Publications (35)171.18 Total impact
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Article: Temperature alters reproductive life history patterns in Batrachochytrium dendrobatidis, a lethal pathogen associated with the global loss of amphibians.
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ABSTRACT: Understanding how pathogens respond to changing environmental conditions is a central challenge in disease ecology. The environmentally sensitive fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the amphibian disease chytridiomycosis, has spread globally causing amphibian extirpations in a wide variety of climatic regions. To gain an in-depth understanding of Bd's responses to temperature, we used an integrative approach, combining empirical laboratory experiments with mathematical modeling. First, we selected a single Bd isolate and serially propagated two lineages of the isolate for multiple generations in two stable thermal conditions: 4°C (cold-adapted lineage) and 23°C (warm-adapted lineage). We quantified the production of infectious zoospores (fecundity), the timing of zoospore release, and zoospore activity in reciprocal temperature transplant experiments in which both Bd lineages were grown in either high or low temperature conditions. We then developed population growth models for the Bd lineages under each set of temperature conditions. We found that Bd had lower population growth rates, but longer periods of zoospore activity in the low temperature treatment (4°C) compared to the high temperature treatment (23°C). This effect was more pronounced in Bd lineages that were propagated in the low temperature treatment (4°C), suggesting a shift in Bd's response to low temperature conditions. Our results provide novel insights into the mechanisms by which Bd can thrive in a wide variety of temperature conditions, potentially altering the dynamics of chytridiomycosis and thus, the propensity for Bd to cause amphibian population collapse. We also suggest that the adaptive responses of Bd to thermal conditions warrant further investigation, especially in the face of global climate change.Ecology and evolution. 09/2012; 2(9):2241-9. -
Article: Impacts of an introduced forest pathogen on the risk of lyme disease in California.
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ABSTRACT: Global changes such as deforestation, climate change, and invasive species have the potential to greatly alter zoonotic disease systems through impacts on biodiversity. This study examined the impact of the invasive pathogen that causes sudden oak death (SOD) on the ecology of Lyme disease in California. The Lyme disease bacterium, Borrelia burgdorferi, is maintained in the far western United States by a suite of animal reservoirs including the dusky-footed woodrat (Neotoma fuscipes) and deer mouse (Peromyscus maniculatus), and is transmitted by the western black-legged tick (Ixodes pacificus). Other vertebrates, such as the western fence lizard (Sceloporus occidentalis), are important tick hosts but are not reservoirs of the pathogen. Previous work found that higher levels of SOD are correlated with greater abundance of P. maniculatus and S. occidentalis and lower N. fuscipes abundance. Here we model the contribution of these tick hosts to Lyme disease risk and also evaluate the potential impact of SOD on infection prevalence of the tick vector. By empirically parameterizing a static model with field and laboratory data on tick hosts, we predict that SOD reduces an important index of disease risk, nymphal infection prevalence, leading to a reduction in Lyme disease risk in certain coastal woodlands. Direct observational analysis of the impact of SOD on nymphal infection prevalence supports these model results. This study underscores the important direct and indirect impacts of invasive plant pathogens on biodiversity, the transmission cycles of zoonotic diseases, and ultimately human health.Vector borne and zoonotic diseases (Larchmont, N.Y.) 05/2012; 12(8):623-32. · 2.61 Impact Factor -
Article: Treatment of amphibians infected with chytrid fungus: learning from failed trials with itraconazole, antimicrobial peptides, bacteria, and heat therapy.
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ABSTRACT: Amphibian conservation goals depend on effective disease-treatment protocols. Desirable protocols are species, life stage, and context specific, but currently few treatment options exist for amphibians infected with the chytrid fungus Batrachochytrium dendrobatidis (Bd). Treatment options, at present, include antifungal drugs and heat therapy, but risks of toxicity and side-effects make these options untenable in some cases. Here, we report on the comparison of several novel treatments with a more generally accepted antifungal treatment in experimental scientific trials to treat Bd-infected frogs including Alytes obstetricans tadpoles and metamorphs, Bufo bufo and Limnodynastes peronii metamorphs, and Lithobates pipiens and Rana muscosa adults. The experimental treatments included commercial antifungal products (itraconazole, mandipropamid, steriplantN, and PIP Pond Plus), antimicrobial skin peptides from the Bd-resistant Pelophylax esculentus, microbial treatments (Pedobacter cryoconitis), and heat therapy (35°C for 24 h). None of the new experimental treatments were considered successful in terms of improving survival; however, these results may advance future research by indicating the limits and potential of the various protocols. Caution in the use of itraconazole is warranted because of observed toxicity in metamorphic and adult frogs, even at low concentrations. Results suggest that rather than focusing on a single cure-all, diverse lines of research may provide multiple options for treating Bd infection in amphibians. Learning from 'failed treatments' is essential for the timely achievement of conservation goals and one of the primary aims for a publicly accessible treatment database under development.Diseases of Aquatic Organisms 02/2012; 98(1):11-25. · 2.20 Impact Factor -
Article: Pathophysiology in mountain yellow-legged frogs (Rana muscosa) during a chytridiomycosis outbreak.
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ABSTRACT: The disease chytridiomycosis is responsible for declines and extirpations of amphibians worldwide. Chytridiomycosis is caused by a fungal pathogen (Batrachochytrium dendrobatidis) that infects amphibian skin. Although we have a basic understanding of the pathophysiology from laboratory experiments, many mechanistic details remain unresolved and it is unknown if disease development is similar in wild amphibian populations. To gain a better understanding of chytridiomycosis pathophysiology in wild amphibian populations, we collected blood biochemistry measurements during an outbreak in mountain yellow-legged frogs (Rana muscosa) in the Sierra Nevada Mountains of California. We found that pathogen load is associated with disruptions in fluid and electrolyte balance, yet is not associated with fluctuations acid-base balance. These findings enhance our knowledge of the pathophysiology of this disease and indicate that disease development is consistent across multiple species and in both laboratory and natural conditions. We recommend integrating an understanding of chytridiomycosis pathophysiology with mitigation practices to improve amphibian conservation.PLoS ONE 01/2012; 7(4):e35374. · 4.09 Impact Factor -
Article: Parameter inference for an individual based model of chytridiomycosis in frogs.
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ABSTRACT: Individual based models (IBMs) and Agent based models (ABMs) have become widely used tools to understand complex biological systems. However, general methods of parameter inference for IBMs are not available. In this paper we show that it is possible to address this problem with a traditional likelihood-based approach, using an example of an IBM developed to describe the spread of chytridiomycosis in a population of frogs as a case study. We show that if the IBM satisfies certain criteria we can find the likelihood (or posterior) analytically, and use standard computational techniques, such as MCMC, for parameter inference.Journal of Theoretical Biology 02/2011; 277(1):90-8. · 2.21 Impact Factor -
Article: Impact of the experimental removal of lizards on Lyme disease risk.
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ABSTRACT: The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (Ixodes pacificus--the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi. Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. Following experimental removal of lizards, we documented incomplete host switching by larval ticks (5.19%) from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae failed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in nymphal tick infection prevalence. The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk through the maintenance of higher vector density and therefore, higher density of infected vectors.Proceedings of the Royal Society B: Biological Sciences 02/2011; 278(1720):2970-8. · 5.41 Impact Factor -
Article: Is chytridiomycosis an emerging infectious disease in Asia?
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ABSTRACT: The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has caused dramatic amphibian population declines and extinctions in Australia, Central and North America, and Europe. Bd is associated with >200 species extinctions of amphibians, but not all species that become infected are susceptible to the disease. Specifically, Bd has rapidly emerged in some areas of the world, such as in Australia, USA, and throughout Central and South America, causing population and species collapse. The mechanism behind the rapid global emergence of the disease is poorly understood, in part due to an incomplete picture of the global distribution of Bd. At present, there is a considerable amount of geographic bias in survey effort for Bd, with Asia being the most neglected continent. To date, Bd surveys have been published for few Asian countries, and infected amphibians have been reported only from Indonesia, South Korea, China and Japan. Thus far, there have been no substantiated reports of enigmatic or suspected disease-caused population declines of the kind that has been attributed to Bd in other areas. In order to gain a more detailed picture of the distribution of Bd in Asia, we undertook a widespread, opportunistic survey of over 3,000 amphibians for Bd throughout Asia and adjoining Papua New Guinea. Survey sites spanned 15 countries, approximately 36° latitude, 111° longitude, and over 2000 m in elevation. Bd prevalence was very low throughout our survey area (2.35% overall) and infected animals were not clumped as would be expected in epizootic events. This suggests that Bd is either newly emerging in Asia, endemic at low prevalence, or that some other ecological factor is preventing Bd from fully invading Asian amphibians. The current observed pattern in Asia differs from that in many other parts of the world.PLoS ONE 01/2011; 6(8):e23179. · 4.09 Impact Factor -
Article: Mitigating amphibian disease: strategies to maintain wild populations and control chytridiomycosis.
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ABSTRACT: Rescuing amphibian diversity is an achievable conservation challenge. Disease mitigation is one essential component of population management. Here we assess existing disease mitigation strategies, some in early experimental stages, which focus on the globally emerging chytrid fungus Batrachochytrium dendrobatidis. We discuss the precedent for each strategy in systems ranging from agriculture to human medicine, and the outlook for each strategy in terms of research needs and long-term potential. We find that the effects of exposure to Batrachochytrium dendrobatidis occur on a spectrum from transient commensal to lethal pathogen. Management priorities are divided between (1) halting pathogen spread and developing survival assurance colonies, and (2) prophylactic or remedial disease treatment. Epidemiological models of chytridiomycosis suggest that mitigation strategies can control disease without eliminating the pathogen. Ecological ethics guide wildlife disease research, but several ethical questions remain for managing disease in the field. Because sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens, we suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Rather, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. We propose population level treatments based on three steps: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations.Frontiers in Zoology 01/2011; 8(1):8. · 4.46 Impact Factor -
Article: Effects of an invasive forest pathogen on abundance of ticks and their vertebrate hosts in a California Lyme disease focus.
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ABSTRACT: Invasive species, including pathogens, can have important effects on local ecosystems, including indirect consequences on native species. This study focuses on the effects of an invasive plant pathogen on a vertebrate community and Ixodes pacificus, the vector of the Lyme disease pathogen (Borrelia burgdorferi) in California. Phytophthora ramorum, the causative agent of sudden oak death, is a non-native pathogen killing trees in California and Oregon. We conducted a multi-year study using a gradient of SOD-caused disturbance to assess the impact on the dusky-footed woodrat (Neotoma fuscipes) and the deer mouse (Peromyscus maniculatus), two reservoir hosts of B. burgdorferi, as well as the impact on the Columbian black-tailed deer (Odocoileus hemionus columbianus) and the western fence lizard (Sceloporus occidentalis), both of which are important hosts for I. pacificus but are not pathogen reservoirs. Abundances of P. maniculatus and S. occidentalis were positively correlated with greater SOD disturbance, whereas N. fuscipes abundance was negatively correlated. We did not find a change in space use by O. hemionus. Our data show that SOD has a positive impact on the density of nymphal ticks, which is expected to increase the risk of human exposure to Lyme disease all else being equal. A positive correlation between SOD disturbance and the density of nymphal ticks was expected given increased abundances of two important hosts: deer mice and western fence lizards. However, further research is needed to integrate the direct effects of SOD on ticks, for example via altered abiotic conditions with host-mediated indirect effects.Oecologia 10/2010; 166(1):91-100. · 3.41 Impact Factor -
Article: Dynamics of an emerging disease drive large-scale amphibian population extinctions.
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ABSTRACT: Epidemiological theory generally suggests that pathogens will not cause host extinctions because the pathogen should fade out when the host population is driven below some threshold density. An emerging infectious disease, chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd) is directly linked to the recent extinction or serious decline of hundreds of amphibian species. Despite continued spread of this pathogen into uninfected areas, the dynamics of the host-pathogen interaction remain unknown. We use fine-scale spatiotemporal data to describe (i) the invasion and spread of Bd through three lake basins, each containing multiple populations of the mountain yellow-legged frog, and (ii) the accompanying host-pathogen dynamics. Despite intensive sampling, Bd was not detected on frogs in study basins until just before epidemics began. Following Bd arrival in a basin, the disease spread to neighboring populations at approximately 700 m/yr in a wave-like pattern until all populations were infected. Within a population, infection prevalence rapidly reached 100% and infection intensity on individual frogs increased in parallel. Frog mass mortality began only when infection intensity reached a critical threshold and repeatedly led to extinction of populations. Our results indicate that the high growth rate and virulence of Bd allow the near-simultaneous infection and buildup of high infection intensities in all host individuals; subsequent host population crashes therefore occur before Bd is limited by density-dependent factors. Preventing infection intensities in host populations from reaching this threshold could provide an effective strategy to avoid the extinction of susceptible amphibian species in the wild.Proceedings of the National Academy of Sciences 05/2010; 107(21):9689-94. · 9.68 Impact Factor -
Article: Enzootic and epizootic dynamics of the chytrid fungal pathogen of amphibians.
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ABSTRACT: Chytridiomycosis, the disease caused by the chytrid fungus, Batrachochytrium dendrobatidis (Bd), has contributed to amphibian population declines and extinctions worldwide. The impact of this pathogen, however, varies markedly among amphibian species and populations. Following invasion into some areas of California's Sierra Nevada, Bd leads to rapid declines and local extinctions of frog populations (Rana muscosa, R. sierrae). In other areas, infected populations of the same frog species have declined but persisted at low host densities for many years. We present results of a 5-year study showing that infected adult frogs in persistent populations have low fungal loads, are surviving between years, and frequently lose and regain the infection. Here we put forward the hypothesis that fungal load dynamics can explain the different population-level outcomes of Bd observed in different areas of the Sierra Nevada and possibly throughout the world. We develop a model that incorporates the biological details of the Bd-host interaction. Importantly, model results suggest that host persistence versus extinction does not require differences in host susceptibility, pathogen virulence, or environmental conditions, and may be just epidemic and endemic population dynamics of the same host-pathogen system. The different disease outcomes seen in natural populations may result solely from density-dependent host-pathogen dynamics. The model also shows that persistence of Bd is enhanced by the long-lived tadpole stage that characterize these two frog species, and by nonhost Bd reservoirs.Proceedings of the National Academy of Sciences 05/2010; 107(21):9695-700. · 9.68 Impact Factor -
Article: Immunization is ineffective at preventing infection and mortality due to the amphibian chytrid fungus Batrachochytrium dendrobatidis.
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ABSTRACT: The fungal pathogen Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, has been implicated in amphibian declines worldwide. It has been hypothesized that low inherent immunogenicity in Bd may be related to the high rates of morbidity and mortality that are associated with Bd-infected anuran populations. To test this idea, juvenile Rana muscosa (mountain yellow-legged frogs) were immunized with adjuvants in combination with a formalin-killed Bd culture to determine if it is possible to stimulate a protective immune response when challenged with a live inoculum of B. dendrobatidis. Three groups of juvenile R. muscosa (6 mo postmetamorphosis) were immunized with saline, Freunds Complete (FCA) and Incomplete Adjuvant (FIA), or the adjuvants in combination with a formalin-killed culture of B. dendrobatidis. The effects of immunization were modeled using survival analysis and a proportional hazards model. No significant differences were found between the groups in overall mortality, time to infection, infection prevalence, or intensity. While this study suggests that immunizing anurans against chytridiomycosis will not alter rates of infection or mortality among individuals, it does raise several questions regarding the attenuation and efficacy of anuran adaptive immune responses and whether they may be protective against this disease.Journal of wildlife diseases 01/2010; 46(1):70-7. · 1.08 Impact Factor -
Article: The ecology and impact of chytridiomycosis: an emerging disease of amphibians.
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ABSTRACT: Emerging infectious diseases are increasingly recognized as key threats to wildlife. Batrachochytrium dendrobatidis (Bd), the causative agent of chytridiomycosis, has been implicated in widespread amphibian declines and is currently the largest infectious disease threat to biodiversity. Here, we review the causes of Bd emergence, its impact on amphibian populations and the ecology of Bd transmission. We describe studies to answer outstanding issues, including the origin of the pathogen, the effect of Bd relative to other causes of population declines, the modes of Bd dispersal, and factors influencing the intensity of its transmission. Chytridiomycosis is an archetypal emerging disease, with a broad host range and significant impacts on host populations and, as such, poses a crucial challenge for wildlife managers and an urgent conservation concern.Trends in Ecology & Evolution 10/2009; 25(2):109-18. · 15.75 Impact Factor -
Article: Skin microbes on frogs prevent morbidity and mortality caused by a lethal skin fungus.
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ABSTRACT: Emerging infectious diseases threaten human and wildlife populations. Altered ecological interactions between mutualistic microbes and hosts can result in disease, but an understanding of interactions between host, microbes and disease-causing organisms may lead to management strategies to affect disease outcomes. Many amphibian species in relatively pristine habitats are experiencing dramatic population declines and extinctions due to the skin disease chytridiomycosis, which is caused by the chytrid fungus Batrachochytrium dendrobatidis. Using a randomized, replicated experiment, we show that adding an antifungal bacterial species, Janthinobacterium lividum, found on several species of amphibians to the skins of the frog Rana muscosa prevented morbidity and mortality caused by the pathogen. The bacterial species produces the anti-chytrid metabolite violacein, which was found in much higher concentrations on frog skins in the treatments where J. lividum was added. Our results show that cutaneous microbes are a part of amphibians' innate immune system, the microbial community structure on frog skins is a determinant of disease outcome and altering microbial interactions on frog skins can prevent a lethal disease outcome. A bioaugmentation strategy may be an effective management tool to control chytridiomycosis in amphibian survival assurance colonies and in nature.The ISME Journal 04/2009; 3(7):818-24. · 7.38 Impact Factor -
Article: Testing a key assumption of host‐pathogen theory: density and disease transmission
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ABSTRACT: Conventional disease theory suggests that extinction with density-dependent transmission is unlikely as the threshold host density (KT) is greater than zero. Extinction may result if transmission is frequency dependent or the pathogen has an environmental reservoir. Given the importance of understanding how pathogens affect species richness and diversity there are few empirical tests of these conclusions. We used an Ambystoma tigrinum–Ambystoma tigrinum virus (ATV) model system in the laboratory to examine disease transmission dynamics. Susceptible A. tigrinum larvae were exposed to three different densities and proportions of infected larvae for 24 h. We then housed susceptible hosts individually for 28 days and monitored them for infection. The density of infected hosts to which susceptible hosts were exposed was the best predictor of infection (p=0.037). There was no effect of host clutch on the probability of becoming infected (p=0.67). Larvae in the highest density treatments died sooner than larvae in lower density treatments (p<0.001). Asymptomatic but infected hosts shed sufficient virus into the water in a 24-h period to infect susceptible hosts without any direct contact between individuals. ATV transmission was best described by a power function, leading to the prediction that extinction of A. tigrinum as a result of this pathogen is unlikely. Indeed, field observations show that larval salamander populations that experience ATV-driven epidemics may decrease, but not to extinction, and then recover. Disease is proposed as a possible explanation for the global decline of amphibians. Ranaviruses infect many amphibian populations, but based on our results may not be a general cause of declines to extinction. In contrast, frequency dependent transmission, environmental reservoirs and alternative hosts may be the most likely explanation for the enigmatic decline, at times to extinction, of some amphibian populations as a result of emerging infectious diseases, like the chytrid fungus Batrachochytrium dendrobatidis.Oikos 10/2008; 117(11):1667 - 1673. · 3.06 Impact Factor -
Article: Effect of temperature on host response to Batrachochytrium dendrobatidis infection in the mountain yellow-legged frog (Rana muscosa).
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ABSTRACT: The pathogenic chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, has been implicated in declines of amphibian populations throughout the world, including declines and extinctions of local populations of mountain yellow-legged frogs, Rana muscosa, in the California Sierra Nevada. Previous studies have shown B. dendrobatidis achieves its maximum growth rate in culture in the temperature range of 17-25 C, and exposure to very high temperatures can clear frogs of B. dendrobatidis infection. Here we present the results of a laboratory experiment in which experimentally infected R. muscosa tadpoles were followed through metamorphosis at temperatures of 17 and 22 C. All infected animals developed clinical disease within a similar time frame. However, frogs housed at 22 C exhibited a significantly lower mortality than those housed at 17 C. Within 35 days after metamorphosis, 50% of the frogs housed at 22 C died, while 95% of the frogs housed at 17 C died. Clinical signs subsided in the surviving frogs at 22 C, despite persistent infection. Because both temperatures are within the optimal thermal range for growth of B. dendrobatidis, we propose that the difference in outcome indicates the effect of temperature on the host's resistance to chytridiomycosis, rather than an effect on the fungus alone.Journal of wildlife diseases 08/2008; 44(3):716-20. · 1.08 Impact Factor -
Article: Spatial dynamics of lyme disease: a review.
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ABSTRACT: Lyme disease (LD), the most frequently reported vector-borne disease in the United States, requires that humans, infected vector ticks, and infected hosts all occur in close spatial proximity. Understanding the spatial dynamics of LD requires an understanding of the spatial determinants of each of these organisms. We review the literature on spatial patterns and environmental correlates of human cases of LD and the vector ticks, Ixodes scapularis in the northeastern and midwestern United States and Ixodes pacificus in the western United States. The results of this review highlight a need for a more standardized and comprehensive approach to studying the spatial dynamics of the LD system. Specifically, we found that the only environmental variable consistently associated with increased LD risk and incidence was the presence of forests. However, the reasons why some forests are associated with higher risk and incidence than others are still poorly understood. We suspect that the discordance among studies is due, in part, to the rapid developments in both conceptual and technological aspects of spatial ecology hastening the obsolescence of earlier approaches. Significant progress in identifying the determinants of spatial variation in LD risk and incidence requires that: (1) existing knowledge of the biology of the individual components of each LD system is utilized in the development of spatial models; (2) spatial data are collected over longer periods of time; (3) data collection and analysis among regions are more standardized; and (4) the effect of the same environmental variables is tested at multiple spatial scales.EcoHealth 07/2008; 5(2):167-95. · 1.70 Impact Factor -
Article: Life-history trade-offs influence disease in changing climates: strategies of an amphibian pathogen.
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ABSTRACT: Life-history trade-offs allow many animals to maintain reproductive fitness across a range of climatic conditions. When used by parasites and pathogens, these strategies may influence patterns of disease in changing climates. The chytrid fungus, Batrachochytrium dendrobatidis, is linked to global declines of amphibian populations. Short-term growth in culture is maximal at 17 degrees-25 degrees C. This has been used in an argument that global warming, which increases the time that amphibians spend at these temperatures in cloud-covered montane environments, has led to extinctions. Here we show that the amphibian chytrid responds to decreasing temperatures with trade-offs that increase fecundity as maturation rate slows and increase infectivity as growth decreases. At 17 degrees-25 degrees C, infectious zoospores encyst (settle and develop a cell wall) and develop into the zoospore-producing stage (zoosporangium) faster, while at 7 degrees-10 degrees C, greater numbers of zoospores are produced per zoosporangium; these remain infectious for a longer period of time. We modeled the population growth of B. dendrobatidis through time at various temperatures using delayed differential equations and observational data for four parameters: developmental rate of thalli, fecundity, rate of zoospore encystment, and rate of zoospore survival. From the models, it is clear that life-history trade-offs allow B. dendrobatidis to maintain a relatively high long-term growth rate at low temperatures, so that it maintains high fitness across a range of temperatures. When a seven-day cold shock is simulated, the outcome is intermediate between the two constant temperature regimes, and in culture, a sudden drop in temperature induces zoospore release. These trade-offs can be ecologically important for a variety of organisms with complex life histories, including pathogenic microorganisms. The effect of temperature on amphibian mortality will depend on the interaction between fungal growth and host immune function and will be modified by host ecology, behavior, and life history. These results demonstrate that B. dendrobatidis populations can grow at high rates across a broad range of environmental temperatures and help to explain why it is so successful in cold montane environments.Ecology 07/2008; 89(6):1627-39. · 4.85 Impact Factor -
Article: The window of vulnerability and its effect on relative parasitoid abundance
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ABSTRACT: 1. The length of time that a gall-forming midge, Rhopalomyia califomica, was vulnerable to attack by four parasitoid species was measured in the field at two locations.2. The midge had a restricted window of vulnerability to each of the parasitoid species, but similar windows of vulnerability were found at the two sites.3. A stage-structured model was used to illustrate that the length of the vulnerable window should have no effect on the fraction parasitized by a single parasitoid species if that species is the only parasitoid attacking the host in a coupled host-parasitoid interaction. However, the length of the window of vulnerability can have a positive effect on the fraction parasitized by a species in competition with other parasitoid species.4. The length of the window of vulnerability can help explain the relative field abundance of four of the common parasitoid species of R.californica.Ecological Entomology 03/2008; 21(2):128 - 140. · 2.00 Impact Factor -
Article: Trophic supplements to intraguild predation
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ABSTRACT: Intraguild predation (IGP) is a dominant community module in terrestrial food webs that occurs when multiple consumers feed both on each other and on a shared prey. This specific form of omnivory is common in terrestrial communities and is of particular interest for conservation biology and biological control given its potential to disrupt management of threatened or pest species. Extensive theory exists to describe the dynamics of three-species IGP, but these models have largely overlooked the potential for other, exterior interactions, to alter the dynamics within the IGP module. We investigated how three forms of feeding outside of the IGP module by intraguild predators (i.e. trophic supplementation) affect the dynamics of the predators (both IG predator and IG prey) and their shared resource. Specifically, we examined how the provision of a constant donor-controlled resource, the availability of an alternative prey species, and predator plant-feeding affect the dynamics of IGP models. All three forms of trophic supplements modified the basic expectations of IGP theory in two important ways, and their effects were similar. First, coexistence was possible without the IG prey being a superior competitor for the original shared resource if the IG prey could effectively exploit one of the types of trophic supplements. However, supplements to the IG predator restricted the potential for coexistence. Second, supplements to the IG prey ameliorated the disruptive effects of the IG predator on the suppression of the shared resource, promoting effective control of the resource in the presence of both predators. Consideration of these three forms of trophic supplementation, all well documented in natural communities, adds substantial realism and predictive power to intraguild predation theory.Oikos 11/2007; 116(4):662 - 677. · 3.06 Impact Factor
Top co-authors
Top Journals
Institutions
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2008–2012
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University of California, Santa Barbara
- Department of Ecology, Evolution, and Marine Biology
Santa Barbara, CA, USA -
University of California, Davis
- School of Veterinary Medicine
Davis, CA, USA
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2001–2011
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University of California, Berkeley
- Department of Integrative Biology
Berkeley, MO, USA
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2010
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San Francisco State University
- Department of Biology
San Francisco, CA, USA
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