Iowa herptile detection histories and landcover metrics

Predictions of species occurrence allow land managers to focus
conservation efforts on locations where species are most likely to occur.
Such analyses are rare for herpetofauna compared to other taxa, despite
increasing evidence that herptile populations are declining because of
land cover change and habitat fragmentation. Our objective was to create
predictions of occupancy and colonization probabilities for 15 herptiles
of greatest conservation need in Iowa. From 2006–2014, we surveyed 295
properties throughout Iowa for herptile presence using timed
visual-encounter surveys, coverboards, and aquatic traps. Data were
analyzed using robust design occupancy modeling with landscape-level
covariates. Occupancy ranged from 0.01 (95% CI = -0.01, 0.03) for prairie
ringneck snake (Diadophis punctatus arnyi) to 0.90 (95% CI = 0.898, 0.904)
for northern leopard frog (Lithobates pipiens). Occupancy for most species
correlated to landscape features at the 1-km scale. General patterns of
species’ occupancy included the negative effects of agricultural features
and the positive effects of water features on turtles and frogs.
Colonization probabilities ranged from 0.007 (95% CI = 0.006, 0.008) for
spiny softshell turtle (Apalone spinifera) to 0.82 (95% CI = 0.62, 1.0)
for western fox snake (Pantherophis ramspotti). Colonization probabilities
for most species were best explained by the effects of water and grassland
landscape features. Predictive models had strong support (AUC >
0.70) for six out of 15 species (40%), including all three turtles
studied. Our results provide estimates of occupancy and colonization
probabilities and spatial predictions of occurrence for herptiles of
greatest conservation need across the state of Iowa.