Date of this Version
J Insect Conserv (2017) 21:183–205, DOI 10.1007/s10841-017-9968-0.
Speyeria idalia populations have declined as much as 95 percent over the last three decades. Here we critically evaluate prairie habitat components along the Platte River in central Nebraska that S. idalia populations require in an effort to better inform conservation efforts. We utilized S. idalia count data from biological monitoring transects where vegetation, soils, land management, and flooding frequency data were also collected to describe the habitat constituents associated with S. idalia presence. We utilize comparative statistics, Pearson’s correlation analysis, and random forest analysis to model S. idalia habitat on land owned and managed by a small conservation NGO. Our findings suggest that S. idalia occupies specific habitat niches with a preference for well-drained soils (Inavale series) dominated by facultative upland plants, most prominently Andropogon gerardii. S. idalia is positively associated with large connected tracts of relict prairie containing Viola sororia and very moderate management regimes that remove shrubby cover (negatively associated) and promote forb cover (positively associated), while providing ample recovery time on burned and grazed patches for litter development (positively associated). Random forest analysis describes the presence of V. sororia, percent forb cover, and habitat isolation as the top three habitat variables of importance in predicting the presence/absence of S. idalia. Our finding that habitat isolation is a major predictor of S. idalia absence suggests many populations may be both spatially and genetically isolated. S. idalia’s future demands the preservation of tallgrass prairie fragments under management regimes that promote healthy populations and habitat connectivity.
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