assessing the factors affecting the decision to adopt mixed species green manure technology indicated that farmer experiences in organic production, farmer age, access to the internet access, and farmers’ perceptions about the benefits of using mixed species green manures were significant factors. Each variables and factors except age had a positive influence. Similarly, probit results for microbial inoculants indicated that education, gender, and access to the internet were significant determinants, and had a negative effect on the probability of adoption. Access to the internet was significant for both mixed species green manures and microbial inoculants but with opposite sign, positive for mixed species green manures and negative for microbial inoculants. / Master of Science

Social behaviour is shaped by complex relationships between evolutionary and ecological processes interacting at different scales. Benefits gained from social associations can range from predator dilution to collective sensing, but little is known about how these can be influenced by social structure and phenotypic composition. In this thesis, I investigated how individual decision-making affects phenotypic social structure, and how this mediates social behaviour through emergent properties of collective group behaviour. First, using mixed-species flocks as a model system, I showed individual tits (Paridae, chapter 2) and thornbills (Acanthizae, chapter 3) varied significantly in their social positions. Within-species variation in network position was as large as between-species variation, sug- gesting that prescribing functional roles at the species level may not sufficiently account for potential differences in fitness operating at the individual level. Rather, this suggested that structure may be driven by phenotypic traits, underpinning network structure (chapter 4). Next, I used an extensive data set of foraging records to explore factors determining the composition, of flocks of great tits (Parus major, chapter 5). For example, assortment by dispersal phenotype (immigration status) was the result of spatial disaggregation, and I showed that this may facilitate social selection for breeding territories (chapter 6). Finally, I investigated how decision-making shaped mixed-species social structure. I found that tits used a common strategy for managing pressures of predation and starvation by shifting from exploration to exploitation at different times of the day (chapter 7). I then found that a very simple interaction rule successfully replicated mixed-species group structure (chapter 8). Strikingly, the same rule was applied to both conspecifics and het- erospecifics, potentially playing an important role in the maintenance of flock structure. Through experimental manipulation of ecological conditions, I found that heightened per- ceived predation resulted in stronger social attraction overall, whereas increased competition led to a reduction in attraction to conspecifics (chapter 9). Simulations suggested this could be one potential mechanism underpinning fission-fusion dynamics in these species. Together, the results in this thesis form a framework linking social behaviour to individ- ual fitness where natural selection is shaped by the social environment. This approach may prove useful for testing whether following common social rules reduces variance in benefits accrued by individuals, and how within-species variation in social behaviour can impact emergent properties of groups.

Orientador: Marcos César de Oliveira Santos / Banca: Marco Aurelio Pizo Ferreira / Banca: Pedro Ferreira Develey / Resumo: A maria-da-restinga (Phylloscartes kronei) é uma espécie da família Tyrannidae descrita recentemente e considerada como globalmente ameaçada de extinção, cuja história natural é pouco conhecida. Visando preencher parte desta lacuna, o objetivo deste estudo foi de caracterizar o comportamento de forrageamento da maria-da-restinga, descrever os bandos mistos aos quais ela se associa, bem como descrever alguns outros aspectos de sua história natural como seus hábitos alimentares, o comportamento de dormir, insights sobre a biologia reprodutiva, o alcance de vôo, encontros agonísticos interespecíficos e a muda. No período de agosto de 2008 a julho de 2009 foram realizadas excursões mensais ao município de Ilha Comprida (~24º S), Estado de São Paulo. Aliado ao esforço anual mencionado, uma visita ao município de Guaraqueçaba (25º18'S e 48º19'W), Estado do Paraná, foi conduzida entre os dias 25 de julho e 1º de agosto de 2008. Foram coletadas 613 amostras de forrageamento, através de observações diretas com auxílio de binóculos com aumento de 10 vezes. Durante os períodos de coleta de dados sobre o forrageamento da espécie, para cada encontro com a mesma foi anotado se esta se encontrava só, aos pares, em grupos ou associada a bandos mistos de aves. Quando em bandos mistos, foram anotadas todas as espécies ocorrentes, visando caracterizar os bandos aos quais se associa. Para a descrição do hábito alimentar da espécie foram analisados os conteúdos estomacais de cinco exemplares coletados na década de 1990 no Estado do Paraná, tendo sido identificados 116 ítens alimentares. Através da análise dos dados obtidos, conclui-se que P. kronei captura suas presas principalmente em folhas verdes, entre 0,5 e 15m acima do solo, utilizando a manobra "investir-atingir". Alimenta-se predominantemente de artrópodes, sendo que os insetos das ordens Coleoptera... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The Restinga Tyrannulet (Phylloscartes kronei) is a recently described and globally threatened species of the family Tyrannidae, whose natural history is poorly known. In this study several information on the natural history of P. kronei were gathered such as several aspects on foraging behavior, association with mixed species bird flocks, feeding habits, the description of the roosting behavior, insights on the reproductive biology, the flying range, interespecific agonistic encounters and moulting. From August 2008 to July 2009, data on this species were collected on a monthly basis in Ilha Comprida (~24º S), São Paulo state, Brazil. In addition, a visit to Guaraqueçaba (25º18'S e 48º19'W), Paraná state, was conducted between 25 July and 01 August 2008. A total of 613 foraging maneuvers were gathered by direct observations with the aid of binoculars with 10x magnification. In all meetings with the species it was reported if individuals were alone, in pairs, in groups or associated with mixed species bird flocks. When mixed species flocks with Restinga Tyrannulets were observed, all species in the flock were identified. Five stomach contents collected in the 1990s in Paraná state were evaluated and 116 food items were identified. The Restinga Tyrannulet captures preys mainly with sally-strikes in green leaves between 0.5 and 15m above the ground. This species feeds mainly on arthropods, especially Coleoptera and Hymenoptera. The observed foraging behaviors and feeding habits were similar to the ones observed in other species of Phylloscartes, but new food items are described for this genus: Anobiidae (Coleoptera), Coccinelidae (Coleoptera), Chalcidoidea (Hymenoptera), Microhymenoptera and two species of fruits (Clusia criuva and Ternstroemia brasiliensis). P. kronei is a sporadic follower of mixed species bird flocks, which had the inclusion of 25 species on their compositions... (Complete abstract click electronic access below) / Mestre

Mixed-species plantations of eucalypts and acacias have the potential to improve stand productivity over that of respective monocultures through the facilitative effect of nitrogen-fixation by acacias, and increased resource capture through above- and belowground stratification. However, growth in mixed-species plantations may not be improved compared to that of monocultures when competitive interactions outweigh the effects of improved nutrient availability and resource capture. Careful selection of sites and species is therefore critical to successfully improving stand productivity using mixed-species plantations. This study set out to examine some of the processes and interactions that occur in mixed-species plantations, and the effect nutrient and water availability can have on the growth of mixtures. In three out of four mixed-species field trials examined in this study, growth was not increased in mixtures compared to monocultures. However, in the fourth field trial, heights, diameters, stand volume and aboveground biomass were higher in mixtures of E. globulus and A. mearnsii from 3-4 years after planting. The range in outcomes from mixing species in these four trials shows that a fundamental understanding of the underlying processes is required to enable a greater predictive capacity for the circumstances under which mixtures will be successful. Therefore the growth dynamics, processes and interactions were examined in the mixtures of E. globulus and A. mearnsii. The difference in productivity between mixtures and monocultures in this trial increased with time up to age 11 years, when 1:1 mixtures contained twice the aboveground biomass of E. globulus monocultures. The positive growth response of trees in mixture compared to monocultures was the result of accelerated rates of nutrient cycling, a shift in C allocation and reductions in light competition through canopy stratification. Nitrogen contents of foliage and soil clearly showed that A. mearnsii influenced the N dynamics in this trial. If these changes in N contents were due to N fixation by A. mearnsii, then about 51 and 86 kg N ha-1 yr-1 was fixed in the 1:1 mixtures and A. mearnsii monocultures, respectively. Nitrogen fixation was also examined using the natural abundance method. The delta15N values of foliage collected at 10 years were grouped according to the mycorrhizal status of the host plant. Therefore the discrimination of 15N during transfer from mycorrhizae to the host plant appeared to vary with mycorrhizal status, and the natural abundance of 15N was not used to quantify N fixation. Rates of N and P cycling in litterfall were significantly higher in stands containing at least 25% A. mearnsii (more than 31 kg N ha-1 yr-1 and more than 0.68 kg P ha-1 yr-1) compared to E. globulus monocultures (24 kg N ha-1 yr-1 and 0.45 kg P ha-1 yr-1). Rates of litter decomposition and N and P release were about twice as high in 1:1 mixtures compared to E. globulus monocultures and were even higher in A. mearnsii monocultures. It is therefore important to select N-fixing species that are capable of cycling nutrients quickly between the plant and soil, and that have readily decomposable litter. The total belowground C allocation was not significantly different between mixtures and monocultures (14 to 16 Mg C ha-1 yr-1). However, since aboveground net primary production was greater in 1:1 mixtures, the changes in nutrient availability appears to have increased total productivity (both above- and belowground), and reduced the proportion of C allocated belowground in mixtures compared to E. globulus monocultures. In a pot trial containing mixtures of E. globulus and A. mearnsii both species grew larger in mixture than in monoculture at low N levels, and mixtures were more productive than monocultures. However, at high N levels, E. globulus suppressed A. mearnsii and mixtures were less productive than E. globulus monocultures. Similar effects were found for high and low levels of P. Therefore resource availability can have a strong influence on the interactions and growth of mixtures. The productivity of mixtures may only be increased on sites where the resource for which competition is reduced in mixture is a major limiting growth resource. For example, if N is not a limiting growth factor then an increase in N availability from N-fixation may not increase growth, and the N-fixing species may compete for other resources such as soil P, moisture or light. This study has shown that mixtures containing a N-fixing trees and a non-N-fixing trees can be more productive than monocultures, but that this increase in productivity will only occur on certain sites. Examination of the growth, interactions and processes that occurred in mixtures in this study provide useful information that can aid the selection of species combinations and sites.