Understanding broad patterns of biodiversity requires developing a unified and rigorously tested theory that explains how species coexist despite the risk of competitive exclusion. Species interactions are fundamentally shaped by environmental variability. Recent theoretical development has predicted a set of general mechanisms that promote species coexistence under variable environments. Nevertheless, this theoretical framework has received limited empirical tests. Biological invasions offer excellent opportunities to empirically test coexistence mechanisms in communities in which the stability of coexistence is likely affected by introduced species. I took this opportunity to directly test the theory of species coexistence in this dissertation work by investigating how environmental variability affected the invasion of introduced species and their coexistence with native species. My collaborators and I started the investigation of diversity maintenance by first examining the range expansion of introduced species. Studying range shifts can reveal drivers of diversity patterns, which are formed by overlapping ranges of different species. We used a novel spatial analysis to determine the scale-dependent expansion rate of an invasive winter annual species, Brassica tournefortii over North America as well as to infer the drivers of this scale dependency. We found that this species expanded rapidly on scales from 5 to 500 km historically but had ceased its current expansion on the 100-500 km scales due to climatic constraints. This finding left open the question why this species continued its spread on the 5-50 km scales and how it would impact native species within its invaded range. To address these questions, we examined relatively local scale interactions between B. tournefortii and its competitors. We compared key demographic rates of B. tournefortii with other invasive and native winter annuals over a Sonoran Desert landscape to check conditions necessary for their spatial and temporal niche differentiation. We found the presence of two essential requirements for their niche differentiation: species-specific germination responses that could differentiate species by their favored environments and buffered population growth in time and space that could prevent catastrophic population declines when species faced unfavorable conditions. These conditions could provide niche opportunities to promote both the establishment of B. tournefortii and the persistence of native species under its presence. Building upon this finding, we directly quantified one general mechanism of spatial niche differentiation between B. tournefortii and its native competitors. We measured the strength of this mechanism, the spatial storage effect, across a hierarchy of spatial scales (subhabitat -> habitat -> landscape). We found that this mechanism did not promote species coexistence on any of these scales over the study period. These species were not differentiated over their tested spatial niches because weak competition following dry growing conditions failed to intensify intraspecific competition relative to interspecific competition. The strength of this mechanism increased from occasionally producing negative effects on lower scales to consistently being non-negative on the highest scale. This scale-dependent pattern was in line with the expectation that coexistence potential would increase with scales as species interacted over a wider range of environmental heterogeneity. Our findings demonstrated empirically that environmental variability in time and space led to scale-dependent patterns of the coexistence potential between introduced and native species. This work showed that introduced and native species could be differentiated by their environmental responses given spatial and temporal environmental heterogeneity on higher scales. However, for those species to stably coexist on higher scales, competitive effects had to follow environmental responses to separate species by their own density-dependent feedback loops. This work is among the first few empirical tests of a body of theory that holds the promise to generalize the mechanisms of spatial and temporal niche differentiation. Its success and limitation can motivate more studies to adopt the guiding mathematical principles and to use similar yet more innovative approaches to address the grand question of biodiversity maintenance.

Mire pools – shallow water-bodies in peat-forming wetlands – are a characteristic feature of New Zealand’s subalpine and alpine landscapes (>1000 m a.s.l.), yet have been the subject of few biological studies to date, particularly of their algal communities. This research focuses on these subalpine systems, and on their diatom communities. Despite the established paradigm of ubiquitous dispersal in micro-organisms, recent taxonomic studies have confirmed a distinctive endemic component in the freshwater diatom flora of the New Zealand / Tasmania / East Australian region. In this study, I examined benthic diatom communities from >320 freshwater sites throughout New Zealand and showed that over 20% of species may be confined to this region. The endemic diatom species had highest densities in stable, unproductive environments, particularly in high-altitude mire pools and tarns. In most cases, non-endemic taxa coexisted with endemic species. This raised questions about (1) the special characteristics of mire pools and tarns (since endemism might be expected in areas that have unique environmental characteristics), and (2) the mechanisms that have allowed existing endemic taxa to withstand displacement by common cosmopolitan taxa, which, by definition, are successful colonisers. I addressed these questions using two years of data from four subalpine mire pools (Bealey Spur wetland, near Arthur’s Pass, South Island). Physico-chemical data showed that water chemistry of these pools may differ from that of many Northern Hemisphere mire systems with respect to the relationship between pH and dissolved ions (especially calcium). This may be due to a combination of high pH rainfall, high rainfall quantities that limit the acidification effects of humic substances, and possibly vegetation differences. Therefore, some endemic taxa may be confined to these habitats because of the characteristic properties of the pools. I investigated the effects of disturbances in these stable environments. In the largest pool endemic species were shown to decline as wind-induced substrate disturbance increased. Endemic species also declined in two pools following small-scale experimental substrate disturbances. In all cases, non-endemic species remained unchanged. The distinctive species Eunophora cf. oberonica was responsible for much of the observed decline in endemic species abundances, which was evidently due to destruction of their specialised habitat within the cyanobacterial mats that made up the pool substrates. I explained pool-specific responses of diatom communities to disturbances by drawing on recent theory of invasibility as an intrinsic environmental property. I further investigated species coexistence by examining several general patterns of interspecific coexistence described for macroscopic organisms (e.g., abundance – occupancy, abundance – persistence). Patterns in mire-pool diatom communities were generally similar to those in larger organisms, and did not differ with respect to geographical range size (endemics vs. non-endemics), except at the scale of single pools. At this scale, endemic taxa, in particular E. cf. oberonica, can persist as dominant species. All the community analyses were underpinned by detailed taxonomic studies, from which I assessed over 40% of the more common species in the pools to be either endemic or likely to be endemic. Two species occurring in the study area are formally described as new species. Overall, this work highlights the vulnerability of this hidden component of New Zealand’s biodiversity to disturbances and environmental changes.

Mire pools – shallow water-bodies in peat-forming wetlands – are a characteristic feature of New Zealand’s subalpine and alpine landscapes (>1000 m a.s.l.), yet have been the subject of few biological studies to date, particularly of their algal communities. This research focuses on these subalpine systems, and on their diatom communities. Despite the established paradigm of ubiquitous dispersal in micro-organisms, recent taxonomic studies have confirmed a distinctive endemic component in the freshwater diatom flora of the New Zealand / Tasmania / East Australian region. In this study, I examined benthic diatom communities from >320 freshwater sites throughout New Zealand and showed that over 20% of species may be confined to this region. The endemic diatom species had highest densities in stable, unproductive environments, particularly in high-altitude mire pools and tarns. In most cases, non-endemic taxa coexisted with endemic species. This raised questions about (1) the special characteristics of mire pools and tarns (since endemism might be expected in areas that have unique environmental characteristics), and (2) the mechanisms that have allowed existing endemic taxa to withstand displacement by common cosmopolitan taxa, which, by definition, are successful colonisers. I addressed these questions using two years of data from four subalpine mire pools (Bealey Spur wetland, near Arthur’s Pass, South Island). Physico-chemical data showed that water chemistry of these pools may differ from that of many Northern Hemisphere mire systems with respect to the relationship between pH and dissolved ions (especially calcium). This may be due to a combination of high pH rainfall, high rainfall quantities that limit the acidification effects of humic substances, and possibly vegetation differences. Therefore, some endemic taxa may be confined to these habitats because of the characteristic properties of the pools. I investigated the effects of disturbances in these stable environments. In the largest pool endemic species were shown to decline as wind-induced substrate disturbance increased. Endemic species also declined in two pools following small-scale experimental substrate disturbances. In all cases, non-endemic species remained unchanged. The distinctive species Eunophora cf. oberonica was responsible for much of the observed decline in endemic species abundances, which was evidently due to destruction of their specialised habitat within the cyanobacterial mats that made up the pool substrates. I explained pool-specific responses of diatom communities to disturbances by drawing on recent theory of invasibility as an intrinsic environmental property. I further investigated species coexistence by examining several general patterns of interspecific coexistence described for macroscopic organisms (e.g., abundance – occupancy, abundance – persistence). Patterns in mire-pool diatom communities were generally similar to those in larger organisms, and did not differ with respect to geographical range size (endemics vs. non-endemics), except at the scale of single pools. At this scale, endemic taxa, in particular E. cf. oberonica, can persist as dominant species. All the community analyses were underpinned by detailed taxonomic studies, from which I assessed over 40% of the more common species in the pools to be either endemic or likely to be endemic. Two species occurring in the study area are formally described as new species. Overall, this work highlights the vulnerability of this hidden component of New Zealand’s biodiversity to disturbances and environmental changes.

Orientadores: Vera Nisaka Solferini, Marlies Sazima / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-21T20:09:03Z (GMT). No. of bitstreams: 1 FernandezOtarola_Mauricio_D.pdf: 8414831 bytes, checksum: 9aabd91ed56ca9aadd06aa11ff07703c (MD5) Previous issue date: 2012 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The abstract is available with the full electronic document / Doutorado / Ecologia / Doutor em Ecologia

Orientador: Rafael Silva Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia. / Made available in DSpace on 2018-08-22T05:52:27Z (GMT). No. of bitstreams: 1 BrumJr._Mauro_M.pdf: 3526243 bytes, checksum: 44324833dc08e57ffd87e138721c4c83 (MD5) Previous issue date: 2013 / Resumo: A partição de recursos hídricos do solo é um dos modelos plausíveis para explicar os mecanismos que promovem a coexistência e a diferenciação de nicho entre espécies em comunidades vegetais. As raízes constituem a principal interface de troca de água entre a planta e o solo, de modo que profundidade radicular é um atributo chave que pode influenciar o funcionamento hidráulico das plantas. O campo rupestre e o campo de altitude são vegetações campestres que ocorrem em montanhas ou chapadas sob diferentes regimes de água devido às diferenças climáticas e pedológicas, sendo o campo rupestre mais árido que o campo de altitude. Essas comunidades são bem conhecidas devido à alta diversidade de espécies, mas pouco se sabe a respeito da diversidade de estratégias de uso de água. Entender as estratégias hidráulicas das plantas é importante para fazer previsões das respostas das comunidades em relação às mudanças climáticas. Diante disso, o nosso objetivo foi responder: quais são os padrões de aquisição e uso de água por plantas que coexistem em uma vegetação de campo rupestre e outra de campo de altitude? Além disso, quais são as estratégias de uso de água entre as plantas com sistemas subterrâneos contrastantes nessas comunidades? Nós avaliamos a composição de isótopos estáveis da água do solo e contrastamos com a composição isotópica da água do xilema de 15 espécies de plantas em cada comunidade. A composição isotópica da água do xilema foi usada como um indicador para estimar a profundidade do solo na qual as plantas estão absorvendo a água. Também fizemos escavações das raízes para verificar qual é o tipo morfológico de cada espécie e contrastar com os resultados da composição isotópica da água do xilema. Além disso, medimos o potencial hídrico da madrugada, do meio dia e a condutância estomática máxima três vezes durante a estação seca (junho, julho e agosto). Nós demonstramos que em ambas as comunidades há uma diversidade interespecífica de formas de sistemas subterrâneos, sendo que o campo rupestre apresentou maior variação interespecífica de uso de água em perfis verticais do solo. As plantas do campo de altitude apresentam raízes mais superficiais do que no campo rupestre. Além disso, demonstramos que a profundidade do sistema radicular é um bom preditor do potencial hídrico da madrugada e do grau de regulação estomática para as plantas do campo rupestre, mas não do campo de altitude. Não encontramos relação entre a profundidade do sistema radicular e o potencial hídrico do meio dia em ambas as comunidades / Abstract: Soil water partitioning is a plausible model to explain the mechanisms that allow species coexistence and niche segregation in plant communities. Roots are the main interface of water exchange between plant and soil, so rooting depth is a key trait that affects whole-plant hydraulic function. The campos rupestres and campos de altitude are two shrubland communities that occur in mountainous plateaus under contrasting water regimes due to differences in their climatic and pedological variables, campos rupestres being more arid than campos de altitude. These communities are well known for their high species diversity but little is known about the diversity of water use strategies. Understanding plant hydraulic strategies is important for improving predictions of community responses to changes in climate. Our goal was to respond: what are the patterns of water acquisition and use in campo rupestres and campo de altitude? Furthermore, what are the water use strategies of plants with contrasting rooting depths in these plants communities? We evaluated the ?D of soil water and xylem water of 15 species in each community. The ?D of xylem water was used as proxy of rooting depth. We also excavated the roots of all species to evaluate their root morphological pattern and to compare with the isotopic data. Furthermore, we measured pre-dawn and midday water potentials and stomatal conductance three times during the dry season (June, July and August, 2012). We found a high interespecific diversity of root types in both communities and higher variance of hydraulic traits at campo rupestre. Campo de altitude plants had shallower roots than campo rupestre. Moreover, we demonstrated that pre-dawn water potential is a good predictor of rooting depth, which in turn is a good predictor of the degree of stomatal control for campo rupestre community but these patterns were not found at campo de altitude. We did not find any relationship between rooting depth and midday water potential for both communities / Mestrado / Ecologia / Mestre em Ecologia

Bumblebees have shown both long and short-term declines throughout their range. These declines may be attributed to a range of factors including changes in land use, alterations in climatic conditions and species introductions. However, management strategies for bumblebee conservation often focus on provision of summer forage resources and other factors are frequently overlooked. Provision of spring forage and nesting sites for bumblebee queens are rarely considered, though colony foundation and early colony growth are two of the most sensitive stages in bumblebee life history. Here, the efficacy of certain agri-environment prescriptions for providing spring forage and nest sites for bumblebees is assessed, highlighting a need for specific schemes targeted towards the provision of these vital resources in the rural environment. The nesting ecology of bumblebees is poorly understood because wild colonies are difficult to locate. However, a greater knowledge of the colony-level effects of environmental change is crucial to understanding bumblebee declines. Attracting bumblebee queens to nest in artificial domiciles could provide a valuable tool for studying colony-level responses. However, domicile trials and the findings of a literature review presented here demonstrate that this approach may be largely impractical for use in the UK. Conversely, a nationwide public bumblebee nest survey produced numerous data regarding nest site preferences among bumblebee species and also demonstrated that citizen science may also provide a sensitive method for detecting declines in currently common bumblebee species. An understanding of the ecology of species interactions and coexistence can provide valuable insights into factors that may influence declines. Data presented here suggest that coexistence between some bumblebee species may be maintained by resource partitioning based on diel activity patterns that are linked to species-specific environmental tolerances. If this is the case, the potential role of climate change in bumblebee declines may be severely underestimated. There is also increasing evidence that genetic factors may play a role in bumblebee losses, accelerating declines of small, fragmented populations as a result of reduction in genetic diversity and inbreeding depression. Here, the feasibility of reintroducing British B. subterraneus (now extinct in the UK) from New Zealand into England is assessed using population genetic techniques. The findings suggest that the population history of B. subterraneus in New Zealand has resulted in a dramatic loss of genetic diversity and high genetic divergence from the original UK population, suggesting that it may not be a suitable for use in the reintroduction attempt. This work draws together some understudied aspects of bumblebee ecology with a particular focus on nest site requirements, availability of spring forage, mechanisms of avoidance of inter-specific competition and population genetic processes. The potential role of these in bumblebee declines is considered and new data relevant to the conservation of these important species is presented. It is hoped that this work will inform future management strategies for bumblebee conservation, highlight areas in need of further study and provide a sound starting point for future research in these areas.

Abstract Animals live in a heterogeneous world where threats and abundance and quality of resources vary across space and time. Heterogeneity induces uncertainty in decisions that animals must make, e.g., where to breed. Adaptive decisions may be facilitated by personally collecting information on the quality of the environment and by observing the behaviour and success of other individuals. Such social information use is common in nature. I investigate information use in relation to ecological threats (brood parasites, nest predators) and long-term information use in breeding site choice in the wild. Moreover, I examine the genetic basis of social cue use in breeding site choice. I demonstrated experimentally that open-nesting hosts of a brood parasite, the common cuckoo (Cuculus canorus), can cue on cuckoo vocalizations to estimate cuckoo abundance and avoid breeding sites with high perceived parasitism risk. Another experiment showed that pied flycatchers (Ficedula hypoleuca) derive predation risk information from the fates of heterospecific nests, can associate the information with a nest site characteristic and generalize the association to own nest site choice. However, apparently only young females that made their choice quickly used the information in nest site choice. Pied flycatchers were further observed to collect habitat quality information based on the old nest contents during the post-breeding period. Use of the information in breeding site choice in the following spring varied between sex and age groups as well as geographically. Some birds integrated the post-breeding period information with the information available during settlement suggesting sequential social information use. Finally, quantitative genetic analyses revealed low additive genetic variances and genetic heritabilities of social cue use in breeding site choice in a collared flycatcher (Ficedula albicollis) population. These results demonstrate new aspects of informed habitat choice in wild animals which have important implications for species coexistence and community ecology, parasite-host coevolution, between-species niche dynamics and evolution. Between-individual variation in information use is highlighted throughout the thesis and warrants further research. The evolutionary potential of information use appears low, but more studies in other populations and species are needed. / Tiivistelmä Eläimet elävät ympäristössä, jossa resurssit ja uhat vaihtelevat ajallisesti ja alueellisesti. Tämä vaihtelu aiheuttaa epävarmuutta eläinten päätöksentekoon, kuten pesimäpaikan valintaan. Hyödyllisten päätösten tekoa voi edesauttaa keräämällä tietoa ympäristön laadusta itsenäisesti tai seuraamalla muiden yksilöiden käytöstä ja menestystä. Tällainen sosiaalisen informaation käyttö on yleistä eläinkunnassa. Tutkin informaation käyttöä ekologisten uhkien (pesäloiset, -pedot) suhteen ja pitkäaikaista informaation käyttöä pesimäpaikan valinnassa luonnonpopulaatioissa. Lisäksi selvitän pesimäpaikan valintaan liittyvän informaation käyton geneettistä periytyvyyttä. Selvitin kokeellisesti, että pesäloisen, käen (Cuculus canorus), isäntälajit voivat käyttää käkien ääntelyä vihjeenä alueellisesta loisintauhasta ja siten välttää korkean uhan alueita pesimäpaikan valinnassa. Toisessa kokeessa havaittiin kirjosieppojen (Ficedula hypoleuca) keräävän tietoa pesäpetouhasta toisen lajin pesätuhojen kautta, kykenevän yhdistämään tiedon erilliseen pesäpaikan ominaisuuteen ja käyttämään tätä assosiaatiota omassa pesäpaikan valinnassa. Kuitenkin vain nuoret naaraat, jotka tekivät valintansa nopeasti, käyttivät kyseistä informaatiota valinnassaan. Lisäksi havaitsin kirjosieppojen keräävän tietoa ympäristön laadusta pesinnän jälkeen vanhojen pesäsisältöjen avulla. Kyseisen tiedon käyttö pesimäpaikan valinnassa seuraavana keväänä vaihteli lintujen sukupuolen ja iän suhteen, kuin myös alueellisesti. Osa linnuista yhdisti pesimäpaikan valinnassaan aikaisempaa, pesinnän jälkeen kerättyä tietoa ja keväällä saatavilla olevaa sosiaalista informaatiota. Geneettinen analyysi viittasi pesimäpaikan valintaan liittyvän informaation käytön alhaiseen additiivisen geneettisen varianssin määrään ja siten alhaiseen geneettiseen periytyvyyteen sepelsiepolla (Ficedula albicollis). Väitöskirjani tulokset kuvaavat uudenlaisia informaation käytön muotoja eläinten pesimäpaikan valinnassa. Havainnot auttavat ymmärtämään pesälois-isäntä rinnakkaisevoluutiota, lajien välisiä vuorovaikutuksia, lajiyhteisöjen toimintaa ja evoluutiota. Yksilöiden välinen vaihtelu informaation käytössä näyttää olevan yleistä, ja lisätutkimuksen tarpeessa. Informaation käytön evolutiivinen potentiaali näyttää rajalliselta, mutta lisätutkimukset eri populaatioilla ja lajeilla ovat tarpeen.

Adaptive radiation – the proliferation of species from a single ancestor and diversification into many ecologically different forms – has long been heralded as an important process in the generation of phenotypic diversity. However, the early stages of adaptive radiation are notoriously elusive to observe and study. In this dissertation, I capitalize on communities of introduced non-native Anolis lizards as analogues of early stage adaptive radiations. In Chapter II, I begin by reviewing the concept of “ecological opportunity” – a classic hypothesis put forward as a potential key to understanding when and how adaptive radiation occurs. In Chapter III, I investigate the mechanisms which allow for coexistence and community assembly among ecologically-similar species. To do this I investigate range dynamics and assembly patterns of introduced anoles on the oceanic island of Bermuda. I discover that interspecific partitioning of the structural environment facilitates species coexistence, however the order of species assembly was an important predictor of final community composition. In Chapter IV, I then investigate how interspecific interactions between coexisting species may drive phenotypic divergence. This is the process of character displacement, which has been widely hypothesized to be an important mechanism driving phenotypic divergence in adaptive radiations. To do this I investigate sympatric and allopatric populations of introduced Cuban brown anoles (Anolis sagrei) and Puerto Rican crested anoles (A. cristatellus) in Miami FL, USA. I identify morphological shifts in sympatry, driven by divergence in habitat use and decreases in abundance. This study provides evidence of how selection on both ecologically and sexually-important traits can both drive phenotypic divergence during character displacement. Finally, in Chapter V, after taking advantage of non-native species as model eco-evolutionary systems in previous chapters, I investigate the potentially harmful effects that their presence may have on vulnerable native biodiversity. To do this I investigate the conservation risk posed by newly-discovered populations of A. sagrei on Bermuda to Critically Endangered endemic Bermuda skinks (Plestiodon longirostris). Through a detailed analysis of habitat use, diet, population size, and morphology of A. sagrei on Bermuda, we conclude it likely poses a high conservation threat to P. longirostris through interspecific competition.

La compréhension des processus écologiques qui sous-tendent l’assemblage des communautés végétales et la coexistence des espèces est un objectif central en écologie. Ces processus sont potentiellement nombreux et de natures contrastées. Ainsi, la composition d’une communauté de plantes dépend de processus déterministes liés aux conditions environnementales abiotiques (climat, conditions physiques et chimiques du sol, lumière) et d’interactions biotiques complexes, positives (facilitation, symbioses) comme négatives (compétition, prédation, pathogènes). En outre, les communautés sont influencées par des processus stochastiques (capacité de dispersion limitée, dérive écologique). Si les mécanismes à l’origine de ces processus sont très différents, ils ont néanmoins en commun la génération de motifs (patterns) spatiaux de distribution d’espèces dans les communautés. L’analyse de la structure spatiale des communautés permet ainsi une étude indirecte des processus régissant les communautés. La nature complexe de ces patterns spatiaux a mené au développement de nombreuses méthodes statistiques de détection et de description de patterns. Les méthodes basées sur des vecteurs propres spatiaux sont parmi les plus puissantes et précises pour détecter des patterns complexes et multi-échelles. Ces vecteurs propres, utilisés comme prédicteurs spatiaux, peuvent être combinés à un ensemble de variables environnementales dans un cadre de partition de variation. Celui-ci permet, en théorie, de démêler les effets uniques et l’effet conjoint des variables environnementales et spatiales sur la variation de composition d’une communauté. Il mène ainsi à une quantification de l’action des processus déterministes et des processus stochastiques sur l’assemblage de la communauté. Néanmoins, je montre dans cette thèse qu’un certain flou méthodologique concernant deux étapes déterminantes des analyses basées sur les vecteurs propres spatiaux a mené une proportion élevée d’études à utiliser ces méthodes de manière sous-optimale, voire fortement biaisée. Ceci compromet la fiabilité des patterns spatiaux détectés et des processus écologiques inférés. Une autre limitation de ce cadre d’analyse concerne la fraction de la partition de variation décrivant l’effet environnemental spatialement structurés qu’aucune méthode ne permet de tester.Cette thèse présente des solutions non biaisées, puissantes et précises à ces différentes limitations méthodologiques et permet d’élargir le cadre de l’inférence de processus écologique à partir de patterns spatiaux de communautés. Les différentes étapes d’amélioration de ces méthodes ont également été illustrées dans la thèse au travers de trois cas d’études fournis par deux communautés d’arbres tropicale et tempérée et une communauté de champignons symbiotiques des arbres. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Heterogenität von Umweltbedingungen gilt als einer der wichtigsten Faktoren für die Verteilung von Artenreichtum weltweit. Laut der Habitatheterogenität-Hypothese bieten räumlich heterogenere Gebiete eine höhere Vielfalt an Umweltparametern und weisen mehr Refugien und Möglichkeiten zur Isolation und Radiation auf. Dadurch begünstigen sie Koexistenz, Persistenz und Diversifikation von Arten. Die Erforschung potentieller positiver Effekte von Heterogenität auf Artenreichtum fasziniert Ökologen und Evolutionsbiologen seit Jahrzehnten. Dementsprechend existieren zahlreiche Studien über die Beziehung zwischen Heterogenität und dem Artenreichum verschiedener Taxa unter unterschiedlichsten ökologischen Gegebenheiten. Heterogenität kann sich auf biotische und abiotische Bedingungen beziehen und wurde daher mittels vieler verschiedener Maße quantifiziert. Diese finden zudem auf sehr unterschiedlichen Skalen Anwendung, die von der Architektur einer einzelnen Pflanze über Landschaftsstruktur bis hin zu topographischem Relief reichen. Die Vielfalt der Maße sowie eine oft unbestimmte und inkonsistente Terminologie, die in der Forschung zu Heterogenität-Artenreichtums-Beziehungen verwendet wird, erschweren das Verständnis, den Vergleich und die Synthese der entsprechenden Studien. Desweiteren gibt es große Unterschiede in der Form und Stärke der Beziehungen: während viele Studien einen positiven Zusammenhang zwischen Heterogenität und Artenreichtum nachwiesen, sind auch negative, unimodale und nicht signifikante Zusammenhänge bekannt. Deshalb existiert bisher kein eindeutiger Konsens bezüglich der generellen Heterogenität-Artenreichtums-Beziehung. Im Rahmen der vorliegenden Dissertation fertige ich ein systematisches Literaturreview an, mit dem ich einen Überblick über die verwendeten Maße und Begriffe gebe, die bisher in der Forschung zu Heterogenität-Artenreichtums-Beziehungen Anwendung fanden. Basierend auf 192 Studien identifiziere ich 165 verschiedene Heterogenitätsmaße, die ich bezüglich ihrer Themenfelder und Berechnungsmethoden klassifiziere. Es werden fünf Themenfelder unterschieden, nämlich Landbedeckung und Vegetation als biotische Komponenten, und Klima, Boden und Topographie als abiotische Komponenten von Heterogenität. Desweiteren identifiziere ich achtzehn verschiedene Berechnungsmethoden, wie z.B. Anzahl, Standardabweichung und Variationskoeffizient. Die Höhenspannweite in einem Gebiet erweist sich als das häufigste Heterogenitätsmaß in der Literatur, wohingegen Maße von klimatischer Heterogenität und Bodenheterogenität unterrepräsentiert sind. Weiterhin stelle ich ein deutliches räumliches und taxonomisches Ungleichgewicht in der Forschung fest, wobei ein Großteil der Studien den Einfluss von Heterogenität in der Paläarktis untersucht und sich auf den Artenreichtum von Vertebraten oder Pflanzen konzentriert. Ich kompiliere über 100 verschiedene Begriffe für Heterogenität, wie z.B. Habitatdiversität oder Habitatheterogenität, und weise auf mangelhafte und teilweise sogar widersprüchliche Definitionen hin. Solche Unklarheiten erschweren das Verständnis der Begriffe und Studien, weshalb ich für eindeutige Terminologie plädiere und mich gegen die Verwendung von Synonymen ausspreche. Desweiteren gebe ich einen Überblick über mögliche Mechanismen, die als Grundlage von positiven Zusammenhängen zwischen Heterogenität und Artenreichtum in der Literatur diskutiert werden. Insgesamt identifiziere ich sieben Hauptmechanismen, die mit der Förderung von Koexistenz, Persistenz und Diversifikation von Arten zusammenhängen. Diese Mechanismen stelle ich in Beziehung zu den Themenfeldern der Heterogenitätsmaße, den Taxa und den räumlichen Skalen, die in den jeweiligen Studien behandelt werden. Basierend auf dem gleichen Datensatz von 192 Studien und 1148 Datenpunkten führe ich anschließend eine Meta-Analyse durch, um die generelle Richtung und Stärke des Zusammenhangs zwischen Heterogenität und dem Artenreichtum terrestrischer Pflanzen und Tiere zu untersuchen. Hierbei weise ich quantitativ nach, dass der Zusammenhang von der Landschaftsebene bis zur globalen Skala über Taxa, Habitattypen und räumliche Skalen hinweg generell positiv ist. Während kein signifikanter Unterschied in der Effektgröße zwischen biotischer und abiotischer Heterogenität besteht, weisen Vegetations- und topographische Heterogenität signifikant stärkere Assoziationen mit Artenreichtum auf als klimatische Heterogenität. Durch gemischte Meta-Regressionen identifiziere ich weiterhin Studieneigenschaften, die die Stärke des Zusammenhangs zwischen Heterogenität und Artenreichtum beeinflussen. Räumliche Skalen, insbesondere Flächenkonstanz, räumliche Auflösung und Ausdehnung, stellen sich als besonders wichtige Einflussgrößen für die untersuchte Beziehung zwischen Artenreichtum und auf Landbedeckung und Höhe basierenden Heterogenitätsmaßen heraus. Ausgehend von den Ergebnissen des Literaturreviews untersuche ich schließlich die Ähnlichkeit zwischen einer Reihe von Heterogenitätsmaßen sowie deren differentiellen Einfluss auf den globalen Artenreichtum terrestrischer Säugetiere. Ich berechne systematisch 51 verschiedene Heterogenitätsmaße auf globaler Ebene, die alle fünf Themenfelder von Heterogenität abdecken und neun verschiedene Berechnungsmethoden beinhalten. Ich zeige, dass manche dieser Maße sich deutlich voneinander abheben, während andere stärker kollinear und zum Teil redundant sind. Ich stelle Ähnlichkeiten und Unterschiede zwischen verschiedenen Regionen in Bezug auf räumliche Muster einzelner Heterogenitätsmaße sowie einen multidimensionalen Heterogenitätsraum heraus, der auf einer Hauptkomponentenanalyse beruht. Außerdem untersuche ich den Zusammenhang zwischen jedem einzelnen Heterogenitätsmaß und dem Säugetierreichtum in einfachen und multiplen Regressionsmodellen, welche zusätzlich den Einfluss von Klima, biogeographischer Region und menschlichem Einfluss berücksichtigen. Mit Hilfe von bedingten Inferenzbäumen analysiere ich den Einfluss der verschiedenen Themenfelder und Berechnungsmethoden der Heterogenitätsmaße auf die Modellgüte über drei räumliche Auflösungen hinweg. Die Wahl der Themenfelder stellt sich dabei als wichtigster Einflussfaktor heraus, wobei sich Maße klimatischer und topographischer Heterogenität besonders positiv auf die Modellgüte auswirken. Desweiteren zeichnen sich Modelle mit Anzahl- oder Spannweitemaßen ebenfalls durch hohe Modellgüte aus, wohingegen der Variationskoeffizient und ein Geländeschroffheitsindex mit relativ geringer Modellgüte zusammenhängen. Insgesamt betonen meine Ergebnisse die hohe Bedeutung methodischer Entscheidungen auf die Ergebnisse von Heterogenität-Artenreichtums-Studien. Dies wiederum dokumentiert wie wichtig es ist, sinnvolle, taxon- und skalenabhängige Heterogenitätsmaße zu verwenden, die dem jeweiligen Untersuchungssystem und dem zu untersuchenden Mechanismus entsprechen. Diese Dissertation stellt die bisher umfangreichste Untersuchung der Quantifizierung und Terminologie von Heterogenität über Themenfelder und verschiedene taxonomische Gruppen hinweg dar. Sie belegt erstmals einen generell positiven Zusammenhang zwischen biotischer und abiotischer Heterogenität und dem Artenreichtum terrestrischer Pflanzen und Tiere auf relativ großen räumlichen Skalen. Meine Forschung demonstriert deutlich die enorme Komplexität von Heterogenität als Thema und Forschungsgebiet. Trotz der beachtlichen Fortschritte, die durch diese Arbeit in der Erforschung von Heterogenität-Artenreichtums-Beziehungen gemacht wurden, gilt es noch zahlreiche offene Fragen zu beantworten. Die vorliegende Dissertation soll eine solide Basis schaffen, um diese Herausforderung in Zukunft anzugehen.