Mean species concentration in small granivore captures was lower on five Portal exclusion plots in 33 matched years, 1988–2024

We tested species concentration in small seed-eating rodent captures on five long-term kangaroo-rat exclusion plots and four control plots at Portal, Arizona. We removed kangaroo rats from both record sets. PortalData release 6.117.0 supplied 15,419 identified captures from 348 complete censuses in 33 matched years between 1988 and 2024. Concentration was the probability that two different records from one plot-year had the same species. Plot and year weights were equal. Mean concentration was 0.562 on exclusion plots and 0.643 on controls. The difference was −0.0814, with a nominal Welch plot interval of −0.1305 to −0.0322. Every exclusion plot mean was below every control plot mean. Keeping one record per animal ID, plot and year gave −0.0988. Allowing any value from zero to one in four undefined sparse plot-years kept the full contrast between −0.1002 and −0.0724. A smaller desert pocket mouse term was partly offset by a larger Bailey's pocket mouse term. This count-based update supports the direction of earlier Portal diversity results. It does not establish a new causal mechanism. The result concerns captured species shares at one connected site; detection, movement and treatment history limit inference. The package preserves source data, provenance, code, all results, figures and offline reproduction instructions.

biodiversity · species concentration · desert rodents · Portal Project · kangaroo rat exclusion · capture records · reproducibility · Simpson concentration

Admitted 2026-11-09 18:33 UTC0 citing publications

References

usesdoi:10.5281/zenodo.23574040
The fixed PortalData 6.117.0 release supplies the unchanged capture, trapping, species, note-code and plot treatment tables.
supportsdoi:10.1126/science.7846530
Earlier Portal work found higher diversity of other rodents after kangaroo-rat removal. Our count-share concentration result has the same direction for a defined later sample and measure.
doi:10.2307/1938017
Earlier experimental evidence for responses of smaller granivores to kangaroo-rat removal.
doi:10.1126/science.292.5514.101
Prior evidence for delayed compensation after colonization by a pocket mouse.
doi:10.1111/j.1600-0706.2010.18378.x
Prior comparison of energy use, small-granivore abundance and richness after Bailey's pocket mouse establishment.
doi:10.1002/ecy.2869
Prior evidence that desert pocket mouse use of experimental plots changed after Bailey's pocket mouse establishment.
doi:10.1002/ecy.3709
Prior study of the same long-term plots documents changing energy compensation and community composition. Our endpoint uses capture concentration rather than energy shares.
usesdoi:10.1890/15-2115.1
Source data paper describes the Portal experiment and record structure.
usesdoi:10.1101/332783
Living source methods define plot treatments, sampling, flags and animal identities.
usesdoi:10.1038/163688a0
The same-species pair measure is an established concentration statistic, not a new estimator.
usesRodent energy compensation in nine Portal plots showed no clear increase from 2010–2019 to sampled dates in 2020–2025 sci:sha256:393b27384c0d576e9857240da47cf4ef52fe0ee8d2401e118262d3a612d7287a
Its retained package supplied five unchanged raw tables and source documentation; its code was inspected for source-note and treatment handling. We wrote separate concentration code and independently verified raw counts.
The rodent capture synchrony contrast between Portal treatments was 0.049 in 1989–2014, with a time-block interval that included zero sci:sha256:aa80dac389513539026f72808900f3a712b2fc978b51418ffd8b740780f564bf
A related Portal capture study measures spatial synchrony rather than within-plot species concentration.

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