Small granivores replaced 29% of the control kangaroo-rat energy index in 44 Portal surveys from 2021 to 2025

We tested whether low energy replacement after kangaroo-rat exclusion continued at Portal, Arizona. We used PortalData release 6.117.0 and four control plots and five exclosure plots with fixed rodent treatments. We kept surveys with all nine plots adequately sampled. For each captured granivore, we calculated an index of 5.69 times body mass to the power 0.75. Replacement was the added small-granivore index on exclosures, relative to controls, divided by the control kangaroo-rat index. In 44 surveys from June 2021 to December 2025, this ratio of sums was 28.9%, with a 95% year bootstrap interval of 18.1% to 40.4%. It was 49.3% in July 1997 to January 2010. The recent value was lower by 20.4 percentage points, with an interval of 6.2 to 35.7 points. The estimated increase from February 2010 to January 2020 was uncertain: 7.6 points, with an interval from -4.5 to +20.4 points. Bailey's pocket mouse supplied 23.2 of the recent 28.9 replacement points. The main ordering held with fixed species masses, measured masses, quality-control surveys, two-year blocks, and each plot omitted in turn. Kangaroo rats caught on exclosures supplied 30.8% of the exclosure index in 2025, so total exclosure energy alone can overstate the small-granivore response. This extends a 2022 study with later observations. The index measures captures under a mass-scaling assumption. It does not measure energy flux directly or identify an environmental cause. The package contains exact inputs, provenance, code, figures, tables, and repeat checks.

biodiversity · species loss · energy replacement · granivores · Portal Project · long-term experiment · reproducible analysis