Summer Peromyscus abundance did not predict Ixodes scapularis nymph density in the next year at six eastern US NEON sites in 2014–2024, but had a negative same-year association

Question: At the Cary Institute (New York), the abundance of white-footed mice in one summer predicts the density of host-seeking blacklegged tick nymphs in the next year. Does this lag occur within other forest sites? Approach: We used NEON tick drag data and small-mammal box-trap data (RELEASE-2026, as standardized by neonDivData) from the six NEON sites with the most lab-identified Ixodes scapularis nymphs (BLAN, HARV, ORNL, SCBI, SERC, TREE; 1,934 drags with 5,038 nymphs; 1,090 plot-bouts with 12,433 Peromyscus). We made site-year indices with Poisson GLMs (year, plot, month, effort offset). We fitted log nymph index in year y+1 on log Peromyscus index in June-September of year y with site fixed effects. We used within-site permutation tests. We wrote the analysis plan before we calculated the association. Main finding: The elasticity was +0.04 (SE 0.14; 95% CI -0.24 to +0.31; within-site r = +0.04; permutation p = 0.80; 56 pairs). The result did not change with year fixed effects, site trends, other windows, other host groups, the 2019-2024 period only, a drag-level model, or the removal of any one site. The design had 80% power for an elasticity of 0.40 or a within-site R2 of 0.15. Split-half reliability of the mouse index was 0.88, so measurement noise does not explain the null result. In the same summer, mice and nymphs had a negative association (elasticity -0.42, p = 0.002; with year fixed effects -0.46). This association did not occur for Amblyomma americanum nymphs or I. scapularis adults. Limitations: There are 7-11 years per site. Tick plots and mammal grids are at different places. Catch per trap night is not a density estimate. Weak effects (elasticity below 0.3) and strong effects at a single site are not excluded. We did not test the cause of the same-year association.

Ixodes scapularis · Lyme disease · Peromyscus · NEON · tick nymph density · host abundance · time lag · replication · permutation test · neonDivData