Matching Items (20)

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A Tale of Two Canyons: Abiotic factors and the distribution of a pathogenic fungus in southeastern Arizona

Description

Chytridiomycosis, an infectious disease caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), has played a significant role in global amphibian declines. Researchers studying Bd aim to gain a better

Chytridiomycosis, an infectious disease caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), has played a significant role in global amphibian declines. Researchers studying Bd aim to gain a better understanding of how this pathogen survives in unique microhabitats to promote persistence of amphibians in their natural habitat. The Arizona Game and Fish Department has worked for the last 12 years to recover populations of Chiricahua Leopard Frogs to ensure the species survives in the Huachuca Mountains in southeastern Arizona. During this time, the department tested for Bd throughout their release sites. As a result of large differences in prevalence noted in prior sampling for Bd in Miller and Ramsey canyons, I investigated abiotic factors that could explain these differences. I analyzed water samples from two canyons in the Huachuca Mountains and used nutrient analysis and filter extraction to test for differences in abiotic factors between these two sites that could affect Bd transmission. Results show that Ramsey Canyon was a positive site for Bd, while Miller Canyon remained negative. Results from water temperature estimates as well as a test for 30 elements revealed possible reasons for differences in Bd transmission between the two canyons.

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Created

Date Created
  • 2017-05

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Paleodistribution modeling in archaeology and paleoanthropology

Description

Species distribution modeling (SDM) is a methodology that has been widely used in the past two decades for developing quantitative, empirical, predictive models of species–environment relationships. SDM methods could be

Species distribution modeling (SDM) is a methodology that has been widely used in the past two decades for developing quantitative, empirical, predictive models of species–environment relationships. SDM methods could be more broadly applied than they currently are to address research questions in archaeology and paleoanthropology. Specifically, SDM can be used to hindcast paleodistributions of species and ecological communities (paleo-SDM) for time periods and locations of prehistoric human occupation. Paleo-SDM may be a powerful tool for understanding human prehistory if used to hindcast the distributions of plants, animals and ecological communities that were key resources for prehistoric humans and to use this information to reconstruct the resource landscapes (paleoscapes) of prehistoric people. Components of the resource paleoscape include species (game animals, food plants), habitats, and geologic features and landforms associated with stone materials for tools, pigments, and so forth. We first review recent advances in SDM as it has been used to hindcast paleodistributions of plants and animals in the field of paleobiology. We then compare the paleo-SDM approach to paleoenvironmental reconstructions modeled from zooarchaeological and archaeobotanical records, widely used in archaeology and paleoanthropology. Next, we describe the less well developed but promising approach of using paleo-SDM methods to reconstruct resource paleoscapes. We argue that paleo-SDM offers an explicitly deductive strategy that generates spatial predictions grounded in strong theoretical understandings of the relation between species, habitat distributions and environment. Because of their limited sampling of space and time, archaeobiological records may be better suited for paleo-SDM validation than directly for paleoenvironmental reconstruction. We conclude by discussing the data requirements, limitations and potential for using predictive modeling to reconstruct resource paleoscapes. There is a need for improved paleoclimate models, improved paleoclimate proxy and species paleodistribution data for model validation, attention to scale issues, and rigorous modeling methods including mechanistic models.

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Created

Date Created
  • 2014-12-17

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Spatial patterns of grassland-shrubland state transitions: a 74-year record on grazed and protected areas

Description

Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to

Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns of shrub proliferation, little is known about how they are influenced by grazing or the extent to which they are influenced by intraspecific interactions. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite plants have lateral roots extending well beyond the canopy. We therefore hypothesized that mesquite distributions would be random on grazed areas mainly due to cattle dispersion and clustered on protected areas due to decreased dispersal and interspecific interference with grasses; and that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948, and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass–shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management.

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Created

Date Created
  • 2014-09-01

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Combined Influences of Model Choice, Data Quality, and Data Quantity When Estimating Population Trends

Description

Estimating and projecting population trends using population viability analysis (PVA) are central to identifying species at risk of extinction and for informing conservation management strategies. Models for PVA generally fall

Estimating and projecting population trends using population viability analysis (PVA) are central to identifying species at risk of extinction and for informing conservation management strategies. Models for PVA generally fall within two categories, scalar (count-based) or matrix (demographic). Model structure, process error, measurement error, and time series length all have known impacts in population risk assessments, but their combined impact has not been thoroughly investigated. We tested the ability of scalar and matrix PVA models to predict percent decline over a ten-year interval, selected to coincide with the IUCN Red List criterion A. 3, using data simulated for a hypothetical, short-lived organism with a simple life-history and for a threatened snail, Tasmaphena lamproides. PVA performance was assessed across different time series lengths, population growth rates, and levels of process and measurement error. We found that the magnitude of effects of measurement error, process error, and time series length, and interactions between these, depended on context. We found that high process and measurement error reduced the reliability of both models in predicted percent decline. Both sources of error contributed strongly to biased predictions, with process error tending to contribute to the spread of predictions more than measurement error. Increasing time series length improved precision and reduced bias of predicted population trends, but gains substantially diminished for time series lengths greater than 10-15 years. The simple parameterization scheme we employed contributed strongly to bias in matrix model predictions when both process and measurement error were high, causing scalar models to exhibit similar or greater precision and lower bias than matrix models. Our study provides evidence that, for short-lived species with structured but simple life histories, short time series and simple models can be sufficient for reasonably reliable conservation decision-making, and may be preferable for population projections when unbiased estimates of vital rates cannot be obtained.

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Created

Date Created
  • 2015-07-15

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The Roles of Dispersal, Fecundity, and Predation in the Population Persistence of an Oak (Quercus engelmannii) under Global Change

Description

A species’ response to climate change depends on the interaction of biotic and abiotic factors that define future habitat suitability and species’ ability to migrate or adapt. The interactive effects

A species’ response to climate change depends on the interaction of biotic and abiotic factors that define future habitat suitability and species’ ability to migrate or adapt. The interactive effects of processes such as fire, dispersal, and predation have not been thoroughly addressed in the climate change literature. Our objective was to examine how life history traits, short-term global change perturbations, and long-term climate change interact to affect the likely persistence of an oak species - Quercus engelmannii (Engelmann oak). Specifically, we combined dynamic species distribution models, which predict suitable habitat, with stochastic, stage-based metapopulation models, which project population trajectories, to evaluate the effects of three global change factors – climate change, land use change, and altered fire frequency – emphasizing the roles of dispersal and seed predation. Our model predicted dramatic reduction in Q. engelmannii abundance, especially under drier climates and increased fire frequency. When masting lowers seed predation rates, decreased masting frequency leads to large abundance decreases. Current rates of dispersal are not likely to prevent these effects, although increased dispersal could mitigate population declines. The results suggest that habitat suitability predictions by themselves may under-estimate the impact of climate change for other species and locations.

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Created

Date Created
  • 2012-05-18

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Changes in a West Indian Bird Community Since the Late Pleistocene

Description

Aim
To establish a chronology for late Quaternary avian extinction, extirpation and persistence in the Bahamas, thereby testing the relative roles of climate change and human impact as causes of

Aim
To establish a chronology for late Quaternary avian extinction, extirpation and persistence in the Bahamas, thereby testing the relative roles of climate change and human impact as causes of extinction.
Location
Great Abaco Island (Abaco), Bahamas, West Indies.
Methods
We analysed the resident bird community as sampled by Pleistocene (> 11.7 ka) and Holocene (< 11.7 ka) fossils. Each species was classified as extinct (lost globally), extirpated (gone from Abaco but persists elsewhere), or extant (still resident on Abaco). We compared patterns of extinction, extirpation and persistence to independent estimates of climate and sea level for glacial (late Pleistocene) and interglacial (Holocene) times.
Results
Of 45 bird species identified in Pleistocene fossils, 25 (56%) no longer occur on Abaco (21 extirpated, 4 extinct). Of 37 species recorded in Holocene deposits, 15 (14 extirpated, 1 extinct; total 41%) no longer exist on Abaco. Of the 30 extant species, 12 were recovered as both Pleistocene and Holocene fossils, as were 9 of the 30 extirpated or extinct species. Most of the extinct or extirpated species that were only recorded from Pleistocene contexts are characteristic of open habitats (pine woodlands or grasslands); several of the extirpated species are currently found only where winters are cooler than in the modern or Pleistocene Bahamas. In contrast, most of the extinct or extirpated species recorded from Holocene contexts are habitat generalists.
Main conclusions
The fossil evidence suggests two main times of late Quaternary avian extirpation and extinction in the Bahamas. The first was during the Pleistocene–Holocene transition (PHT; 15–9 ka) and was fuelled by climate change and associated changes in sea level and island area. The second took place during the late Holocene (< 4 ka, perhaps primarily < 1 ka) and can be attributed to human impact. Although some species lost during the PHT are currently found where climates are cooler and drier than in the Bahamas today, a taxonomically and ecologically diverse set of species persisted through that major climate change but did not survive the past millennium of human presence.

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Created

Date Created
  • 2015-03-01

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Abiotic and Biotic Drivers of Turnover and Community Assembly in African Mammals

Description

Climate and environmental forcing are widely accepted to be important drivers of evolutionary and ecological change in mammal communities over geologic time scales. This paradigm has been particularly influential in

Climate and environmental forcing are widely accepted to be important drivers of evolutionary and ecological change in mammal communities over geologic time scales. This paradigm has been particularly influential in studies of the eastern African late Cenozoic fossil record, in which aridification, increasing seasonality, and C4 grassland expansion are seen as having shaped the major patterns of human and faunal evolution. Despite the ubiquity of studies linking climate and environmental forcing to evolutionary and ecological shifts in the mammalian fossil record, many central components of this paradigm remain untested or poorly developed. To fill this gap, this dissertation employs biogeographical and macroecological analyses of present-day African mammal communities as a lens for understanding how abiotic change may have shaped community turnover and structure in the eastern African Plio-Pleistocene. Three dissertation papers address: 1) the role of ecological niche breadth in shaping divergent patterns of macroevolutionary turnover across clades; 2) the effect of climatic and environmental gradients on community assembly; 3) the relative influence of paleo- versus present-day climates in structuring contemporary patterns of community diversity. Results of these papers call into question many tenets of current theory, particularly: 1) that niche breadth differences (and, by extension, their influence on allopatric speciation) are important drivers of macroevolution, 2) that climate is more important than biotic interactions in community assembly, and 3) that communities today are in equilibrium with present-day climates. These findings highlight the need to critically reevaluate the role and scale-dependence of climate in mammal evolution and community ecology and to carefully consider potential time lags and disequilibrium dynamics in the fossil record.

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Created

Date Created
  • 2018

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Anthropogenic fire and the development of Neolithic agricultural landscapes: connecting archaeology, paleoecology, and fire science to evaluate human impacts on fire regimes

Description

The recent emergence of global ‘megafires’ has made it imperative to better understand the role of humans in altering the size, distribution, and seasonality of fires. The dynamic relationship between

The recent emergence of global ‘megafires’ has made it imperative to better understand the role of humans in altering the size, distribution, and seasonality of fires. The dynamic relationship between humans and fire is not a recent phenomenon; rather, fire has deep roots in our biological and cultural evolution. Because of its long-term perspective, archaeology is uniquely positioned to investigate the social and ecological drivers behind anthropogenic fire. However, the field faces challenges in creating solution-oriented research for managing fire in the future. In this dissertation, I originate new methods and approaches to archaeological data that enable us to interpret humans’ long-term influences on fire regimes. I weave together human niche construction theory and ecological resilience, creating connections between archaeology, paleoecology, and fire ecology. Three, stand-alone studies illustrate the usefulness of these methods and theories for charting changes in land-use, fire-regimes, and vegetation communities during the Neolithic Transition (7600 - 3800 cal. BP) in eastern Spain. In the first study (Ch. II), I analyze archaeological survey data using Bayesian methods to extract land-use intensities from mixed surface assemblages from a case study in the Canal de Navarrés. The second study (Ch. III) builds on the archaeological data collected computational model of landscape fire, charcoal dispersion, and deposition to test how multiple models of natural and anthropogenic fire activity contributed to the formation a single sedimentary charcoal dataset from the Canal de Navarrés. Finally, the third study (Ch. IV) incorporates the modeling and data generated in the previous chapters into sampling and analysis of sedimentary charcoal data from alluvial contexts in three study areas throughout eastern Spain. Results indicate that anthropogenic fire played a significant role in the creation of agricultural landscapes during the Neolithic period, but sustained, low-intensity burning after the late Neolithic period maintained the human created niche for millennia beyond the arrival of agro-pastoral land-use. With global fire activity on the rise, it is vital to incorporate perspectives on the origins, development, and maintenance of human-fire relationships to effectively manage fire in today’s coupled social-ecological landscapes.

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Created

Date Created
  • 2019

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Effects of climate change and urban development on the distribution and conservation of vegetation in a Mediterranean type ecosystem

Description

Climate and land use change are projected to threaten biodiversity over the coming century. However, the combined effects of these threats on biodiversity and the capacity of current conservation networks

Climate and land use change are projected to threaten biodiversity over the coming century. However, the combined effects of these threats on biodiversity and the capacity of current conservation networks to protect species' habitat are not well understood. The goals of this study were to evaluate the effect of climate change and urban development on vegetation distribution in a Mediterranean-type ecosystem; to identify the primary source of uncertainty in suitable habitat predictions; and to evaluate how well conservation areas protect future habitat in the Southwest ecoregion of the California Floristic Province. I used a consensus-based modeling approach combining three different species distribution models to predict current and future suitable habitat for 19 plant species representing different plant functional types (PFT) defined by fire-response (obligate seeders, resprouting shrubs), and life forms (herbs, subshurbs). I also examined the response of species grouped by range sizes (large, small). I used two climate models, two emission scenarios, two thresholds, and high-resolution (90m resolution) environmental data to create a range of potential scenarios. I evaluated the effectiveness of an existing conservation network to protect suitable habitat for rare species in light of climate and land use change. The results indicate that the area of suitable habitat for each species varied depending on the climate model, emission scenario, and threshold combination. The suitable habitat for up to four species could disappear from the ecoregion, while suitable habitat for up to 15 other species could decrease under climate change conditions. The centroid of the species' suitable environmental conditions could shift up to 440 km. Large net gains in suitable habitat were predicted for a few species. The suitable habitat area for herbs has a small response to climate change, while obligate seeders could be the most affected PFT. The results indicate that the other two PFTs gain a considerable amount of suitable habitat area. Several rare species could lose suitable habitat area inside designated conservation areas while gaining suitable habitat area outside. Climate change is predicted to be more important than urban development as a driver of habitat loss for vegetation in this region in the coming century. These results indicate that regional analyses of this type are useful and necessary to understand the dynamics of drivers of change at the regional scale and to inform decision making at this scale.

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Created

Date Created
  • 2012

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A Seed Bank Study of Southwestern Riparian Areas: Temperature Effects and Diversity

Description

Throughout the Southwest, complex geology and physiography concomitant with climatic variability contribute to diverse stream hydrogeomorphologies. Many riparian plant species store their seeds in soil seed banks, and germinate

Throughout the Southwest, complex geology and physiography concomitant with climatic variability contribute to diverse stream hydrogeomorphologies. Many riparian plant species store their seeds in soil seed banks, and germinate in response to moisture pulses, but the climatic controls of this response are poorly understood. To better understand the ecological implications of a changing climate on riparian plant communities, I investigated seed bank responses to seasonal temperature patterns and to stream hydrogeomorphic type. I asked the following questions: Are there distinct suites of warm and cool temperature germinating species associated with Southwestern streams; how do they differ between riparian and terrestrial zones, and between ephemeral and perennial streams? How does alpha diversity of the soil seed bank differ between streams with ephemeral, intermittent, and perennial flow, and between montane and basin streams? Do streams with greater elevational change have higher riparian zone seed bank beta-diversity? Does nestedness or turnover contribute more to within stream beta-diversity?

I collected soil samples from the riparian and terrestrial zones of 21 sites, placing them in growth chambers at one of two temperature regimes, and monitoring emergence of seedlings for 12 weeks. Results showed an approximately equal number of warm and cool specialists in both riparian and terrestrials zones; generalists also were abundant, particularly in the riparian zone. The number of temperature specialists and generalists in the riparian zones did not differ significantly between perennial headwater and ephemeral stream types. In montane streams, alpha diversity of the soil seed bank was highest for ephemeral reaches; in basin streams the intermittent and perennial reaches had higher diversity. Spatial turnover was primarily responsible for within stream beta-diversity—reaches had different species assemblages. The large portion of temperature specialists found in riparian seed banks indicates that even with available moisture riparian zone plant community composition will likely be impacted by changing temperatures. However, the presence of so many temperature generalists in the riparian zones suggests that some component of the seed bank is adapted to variable conditions and might offer resilience in a changing climate. Study results confirm the importance of conserving multiple hydrogeomorphic reach types because they support unique species assemblages.

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Created

Date Created
  • 2016