|
Monzon, J.D., and
N.A. Friedenberg. 2023. Toward rapid population assessment
for raptor conservation: subadults, floaters, strawmen, and context.
A response to Hunt and Law. Journal of Raptor Research 57(3) doi: 10.3356/JRR-22-117 |
van Voorn, G.A.K., M.P. Boer, S.H. Truong,
N.A. Friedenberg, S. Gugushvili, R. McCormick, D.B. Korts, C.D. Messina,
F.A. van Eeuwijk. 2023. A conceptual framework for the dynamic modeling of time-resolved phenotypes
for sets of genotype-environment-management combinations: a model library. Frontiers in Plant Science
14:1172359. Dynamic crop growth models are an important tool to predict complex traits, like crop yield, for modern and future genotypes in their current and evolving environments, as those occurring under climate change. Phenotypic traits are the result of interactions between genetic, environmental, and management factors, and dynamic models are designed to generate the interactions producing phenotypic changes over the growing season. Crop phenotype data are becoming increasingly available at various levels of granularity, both spatially (landscape) and temporally (longitudinal, time-series) from proximal and remote sensing technologies... |
Friedenberg,
N.A. and
W.F. Frick. 2021. Assessing fatality minimization for hoary bats
amid continued wind energy development. Biological Conservation
262:109309 Wind energy is an important sector of the renewable energy market. Observations of bat fatalities at wind farms raise concern about impacts to biodiversity, particularly amid projections of wind energy build-out. We investigated how continued wind energy development in the United States and Canada, as well as adoption of measures to reduce bat fatality rates, influence the population viability of the hoary bat (L. cinereus). Our model included uncertainty about population size and dynamics as well as future wind energy development. Results indicate that current levels of wind energy build-out may have already caused substantial population declines. Under our lowest-risk scenario of high maximum growth rate and low wind energy build-out, the median simulated population of 2.25 million hoary bats experienced a 50% decline by 2028. We show that risks of decline and extinction may still be mediated with rapid adoption of measures to reduce bat fatalities. We find that levels of fatality reduction shown to be achievable in empirical studies of fatality minimization, by turbine curtailment, may be sufficient to manage risks. Simulations of population trends suggest that declines exceeding 5% per year support fatality reduction to manage extinction risk. Importantly, both the risks and the level of fatality reduction necessary to manage them were highly uncertain. Population size remains the most critical data gap to determining population viability of hoary bats. Studies to empirically determine baseline estimates of population size and trends over time remain urgently needed to inform conservation action. |
Friedenberg,
N.A. and
N.L. Kinlock. 2020. Trend To N: Conservative estimation of population
size from trend and fatality information. Technical Report 3002017926.
Electric
Power Research Institute, Palo Alto, CA. While population size can be difficult to measure, information on fatalities and trends in relative abundance is often collected in the course of monitoring for regulatory compliance. This project examined the feasibility of developing a general tool for combining information on fatalities and trends in relative abundance to produce a conservative estimate of population size. The approach used Bayesian inference to provide a probability distribution of population size over time... Nick Friedenberg: PI, analysis, report preparation. Nicole
Kinlock: model formulation and implementation. |
Friedenberg, N.A. 2020. Population-level
risk to hoary bats amid continued wind energy development: assessing
fatality reduction targets under broad uncertainty. Technical Report
3002017671. Electric Power Research Institute, Palo Alto, CA. Across the U.S. and Canada, hoary bats (Lasiurus cinereus) are the most common species among reported bat fatalities at wind farms. Although large gaps in our knowledge about hoary bat population size and dynamics makes the impact of wind turbine fatality difficult to assess, expert opinion places the population parameters in a range where the risk of decline or extinction may be high. A key question for the wind energy industry, regulators, and conservation groups is whether fatality minimization strategies such as operational curtailment or the use of bat deterrent devices could manage population level risks, particularly in light of continued growth in installed capacity... With special thanks to W.F. Frick, Bat Conservation International. |
Kinlock, N.L., A.J. Laybourn, C.E.
Murphy, J.J. Hoover, N.A. Friedenberg. 2020. Modelling
bioenergetic and population-level impacts of invasive bigheaded
carps (Hypophthalmichthys spp.) on native paddlefish (Polyodon
spathula) in
backwaters of the lower Mississippi River. Journal of Freshwater
Biology 65:1086-1100. DOI:10.1111/fwb.13494
Nicholas Friedenberg: PI, modeling approach and study design,
contributions to writing and analysis |
Friedenberg, N.A., and J. Siegrist.
2019. Appendix C: Computation of pallid sturgeon entrainment and population-level
risk. In EIS No. 20210025, Draft, Proposed Mid-Barataria Sediment Diversion
Project in Plaquemines Parish, Louisiana, Appendix O: Biological Assessment
and Biological Opinion. U.S. Army Corps of Engineers, New Orleans, LA. We considered two estimates of a volumetric entrainment rate of
combined sturgeon species from the lower
The FWS rate
for combined sturgeon species was 1 sturgeon per 2.368 x 109
cubic feet diverted. Nick Friedenberg: PI, lead author |
Friedenberg, N.A., and C.M. Foley.
2018. From wind to wires: insight into a developing framework for
incidental take permits for eages. Electric Power
Research Institute, Palo Alto, CA. The 2016 final rule revising the permitting of incidental take under the U.S. Bald and Golden Eagle Protection Act (BGEPA) indicated that new protocols and permit terms and conditions will be developed for take by transmission and distribution line projects, but at the present time many of the details are uncertain. This report is intended to provide an overview of the issues involved and a summary of some of the changes that may be enacted, as well as opportunities that exist for stakeholder contributions to the emerging framework. Nick Friedenberg: PI, lead author |
Trump, B.D., C. Foran, T.
Rycroft, M.D. Wood, N. Bandolin, M. Cains, T. Cary, F. Crocker,
N.A. Friedenberg, P. Gurian, K. Hamilton, J.J.
Hoover, C. Meyer, K. Pokrzywinski, R. Ritterson, P. Schulte, C.
Warner, E. Perkins,
I. Linkov. 2018. Development of community of practice to support
quantitative risk assessment for synthetic biology products: contaminant
bioremediation and invasive carp control as cases. Environment
Systems and Decisions 38(4): 517-527. Synthetic biology has the potential for a broad array of applications. However, realization of this potential is challenged by the paucity of relevant data for conventional risk assessment protocols, a limitation due to to the relative nascence of the field, as well as the poorly characterized and prioritized hazard, exposure, and dose–response considerations associated with the development and use of synthetic biology-derived organisms. Where quantitative risk assessment approaches are necessarily to fulfill regulatory requirements for review of products containing genetically modified organisms, this paper reviews one potential avenue for early-stage quantitative risk assessment for biosafety considerations of synthetic biology organism deployment into the environment. Building from discussion from a March 2018 US Army Engineer Research and Development Center workshop on developing such quantitative risk assessment for synthetic biology, this paper reviews the findings and discussion of workshop participants. This paper concludes that, while synthetic biology risk assessment and governance will continue to refine and develop in the coming years, a quantitative framework that builds from existing practice is one potentially beneficial option for risk assessors that must contend with the technology’s limited hazard characterization or exposure assessment considerations in the near term. Nicholas A.Friedenberg: Workshop participant, provided comments
on manuscript drafts. |
Martinez, J.C., M.A. Caprio,
and N.A. Friedenberg. 2018. Density dependence
and growth rate: evolutionary effects on resistance development
to Bt (Bacillus thuringiensis). Journal of Economic Entomology
111: 382-390. It has long been recognized that pest population dynamics can affect the durability of a pesticide, but dose remains the primary component of insect resistance management (IRM). For transgenic pesticidal traits such as Bt (Bacillus thuringiensis Berliner (Bacillales: Bacillaceae)), dose (measured as the mortality of susceptibles caused by a toxin) is a relatively fixed characteristic and often falls below the standard definition of high dose. Hence, it is important to understand how pest population dynamics modify durability and what targets they present for IRM. We used a deterministic model of a generic arthropod pest to examine how timing and strength of density dependence interacted with population growth rate and Bt mortality to affect time to resistance. As in previous studies, durability typically reached a minimum at intermediate doses. However, high population growth rates could eliminate benefits of high dose. The timing of density dependence had a more subtle effect. If density dependence operated simultaneously with Bt mortality, durability was insensitive to its strengths. However, if density dependence was driven by postselection densities, decreasing its strength could increase durability. The strength of density dependence could affect durability of both single traits and pyramids, but its influence depended on the timing of density dependence and size of the refuge. Our findings suggest the utility of a broader definition of high dose, one that incorporates population-dynamic context. That maximum growth rates and timing and strength of interactions causing density dependent mortality can all affect durability, also highlights the need for ecologically integrated approaches to IRM research. Nicholas Friedenberg: Contributed to study design,
modeling, analysis, and manuscript preparation. |
Monzon, J.D., and N.A.
Friedenberg.
2018. Metrics of population status for long-lived territorial birds:
a case study of golden eagle demography. Biological Conservation
220: 280-289. The development of "snapshot" metrics that can serve as reliable diagnostic tools for rapidly assessing population status has great appeal. We used stochastic simulation moeling and recursive partitioning to evaluate the reliability of two proposed snapshot metrics in territorial raptors: the floater/breeder ratio and the rate of nest occupancy by immature subadults. A demographic model, parameterized with field data from an intensively studies population of golden eagle (Aquila chrysaetos), showed that neither metric, along or together, is a good indicator of population status. However, one snaptshot metric, the floater/breeder ratio/ can help predict the risk of population decline when considered in combination with other information about the population or environment that may be quickly appraised in the field or literature. Specifically, qualitative knowledge of adult survival and whether the population is limited by prey or habitat availability can help with rapid risk assessment of raptor populations. Also available as an article adapted for high school STEM eductation
in Science
For Kids. Nick Friedenberg: Project management, contributed
to study design, analysis, and manuscript preparation. |
Friedenberg, N.A.,
J.J. Hoover, K. Boysen, and K.J. Killgore. 2018. Estimating abundance
without recaptures of marked pallid sturgeon in the Mississippi
River. Conservation Biology 32:457-465. Abundance estimates are essential for estimating the viability of populations and the risks posed by alternative management actions. An effort to estimate abundance via a repeated mark-recapture experiment may fail to recapture marked individuals. We present a framework for obtaining lower bounds on abundance in the absence of recaptures for both panmictic and spatially-structured populations. We applied this nil-recapture method to data from a 12-year survey of pallid sturgeon (Scaphirhynchus albus) in the lower and middle Mississippi River; none of the 241 individuals marked were recaptured in the survey. After accounting for survival and movement, our model-averaged estimate of the total abundance of age 3+ pallid sturgeon in the study area had a 1%, 5%, or 25% chance of being less than 4,600, 7,000, or 15,000, respectively. If we assumed fish were distributed in proportion to survey catch-per-unit-effort, then the furthest downstream reach in the survey hosted at least 4.5-15 fish per river kilometer (rkm), whereas the remainder of the reaches in the lower and middle Mississippi River hosted at least 2.6-8.5 fish rkm-1 for all model variations examined. The lower Mississippi River had an average density of at least 3.0-9.8 age-3+ pallid sturgeon rkm-1. The choice of Bayesian prior was the largest source of uncertainty considered in this study, but did not alter the order of magnitude of lower bounds. Nil-recapture estimates of abundance are highly uncertain and require careful communication but can deliver insights from experiments that might otherwise be considered a failure. Nicholas Friedenberg: Led statistical method development, application
to case study, and manscript preparation. |
Powell, J.A., M.J. Garlick,
B.J. Bentz, N.A. Friedenberg. 2018. Differential
dispersal and the Allee effect create power-law behavior: distribution
of
spot infestations
during mountain pine beetle outbreaks. Journal of Animal Ecology 87:73-86.
Nick Friedenberg: Contributed to manscript preparation. |
Friedenberg, N.
and C. Foley. 2016. Defining protection of endangered
species from an integrated multispecies perspective. Technical
Report 3002008418. Electric Power Research Institute, Palo Alto,
CA. With respect to conservation planning, the United States has for some time been moving toward multispecies approaches. This shift recognizes the fundamental ecological fact that species do not exist in isolation, and it is thus possible to move from reactive to proactive management in order to reduce the need for future listings under the Endangered Species Act (ESA). Conservation aimed at higher ecological scales such as landscapes and ecosystems creates opportunities for coordination of conservation actions and public-private partnerships. This report examines the integrated multispecies perspective on management of endangered species. Nicholas Friedenberg: Project director. Contributed to literature review, analysis, and report preparation. |
Friedenberg, N.A.
and K.T. Shoemaker. 2014. RAMAS IRM
version 2.0: Software for risk-based durability assessment. Applied
Biomathematics, Setauket, NY RAMAS® IRM (Insect Resistance Management) is a software platform for modeling the risk of pest adaptation to Bt crops under a broad range of resistance management strategies. The tool has enough flexibility to address all major insect crop pests through user-defined life histories. IRM modeling investigates the complex interaction of insect pest population dynamics and population genetics with agricultural technology and farming practices. The total integration of landscape, demography, and evolution places IRM at the cutting edge of landscape genetics and applied evolution. Our goal is to provide a common platform for IRM modeling that fosters both transparency and innovation in the devlopment and management of transgenic pesticidal crops. A guiding principle in the development of this flexible tool is that it should remove barriers to powerful modeling. That means pushing the limits of what is currently practical in terms of complexity while keeping the software easy to use even for beginning modelers. Nick Friedenberg: Project director. Contributed to software design, coding, validation, and documentation. |
Thomas, M.J., M.L. Peterson, N.
Friedenberg,
J.P. Van Eenennaam, J.R. Johnson, J.J. Hoover, A.P. Klimley. 2013.
Stranding of spawning run green sturgeon in the Sacramento River: post-rescue
movements and potential population-level effects. North American Journal
of Fisheries Management 33:287-297. The lower portion of the Sacramento River, California, has been highly engineered to protect low-lying surrounding communities from annual flood events. While engineered floodplains have provided adequate protection for the surrounding communities, there remain unintended consequences to migratory fish that become stranded during high flow events. In April, 2011, we rescued 24 threatened Green Sturgeon (Acipenser medirostris) that were stranded in two flood diversions along the Sacramento River. We tagged these 24 Green Sturgeon with acoustic tags and analyzed their survival and migration success to their spawning grounds. Additionally, we provided a population viability analysis to show the potential impacts of stranding and the benefits of conducting rescues at the population level. We found that 17 of these 24 individuals continued their upstream migration to the spawning grounds.Modeling suggests that recurrent stranding of a similar magnitude without rescue could affect the long-term viability of Green Sturgeon in the Sacramento River. Population viability analyses of rescue predicted a 7% decrease below the population baseline model over 50 years as opposed to 33% without rescue. Despite the mitigated impact to the population with rescue, fish passage improvements should be considered as a long-term goal for preventing population risks at flood control diversions. Nicholas Friedenberg: Contributed modeling and analysis, aided in manuscript preparation. |
Ayres, MP,
SJ Martinson, NA Friedenberg. 2011. Southern pine beetle ecology:
popuations within stands, In Southern Pine Beetle II.
Coulson, RN and K Klepzig, eds. USDA Forest Service, GTR-SRS-140,
Southern Research Station, Asheville, NC Populations of southerrn pine beetle (SPB) are typically substructured into local aggregations, each with tens of thousands of individual beetles. These aggregations, known as "spots" because of their appearance during aerial surveys, are the basic unit for the monitoring and management of SPB populations in forested regions. They typically have a maximum lifespan of 1 year, being born in the spring when dispersing SPB aggregate at point in the forest. Sporst that survive to the following spring produce the dispersing beetles that form a new population of spots. SPB epidemics rise and fall with interannual variation in the number of spots within a region. Many spots, especially those that begin small, die an early death by midsummer. Others may grow throughout the summer and into the winter via a self-propagating progression of tree attacks that is critically structured by semiochemicals. Forces that influence the growth of populations within spots strongly influence the dynamic fluctuations in SPB impacts on regional forests. These forces include pine species composition, habitat edges, age and basal area of pine stands, tree defenses, the predator Thanasimus dubius, interactions with phretic mites and fungi, climate, and movement of beetles into and out of spots. Nick A. Friedenberg: Contributed to underlying research. |
Dennehy, J.J., N.A.
Friedenberg,
R.C. McBride, R.D. Holt, and P.E. Turner. 2010. Experimental evidence
that source genetic variation drives pathogen emergence. Proceedings
of the Royal Society, Series B 277: 3113-3121. A pathogen can readily mutate to infect new host types, but this does not guarantee successful establishment in the new habitat. What factors, then, dictate emergence success? One possibility is that the pathogen population cannot sustain itself on the new host type (i.e. host is a sink), but migration from a source population allows adaptive sustainability and eventual emergence by delivering beneficial mutations sampled from the source’s standing genetic variation. This idea is relevant regardless of whether the sink host is truly novel (host shift) or whether the sink is an existing or related, similar host population thriving under conditions unfavourable to pathogen persistence (range expansion). We predicted that sink adaptation should occur faster under range expansion than during a host shift owing to the effects of source genetic variation on pathogen adaptability in the sink. Under range expansion, source migration should benefit emergence in the sink because selection acting on source and sink populations is likely to be congruent. By contrast, during host shifts, source migration is likely to disrupt emergence in the sink owing to uncorrelated selection or performance tradeoffs across host types. We tested this hypothesis by evolving bacteriophage populations on novel host bacteria under sink conditions, while manipulating emergence via host shift versus range expansion. Controls examined sink adaptation when unevolved founding genotypes served as migrants. As predicted, adaptability was fastest under range expansion, and controls did not adapt. Large, similar and similarly timed increases in fitness were observed in the host-shift populations, despite declines in mean fitness of immigrants through time. These results suggest that source populations are the origin of mutations that drive adaptive emergence at the edge of a pathogen’s ecological or geographical range. Nicholas A.Friedenberg: Contributed to study design, modeling, analysis, and manuscript preparation. |
Friedenberg, N.A., S.
Sarkar, N. Kouchoukos, R.F. Billings, M.P. Ayres. 2008. Temperature
extremes, density dependence, and southern pine beetle (Coleoptera:
Curculionidae) population dynamics in east Texas. Environmental
Entomlogy 37: 650-659 Previous studies of the southern pine beetle, Dendroctonus frontalis Zimm., established that its population in east Texas responds to a delayed density-dependent process, whereas no clear role of climate has been determined.We tested two biological hypotheses for the influence of extreme temperatures on annual southern pine beetle population growth in the context of four alternative hypotheses for density-dependent population regulation. The significance of climate variables and their interaction with population regulation depended on the model of density dependence. The best model included both direct and delayed density dependence of a cubic rather than linear form. Population growth declined with the number of days exceeding 32 C, temperatures previously reported to reduce brood survival. Growth was highest in years with average minimum winter temperatures. Severely cold winters may reduce survival, whereas warm winters may reduce the efficiency of spring infestation formation. Whereas most previous studies have incorporated climate as an additive effect on growth, we found that the form of delayed density dependence changed with the number of days over 32 C. The interaction between temperature and regulation, a potentially common phenomenon in ecology, may explain why southern pine beetle outbreaks do not occur at perfectly regular intervals. Factors other than climate, such as forest management and direct suppression, may have contributed significantly to the timing, severity, and eventual cessation of outbreaks since the mid-1950s. Nick Friedenberg: Led study design, database development, analysis, and manuscript preparation. |
Friedenberg, N.A., B.M.
Whited, D.H. Slone, S.J. Martinson, M.P. Ayres. 2007. Differential
impacts of the southern pine beetle, Dendroctonus frontalis,
on Pinus palustris and Pinus taeda. Canadian Journal
of Forest Research 37: 1427-1437 Patterns of host use by herbivore pests can have serious consequences for natural and managed ecosystems, but are often poorly understood. Here, we provide the first quantification of large differential impacts of the southern pine beetle, Dendroctonus frontalis Zimmermann, on loblolly pine, Pinus taeda, and longleaf pine, P. palustris, and evaluate putative mechanisms for the disparity. Spatially extensive survey data from recent epidemics indicate that, per km2, stands of loblolly vs. longleaf pine in four forests (380-1273 km2) sustained 3-18 times more local infestations and 3-116 times more tree mortality. Differences were not attributable to size or age structure of pine stands. Using pheromone-baited traps, we found no differences in the abundance of dispersing D. frontalis or its predator, Thanasimus dubius Fabricius, between loblolly and longleaf stands. Trapping triggered numerous attacks on trees, but the pine species did not differ in the probability of attack initiation, nor in the surface area of bark attacked by growing aggregations. We found no evidence for post-aggregation mechanisms of discrimination or differential success on the two hosts, suggesting that early colonizers discriminate between host species before a pheromone plume is present. Nicholas Friedenberg: Led study design, data collection, analysis, and manuscript preparation. |
Friedenberg, N.A.,
J.A. Powell, M.P. Ayres. 2007. Synchrony's double edge: transient
dynamics and the Allee effect in stage structured populations. Ecology
Letters 10: 564-573 In populations subject to positive density dependence, individuals can increase their fitness by synchronizing the timing of key life history events. However, phenological synchrony represents a perturbation from a population’s stable stage structure and the ensuing transient dynamics create troughs of low abundance that can promote extinction. Using an ecophysiological model of a mass-attacking pest insect, we show that the effect of synchrony on local population persistence depends on population size and adult lifespan. Results are consistent with a strong empirical pattern of increased extinction risk with decreasing initial population size. Mortality factors such as predation on adults can also affect transient dynamics. Throughout the species range, the seasonal niche for persistence increases with the asynchrony of oviposition. Exposure to the Allee effect after establishment may be most likely at northern range limits, where cold winters tend to synchronize spring colonization, suggesting a role for transient dynamics in the determination of species distributions. Nick Friedenberg: Led study design and manuscript preparation, contributed to analysis. |
Dennehy, J.J., N.A.
Friedenberg, Y. Yang, P.E. Turner. 2007. Virus population
extinction via ecological traps. Ecology Letters 10: 230-240 Populations are at risk of extinction when unsuitable or when sink habitat exceeds a threshold frequency in the environment. Sinks that present cues associated with highquality habitats, termed ecological traps, have especially detrimental effects on net population growth at metapopulation scales. Ecological traps for viruses arise naturally, or can be engineered, via the expression of viral-binding sites on cells that preclude viral reproduction. We present a model for virus population growth in a heterogeneous host community, parameterized with data from populations of the RNA bacteriophage U6 presented with mixtures of suitable host bacteria and either neutral or trap cells. We demonstrate that viruses can sustain high rates of population growth in the presence of neutral non-hosts as long as some host cells are present, whereas trap cells dramatically reduce viral fitness. In addition, we demonstrate that the efficacy of traps for viral elimination is frequency dependent in spatially structured environments such that population viability is a nonlinear function of habitat loss in dispersal-limited virus populations. We conclude that the ecological concepts applied to species conservation in altered landscapes can also contribute to the development of trap cell therapies for infectious human viruses. Nicholas Friedenberg: Contributed to study design, modeling, analysis, and manuscript preparation. |
Dennehy, J.J., N.A.
Friedenberg, Y. Yang, P.E. Turner. 2006. Bacteriophage
migration via nematode vectors: host-parasite-consumer interactions
in laboratory microcosms. Applied and Environmental Microbiology
72: 1974-1979 Pathogens vectored by nematodes pose serious agricultural, economic, and health threats; however, little is known of the ecological and evolutionary aspects of pathogen transmission by nematodes. Here we describe a novel model system with two trophic levels, bacteriophages and nematodes, each of which competes for bacteria. We demonstrate for the first time that nematodes are capable of transmitting phages between spatially distinct patches of bacteria. This model system has considerable advantages, including the ease of maintenance and manipulation at the laboratory bench, the ability to observe many generations in short periods, and the capacity to freeze evolved strains for later comparison to their ancestors. More generally, experimental studies of complex multispecies interactions, host-pathogen coevolution, disease dynamics, and the evolution of virulence may benefit from this model system because current models (e.g., chickens, mosquitoes, and malaria parasites) are costly to maintain, are difficult to manipulate, and require considerable space. Our initial explorations centered on independently assessing the impacts of nematode, bacterium, and phage population densities on virus migration between host patches. Our results indicated that virus transmission increases with worm density and host bacterial abundance; however, transmission decreases with initial phage abundance, perhaps because viruses eliminate available hosts before migration can occur. We discuss the microbial growth dynamics that underlie these results, suggest mechanistic explanations for nematode transmission of phages, and propose intriguing possibilities for future research. Nick Friedenberg: Led project design and analysis, contributed to manuscript preparation. |
Dennehy, J.J., N.A.
Friedenberg,
R.D. Holt, P.E. Turner. 2006. Viral ecology and the maintenance
of novel host use. American Naturalist 167: 429-439 Viruses can occasionally emerge by infecting new host species. However, the early phases of emergence can hinge upon ecological sustainability of the virus population, which is a product of both within-host population growth and between-host transmission. Insufficient growth or transmission can force virus extinction before the latter phases of emergence, where genetic adaptations that improve host use may occur. We examined the early phase of emergence by studying the population dynamics of RNA phages in replicated laboratory environments containing native and novel host bacteria. To predict the breadth of transmission rates allowing viral persistence on each species, we developed a simple model based on in vitro data for phage growth rate over a range of initial population densities on both hosts. Validation of these predictions using serial passage experiments revealed a range of transmission rates for which the native host was a source and the novel host was a sink. In this critical range of transmission rates, periodic exposure to the native host was sufficient for the maintenance of the viral population on the novel host. We argue that this effect should facilitate adaptation by the virus to utilize the novel host—often crucial in subsequent phases of emergence. Nicholas Friedenberg: Contributed to study design, modeling, analysis, and manuscript preparation. |
Friedenberg, N.A.
2003. Determinism in a transient assemblage: the roles of dispersal
and local competition. American Naturalist 162: 586-596 Both dispersal and local competitive ability may determine the outcome of competition among species that cannot coexist locally. I develop a spatially implicit model of two-species competition at a small spatial scale. The model predicts the relative fitness of two competitors based on local reproductive rates and regional dispersal rates in the context of the number, size, and extinction probability of habitat patches in the landscape. I test the predictions of this model experimentally using two genotypes of the bacteriophagous soil nematode Caenorhabditis elegans in patchy microcosms. One genotype has higher fecundity while the other is a better disperser. With such a fecundity-dispersal trade-off between competitors, the model predicts that relative fitness will be affected most by local population size when patches do not go extinct and by the number of patches when there is a high probability of patch extinction. The microcosm experiments support the model predictions. Both approaches suggest that competitive dominance in a patchily distributed transient assemblage will depend upon the architecture and predictability of the environment. These mechanisms, operating at a small scale with high spatial admixture, may be embedded in a larger metacommunity process. Nicholas A. Friedenberg: Sole author based on thesis work. |
Friedenberg, N.A.
2003. Experimental evolution of dispersal in spatiotemporally variable
microcosms. Ecology Letters 6: 953-959 The world is an uncertain place. Individuals' fates vary from place to place and from time to time. Natural selection in unpredictable environments should favour individuals that hedge their bets by dispersing offspring. I confirm this basic prediction using Caenorhabditis elegans in experimental microcosms. My results agree with evolutionary models and correlations found previously between habitat stability and individual dispersal propensity in nature. However, I also find that environmental variation that triggers conditional dispersal behaviour may not impose selection on baseline dispersal rates. These findings imply that an increased rate of disturbance in natural systems has the potential to cause an evolutionary response in the life history of impacted organisms. Nick Friedenberg: Sole author based on thesis work. |
Hampton, S.E., and N.A.
Friedenberg. 2001. Nocturnal increases in the use of
near-surface water by pond animals. Hydrobiologia 477: 171-179 We assessed diel animal habitat use in three shallow ponds, using unbaited funnel traps, a large column sampler, and sweep net collections in the upper stratum (0–0.3 m) of littoral and open habitats. In all three ponds, more animals were caught at night than during the day, indicating that use of near-surface waters was greatest at night, particularly in the fishless ponds. All methods yielded similar patterns. Our results demonstrate that nocturnal observations of pond animals are necessary to describe their ecology, even in fishless ponds where diel differences in habitat use or behavior might not be anticipated. Nicholas Friedenberg: Contributed to data collection, species identification, analysis, and manuscript preparation. |
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RAMAS is a registered trademark of Applied Biomathematics. |