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  • Fatal, Netta (Helsingin yliopisto, 2004)
  • Szilvay, Géza R. (Helsingin yliopisto, 2007)
    Hydrophobins are small surface active proteins that are produced by filamentous fungi. The surface activity of hydrophobin proteins leads to the formation of a film at the air-water interface and adsorption to surfaces. The formation of these hydrophobin films and coatings is important in many stages of fungal development. Furthermore, these properties make hydrophobins interesting for potential use in technical applications. The surfactant-like properties of hydrophobins from Trichoderma reesei were studied at the air-water interface, at solid surfaces, and in solution. The hydrophobin HFBI was observed to spontaneously form a cohesive film on a water drop. The film was imaged using atomic force microscopy from both sides, revealing a monomolecular film with a defined molecular structure. The use of hydrophobins as surface immobilization carriers for enzymes was studied using fusion proteins of HFBI or HFBII and an enzyme. Furthermore, sitespecifically modified variants of HFBI were shown to retain their ability to selfassemble at interfaces and to be able to bind a second layer of proteins by biomolecular recognition. In order to understand the function of hydrophobins at interfaces, an understanding of their overall behavior and self-assembly is needed. HFBI and HFBII were shown to associate in solution into dimers and tetramers in a concentration-dependent manner. The association dynamics and protein-protein interactions of HFBI and HFBII were studied using Förster resonance energy transfer and size exclusion chromatography. It was shown that the surface activity of HFBI is not directly dependent on the formation of multimers in solution.
  • Zohdy, Sarah (Helsingin yliopisto, 2012)
    Mouse lemurs are the world s smallest primates and a model species for ancestral primates that lived 55 million years ago. In captive conditions, mouse lemurs live over six times longer than similarly sized mice and have been found to exhibit many symptoms of human senescence, including Alzheimer s-like neurodegeneration. These traits make captive mouse lemurs an exemplary model for aging. Despite this, to date no study has examined the aging process in wild mouse lemurs. This thesis addresses multidisciplinary questions relating to mouse lemur aging and life history. Through mark-recapture data and a combination of field and laboratory techniques I examine the aging process in wild brown mouse lemurs (Microcebus rufus). To estimate ages of individual wild mouse lemurs a technique was developed using dental wear. I found that in their natural habitat these tiny primates live up to 8 years of age, well past the captive age of senescence (5 yrs). Among old individuals, both males and females are represented, and unlike other polygamous vertebrates age-dependent survival rates do not differ between sexes. With the ages of wild mouse lemurs identified, other age-related factors such as hormone levels and parasite loads were subsequently examined. Contrary to findings in captivity no observable physical symptoms of senescence were found in old mouse lemurs, i.e. over the age of five. Further, new findings highlight mouse lemurs as an exception to many assumptions of mammalian physiology. In this study, testosterone levels were found to be comparable in both males and females, potentially providing an explanation for the lack of difference in survival rates between sexes. Testosterone and DHEA-S, two hormones typically found to decrease with age, did not differ between young and old lemurs. However, cortisol, the stress hormone, did decrease with age in male mouse lemurs, but not in females. Differences in immunity with age were examined indirectly via parasite dynamics. Specifically, I described the ectoparasites found on brown mouse lemurs, and created and implemented a novel method which allows the tracking of the natural flow of parasites between known individuals in a wild. This method revealed that parasite movement between lemurs suggests a much more complex social network than indicated by trapping, provided new insight about how parasites/pathogens move among wild populations, and revealed that only a few individual lemurs could be responsible for population-wide louse-borne epidemic. In addition to shedding light on the social behavior of mouse lemurs, I used the presence of ecto- and endoparasites as an indicator of immune health in young and old individuals, exposing a decline in endoparasites with age, but not in ectoparasites. Hormone measures and parasite loads were also employed to test the immunocompetence handicap hypothesis (ICHH) (which implicates testosterone as a cause for immunosuppression and hence higher parasite intensities) in both sexes. Contrary to the ICHH no correlation between testosterone and parasite intensities was found; however, when cortisol and testosterone positively co-varied higher parasite loads were observed in both sexes. In conclusion, in the search for a better understanding of the aging process in wild brown mouse lemurs I examined the multifaceted physiological transformations (parasitological, endocrinological, and dental wear). This research produced novel, replicable methodologies and findings with wide-reaching implications that extend beyond aging and challenge some of the previously-held assumptions of mammalian biology.
  • Niemi, Katri (Helsingin yliopisto, 2012)
    The immune response is operated by two integrated systems, the adaptive and innate immune responses. Innate immunity includes both cellular and soluble components. The cellular part consists of host cells at the front line of defence - macrophages, monocytes, dendritic cells, neutrophils, endothelial cells and mast cells - that express receptors capable of recognizing common pathogen constituents, hence called pattern-recognition receptors, PRRs. Several cooperating PRR families, for example Toll-like receptors (TLRs) and receptors with nucleotide-binding domain leucine-rich repeats (NLRs), have been identified. They recognize two different classes of structures, pathogen-associated molecular patterns (PAMPs) and non-microbial, danger-associated molecular patterns (DAMPs). The soluble component of the innate immune system includes an arsenal of acute-phase proteins, the expression of which is induced during the acute-phase response (APR), an immediate systemic reaction triggered by a local or systemic abnormal condition such as tissue injury, infection or trauma. In addition, the innate immune response is driven by numerous proinflammatory cytokines and mediators, most notably interleukin (IL-) 1β. The activity of IL-1β is tightly controlled; the induction of gene expression and the activation of pro-IL-1β require separate stimuli. IL-1β maturation takes place in cytosolic protein platforms called inflammasomes, of which NLRP3 is the most characterized. The major acute-phase proteins in human are C-reactive protein (CRP) and serum amyloid A (SAA). In response to inflammatory stimulus, SAA concentration in plasma can increase up to 1000-fold. SAA circulates in association with high-density lipoprotein (HDL) and is, thus, suggested to play a role in lipid metabolism and transport. In addition, SAA possesses strong cytokine-like and proinflammatory properties. A pathogenic role for SAA has most clearly been implicated in AA amyloidosis, a systemic protein misfolding disease that can complicate chronic inflammatory conditions. Current evidence indicates that SAA is also as an active mediator in cardiovascular diseases. The aim of the study was to elucidate the interaction between SAA and two types of innate immune system cells, human mast cells and macrophages, and the consequences of this interaction in the pathogenesis of AA amyloidosis and atherosclerosis, as well as the regulation of SAA in inflammation. It was demonstrated that SAA is a potent activator of mast cells and macrophages, as indicated by a dose-dependent production of key proinflammatory cytokines, IL-1β and tumor necrosis factor (TNF) -α, in both cell types. In mast cells, this activation led to the degradation of SAA by the mast cell-derived protease tryptase and to the formation of amyloid-like structures, suggesting a pathogenic role for mast cells in AA amyloidosis. The secretion of IL-1β was studied in more detail in human macrophages, in which SAA was found to be able to induce both the gene expression of IL1B, via TLR2 and TLR4, and the activation of the NLRP3 inflammasome, resulting in the secretion of mature IL-1β. The activation of NLRP3 involved the ATP-receptor P2X7 and cathepsin B activity. Native serum lipoproteins were shown to inhibit the activity of SAA and this inhibition was further enhanced by lipoprotein oxidation. Besides the expression of IL1B, oxidized LDL inhibited also the activation of the NLRP3 inflammasome. A decrease in the SAA-induced IL-1β production was observed also in vivo, suggesting that oxidized LDL, although possessing many pathological features, may represent a novel and significant regulator of SAA activity in inflamed tissues, including atherosclerotic lesions. All together, the findings of this study stress the significance of SAA in the pathogenesis of inflammatory diseases, such as atherosclerosis, and provide new insights into mechanisms leading to AA amyloidogenesis.
  • Karell, Patrik (Helsingin yliopisto, 2007)
    Life-history theory states that although natural selection would favour a maximisation of both reproductive output and life-span, such a combination can not be achieved in any living organism. According to life-history theory the reason for the fact that not all traits can be maximised simultaneously is that different traits compete with each other for resources. These relationships between traits that constrain the simultaneous evolution of two or more traits are called trade-offs. Therefore, during different life-stages an individual needs to optimise its allocation of resources to life-history components such as growth, reproduction and survival. Resource limitation acts on these traits and therefore investment in one trait, e.g. reproduction, reduces the resources available for investment in another trait, e.g. residual reproduction or survival. In this thesis I study how food resources during different stages of the breeding event affect reproductive decisions in the Ural owl (Strix uralensis) and the consequences of these decisions on parents and offspring. The Ural owl is a suitable study species for such studies in natural populations since they are long-lived, site-tenacious, and feed on voles. The vole populations in Fennoscandia fluctuate in three- to four-year cycles, which create a variable food environment for the Ural owls to cope with. The thesis gives new insight in reproductive costs and their consequences in natural animal populations with emphasis on underlying physiological mechanisms. I found that supplementary fed Ural owl parents invest supplemented food resources during breeding in own self-maintenance instead of allocating those resources to offspring growth. This investment in own maintenance instead of improving current reproduction had carry-over effects to the following year in terms of increased reproductive output. Therefore, I found evidence that reduced reproductive costs improves future reproductive performance. Furthermore, I found evidence for the underlying mechanism behind this carry-over effect of supplementary food on fecundity. The supplementary-fed parents reduced their feeding investment in the offspring compared to controls, which enabled the fed female parents to invest the surplus resources in parasite resistance. Fed female parents had lower blood parasite loads than control females and this effect lasted until the following year when also reproductive output was increased. Hence, increased investment in parasite resistance when resources are plentiful has the potential to mediate positive carry-over effects on future reproduction. I further found that this carry-over effect was only present when potentials for future reproduction were good. The thesis also provides new knowledge on resource limitation on maternal effects. I found that increased resources prior to egg laying improve the condition and health of Ural owl females and enable them to allocate more resources to reproduction than control females. These additional resources are not allocated to increase the number of offspring, but instead to improve the quality of each offspring. Fed Ural owl females increased the size of their eggs and allocated more health improving immunological components into the eggs. Furthermore, the increased egg size had long-lasting effects on offspring growth, as offspring from larger eggs were heavier at fledging. Limiting resources can have different short- and long-term consequences on reproductive decisions that affect both offspring number and quality. In long-lived organisms, such as the Ural owl, it appears to be beneficial in terms of fitness to invest in long breeding life-span instead of additional investment in current reproduction. In Ural owls, females can influence the phenotypic quality of the offspring by transferring additional resources to the eggs that can have long-lasting effects on growth.
  • Matveinen-Huju, Katja (Helsingin yliopisto, 2007)
    Forestry has influenced forest dwelling organisms for centuries in Fennoscandia. For example, in Finland ca. 30% of the threatened species are threatened because of forestry. Nowadays forest management recommendations include practices aimed at maintaining biodiversity in harvesting, such as green-tree retention. However, the effects of these practices have been little studied. In variable retention, different numbers of trees are retained, varying from green-tree retention (at least a few live standing trees in clear-cuts) to thinning (only individual trees removed). I examined the responses of ground-dwelling spiders and carabid beetles to green-tree retention (with small and large tree groups), gap felling and thinning aimed at an uneven age structure of trees. The impacts of these harvesting methods were compared to those of clear-cutting and uncut controls. I aimed to test the hypothesis that retaining more trees positively affects populations of those species of spiders and carabids that were present before harvesting. The data come from two studies. First, spiders were collected with pitfall traps in south-central Finland in 1995 (pre-treatment) and 1998 (after-treatment) in order to examine the effects of clear-cutting, green-tree retention (with 0.01-0.02-ha sized tree groups), gap felling (with three 0.16-ha sized openings in a 1-ha stand), thinning aiming at an uneven age structure of trees and uncut control. Second, spiders and carabids were caught with pitfall traps in eastern Finland in 1998-2001 (pre-treatment and three post-treatment years) in eleven 0.09-0.55-ha sized retention-tree groups and clear-cuts adjacent to them. Original spider and carabid assemblages were better maintained after harvests that retained more trees. Thinning maintained forest spiders well. However, gap felling and large retention-tree groups maintained some forest spider and carabid species in the short-term, but negatively affected some species over time. However, use of small retention-tree groups was associated with negative effects on forest spider populations. Studies are needed on the long-term effects of variable retention on terrestrial invertebrates; especially those directed at defining appropriate retention patch size and on the importance of structural diversity provided by variable retention for invertebrate populations. However, the aims of variable retention should be specified first. For example, are retention-tree groups planned to constitute life-boats , stepping-stones or to create structural diversity? Does it suffice that some species are maintained, or do we want to preserve the most sensitive ones, and how are these best defined? Moreover, the ecological benefits and economic costs of modified logging methods should be compared to other approaches aimed at maintaining biodiversity.
  • Saj, Stéphane (Helsingin yliopisto, 2008)
    Plant species differ in their effects on ecosystem productivity and it is recognised that these effects are partly due to plant species-specific influences on soil processes. Until recently, however, not much attention was given to the potential role played by soil biota in these species-specific effects. While soil decomposers are responsible for governing the availability of nutrients for plant production, they simultaneously depend on the amount of carbon provided by plants. Litter and rhizodeposition constitute the two basal resources that plants provide to soil decomposer food webs. While it has been shown that both of these can have effects on soil decomposer communities that differ among plant species, the putative significance of these effects for plant nitrogen (N) acquisition is currently understudied. My PhD work aimed at clarifying whether the species-specific influences of three temperate grassland plants on the soil microfood-web, through rhizodeposition and litter, can feed back to plant N uptake. The methods and approach used (15N labelling of plant litter in microcosm experiments) revealed to be an effective combination of tools in studying these feedbacks. Plant effects on soil organisms were shown to differ significantly between plant species and the effects could be followed across several trophic levels. The labelling of litter further permitted the evaluation of plant acquisition of N derived from soil organic matter. The results show that the structure of the soil microfood-web can have a significant role in plant N acquisition when the structure is experimentally manipulated, such as when comparing systems consisting of microbes to those consisting of microbes and their grazers. However, despite this, the results indicate that differences in N uptake from soil organic matter between different plant species are not related to the effects these species exert on the structure of the soil microfood-web. Rather, these differences in N uptake seem to be determined by other species-specific traits of live plants and their litter. My results thus indicate that different resources provided by different plant species may not induce species-specific decomposer feedbacks on plant N uptake from soil organic matter. This further suggests that the species-specific plant effects on soil decomposer communities may not, at least in the short term, have significant consequences on plant production.
  • Pohjamo, Maria (Helsingin yliopisto, 2008)
    The area of intensively managed forests, in which required conditions for several liverwort species are seldom found, has expanded over the forest landscape during the last century. Liverworts are very sensitive to habitat changes, because they demand continuously moist microclimate. Consequently, about third of the forest liverworts have been classified as threatened or near threatened in Finland. The general objective of this thesis is to increase knowledge of the reproductive and dispersal strategies of the substrate-specific forest bryophytes. A further aim was to develop recommendations for conservation measures for species inhabiting unstable and stable habitats in forest landscape. Both population ecological and genetic methods have been applied in the research. Anastrophyllum hellerianum inhabits spatially and temporally limited substrate patches, decaying logs, which can be considered as unstable habitats. The results show that asexual reproduction by gemmae is the dominant mode of reproduction, whereas sexual reproduction is considerably infrequent. Unlike previously assumed, not only spores but also the asexual propagules may contribute to long-distance dispersal. The combination of occasional spore production and practically continuous, massive gemma production facilitates dispersal both on a local scale and over long distances, and it compensates for the great propagule losses that take place preceding successful establishment at suitable sites. However, establishment probability of spores may be restricted because of environmental and biological limitations linked to the low success of sexual reproduction. Long-lasting dry seasons are likely to result in a low success of sexual reproduction and decreased release rate of gemmae from the shoots, and consequent fluctuations in population sizes. In the long term, the substratum limitation is likely to restrict population sizes and cause local extinctions, especially in small-sized remnant populations. Contrastingly, larger forest fragments with more natural disturbance dynamics, to which the species is adapted, are pivotal to species survival. Trichocolea tomentella occupies stable spring and mesic habitats in woodland. The relatively small populations are increasingly fragmented with a high risk for extinction for extrinsic reasons. The results show that T. tomentella mainly invests in population persistence by effective clonal growth via forming independent ramets and in competitive ability, and considerably less in sexuality and dispersal potential. The populations possess relatively high levels of genetic diversity regardless of population size and of degree of isolation. Thus, the small-sized populations inhabiting stable habitats should not be neglected when establishing conservation strategies for the species and when considering the habitat protection of small spring sites. Restricted dispersal capacity, also on a relatively small spatial scale, is likely to prevent successful (re-)colonization in the potential habitat patches of recovering forest landscapes. By contrast, random short-range dispersal of detached vegetative fragments within populations at suitable habitat seems to be frequent. Thus, the restoration actions of spring and streamside habitats close to the populations of T. tomentella may contribute to population expansion. That, in turn, decreases the harmful effects of environmental stochasticity.
  • Tallberg, Petra (Helsingin yliopisto, 2000)
  • Munne, Pauliina (Helsingin yliopisto, 2010)
    This thesis work focuses on the role of TGF-beta family antagonists during the development of mouse dentition. Tooth develops through an interaction between the dental epithelium and underlying neural crest derived mesenchyme. The reciprocal signaling between these tissues is mediated by soluble signaling molecules and the balance between activatory and inhibitory signals appears to be essential for the pattern formation. We showed the importance of Sostdc1 in the regulation of tooth shape and number. The absence of Sostdc1 altered the molar cusp patterning and led to supernumerary tooth formation both in the molar and incisor region. We showed that initially, Sostdc1 expression is in the mesenchyme, suggesting that dental mesenchyme may limit supernumerary tooth induction. We tested this in wild-type incisors by minimizing the amount of mesenchymal tissue surrounding the incisor tooth germs prior to culture in vitro. The cultured teeth phenocopied the extra incisor phenotype of the Sostdc1-deficient mice. Furthermore, we showed that minimizing the amount of dental mesenchyme in cultured Sostdc1-deficient incisors caused the formation of additional de novo incisors that resembled the successional incisor development resulting from activated Wnt signaling. Sostdc1 seemed to be able to inhibit both mesenchymal BMP4 and epithelial canonical Wnt signaling, which thus allows Sostdc1 to restrict the enamel knot size and regulate the tooth shape and number. Our work emphasizes the dual role for the tooth mesenchyme as a suppressor as well as an activator during tooth development. We found that the placode, forming the thick mouse incisor, is prone to disintegration during initiation of tooth development. The balance between two mesenchymal TGF-beta family signals, BMP4 and Activin is essential in this regulation. The inhibition of BMP4 or increase in Activin signaling led to the splitting of the large incisor placode into two smaller placodes resulting in thin incisors. These two signals appeared to have different effects on tooth epithelium and the analysis of the double null mutant mice lacking Sostdc1 and Follistatin indicated that these TGF-beta inhibitors regulate the mutual balance of BMP and Activin in vivo. In addition, this work provides an alternative explanation for the issue of incisor identity published in Science by Tucker et al. in 1998 and proposes that the molar like morphology that can be obtained by inhibiting BMP signaling is due to partial splitting of the incisor placodes and not due to change in tooth identity from the incisor to the molar. This thesis work presents possible molecular mechanisms that may have modified the mouse dental pattern during evolution leading to the typical rodent dentition of modern mouse. The rodent dentition is specialized for gnawing and consists of two large continuously growing incisors and toothless diastema region separating the molars and incisors. The ancestors of rodents had higher number of more slender incisors together with canines and premolars. Additionally, murine rodents, which include the mouse, have lost their ability for tooth replacement. This work has revealed that the inhibitory molecules appear to play a role in the tooth number suppression by delineating the spatial and temporal action of the inductive signals. The results suggest that Sostdc1 plays an essential role in several stages of tooth development through the regulation of both the BMP and Wnt pathway. The work shows a dormant sequential tooth forming potential present in wild type mouse incisor region and gives a new perspective on tooth suppression by dental mesenchyme. It reveals as well a novel mechanism to create a large mouse incisor through the regulation of mesenchymal balance between inductive and inhibitory signals.
  • Piha, Markus (Helsingin yliopisto, 2007)
    During the past decades agricultural intensification has caused dramatic population declines in a wide range of taxa related to farmland habitats, including farmland birds. In this thesis, I studied how boreal farmland landscape characteristics and agricultural land use affect the abundance and diversity of farmland birds using extensive field data collected by territory mapping of breeding farmland birds in various parts of Finland. My results show that the area and openness of agricultural areas are key determinants of farmland bird abundance and distribution. A landscape composition with enough open farmland combined with key habitats such as farmyards and wetland is likely to provide essential prerequisites for the occurrence of a rich farmland avifauna. In Finland, the majority of large areas suitable for open habitat specialists are located in southern and western parts of the country. However, the diversity of the species with an unfavourable conservation status in Europe (SPECs) had notable hotspot areas in northern and north-western agricultural areas. I found that in boreal agroecosystems farmland birds favour fields with springtime vegetative cover, especially agricultural grasslands and set-asides. Hence, in the spring cereal dominated Finnish agroecosystems it is the absence of field vegetation that may limit populations of many farmland bird species. It is likely that the decrease of crops providing vegetative cover in the spring, such as permanent grasslands, cultivated grass, and autumn-sown cereals, has greatly contributed to the declines of Finnish farmland birds. Grass crops have persistently declined in Finland as a consequence of specialization in crop production and the large-scale decline in livestock husbandry. Small-scale non-crop habitats, especially ditches and ditch margins, are also important for many bird species in the Finnish agroecosystems, but have dramatically declined during the last decades. A major problem for farmland bird conservation in Finland is the conflict between landscape structure and agricultural management. Areas with mixed and cattle farming are virtually absent from the large agricultural plains of southern and south-western Finland, where the landscape structure is more likely to be favourable for rich farmland bird assemblages. On the other hand, mixed and cattle farming is still rather frequent in northern and central parts of the country, where the landscape structure is not suitable for many farmland specialist birds requiring open landscapes. My results provide useful guidelines for farmland bird conservation, and imply that considerable attention needs to be paid to landscape factors when selecting areas for various conservational management actions, such as agri-environment schemes. Actions promoting the abundance of set-asides, grass crops, and ditches would markedly benefit Finnish farmland bird populations. Organic farming may benefit farmland birds, but it is not clear how general its beneficial effect is in boreal agroecosystems. The most urgent action aiming to preserve farmland biodiversity would be to support re-introducing and sustaining cattle farming by environmental subsidies. This would be especially beneficial in the southern parts of Finland, where the landscape characteristics and abundance of agricultural areas are most suitable for farmland birds and where cattle farming is currently rare.
  • Lehtomäki, Joona (Helsingin yliopisto, 2014)
    In a world of competing interests and increasing land use pressures, the allocation of limited resources for biodiversity conservation need to be prioritized. Spatial conservation prioritization deals with the cost-efficient and well-balanced identification of priority areas for biodiversity, as well as with the allocation and scheduling of alternative conservation actions. Finland is the most forested country in Europe, but more than 90 percents of Finland s forests are under commercial management. A history of widespread and relatively intensive forest management has led to many specialist species and habitats becoming threatened. At the same time, the protected area network is unequally distributed over the country, with largest areas in the north where species diversity is lowest. Consequently, the current main priority for conservation action for forest habitats is expanding the protected area network in the southern parts of the country in an ecologically justified way. In this thesis, I have three specific objectives. First, I examine the suitability of commonly available forest inventory data for informative high-resolution spatial conservation prioritization. Second, I clarify the effects of spatial scale and connectivity on spatial conservation prioritization at regional and national extents. Finally, I develop, demonstrate, and implement a practical workflow for regional- and national-scale forest conservation management planning in Finland, using the Zonation framework and software for spatial prioritization. I show how habitat quality indices based on forest inventory data and expert knowledge can be used as a basis of conservation prioritization. Comparison against validation datasets reveals that the analyses do indeed produce informative priorities. Case studies involving the expansion of the national protected area network both on public and private land demonstrate how the results can be applied in the context of a national forest conservation program, METSO. The spatial resolution of input data should closely match those of the planning objectives and the ecological processes involved. Furthermore, the level of detail in the forest inventory data defines how well the prioritization is able to identify small occurrences of important forest types and key habitats. The quality and the quantity of suitable habitat between protected areas are important for many forest species. Accounting for connectivity in the prioritization analyses produces spatially more aggregated priority patterns. However, emphasizing connectivity will lower the relative value of locally high quality, but poorly connected sites. Therefore, the balance between connectivity and local habitat quality merits careful consideration in spatial prioritization. The thesis highlights important factors. First, data availability often restricts the types of prioritization analyses that can be undertaken. Therefore, long-term development of high-quality open access data is crucial for making best use of spatial prioritization approaches. Second, establishing a conceptual model for the prioritization process can help formulate the right questions, to select the most suitable tools, and to estimate the costs and benefits involved. Finally, a successful conservation prioritization requires participation of experts and stakeholders. Methods, analyses, workflows and visualization techniques summarized in this thesis can serve as starting points for other similar applications elsewhere and support meeting local, regional and global conservation goals.
  • Tack, Ayco (Helsingin yliopisto, 2010)
    Habitat fragmentation is currently affecting many species throughout the world. As a consequence, an increasing number of species are structured as metapopulations, i.e. as local populations connected by dispersal. While excellent studies of metapopulations have accumulated over the past 20 years, the focus has recently shifted from single species to studies of multiple species. This has created the concept of metacommunities, where local communities are connected by the dispersal of one or several of their member species. To understand this higher level of organisation, we need to address not only the properties of single species, but also establish the importance of interspecific interactions. However, studies of metacommunities are so far heavily biased towards laboratory-based systems, and empirical data from natural systems are urgently needed. My thesis focuses on a metacommunity of insect herbivores on the pedunculate oak Quercus robur a tree species known for its high diversity of host-specific insects. Taking advantage of the amenability of this system to both observational and experimental studies, I quantify and compare the importance of local and regional factors in structuring herbivore communities. Most importantly, I contrast the impact of direct and indirect competition, host plant genotype and local adaptation (i.e. local factors) to that of regional processes (as reflected by the spatial context of the local community). As a key approach, I use general theory to generate testable hypotheses, controlled experiments to establish causal relations, and observational data to validate the role played by the pinpointed processes in nature. As the central outcome of my thesis, I am able to relegate local forces to a secondary role in structuring oak-based insect communities. While controlled experiments show that direct competition does occur among both conspecifics and heterospecifics, that indirect interactions can be mediated by both the host plant and the parasitoids, and that host plant genotype may affect local adaptation, the size of these effects is much smaller than that of spatial context. Hence, I conclude that dispersal between habitat patches plays a prime role in structuring the insect community, and that the distribution and abundance of the target species can only be understood in a spatial framework. By extension, I suggest that the majority of herbivore communities are dependent on the spatial structure of their landscape and urge fellow ecologists working on other herbivore systems to either support or refute my generalization.
  • Gripenberg, Sofia (Helsingin yliopisto, 2007)
    Herbivorous insects comprise a major part of terrestrial biodiversity, and their interactions with their host plants and natural enemies are of vast ecological importance. A large body of research demonstrates that the ecology and evolution of these insects may be affected by trophic interactions, by abiotic influences, and by intraspecific processes, but so far research on these individual aspects has rarely been combined. This thesis uses the leaf-mining moth Tischeria ekebladella and the pedunculate oak (Quercus robur) as a case study to assess how spatial variation in trophic interactions and the physical distribution of host trees jointly affect the distribution, dynamics and evolution of a host-specific herbivore. With respect to habitat quality, Tischeria ekebladella experiences abundant variation at several spatial scales. Most of this variation occurs at small scales notably among leaves and shoots within individual trees. While hypothetically this could cause moths to evolve an ability to select leaves and shoots of high quality, I did not find any coupling between female preference and offspring performance. Based on my studies on temporal variation in resource quality I therefore propose that unpredictable temporal changes in the relative rankings of individual resource units may render it difficult for females to predict the fate of their developing offspring. With respect to intraspecific processes, my results suggest that limited moth dispersal in relation to the spatial distribution of oak trees plays a key role in determining the regional distribution of Tischeria ekebladella. The distribution of the moth is aggregated at the landscape level, where local leaf miner populations are less likely to be present where oaks are scarce. A modelling exercise based on empirical dispersal estimates revealed that the moth population on Wattkast an island in south-western Finland is spatially structured overall, but that the relative importance of local and regional processes on tree-specific moth dynamics varies drastically across the landscape. To conclude, my work in the oak-Tischeria ekebladella system demonstrates that the local abundance and regional distribution of a herbivore may be more strongly influenced by the spatial location of host trees than by their relative quality. Hence, it reveals the importance of considering spatial context in the study of herbivorous insects, and forms a bridge between the classical fields of plant-insect interactions and spatial ecology.
  • Roslin, Tomas (Helsingin yliopisto, 1999)
  • Kaartinen, Riikka (Helsingin yliopisto, 2011)
    Herbivorous insects, their host plants and natural enemies form the largest and most species-rich communities on earth. But what forces structure such communities? Do they represent random collections of species, or are they assembled by given rules? To address these questions, food webs offer excellent tools. As a result of their versatile information content, such webs have become the focus of intensive research over the last few decades. In this thesis, I study herbivore-parasitoid food webs from a new perspective: I construct multiple, quantitative food webs in a spatially explicit setting, at two different scales. Focusing on food webs consisting of specialist herbivores and their natural enemies on the pedunculate oak, Quercus robur, I examine consistency in food web structure across space and time, and how landscape context affects this structure. As an important methodological development, I use DNA barcoding to resolve potential cryptic species in the food webs, and to examine their effect on food web structure. I find that DNA barcoding changes our perception of species identity for as many as a third of the individuals, by reducing misidentifications and by resolving several cryptic species. In terms of the variation detected in food web structure, I find surprising consistency in both space and time. From a spatial perspective, landscape context leaves no detectable imprint on food web structure, while species richness declines significantly with decreasing connectivity. From a temporal perspective, food web structure remains predictable from year to year, despite considerable species turnover in local communities. The rate of such turnover varies between guilds and species within guilds. The factors best explaining these observations are abundant and common species, which have a quantitatively dominant imprint on overall structure, and suffer the lowest turnover. By contrast, rare species with little impact on food web structure exhibit the highest turnover rates. These patterns reveal important limitations of modern metrics of quantitative food web structure. While they accurately describe the overall topology of the web and its most significant interactions, they are disproportionately affected by species with given traits, and insensitive to the specific identity of species. As rare species have been shown to be important for food web stability, metrics depicting quantitative food web structure should then not be used as the sole descriptors of communities in a changing world. To detect and resolve the versatile imprint of global environmental change, one should rather use these metrics as one tool among several.
  • Cabeza, Mar (Helsingin yliopisto, 2003)