No description available.

No description available.

No description available.

There has been a global decline of specialist species observed in recent decades due to the impacts of climate change, invasive species, and habitat loss. Habitat loss and degradation may lead to a mismatch between habitat attractiveness and actual quality, otherwise known as an ecological trap. Ecological traps occur when an organism is constrained by its evolutionary past to select for cues that no longer accurately predict habitat quality. Specialist species are more susceptible to ecological traps due to greater reliance on and fidelity to historic sites and resources. The burrowing owl (Athene cunicularia), a specialist bird species adapted to open ecosystems, has declined throughout its extent. Anthropogenic activity has drastically and rapidly altered burrowing owl native habitat, exposing their habitat to disturbances such as cheatgrass (Bromus tectorum) invasion. The presence of cheatgrass is known to impact the biota of a region and understanding those impacts is becoming increasingly important. The purpose of this study was to quantify the impact of cheatgrass on burrowing owl populations. By assessing how cheatgrass influences the resource selection, nesting success, and food habits of burrowing owls, we provided information that can be utilized to make more informed decisions on how to conserve burrowing owls and their critical nesting habitat. In addition, this information can provide insight into the risk of ecological traps occurring to all specialist species experiencing degradation of their native habitat.

Orientador: Gustavo Quevedo Romero / Banca: Lilian Casatti / Banca: Simone Aparecida Vieira / Resumo: É amplamente sabido que os subsídios alóctones entram nas teias alimentares receptoras participando diretamente da dinâmica dos consumidores e indiretamente sobre as interações predador-presa. No entanto, este conhecimento se baseia em estudos feitos em florestas temperadas e por conseguinte ainda há lacunas no conhecimento dos sistemas tropicais, onde a abundância e variedade das presas é maior. Neste trabalho, buscamos descrever o efeito dos insetos aquáticos emergentes sobre a dinâmica predador-presa das teias alimentares terrestres presentes em zonas ripárias de uma floresta tropical. Para testar este efeito, utilizamos um desenho experimental de blocos aleatorizados. Deste modo, manipulamos a emergencia de insetos adultos de um riacho, utilizando um tratamento de exclusão com uma cobertura plástica sobre o riacho e um tratamento de controle, onde permitimos a emergência natural dos insetos para a terra. Amostramos os insetos aquáticos emergentes com armadilhas adesivas e os artrópodes terrestres (predadores, fitófagos, onívoros, detritívoros) usando diversos métodos. A abundância de insetos aquáticos emergentes foi cinco vezes menor no tratamento de exclusão do que no tratramento de controle, mas como esperado, não houve diferenças nas abundâncias de insetos alados terrestres entre os tratamentos; insetos terrestres foram três vezes mais abundantes que os insetos aquáticos emergentes. PERMANOVA revelou que a abundância de predadores terrestres foi afetada pelo tratamento de exclusão de subsídios, mas não a biomassa. No entanto, análises univariadas mostraram que apenas 11,5% dos taxons de predadores (Anyphaenidae, Araneidae e Theridiidae) diminuíram sua abundância no tratamento de exclusão e o 7,7% deles (Araneidae e Theridiidae) diminuíram sua biomassa na exclusão. A abundância dos fitófagos, detritívoros e onívoros não foi afetada pela exclusão de subsídios, mas a biomassa dos fitófagos ... / Abstract: It is widely known that input of allochthonous subsidies in recipient food webs directly participate in the dynamics of consumers and indirectly on predator-prey interactions. However, this knowledge is based on studies from temperate forests, thus there is still a gap in the knowledge of tropical systems where the abundance and diversity of terrestrial prey is high. In this study, we investigate the effects of emergent aquatic insects on predator-prey dynamics of tropical terrestrial food webs. To test this effect, we excluded allochthonous aquatic insects using greenhouse type exclosures, and allowed emergence of insects through unmanipulated stream reaches using a randomized design. Emergent aquatic insects and terrestrial flying insects were collected through sticky traps. Terrestrial arthropods in shrubs and ground were collected manually in nocturnal and diurnal surveys, and were classified in predators, phytophages, detritivores and omnivores. The abundance of aquatic insects was five times lower in exclosures than control, but there was no effect of treatment on abundance of terrestrial fly insects; abundance of terrestrial insects were three times more abundant that aquatic insects. PERMANOVA revealed that abundance of terrestrial predators, but not their biomass, was affected by exclosure treatment. Univariate analysis show that only 11.5% of predatory taxa (Anyphaenidae, Araneidae and Theridiidae) decreased its abundance in exclosure treatment and only 7.7% of them (Araneidae and Theridiidae) decreased its biomass. Abundance of phytophages, detritivores and omnivores was not affected by treatments, but the biomass of phytophages increased six times in exclosure treatment. Despite the abundance and biomass of only few predators were affected by exclosure, we observed that predators overall derived more than 80% of N and C of aquatic prey. Our results demonstrate that allochthonous subsidies participate on terrestrial food web ... / Mestre

The prey consumption by benthivorous fish predators can have profound top-down effects in stream food webs. To analyse this effects in small temperate stream ecosystems, a long-term field experiment was conducted in two streams in South-eastern Germany, Gauernitzbach and Tännichtgrundbach, from 2004 to 2011. The densities of two small-bodied benthivorous fish species, gudgeon (Gobio gobio) and stone loach (Barbatula barbatula), were manipulated following a Before-After-Control-Impact design. The top predator regime affected the benthic community composition of the streams mainly in pools, whereas the total benthic invertebrate biomass was not affected in any mesohabitat. The present work describes a causal analysis of the observed food web effects using additional field analyses and laboratory experiments, with a special focus on the habitat use and foraging behaviour of the fish as top predators. The probably most important of the analysed mechanisms was mesohabitat-specific predation by the fish. Three 24-h field video surveys combined with benthic invertebrate sampling showed that constraints in habitat use, especially for gudgeon, induced a differential predator-prey habitat overlap which resulted in a higher predation risk for the invertebrate prey in pools than in riffles. Another important mechanism was selective predation of both fish species. Their prey selectivity was largely explained by a small number of prey variables being connected to the partly non-visual foraging mode of these benthic predators. Besides the traits body size and feeding type, long-term mean abundance played a central role, small and highly abundant invertebrates, grazers and sediment feeders being preferred by gudgeon and stone loach. The preference for small and abundant prey taxa (chironomids) exceeded purely opportunistic feeding and probably facilitated resource partitioning between the two fish species having very similar diets. In addition to active selectivity, different predator avoidance strategies of the invertebrates analysed in laboratory experiments explained the passive selectivity of the fish predators for certain prey taxa in the streams. This could be shown for two abundant taxa being consumed by the fish predators in very different quantities, Gammarus pulex and Hydropsyche instabilis. These three mechanisms, although probably interacting with several other factors, could explain a large part of the effects the top-down food web manipulation had on the benthic community, especially the observed high degree of mesohabitat and species specificity. Confirming this, quantitative characteristics of predation food webs, for instance the importance of intraguild predation, differed markedly between pool and riffle mesohabitats. From the results of this study it can be concluded that the benthivorous fish affected benthic community structure mainly by mesohabitat-specific and selective predation. A manipulation of this (native) top predator type therefore will probably have such rather subtle but not catastrophic consequences in ecosystems with a high biotic diversity and a rich natural habitat structure and connectivity.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The fynbos eco-region in the Western Cape lowlands has been extensively transformed by anthropogenic activities such as agriculture and urban development, as well as invasive alien plants. Elandsberg Private Nature Reserve and Farms lies on Swartland Alluvium Fynbos and has been largely fragmented by agricultural crop production, whilst Riverlands Nature Reserve together with the Pella Research Site, which lie on Atlantis Sand Fynbos, are under severe threat from the invasive woody alien Port Jackson Willow (Acacia saligna) which forms dense stands in the lands adjacent the nature reserve. Habitat transformation has resulted in subsequent loss of habitat and a reduction in habitat value for small mammal communities by creating a mosaic of optimal and sub-optimal habitats. The success of A. saligna is, in part, attributed to its production of copious amounts of small hard-shelled seeds and well established soil seed banks. In the first part of this study we investigated the effect of habitat transformation on resident small mammal communities by comparing small mammal species richness, diversity and abundance between natural and transformed habitats as well as between the two vegetation types. We also investigated the population demographics of the striped mouse (Rhabdomys pumilio) in the different habitats. Our study shows that whilst fragments of natural habitats, especially at Riverlands and Pella, may be playing an important role in harbouring rare and possibly endangered species, transformed habitats are also important as secondary habitats providing both cover as well as seasonal food resources. Reproduction and body condition in R. pumilio were dependent on seasonal changes such as availability of water and food resources in the habitats. The second part of this study was carried out to investigate the effect of alien plant invasion on the resident small mammal communities at Riverlands Nature Reserve and to determine the role of small mammals in the removal and predation of A. saligna seeds. Rodent species richness, diversity and abundance were very low in the A. saligna stands compared to the adjacent fynbos vegetation. The interaction of rodents with seeds (removal or predation) was dependent upon seed size and seed abundance in the habitats. Whilst rodents may play an important role in predator limitation in the acacias, it is also possible that they may be playing a significant role in dispersing the seeds of acacias into the fynbos. More work is required to fully understand the role small mammals play in seed predation, dispersal and limitation in alien invaded fynbos systems.

abstract / Biological Sciences / Doctoral / Doctor of Philosophy

Predicting the impacts of non-native species remains one of the greatest challenges to invasion ecologists. Because of their insularity, freshwater systems are particularly vulnerable to invasions, especially from non-native predators. The research in this thesis explores the role of abiotic and biotic factors in mediating the distribution and impact of Bythotrephes longimanus, a predatory cladoceran that has been introduced to freshwater systems in North America. Although the general impacts of this invasion have been documented, little is known about the factors that modulate them. Using a combination of field surveys and experiments, I tested several hypotheses concerning the influence of interactions with native species, as well as the role of heterogeneity in the light environment, in mediating the impact of Bythotrephes. Results demonstrated that biotic resistance by native macroinvertebrate predators does not play a limiting role in the establishment success of Bythotrephes. However, the within-lake distribution of Bythotrephes was influenced by these macroinvertebrates, suggesting that the native predator context matters when trying to understand the impacts of non-native predators. This was demonstrated with a mesocosm experiment in which the impact of Bythotrephes was constrained by the native Chaoborus larvae. In terms of the abiotic environment, in situ feeding experiments demonstrated that refuges from impact could exist for some prey taxa, as the outcome of predation by Bythotrephes was dependent on light availability and some prey taxa were more successful at evading predation under low light conditions. Finally, results show that adaptive behaviour by prey is also an important determinant of impact, as migrating Daphnia can escape predation effects by Bythotrephes. The combination of light-limited predation and a shallow distribution by Bythotrephes selects for prey that occupy relatively deeper positions during the day. As a whole, this research highlights the importance of complex interactions in mediating the impact of Bythotrephes and may help to explain some of the variation that has been documented among invaded lakes. A better understanding of these complex interactions can improve our ability to anticipate impacts as Bythotrephes continues to spread, as well as provide insight on some of the long-term effects following invasion. / Thesis (Ph.D, Biology) -- Queen's University, 2013-06-17 09:26:35.221

En Afrique de l'Ouest, le moustique An. gambiae s.s vecteur majeur du paludisme est subdivisé en deux formes moléculaires, M et S, génétiquement et écologiquement différenciées. La forme moléculaire M se développe préférentiellement dans des collections d'eau pérennes en zone aride, généralement d'origine anthropique, permettant sa présence tout au long de l'année alors que la forme S se reproduit principalement dans des gîtes temporaires de savane humide dépendant des précipitations et disparaît en saison sèche. Cette subdivision génère des profils de dynamique de transmission palustre différents en fonction des zones où ces formes sont implantées. Dans ce contexte, cette thèse a pour objectif l'étude des facteurs écologiques de différenciation entre M et S, en se focalisant notamment sur leur écologie larvaire, afin de mieux appréhender leur distribution actuelle et future. L'étude de la distribution des populations naturelles de ces vecteurs dans une zone d'endémie palustre au Burkina Faso a permis de mettre en évidence que les niches écologiques de ces deux formes sont en étroite corrélation avec la temporalité des milieux aquatiques et la complexité des écosystèmes qu'ils hébergent. La forme M apparaît clairement liée aux habitats permanents anthropiques et à la structure des communautés qu'ils soutiennent alors que la forme S ainsi que l'espèce jumelle An. arabiensis sont associées aux habitats simples et temporaires, majoritairement retrouvés en zone rurale de savane.Cette distribution des deux formes le long d'un gradient d'hydropériode est en accord avec les interactions dominantes et les adaptations qu'elles induisent afin de pouvoir exploiter ces milieux. La forme S, associée aux milieux temporaires, s'est révélée plus compétitive que la forme M en diminuant son temps de développement larvaire en présence de compétiteurs (forme M). L'étude de la pression de sélection due à la prédation, interaction dominante dans les milieux permanents, démontre que la forme M est moins susceptible que la forme S. L'analyse du comportement larvaire a permis de mettre en évidence des différences entre ces deux formes, notamment l'existence d'un comportement plus plastique chez la forme M qui réduit son activité en présence d'un prédateur. Ce mécanisme est une des adaptations qui a favorisé le succès d'An.gambiae dans les milieux permanents.Notre approche, basée sur l'écologie larvaire des formes M et S d'An. gambiae nous a permis de mieux comprendre les processus par lesquels ces vecteurs ont évolué et se sont adaptés à différents contextes écologiques. Ces adaptations reflètent la spécialisation de ces deux formes dans leur milieu respectif et permettent en partie d'expliquer la ségrégation écologique observée sur le terrain. L'amélioration de nos connaissance sur la bio-écologie de ces vecteurs est primordiale afin d'en apprécier le potentiel évolutif dans le contexte actuel des changements globaux. / In West Africa, the main Malaria vector, the mosquito Anopheles gambiae is actually subdivided into two molecular forms named M and S, which can be genetically and environmentally differentiated. The M form preferentially breeds in permanent freshwater collections mainly resulting from human activity and is reproductively active all year round, whereas the S form thrives in temporary breeding sites and is present during the rainy season only. This subdivision generates different dynamics of Malaria transmission in areas where these forms are found. In this context, this thesis aims to study the ecological factors of differentiation between M and S, focusing on their larval ecology to better understand their current and future distribution.The study of the distribution of natural populations of these vectors in an endemic area in Burkina Faso has provided evidence that the ecological niches of these forms are closely correlated with the degree of temporality and the community complexity of aquatic ecosystems. The M form is clearly linked to permanent anthropogenic habitats and the structures they support, while the S form and its sibling species An. arabiensis are associated with simple and temporary habitats, mostly found in rural savannas.The distribution of the two forms along a hydroperiod gradient is consistent with the dominant interactions and adaptations they induce in order to be able to exploit their environments. In relation to temporary habitat, the S form was more competitive than the M form by reducing its larval development time in the presence of competitor (M form). The study of selection pressure due to predation, dominant interaction in permanent habitat, shows that the M forms suffer lesser predation rate than the S form. Analysis of larval behavior highlighted differences between these two forms, such as the existence of a more plastic behavior in the form M, which reduced its rate of activity in predator presence. This mechanism is one of the adaptations that have facilitated the success of An. gambiae in permanent aquatic habitats.Our approach, based on the larval ecology of M and S forms of An. gambiae has enabled us to better understand the processes by which these vectors have evolved and adapted to different ecological contexts. These adaptations reflect the specialization of these two forms in their respective habitats and can partially explain the ecological segregation observed in the field. Improving our knowledge on bio-ecology of these vectors is essential to appreciate their evolutionary potential in the current context of global change.