The Scaling of Host Density with Richness Affects the Direction, Shape, and Detectability of Diversity-Disease Relationships

Mihaljevic, Joseph R.; Joseph, Maxwell B.; Orlofske, Sarah A.; Paull, Sara H.

doi:10.1371/journal.pone.0097812

Cited by 67 publications

(120 citation statements)

References 33 publications

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“…Moreover, whether diversity inhibits transmission and subsequent disease risk often depends strongly on the type of transmission involved (e.g., density‐dependent or density‐independent) as well as whether communities assemble additively or substitutively (i.e., does total host abundance increase with diversity or remain constant? ; Dobson, ; Johnson, Ostfeld, et al., ; Mihaljevic, Joseph, Orlofske, & Paull, ). Further research would be required to investigate these points specifically for ranaviruses, as well as to obtain more high‐resolution estimates of infection over time.…”

Section: Discussionmentioning

confidence: 99%

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

et al. 2018

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A fundamental goal of disease ecology is to determine the landscape and environmental processes that drive disease dynamics at different biological levels to guide management and conservation. Although ranaviruses (family ) are emerging amphibian pathogens, few studies have conducted comprehensive field surveys to assess potential drivers of ranavirus disease dynamics.We examined the factors underlying patterns in site-level ranavirus presence and individual-level ranavirus infection in 76 ponds and 1,088 individuals representing 5 amphibian species within the East Bay region of California.Based on a competing-model approach followed by variance partitioning, landscape and biotic variables explained the most variation in site-level presence. However, biotic and individual-level variables explained the most variation in individual-level infection.Distance to nearest ranavirus-infected pond (the landscape factor) was more important than biotic factors at the site-level; however, biotic factors were most influential at the individual-level. At the site level, the probability of ranavirus presence correlated negatively with distance to nearest ranavirus-positive pond, suggesting that the movement of water or mobile taxa (e.g., adult amphibians, birds, reptiles) may facilitate the movement of ranavirus between ponds and across the landscape.Taxonomic richness associated positively with ranavirus presence at the site-level, but vertebrate richness associated negatively with infection prevalence in the host population. This might reflect the contrasting influences of diversity on pathogen colonization versus transmission among hosts.Amphibian host species differed in their likelihood of ranavirus infection: American bullfrogs () had the weakest association with infection while rough-skinned newts () had the strongest. After accounting for host species effects, hosts with greater snout-vent length had a lower probability of infection.Our study demonstrates the array of landscape, environmental, and individual-level factors associated with ranavirus epidemiology. Moreover, our study helps illustrate that the importance of these factors varies with biological level.

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Section: Discussionmentioning

confidence: 99%

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

et al. 2018

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“…Predicting how total transmission among all hosts should change with host diversity may be less clear if contact rate is a non-linear function of host density [4]. For example, some trematodes release more cercariae infective stages when their current first intermediate hosts are in the presence of more second intermediate hosts [32], [33].…”

Section: Introductionmentioning

confidence: 99%

Host Density and Competency Determine the Effects of Host Diversity on Trematode Parasite Infection

et al. 2014

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Variation in host species composition can dramatically alter parasite transmission in natural communities. Whether diverse host communities dilute or amplify parasite transmission is thought to depend critically on species traits, particularly on how hosts affect each other’s densities, and their relative competency as hosts. Here we studied a community of potential hosts and/or decoys (i.e. non-competent hosts) for two trematode parasite species, Echinostoma trivolvis and Ribeiroia ondatrae, which commonly infect wildlife across North America. We manipulated the density of a focal host (green frog tadpoles, Rana clamitans), in concert with manipulating the diversity of alternative species, to simulate communities where alternative species either (1) replace the focal host species so that the total number of individuals remains constant (substitution) or (2) add to total host density (addition). For E. trivolvis, we found that total parasite transmission remained roughly equal (or perhaps decreased slightly) when alternative species replaced focal host individuals, but parasite transmission was higher when alternative species were added to a community without replacing focal host individuals. Given the alternative species were roughly equal in competency, these results are consistent with current theory. Remarkably, both total tadpole and per-capita tadpole infection intensity by E. trivolvis increased with increasing intraspecific host density. For R. ondatrae, alternative species did not function as effective decoys or hosts for parasite infective stages, and the diversity and density treatments did not produce clear changes in parasite transmission, although high tank to tank variation in R. ondatrae infection could have obscured patterns.

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“…To this end, we have deliberately avoided providing quantitative results, as doing so would be claiming a false accuracy. We also remind readers that additive and substitutive host changes lie at extremes of a continuum and that disease outcomes in complex communities are unlikely to follow simple rules (e.g., Roche et al 2013;Mihaljevic et al 2014). Our results have, however, clearly demonstrated that modeling FD transmission without explicitly considering the vector can limit model applicability to real-world VBD systems.…”

Section: Discussionmentioning

confidence: 83%

“…In our pair of models, additive host change and FD transmission causes amplification of DIV (under certain combinations of transmission success and host recovery probabilities). Previous models have suggested that amplification ought not to occur when transmission is FD, even when the host change is additive (Rudolf and Antonovics 2005;Mihaljevic et al 2014). Indeed, if one considers only PIH (the prevalence of infection in hosts), it does not (note that the NR3 scenario is not strictly FD).…”

Section: Discussionmentioning

confidence: 99%

“…DD transmission is assumed to apply to directly transmitted diseases such as influenza or measles, whereas FD transmission best describes sexually transmitted infections such as HIV but is also typically applied to VBDs. Increased host diversity is held to dilute individual disease risk where transmission is FD (Rudolf and Antonovics 2005;Ostfeld and Keesing 2012;Mihaljevic et al 2014), but when DD transmission is assumed, the outcome should depend on the nature of the host change (see below).…”

Section: Introductionmentioning

confidence: 99%

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Epidemiological Implications of Host Biodiversity and Vector Biology: Key Insights from Simple Models

Dobson

Auld

2016

The American Naturalist

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Online enhancement: zip file. Dryad data: http://dx.doi.org/10.5061/dryad.t24pq.abstract: Models used to investigate the relationship between biodiversity change and vector-borne disease risk often do not explicitly include the vector; they instead rely on a frequency-dependent transmission function to represent vector dynamics. However, differences between classes of vector (e.g., ticks and insects) can cause discrepancies in epidemiological responses to environmental change. Using a pair of disease models (mosquito-and tick-borne), we simulated substitutive and additive biodiversity change (where noncompetent hosts replaced or were added to competent hosts, respectively), while considering different relationships between vector and host densities. We found important differences between classes of vector, including an increased likelihood of amplified disease risk under additive biodiversity change in mosquito models, driven by higher vector biting rates. We also draw attention to more general phenomena, such as a negative relationship between initial infection prevalence in vectors and likelihood of dilution, and the potential for a rise in density of infected vectors to occur simultaneously with a decline in proportion of infected hosts. This has important implications; the density of infected vectors is the most valid metric for primarily zoonotic infections, while the proportion of infected hosts is more relevant for infections where humans are a primary host.

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The Scaling of Host Density with Richness Affects the Direction, Shape, and Detectability of Diversity-Disease Relationships

Cited by 67 publications

References 33 publications

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage

Host Density and Competency Determine the Effects of Host Diversity on Trematode Parasite Infection

Epidemiological Implications of Host Biodiversity and Vector Biology: Key Insights from Simple Models

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