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<p>Landscape effects on species performance currently receives much attention. Habitat loss and fragmentation are considered major threats to species diversity. Deciduous forests in southern Sweden are previous wooded pastures that have become species-rich communities appearing as islands in agricultural landscapes, varying in species composition. <i>Actaea spicata</i> is a long-lived plant occurring in these forests. In 150 populations in a 10-km² area, I studied pre-dispersal seed predation, seed dispersal and pollination. I investigated spatio-temporal dynamics of a tritrophic system including<i> Actaea</i>, a specialist seed predator, <i>Eupithecia immundata</i>, and its parasitoids. In addition, effects of biotic context on rodent fruit dispersal and effects of flowering time and flower number on seed set, seed predation and parasitization were studied. Insect incidences of both trophic levels were related to resource population size and small <i>Eupithecia</i> populations were maintained by the rescue effect. There was a unimodal relationship between seed predation and plant population size. Seed predator populations frequently went extinct in small plant populations, resulting in low average seed predation. Parasitoids were present in large plant populations but did not affect seed predator density. Seed predators aggregated at edges, relaxing seed predation in patch interiors. Flowering phenology was unrelated to seed set and insect incidence. A higher flower number did not influence seed predation but was associated with higher seed set and a tendency for a higher parasitization rate. In the study on fruit dispersal more fruits were removed inside than outside populations. Within plant populations more fruits were removed from large aggregations. Overall, this thesis underlines the importance of plant-animal interactions during different phases of the life cycle. The spatial configuration of host plants plays an important role for the outcome of plant-animal interactions and trophic cascades.</p>

Landscape effects on species performance currently receives much attention. Habitat loss and fragmentation are considered major threats to species diversity. Deciduous forests in southern Sweden are previous wooded pastures that have become species-rich communities appearing as islands in agricultural landscapes, varying in species composition. Actaea spicata is a long-lived plant occurring in these forests. In 150 populations in a 10-km2 area, I studied pre-dispersal seed predation, seed dispersal and pollination. I investigated spatio-temporal dynamics of a tritrophic system including Actaea, a specialist seed predator, Eupithecia immundata, and its parasitoids. In addition, effects of biotic context on rodent fruit dispersal and effects of flowering time and flower number on seed set, seed predation and parasitization were studied. Insect incidences of both trophic levels were related to resource population size and small Eupithecia populations were maintained by the rescue effect. There was a unimodal relationship between seed predation and plant population size. Seed predator populations frequently went extinct in small plant populations, resulting in low average seed predation. Parasitoids were present in large plant populations but did not affect seed predator density. Seed predators aggregated at edges, relaxing seed predation in patch interiors. Flowering phenology was unrelated to seed set and insect incidence. A higher flower number did not influence seed predation but was associated with higher seed set and a tendency for a higher parasitization rate. In the study on fruit dispersal more fruits were removed inside than outside populations. Within plant populations more fruits were removed from large aggregations. Overall, this thesis underlines the importance of plant-animal interactions during different phases of the life cycle. The spatial configuration of host plants plays an important role for the outcome of plant-animal interactions and trophic cascades.

No description available.

Submitted by Edineia Teixeira (edineia.teixeira@unioeste.br) on 2018-03-05T18:57:19Z No. of bitstreams: 2 Andre _Xavier2016.pdf: 898699 bytes, checksum: d75d5de091bdf6639454359b01d27f0a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-03-05T18:57:19Z (GMT). No. of bitstreams: 2 Andre _Xavier2016.pdf: 898699 bytes, checksum: d75d5de091bdf6639454359b01d27f0a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-04-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Trophic relationships are central themes in ecology, and the interaction between predators and prey is one of the main topics addressed on the balance of relationships. These questions are very discussed associated with impacted environments with differentiated characteristics such as hydroelectric plant reservoirs, whose damming affects the forms of trophic interactions of the remaining post-dam species. About the interactions of predation, it is known that some abiotic factors such as temperature and water transparency participate in the mediation of foraging, which may favor predatory success and increases in the proportion of predators in relation to prey. For this reason, considering that excessive increases of predators may threaten the trophic balance of communities, as well as environmental exclusions presented by impacted systems such as reservoirs, this study evaluated through logistic models, if during a period of 36 months thermal elevations and visibility Of the water corresponded to increases in the proportion of piscivorous fish in relation to non piscivorous fish, taking as reference 17 neotropical reservoirs. The results showed an increase of about 14% in the proportion of piscivorous when correlated to higher values of temperature and transparency acting together, indicating that small positive changes in these variables may be sufficient to increase the proportion of these predators. The discussions focused on the relationships between environmental variables and predatory events. / Relações tróficas fazem parte de temas centrais em ecologia, e a interação entre predadores e presas é um dos principais assuntos abordados acerca do equilíbrio destas relações. Estas questões são bastante discutidas associando ambientes impactados e de características exclusivas como os reservatórios de usinas hidrelétricas, cujo represamento afeta as formas de interações tróficas das espécies remanescentes pós-barragem. Sobre as interações de predação, sabe-se que alguns fatores abióticos como a temperatura e transparência da água participam na mediação do forrageio, podendo favorecer sucesso predatório e aumentos na proporção de predadores em relação às presas. Por esta razão, considerando que aumentos excessivos de predadores possam ameaçar o equilíbrio trófico das comunidades, bem como exclusividades ambientais apresentadas por sistemas impactados como reservatórios, este estudo avaliou através de modelos logísticos, se durante um período de 36 meses as elevações térmicas e na visibilidade da água corresponderam a aumentos na proporção de peixes piscívoros em relação aos não piscívoros, tomando como referência 17 reservatórios neotropicais. Os resultados constataram aumento de cerca de 14% na proporção dos piscívoros quando correlacionada aos valores mais elevados de temperatura e transparência atuando em conjunto, evidenciando que pequenas alterações positivas nestas variáveis podem ser suficientes ao aumento da proporção destes predadores. As discussões focaram-se às relações entre as variáveis ambientais e eventos predatórios.

Trophic downgrading of ecosystems necessitates a functional understanding of trophic cascades. Identifying the presence of cascades, and the mechanisms through which they occur, is particularly important for seagrass meadows, which are among the most threatened ecosystems on Earth. Shark Bay, Western Australia provides a model system to investigate the potential importance of top-down effects in a relatively pristine seagrass ecosystem. The role of megagrazers in the Shark Bay system has been previously investigated, but the role of macrograzers (i.e., teleosts), and their importance relative to megagrazers, remains unknown. The objective of my dissertation was to elucidate the importance of teleost macrograzers in transmitting top-down effects in seagrass ecosystems. Seagrasses and macroalgae were the main food of the abundant teleost Pelates octolineatus, but stable isotopic values suggested that algae may contribute a larger portion of assimilated food than suggested by gut contents. Pelates octolineatus is at risk from numerous predators, with pied cormorants (Phalacrocorax varius) taking the majority of tethered P. octolineatus. Using a combination of fish trapping and unbaited underwater video surveillance, I found that the relative abundance of P. octolineatus was greater in interior areas of seagrass banks during the cold season, and that the mean length of P. octolineatus was greater in these areas compared to along edges of banks. Finally, I used seagrass transplants and exclosure experiments to determine the relative effect of megagrazers and macrograzers on the establishment and persistence of three species of seagrasses in interior microhabitats. Teleost grazing had the largest impact on seagrass species with the highest nutrient content, and these impacts were primarily observed during the warm season. My findings are consistent with predictions of a behaviorally-mediated trophic cascade initiated by tiger sharks (Galeocerdo cuvier) and transmitted through herbivorous fishes and their predators.

Depuis le début du 20ième siècle, les changements d'usage des terres, la disparition des prédateurs et les régulations de la chasse ont provoqué une augmentation des populations de cervidés dans les forêts tempérés et boréales. Ce phénomène, qui est un grand succès de la conservation de ces espèces, a toutefois conduit à des surabondances qui ont entrainé des effets négatifs en cascades sur la végétation et les communautés animales qui en dépendent.J'ai utilisé l'expérience naturelle qu'est l'introduction du cerf à queue noire sur l'archipel d'Haïda Gwaii pour étudier les conséquences de sa surabondance sur un écosystème tempéré peu perturbé par les activités anthropiques. J'ai ainsi pu mettre en évidence les contrôles descendants directs et indirects qu'exerce l'herbivore sur les Bryophytes (positifs), les plantes vasculaires (négatifs) et sur l'avifaune (négatifs) quand il n'est pas limité par les prédateurs ou la chasse.J'ai complété ces résultats par une analyse régionale sur 20 ans pour montrer que la perte de biodiversité enclenchée par la surabondance de ces cerfs était un phénomène d'érosion continu se prolongeant bien au-delà de l'impact initial. A l'échelle de l'Amérique du Nord, j'ai ensuite pu montrer, conformément aux prédictions faite à partir des études locales, qu'il existait une relation entre surabondance des populations d'ongulés et déclin de l'avifaune du sous-bois du continent. Enfin, j'ai analysé les suivis d'une expérience de réduction des densités de cerfs entamée sur deux îles il y a 13 ans. La végétation et l'avifaune se sont partiellement reconstituées démontrant qu'il est possible (1) de restaurer les réseaux trophiques fortement modifiés et (2) qu'une telle restauration si elle est possible prendra du temps et ne convergera pas (rapidement) vers un état initial. Afin de limiter les conséquences dommageables provoquées par la surabondance des cervidés, la conservation des prédateurs et l'augmentation de la chasse doivent être favorisés. / Since the past century land use changes, elimination of predators and hunting regulations triggered an increase of deer populations in temperate and boreal forests. This remarkable conservation success, lead to deer overabundance and to a cascade of negative effects on vegetation and on animal communities depending on it. I used the natural experiment provided by the introduction of black-tailed deer to Haida Gwaii to analyze the consequences of overabundant herbivore populations on temperate ecosystem only slightly modified by human activities. This unique situation allowed me to demonstrate the direct and indirect top-down effects that herbivores uncontrolled by predation or hunting exert on Bryophytes (positive) and Vascular plants (negative) as well as on songbirds (negative).I used an analysis of regional trends spanning over 20 years to show that biodiversity erosion caused by overabundant deer extends far beyond the initial impact. At the North-American scale I was able to establish a relationship between expanding deer populations and continent wide declines in understory birds. Finally I analyzed the results of an experimental reduction in deer populations initiated 13 years ago on two islands. The understory plants and songbirds responded positively and we show that (1) it is possible to restore trophic networks even after their dramatically modification, (2) that such a restoration while possible takes time and does not (rapidly) converge towards an identified initial state. From a practical standpoint I recommend that to mitigate negative effects of overabundant deer, predator conservation and hunting have to be promoted.

<p>I have, in this thesis, studied the interactions between gray-sided voles (Clethrionomys rufocanus) and tundra vegetation, on islands in, and mainland sites close to the lake Iešjávri, in northern Norway. As isolated islands are virtually free of predation, I have been able to compare plant-herbivore interactions in the presence and absence of predators. I transplanted vegetation from an island with predators and voles, to predator-free islands with and with out voles. The results reveal the existence of a terrestrial trophic cascade as voles had a severe impact on the transplanted vegetation on the predator-free islands, but only minor effects on the mainland where predators are present. Moreover, this study shows that plant defence was only a successful strategy when predators were present. Voles reduced the abundance of all available plants during winter on the predator-free islands. The results imply that cascading effects of predation are most important for well-defended plants with grazing-sensitive morphology as these plants escape herbivore impacts in the presence of predators but are vulnerable in their absence</p><p>I studied the recovery of intensively grazed vegetation by building exclosures on islands that have been heavily grazed by voles for almost a decade.This study shows that the collective biomass of vascular plants recovered completely on three years, when voles were excluded. Although most species that are dominating the ungrazed vegetation recovered rapidly in the exclosures, the vegetation did not simply return to its ungrazed state. Herbaceous plants increased and there were pronounced differences in response among evergreen dwarf-shrub species. The semi-prostrate and tannin rich crowberry (Empetrum nigrum), showed the strongest recovery of all species, while the erect lingonberry (Vaccinium vitis-idaea) only showed weak signs of recovery. Thus, growth form determined the potential of plants to recover, whereas the trade-off between defensive investments and capacity to recover was weak or absent.</p><p>I studied the interaction between gray-sided voles and their main winter food plant, bilberry (Vaccinium myrtillus) on islands in and mainland sites close to the lake Iešjávri. I compared the abundance, population structure and palatability of bilberry ramets between vole-free islands, islands with voles but no predators and mainland sites with both voles and predators. Voles decreased the abundance of bilberry on the mainland, but the effect was much stronger on predator-free islands. Bilberry was fairly tolerant to grazing as it partially compensated for the lost tissue by producing more new ramets. Moreover, a cafeteria experiment showed that voles preferred the ramets from predator-free islands, which is inconsistent with conjectures emphasizing inducible plant defenses. The vole-bilberry interaction lacks features of delayed density dependence that could explain the vole cycles. I conducted a clipping and fertilization experiment to further investigate the effects of herbivory on palatability of bilberry shoots. Fertilization decreased the concentration of condensed tannins in shoots of bilberry and voles preferred fertilized and clipped shoots. I found no indication of induced defense that could reduce the palatability of bilberry twigs in response to herbivory.</p><p>The relationships between gray-sided vole densities, levels of invertebrate herbivory and chemical quality of leaves of Northern willow (Salix glauca) were studied on islands and mainland sites with contrasting vole densities. I found a positive correlation between level of invertebrate herbivory and vole density. The number of leaves per shoot, leaf size and leaf nitrogen content were also positively correlated with vole densities, while leaf C/N ratios were negatively correlated with vole densities. The positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry.</p>

I have, in this thesis, studied the interactions between gray-sided voles (Clethrionomys rufocanus) and tundra vegetation, on islands in, and mainland sites close to the lake Iešjávri, in northern Norway. As isolated islands are virtually free of predation, I have been able to compare plant-herbivore interactions in the presence and absence of predators. I transplanted vegetation from an island with predators and voles, to predator-free islands with and with out voles. The results reveal the existence of a terrestrial trophic cascade as voles had a severe impact on the transplanted vegetation on the predator-free islands, but only minor effects on the mainland where predators are present. Moreover, this study shows that plant defence was only a successful strategy when predators were present. Voles reduced the abundance of all available plants during winter on the predator-free islands. The results imply that cascading effects of predation are most important for well-defended plants with grazing-sensitive morphology as these plants escape herbivore impacts in the presence of predators but are vulnerable in their absence I studied the recovery of intensively grazed vegetation by building exclosures on islands that have been heavily grazed by voles for almost a decade.This study shows that the collective biomass of vascular plants recovered completely on three years, when voles were excluded. Although most species that are dominating the ungrazed vegetation recovered rapidly in the exclosures, the vegetation did not simply return to its ungrazed state. Herbaceous plants increased and there were pronounced differences in response among evergreen dwarf-shrub species. The semi-prostrate and tannin rich crowberry (Empetrum nigrum), showed the strongest recovery of all species, while the erect lingonberry (Vaccinium vitis-idaea) only showed weak signs of recovery. Thus, growth form determined the potential of plants to recover, whereas the trade-off between defensive investments and capacity to recover was weak or absent. I studied the interaction between gray-sided voles and their main winter food plant, bilberry (Vaccinium myrtillus) on islands in and mainland sites close to the lake Iešjávri. I compared the abundance, population structure and palatability of bilberry ramets between vole-free islands, islands with voles but no predators and mainland sites with both voles and predators. Voles decreased the abundance of bilberry on the mainland, but the effect was much stronger on predator-free islands. Bilberry was fairly tolerant to grazing as it partially compensated for the lost tissue by producing more new ramets. Moreover, a cafeteria experiment showed that voles preferred the ramets from predator-free islands, which is inconsistent with conjectures emphasizing inducible plant defenses. The vole-bilberry interaction lacks features of delayed density dependence that could explain the vole cycles. I conducted a clipping and fertilization experiment to further investigate the effects of herbivory on palatability of bilberry shoots. Fertilization decreased the concentration of condensed tannins in shoots of bilberry and voles preferred fertilized and clipped shoots. I found no indication of induced defense that could reduce the palatability of bilberry twigs in response to herbivory. The relationships between gray-sided vole densities, levels of invertebrate herbivory and chemical quality of leaves of Northern willow (Salix glauca) were studied on islands and mainland sites with contrasting vole densities. I found a positive correlation between level of invertebrate herbivory and vole density. The number of leaves per shoot, leaf size and leaf nitrogen content were also positively correlated with vole densities, while leaf C/N ratios were negatively correlated with vole densities. The positive correlation between vole densities and level of invertebrate herbivory is probably due to a facilitative effect of voles on invertebrate herbivores, mediated through changes in plant chemistry.

No description available.