Data from: Localized hotspots drive continental geography of abnormal amphibians on U.S. wildlife refuges

Amphibians with missing, misshapen, and extra limbs have garnered public
and scientific attention for two decades, yet the extent of the phenomenon
remains poorly understood. Despite progress in identifying the causes of
abnormalities in some regions, a lack of knowledge about their broader
spatial distribution and temporal dynamics has hindered efforts to
understand their implications for amphibian population declines and
environmental quality. To address this data gap, we conducted a
nationwide, 10-year assessment of 62,947 amphibians on U.S. National
Wildlife Refuges. Analysis of a core dataset of 48,081 individuals
revealed that consistent with expected background frequencies, an average
of 2% were abnormal, but abnormalities exhibited marked spatial variation
with a maximum prevalence of 40%. Variance partitioning analysis
demonstrated that factors associated with space (rather than species or
year sampled) captured 97% of the variation in abnormalities, and the
amount of partitioned variance decreased with increasing spatial scale
(from site to refuge to region). Consistent with this, abnormalities
occurred in local to regional hotspots, clustering at scales of tens to
hundreds of kilometers. We detected such hotspot clusters of
high-abnormality sites in the Mississippi River Valley, California, and
Alaska. Abnormality frequency was more variable within than outside of
hotspot clusters. This is consistent with dynamic phenomena such as
disturbance or natural enemies (pathogens or predators), whereas
similarity of abnormality frequencies at scales of tens to hundreds of
kilometers suggests involvement of factors that are spatially consistent
at a regional scale. Our characterization of the spatial and temporal
variation inherent in continent-wide amphibian abnormalities demonstrates
the disproportionate contribution of local factors in predicting hotspots,
and the episodic nature of their occurrence.