Biodiversity and disease: a synthesis of ecological perspectives on Lyme disease transmission

150

132

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

Section: Resultsmentioning

confidence: 64%

mentioning

confidence: 99%

Spatial scale modulates the strength of ecological processes driving disease distributions

Cohen

Civitello

Brace

et al. 2016

150

132

“…Related research has indicated that hosts with a high intrinsic rate of increase are both more ecologically resilient and reservoir competent (58). Other work has emphasized the idiosyncratic nature of particular disease/ecology relationships (63), and still other efforts have concluded that generalizations about the effect of biodiversity on disease transmission have been premature (64). Clarifying the impacts of disruption of natural systems on transmission of vectorborne disease and the extent to which such relationships can be generalized across diseases and ecosystems remains an important area for future research.…”

Section: Highlights Of the Recent Literaturementioning

confidence: 99%

Human health impacts of ecosystem alteration

Myers

Gaffikin²,

Golden

et al. 2013

377

261

Human activity is rapidly transforming most of Earth's natural systems. How this transformation is impacting human health, whose health is at greatest risk, and the magnitude of the associated disease burden are relatively new subjects within the field of environmental health. We discuss what is known about the human health implications of changes in the structure and function of natural systems and propose that these changes are affecting human health in a variety of important ways. We identify several gaps and limitations in the research that has been done to date and propose a more systematic and comprehensive approach to applied research in this field. Such efforts could lead to a more robust understanding of the human health impacts of accelerating environmental change and inform decision making in the land-use planning, environmental conservation, and public health policy realms.At least since Hippocrates wrote On Airs, Waters, and Places, the natural environment has been viewed as an important determinant of human health. However, over the last century, the field of environmental health has focused increasingly on quantifying exposure-response relationships for toxins encountered in the human-dominated environment: from an initial focus on workplace exposures, to a population-level focus on radiation, heavy metals, air and water pollution, and more recently, to exposure to endocrinedisrupting chemicals. Over this period, relatively little attention has been paid to how changes in the structure and function of Earth's natural systems might affect human health. Growing evidence that changes in these natural systems can affect human health in a variety of important ways and the increasing pace and extent of these changes has prompted this Perspective. In it, we review current understanding of this field, identify some of its gaps and limitations, and suggest an approach to expanding our understanding.Human activity is transforming nearly all of Earth's natural systems. With the human population now exceeding 7 billion people and rapid growth in per capita consumption of goods and services, humanity's growing ecological footprint is altering the planet's land cover, rivers and oceans, climate system, biogeochemical cycles, and the

“…On the other hand, increases in host diversity are also hypothesized to promote parasite diversity by enhancing colonization opportunities and supporting a wider suite of parasite life cycles (host diversity begets parasite diversity hypothesis; ref. 16), such that host diversity and parasite diversity correlate positively (17,18). Rather than contradicting each other, these seemingly divergent perspectives on the diversity-disease relationship emphasize differences in both terminology and ecological process.…”

mentioning

confidence: 99%

Host and parasite diversity jointly control disease risk in complex communities

Johnson

Preston

Hoverman

et al. 2013

131

136

Host-parasite interactions are embedded within complex communities composed of multiple host species and a cryptic assemblage of other parasites. To date, however, surprisingly few studies have explored the joint effects of host and parasite richness on disease risk, despite growing interest in the diversity-disease relationship. Here, we combined field surveys and mechanistic experiments to test how transmission of the virulent trematode Ribeiroia ondatrae was affected by the diversity of both amphibian hosts and coinfecting parasites. Within natural wetlands, host and parasite species richness correlated positively, consistent with theoretical predictions. Among sites that supported Ribeiroia, however, host and parasite richness interacted to negatively affect Ribeiroia transmission between its snail and amphibian hosts, particularly in species-poor assemblages. In laboratory and outdoor experiments designed to decouple the relative contributions of host and parasite diversity, increases in host richness decreased Ribeiroia infection by 11-65%. Host richness also tended to decrease total infections by other parasite species (four of six instances), such that more diverse host assemblages exhibited ∼40% fewer infections overall. Importantly, parasite richness further reduced both per capita and total Ribeiroia infection by 15-20%, possibly owing to intrahost competition among coinfecting species. These findings provide evidence that parasitic and free-living diversity jointly regulate disease risk, help to resolve apparent contradictions in the diversity-disease relationship, and emphasize the challenges of integrating research on coinfection and host heterogeneity to develop a community ecology-based approach to infectious diseases. biodiversity | dilution effect | community assembly | amphibian decline | disease ecology