Browsing by Author "Rudolf, Volker H.W."
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Item Cannibalism and Infectious Disease: Friends or Foes?(The University of Chicago Press, 2017) Van Allen, Benjamin G.; Dillemuth, Forrest P.; Flick, Andrew J.; Faldyn, Matthew J.; Clark, David R.; Rudolf, Volker H.W.; Elderd, Bret D.Cannibalism occurs in a majority of both carnivorous and noncarnivorous animal taxa from invertebrates to mammals. Similarly, infectious parasites are ubiquitous in nature. Thus, interactions between cannibalism and disease occur regularly. While some adaptive benefits of cannibalism are clear, the prevailing view is that the risk of parasite transmission due to cannibalism would increase disease spread and, thus, limit the evolutionary extent of cannibalism throughout the animal kingdom. In contrast, surprisingly little attention has been paid to the other half of the interaction between cannibalism and disease, that is, how cannibalism affects parasites. Here we examine the interaction between cannibalism and parasites and show how advances across independent lines of research suggest that cannibalism can also reduce the prevalence of parasites and, thus, infection risk for cannibals. Cannibalism does this by both directly killing parasites in infected victims and by reducing the number of susceptible hosts, often enhanced by the stage-structured nature of cannibalism and infection. While the well-established view that disease should limit cannibalism has held sway, we present theory and examples from a synthesis of the literature showing how cannibalism may also limit disease and highlight key areas where conceptual and empirical work is needed to resolve this debate.Item Cannibalism and Intraguild Predation Community Dynamics: Coexistence, Competitive Exclusion, and the Loss of Alternative Stable States(The University of Chicago Press, 2017) Toscano, Benjamin J.; Hin, Vincent; Rudolf, Volker H.W.Predators often exert strong top-down regulation of prey, but in many systems, juvenile predators must compete with their future prey for a shared resource. In such life-history intraguild predation (LHIGP) systems, prey can therefore also regulate the recruitment and thus population dynamics of their predator via competition. Theory predicts that such stage-structured systems exhibit a wide range of dynamics, including alternative stable states. Here we show that cannibalism is an exceedingly common interaction within natural LHIGP systems that determines what coexistence states are possible. Using a modeling approach that simulates a range of ontogenetic diet shift scenarios along a productivity gradient, we demonstrate that only if the predator is competitively dominant can cannibalism promote coexistence by allowing prey to persist. If the prey is competitively dominant, cannibalism instead results in competitive exclusion of the predator and the loss of potential alternative stable states. Further, predator exclusion occurs at low cannibalistic preference relative to empirical estimates and is consistent across LHIGP systems in which the predator undergoes a complete diet shift or diet broadening over ontogeny. Given that prey is frequently competitively dominant in natural systems, our results demonstrate that even weak cannibalism can inhibit predator persistence, prompting exploration of mechanisms that reconcile theory with the common occurrence of such interactions in nature.Item Carbon cycle and climate fluctuations during the early Paleogene: Sedimentological characteristics and environmental ramifications(2014-11-13) Slotnick, Benjamin; Dickens, Gerald R.; Lee, Cin-Ty A.; Anderson, John B.; Masiello, Carrie A.; Rudolf, Volker H.W.The early Paleogene was marked by extensive changes related to Earth surface temperature, carbon cycling, and the hydrological cycle. This included at least two, and probably more, geologically brief (~200-k.yr.) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and the Eocene thermal maximum-2 (ETM-2) along with a moderately-long (~1.5-2 M.yr.) period of warmth (i.e.; Early Eocene Climatic Optimum [EECO]). This was preceded by a moderately-long (~2 M.yr.) period of cool conditions (i.e. Paleocene Carbon Isotope Maximum [PCIM]) and followed by the initiation of long-term cooling through the Cenozoic. The long-term rise in warmth and numerous short-term “hyperthermal” events, marked by pronounced negative carbon isotope excursions and clay-rich horizons (Zachos et al., 2005; Nicolo et al., 2007), have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and intense global climate change, but the exact character of the hyperthermals is not well-recognized. To better constrain and understand their occurrences, well-resolved and high-resolution records across the entire interval of interest is necessary. Preceding studies demonstrated major fluctuations in carbon cycling and terrestrial weathering (e.g.; Nicolo et al., 2007) during the latest Paleocene and earliest Eocene as well as a significant drop of dissolved oxygen concentrations during the PETM onset (Nicolo et al., 2010). However, causes, environmental impact, and relationships relating carbon release and capture to terrigenous runoff and surface temperatures throughout the exogenic system, particularly in spatial and temporal contexts, remain unclear. The southern Pacific region (Clarence Valley) and Indian Ocean (Ninetyeast Ridge) represent large realms of our planet’s ocean system that have been largely overlooked in part due to limited Paleogene core availability from Integrated Ocean Drilling Program (IODP). There is a need to better improve records related to carbon in the exogenic system throughout the Cenozoic, and in particular, the Paleogene. As of now, records lack in these regions. Clarence Valley in eastern Marlborough, New Zealand trends southwest for ~80 km between the Seaward and Inland Kaikouras. Along the northwest margin is a succession of streams, including Mead and Branch Streams, which have incised and exposed an uplifted and rotated block consisting of Amuri Limestone, a calcareous-rich formation within the Muzzle Group. These outer shelf and upper continental slope strata originally accumulated as terrigenous detrital clay minerals, biogenic silica, and biogenic carbonate. This was situated contiguous to a neritic carbonate platform along a passive margin of proto-New Zealand at ~55-50°S latitude. Ninetyeast Ridge, one of the longest near-linear features on Earth with a length of ~4600 km (from ~10ºN to ~31ºS), is located in the Indian Ocean. Numerous Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP) sites have been drilled adjacent to or along the ridge crest. Three sites in particular drilled during DSDP Leg 22 (i.e.; Sites 213, 214, and 215) include calcareous-rich material from much of the Paleogene. These sediments can provide additional constraints to further our understanding of Indian Ocean paleoceanographic changes during the Paleogene. The lack of data for the Paleogene has been an issue for quite some time now. As such, the Paleogene remains a specific interval of time that has the potential to be much better understood by integrating current views of carbon cycling to new and wellresolved data-sets. Here I analyzed sequences exposed in Clarence Valley and sections from Ninetyeast Ridge DSDP Sites to address these issues. These records were integrated into a global context to relate short-term (<100 k.yr.) and long-term (> 1 m.yr) changes. I generated lithologic and carbon isotopic records to evaluate the entire period of interest, including the PCIM, specific hyperthermals, EECO, and the Middle Eocene Climatic Optimum (MECO). Integration of each section revealed similarities, including long-term trends with similar carbon isotopic baselines and short-term events. Expanded marl-rich units concurrent to lower δ13C, specifically across CIEs, generally characterized marginal sedimentation whereas condensed intervals largely spanned deep-water settings, resulting from carbonate dissolution. Together, these studies indicate carbon addition and removal mechanisms repeatedly spanned much of the Paleogene, causing calcite compensation depth (CCD) fluctuations, related to lithologic, and carbon isotopic changes.Item Ghosts of Habitats Past: Environmental Carry-Over Effects Drive Population Dynamics in Novel Habitat(The University of Chicago Press, 2013-05) Van Allen, Benjamin G.; Rudolf, Volker H.W.The phenotype of adults can be strongly influenced by the environmental conditions experienced during development. Consequently, variation in habitat quality across space and through time also leads to differences in the phenotypes of adults. This could create carry-over effects where differences in the natal habitat quality of colonizers influence population dynamics in new habitats. We tested this hypothesis experimentally by simulating dispersal of Tribolium castaneum from low- or high-quality natal habitat into new patches of low- or high-quality habitat. Differences in the natal habitat quality of colonizers altered population growth trajectories and led to carrying capacities that differed by up to 63% within a habitat type, indicating that patch dynamics are determined by the interaction of past and current habitat quality. Interestingly, even after multiple generations, the natal habitat of colonizers determined differences in adult traits that were related to density-dependent population regulation. These changes in adult phenotype could at least partially explain why carry-over effects continued to alter population dynamics for multiple generations until the end of the experiment. These results highlight the importance of variable habitat quality and carryover effects for population dynamics.Item Individual and combined effects of two types of phenological shifts on predator–prey interactions(Ecological Society of America, 2016) Rasmussen, Nick L.; Rudolf, Volker H.W.Timing of phenological events varies among years with natural variation in environmental conditions and is also shifting in response to climate change. These phenological shifts likely have many effects on species interactions. Most research on the ecological consequences of phenological shifts has focused on variation in simple metrics such as phenological firsts. However, for a population, a phenological event exhibits a temporal distribution with many attributes that can vary (e.g., mean, variance, skewness), each of which likely has distinct effects on interactions. In this study, we manipulated two attributes of the phenological distribution of a prey species to determine their individual and combined effects on predatorﾖprey interactions. Specifically, we studied how shifts in the mean and variation around the mean (i.e., synchrony) of hatching by tadpoles (Hyla cinerea) affected interactions with predatory dragonfly naiads (Tramea carolina). At the end of larval development, we quantified survival and growth of predator and prey. We found that both types of shifts altered demographic rates of the prey; that the effects of synchrony shifts, though rarely studied, were at least as strong as those due to mean shifts; and that the combined effects of shifts in synchrony and mean were additive rather than synergistic. By dissecting the roles of two types of shifts, this study represents a significant step toward a comprehensive understanding of the complex effects of phenological shifts on species interactions. Embracing this complexity is critical for predicting how climate change will alter community dynamics.Item Intraspecific priority effects and disease interact to alter population growth(Ecological Society of America, 2014) Dibble, Christopher J.; Hall, Spencer R.; Rudolf, Volker H.W.Intraspecific variation may shape colonization of new habitat patches through a variety of mechanisms. In particular, trait variation among colonizing individuals can produce intraspecific priority effects (IPEs), where early arrivers of a single species affect the establishment or growth of later conspecifics. While we have some evidence for the importance of IPEs, we lack a general understanding of factors affecting their presence or magnitude across a landscape. Specifically, IPEs should depend strongly on success of colonizers in the new habitat patch. This success hinges on interactions between colonizer traits and local selective pressures, but such context dependence remains unexplored experimentally. We addressed this gap by looking for the dynamical signature of IPEs in environments with and without a selective (parasite) pressure. We tested whether IPEs affected the population dynamics of a zooplankton host species (Daphnia dentifera) collected from two populations showing a tradeoff between growth rate and resistance to a fungal parasite (Metschnikowia bicuspidata). Differences in arrival order significantly altered population growth during a period of rapid resource depletion, driving large (up to 65%) differences in population abundance. Furthermore, the presence of IPEs was context dependent, as parasites reduced the impact of early arrivers on later arrivers. Such context-dependent IPEs, mediated by colonizer traits, colonization order, and selective pressures, may play an unanticipated role in the ecological and evolutionary dynamics of natural metapopulations. This mechanism highlights the overall importance of intraspecific variation for understanding ecological patterns.Item Linking phenological shifts to species interactions through size-mediated priority effects(British Ecological Society, 2014) Rasmussen, Nick L.; Van Allen, Benjamin G.; Rudolf, Volker H.W.Interannual variation in seasonal weather patterns causes shifts in the relative timing of phenological events of species within communities, but we currently lack a mechanistic understanding of how these phenological shifts affect species interactions. Identifying these mechanisms is critical to predicting how interannual variation affects populations and communities. Species phenologies, particularly the timing of offspring arrival, play an important role in the annual cycles of community assembly. We hypothesize that shifts in relative arrival of offspring can alter interspecific interactions through a mechanism called size-mediated priority effects (SMPE), in which individuals that arrive earlier can grow to achieve a body size advantage over those that arrive later. In this study, we used an experimental approach to isolate and quantify the importance of SMPE for species interactions. Specifically, we simulated shifts in relative arrival of the nymphs of two dragonfly species to determine the consequences for their interactions as intraguild predators. We found that shifts in relative arrival altered not only predation strength but also the nature of predatorﾖprey interactions. When arrival differences were great, SMPE allowed the early arriver to prey intensely upon the late arriver, causing exclusion of the late arriver from nearly all habitats. As arrival differences decreased, the early arriverﾒs size advantage also decreased. When arrival differences were smallest, there was mutual predation, and the two species coexisted in similar abundances across habitats. Importantly, we also found a nonlinear scaling relationship between shifts in relative arrival and predation strength. Specifically, small shifts in relative arrival caused large changes in predation strength while subsequent changes had relatively minor effects. These results demonstrate that SMPE can alter not only the outcome of interactions but also the demographic rates of species and the structure of communities. Elucidating the mechanisms that link phenological shifts to species interactions is crucial for understanding the dynamics of seasonal communities as well as for predicting the effects of climate change on these communities.Item Ontogenetic development underlies population response to mortality(Wiley, 2021) Toscano, Benjamin J.; Figel, Alexandra S.; Rudolf, Volker H.W.Understanding demographic responses to mortality is crucial to predictive ecology. While classic ecological theory posits reductions in population biomass in response to extrinsic mortality, models containing realistic developmental change predict the potential for counterintuitive increase in stage‐specific biomass, i.e. biomass overcompensation. Patterns of biomass overcompensation should be predictable based on differences in the relative energetic efficiencies of juvenile maturation and adult reproduction. Specifically, in populations where reproduction is the limiting process, adult‐specific mortality should enhance total reproduction and thus juvenile biomass. We tested this prediction by inducing an array of stage‐specific harvesting treatments across replicate populations of Daphnia pulex. In accordance with reproductive regulation, the greatest biomass response occurred in the juvenile Daphnia stage and this response occurred most strongly in response to adult mortality. Nevertheless, we failed to detect significant biomass overcompensation and instead report largely compensatory effects. In total, our work demonstrates that knowledge of population structure is necessary to accurately predict population dynamics, but cautions that further research is needed to illuminate the factors generating over‐compensatory versus compensatory responses across natural populations.Item Ontogenetic functional diversity: Size structure of a keystone predator drives functioning of a complex ecosystem(Wiley, 2013) Rudolf, Volker H.W.; Rasmussen, Nick L.A central challenge in community ecology is to understand the connection between biodiversity and the functioning of ecosystems. While traditional approaches have largely focused on species-level diversity, increasing evidence indicates that there exists substantial ecological diversity among individuals within species. By far, the largest source of this intraspecific diversity stems from variation among individuals in ontogenetic stage and size. Although such ontogenetic shifts are ubiquitous in natural communities, whether and how they scale up to influence the structure and functioning of complex ecosystems is largely unknown. Here we take an experimental approach to examine the consequences of ontogenetic niche shifts for the structure of communities and ecosystem processes. In particular we experimentally manipulated the stage structure in a keystone predator, larvae of the dragonfly Anax junius, in complex experimental pond communities to test whether changes in the population stage or size structure of a keystone species scale up to alter community structure and ecosystem processes, and how functional differences scale with relative differences in size among stages. We found that the functional role of A. junius was stage-specific. Altering what stages were present in a pond led to concurrent changes in community structure, primary producer biomass (periphyton and phytoplankton), and ultimately altered ecosystem processes (respiration and net primary productivity), indicating a strong, but stage-specific, trophic cascade. Interestingly, the stage-specific effects did not simply scale with size or biomass of the predator, but instead indicated clear ontogenetic niche shifts in ecological interactions. Thus, functional differences among stages within a keystone species scaled up to alter the functioning of entire ecosystems. Therefore, our results indicate that the classical approach of assuming an average functional role of a species can be misleading because functional roles are dynamic and will change with shifts in the stage structure of the species. In general this emphasizes the importance of accounting for functional diversity below the species level to predict how natural and anthropogenic changes alter the functioning of natural ecosystems.Item Phenological synchronization drives demographic rates of populations(Ecological Society of America, 2015) Rasmussen, Nick L.; Rudolf, Volker H.W.Phenology is increasingly recognized as an important factor structuring communities because it determines when and at what life stage organisms interact. Previous work indicates that changes in first or mean timing of a phenological event can affect populations and communities, but little is known about the consequences of changes in the distribution (e.g., synchrony) of a phenological event. We conducted an experiment using an anuran study system to determine how synchrony of reproduction and egg hatching affects offspring performance, whether the effects are density dependent, and how hatching synchrony influences the synchrony of a subsequent phenological event (metamorphosis). Changes in hatching synchrony altered survival, development rates, and body size at metamorphosis, which can affect post-metamorphosis performance. The degree of synchrony at hatching also affected the degree of synchrony at metamorphosis, indicating that timing of one stage can carry over to affect that of later ones. Importantly, these effects were all density dependent, likely because decreasing hatching synchrony switched intraspecific interactions from scramble to contest competition. This study demonstrates that phenological synchrony has important consequences for ecological interactions and population dynamics, emphasizing the need to develop a comprehensive understanding of how shifts in phenological distributions affect communities.Item Prey Limitation Drives Variation in Allometric Scaling of Predator-Prey Interactions(The University of Chicago Press, 2018) Costa-Pereira, Raul; Araújo, Márcio Silva; Olivier, Renan da Silva; Souza, Franco L.; Rudolf, Volker H.W.Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, predator-prey size ratios (PPSRs) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from optimal foraging theory. We analyzed >6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.Item Resolving the roles of body size and species identity in driving functional diversity(the Royal Society, 2014) Rudolf, Volker H.W.; Rasmussen, Nick L.; Dibble, Christopher J.; Van Allen, Benjamin G.Efforts to characterize food webs have generated two influential approaches that reduce the complexity of natural communities. The traditional approach groups individuals based on their species identity, while recently developed approaches group individuals based on their body size. While each approach has provided important insights, they have largely been used in parallel in different systems. Consequently, it remains unclear how body size and species identity interact, hampering our ability to develop a more holistic framework that integrates both approaches. We address this conceptual gap by developing a framework which describes how both approaches are related to each other, revealing that both approaches share common but untested assumptions about how variation across size classes or species influences differences in ecological interactions among consumers. Using freshwater mesocosms with dragonfly larvae as predators, we then experimentally demonstrate that while body size strongly determined how predators affected communities, these size effects were species specific and frequently nonlinear, violating a key assumption underlying both size- and species-based approaches. Consequently, neither purely species- nor size-based approaches were adequate to predict functional differences among predators. Instead, functional differences emerged from the synergistic effects of body size and species identity. This clearly demonstrates the need to integrate size- and species-based approaches to predict functional diversity within communities.Item Revenge of the host: cannibalism, ontogenetic niche shifts, and the evolution of life-history strategies in host-parasitoid systems(Evolutionary Ecology, Ltd., 2012) Rudolf, Volker H.W.; Sorrell, Ian; Pederson, Amy B.Question: How does cannibalism in the host alter the evolution of a parasitoid’s oviposition strategy? Can differences in cannibalism risk between parasitized and healthy hosts alter the stage-specific foraging of parasitoids? Can host-specific differences in cannibalistic behaviour explain why parasitoids vary in what host stages they attack? Mathematical methods: We examined the evolutionary dynamics of a stage-structured host–parasitoid model using two complementary approaches: (1) individual-based numerical simulations of evolutionary dynamics, and (2) the theory of adaptive dynamics focusing on evolutionarily stable strategies (ESSs). Assumptions: Cannibalism in the host is assumed to be stage structured, with larger stages consuming smaller stages. The consumption of parasitized hosts also results in killing of the parasitoid’s offspring. Vulnerability to cannibalism of parasitized versus healthy hosts was allowed to vary. The parasitoid’s preference for attacking early versus late host stages was the trait under selection and allowed to evolve. Results: When cannibalism rates increase relative to the parasitoid’s attack rates, the ESS of the parasitoid shifts from attacking only early host stages to attacking only late host stages. This shift occurs at lower cannibalism rates when parasitized hosts are more susceptible to cannibalism than healthy hosts. Under equilibrium conditions, a small boundary area exists between these two regions where attacking only early or only late host stages are alternative ESSs. The threshold and alternative stable ESSs are the result of cannibalism, which creates a positive feedback between the parasitoid’s oviposition rate and its own mortality. Intermediate strategies, where parasitoids evolve to attack both stages, occur only when host populations exhibit large population oscillations or when generalist parasitoids that attack both stages have a foraging advantageItem Embargo The temporal dimension of species interactions at multiple scales(2024-04-16) Zou, Hengxing; Rudolf, Volker H.W.Time structures ecological communities. The strength and outcomes of species interactions are often determined by the temporal sequence and interval of species arrival, a phenomenon termed priority effects. As climate change shifts species timing (phenology) worldwide, we need a general theoretical framework to understand the diverse biological mechanisms underlying priority effects and their consequences in various communities. I first propose a general categorization of priority effects based on their biological mechanisms and the time scales at which they operate. With simulation and experiments of two species communities, I show that the importance of the two categories of mechanisms depends on relative scales between differences in arrival times and the length of the life cycles. Scaling up, I show that how biodiversity changes with dispersal in spatially structured, multispecies communities is also determined by the category of priority effects. Finally, I extend priority effects beyond pairwise interaction with a three-species mechanistic model of plant-soil feedback and propose a general framework to quantify such time-dependent interaction modifications. Together, these works provide a new direction in studying temporal processes in complex communities.Item Within-Host Priority Effects Systematically Alter Pathogen Coexistence(The University of Chicago Press, 2019) Clay, Patrick A.; Dhir, Kailash; Rudolf, Volker H.W.; Duffy, Meghan A.Coinfection of host populations alters pathogen prevalence, host mortality, and pathogen evolution. Because pathogens compete for limiting resources, whether multiple pathogens can coexist in a host population can depend on their within-host interactions, which, in turn, can depend on the order in which pathogens infect hosts (within-host priority effects). However, the consequences of within-host priority effects for pathogen coexistence have not been tested. Using laboratory studies with a coinfected zooplankton system, we found that pathogens had increased fitness in coinfected hosts when they were the second pathogen to infect a host, compared to when they were the first pathogen to infect a host. With these results, we parameterized a pathogen coexistence model with priority effects, finding that pathogen coexistence (1) decreased when priority effects increased the fitness of the first pathogen to arrive in coinfected hosts and (2) increased when priority effects increased the fitness of the second pathogen to arrive in coinfected hosts. We also identified the natural conditions under which we expect within-host priority effects to foster coexistence in our system. These outcomes were the result of positive or negative frequency dependence created by feedback loops between pathogen prevalence and infection order in coinfected hosts. This suggests that priority effects can systematically alter conditions for pathogen coexistence in host populations, thereby changing pathogen community structure and potentially altering host mortality and pathogen evolution via emergent processes.