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<p>Dans ce travail, les préférences alimentaires pour les espèces végétales consommées par les lombriciens peuplant certains îlots des pelouses de l’avenue Roosevelt ont été étudiées. L’analyse des contenus digestifs et des fèces des vers a montré que les plantes identifiées dans les pelouses ne sont pas toutes consommées.<br> Mesurée par l’indice d’Ivlev, la sélectivité des items végétaux est variable en fonction de l’espèce de ver, de la classe d’âge et de la saison. Lorsque les dicotylédones sont en plein développement au printemps et en été, les choix des vers sont surtout manifestés pour les monocotylédones. En automne et en hiver, les monocotylédones prédominent et, les dicotylédones se retrouvant dans la litière, font l’objet de préférences marquées qui induisent des rejets relatifs de monocotylédones. Bien que Lolium perenne soit la plante la plus consommée, Bellis perennis est la dicotylédone la plus appréciée, Trifolium repens et Poa trivialis étant les plantes généralement rejetées.<br> L’indice d’Ivlev n’ayant permis de connaître que les rangs de préférences des différentes espèces végétales, les analyses ont été complétées par des tests du χ² qui ont montré que la consommation des plantes par les vers ne se fait pas au hasard. <p>Les épigés Satchellius mammalis et Lumbricus rubellus sont les espèces qui présentent le taux le plus élevé de matière organique figurée (respectivement 27 % et 26 % [19 % chez les jeunes Lumbricus spp]) dans leurs contenus digestifs. Chez les anéciques Aporrectodea longa et Lumbricus terrestris, ces taux sont très faibles (respectivement 6 % [2 fois plus chez les jeunes vers] et 11 %). Les endogés (Aporrectodea caliginosa, A. icterica et A. rosea) présentent des taux variant respectivement de 21 % [9 % chez les jeunes vers] à 8 % et 11 %. <p>L’axe de la taille des particules consommées n’a pas permis une ségrégation des niches (d’après notre étude, la taille des vers n’affecte pas celle des particules ingérées), mais l’axe de la nature des particules consommées est plus discriminant. Dans la niche tridimensionnelle (taille et nature des particules ingérées, notre étude, et les cycles annuels d’activité [Tiho, 2001]), le seul recouvrement fort qui se maintienne est celui de la niche de L. rubellus sur celle de L. terrestris. Un recouvrement marginal (α = 0,66) est observé, celui de la niche de A. longa sur celle de L. terrestris. Ceci révèle une compétition interspécifique entre ces trois espèces ayant des régimes alimentaires très proches. <p> <p>In this study, preferences for plants consumed by earthworms inhabiting certain islets of the Roosevelt avenue lawns have been studied. Examination of gut contents and faeces showed that not all of the plants identified in the lawns are consumed.<br> Measured by the Ivlev’s electivity index, the selectivity of plants is variable according to the earthworm species, its size class and the season. When the dicotyledons are developing in spring and in summer, the choices of the earthworms are particularly observed for the monocotyledons. In autumn and winter, the monocotyledons are developing and the dicotyledons in the litter are highly chosen, leading the relative reject of the monocotyledons.<br> Although Lolium perenne is the most consumed plant, Bellis perennis is the most appreciated dicotyledon, Trifolium repens and Poa trivialis being generally rejected.<br> As the Ivlev’s index of preference has only permit to know the rank of preference of the different plants, the analysis was completed by the χ² tests which demonstrated that the consumption of plants by earthworms is not done randomly. <p>The epigées Satchellius mammalis and Lumbricus rubellus are the species which present the highest rate of organic matter (respectively 27 % and 26 % [19 % for the immatures Lumbricus spp] in their gut contents.<br> For the anéciques Aporrectodea longa and Lumbricus terrestris, these rates are very low (respectively 6 % [twice more for the immatures worms] and 11 %).<br> The endogées (Aporrectodea caliginosa, Aporrectodea icterica and Aporrectodea rosea) present rates varying respectively from 21 % [9 % for the young worms] to 8 % and 11 %. <p>The axis of the particles size ingested did not permit the niches segregation (in our study, the earthworms size does not affect the size of the particles ingested), but the axis of the nature of the particles ingested is more discriminant. In the three-dimensional niche (size and nature of particles ingested [our study] and the annuals cycles of activity [Tiho, 2001]), the young worms not being considered, only one high overlap is maintained, that of L. rubellus niche on that of L. terrestris. A marginal overlap (α = 0.66) is observed, that of A. longa niche on that of L. terrestris. Having a similar trophic resource (consumption of litter), an interspecific competition must exist between these three species for the access to the food.

A research report submitted to the Faculty of Science, University of Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science (Resource Conservation Biology). Johannesburg, 2015 / The vegetation of the Kgaswane Mountain Reserve, in North West Province, South Africa, was mapped according to seven vegetation structure types, based on tree density and height, and grass height. Free-living ticks were collected by drag-sampling the vegetation from each structure type in November 2014, prior to the onset of the summer rains, and February 2015, once most of the seasonal rains had fallen. Eland (Taurotragus oryx) location information was recorded from four GPS collared cows over the two sample periods. Tick abundance was consistently lower in shorter, open, more exposed vegetation structure types, and higher in more sheltered types. Position higher up in the landscape nullified the positive impacts of trees on beneath-canopy microclimate in tall open woodlands, as indicated by comparatively lower tick numbers than in more sheltered woodland types. Tick abundance is influenced by vegetation structure and the availability of hosts. The majority of ticks trapped during both periods were larvae, with nymphs mostly present in November and adults mostly present later in the season, indicating the seasonal nature of tick cohort recruitment. Eland calving behaviour centred on areas with low adult tick abundance. Eland did not respond to total tick abundance during either sampling period. They did select areas with low adult tick abundance, and avoided areas with high adult tick abundance. This corresponded with an improvement in upland forage quality, which allowed them to avoid foraging in areas with high adult tick abundance. It is plausible that the potential for infestation by adult ticks may be a supplementary influence driving the use of space by eland.

How so many species coexist while utilizing the same resources is both of ecological interest and important for the management of wildlife communities and parks. This thesis endeavours to understand how grazing herbivores co-exist, with special emphasis on understanding the mechanisms of competition and facilitation over temporal and spatial scales. I compared the dry season use of grasslands, grass species, grass height and grass greenness by white rhino and three other ungulate species, zebra, wildebeest, and impala. I was specifically interested in the extent to which white rhinos, with their capacity to graze both short and tall grass, either competed with or facilitated other grazers. In Chapter Two, I clarify the mechanisms of facilitation and competition in terms of temporal and spatial scales, and discuss why there is little evidence in the literature to support these mechanisms. I conclude that evidence for facilitation through stimulation of grass re-growth during the growing season appears stronger than that for increased resource access through removal of obstructing grass structures during the dormant season. Facilitation may benefit the nutritional gains obtained by certain species in the short term, but these benefits do not appear to be translated into the expected population consequences. In collaboration with co-author Norman Owen-Smith, we suggested this could be due to seasonal tradeoffs between facilitation and competition, as well as to restrictions on the spatial extent of trophic overlap. In Chapter 3 Norman Owen-Smith and I compared the grass height use in relation to body size. We expected that the grass height favoured would increase with the body size of the herbivore species, as suggested from past studies of resource partitioning among large mammalian herbivores. Instead we found that the largest of these species, white rhino, concentrated on the shortest grass, while the smallest species, impala, favoured grass heights intermediate between those grazed by wildebeest and zebra. Results suggest that the scaling of mouth width relative to body size, and hence metabolic demands, is the primary factor governing grass height selection, rather than body size alone. Hence grazing successions governed by body size differences may not be a typical feature of their ecology, contrary to past suggestions. Furthermore, there was considerable overlap in grass height grazed among these four species, indicating that niche separation by grass height is inadequate alone to explain their coexistence. More attention needs to be paid to other aspects such as the grass species selected and habitat structure favoured. Chapter Four compared the overlap in grassland use and grass species use, as well as grass height and grass greenness of swards utilized by the herbivores as the dry season advances. I show that all species prefer grazing lawns during times of abundance, and that zebra leave grazing lawns before other species, and wildebeest leave grazing lawns before white rhino and impala. This suggests zebra and wildebeest may be competitively excluded from grazing lawns through a reduction in grass height, by white rhino and impala, during the dry season. However, white rhino are also potentially the ‘supreme’ facilitator increasing the availability of nutritious grazing lawns, as well as increasing the quality of those lawns through grazing in the wet season. A better understanding of the trade-off between “habitat facilitation” and competitive exclusion by white rhino, allows us to better understand how grazing herbivores co-exist.

O objetivo deste estudo foi determinar a composição da ictiofauna de riachos da sub-bacia do Alto Jacuí, região centro-norte do Rio Grande do Sul, bem como descrever e compreender as relações que permeiam a biologia alimentar de espécies de Siluriformes e de Characidae nestes mesmos riachos. As coletas foram realizadas bimensalmente de julho de 2012 a junho de 2013, através da técnica de pesca elétrica em 10 riachos. Um total de 13.247 indivíduos foram coletados, pertencentes a 42 espécies, 10 famílias e seis ordens, das quais as que mais contribuíram foram Characiformes (36%), Cichliformes (24%) e Siluriformes (14%), com 15, dez e seis espécies respectivamente. Nós reportamos o primeiro registro de Phalloceros spiloura para o sistema da Laguna dos Patos e cinco espécies ficaram ao nível de gênero devido ao fato de se tratarem de novas espécies e estão sendo revisadas e descritas. O conteúdo estomacal de 1.948 indivíduos, pertencentes a três espécies (Heptapterus sp., Rhamdia quelen e Trichomycterus poikilos) foram analisados pelo método volumétrico, sendo 59 itens alimentares identificados. Em geral, Heptapterus sp. consumiu uma alta proporção de Aegla sp., restos de plantas terrestres e Megaloptera; R. quelen consumiu peixe e Oligochaeta, seguido de Aegla sp.; enquanto a dieta de T. poikilos foi baseada em Simuliidae, Ephemeroptera e Trichoptera. A segregação alimentar das espécies, bem como do fator espécie mais classe de tamanho, foram observadas. Os valores de amplitude de nicho foram altos para todas as espécies, e somente foram baixos para os maiores tamanhos de R. quelen e Heptapterus sp. No geral, as espécies mostraram baixos valores de sobreposição de nicho, e houve uma grande frequência de sobreposição alta e intermediária para as menores classes de tamanho. O modelo nulo confirmou a partição de nicho entre as espécies e uma partilha de recursos quando analisado espécie mais classe de tamanho. Posteriormente, 1.525 estômagos de 11 espécies de Characidae foram analisados. Observou-se uma diferença significativa entre a dieta dessas espécies, com plantas terrestres e aquáticas, restos de insetos terrestres e aquáticos e adultos de Hymenoptera, mostrando-se os itens mais importantes para esta diferenciação. As análises mostraram que os padrões de alimentação estão associados as características morfológicas. A posição subterminal da boca se correlacionou com a ingestão de itens bentônicos (insetos aquáticos e matéria orgânica); boca grande permitiu a ingestão de itens mais robustos como Aegla sp. e peixes; espécies com menor variação de dentes ao longo da série externa do prémaxilar consumiram elevada proporção de plantas e insetos terrestres, assim como as espécies que apresentaram menor número de dentes na maxila. O hábito insetívoro aquático foi observado nos indivíduos com números intermediários e altos de cúspides nos dentes do maxilar. Buscando compreender a coexistência de quatro espécies sintópicas de Characidae, nós calculamos a sobreposição de nicho das espécies por período amostral e para avaliar a importância destes itens alimentares como fontes de nutrientes nós usamos análises de isótopos de carbono (13C) e nitrogênio (14N) para estimar a assimilação relativa. Todos os Characidae consumiram grandes proporções de plantas e insetos aquáticos. As espécies apresentaram baixa sopreposição na maioria dos períodos amostrados. Também, houve uma alta correspondência entre a análise do conteúdo estomacal e o resultado da análise isotópica. Astyanax xiru e Astyanax procerus assimilaram grandes frações de invertebrados terrestres e plantas aquáticas. Bryconamericus iheringi assimilou principalmente invertebrados aquáticos e secundariamente algas, enquanto Bryconamericus sp. assimilou principalmente invertebrados aquáticos e terrestres. Assim, nós demonstramos que as espécies congenéricas têm dietas mais similares, mas que estas quatro espécies de Characidar coexistem por partição de recursos, e que a assimilação de nutrientes dessas espécies coincide com o consumo relativo dos itens alimentares ingeridos. / The objective of this study was to determine the composition of fishes of Alto Jacuí subbasin streams, north-central region of Rio Grande do Sul, as well as describe and understand the relationships that permeate the feeding biology of species of Siluriformes and Characidae in these same streams. Samples were collected bimonthly from July 2012 to June 2013, through electrofishing technique in 10 streams. A total of 13,247 individuals were collected, belonging to 42 species, 10 families and six orders, of which the most contributed, were Characiformes (36%), Cichliformes (24%) and Siluriformes (14%), with 15, ten and six species, respectively. We report the first record of Phalloceros spiloura to the Laguna dos Patos system and five species were to genus level due to the fact they refer to new species and are being reviewed and described. The stomach contents of 1,948 individuals belonging to three species (Heptapterus sp., Rhamdia quelen and Trichomycterus poikilos) were analyzed by volumetric method, with 59 identified food items. Overall, Heptapterus sp. consumed a high proportion of Aegla sp., remains of terrestrial plants and Megaloptera; R. quelen consumed fish and Oligochaeta, followed by Aegla sp.; while T. poikilos diet was based on Simuliidae, Ephemeroptera and Trichoptera. Food segregation of species as well as species plus size class factors, were observed. The niche breadth values were high for all species, and only were low for the larger sizes of R. quelen and Heptapterus sp. Overall, the species showed low niche overlap values, and there was a high frequency overlay high and intermediate for smaller size classes. The null model confirmed the niche partitioning among species and a sharing of resources when analyzed species plus size class. Subsequently, 1,525 stomachs were analyzed representing 11 species of Characidae. There was a significant difference between the diet of these species, with terrestrial and aquatic plants, terrestrial and aquatic insect remains and adult Hymenoptera, being the most important items for this differentiation. The analysis showed that feeding patterns associated with many morphological features. Sub-terminal mouth positions correlated with the ingestion of benthic items (e.g., aquatic insects and organic matter); large mouths permited ingestion of robust items such as macrocrustaceans (e.g., Aegla) and fish; species that have small teeth variation along the outer row of the premaxilla consumed high proportion of plants and terrestrial insects as well as those species that showed a lower number of teeth on the maxilla. Aquatic insectivory was observed in those individuals with intermediary and high number of cusps in the maxilla teeth. To understand the coexistence of four syntopic Characidae species we calculated niche overlap of species for each sampling period, and to evaluate the importance of these food items as nutrient sources, we used carbon (13C) and nitrogen (14N) isotopes analyses to estimate relative assimilation. All characids consumed large proportions of plant material and aquatic insects. The species showed low dietary overlap throughout most of the sampling period. There was high correspondence between the gut content analyses and isotope mixing model estimates. Astyanax xiru and Astyanax procerus assimilated large fractions of terrestrial invertebrates and aquatic plants. Bryconamericus iheringi assimilated primarily aquatic invertebrates and secondarily algae, whereas Bryconamericus sp. assimilated primarily aquatic and terrestrial invertebrates. Therefore, we demonstrate that the congeneric species have more similar diets, but that these four Characidae species coexist by resource partitioning, and that they assimilate nutrients agree with the relative consumption of food items.

Crested wheatgrass (Agropyron cristatum [L.] Gaertn.) is one of the most commonly seeded exotic species in the western United States. Although many degraded Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) plant communities have been seeded with crested wheatgrass during rehabilitation efforts, seed banks of these communities have not been characterized. I sought to characterize and explain the variation among 33 seeded communities in the northeastern Great Basin. Hierarchical clustering and principal components analysis identified four possible seed bank categories in these communities. Seed bank categories varied from high to low crested wheatgrass dominance. The crested wheatgrass-dominated category is a particularly attractive setting to develop management strategies that reduce crested wheatgrass dominance and increase native plant diversity. It is also a common practice to seed crested wheatgrass in mixture with native species after a disturbance to increase diversity. Empirical estimates as to how the density of crested wheatgrass seed and seedlings interfere with native species establishment have not been defined. A greenhouse experiment was established using an addition series design to determine the influence of interference between crested wheatgrass and four important native species. The existence of seed bank categories of Wyoming big sagebrush communities seeded with crested wheatgrass agrees with the hypothesis that seed banks closely resemble floristic composition. In addition, these results support the hypothesis that seed bank composition has a strong influence on succession in these communities, and characterizing seed banks is necessary to develop ecologically based management strategies for seeded Wyoming big sagebrush communities. Interference from crested wheatgrass on many native species suggests that further management practices to enhance diversity in crested wheatgrass-dominated communities are necessary to reduce competition from crested wheatgrass in the seed bank as well as the aboveground vegetation. These results also suggest that the practice of simultaneously seeding native species with crested wheatgrass may likely result in poor native species persistence unless combined seed bank density and seeding rate of crested wheatgrass is sufficiently low.

All organisms are subjected to the living and non-living influences of their surroundings. They derive their energy and essential materials, such as sunlight and nutrients, from their environment, sharing their world not only with members of their own species but also with members of other species. These interactions are central to the survival of the organism, forming reciprocating and integrated systems with other members of their environment. Paleoecology uses the fossil record to interpret and reconstruct life habits of past organisms and environments. By examining well-preserved fossil populations we can assess the relationship between the organisms and their surrounding environment, their distribution within their environment, and the nature of their interactions. Edrioasteroids, an extinct clade of gregarious, obligate-encrusting echinoderm typical of the Late Ordovician, are rarely encountered in the fossil record as their multi-part skeleton rapidly disarticulates post-mortem. Therefore, the discovery of large pavements encrusted by articulated edrioasteroids indicates that obrution, or a sudden input of sediment that smothers the benthic community, occurred. The near instantaneous nature of obrution allows for the examination of a zero-time-averaged census assemblage rather than a time-averaged death assemblage. This dissertation aims to increase our understanding of the paleoecology and biogeography of Ordovician edrioasteroids in three chapters. The first study examines a carbonate hardground encrusted with four species of isorophid edrioasteroids collected from Upper Ordovician strata near Maysville, Kentucky. Detailed paleoecologic analyses include edrioasteroid age structure, thecal orientation, inter- and intraspecific spatial utilization and settlement patterns, and degree of post-mortem disarticulation. Chapter two examines edrioasteroid paleoecology on Upper Ordovocian shell pavements using a brachiopod shell pavement from Florence, Kentucky and a bivalve shell pavement from Sharonville, Ohio. The results are then compared with those from the Maysville hardground. The final chapter of this dissertation summarizes the paleogeographic distribution patterns of the edrioasteroids during the Ordovician. For this study we collected the geographic distribution data for Ordovician edrioasteroids from published faunal reports and plotted these occurrences on paleogeographic maps with the hope that this information will help better predict localities where additional specimens of Ordovician edrioasteroids may be found.

This study aims to investigate the temporal-spatial distribution and reproduction of the Callionymidae, a dominant bottom-dwelling family at southwestern Taiwan. Samples were collected once every 1~2 month from January 2001 to January 2005 at seven stations, including Jiading, Zuoying, Jhongjhou, Linyuan, Dapeng Bay, Linbian and Fangliao, along the southwestern coast of Taiwan. A total of 5,846 samples was obtained, including 3 genera and 15 species. More species were found in this study than previous ones. The distribution of callionymids showed the significant variations in season, site and year. The highest abundance months occurred during March to October annually, with the most abundant at Jiading, then decreased in numbers southwards. Callionymus planus (52%)¡BCallionymus curvicornis (28%)¡BCallionymus virgis (7%) and Callionymus filamentosus (6%) were the top four dominant species. The four dominant species appeared abundantly around their spawning season. C. planus, C. curvicornis and C. filamentous were serial spawners, with peaking period at March-May, November-March and February-April, respectively. Both C. planus and C. curvicornis were most abundant at Jiading, and decreased southwardly, whereas the C. virgis and C. filamentosus were most abundant at Fangliao and Zuoying, respectively. All dominant species were revealed resource partitioning in relation to their reproductive activities. Callionymus planus that grew fast and recovered quickly among the callionymids, predominated in this area. Both C. planus and C. curvicornis showed significant reproductive isolation at the same area, both with a southward decrease in number. Calllionymus virgis separated from others and lived in the southmost site. Furthermore, C. filamentosus had a spawning period between C. planus and C. curvicornis.

For three consecutive years, I monitored the spring stream residency and spawning of five species of fishes using a tributary stream of the Gouin Reservoir (north central Quebec). Timing of spawning of the distantly related species was different whereas the spawning activity of the closely related suckers overlapped in time and space. Intra- and inter-specific egg predation by the two sucker species was observed as well as predation by lake whitefish (Coregonus clupeaformis) on sucker eggs. Synchronisation of the spawning of the suckers may allow them to "swamp" egg predators with drifting eggs. Abundance of spawning fish was affected by water management practices in the reservoir. When water levels were low, fewer fish of all species had access to the stream possibly because of the development of rapids. / The courtship behavior of the two sucker species was described and compared in the same period, to determine if behavioral isolating mechanisms which prevented hybridization existed.

Great tits (Aves: Passeriformes; Parus major) and blue tits (Parus caeruleus) nested in boxes in Wytham Woods near Oxford. The breeding densities of both species were limited by the availability of nest sites. The larger great tits were dominant in obtaining nest boxes. This was most important where breeding sites were scarce. The two species did not maintain interspecific territories or interfere with interspecific nest site spacing beyond the immediate vicinity of the nest. Blue and great tit numbers fluctuated in parallel where nest sites were not limiting resources. Annual changes in breeding numbers of great tits were negatively related to blue tit breeding density but great tit density did not seem to affect changes in the blue tit population. Overlap in the feeding sites of blue and great tits was greatest during the summer and interference competition was lowest at this time. The nestling diets of the two species were very similar. Despite an apparent abundance of food for nestlings, adults were pressed to feed large broods. Food for nestlings was probably a limiting and depletable resource. The date of clutch initiation of great tits, but not blue tits, was retarded at high densities of blue or great tits. The clutch sizes of both species were probably negatively affected by high breeding densities of congeners but the results were not clear cut. Heavy great tit fledglings are most likely to survive to breed. Great tit fledglings were heavier at low densities of blue tits. An experiment in which blue tit young were removed from a section of the Woods, showed that great tit nestlings were heavier and developed faster, and that female condition was better, than in a control section or section where blue tit broods were supplemented. In terms of resource competition, blue tits were the better scramble competitors and great tits the better interference competitors.