Spatial scale modulates the strength of ecological processes driving disease distributions

Abstract

Humans are altering the distribution of species by changing the climate and disrupting biotic interactions and dispersal. A fundamental hypothesis in spatial ecology suggests that these effects are scale dependent; biotic interactions should shape distributions at local scales, whereas climate should dominate at regional scales. If so, common single-scale analyses might misestimate the impacts of anthropogenic modifications on biodiversity and the environment. However, large-scale datasets necessary to test these hypotheses have not been available until recently. Here we conduct a crosscontinental, cross-scale (almost five orders of magnitude) analysis of the influence of biotic and abiotic processes and human population density on the distribution of three emerging pathogens: the amphibian chytrid fungus implicated in worldwide amphibian declines and West Nile virus and the bacterium that causes Lyme disease (Borrelia burgdorferi), which are responsible for ongoing human health crises. In all three systems, we show that biotic factors were significant predictors of pathogen distributions in multiple regression models only at local scales (∼10 2 -10 3 km 2 ), whereas climate and human population density always were significant only at relatively larger, regional scales (usually >10 4 km 2 ). Spatial autocorrelation analyses revealed that biotic factors were more variable at smaller scales, whereas climatic factors were more variable at larger scales, as is consistent with the prediction that factors should be important at the scales at which they vary the most. Finally, no single scale could detect the importance of all three categories of processes. These results highlight that common single-scale analyses can misrepresent the true impact of anthropogenic modifications on biodiversity and the environment.ecology | dilution effect | chytridiomycosis | West Nile virus | Lyme disease

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

“…In particular, landscape factors explained more variance at higher biological levels (site level) while biotic and individual‐level factors explained more variance at lower biological levels (individual level). Our findings are similar to those suggested for other disease systems and highlight the importance of investigating factors influencing disease epidemiology at multiple biological levels (Cohen et al., ; Johnson, De Roode, et al., ; Schotthoefer et al., ). Several variables such as cattle presence and water chemistry parameters, which are often cited to influence ranavirus epidemiology (Forson & Storfer, ,b; Kerby & Storfer, ; Kerby et al., ), were not influential in our study.…”

“…Recent studies have highlighted the importance of investigating the influence of factors at multiple biological levels of organisation because of contrasting results between levels (e.g., site‐ [higher level] versus individual level [lower level]; Borcard, Legendre, Avois‐Jacquet, & Tuomisto, ; Cohen et al., ; Dunn, Davies, Harris, & Gavin, ; Johnson, De Roode, & Fenton, ; Schotthoefer et al., ). It has been hypothesised that abiotic factors influence distributional patterns at higher levels, whereas biotic factors (e.g., species interactions) influence distributional patterns at lower levels (Cohen et al., ; Levin, ; Mcgill, ; Rahbek, ; Wiens, ). Accordingly, abiotic (e.g., temperature, precipitation, altitude) and biotic (e.g., host richness) factors were highly important in predicting the distribution of three pathogens (the pathogenic fungus Batrachochytrium dendrobatidis [Bd], West Nile virus and the bacterium that causes Lyme disease [ Borrelia burgdorferi ]) at higher levels, but biotic factors were more important at lower levels (Cohen et al., )).…”

“…It has been hypothesised that abiotic factors influence distributional patterns at higher levels, whereas biotic factors (e.g., species interactions) influence distributional patterns at lower levels (Cohen et al., ; Levin, ; Mcgill, ; Rahbek, ; Wiens, ). Accordingly, abiotic (e.g., temperature, precipitation, altitude) and biotic (e.g., host richness) factors were highly important in predicting the distribution of three pathogens (the pathogenic fungus Batrachochytrium dendrobatidis [Bd], West Nile virus and the bacterium that causes Lyme disease [ Borrelia burgdorferi ]) at higher levels, but biotic factors were more important at lower levels (Cohen et al., )). Landscape factors, such as connectivity among habitat patches, can also influence disease dynamics and the dispersal of pathogens.…”

The complex drivers of thermal acclimation and breadth in ectotherms

“…; Cohen et al . ). Moreover, our results suggest that global warming might generally give smaller species an edge in species interactions, resulting in asymmetries in species interactions (Dell et al .…”

Effect of spatial scale and latitude on diversity–disease relationships

“…The effect of spatial scale on diversity–disease relationships is relevant to both basic biology and conservation policy. The detection of scale dependence or latitude dependence would help narrow the search for causal mechanisms to those that predominate at a particular spatial scale (Johnson et al , Cohen et al ). Similarly, if high diversity is associated with reduced disease risk at some scales or latitudes but not others, the management of diversity for health benefits could be directed at relevant scales and latitudes where a desired impact is more likely.…”