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Abstract The dilution effect hypothesis posits that increasing biodiversity reduces infectious disease transmission. Here, we propose that habitat quality might modulate this negative biodiversity–disease relationship. Habitat may influence pathogen prevalence directly by affecting host traits like nutrition and immune response (we coined the term “habitat–disease relationship” to describe this phenomenon) or indirectly by changing host biodiversity (biodiversity–disease relationship). We used a path model to test the relative strength of links between habitat, biodiversity, and pathogen prevalence in a pollinator–virus system. High‐quality habitat metrics were directly associated with viral prevalence, providing evidence for a habitat–disease relationship. However, the strength and direction of specific habitat effects on viral prevalence varied based on the characteristics of the habitat, host, and pathogen. In general, more natural area and richness of land‐cover types were directly associated with increased viral prevalence, whereas greater floral density was associated with reduced viral prevalence. More natural habitat was also indirectly associated with reduced prevalence of two key viruses (black queen cell virus and deformed wing virus) via increased pollinator species richness, providing evidence for a habitat‐mediated dilution effect on viral prevalence. Biodiversity–disease relationships varied across viruses, with the prevalence of sacbrood virus not being associated with any habitat quality or pollinator community metrics. Across all viruses and hosts, habitat–disease and biodiversity–disease paths had effects of similar magnitude on viral prevalence. Therefore, habitat quality is a key driver of variation in pathogen prevalence among communities via both direct habitat–disease and indirect biodiversity–disease pathways, though the specific patterns varied among different viruses and host species. Critically, habitat–disease relationships could either contribute to or obscure dilution effects in natural systems depending on the relative strength and direction of the habitat–disease and biodiversity–disease pathways in that host–pathogen system. Therefore, habitat may be an important driver in the complex interactions between hosts and pathogens.
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Dilution effects in disease ecology
Abstract For decades, people have reduced the transmission of pathogens by adding low‐quality hosts to managed environments like agricultural fields. More recently, there has been interest in whether similar ‘dilution effects’ occur in natural disease systems, and whether these effects are eroded as diversity declines. For some pathogens of plants, humans and other animals, the highest‐quality hosts persist when diversity is lost, so that high‐quality hosts dominate low‐diversity communities, resulting in greater pathogen transmission. Meta‐analyses reveal that these natural dilution effects are common. However, studying them remains challenging due to limitations on the ability of researchers to manipulate many disease systems experimentally, difficulties of acquiring data on host quality and confusion about what should and should not be considered a dilution effect. Because dilution effects are widely used in managed disease systems and have been documented in a variety of natural disease systems, their existence should not be considered controversial. Important questions remain about how frequently they occur and under what conditions to expect them. There is also ongoing confusion about their relationships to both pathogen spillover and general biogeographical correlations between diversity and disease, which has resulted in an inconsistent and confusing literature. Progress will require rigorous and creative research.
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- Award ID(s):
- 1948419
- PAR ID:
- 10366663
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 24
- Issue:
- 11
- ISSN:
- 1461-023X
- Page Range / eLocation ID:
- p. 2490-2505
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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