The impacts of habitat fragmentation are often measured in landscape metrics like patch size, isolation, and connectivity. While these metrics are commonly used to understand the movement of plants and animals, they also have the potential to explain in part how diseases are transmitted. Linking landscape ecology to disease dynamics can provide a better picture of how pathogen and host communities move through fragmented areas and impact human risk for infection.
The most prevalent vector-born diseases in the U.S., including Lyme disease, are carried by ticks, which are regularly found in non-intact habitats. While some research links fragmentation and patch size to Lyme disease, little is known about how habitat connectivity specifically impacts pathogen and host communities and alters disease risk.
Shaw, G., Lilly, M., Mai, V., Clark, J., Summers, S., Slater, K., Karpathy, S., Nakano, A., Crews, A., Lawrence, A. and Salomon, J. 2024. The roles of habitat isolation, landscape connectivity and host community in tick-borne pathogen ecology. Royal Society Open Science 11(11): 240837.
A new study looks at the relationship between habitat connectivity and tick-borne pathogens, specifically western blacklegged ticks in California that are known to carry the bacteria causing Lyme disease. Across 19 sites ranging from small urban parks to large nature preserves, over 2,000 tick nymphs were collected over five years and a subset were analyzed for the presence of four bacterial pathogens. Wildlife surveys were also conducted at 14 of the sites, including live traps to determine rodent abundance and camera traps to determine overall wildlife abundance. This data was then linked to three categories of landscape metrics: site composition, nearby habitat, and isolation/connectivity to intact habitat.
The results highlight how local measures of landscape configuration like connectivity can be more important for predicting tick pathogens than habitat patch size. Larger patches with greater connectivity had higher densities of nymphs, and almost any level of patch isolation had the potential to lead to no nymphs present. Larger patches that were more isolated had lower densities of nymphs infected with one of the pathogens known to cause Lyme disease, although these densities increased with higher wildlife diversity.
There were also a higher number of pathogens present in nymphs when there was more surrounding green space that was well-connected. This suggests that humans are more likely to run into ticks in bigger habitat patches, but Lyme disease risk is highest in small habitat fragments with high connectivity. The type of bacterial transmission also made a difference: wildlife predictors, not landscape predictors, were significant in determining the prevalence for horizontally transmitted bacteria but not vertically transmitted bacteria.
These results emphasize how effectively island biogeography principles can be applied to vector-born disease systems to better understand their dynamics. While these results suggest that in fragmented urban areas, making green space more isolated would potentially decrease the risk of human Lyme disease risk, there are other benefits to connecting urban green spaces that need to be considered. Understanding both the benefits and drawbacks of creating connected habitats can help inform management decisions and lead to more effective conservation planning.
Related Posts
Connectivity and climate impact wildlife disease in cities
A multi-city study of urban coyotes shows how connectivity and climate change can interact to shape the distribution of wildlife disease.
Landscape quality drives ecological responses to habitat loss and fragmentation
A large-scale experiment of cactus bugs in central Florida underscores how the quality of the surrounding landscape can have outsized effects on habitat patches.
Reviewing four decades of fragmentation metrics
A review of fragmentation metrics since 1990 shows how methodologies have shifted over time, and what work still needs to be done to ensure transferable and ecologically grounded research.
