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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Body Size and Social Status in Medieval and Post-Medieval Italy: A Comparison of Alba (CN) and Trino (VC)

Weiss, Nicole Marie 01 September 2017 (has links)
No description available.
102

Bird Balloon Bones: The Evolution of Postcranial Skeletal Pneumaticity in Birds and itsRelationship with Skeletal Form and Function

Gutherz, Samuel Benjamin 16 September 2022 (has links)
No description available.
103

Climatic Dependence of Terrestrial Species Assemblage Structure

Walker, Kevin R. 22 January 2013 (has links)
An important goal of ecological studies is to identify and explain patterns or variation in species assemblages. Ecologists have discovered that global variation in the number of species in an assemblage relates strongly to climate, area, and topographic variability in terrestrial environments. Is the same true for other characteristics of species assemblages? The focus of this thesis is to determine whether species assemblage structure, defined primarily as the body mass frequency distributions and species abundance distributions relate in convergent ways to a set of a few environmental variables across broad spatial scales. First, I found that for mammals and trees most of their geographic variation across North and South America in assemblage structure is statistically related to temperature, precipitation, and habitat heterogeneity (e.g. different vegetation types) in convergent ways. I then examined bird assemblages across islands and continents. Despite the evolutionary and ecological differences between island and continental assemblages, I found that much of the variation in bird assemblage structure depends on temperature, precipitation, land area, and island isolation in congruent patterns in continent and island bird assemblages. Frank Preston modeled species richness based on the total number of individuals and the number of individuals of the rarest species. Building on Preston’s model, Chapter 2 hypothesized that gradients of diversity correlate with gradients in the number of individuals of the rarest species, which in turn are driven by gradients in temperature and precipitation. This hypothesis assumes that species abundance distributions relate to temperature and precipitation in similar ways anywhere in the world. I found that both the number of individuals of the rarest species (m) and the proportion of species represented by a single individual in samples of species assemblages (Φ) were strongly related to climate. Moreover, global variation in species richness was more strongly related to these measures of rarity than to climate. I propose that variation in the shape of the log-normal species abundance distribution is responsible for global gradients of species richness: rare species (reflected in m and Φ) persist better in benign climates. Even though body mass frequency distributions of assemblages show convergent patterns in relation to a set of a few environmental variables, the question remains as to what processes are responsible for creating the geographical variation in the body-size distribution of species. Several mechanisms (e.g. heat conservation and resource availability hypotheses) have been proposed to explain this variation. Chapter 5 tested and found no empirical support for the predictions derived from each of these mechanisms; I showed that species of all sizes occur across the entire temperature gradient. In conclusion, assemblage structure among various taxonomic groups across broad spatial scales relate in similar ways to a set of a few environmental variables, primarily mean annual temperature and mean annual precipitation. While the exact mechanisms are still unknown, I hypothesize several to explain the patterns of convergent assembly. Résumé Un but important de l'écologie est d'identifier et d'expliquer la variation de premier ordre dans les caractéristiques des assemblages d'espèces. Un des patrons ayant déjà été identifié par les écologistes, c'est que la variation mondiale de la richesse en espèces est liée à la variation du climat, de l'aire et de la topographie. Est-ce que d'autres caractéristiques des assemblages d'espèces peuvent être reliées à ces mêmes variables? Le but de cette thèse est de déterminer si la structure des assemblages d'espèces, ici définie comme la distribution des fréquences de masse corporelle ainsi que la distribution d'abondances des espèces, est reliée de manière convergente à un petit ensemble de variables environnementales, et ce, partout dans le monde. D'abord, j'ai déterminé que, pour les mammifères et les arbres, la majorité de la variation géographique dans la structure des assemblages d'espèces est reliée statistiquement à température, précipitation, et l’hétérogénéité du couvert végétal , et ce, de manière convergente pour l'Amérique du Nord et du Sud. Je me suis ensuite penché sur l'assemblage des oiseaux sur les îles et les continents. Malgré les larges différences évolutives et écologiques qui distinguent les îles des continents, je démontre que la majorité de la variation dans la structure des assemblages d'oiseaux dépend de la température, la précipitation, la superficie et l’isolation de façon congruente sur les îles et les continents. Frank Preston a modélisé la richesse en espèces d'une localité, basée sur le nombre total d'individus ainsi que le nombre d'individus de l’espèce la plus rare. En s'appuyant sur les modèles de Preston, Chapître 3 propose une nouvelle hypothèse voulant que les gradients de diversité dépendent des gradients du nombre d'individus de l’espèce la plus rare. Celle-ci dépend des gradients de température et de précipitation. Cette hypothèse repose sur le postulat que la distribution d’abondances des espèces dépend de la température et la précipitation, et ce, de la même manière n’importe où au monde. J’ai mis en évidence que le nombre d’individus de l’espèce la plus rare (m), ainsi que la proportion d’espèces représentées par un individu unique () dans des échantillons locaux étaient fortement reliés au climat. D’ailleurs, la variation globale de la richesse en espèces était plus fortement reliée à ces indices de rareté qu’au climat. Je propose que la variation dans la forme de la distribution log-normale d’abondances d’individus soit responsable des gradients mondiaux de richesse en espèces. En d’autres mots, les espèces rares (indiquées par m et ) persistent mieux dans des climats bénins. Malgré que la distribution des fréquences de masse corporelle des assemblages d'espèces soit liée de manière convergente à seulement quelques variables environnementales, la question demeure à savoir quels processus sont responsables des gradients géographiques de variation en masse corporelle des espèces. Plusieurs mécanismes ont été proposés pour expliquer cette variation. Dans Chapitre 5, j'ai testé les prédictions dérivées de chacun de ces mécanismes sans trouver de support empirique pour aucun. Je démontre aussi que des espèces de toutes tailles se retrouvent sur le gradient de température en entier. En conclusion, la structure des assemblages d'espèces, pour différents groupes taxonomiques et à travers le monde, est liée de façon similaire à un petit nombre de variables environnementales. Bien que les mécanismes soient encore inconnus, j'en propose plusieurs pouvant expliquer ces patrons d'assemblages convergents.
104

Climatic Dependence of Terrestrial Species Assemblage Structure

Walker, Kevin R. 22 January 2013 (has links)
An important goal of ecological studies is to identify and explain patterns or variation in species assemblages. Ecologists have discovered that global variation in the number of species in an assemblage relates strongly to climate, area, and topographic variability in terrestrial environments. Is the same true for other characteristics of species assemblages? The focus of this thesis is to determine whether species assemblage structure, defined primarily as the body mass frequency distributions and species abundance distributions relate in convergent ways to a set of a few environmental variables across broad spatial scales. First, I found that for mammals and trees most of their geographic variation across North and South America in assemblage structure is statistically related to temperature, precipitation, and habitat heterogeneity (e.g. different vegetation types) in convergent ways. I then examined bird assemblages across islands and continents. Despite the evolutionary and ecological differences between island and continental assemblages, I found that much of the variation in bird assemblage structure depends on temperature, precipitation, land area, and island isolation in congruent patterns in continent and island bird assemblages. Frank Preston modeled species richness based on the total number of individuals and the number of individuals of the rarest species. Building on Preston’s model, Chapter 2 hypothesized that gradients of diversity correlate with gradients in the number of individuals of the rarest species, which in turn are driven by gradients in temperature and precipitation. This hypothesis assumes that species abundance distributions relate to temperature and precipitation in similar ways anywhere in the world. I found that both the number of individuals of the rarest species (m) and the proportion of species represented by a single individual in samples of species assemblages (Φ) were strongly related to climate. Moreover, global variation in species richness was more strongly related to these measures of rarity than to climate. I propose that variation in the shape of the log-normal species abundance distribution is responsible for global gradients of species richness: rare species (reflected in m and Φ) persist better in benign climates. Even though body mass frequency distributions of assemblages show convergent patterns in relation to a set of a few environmental variables, the question remains as to what processes are responsible for creating the geographical variation in the body-size distribution of species. Several mechanisms (e.g. heat conservation and resource availability hypotheses) have been proposed to explain this variation. Chapter 5 tested and found no empirical support for the predictions derived from each of these mechanisms; I showed that species of all sizes occur across the entire temperature gradient. In conclusion, assemblage structure among various taxonomic groups across broad spatial scales relate in similar ways to a set of a few environmental variables, primarily mean annual temperature and mean annual precipitation. While the exact mechanisms are still unknown, I hypothesize several to explain the patterns of convergent assembly. Résumé Un but important de l'écologie est d'identifier et d'expliquer la variation de premier ordre dans les caractéristiques des assemblages d'espèces. Un des patrons ayant déjà été identifié par les écologistes, c'est que la variation mondiale de la richesse en espèces est liée à la variation du climat, de l'aire et de la topographie. Est-ce que d'autres caractéristiques des assemblages d'espèces peuvent être reliées à ces mêmes variables? Le but de cette thèse est de déterminer si la structure des assemblages d'espèces, ici définie comme la distribution des fréquences de masse corporelle ainsi que la distribution d'abondances des espèces, est reliée de manière convergente à un petit ensemble de variables environnementales, et ce, partout dans le monde. D'abord, j'ai déterminé que, pour les mammifères et les arbres, la majorité de la variation géographique dans la structure des assemblages d'espèces est reliée statistiquement à température, précipitation, et l’hétérogénéité du couvert végétal , et ce, de manière convergente pour l'Amérique du Nord et du Sud. Je me suis ensuite penché sur l'assemblage des oiseaux sur les îles et les continents. Malgré les larges différences évolutives et écologiques qui distinguent les îles des continents, je démontre que la majorité de la variation dans la structure des assemblages d'oiseaux dépend de la température, la précipitation, la superficie et l’isolation de façon congruente sur les îles et les continents. Frank Preston a modélisé la richesse en espèces d'une localité, basée sur le nombre total d'individus ainsi que le nombre d'individus de l’espèce la plus rare. En s'appuyant sur les modèles de Preston, Chapître 3 propose une nouvelle hypothèse voulant que les gradients de diversité dépendent des gradients du nombre d'individus de l’espèce la plus rare. Celle-ci dépend des gradients de température et de précipitation. Cette hypothèse repose sur le postulat que la distribution d’abondances des espèces dépend de la température et la précipitation, et ce, de la même manière n’importe où au monde. J’ai mis en évidence que le nombre d’individus de l’espèce la plus rare (m), ainsi que la proportion d’espèces représentées par un individu unique () dans des échantillons locaux étaient fortement reliés au climat. D’ailleurs, la variation globale de la richesse en espèces était plus fortement reliée à ces indices de rareté qu’au climat. Je propose que la variation dans la forme de la distribution log-normale d’abondances d’individus soit responsable des gradients mondiaux de richesse en espèces. En d’autres mots, les espèces rares (indiquées par m et ) persistent mieux dans des climats bénins. Malgré que la distribution des fréquences de masse corporelle des assemblages d'espèces soit liée de manière convergente à seulement quelques variables environnementales, la question demeure à savoir quels processus sont responsables des gradients géographiques de variation en masse corporelle des espèces. Plusieurs mécanismes ont été proposés pour expliquer cette variation. Dans Chapitre 5, j'ai testé les prédictions dérivées de chacun de ces mécanismes sans trouver de support empirique pour aucun. Je démontre aussi que des espèces de toutes tailles se retrouvent sur le gradient de température en entier. En conclusion, la structure des assemblages d'espèces, pour différents groupes taxonomiques et à travers le monde, est liée de façon similaire à un petit nombre de variables environnementales. Bien que les mécanismes soient encore inconnus, j'en propose plusieurs pouvant expliquer ces patrons d'assemblages convergents.
105

Climatic Dependence of Terrestrial Species Assemblage Structure

Walker, Kevin R. January 2013 (has links)
An important goal of ecological studies is to identify and explain patterns or variation in species assemblages. Ecologists have discovered that global variation in the number of species in an assemblage relates strongly to climate, area, and topographic variability in terrestrial environments. Is the same true for other characteristics of species assemblages? The focus of this thesis is to determine whether species assemblage structure, defined primarily as the body mass frequency distributions and species abundance distributions relate in convergent ways to a set of a few environmental variables across broad spatial scales. First, I found that for mammals and trees most of their geographic variation across North and South America in assemblage structure is statistically related to temperature, precipitation, and habitat heterogeneity (e.g. different vegetation types) in convergent ways. I then examined bird assemblages across islands and continents. Despite the evolutionary and ecological differences between island and continental assemblages, I found that much of the variation in bird assemblage structure depends on temperature, precipitation, land area, and island isolation in congruent patterns in continent and island bird assemblages. Frank Preston modeled species richness based on the total number of individuals and the number of individuals of the rarest species. Building on Preston’s model, Chapter 2 hypothesized that gradients of diversity correlate with gradients in the number of individuals of the rarest species, which in turn are driven by gradients in temperature and precipitation. This hypothesis assumes that species abundance distributions relate to temperature and precipitation in similar ways anywhere in the world. I found that both the number of individuals of the rarest species (m) and the proportion of species represented by a single individual in samples of species assemblages (Φ) were strongly related to climate. Moreover, global variation in species richness was more strongly related to these measures of rarity than to climate. I propose that variation in the shape of the log-normal species abundance distribution is responsible for global gradients of species richness: rare species (reflected in m and Φ) persist better in benign climates. Even though body mass frequency distributions of assemblages show convergent patterns in relation to a set of a few environmental variables, the question remains as to what processes are responsible for creating the geographical variation in the body-size distribution of species. Several mechanisms (e.g. heat conservation and resource availability hypotheses) have been proposed to explain this variation. Chapter 5 tested and found no empirical support for the predictions derived from each of these mechanisms; I showed that species of all sizes occur across the entire temperature gradient. In conclusion, assemblage structure among various taxonomic groups across broad spatial scales relate in similar ways to a set of a few environmental variables, primarily mean annual temperature and mean annual precipitation. While the exact mechanisms are still unknown, I hypothesize several to explain the patterns of convergent assembly. Résumé Un but important de l'écologie est d'identifier et d'expliquer la variation de premier ordre dans les caractéristiques des assemblages d'espèces. Un des patrons ayant déjà été identifié par les écologistes, c'est que la variation mondiale de la richesse en espèces est liée à la variation du climat, de l'aire et de la topographie. Est-ce que d'autres caractéristiques des assemblages d'espèces peuvent être reliées à ces mêmes variables? Le but de cette thèse est de déterminer si la structure des assemblages d'espèces, ici définie comme la distribution des fréquences de masse corporelle ainsi que la distribution d'abondances des espèces, est reliée de manière convergente à un petit ensemble de variables environnementales, et ce, partout dans le monde. D'abord, j'ai déterminé que, pour les mammifères et les arbres, la majorité de la variation géographique dans la structure des assemblages d'espèces est reliée statistiquement à température, précipitation, et l’hétérogénéité du couvert végétal , et ce, de manière convergente pour l'Amérique du Nord et du Sud. Je me suis ensuite penché sur l'assemblage des oiseaux sur les îles et les continents. Malgré les larges différences évolutives et écologiques qui distinguent les îles des continents, je démontre que la majorité de la variation dans la structure des assemblages d'oiseaux dépend de la température, la précipitation, la superficie et l’isolation de façon congruente sur les îles et les continents. Frank Preston a modélisé la richesse en espèces d'une localité, basée sur le nombre total d'individus ainsi que le nombre d'individus de l’espèce la plus rare. En s'appuyant sur les modèles de Preston, Chapître 3 propose une nouvelle hypothèse voulant que les gradients de diversité dépendent des gradients du nombre d'individus de l’espèce la plus rare. Celle-ci dépend des gradients de température et de précipitation. Cette hypothèse repose sur le postulat que la distribution d’abondances des espèces dépend de la température et la précipitation, et ce, de la même manière n’importe où au monde. J’ai mis en évidence que le nombre d’individus de l’espèce la plus rare (m), ainsi que la proportion d’espèces représentées par un individu unique () dans des échantillons locaux étaient fortement reliés au climat. D’ailleurs, la variation globale de la richesse en espèces était plus fortement reliée à ces indices de rareté qu’au climat. Je propose que la variation dans la forme de la distribution log-normale d’abondances d’individus soit responsable des gradients mondiaux de richesse en espèces. En d’autres mots, les espèces rares (indiquées par m et ) persistent mieux dans des climats bénins. Malgré que la distribution des fréquences de masse corporelle des assemblages d'espèces soit liée de manière convergente à seulement quelques variables environnementales, la question demeure à savoir quels processus sont responsables des gradients géographiques de variation en masse corporelle des espèces. Plusieurs mécanismes ont été proposés pour expliquer cette variation. Dans Chapitre 5, j'ai testé les prédictions dérivées de chacun de ces mécanismes sans trouver de support empirique pour aucun. Je démontre aussi que des espèces de toutes tailles se retrouvent sur le gradient de température en entier. En conclusion, la structure des assemblages d'espèces, pour différents groupes taxonomiques et à travers le monde, est liée de façon similaire à un petit nombre de variables environnementales. Bien que les mécanismes soient encore inconnus, j'en propose plusieurs pouvant expliquer ces patrons d'assemblages convergents.
106

Climate change and invasion impacts in the sub-Antarctic

Treasure, Anne M. (Anne Margaret) 03 1900 (has links)
Thesis (PhD)-- Stellenbosch University, 2012. / ENGLISH ABSTRACT: Climate change and biological invasions are major threats to biodiversity. In particular, these threats are predicted to influence terrestrial systems in the sub-Antarctic, where significant ecosystem responses to both have already been seen. In this thesis, the sub-Antarctic Prince Edward Island group is used as a model system in which to investigate key questions relating to climate change and invasive species impacts. The island group comprises two islands, Marion (MI) and Prince Edward (PEI), both of which are experiencing rapid warming, yet have different invasive assemblages and in consequence are experiencing different impacts. Variation in the patterns of invasive species richness and abundance and their underlying causes are matters of considerable ecological and conservation significance. While an increase in thermal energy availability typically results in an increase in species richness, the mechanisms underlying these patterns are poorly understood. In Chapter 2 of this thesis, these relationships are explored for springtails, an important component of the soil fauna on Marion Island. Energy explains a large amount of the spatial variation in indigenous and invasive springtail species richness. Disturbance thresholds and stressful temperatures are more important than increased population sizes in determining this variation in species richness. As both indigenous and invasive springtail species richness and abundance are strongly related to temperature, a warming climate could have far-reaching consequences for these organisms. In particular, invasive species are predicted to be at an advantage relative to indigenous species under warming conditions. One species where this seems especially likely, given its physiological responses to experimental warming and drying, is the large invasive tomocerid, Pogonognathellus flavescens. Determining whether this will be the case depends on understanding the factors underlying its range limits and abundance structure. Moreover, few studies have sought to distinguish the causal basis of abundance structure and range limits, particularly for invasive species. Thus, in Chapter 3, local microclimate variables and physiological tolerances of the invasive springtail, P. flavescens (a habitat generalist), are examined. The results suggest that the species should be widely distributed across a range of habitats on MI. However, the springtail is restricted to indigenous Poa cookii tussock grassland habitats in the southeast. The current range limits are set by dispersal limitation (i.e. contingent absences) whilst abundance structure is a function of variation in soil substrate quality. However, over time, the widening distribution of P. cookii, as a consequence of a major management intervention (the eradication of feral cats), may enable P. flavescens to colonise all suitable areas. In Chapter 4, the focus changes to what has been considered the third major response to climate change, along with range and phenological responses - changing animal body sizes. Body size is one of the most significant and obvious features of animals and is of considerable ecological and physiological importance. A prediction of the temperature-size rule (TSR) is that with warming, body size of the weevil species on both MI and PEI should decline. However, predation by mice of the weevils on MI should fundamentally affect the pattern of such change, causing it to differ from neighbouring PEI, indicating synergistic impacts between climate change and invasions. Analysis of a 24-year data set indicates a decline in the body size of all weevil species on PEI with increasing temperature. However, on MI, a negative relationship between mean annual temperature and body size is found only for Palirhoeus eatoni, a species not eaten by mice. A possible explanation for the positive relationships found for the other species could be due to higher metabolic demands imposed on mice in colder years than in warmer ones. Any increase in predation coupled with a preference for larger sizes, which the mice clearly show, would lead to a decline in the mean size of the weevil species. Due to the relationship between body size and metabolic rate and the importance of the weevils in the islands’ food webs, changes to the body size of these organisms could have significant consequences for the island ecosystems’ functioning. The thermal environment experienced by organisms also has a direct effect on survival, growth and reproduction. The physiological response of organisms to rapidly changing climates is therefore a primary concern. Organisms may respond to variable environmental conditions through phenotypic plasticity as well as behaviour. Chapter 5 of this thesis shows that of the weevil species and populations investigated on MI, most display phenotypic plasticity, the form of which is in keeping with the ‘Hotter is Better’ hypothesis. This could be due to rare extreme temperature events and the advantage for the performance curves to incorporate high temperatures experienced in the environment. Mismatches between thermal optima and preferred temperatures displayed by all species could mean that these weevils are well equipped to cope with warming conditions on MI unless the prediction of an increase of rare extreme events such as extreme temperatures is realised. Rapidly changing climates and an increase in the introduction of non-indigenous species are issues of major conservation concern. This has increased the significance of studies on the impacts of these threats. However, this thesis shows that to understand such processes, it is essential that an integration of disciplines be undertaken. This thesis thus adopts a multidisciplinary approach and highlights key issues associated with both climate change and biological invasions. The patterns and predictions of species and community responses to these environmental changes are complex. Moreover, predicting such responses is likely to be problematic, especially as multiple factors will change concurrently and how these factors might change is unclear. This highlights the importance of long-term records for understanding organism responses to such changes. Furthermore, impacts on indigenous species are likely to be exacerbated by the predicted increase in the rate of introductions with climate change. This makes the case for preventing the dispersal of invasive species to new areas all the more important. / AFRIKAANSE OPSOMMING: Klimaatsverandering en indringer spesies is belangrike bedreigings vir biodiversiteit. In besonder word voorspel dat hierdie bedreigings terrestriële sisteme in die sub-Antarktiese sal beïnvloed, waar beduidende ekosisteem reaksie aan beide reeds gesien is. In hierdie tesis word die sub-Antarktiese Prince Edward eiland groep as a model sisteem gebruik om belangrike vrae met betrekking tot klimaatsverandering en die impak van indringer spesies te ondersoek. Die eiland groep bestaan uit twee eilande, Marion (ME) en Prince Edward (PEE), wat beide versnellende verwarming ervaar, maar tog verskillende indringer samestellings het en vervolgens verskillende impakte ervaar. Variasie in die patrone van indringerspesierykheid en vollopheid en hulle onderliggende oorsake is van aansienlike omgewings en bewarings betekenis. Terwyl 'n toename in die beskikbaarheid van energie tipies lei tot 'n toename in spesierykheid, word die onderliggend meganismes van hierdie patrone swak verstaan. In Hoofstuk 2 van hierdie tesis, word hierdie verhoudings vir springsterte ondersoek, 'n belangrike komponent van die grond fauna op ME. Energie verduidelik 'n groot hoeveelheid van die ruimtelike variasie in inheemse en indringende springstert spesierykheid. Versteuringsdrempels en stressvolle temperature is meer belangrik as die toename in bevolking groottes in die bepaling van hierdie variasie in spesierykheid. Aangesien beide inheemse en indringende springstert spesierykheid en vollopheid sterk verwant is aan temperatuur, kan 'n verwarmende klimaat verreikende gevolge vir hierdie organismes hê. In die besonder word voorspel dat indringerspesies bevoordeeld sal wees relatief tot inheemse spesies onder verwarmende toestande. Een spesie waar dit veral blyk om geneig te wees, gegewe sy fisiologiese reaksie tot eksperimentele verhitting en uitdroging, is die groot indringer tomocerid, Pogonognathellus flavescens. Om te bepaal of dit die geval sal wees, hang af van die begrip van die onderliggende faktore van sy voorkomsgrense en vollopheidstruktuur. Daarbenewens is daar min studies wat gepoog het om te onderskei tussen die veroorsakende basis van vollopheidstruktuur en voorkomsgrense, veral vir indringerspesies. Dus, in Hoofstuk 3, word plaaslike mikroklimaat veranderlikes en fisiologiese toleransies van die indringer springstert, P. flavescens ('n habitat generalis), ondersoek. Die resultate stel voor dat die spesie wyd verspreid moet wees oor 'n verskeidenheid van habitatte op ME. Maar, die springstert is beperk tot inheemse Poa cookii polle grasveldhabitatte in die suidooste. Die huidige voorkomsgrense word daar gestel deur verspreidingsbeperking (dws voorwaardelike afwesighede), terwyl vollopheidstruktuur 'n funksie is van die variasie in die grond substraat kwaliteit. Maar, die uitbreidende verspreiding van P. cookii as gevolg van 'n groot bestuursingryping (die uitwissing van wilde huiskatte), kan P. flavescens in staat stel om alle geskikte gebiede te koloniseer met verloop van tyd. In Hoofstuk 4 verander die fokus na wat as die derde groot reaksie op klimaatsverandering beskou word, saam met voorkoms en fenologiese reaksies - veranderende diere liggaamsgroottes. Liggaamsgrootte is een van die beduidendste en mees voor die hand liggende eienskappe van diere en is van aansienlike ekologiese en fisiologiese belang. 'n Voorspelling van die temperatuur-grootte-reël (TGR) is dat met verwarming, liggaamsgrootte van die snuitkewerspesies op beide ME en PEE sal afneem. Hoe ookal, predasie deur muise van die snuitkewers op ME moet fundamenteel die patroon van sodanige verandering op PEE beïnvloed, wat sinergistiese impakte tussen klimaatsverandering en indringings aandui. Die ontleding van 'n 24-jarige datastel dui aan op 'n afname in die liggaamsgrootte van alle snuitkewer spesies op PEI met ‘n toename in temperatuur. Maar, op ME is 'n negatiewe verhouding tussen die gemiddelde jaarlikse temperatuur en liggaamsgrootte net gevind vir Palirhoeus eatoni, 'n spesie wat nie deur die muise geëet word nie. 'n Moontlike verduideliking vir hierdie positiewe verhoudings wat gevind is vir die ander spesies kan wees as gevolg van hoër metaboliese eise op die muise in kouer jare as in warmer jare. Enige toename in predasie, tesame met 'n voorkeur vir groter mates, wat die muise duidelik wys, sou lei tot 'n afname in die gemiddelde grootte van die snuitkewer spesies. As gevolg van die verhouding tussen liggaamsgrootte en metaboliese tempo, sowel as die belangrikheid van die snuitkewers in die eilande se voedselwebbe, kan veranderinge in die liggaamsgrootte van hierdie organismes beduidende gevolge op die eiland ekosisteme se funksionering hê. Die termiese omgewing wat deur organismes ervaar word het ook 'n direkte invloed op oorlewing, groei en voortplanting. Die fisiologiese reaksie van organismes op vinnig veranderende klimate is dus 'n primêre bron van kommer. Organismes kan reageer op veranderlike omgewingstoestande deur fenotipiese plastisiteit sowel as gedrag. Hoofstuk 5 van hierdie tesis toon dat van die snuitkewerspesies en bevolkings wat ondersoek is op ME, die meeste fenotipiese plastisiteit vertoon, die vorm wat in ooreenstemming is met die ‘Warmer is Beter’ hipotese. Dit kan wees as gevolg van seldsame uiterste temperatuur gebeure en die voordeel vir die prestasie kurwes om hoë temperature wat ervaar word in die omgewing in te sluit. Mismatches tussen termiese optima en voorkeur temperature vertoon deur alle spesies kan beteken dat hierdie snuitkewers goed toegerus is om die verhitting op ME te hanteer, tensy die voorspelling van 'n toename van seldsame uiterste gebeure soos uiterste temperature gerealiseer word. Vinnig veranderende klimate en 'n toename in die bekendstelling van nie-inheemse spesies is kwessies van groot bewarings kommer. Dit het die betekenis van studies oor die impak van hierdie bedreigings verhoog. Hierdie tesis toon egter dat om sulke prosesse te verstaan, dit noodsaaklik is dat 'n integrasie van die dissiplines onderneem word. Hierdie tesis aanvaar dus 'n multi-dissiplinêre benadering en beklemtoon die belangrike kwessies wat verband hou met beide klimaatverandering en biologiese indringing. Die patrone en voorspellings van spesies en die gemeenskapsreaksies op hierdie omgewingsveranderinge is kompleks. Verder, die voorspelling van sodanige reaksies sal waarskynlik problematies wees, veral omdat verskeie faktore gelyktydig sal verander en hoe hierdie faktore kan verander is onduidelik. Dit beklemtoon die belangrikheid van lang termyn rekords vir die begrip van organisme reaksies op sulke veranderinge. Verder, die impak van inheemse spesies is geneig om te vererger deur die voorspelde toename in die tempo van bekendstellings met klimaatsverandering. Dit maak die taak vir die bestuur van die voorkoming dat indringerspesies nuwe gebiede bereik al hoe meer belangrik.
107

A paleozoological perspective on predator extermination and white-tailed deer (Odocoileus virginianus Boddaert) overabundance in central Texas.

Wolverton, Steven J. 05 1900 (has links)
Archaeological and paleontological datasets are used in conservation to add time-depth to ecology. In central Texas several top carnivores including prehistoric Native American hunters have been extirpated or have had their historic ranges restricted, which has resulted in pest-level white-tailed deer (Odocoileus virginianus texana) populations in some areas. Predator extermination has dramatically reduced the average body size of members of the extant predator guild, and large carnivores most capable of hunting white-tailed deer are extirpated. Character release in the remaining “large” predatorsmesocarnivoresis a predicted outcome related to the adaptive vacuum at the top of the trophic hierarchy. Differences in body size of deer between prehistory and modernity are expected given that a lack of predation likely has increased intraspecific competition for forage among deer resulting in smaller body size today. In fact modern deer from settings without harvest pressure are significantly smaller than those from harvested areas and from prehistoric deer. From a natural history perspective, this research highlights potential evolutionary causes and effects of top-predator removal on deer populations and related components of biological communities in central Texas.
108

Comparative analysis of organ size, shape, and patterning in diverse species

Siomava, Natalia 21 December 2016 (has links)
No description available.
109

Influência da umidade relativa no desempenho da tarefa de busca de água em formigas-cortadeiras da espécie Atta sexdens rubropilosa (Forel, 1908). / Influence of relative humidity on the task of water collection in the leaf-cutting ant Atta sexdens rubropilosa (Forel, 1908).

Estrella, Nathalia Sena Polydoro 18 May 2018 (has links)
Fatores ambientais abióticos, como o clima, possuem um efeito profundo sobre a biologia dos organismos e sua distribuição em diferentes habitats. Os insetos, sendo o grupo animal mais abundante do planeta, tem papel importante no entendimento de como as variações climáticas afetam a vida na Terra. Neste estudo, utilizamos as formigas-cortadeiras, da espécie Atta sexdens rubropilosa,, para tratar da importância da umidade na escolha de trilhas de forrageio. As colônias utilizadas foram separadas em dois grupos: um grupo controle, mantido em condições normais de alimentação, e um grupo experimental, alimentado com substrato seco, provocando desidratação da colônia. Os dois grupos foram submetidos a um teste de escolha de trilhas para coleta de água: uma das trilhas foi mantida úmida e a outra mantida seca. As formigas que passaram pelas trilhas, por 24 horas, foram contadas e medidas (estas últimas selecionadas aleatoriamente nas trilhas). Após análise de vídeos, os resultados mostraram que, para o fluxo, houve diferença significativa, tanto entre os grupos quanto entre as trilhas. O fluxo foi sempre maior no grupo experimental, em relação ao controle, e maior na trilha úmida que na trilha seca - sendo assimetricamente maior no grupo experimental. Este resultado demonstra que o estado fisiológico da colônia e das operárias influencia fortemente a saída de forrageadoras e a coleta de água. Além disso, mostra que a escolha da trilha foi influenciada pelo ambiente, com grande preferência das formigas pela trilha úmida. Com relação aos tamanhos, a diferença foi significativa para dois fatores: as formigas nas trilhas do grupo experimental eram, em média, menores do que as formigas do grupo controle. Há relatos de que formigas menores são especializadas em coletar água, o que explica este resultado: no grupo experimental, a dessecação impulsiona as formigas a coletar água de maneira sistemática para reidratação. No grupo experimental, as formigas eram menores na trilha seca do que as da trilha úmida, o que vai contra o esperado se levar em consideração as relações alométricas de perda evaporativa de água. É provável que esse fator esteja ligado ao engajamento na tarefa de coleta de água pelas formigas menores, que é constante nas duas trilhas, dada a necessidade da colônia. Mais estudos, no entanto, são necessários para aprimorar e aprofundar estas questões, especialmente levando em conta a dicotomia entre o comportamento individual e o coletivo / Environmental abiotic factors, such as weather, have a profound impact over the biology of organisms e their distribution on different habitats. Insects, being the most abundant animal group on the planet, play an important role to understand how climatic changes affect life on Earth. In this study, we use leafcutter ants of the species Atta sexdens rubropilosa in order to approach the importance of humidity in the choice of foraging trails. The colonies used were separated in two groups: a control group, kept under normal feeding conditions and an experimental group, fed with dry substrate, which provoked dehydration on the colony. Both groups were submitted to a test of trail choice for water collection: one of the trails was kept humid, while the other was kept dry. Ants that travelled through the trails over 24 hours were counted and measured (in the last case, randomly chosen on the trails). After video analysis, the results show that, regarding to flow, there was a significant difference between groups and between trails. Ants flow were always higher on the experimental group than on the control group, and higher on the humid trail than on the dry trail - being asymmetrically higher on the experimental group. These results show that the physiological state of the colony and the workers strongly influences the exit of foragers and the collection of water. Besides, it shows that trail choice was influenced by the environment, with ants preferring the humid trail. Regarding body size, the difference was significant for two factors: ants on the trails of the experimental group were, on average, smaller than ants from the control group. There are reports that smaller ants are specialized on water collection, which explains that difference: on the experimental group, dehydration pushes ants to collect water systematically for rehydrating. On the experimental group, ants were smaller on the dry trail than the ones on the humid trail, which goes against expected when we consider allometric relations for evaporative water loss. It is likely that this factor is connected to the smaller ant´s engagement to the water collection task, which is constant on both trails due the needs of the colony for water. More studies, however, are necessary to improve and deepen those questions, specially taking onto account the dichotomy between individual and collective behavior
110

Are You Creating Socially Responsible Visual Communication? : An Exploratory Study of Fashion Companies’ External Social Responsibility on Instagram: A Marketer’s Perspective

Diliwi, Avesta, Bäcker, Josefin January 2019 (has links)
Background: Following the development of digitalization and the emergence of social media a lot of attention has been drawn upon how these platforms are influencing the fashion industry and fashion marketing. As society is becoming more ethics and health conscious, fashion companies’ visual representations in social media are drawing more attention - who is represented and how are these representations portrayed. Previous research has shown that white and thin models are a recurrent over-representation in media, consumers through these see the ‘ideal’ or stereotypical body types or norms, and not an actual or full representation of society. The issue is, however, not that white or thin people are represented in media. The problem is how companies portray these representations and how the portrayals lead to the exclusion and misrepresentation of other groups in society. Purpose: The purpose of this study is to investigate the CSR practice of fashion companies regarding the body image representations in social media marketing communications, with specific focus on the marketer’s perspective. Methodology: For this study an exploratory cross-sectional case-study research design approach was applied. Four corporate cases of fashion companies were analyzed using data triangulation methods on the basis of content analysis and semi-structured interviews. First, case analysis of social media contents and interviews were conducted, followed by cross- sectional analysis to find out if fashion companies’ practiced social responsibility is aligned with the verbally expressed social responsibility. Findings: The findings of this study demonstrate that fashion companies consider external social responsibility as an important issue, however, a gap between the companies practiced social responsibility and verbally expressed social responsibility remains. The study shows that two of the companies’ practiced social responsibility on their Instagram channel is in alignment with their verbally expressed social responsibility, when it comes to representing diversity in terms of body size, ethnicity and skin color. However, when it comes to the representational conventions it was noted that all the companies are lacking in external responsibility due to the continuous signs of idealization and body-ism on all the companies’ Instagram channels. Conclusion: This study contributes to the research field regarding companies’ external social responsibility on Instagram. The findings provide companies and researchers with awareness of which representational conventions/key social aspects are currently lacking in corporate marketing activities and should become the focus for further improvement. Based on obtained results, a modified framework for image analysis and criteria for image/content creation are suggested. The framework and criteria can assist future researchers, help content creators and other practitioners to understand the complexity of external social responsibility and how to implement it in practice.

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