Atmospheric aerosols affect climate directly by scattering and absorbing solar radiation, and indirectly by affecting the albedo and lifetime of clouds through their role as cloud condensation nuclei. Aerosol sources, and the processes that govern their evolution in the atmosphere are not well understood, making the aerosol effects a significant source of uncertainty in future climate predictions. The tropics experience a large solar flux meaning that any radiative forcing in this region is particularly important. Despite this, there is a paucity of data from the tropics, with the majority of previous studies performed in the northern mid-latitudes. The few in-situ studies of aerosol composition that have been performed are all in the continental settings of Amazonia or Africa. Until now the 'maritime continent' region of South East Asia has remained unstudied. Presented here are Aerosol Mass Spectrometer composition measurements from the Oxidant and Particulate Processes Above a South East Asian Rainforest project, performed from ground and airborne measurement platforms in and around the rainforest of Borneo, South-East Asia. Unlike the previous tropical studies, this allows for the characterisation of a region of mixed terrestrial and marine biogenic emissions. The region is also undergoing rapid land use change, with forest being converted for agriculture, particularly the cultivation of oil palms. This study also allows for the characterisation of a region that is beginning to undergo land use change, providing insight into emissions from different land use types, and providing a benchmark to measure the effects of land use change against in the future.Total sub-micron aerosol loadings were found to be lower than studies in the northern mid-latitudes, similar to previous tropical studies. However, aerosol composition was different to that observed in Amazonia, with much greater sulphate loadings in Borneo. A regional background of sulphate and highly oxidised organic aerosol was identified, with organic aerosol that is less oxidised originating inland. Aerosol confined to a shallow marine boundary layer upwind of Borneo is lofted higher into the troposphere as it advects across the island, with regional aerosol being removed and biogenic terrestrial aerosol added. The lofting of this aerosol is expected to extend its atmospheric lifetime and change its role in the Earth's radiative budget. A novel organic aerosol signal was identified which correlated with gas phase isoprene oxidation products, strongly suggesting that it was significant of isoprene SOA. Aerosol associated with this signal made up a substantial fraction of the organic aerosol loading. This opens up the opportunity for future studies to make isoprene SOA measurements using the Aerosol Mass Spectrometer in other studies. A substantial amount of the organic aerosol in Borneo was attributed to isoprene oxidation.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18842号 / 理博第4100号 / 新制||理||1589(附属図書館) / 31793 / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 幸島 司郎, 教授 伊谷 原一, 教授 村山 美穂 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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Interactions are important drivers of selection and community structure, which makes the study of multi-species interactions critical for understanding the ecology and evolution of organisms. This dissertation includes four data chapters that examine the biotic and abiotic mechanisms that shape multi-species interactions in both tropical and temperate ecosystems. The first three data chapters (Chapters 2–4) were completed within a Neotropical rainforest in Costa Rica and focus on one plant genus, Piper (Piperaceae). The final data chapter (Chapter 5) was conducted within a working landscape of soybean (Glycine max) fields in eastern Maryland, USA. In Chapter 2, I explore intra- and inter-specific dietary niche partitioning of Piper fruits among three frugivorous bats, illustrating the importance of fine-scale mechanisms that facilitate species coexistence and influence plant–animal interactions. In Chapter 3, I demonstrate how the chemical ecology of a Neotropical shrub, Piper sancti-felicis, shapes fruit interactions with antagonists (fruit fungi) and mutualists (frugivorous bats and birds), developing a foundation for understanding evolutionary ecology of plant chemical traits based on phytochemical investment patterns. In Chapter 4, I describe the direct and indirect impacts of elevated temperature and CO2 concentration on the plant traits and interactions in Piper generalense, improving our understanding of the effects of climate change on a Neotropical plant–herbivore system. In Chapter 5, I explore the biotic (herbivore-induced plant volatiles) and abiotic (fine-scale weather conditions) drivers affecting insectivorous bat foraging in soybean fields in eastern Maryland, providing a pathway to further investigate new strategies for integrated pest management. As a collective work, this dissertation disentangles the nuances of multi-species interactions, exploring foundational mechanisms underlying biodiversity maintenance as well as answering applied questions to address a changing climate and aid sustainable agriculture. / Doctor of Philosophy / Everything in nature is connected, so studying ecological interactions requires us to view them from many different angles. As with most relationships, ecological interactions are multi-faceted and context-dependent. In this dissertation, I describe both tropical and temperate systems, collecting a variety of measurements from plants, microbes, and animals to explore the complicated relationships that exist between them. In Chapter 2, I explore how three species of fruit-eating bats may divide the use of a shared food resource (tropical pepper fruits in the genus Piper) to maintain separate populations and how those foraging differences may affect Piper plant populations. In Chapter 3, I characterize a chemical compound found in the fruits of a Piper plant species and test the effect of that compound on fruit fungi and fruit-eating bats and birds, leading to a better understanding of the selective pressures affecting fruit chemistry. In Chapter 4, I describe the direct and indirect effects of climate change on a Piper plant in the first study to measure the responses of tropical understory plants to treatments that mimic climate change using active warming and CO2 supplementation. In Chapter 5, I explore the fine-scale drivers of bat activity in soybean fields, including how weather conditions and the specific compounds emitted by insect-damaged plants may affect bat activity. As a collective work, this dissertation describes the complex relationships among plants and their many interactors, exploring questions from biodiversity maintenance to integrated pest management strategies.

This study investigated the utility to vertebrates of upland linear riparian rainforest fragments on the Atherton and Evelyn Tablelands in the Australian Wet Tropics region, north Queensland. Similar linear fragments were selected, that varied in forest age and their connectivity to large areas of continuous forest:- (connected primary (N=6), isolated primary (N=5), connected secondary (N=6) and isolated secondary (N=7)). Primary sites had either never been cleared or only subject to selective logging, while secondary forest had been completely cleared and allowed to regenerate for at least 30 years. These linear fragments were contrasted with riparian sites within continuous forest sites (N=6 to 7), which were situated in State Forest or National Parks, and sites within the cleared matrix (pasture, N=6). Vertebrates surveyed were birds, ground-dwelling mammals and reptiles, particularly leaf-litter skinks. All surveys were conducted between September and December in 2001 and/or 2000. Chapter 2 investigates the effects of forest age, isolation and structural vegetation features on bird assemblages within linear riparian fragments of rainforest. Bird surveys and structural vegetation assessments were conducted within connected and isolated primary and secondary linear fragments, and compared with those of continuous forest habitat (N=6) and pasture. There were strong effects of forest age; all three types of primary rainforest had higher values than secondary rainforest for most measured attributes of vegetation structure (including canopy height and cover; and frequency of large-diameter trees, lianes, epiphytes, strangler figs; and woody debris), but lower frequencies of tree ferns and thorny scramblers. Sites within primary rainforest also had a greater frequency of many bird species across different guilds of habitat, feeding and movement. Assemblages of rainforest-dependent birds showed an effect of isolation, although its strength was less than that of forest age. Isolated fragments of primary rainforest differed significantly from continuous primary rainforest in their rainforest-dependent bird species assemblages (and had lower species richness), and isolated fragments of secondary rainforest differed from those that were connected. There was a significant association between the species composition of rainforest birds and some measured vegetation parameters across all sites, but not within primary or secondary sites. Vegetation differences did not explain the lowered frequency of several species in isolated fragments. Limited dispersal seems unlikely to be a main cause, and causal processes probably vary among species. Specialist rainforest species endemic to the Wet Tropics region showed stronger responses to present-day rainforest age and fragmentation than those not endemic. Variation in nest depredation levels associated with rainforest fragmentation (edge effects) is examined in Chapter 3. Artificial nests were placed in the forest understorey at seven edge sites where continuous forest adjoined pasture, seven interiors (about one kilometre from the edge), and six primary linear riparian forest remnants (50-100 m wide) that were connected to continuous forest. Four nest types were compared, representing different combinations of two factors; height (ground, shrub) and shape (open, domed). At each site, four nests of each type, containing one quail egg and two model plasticine eggs, were interspersed about 15 m apart within a 160 m transect. Predators were identified from marks on the plasticine eggs. The overall depredation rate was 66.5% of 320 nests' contents damaged over a three-day period. Large rodents, especially the rat Uromys caudimaculatus, and birds, especially the spotted catbird Ailuroedus melanotis, were the main predators. Mammals comprised 56.5% and birds 31.0% of identified predators, with 12.5% of unknown identity. The depredation rate did not vary among site-types, or between open and domed nests, and there were no statistically significant interactions. Nest height strongly affected depredation rates by particular types of predator; depredation rates by mammals were highest at ground nests, whereas attacks by birds were most frequent at shrub nests. These effects counterbalanced so that overall there was little net effect of nest height. Mammals accounted for 78.4% of depredated ground nests and birds for at least 47.4% of shrub nests (and possibly up to 70.1%). The main predators were species characteristic of rainforest, rather than habitat generalists, open-country or edge specialists. For birds that nest in the tropical rainforest understorey of the study region, it is unlikely that edges and linear remnants presently function as ecological population sinks due to mortality associated with increased nest depredation. The use of linear riparian remnants by small ground-dwelling mammals and reptiles (mainly leaf litter skinks), is reported in Chapter 4. Site types were continuous rainforest, connected and isolated linear fragments of both uncleared primary rainforest and secondary regrowth rainforest. Mammals were also surveyed in pasture sites. Neither reptile species richness nor abundance varied significantly among site types. Although mammal species richness varied significantly between site types, with isolated primary sites containing highest species richness, overall mammal abundance did not differ significantly among site types. Pasture sites differed significantly from all rainforest sites in their mammal species composition, and were dominated by the introduced house mouse (Mus musculus). This species was absent from all rainforest sites, which were characterised by moderate abundances of bush rat/Cape York rat Rattus fuscipes/leucopus, fawn-footed melomys Melomys cervinipes and giant white-tailed rat Uromys caudimaculatus. None of these species varied significantly in abundance among site types, although the giant white-tailed rat showed a trend (P=0.09) for reduced abundance in isolated secondary sites. A single reptile species, the prickly forest skink Gnypetoscincus queenslandiae, occurred in sufficient numbers for individual analysis, and its abundance varied significantly among the forested site types, being less abundant in all linear fragments than in continuous forest sites. The utility of linear riparian rainforest for vertebrates appears to be species-specific and involves many factors. However, overall, species endemic to the Wet Tropics (which are hence of the highest conservation significance) appear to be the most sensitive to fragmentation. These species were most likely to show altered abundances or frequencies of occurrence due to isolation, forest age, and habitat linearity. The ecology of species within this group warrants further investigation within fragmented and non-fragmented regions of the Tablelands. For many other vertebrates examined in this study, there appears to be sufficient functional connectedness between remnants on the Tablelands to minimise the effects of fragmentation. Nevertheless, the lower density of many of these species in pasture may indicate that their long-term persistence within the fragmented rainforest areas could benefit from the maintenance or establishment of habitat linkages. Certainly, if the current rainforest vegetation cover were further reduced, or if the land use in the matrix became more intensive, the establishment of specific habitat linkages could become more important as existing dispersal routes could be lost. It also appears that nest depredation levels are unlikely to limit the value of linear rainforest remnants and other small rainforest remnants as breeding habitat for birds (at least for understorey-nesting species), relative to more intact rainforest, in the study region.

This thesis examines how early warning signals perform when tested on climate systems thought to exhibit future tipping point behaviour. A tipping point in a dynamical system is a large and sudden change to the state of the system, usually caused by changes in external forcing. This is due to the state the system occupies becoming unstable, causing the system to settle to a new stable state. In many cases, there is a degree of irreversibility once the tipping point has been passed, preventing the system from reverting back to its original state without a large reversal in forcing. Passing tipping points in climate systems, such as the Amazon rainforest or the Atlantic Meridional Overturning Circulation, is particularly dangerous as the effects of this will be globally felt. Fortunately there is potential for early warning signals, designed to warn that the system is approaching a tipping point. Generally, these early warning signals are based on analysis of the time series of the system, such as searching for ‘critical slowing down’, usually estimated by an increasing lag-1 autocorrelation (AR(1)). The idea here is that as a system’s state becomes less stable, it will start to react more sluggishly to short term perturbations. While early warning signals have been tested extensively in simple models and on palaeoclimate data, there has been very little research into how these behave in complex models and observed data. Here, early warning signals are tested on climate systems that show tipping point behaviour in general circulation models. Furthermore, it examines why early warning signals might fail in certain cases and provides prospect for more ‘system specific indicators’ based on properties of individual tipping elements. The thesis also examines how slowing down in a system might affect ecosystems that are being driven by it.

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No description available.

The use of spatial statistics to investigate ecological processes in plant communities is becoming increasingly widespread. In diverse communities such as tropical rainforests, analysis of spatial structure may help to unravel the various processes that act and interact to maintain high levels of diversity. In particular, a number of contrasting mechanisms have been suggested to explain species coexistence, and these differ greatly in their practical implications for the ecology and conservation of tropical forests. Traditional first-order measures of community structure have proved unable to distinguish these mechanisms in practice, but statistics that describe spatial structure may be able to do so. This is of great interest and relevance as spatially explicit data become available for a range of ecological communities and analysis methods for these data become more accessible. This thesis investigates the potential for inference about underlying ecological processes in plant communities using spatial statistics. Current methodologies for spatial analysis are reviewed and extended, and are used to characterise the spatial signals of the principal theorised mechanisms of coexistence. The sensitivity of a range of spatial statistics to these signals is assessed, and the strength of such signals in natural communities is investigated. The spatial signals of the processes considered here are found to be strong and robust to modelled stochastic variation. Several new and existing spatial statistics are found to be sensitive to these signals, and offer great promise for inference about underlying processes from empirical data. The relative strengths of particular processes are found to vary between natural communities, with any one theory being insufficient to explain observed patterns. This thesis extends both understanding of species coexistence in diverse plant communities and the methodology for assessing underlying process in particular cases. It demonstrates that the potential of spatial statistics in ecology is great and largely unexplored.

O contato pretérito Amazônia-Mata Atlântica vem sendo recorrentemente citado na literatura para diversos grupos da fauna Neotropical e teria ocorrido por diferentes rotas geográficas e períodos temporais. Segundo esta hipótese, em períodos quentes e úmidos as florestas se expandiram provocando retração/fragmentação das áreas abertas, ao passo que em períodos frios e secos, o inverso ocorreria. Assim, utilizando-se de crotalíneos como modelo, esta tese pretende: (1) testar o pretérito contato Amazônia-Mata Atlântica, assim como o tempo de separação entre as linhagens relictuais nesses ambientes florestados, elucidando a história demográfica das espécies de Bothrops do grupo jararacuçu, do grupo atrox e de B. bilineatus; (2) paralelamente Crotalus durissus, espécie associada à diagonal de áreas abertas da América do Sul (Caatinga, Cerrado e Chaco), foi utilizada para testar a ocorrência de expansão desses ambientes, o que levaria a quebra da hipotetizada ponte florestada Amazônia-Mata Atlântica. Através de dataset multi-locus sob Inferência Bayesiana (quatro genes mitocondriais e cinco nucleares) foram testadas as relações filogenéticas e filogeográficas entre as amostras em Bothrops e Crotalus. Cenários históricos alternativos foram testados com base em simulações coalescentes e ABC (approximate Bayesian computation). Adicionalmente, foi empregado teste de delimitação de linhagens evolutivas para o reconhecimento da diversidade, a nível de espécie, em cada grupo estudado, usando a implementação Bayesiana do algoritimo Generalized Mixed Yule-Coalescent. Os resultados filogenéticos e análises de delimitação de espécies indicam diversidade críptica para os grupos jararacussu, atrox e taeniatus. Os testes de cenários históricos sugerem (1) múltiplas conexões florestais Amazônia-Mata Atlântica nos últimos 2.5 milhões de anos, com intercâmbio faunístico em ambas as direções e (2) expansão das áreas abertas do Cerrado e Caatinga em sincronia temporal com perda de conectividade florestal Amazônia-Mata Atlântica durante o Pleistoceno tardio (3) que a formação e estabilização do Rio Amazonas teve influência na diversificação do grupo jararacuçu, gerando diversidade. Os resultados trazem informações sobre o dinamismo histórico das paisagens florestadas e abertas no Neotrópico ao longo do tempo, assim como o papel dos rios amazônicos na diversificação da fauna. Adicionalmente, os resultados apontam para instabilidade taxonômica e diversidade críptica em diversos grupos em Bothrops e em Crotalus durissus, revelando a necessidade do aprofundamento sistemático para essas serpentes venenosas de importância médica / The hypotetized historical contact Amazon-Atlantic Forest has been recurrently cited in the literature for several groups of Neotropical fauna and would have occurred by different geographic routes and time periods. According to this hypothesis, in hot and humid periods the forests expanded causing retraction / fragmentation of the open areas, while in cold and dry periods, the reverse would occur. Thus, by using Neotropical pit vipers as a model, this thesis aims to: (1) test the historical forest contact Amazon-Atlantic Forest, as well as the time of separation between relict lineages in these forested environments, elucidating the demographic history of Bothrops species from jararacussu group, atrox group and B. bilineatus; (2) Crotalus durissus, a species associated with the diagonal of open areas of South America (Caatinga, Cerrado and Chaco), was used in parallel to test the occurrence of expansion of these environments, which would lead to the breakage of the hypothetical Amazon-Atlantic Forest forested bridge. Phylogenetic and phylogeographic relationships between samples of Bothrops and Crotalus were tested through a multi-locus dataset (four mitochondrial genes and five nuclear) under Bayesian Inference. Alternative historical scenarios were tested based on coalescent simulations and ABC (approximate Bayesian computation). In addition, was inferred independently evolving lineages to recognized species diversity in each group studied, using Bayesian implementation of the molecular species delimitation algorithm Generalized Mixed Yule-Coalescent. Phylogenetic results and analyzes of species delimitation indicate cryptic diversity for the groups jararacussu, atrox and taeniatus. The tests of historical scenarios suggest (1) multiple Amazon-Atlantic Forest forest connections in the last 2.5 million years, with faunal exchange in both directions and (2) expansion of the open areas of the Cerrado and Caatinga in temporal synchrony with loss of forest bridge Amazon-Atlantic Forest during late Pleistocene (3) that the formation and stabilization of the Amazon River influenced the diversification of the jararacussu group, generating diversity. The results provide information on the historical dynamism of forested and open landscapes in the Neotropics over time, as well as the role of Amazonian rivers in the diversification of fauna. Moreover, the results point to taxonomic instability and cryptic diversity in several groups within Brothrops and Crotalus durissus, revealing the need for systematic deepening for these medically important venemous snakes