Using neutral landscape models to evaluate the umbrella species concept in an ecotone

Context

Steep declines in North American rangeland biodiversity have prompted researchers and managers to use umbrella species as a tool to manage diverse suites of co-occurring wildlife, but efficacy of this method has been variable. Evaluation of prairie and shrubland grouse as umbrellas is typically restricted to observed overlap between umbrella and background species, but this approach does not distinguish between overlap due to ubiquity or niche overlap.

Objectives

We demonstrate a novel application of neutral landscape models (NLMs) to test the effectiveness of greater sage-grouse (Centrocercus urophasianus) as an umbrella species for grassland songbirds at a grassland-sagebrush ecotone in northeastern Wyoming, USA.

Methods

We leveraged existing spatial data representing sage-grouse habitat in two distinct seasons (nesting and late brood-rearing) and density and distribution of eight grassland songbirds. We applied a permutation-based analysis using NLMs to determine whether overlap between background species and greater sage-grouse was greater than expected by chance.

Results

Three species (western meadowlark Sturnella neglecta, loggerhead shrike Lanius ludovicianus, and lark bunting Calamospiza melanocorys) had greater overlap than expected with at least one type of greater sage-grouse habitat, while western kingbirds (Tyrannus verticalis) indicated avoidance of all sage-grouse habitat assessed.

Conclusions

NLMs provided a more nuanced evaluation of the umbrella species concept than previously available and allowed us to differentiate between overlap due to ubiquity (e.g., vesper sparrow; Pooecetes gramineus) rather than overlap in habitat use. All grassland passerine species with greater than expected overlap with sage-grouse habitat either nest in sagebrush (loggerhead shrike) or often select nest locations underneath small shrubs (western meadowlark, lark bunting). These results indicate that nesting substrate is a potential niche axis to consider when evaluating the umbrella species concept, especially within sagebrush-grassland ecotones.