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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.

1. Fluctuations in abundance of blacklegged ticks in space and time are well‐documented, but the extent to which populations fluctuate synchronously across habitat types is poorly understood. In oak forests, blacklegged tick density depends on small mammal abundance, which is in turn driven by fluctuations in acorn production. It is currently unknown whether fluctuations in tick abundance in oak forest, long understood to depend largely on masting events, are shared with nearby non‐oak forest.

2. In this study, we analysed 22 years of tick population data from nine forest plots in south‐eastern New York in order to compare fluctuations of nymphal and larval blacklegged tick populations in oak‐dominant forests and non‐oak forests.

3. We found that population peak densities of nymphal ticks were strongly synchronous in oak and non‐oak forests among years and that larval population dynamics were weakly synchronous between these two forest types.

4. Our results suggest that drivers of immature tick density in oak‐dominant forest, including climatic factors and mast‐driven host dynamics, may also influence tick population fluctuations in the surrounding landscape.