Biology subjects

Rohr, J. R.

Publications and source records attributed to Rohr, J. R..

At least 19 recordsLinked to original sources

bioRxiv2026

From protection to amplification: Imperfect chytridiomycosis prophylaxis increases infections in wild amphibians

Wildlife vaccination could become a powerful strategy to mitigate disease-induced biodiversity losses, yet many vaccines for wildlife diseases provide only limited protection. Notably, tools to control the fungal pathogen Batrachochytrium dendrobatidis (Bd) are urgently needed for amphibian conservation. Laboratory experiments have demonstrated that prophylactic exposure to Bd metabolites increases host resistance, significantly reducing infection intensity in amphibians subsequently challenged with live Bd. Because Bd metabolites are non-infectious and applied topically, this treatment has potential to be administered to waterbodies to vaccinate and protect amphibians. We developed an agent-based model that indicated imperfect vaccination could reduce or amplify Bd infections at the population level, depending on degree of enhanced resistance or tolerance. Utilizing a Before-After-Control-Impact design with ten years of data, we conducted an ecosystem-level trial where we applied low levels of Bd metabolites or a sham control treatment to ponds in California and subsequently quantified Bd prevalence and infection intensity in metamorphosing Pacific chorus frogs (Pseudacris regilla). Unexpectedly, infection intensity was significantly greater in treated ponds relative to control ponds following metabolite addition. Additional model simulations indicated that this could occur via two mechanisms: (1) if treatment greatly increased tolerance alone or in combination with smaller increases in resistance, or (2) if a deleterious environmental interaction caused the treatment to increase susceptibility, rather than promote resistance. Future research is needed to determine whether tolerance or environmental factors drove heightened Bd infection intensities in this field trial to identify contexts in which this treatment can be used as a conservation tool. Significance statementAlthough wildlife vaccination is increasingly explored as a strategy to mitigate disease-induced population declines, many available vaccines provide limited protection, requiring careful consideration to design successful conservation campaigns. Here, we use both an eco-epidemiological model and field manipulation experiment to assess the effectiveness of an imperfect prophylactic treatment (akin to a prototype vaccine) for chytridiomycosis, a disease implicated in the massive decline of amphibian biodiversity worldwide. We unexpectedly found that prophylaxis-treated ponds had higher pathogen loads relative to control populations and models suggest this could result from enhanced tolerance or an adverse environmental interaction.

ecology↗

bioRxiv2026

Insecticide temephos alters thermal dependence of dengue vector

O_LIAlthough ecological research has long focused on the effects of temperature on population growth, arthropod pests are exposed to a wide variety of environmental factors that affect their performance, such as chemical pesticides targeted against them. Moreover, these environmental factors likely do not act in isolation. Identifying the extent to which abiotic factors interact to affect pest population dynamics can strengthen current and future pest management programs. C_LIO_LIHere, we investigated the extent to which temephos, a common pesticide applied to aquatic environments for mosquito control, influences the thermal performance of juvenile survival and development rate, as well as the intrinsic population growth rate, of the invasive mosquito pest, Aedes aegypti. We implemented a response surface experimental design to measure these traits across seven temperatures and five temephos concentrations and fit temperature- and insecticide-dependent performance curves to assess impacts on the overall performance and the thermal optimum, minimum, and maximum. C_LIO_LITemephos exposure profoundly altered the thermal performance of juvenile survival by reducing survival across all temperatures, shrinking the thermal breadth, and shifting the thermal optimum to warmer temperatures. Through this, temephos also altered the thermal performance of population growth primarily by reducing its thermal breadth. C_LIO_LISynthesis and applications: Our findings demonstrate that interactions between temperature and insecticide exposure can fundamentally reshape pest population dynamics, rather than acting as independent stressors. By quantifying this interaction, we showed that temphos is most effective below the pests thermal optimum, suggesting that larvicides may yield the greatest population suppression in cooler regions or during cooler periods of the year. Incorporating such temperature-dependent efficacy into pest management strategies could improve the timing and spatial targeting of control efforts. More broadly, these results highlight the need to integrate anthropogenic stressors with climatic drivers when predicting pest risk and optimizing management under ongoing environmental change. C_LI

ecology↗

bioRxiv2026

Assessing the impact of host density on vector abundance and transmission scaling of Culicoides-transmitted pathogens

The spread of any pathogen depends on the dynamics of its hosts, with transmission rates typically assumed to either scale linearly with host population density (density-dependent transmission) or to be independent of it (frequency-dependent transmission). For vector-transmitted pathogens, a key determinant of transmission scaling is whether vector abundance is constant or sensitive to host abundance, with the latter being consistent with density-dependent transmission. Here, we assess whether Culicoides vector abundance increases in a manner that indicates density-dependent transmission of Culicoides-transmitted pathogens. To test this, we conducted trapping of Culicoides midges on eight livestock operations across a wide range of cattle abundances, placing traps at varying distances from the host aggregation. We used hierarchical Bayesian models to estimate the effect of host abundance on the vector-to-host ratio while accounting for differences in trapping efficacy between locations. Our results indicate a positive linear effect of host abundance on the ratio of vectors to hosts, with a posterior probability of 0.83. Median posterior values of the effect of host abundance on vector density predict a 2.3% increase (95% credible interval: -0.8, 23.2%) in the vector-to-host ratio with every 1,000 additional hosts. The weight of evidence from our study suggests that Culicoides-transmitted pathogens are likely subject to density-dependent transmission, and that transmission may be amplified in high-concentration livestock environments.

ecology↗

bioRxiv2026

Multi-axis spatiotemporal niche partitioning between coexisting top predators in ponds

O_LIUnderstanding how ecologically similar species coexist remains a central challenge in ecology, particularly in small, spatially constrained systems where opportunities for segregation may be limited. Classical niche theory predicts that coexistence is facilitated when species partition resources across multiple niche axes, yet few empirical studies quantify how spatial, temporal, and environmental dimensions jointly structure realized niches in natural systems. C_LIO_LIWe examined spatiotemporal niche partitioning between two coexisting top predators--the eastern red-spotted newt (Notophthalmus viridescens) and bluegill sunfish (Lepomis macrochirus)--in a pond lacking piscivorous fish. Using year-round trapping data collected across depth strata, diel periods, and seasons, we combined hierarchical count models, temperature-informed partial effect analyses, and null-model tests of niche overlap. C_LIO_LINewts and sunfish exhibited strongly contrasting patterns of habitat use across multiple axes. Newt capture rates were highest during cooler periods, in deeper habitats, and during morning sampling, whereas sunfish capture rates peaked during warmer periods, in shallow habitats, and during afternoon sampling. Model-based analyses revealed opposing responses to temperature, with predicted newt captures declining and sunfish captures increasing as temperature rose, even after accounting for seasonal effects. As a result, niche overlap across combined season-by-depth-by-time states was consistently lower than expected under randomized null models. C_LIO_LIAcross all analyses, newts and sunfish exhibited strong and consistent spatiotemporal niche partitioning, with opposing seasonal trajectories, contrasting depth and diel activity patterns, divergent thermal responses, and niche overlap significantly lower than expected under null models. These results demonstrate that fine-scale spatiotemporal structure across interacting niche axes can generate pronounced segregation among coexisting top predators, even in small and physically constrained ecosystems. Rather than reflecting partitioning along a single dominant axis, niche differentiation in this system appears to emerge from the coordinated interaction of season, habitat, diel activity, and temperature, highlighting how multi-axis dynamics shape realized niches in natural communities. C_LI Significance StatementCoexisting predators often exploit the same prey and habitats, raising the question of how overlap is reduced in spatially constrained ecosystems such as ponds. By integrating seasonal, diel, habitat, and thermal dimensions, this study demonstrates that two ecologically similar top predators--newts and sunfish--exhibit strong spatiotemporal niche partitioning that substantially lowers overlap relative to random expectations. Our results show that fine-scale temporal and habitat structure can play a major role in organizing predator assemblages, even in small freshwater systems, and highlight the importance of multi-axis niche frameworks for understanding species interactions and persistence in natural communities.

ecology↗

bioRxiv2026

A Common Agrochemical Mixture Increases Snail Hosts and Ecological Drivers of Schistosomiasis Risk

O_LIAgricultural intensification is accelerating across tropical regions, increasing fertilizer and pesticide inputs into freshwater ecosystems that regulate the transmission of many environmentally mediated diseases. For schistosomiasis, a major neglected tropical disease, transmission risk is strongly governed by the abundance of freshwater snail intermediate hosts and their aquatic habitat, yet most agrochemical studies have focused on single compounds rather than realistic mixtures. C_LIO_LIUsing replicated semi-natural aquatic microcosms, we experimentally tested how nitrogen- urea fertilizer and the widely used herbicide atrazine, applied alone and in combination at environmentally relevant concentrations, alter snail hosts (Biomphalaria glabrata), submerged aquatic vegetation (Ceratophyllum demersum), and algal resources that underpin schistosomiasis transmission. C_LIO_LIFertilizer and atrazine, both singly and together, increased snail habitat (C. demersum) and adult snail abundance. By reducing phytoplankton, atrazine likely alleviated shading on vegetation, thereby promoting habitat that supported snails through indirect bottom-up pathways. Agrochemical mixtures produced non-additive effects on host and habitat dynamics, indicating that transmission-relevant ecological responses cannot be predicted from single-compound exposures alone. Although parasite infection levels were low, the observed increases in snail hosts and habitat represent reliable ecological drivers of schistosomiasis risk. C_LIO_LISynthesis and applications. Our findings demonstrate that common agrochemical mixtures can restructure freshwater food webs in ways likely to elevate disease risk, highlighting the need to incorporate mixture-driven ecological responses into agrochemical risk assessment and agricultural management strategies in disease-endemic regions. C_LI

ecology↗

bioRxiv2025

Rice-Fish Co-Culturing for Sustainability, Food Security, and Disease and Poverty Reduction

Over 140 million households cultivate rice worldwide. However, rice production contributes to exceedances of planetary boundaries, such as freshwater use and biogeochemical flows. Additionally, rice-farming families may face increased risk of acquiring schistosomiasis, a parasitic disease transmitted by freshwater snails that contributes to reinforcing cycles of poverty and disease. Using data from 405 households in rural Senegal, we show that children in rice-farming households had higher Schistosoma mansoni prevalence and S. haematobium intensities than non-farming peers. To address this environmental-health challenge, we integrated native Nile Tilapia (Oreochromis niloticus) and African Bonytongue (Heterotis niloticus) into rice fields. The fish thrived, suppressed insects and snail pests, improved soil nutrients, and boosted rice yields by >25% with a net benefit of 1,805-3,415 USD/ha/year (benefit-to-cost ratio = 7.42). Hence, low-input rice-fish co-culturing offers a scalable planetary health solution that simultaneously advances sustainability, nutrition, health, and rural livelihoods. ResumePlus de 140 millions de foyers a travers le monde cultivent du riz. Cependant, cette production exerce une pression importante sur les ressources naturelles, notamment les reserves deau douce. Par ailleurs, les menages pratiquant la riziculture peuvent etre plus exposes au risq ue de bilharziose, une maladie parasitaire transmise par des escargots deau douce, qui contribue au cycle de pauvrete. A partir de donnees collectees aupres de 405 menages dans des villages senegalais, nous montrons que les enfants issus de familles pratiquant la riziculture presentent une prevalence plus elevee dinfection a Shistosoma mansoni et des intensites dinfection a S. haematobium plus importantes que ceux issues de familles ne cultivant pas le riz. Pour remedier a cela, nous avons integre deux especes locales de poissons, le tilapia du Nil (Oreochromis niloticus) et lHeterotis (Heterotis niloticus), dans les rizieres, afin de reduire les population descargots hotes, ameliorer les rendements agricoles et augmenter les revenus. Ces poissons ont montre une bonne croissance, ont contribue a la regulation des insectes et des escargots nuisibles, ont enrichi le sol en nutriments, et accru les rendements rizicoles de plus de 25%, avec un benefice net estime entre 1 805 et 3 415 USD/ha/an (ratio benefice-cout = 7,42). Ainsi, la co-culture riz-poisson a faibles intrants constitue une solution reproductible en faveur de la sante publique, permettant de concilier durabilite, nutrition et amelioration des moyens de subsistance en milieu rural.

ecology↗

bioRxiv2025

Early warning signals of emerging infectious diseases

Establishing early warning systems for infectious disease outbreaks could save millions of lives by enabling rapid response and containment. One promising approach draws on the concept of critical slowing down (CSD)--a phenomenon in which complex systems lose resilience before tipping points--detected using resilience indicators (RIs) derived from the statistical properties of time series. While disease outbreaks may exhibit such early warning signals of critical transitions, most prior applications of CSD theory to global health have been limited to single diseases or locations, without broad assessments of predictive accuracy or lead time--the interval between the detection of warning signals and the onset of an outbreak. To address these limitations, we integrate CSD theory with time-to-event analyses to evaluate the predictive performance of 17 RIs across 31 infectious diseases in 134 regions worldwide. We find that both RIs and time- to-event analyses provide ample time to implement control measures, reliably anticipating outbreaks with a mean lead time of 17-21 days. Lead time was greater for pathogens with longer incubation periods and in regions with higher Human Development Index. Additionally, temperature and precipitation exhibited unimodal effects on lead time predictions for vector-borne and viral diseases. These findings highlight the value of incorporating socio-environmental drivers into outbreak forecasting models and lay the foundation for a local-to-global early warning system capable of guiding proactive public health interventions.

ecology↗

bioRxiv2025

Larval development habitats of Culicoides midges in the western United States

Culicoides midges are vectors of bluetongue virus (BTV), an arbovirus affecting wild and domestic ruminants. Bluetongue distribution generally overlaps with vector range, so understanding the vectors ecology is necessary for predicting BTV risk. Culicoides require moist substrate for oviposition and development, and C. sonorensis, the primary vector in the western United States, is classically associated with livestock wastewater ponds. However, it is well-known that BTV can be found outside of managed livestock areas, with transmission also occurring in natural settings. To better classify development habitat for Culicoides, we conducted a broad biweekly survey of moist and wet habitats from June to September of 2022 in northern Colorado at ten sites, including large livestock operations, non-commercial domestic operations, and natural spaces. Samples were maintained in the insectary for 11 weeks and monitored for emergence of adult midges. Standing water substrates displayed higher presence and abundance of midges than running or transient habitats, though all microhabitats showed emergence. Additionally, livestock sites did not produce more midges than other site types, and in fact more midges were observed in natural spaces per sample and overall. Livestock spaces did, however, show significantly higher proportions of C. sonorensis midges, which are thought to be the most competent vectors of BTV in this region. These results suggest that development sites in natural areas may play an important role in maintaining vector populations in the western U.S. outside of previously implicated livestock operations, and that differences in larval habitat lead to differences in vector species composition.

ecology↗

bioRxiv2023

Abnormal weather drives disease outbreaks in wild and agricultural plants

Predicting effects of climate change on plant disease is critical for protecting ecosystems and food production. Climate change could exacerbate plant disease because parasites may be quicker to acclimate and adapt to novel climatic conditions than their hosts due to their smaller body sizes and faster generation times. Here we show how disease pressure responds to the anomalous weather that will increasingly occur with climate change by compiling a global database (5380 plant populations; 437 unique plant-disease combinations; 2,858,795 individual plant-disease samples) of disease incidence in both agricultural and wild plant systems. Because wild plant populations are assumed to be adapted to local climates, we hypothesized that large deviations from historical conditions would increase disease incidence. By contrast, since agricultural plants have been transported globally, we did not expect the historical climate where they are currently grown to be as predictive of disease incidence. Supporting these hypotheses, we found that disease outbreaks tended to occur during periods of warm temperatures in agricultural and cool-climate wild plant systems, but also occurred in warm-adapted wild (but not agricultural) plant systems experiencing anomalously cool weather. Outbreaks were additionally associated with higher rainfall in wild systems, especially those with historically wet climates. Our results suggest that historical climate affects susceptibility to disease for wild plant-disease systems, while warming drives risks for agricultural plant disease outbreaks regardless of historical climate.

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bioRxiv2022

Global change drivers and the risk of infectious disease

Anthropogenic change is contributing to the rise in emerging infectious diseases, but it remains unclear which global change drivers most increase disease and under what contexts. We amassed a dataset from the literature that includes 1,832 observations of infectious disease responses to global change drivers across 1,202 host-parasite combinations. We found that biodiversity loss, climate change, and introduced species were associated with increases in disease-related endpoints or harm (i.e., enemy release for introduced species), whereas urbanization was associated with decreases in disease endpoints. Natural biodiversity gradients, deforestation, forest fragmentation, and most classes of chemical contaminants had non-significant effects on these endpoints. Overall, these results were consistent across human and non-human diseases. Context-dependent effects of the global change drivers on disease were common and are discussed. These findings will help better target disease management and surveillance efforts towards global change drivers that increase disease. One-Sentence SummaryHere we quantify which global change drivers increase infectious diseases the most to better target global disease management and surveillance efforts.

ecology↗

bioRxiv2021

Functional similarity, not phylogenetic relatedness, predicts the relative strength of competition

Predicting the outcome and strength of species interactions is a central goal of community ecology. Researchers have proposed that outcomes of species interactions (competitive exclusion and coexistence) are a function of both phylogenetic relatedness and functional similarity. Studies relating phylogenetic distance to competition strength have shown conflicting results. Work investigating the role of phylogenetic relatedness and functional similarity in driving competitive outcomes has been limited in terms of the breadth of taxa and ecological contexts examined, which makes the generality of these studies unclear. Consequently, we gathered 1,748 pairwise competition effect sizes from 269 species and 424 unique species pairs with divergence times ranging from 1.14 to 1,275 million years and used meta-regression and model selection approaches to investigate the importance of phylogenetic relatedness and functional similarity to competition across ecological contexts. We revealed that functional similarity, but not phylogenetic relatedness, predicted the relative strength of interspecific competition (defined as the strength of interspecific competition relative to intraspecific competition). Further, we found that the presence of predators, certain habitats, increasing density of competitors, and decreasing spatial grain of experiments were all associated with more intense interspecific competition relative to intraspecific competition. Our results demonstrate that functional similarity, not phylogenetic relatedness, may explain patterns of competition-associated community assembly, highlighting the value of trait-based approaches in clarifying biotic assembly dynamics.

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bioRxiv2021

Do host-consumed resources increase endoparasitic but decrease ectoparasitic infections?

Habitat loss and disease outbreak play a major role in the decline of biodiversity. Habitat degradation is often associated with reduced food resources, which can lead to less investment in host immunity and increased infections. However, pathogens use host resources for replication and pathogen traits, such as infecting hosts internally or short generation times, might allow pathogens to rapidly capitalize on host-consumed nutrients. Thus, it is unclear whether increased food consumption by hosts should reduce or amplify pathogen levels. We conducted experiments on Cuban treefrogs (Osteopilus septentrionalis) to test how food availability affects infection levels of Ranavirus and the fungal pathogen Batrachochytrium dendrobatidis (Bd), which are both associated with mass die-offs of amphibians. Given that Ranavirus is an endoparasite with a much shorter generation time than the ectoparasitic Bd, we postulated that Ranavirus might be able to capitalize on host-consumed resources more quickly than Bd. We hypothesized that increased food availability to hosts might reduce Bd infections more than Ranavirus infections. As predicted, augmenting food access decreased Bd infection intensity, but increased Ranavirus infection intensity. Future work should assess whether pathogen traits, such as generation time and endo- versus ectoparasitism, generally affect whether food resources more positively benefit hosts or pathogens.

ecology↗

bioRxiv2021

Environmental persistence but not per capita transmission rates of a chytrid fungus determines infection prevalence

AO_SCPLOWBSTRACTC_SCPLOWUnderstanding local-scale variability in disease dynamics can be important for informing strategies for surveillance and management. For example, the amphibian chytrid fungus (Batrachochytrium dendrobatidis; Bd), which is implicated in population declines and species extinctions of amphibians, causes spatially variable epizootics and extirpations of its hosts. Outbreak heterogeneity could be driven by differential survival of zoospores, the free-living infectious life stage of Bd, or the persistence of dead zoospores and/or its metabolites in water, which could induce resistance among hosts. To gain a mechanistic understanding of the potential for variation in local transmission dynamics of Bd, we conducted Bd survival and infection experiments and then fit models to discern how Bd mortality, decomposition, and per-capita transmission rate vary among water sources. We found that infection prevalence differed among water sources, which was driven by differences in mortality rates of Bd zoospores, rather than differences in per-capita transmission rates. Specifically, zoospore mortality rates varied significantly among pond water treatments and were lower in artificial spring water compared to pond water sources. These results suggest that variation in Bd infection dynamics could be a function of differences in exposure of hosts to live Bd. In contrast to the persistence of live zoospores, we found that rates of decomposition of dead zoospores did not vary among water sources. These results may suggest that exposure of hosts to dead Bd or its metabolites, which have been shown to induce acquired resistance, might not commonly vary among nearby sites. Ultimately, a mechanistic understanding of the drivers of variable epizootics of Bd could lead to increases in the effectiveness of surveillance and management strategies.

ecology↗

bioRxiv2021

Reducing disease and producing food: Effects of 13 agrochemicals on snail biomass and human schistosomes

Agrochemical use is predicted to increase 2-5 fold by 2050 to meet food demand. Evidence suggests that agrochemical pollution could increase snails that transmit the disease schistosomiasis to 250 million people, but most agrochemicals remain unexamined. Here we quantify the relative effects of fertilizer, six insecticides, and six herbicides on snail genera responsible for 90% of global schistosomiasis cases. We identified fertilizers and 4 of 6 insecticides as high risk for increasing snail biomass by increasing snail resources (vegetative habitat and periphytic food) and reducing snail predators, respectively. Herbicides generally had negative effects on snails by reducing vegetative habitat, with two herbicides increasing snails in the absence of aquatic vegetation. Parasite production, which reflects human infection risk, scaled positively to snail biomass. Our findings suggest that fertilizers and insecticides are more likely to increase human schistosomiasis than herbicides and revealed several low risk agrochemicals that might increase crop production without increasing schistosomiasis.

ecology↗

bioRxiv2021

Identifying low risk insecticides to address both food shortages and the biocontrol of human schistosomiasis

Use of agrochemicals, including insecticides, is vital to food production and predicted to increase 2-5 fold by 2050. Previous studies have shown a positive association between agriculture and the human infectious disease schistosomiasis, which is problematic as this parasitic disease infects approximately 250 million people worldwide. Certain insecticides might runoff fields and be highly toxic to invertebrates, such as prawns in the genus Macrobrachium, that are biocontrol agents for snails that transmit the parasites causing schistosomiasis. We used a laboratory dose-response experiment and an observational field study to determine the relative toxicities of three pyrethroid (esfenvalerate, {lambda}-cyhalothrin, and permethrin) and three organophosphate (chlorpyrifos, malathion, and terbufos) insecticides to Macrobrachium prawns. In the lab, pyrethroids were consistently several orders of magnitude more toxic than organophosphate insecticides, and more likely to runoff fields at lethal levels according to modeling data. In the field, we found that Macrobrachium prawn survival at 31 water contact sites in the lower basin of the Senegal River where schistosomiasis is endemic was predicted by pyrethroid application rates to nearby crop fields after controlling for abiotic and prawn-level factors. Our findings suggest that widely used pyrethroid insecticides can have strong non-target effects on Macrobrachium prawns that are biocontrol agents where 400 million people are at risk of human schistosomiasis. Understanding the ecotoxicology of high-risk insecticides may help improve human health in schistosomiasis-endemic regions undergoing agricultural expansion.

ecology↗

bioRxiv2020

Reservoir host community and vector density predict human tick-borne diseases across the United States

In the United States, tick-borne disease cases have tripled since the 1990s and cost upwards of 10 billion USD annually. Tick density and densities and diversity of non-human mammalian reservoir hosts are hypothesized to drive tick-borne disease dynamics and are targets for interventions. Here, we relate human prevalence of four tick-borne diseases (Lyme disease, monocytic ehrlichiosis, granulocytic anaplasmosis, and babesiosis) to tick and reservoir host community data collected by the U.S. National Ecological Observatory Network (NEON) across the contiguous U.S. We show that human disease prevalence is correlated positively with tick and reservoir host densities and negatively with mammalian diversity for Lyme disease and ehrlichiosis, but positively for anaplasmosis and babesiosis. Our results suggest that the efficacy of tick-borne disease interventions depends on tick and host densities and host diversity. Thus, policymakers and disease managers should consider these ecological contexts before implementing preventative measures. SignificanceTick-borne disease incidence has increased in the United States over the last three decades. Because life-long symptoms can occur if reactive antibiotics are not administered soon after the tick bite, prevention is imperative. Yet, control of tick-borne zoonoses has been largely unsuccessful, at least partly because of a limited understanding of the ecological complexities of these diseases, especially non-Lyme disease tick-borne zoonoses. We use continental-scale data to quantify the relationships among four tick-borne diseases and tick and reservoir host communities, revealing that disease incidence is driven by a combination of tick densities and reservoir host densities and diversity. Thus, the efficacy of tick-borne disease interventions is likely dependent on these ecological contexts.

ecology↗

bioRxiv2020

Biodiversity loss underlies the dilution effect of biodiversity

The dilution effect predicts increasing biodiversity to reduce the risk of infection, but the generality of this effect remains unresolved. Because biodiversity loss generates predictable changes in host community competence, we hypothesized that biodiversity loss might drive the dilution effect. We tested this hypothesis by reanalyzing four previously published meta-analyses that came to contradictory conclusions regarding generality of the dilution effect. In the context of biodiversity loss, our analyses revealed a unifying pattern: dilution effects were inconsistently observed for natural biodiversity gradients, but were commonly observed for biodiversity gradients generated by disturbances causing losses of native biodiversity. Incorporating biodiversity loss into tests of generality of the dilution effect further indicated that scale-dependency may strengthen the dilution effect only when biodiversity gradients are driven by biodiversity loss. Together, these results help to resolve one of the most contentious issues in disease ecology: the generality of the dilution effect.

ecology↗

bioRxiv2020

The application of community ecology theory to co-infections in wildlife hosts

Priority effect theory, a foundational concept from community ecology, states that the order and timing of species arrival during species assembly can affect species composition. Although this theory has been applied to co-infecting parasite species, it has almost always been with a single time lag between co-infecting parasites. Thus, how the timing of parasite species arrival affects co-infections and disease remains poorly understood. To address this gap in the literature, we exposed post-metamorphic Cuban tree frogs (Osteopilus septentrionalis) to Ranavirus, the fungus Batrachochytrium dendrobatidis (Bd), a nematode Aplectana hamatospicula, or pairs of these parasites either simultaneously or sequentially at a range of time lags and quantified load of the secondary parasite and host growth, survival and parasite tolerance. Prior exposure to Bd or A. hamatospicula significantly increased viral loads relative to hosts singly infected with Ranavirus, whereas A. hamatospicula loads in hosts were higher when co-exposed to Bd than when co-exposed to Ranavirus. There was a significant positive relationship between time since Ranavirus infection and Bd load, and prior exposure to A. hamatospicula decreased Bd loads compared to simultaneous co-infection with these parasites. Infections with Bd and Ranavirus either singly or in co-infections decreased host growth and survival. This research reveals that time lags between co-infections can affect parasite loads, in line with priority effects theory. As co-infections in the field are unlikely to be simultaneous, an understanding of when co-infections are impacted by time lags between parasite exposures may play a major role in controlling problematic co-infections.

ecology↗