A 1.10 taxon capture ratio permits both warmth-slope signs for empirical moth dominance in four UK samples in 1992-2015

We give exact bounds for the largest taxon share when relative capture rates have a fixed ratio limit. We apply the bounds to empirical catches from 685 trap-months in England and Scotland in 1992-2003 and 2004-2015. All four catch warmth slopes are negative, and all four adjusted confidence intervals include zero. A within-month maximum-to-minimum taxon capture ratio of 1.10 permits both slope signs in every sample. Ratios that first permit zero range from 1.004 to 1.041. Explicit capture corrections attain the bounds. Independent linear programs check the formulas. These are fixed-catch sensitivity ranges, not confidence regions for true community composition. Capture rates can vary freely between months. Finite catches, missing taxa, selected samples and coarse weather limit biological inference. Code, source hashes, aggregate results and a figure are included. Record-level data remain external.