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Although biological communities are intrinsically dynamic, with both, species and interactions changing over time, interaction networks analyses to date are still largely static. We implemented a temporal multilayer network approach to explore the changes on species roles and on the emergent structure of a seed-dispersal network over five years. Network topology was relatively constant, with four well defined interaction modules spanning across all years. Importantly, species that were present on more years, were also disproportionally important on each year, thus forming a core of temporally reliable species that are critical to the cohesiveness of the multilayer network structure. We propose a new descriptor termed species activity that reflects the number of temporal, spatial or functional layers (e.g., different years, habitats, or functions) that each species integrates, providing a simple and powerful index of species importance for multilayer network cohesion.

Tese de doutoramento em Biociências, na especialidade de Ecologia, apresentada ao Departamento de Ciências da Vida da Faculdade de Ciências e Tecnologia da Universidade de Coimbra As aves insectívoras foram o objecto desta investigação sistemática realizada no montado com o propósito de determinar a sua importância no controlo de pragas de sobreiro (Quercus suber) e azinheira (Q. rotundifolia), nomeadamente desfolhadores. Numa revisão bibliográfica focada na dieta e ecologia alimentar das aves reprodutoras, invernantes e residentes no sudoeste da Península Ibérica foram identificadas vinte e seis espécies como potenciais predadores regulares das principais pragas de sobreiro e azinheira. Os nichos alimentares destas aves mostraram uma relação com a biologia das pragas consumidas: aves que se alimentam no solo ingerem pupas e larvas de insectos carpófagos, aves que se alimentam nas árvores consomem ovos, larvas e pupas de desfolhadores e de insectos xilófagos, e aves que se alimentam em voo capturam insectos voadores na fase adulta. No que respeita aos desfolhadores, o impacto das aves nas suas populações supõe-se maior durante a Primavera-Verão, coincidindo com a fase de desenvolvimento larvar nas folhas na qual estes estão particularmente expostos à predação por várias espécies de passeriformes arborícolas que ocorrem em densidades elevadas e apresentam uma larga distribuição no montado. Este princípio foi verificado no terreno, ao mesmo tempo que a selecção entre sobreiro e azinheira pelas aves insectívoras foi investigada tendo em conta a espécie arbórea dominante no montado. Quase 95% da predação de artrópodes pelas aves nas árvores foi efectuada por apenas sete espécies de passeriformes, que, por sua vez, representaram mais de 60% da abundância total de aves: chapim-azul (Cyanistes caeruleus), chapim-real (Parus major), chapim-de-crista (Lophophanes cristatus), tentilhão (Fringilla coelebs), toutinegra-de-cabeça-preta (Sylvia melanocephala), trepadeira-azul (Sitta europaea) e trepadeira-comum (Certhia brachydactyla). As variações na dominância de sobreiro e azinheira tiveram pouca influência nas comunidades de aves nidificantes do montado, contudo as aves que se alimentam na casca preferiram moderadamente o sobreiro. Também foi sugerido, via modelação estatística do tempo dispendido pelas aves em alimentação em cada árvore, que algumas características morfológicas, fenológicas e fisiológicas relacionadas com a abundância de artrópodes nos sobreiros e azinheiras podem ser utilizadas para avaliar a qualidade do habitat para as aves insectívoras florestais. As respostas numéricas e funcionais das aves insectívoras a surtos localizados de larvas de duas importantes pragas de desfolhadores, a lagarta-do-sobreiro (Lymantria dispar) e a lagarta-verde (Periclista andrei), em montados de sobro foram comparadas com uma área-controlo não-infestada. Quatro espécies responderam positivamente aos surtos de desfolhadores: as densidades de trepadeira-azul e de tentilhão foram superiores nas áreas atacadas por lagarta-do-sobreiro e lagarta-verde, respectivamente (respostas numéricas), e o chapim-azul e o chapim-de-crista passaram mais tempo em alimentação nas árvores infestadas por lagarta-do-sobreiro (respostas funcionais). Estes resultados estão de acordo com as teorias de predação generalista e salientam a importância do controlo biológico natural pelas aves, nomeadamente através de mecanismos de regulação dependentes da densidade das pragas. A função das aves como predadores de larvas de desfolhadores foi avaliada em diferentes nichos das árvores na ausência de surtos, comparando a densidade, o tamanho e a composição das lagartas capturadas e a frequência de alimentação de crias em caixas-ninho de três espécies-chave: chapim-azul, chapim-real e trepadeira-azul. As lagartas foram a principal ou a segunda principal presa consumida pelas crias das três espécies. Em particular, o chapim-azul consumiu uma percentagem de lagartas significativamente mais elevada do que as outras espécies, e apresentou igualmente uma taxa de remoção de lagartas significativamente maior à escala do habitat. Por outro lado, não se verificaram diferenças entre as três espécies na provisão de biomassa de lagartas à escala do habitat devido a uma predação complementar dos instars iniciais e finais das lagartas pelo chapim-azul e pelas outras duas espécies, respectivamente. Por fim, numa experiência onde se testou o aumento da densidade reprodutora de passeriformes por intermédio da colocação de caixas-ninho, foi registado um aumento significativo na densidade de chapim-azul nas parcelas onde foram colocadas caixas-ninho em comparação com as parcelas-controlo (+ 38.2%), tendo as caixas-ninho contribuído também para um aumento considerável das populações nidificantes de chapim-real e trepadeira-azul (+ 26.8% e + 14.3%, respectivamente). No geral, esta tese afirma a importância do controlo biológico natural proporcionado por espécies comuns de passeriformes residentes no montado e apela aos proprietários para considerarem o efeito das práticas de gestão nas populações destas aves de modo a prevenir surtos de pragas. A systematic investigation on insect predation by birds was conducted in Mediterranean oak woodlands of southwestern Iberian Peninsula with the purpose of assessing the services provided by insectivorous birds in the control of cork oak (Quercus suber) and holm oak (Q. rotundifolia) pests, particularly defoliators. Through a literature review concerning foraging ecology and diet of breeding, wintering and resident birds in southwestern Iberian Peninsula, twenty-six species were listed as potential regular predators of the main cork and holm oak pests. A strong interaction was found between bird foraging guilds and the biology of consumed pests: ground-foragers prey on overwintering pupae and larvae of seed-borers, tree-foragers prey on eggs, larvae and pupae of defoliator and wood-boring pests, and aerial-sweepers prey on airborne imagines. Regarding defoliators, spring-summer was recognized as the period when bird predation is supposed to have the greatest impact on their populations because caterpillars, throughout their development on foliage, are highly vulnerable to predation by various tree-foraging passerine species which occur in high densities and are widespread in Mediterranean oak woodlands. Such prediction was validated in the field at the same time that tree selection between cork oak and holm oak by insectivorous birds was studied with respect to dominant tree species of Mediterranean oak woodlands. Approximately 95% of arthropod predation by birds on trees was carried out by only seven passerine species, which, by themselves, represented more than 60% of total bird abundance: blue tit (Cyanistes caeruleus), great tit (Parus major), crested tit (Lophophanes cristatus), chaffinch (Fringilla coelebs), Sardinian warbler (Sylvia melanocephala), nuthatch (Sitta europaea) and short-toed treecreeper (Certhia brachydactyla). Local scale variation in cork oak- and holm oak-dominance had little effect on breeding bird communities, although bark-gleaners moderately preferred cork oak. It was also suggested, via statistical modeling of the time spent by foraging birds on each tree, that some characteristics regarding morphology, phenology and physiological condition of cork and holm oak trees can be used to predict habitat quality for insectivorous forest birds. Numerical and functional responses of the tree-foraging guild to localized larval outbreaks of two major defoliator pests – gypsy moth (Lymantria dispar) and the sawfly Periclista andrei – in cork oak woodlands were compared with a non-infested control. Four species evidenced positive responses to defoliator outbreaks: densities of nuthatch and chaffinch were higher in the outbreak areas of gypsy moth and P. andrei, respectively (numerical responses), and blue tits and crested tits spent a significantly larger amount of time foraging on trees infested with gypsy moth (functional responses). These results are consistent with predictions of the generalist predator hypothesis and drawed attention to the importance of natural biological control by birds, namely through density-dependent mechanisms of pest regulation. Bird predation on defoliator caterpillars was estimated in non-outbreak conditions, through identification of food given to nestlings by three hole-nesting passerine species which forage on different niches of trees: blue tit (Cyanistes caeruleus; foliage-gleaner), great tit (Parus major; bark-foliage-gleaner) and nuthatch (Sitta europaea; bark-gleaner). Their specific roles were compared using breeding densities, size and composition of preyed caterpillars and provisioning rates to nestlings reared in nest-boxes. Caterpillars were the most, or second-most, common prey consumed by nestlings of the three species. Blue tits, in particular, consumed a significantly higher percentage of caterpillars than the other two passerine species, and showed a significantly higher removal rate of caterpillars at the habitat scale. On the other hand, the supply of caterpillar biomass to each species showed little differences at the habitat scale due to caterpillar size segregation between blue tit and the other two species, which preyed on early and late instars of caterpillars, respectively. Finally, a before-after control-impact (BACI) experience used to test the increase of the breeding density of hole-nesting passerines by setting nest-boxes, achieved a significant increase in the density of blue tit in manipulated nest-box plots compared with control plots (+ 38.2%) while it also contributed for a considerable increase in breeding populations of great tit and nuthatch (+ 26.8% and + 14.3%, respectively). On the whole, this thesis shows the importance of natural biological control by common resident passerine species in Mediterranean oak woodlands and calls on landowners to consider the effect of management interventions on their populations in order to prevent pest outbreaks. FCT - SFRH/BD/78813/2011

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.

Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs., Randomised controlled experiments are the gold standard for scientific inference, but environmental and social scientists often rely on different study designs. Here the authors analyse the use of six common study designs in the fields of biodiversity conservation and social intervention, and quantify the biases in their estimates.