R-3 Repository :: Browsing by Author "Rudolf, Volker H. W."

Browsing by Author "Rudolf, Volker H. W."

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Carry-over effects in space: Beyond single species studies and towards metacommunity dynamics
(2014-04-25) Van Allen, Benjamin G; Rudolf, Volker H. W.; Miller, Thomas E.; Dunham, Amy E.; Lane, David M.
The behavioral and physical traits of adults can be strongly influenced by conditions experienced during development. Consequently, variation in natal habitat quality across a landscape and through time can also lead to differences in the traits of adults. When individuals move across the landscape, this could create carry-over effects where differences in the natal habitat quality of colonizers influence population dynamics and species interactions in new habitats. I studied how these carry-over effects, which are known to alter individual traits and population dynamics, scale up to larger effects on community and metacommunity (multiple communities across a landscape connected by dispersing individuals) dynamics. I tested these questions on carry-over effects in a spatial context using a Tribolium spp. flour beetle system with habitat patches of flour. I generated carry-over effects by using flour types which predictably alter the traits of flour beetles who develop in them. The first chapter identified that carry-over effects which alter population dynamics occur in this system. It also discovered novel and powerful mechanisms for carry-over effects to influence population dynamics. The second chapter shows how carry-over effects and population density interact to affect dispersal decisions, which is important for understanding how carry-over effects will propagate across landscapes. The third chapter shows that carry-over effects can decisively alter competitive dynamics and outcomes, but that how may not be immediately predictable from their influence on single population dynamics. Finally, my fourth chapter manipulated whether carry-over effects occurred across multi-patch landscapes to test whether they influence species dynamics across a metacommunity. This final chapter shows that at the landscape scale, carry-over effects can have even more strong emergent effects. For example, carry-over effects increased population sizes across landscapes by ~10% while dramatically promoting different species under different conditions of dispersal and habitat arrangement. Thus, the influences of carry-over effects on population and community dynamics at the landscape level may be strong, but context dependent on other spatial processes. Further work to understand how landscape habitat patterns and dispersal shape the influence of carry-over effects on metacommunity dynamics could improve understanding of natural population and community dynamics.
Climate warming promotes pesticide resistance through expanding overwintering range of a global pest
(Springer Nature, 2021) Ma, Chun-Sen; Zhang, Wei; Peng, Yu; Zhao, Fei; Chang, Xiang-Qian; Xing, Kun; Zhu, Liang; Ma, Gang; Yang, He-Ping; Rudolf, Volker H. W.
Climate change has the potential to change the distribution of pests globally and their resistance to pesticides, thereby threatening global food security in the 21st century. However, predicting where these changes occur and how they will influence current pest control efforts is a challenge. Using experimentally parameterised and field-tested models, we show that climate change over the past 50 years increased the overwintering range of a global agricultural insect pest, the diamondback moth (Plutella xylostella), by ~2.4 million km2 worldwide. Our analysis of global data sets revealed that pesticide resistance levels are linked to the species’ overwintering range: mean pesticide resistance was 158 times higher in overwintering sites compared to sites with only seasonal occurrence. By facilitating local persistence all year round, climate change can promote and expand pesticide resistance of this destructive species globally. These ecological and evolutionary changes would severely impede effectiveness of current pest control efforts and potentially cause large economic losses.
Evolutionary responses to global change: an experimental test of the effect of altered precipitation on hybridization rates in sunflower (Helianthus)
(2013-07-24) Sneck, Michelle; Whitney, Kenneth D.; Miller, Thomas E.; Rudolf, Volker H. W.
Climate change is rapidly altering natural ecosystems. Plastic and adaptive responses to climate change (i.e., range shifts and phenology) have been widely noted across taxa. However, the effects of climate change on evolutionary processes such as interspecific gene flow (hybridization) are less well known. In this study, we quantified hybridization rates in response to experimental manipulations of rainfall, an important dimension of global change. We used rain-out shelters in the field and quantified rates of hybridization between two congeners, Helianthus annuus (common sunflower) and H. petiolaris (prairie sunflower). We found that H. annuus maternal plants produced hybrid progeny more than H. petiolaris maternal plants, with a trend for decreased rates of hybridization with increased soil moisture (when rain-out shelters were absent). The relative number of open inflorescences of each species predicted hybridization rates. Thus, this study demonstrates how changing environmental conditions, specifically precipitation, could influence hybridization rates.
Evolutionary Trajectories to Daptomycin Resistance in Enterococcus faecalis
(2013-11-18) Miller, Corwin; Olson, John S.; Shamoo, Yousif; Bennett, Matthew R.; Rudolf, Volker H. W.; Tao, Yizhi Jane
With increasing amounts of hospital-acquired antibiotic resistant infections each year and staggering healthcare costs, there is a clear need for new antimicrobial agents, as well as novel strategies to extend their clinical efficacy. While genomic studies have provided a wealth of information about the alleles associated with adaptation to antibiotics, they do not provide essential information about relative importance of genomic changes, their order of appearance, or potential epistatic relationships between adaptive changes. In this thesis, I have combined experimental evolution, comparative whole genome sequencing, and allelic frequency measurements to study daptomycin (DAP) resistance in the vancomycin resistant clinical pathogen Enterococcus faecalis strain S613. Maintaining cells inside a turbidostat, a single polymorphic culture was grown sustaining both planktonic and non-planktonic (e.g. biofilm) populations in co-culture as the concentration of antibiotic was raised, facilitating the development of more ecological complexity than is typically observed in laboratory evolution. This approach revealed a clear order and hierarchy of genetic changes leading to resistance, the signaling and metabolic pathways responsible, and the relative importance of these mutations to the evolution of DAP resistance. Genetic and phenotypic comparisons between resistant isolates also identified convergent evolutionary trajectories, suggesting a common biochemical mechanism of resistance. Despite the relative ecological simplicity of this approach compared to the complexity of the human body, I show that experimental evolution can be used to rapidly identify clinically relevant adaptive molecular pathways and new targets for drug design in pathogens.
Intraspecific variation in metacommunities: Linking regional heterogeneity to local population dynamics
(2014-12-03) Dibble, Christopher Joseph; Rudolf, Volker H. W.; Miller, Tom; Kohn, Michael; Lane, David
Variation within species drives differences in population dynamics, interactions between species, and the functioning of complex ecosystems. Fittingly, understanding the factors that govern this intraspecific variation remains a central goal of ecology and evolutionary biology. Local processes such as adaptation tend to increase divergence among distinct populations, while regional processes such as dispersal and gene flow tend to homogenize those differences. My research addresses how heterogeneity is maintained despite the movement of individuals around a landscape. Specifically, I use an experimental host-parasite system to propose and test mechanisms contributing to ecological differentiation. Initially, I found that variation in colonizer traits makes the order in which they arrive to a new habitat important. Intraspecific priority effects (IPEs) occur when early arrivers limit the growth of late arrivers, and drive context-dependent differences in growth among populations (Chapter 1). These effects of variation in individual traits and arrival order extended to alter interspecific competition and host/parasite interactions. My research indicates, then, that the process of community assembly depends not only on the traits of a dominant species in the environment, but also which individuals of that species get there first (Chapter 2). The relatively short-term importance of IPEs, however, may wane over time as individuals continue to disperse among populations. I tested the consequences of repeated dispersal, and found that they depend heavily on the expected fitness of migrants in their new habitat. That is, dispersal from a common source can increase ecological heterogeneity among populations if migrants have different effects in different environments (Chapter 3). The context-dependent effects of dispersal suggested an underlying trait-based mechanism. Specifically, I hypothesized that the effects of increasing trait variance in a population (e.g. via immigration) depend on the relationship between a population’s trait mean and the local environmental optimum. I found that increasing trait variance helps populations with suboptimal trait means, but harms populations already well-suited to the local environment, doubling their disease burden (Chapter 4). Overall, my research identifies novel ways in which intraspecific variation contributes to its own maintenance, limiting the ability of individual movement among populations to homogenize ecological and evolutionary differentiation.
Late Quaternary Mixed Carbonate-Siliciclastic Sediment Slope Accumulation: Unexpected Responses of Australia and Papua New Guinea Reefs to Glacio-Eustatic Sea Level Fluctuations
(2014-06-24) Harper, Brandon Babbel; Droxler, Andre W; Dickens, Gerald R; Anderson, John B; Sawyer, Dale S; Rudolf, Volker H. W.
Overtime, the north Queensland (Australia) and Gulf of Papua (Papua New Guinea) margin has been constructed by the biogenic carbonate growth and development of large barrier reefs on the mid-to-outer shelves and offshore platform/atoll tops, in conjunction with latitudinally variable riverine delivery of terrigenous siliciclastic material to the coast and inner shelf. This association forms Earth’s longest tropical mixed carbonate-siliciclastic system. Spatial and temporal variations of neritic carbonate (chiefly aragonite) production and siliciclastic sediment supply are controlled by late Quaternary high amplitude sea level fluctuations and climate changes. Sediment accumulation on the upper slopes adjacent to mixed margins is an important indicator of reef establishment/demise and siliciclastic shelf bypass during a time when glacio-eustatic sea level fluctuations are well understood and sediment dating techniques well developed. Sedimentation variability since the last deglaciation and, to some degree, during the last glacial cycle, is well understood and described by the transgressive and highstand shedding, reciprocal and coeval sedimentation concepts; based on low resolution records. My Ph.D. research results enhance the understanding of reef initiation, accretion, and demise along the Great Barrier Reef and Gulf of Papua margin by adding new cores and elemental (Sr, Ca, Si, K, Al) data from high resolution x-ray fluorescence core scanning. Sea level related reef evolution along this margin is more complex than previously thought. Contrary to established models, the central Great Barrier Reef exited the photic zone during peak interglacial, Marine Isotope Stage (MIS) 5e, resulting in the drowning of the reef and extremely low aragonite mass accumulation on the upper slopes. When sea level fell, reef-tops re-entered the photic zone increased production and export of aragonite to the upper slopes. The precise timing and elevation of sea level during MIS-5a is defined by the presence and absence of aragonite within slope sediments from the flooding and exposure of reef-tops. Additionally, along the Papuan Peninsula, a barrier reef established on a glacial shelf edge delta during re-flooding at 19 ka, followed by the subsequent drowning and back-stepping of the reef, synchronous to Termination I melt water pulses, away from siliciclastics.
Nonrandom seed dispersal by lemur frugivores: mechanism, patterns and impacts
(2015-04-23) Razafindratsima, Onja Harinala Franckline Eva; Dunham, Amy E.; Rudolf, Volker H. W.; Siemann, Evan; Masiello, Caroline A.; Erhart, Elizabeth M.
Frugivores act as seed-dispersal agents in many ecosystems. Thus, understanding the roles and impacts of seed dispersal by frugivores is important to understand the structure and diversity maintenance of plant communities. Frugivore-mediated seed dispersal is behaviorally driven, generating nonrandom patterns of seed dispersion; but, we know relatively little about how this might affect plant populations or communities. I examined how frugivores affected plants from the individual level to the population and community levels. To do this, I used modeling, trait-based and phylogenetic approaches combined with field observations and experiments, focusing on seed dispersal by three frugivorous lemur species in the biodiverse rainforest of Ranomafana National Park, Madagascar. An analysis of traits suggested that 84% of trees in Ranomafana are adapted for animal dispersal, of which more than 70% are dispersed by these three lemur species indicating their role as generalist dispersers. The distribution of fruit and seed size of bird-dispersed species was nested within the wide spectrum of size distribution associated with lemur dispersal. Nonrandom seed dispersal by these three frugivores increased per capita recruitment of the seeds of a long-lived canopy tree, Cryptocarya crassifolia, by four-fold compared with no dispersal, even though it was not an overall advantage compared to random dispersal. The three frugivores not only dispersed seeds away from parent and conspecific adult-trees, but also biased seed dispersal toward certain microhabitats. By using fruiting trees as seed dispersal foci, lemur frugivores structure the spatial associations between dispersed seeds and adult-trees nonrandomly, in terms of fruiting time, dispersal mode and phylogenetic relatedness. However, lemur-dispersed tree species were not more likely to be each other’s neighbors as adults. Interestingly, co-fruiting neighboring trees sharing lemur dispersers were more phylogenetically distant than expected by chance despite a phylogenetic signal in lemur dispersal mode, although there was no phylogenetic signal in the timing of fruiting among lemur-dispersed tree species. Results suggest an important link between frugivore foraging behavior and the spatial, temporal and phylogenetic patterning of seed dispersal. The critical role of frugivores in structuring seed dispersion and seed-adult plant associations has critical implications for plant-plant interactions, biodiversity patterns and community structure.
Phenological shifts and species interactions: Disentangling the role of timing and synchrony
(2014-10-14) Rasmussen, Nicholas; Rudolf, Volker H. W.; Miller, Tom EX; Cox, Dennis D; Dunham, Amy E
Most habitats exhibit seasonal changes in environmental conditions. These seasonal patterns can vary among years, which can alter the timing of the seasonal life-history events, or phenologies, of species (e.g., emergence from dormancy, migration, reproduction). Species, and individuals within species, oftentimes differ in their phenological responses to year-specific conditions, which could alter the stage at which species interact. We do not have a good understanding of how these shifts in the timing of species interactions affect the outcome of those interactions, but determining the consequences is critical for understanding the dynamics of natural communities. Here, I use a series of experiments with communities of pond-dwelling insects and amphibians to determine how shifts in phenological timing affect intra- and interspecific interactions and whether these effects scale up to alter demographic rates, community structure, and ecosystem functioning. Specifically, I manipulated the mean hatching time (i.e., time of arrival to the habitat) for one species relative to another and/or the amount of variation in arrival time by individuals of a species around a mean date (i.e., degree of synchrony). First, I manipulated differences in mean arrival time for two species that interact as intraguild predators and found that the changes in relative size mediated by shifts in arrival time had strong effects on interactions. Specifically when arrival differences were small, the two species coexisted in similar abundances, but when arrival differences were large, the early arriver excluded the late arriver through predation. Second, I manipulated mean arrival time of one species relative to a predator and a competitor to determine how phenological shifts affected predator-prey and competitive interactions. I found that shifts in the arrival time of a single species within a community can affect the outcome of both interaction types strongly enough to alter community structure, and these changes to community structure scaled up to affect one of three ecosystem-level processes measured. Third, I manipulated variation in the synchrony of arrival, as well as initial density, of a species to determine the consequences for intraspecific competition. I found that variation in synchrony altered several demographic rates of the species, and these effects were density dependent. Finally, I used a factorial manipulation of the mean and synchrony of arrival by a prey species in the presence of a predator to determine how this variation affected predator-prey interactions. I found that the effects of variation in these two aspects of phenology on prey survival were additive, with survival declining with later arrival and lower arrival synchrony. Taken together, these results clearly demonstrate that shifts in phenological timing can have strong effects on intra- and interspecific interactions. These effects of phenological shifts on species interactions frequently scaled up to alter the structure of communities, and were even capable of affecting ecosystem-level processes. This work represents an important and novel contribution to our understanding of the dynamics of seasonal communities and will also be useful in understanding how climate change will alter these dynamics.
Restoration ecology of ecosystems invaded by Triadica sebifera (Chinese tallow tree): theory and practice
(2013-07-24) Gabler, Christopher; Siemann, Evan; Dunham, Amy E.; Bedient, Philip B.; Rudolf, Volker H. W.
Invasive exotic species threaten biodiversity and ecosystem functions globally, creating need for and encumbering ecological restoration. When restoring exotic plant-dominated ecosystems, reinvasion pressure is the rate of new exotic recruitment following mature exotic removal. It can vary broadly among similarly invaded habitats and is crucial to restoration outcomes and costs, but is difficult to predict and poorly understood. Initial results from the experimental restoration of a wetland dominated by Triadica sebifera led us to develop the ‘outgrow the stress’ hypothesis. It holds: (1) Variation in reinvasion pressure is driven by differences in propagule abundance and spatiotemporal availability of realized recruitment windows, which are defined by abiotic conditions and biotic interactions. (2) Differences in reinvasion pressure become masked by exotic dominance when increases in niche breadth during development enable exotic persistence across sites where recruitment windows range from frequent to episodic. We validated this hypothesis. First, we used greenhouse and field experiments to quantify Triadica’s moisture niche early in development. By two months post-germination, seedling tolerances broadened to include conditions unsuitable for germination. This clearly demonstrated a rapid ontogenetic niche expansion, which could decouple mature Triadica density and average reinvasion pressure. Second, we used a greenhouse mesocosm experiment to quantify how recruitment window duration, competition and fertility impacted population-level Triadica establishment in stressful environments. As ‘outgrow the stress’ predicts, longer windows increased Triadica success and multi-factor interactions were common, with competition and fertility effects varying among environmental contexts. Third, we substantiated predictions of ‘outgrow the stress’ regarding propagule availability and soil moisture by manipulating these in a multi-site field experiment spanning eleven experimental restorations of Triadica-dominated habitats along a moisture gradient. Triadica reinvasion pressure varied broadly among sites but correlated with moisture and fertility. Propagule availability drove reinvasion in favorable environments, but availability of suitable conditions trumped propagules in extreme environments. Competition reduced Triadica performance and sometimes survival. Triadica prevalence reduced native plant prevalence. Six restorations require minimal Triadica management for success. This work advances our understanding and enables better predictions of reinvasion pressure and invasions in general. Accurate predictions enhance restoration efficiency by informing site selection and optimal management strategies.
VARIATION IN SPECIES INTERACTIONS AND THEIR EVOLUTIONARY CONSEQUENCES
(2013-05-13) Chamberlain, Scott A.; Whitney, Kenneth D.; Rudgers, Jennifer A.; Cox, Dennis D.; Rudolf, Volker H. W.
Species interactions restrict or promote population growth, structure communities, and contribute to evolution of diverse taxa. I seek to understand how multiple species interactions are maintained, how human altered species interactions influence evolution, and explore factors that contribute to variation in species interactions. In Chapter 1, I examine how plants interact with multiple guilds of mutualists, many of which are costly interactions. The evolution of traits used to attract different mutualist guilds may be constrained due to ecological or genetic mechanisms. I asked if two sets of plant traits that mediate interactions with two guilds of mutualists, pollinators and ant bodyguards, were positively or negatively correlated across 36 species of Gossypium (cotton). Traits to attract pollinators were positively correlated with traits to attract ant bodyguards. Rather than interaction with one mutualist guild limiting interactions with another mutualist guild, traits have evolved to increase attraction of multiple mutualist guilds simultaneously. In Chapters 2 and 3, motivated by the fact that agriculture covers nearly 50% of the global vegetated land surface, I explore the consequences of changes in plant mutualist and antagonist guilds in agriculture for selection on plant traits. I first explore how agriculture alters abundance and community structure of mutualist pollinators and antagonist seed predators of wild Helianthus annuus texanus. Mutualists were more abundant near crops, whereas antagonists were more abundant far from crops near natural habitat. In addition, mutualist pollinator communities were more diverse near sunflower crops. Plant mutualists and antagonists respond differently to agriculture. Next, I explore how these changes in abundance and community structure of mutualists and antagonists influenced natural selection on H. a. texanus floral traits. Natural selection on heritable floral traits differed near versus far from crop sunflowers, and overall selection was more heterogeneous near crop sunflowers. Furthermore, mutualist pollinators and antagonist seed predators mediated these differences in selection. Finally, in Chapter 4, I ask if variation in interaction outcomes differs across types of species interactions. Furthermore, I examined the relative importance of factors that create context-dependency in species interactions. Using meta-analysis of 353 papers, we found that mutualisms were more likely to change sign of the interaction outcome when compared across contexts than competition, and predation was the least likely to change sign. Overall, species identity caused the greatest variation in interaction outcomes: whom you interact with is more important for context-dependency than where or when the interaction occurs. Additionally, the most important factors driving context-dependency differed significantly among species interaction types. Altogether, my work makes progress in understanding how species maintain interactions with multiple guilds of mutualists, how agriculture alters species interactions and subsequent natural selection, and the variation in species interaction outcomes and their causes.

Browsing by Author "Rudolf, Volker H. W."

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