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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.
1

Allometry of sexual size dimorphism in turtles| A comparison of mass and length data

Regis, Koy William 16 July 2016 (has links)
<p> The macroevolutionary pattern of Rensch&rsquo;s Rule, i.e., positive allometry of sexual size dimorphism, has had mixed support in turtles. Using the largest carapace length dataset and the only large-scale body mass dataset heretofore assembled for this group, we determine (a) whether turtles conform to Rensch&rsquo;s Rule at the order, suborder, and family levels, and (b) whether inferences regarding allometry of sexual size dimorphism differ based on choice of body size metric used for analyses. We compiled large databases of mean body mass and carapace length for males and females of as many populations and species as possible using mostly primary literature. We then determined scaling relationships between males and females for average body mass and straight carapace length across species of turtles using traditional and phylogenetic comparative methods. We also used linear regression analyses to evaluate sex-specific differences in the variance explained by carapace length on body mass. </p><p> In non-phylogenetic analyses, body mass supports Rensch&rsquo;s Rule, whereas straight carapace length supports isometry. Using phylogenetic independent contrasts, both body mass and straight carapace length support Rensch&rsquo;s Rule with strong congruence between body size metrics. More variance is explained by mass than carapace length. At the family level, support for Rensch&rsquo;s Rule is more frequent when mass is used as a body size metric and in phylogenetic comparative analyses. Turtles do not differ in their mass-to-length regressions by sex. Turtles display Rensch&rsquo;s Rule overall and within some families of Cryptodires, but not in Pleurodire families. At broad scales, mass and length are strongly congruent with respect to Rensch&rsquo;s Rule in turtles, and discrepancies are observed mostly at the family level (which is the level where Rensch&rsquo;s Rule is most often evaluated). At macroevolutionary scales, the purported advantages of length measurements over weight measurements are not supported in these ectothermic vertebrates.</p>
2

Patterns of Species Rarity as a Driving Mechanism for Species Richness Gradients

Giles, Mark 04 June 2020 (has links)
Broad scale geographic variation in species diversity correlates with environmental variables in most taxa, but a mechanistic understanding of this relationship has remained elusive. More than a half-century ago, F.W. Preston observed that the number of individuals per species in species assemblages is log-normally distributed (with two parameters: the total number of individuals, I, and the number of individuals of the rarest species, m). Here, we show that ϕ, a proxy for m, is correlated with environmental variables in several datasets of trees, birds, fish, and invertebrates. Moreover, variation in species richness is more strongly related to this measure of rarity than to environment. In all the datasets we examined, structural equation models are consistent with the hypothesis that environmental variables affect species richness principally by affecting rarity, which in turn affects richness. We propose that geographic variation in the ability of species to persist at low densities provides a possible unifying explanation for global gradients of species richness. Our findings may have important implications regarding Earth’s biodiversity, highlighting the rarest species as those most at-risk but also important indicators for the ongoing consequences of climate change.
3

Studies in lepidopteran evolution

Symons, F. B. January 2001 (has links)
No description available.
4

The Role of Scale in Ecological Inference| Implications for Interpreting Hominin Paleoecology

Du, Andrew 25 January 2017 (has links)
<p> Modern and fossil ecological data exist at very different taxonomic, spatial, and temporal scales. For modern ecology, data are typically collected at the species-level, cover square meter quadrats to the entire globe, and span days to decades at most. For fossil assemblages, spatial scale might be comparable to that studied by modern ecologists, but fossil data are taxonomically and temporally much coarser (respectively, order-, family-, genus-level at best, and 104-108 years). Recent research has shown that ecological patterns and the processes affecting them change across scale. Therefore, using modern ecological theory and methods to study fossil data is an incommensurate exercise and potentially produces spurious results. Moreover, scale varies by orders of magnitude even among fossil assemblages, so comparing fossil sites without an appreciation of scale may also lead to ambiguous conclusions. </p><p> I argue that a disregard of scale within paleoanthropology has contributed to its inability to synthesize seemingly disparate paleoecological results into a coherent, unified framework. As a result, paleoanthropology has remained relatively stagnant regarding its understanding of how paleoecological processes drove hominin evolution. With this in mind, I adopt scale as a central theme in my dissertation and attempt to understand how ecological pattern and process change across modern and fossil scales in East African large mammal communities, and if these scale differences can be analytically reconciled. </p><p> The results from my three research chapters show ecological patterns (and the relevant processes driving them) fundamentally change across modern and fossil scales. Thus, modern and paleoecological theory and data are each incomplete: modern ecologists need to analyze fossil data if they want to study ecology at large time scales, and paleoecologists need to examine modern data and theory in order to understand smaller-scale processes; simple extrapolation and interpolation will not do. For paleoanthropologists, that means it is less than straightforward to infer smaller-scale ecological processes (e.g., paleoenvironmental reconstruction, interspecific interactions) from fossil assemblages, and caution should be exercised when attempting to do so. I by no means offer a panacea for this scale issue, but hopefully my research will make paleoanthropologists more cognizant of scale and encourage future research on this topic. Only then can we finally begin to understand what exactly were the important ecological drivers affecting hominin behavior and evolution. </p>
5

Patterns and drivers of marine phytoplankton change over the past century

Boyce, Daniel 03 October 2013 (has links)
Marine phytoplankton produce the vast majority of primary production in the world’s oceans and sustain virtually all marine ecosystems. Despite this importance, it is currently unclear how global marine phytoplankton concentrations have been changing over the available oceanographic record, and what the causes and consequences of any such changes may be. In this thesis I use observational datasets, statistical modeling, theory, and experiments, to estimate how the global standing stock of marine phytoplankton (referenced by chlorophyll) has changed over the past century, and what the causes and consequences of any changes may be. I inter-calibrated shipboard measurements of upper ocean chlorophyll, transparency, and colour to generate a publicly-available global chlorophyll database spanning from 1890 to 2010. Generalized additive models and multi-model inference were used to estimate the magnitude and nature of changes over the available record, and to explore the effects of multiple oceanographic and climatic variables on these changes. Finally, I worked collaboratively to design and run a mesocosm experiment to test the mechanisms by which rising ocean temperatures influence phytoplankton and plankton community structure. I observed declining trends in upper ocean chlorophyll concentrations at local, regional, and global scales over the past century. Increasing trends were observed closer to coastlines, and were possibly related to increased land-based nutrient deposition there. I also observed inter-annual to multi-decadal fluctuations overlying the longterm trends, which were partly related to climate variability. Sea surface temperature was a consistently strong driver of observed chlorophyll trends. Strong negative effects of rising ocean temperatures on chlorophyll concentration were observed at mid, and low latitudes, and positive effects were observed at high latitudes. The overall effect of increasing temperature on chlorophyll was negative, yet the mesocosm experiment revealed that the primary mechanisms explaining this effect depend on the nature of the ecosystem. Under nutrient limitation, the physically-mediated effects (stratification) of increasing SST were dominant, while under nutrient saturation, the biologically-mediated effects (trophic) were dominant. This thesis provides new evidence that sustained declines in marine phytoplankton over the past century have occurred across multiple spatial scales and that rising ocean temperatures have contributed to this trend. The possible implications of this sustained decline are wide-ranging, with likely impacts on climate, geochemical cycling, fisheries, and ecosystem structure.
6

Predicting Broad-scale Patterns in Species Distributions

Boucher-Lalonde, Véronique January 2016 (has links)
Species richness of virtually all high-level taxonomic groups is strongly statistically related to climatic variables such as temperature and precipitation, and consistently so across space and time. These observations are consistent with a causal link between the number of species that occur in a given region and its climate. Although dozens of hypotheses have been proposed, the main mechanisms underlying this pattern remain largely unresolved. And, few ecological studies have attempted to identify regularities in the individual species distributions that make up the richness–climate relationship. Despite the complexities of species’ biologies, I found that, to a first approximation, species’ probability of occupancy at continental scales were generally well statistically explained by a Gaussian function of temperature and precipitation. This simple model appeared general among species, taxa and regions. However, although individual species’ ranges are strongly statistically related to climate, spatial variations in richness cannot be explained by systematic variations in species’ climatic niches. And, individual species track changes in climatic variables through time much more weakly than species richness tracks these changes, suggesting that richness is at least partly constrained by mechanisms independent of species identities. Moreover, at macro-scales, species richness was also not strongly predictable from the temperature at which clades have originated, from historical variability in climatic variables nor from local short-term extirpation rates. In sum, I rejected several prominent hypotheses aiming to explain richness–climate relationship and found several lines of evidence inconsistent with the common idea that climatic constraints on individual species, by themselves, can explain richness–climate relationship. I propose a mechanism to explain, as a first approximation, the continental biogeography of species distributions that relies on neutral processes of dispersal and local extinctions within species’ broad deterministic thermal tolerances.
7

The Adaptive Significance of Inflorescence Pigmentation and its Potential Influence on the Diversification Dynamics of North American Sedges (Carex, Cyperaceae)

Longert, Dylan 21 March 2022 (has links)
Although pollinator-driven selection is known to generate pigmentation variation in plants, the contribution of abiotic factors in the evolution of pigmentation is still poorly understood. This is largely due to a lack of research on pigmentation variation in wind-pollinated (anemophilous) plants, where the confounding effect of pollinators can be excluded. Here, I study pigmentation variation in Carex, the world’s largest anemophilous genus. Using 456 North American species, I use phylogenetic comparative methods to test (1) whether darker inflorescence parts are correlated with short growing seasons and (2) whether inflorescence pigmentation has affected the diversification dynamics of Carex throughout time. I also examine UV irradiance and precipitation at both the interspecific and intraspecific (four wide-ranging species, >100 accessions each) levels, factors previously associated with floral darkness at high altitude and latitude. At the inter- and intraspecific level, darker inflorescence parts are associated with short growing seasons, as seen in arctic and alpine regions. Additionally, dark pigmentation is associated with stronger UV irradiance and higher precipitation in the intraspecific dataset. Finally, despite the adaptive importance of pigmentation in arctic and alpine regions, it has not contributed to the diversification dynamics of Carex. The results suggest that climatic conditions can promote pigmentation variation in anemophilous plants, and are most consistent with the hypothesis that dark inflorescence parts accelerate reproductive development by absorbing solar energy. Finally, despite the adaptive importance of pigmentation in arctic and alpine regions, it has not contributed to the diversification dynamics of Carex.
8

COEXISTENCE, RESILIENCE AND RESISTANCE OF MARINE INVERTEBRATE COMMUNITIES ACROSS A LATITUDINAL GRADIENT

Bonfim Pinto Mendes, Mariana January 2021 (has links)
Biogeographic barriers have limit the movement of organisms, leading to speciation and shaping the development of unique regional biotas. Human-aided circumvention of biogeographic barriers, however, has increased the connectivity of isolated biotas, while changes in climate have been altering species geographic ranges, restructuring ecological networks, modifying ecological niche arrangements and increasing the frequency and intensity of natural pulse disturbances. In this context, examination of some of the most fundamental processes underlying the patterns of species diversity and community structure across biogeographical scales is therefore vital, especially as humans increasingly modify these relationships established over the course of geological history. The latitudinal diversity gradient is the most well-established and predominantly studied biogeographic diversity pattern on Earth. Higher tropical biodiversity with a decline towards higher latitudes occur in both hemispheres and has been observed for various systems including terrestrial, freshwater and marine. In my dissertation, I explored latitudinal variation in factors that can inform and modify fundamental ecological principles such as coexistence, community stability, and resistance. I studied communities of marine invertebrates across over 7000 km of continuous coastal habitat spanning 47-degree latitudinal range on the Eastern North and Central Pacific coast, from tropical Panama to subarctic Alaska. Experiments were based on the manipulation of recently recruited or adult communities of sessile marine invertebrates, such as barnacles, marine worms and encrusting colonial organisms. These organisms inhabit coastal ecosystems across continental scales and can colonize artificial substrates such as hull of commercial vessels that travel across oceans serving as vectors for marine biological invasions. Among my three aims I was able to: (1) examine how the complementarity of ecological niches varies from the tropics to subarctic among recruiting taxa, and how the differentiation of these recruitment pulses through time help inform coexistence across large spatial scales; (2) document distinct resilience responses to pulse disturbances between lower and high latitude sites, while exploring the interplay between compositional and functional recovery in biological communities; and finally, (3) implement a novel component to pre-existing models to predict probability of biological invasions based on the distinct pressures of propagule introduction, environmental similarity between donor and recipient regions, and the potential for biotic resistance. My dissertation yields empirical evidence of processes varying with latitude, advancing our knowledge in some of the most fundamental questions in classic and contemporary ecology. Large-scale documentation of the mechanisms and processes that maintain global patterns of biodiversity are uppermost in the design of global conservation strategies, especially in a more connected world. / Biology
9

BUILDING FRAMEWORKS FOR UNDERSTANDING INVASIONS AND EXTINCTIONS FOR BIODIVERSITY SCIENCE

Huron, Nicholas, 0000-0001-6835-1390 January 2022 (has links)
Scientists have long been interested in mechanisms that increase and decrease biodiversity on Earth and the effects they have on organisms’ interactions and functions. Global biodiversity loss is now outstripping accumulation and far exceeds expected background levels and has drawn comparisons to previous mass extinctions. The ongoing Holocene–Anthropocene extinctions differ from prior biodiversity loss, because humans have been directly implicated as major drivers of current loss—overexploitation, habitat modification and destruction, climate variability, spread of pathogens, and invasion by exotic species. Biodiversity change and especially loss can alter ecological assemblages irreversibly, which consequently can change the direction and magnitude of key ecosystem functions that organisms, including humans, rely on. Therefore, it is increasingly important to develop methods for quantifying and understanding phenomena linked to biodiversity change. In my dissertation, I develop methods to: (1) assess risk of a global-scale invasion of a pest species, (2) predict host associations for a generalist pest species, and (3) develop models to understand extinction dynamics within a clade of conservation interest. In my first chapter, I developed a framework and used it to assess a rapidly spreading regional U.S. grape pest, the spotted lanternfly planthopper (Lycorma delicatula; SLF), to spread and disrupt the global wine market. I found that SLF invasion potentials are aligned globally because important viticultural regions with suitable environments for SLF also heavily trade with invaded U.S. states. For my second chapter, I estimated host plant associations for SLF with phylogenetic imputation and predicted SLF host associations for the U.S. Many known and predicted high association host species are found in the uninvaded Midwest, Southeast, and West Coast as well as the Mid-Atlantic and Northeast, where SLF is present. Should SLF spread further, these regions are likely to experience impacts to resident trees. For my third chapter, I proposed a method for detecting three non-random extinction models and used the imperiled Caribbean lizard genus Leiocephalus as a case study to test it. Past extinctions showed directional loss of larger Leiocephalus species. However, future predicted extinctions are random for body size but show stabilizing extinction of species with either smaller or larger limb and tail lengths. Shifting extinction for Leiocephalus may occur because of changing pressures that now include anthropogenic habitat loss. Altogether, these studies attest to the value of developing and evaluating approaches to describe biodiversity dynamics in the Anthropocene. / Biology
10

Spatial and Temporal Variability in Marine Invasion and Trophic Dynamics

Papacostas, Katherine J January 2014 (has links)
Species interactions are central to the study of community ecology, but these interactions can change with context. For instance, predator-prey interactions can vary with species introductions, spatial scale and temporal scale, and we are still learning how such factors can influence the strength of these interactions. Studying species interactions via multifaceted approaches and at different scales aids in the understanding of local and large scale processes, and can lead to predictions of how our ecosystems will persist in the face of continued anthropogenic alteration of the globe. The present series of studies sought to explore spatial and temporal variability in marine predator-prey interactions and invasion dynamics. The first objective was to assess biogeographic variability in predator invasions in the field. The second examined spatial variation in niche breadth via field collections, laboratory dissections, and database development, and the third involved a series of laboratory and field experiments as well as population modeling to examine temporal variability in native and non-native behavioral interactions. Specifically for the first objective, I examined the strength of marine invasive species-induced trophic cascades across latitude, hypothesizing that a non-native tertiary consumer could facilitate non-native basal prey establishment through the consumption of a native secondary consumer. I further predicted that the ecological importance of this cascade may be reduced in the subtropics relative to the temperate zone due to stronger predation pressure at lower latitudes. I found evidence of a trophic cascade in both regions, but it was only maintained under ambient predation pressure in the temperate zone. My results also suggest that strong predation pressure on the non-native intermediate predators in the subtropics may explain the weakened cascade under ambient conditions. For the second objective, I tested the hypothesis of increased specialization at lower latitudes using Brachyuran crabs as a model system and diet as my measure for niche breadth, while controlling for range size, body size and evolutionary relatedness. I compiled a dataset on 39 crab species' diets from existing studies and conducted my own diet analyses on species collected in a temperate, subtropical and tropical region, resulting in a global comparison. I found that latitudinal position was correlated with range size for temperate species, but not for tropical species, and found no correlation between the other focal variables and latitude. These results suggest that ecological mechanisms (i.e. competition strength) may be driving patterns of niche breadth in the temperate zone, while evolutionary mechanisms may be more important in predicting niche breadth patterns in tropical systems. For the third objective, I examined the influence of native and non-native prey naïveté on intermediate predator invasion success. I hypothesized that 1) naïveté is greatest in earlier stages of invasion across all trophic levels, decreasing the longer a non-native species is established in a system, 2) Native prey naïveté results in resource effects which increases invasion success, or 3) predator effects on non-native species would outweigh the importance of basal native prey naïveté, preventing an increase in non-native population growth. Through laboratory trials, I found support for naïveté being stronger at earlier stages of invasion, for both native basal prey and non-native intermediate predators. I also found weak predation on the more recently established intermediate predator in the field. However, my population model predicted that growth independent of basal prey naïveté. These results suggest that physiological traits, such as conversion efficiency and growth rates of the invasive crab may be driving its population growth more-so than foraging benefits. My studies surrounding the variability of species interactions are the first to examine the strength of invasive species-induced trophic cascades across latitude, one of very few marine empirical studies to examine diet breadth at a large spatial scale, and the first to examine multi-trophic behavioral effects on invasion success respectively. They highlight the importance of studying multi-trophic interactions, as examining more pieces of the food web is increasingly important in developing a broader understanding of interactions and adaptations within invaded communities. My research also highlights the importance of studying interactions from a macroecological perspective. Tracking both invasions and native species interactions through space and time provides insight into marine community dynamics and may elucidate possible mechanisms of species coexistence. / Biology

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