Niche partitioning between two sympatric genetically distinct cave bears (Ursus spelaeus and Ursus ingressus) and brown bear (Ursus arctos) from Austria: Isotopic evidence from fossil bones

Hervé Bocherrens
Mathias Stiller
Keith A. Hobson
Marrtina Pacher
Gernot Rabeder
James A. Burns
Thomas Tütken
Michael Hofreiter

Abstract

In the Austrian caves of Gamssulzen and Ramesch, two genetically distinct cave bears, Ursus ingressus and Ursus spelaeus eremus, apparently lived side by side for 15,000 years, together with brown bears Ursus arctos. The possible ecological partitioning of these three types of bears was investigated using multi-isotopic tracking of organic (δ13Ccoll, δ15Ncoll) and inorganic (δ13Ccarb, δ18Ocarb, δ18OPO4) fractions of bone. The cave bears from Ramesch, Ursus spelaeus eremus, were ecologically distinct from the cave bears from Gamssulzen, Ursus ingressus, both being ecologically distinct from brown bears from Ramesch, Ursus arctos. Both cave bear types were purely herbivorous but likely consumed different plant types and/or plants from different habitats, while brown bears included some animal proteins in their diet. Bone apatite δ18O values strongly suggest that both types of cave bears used isotopically distinct water sources, indicating that they may not have occupied the same landscape, either separated in space or in time due to climatic shifts. Therefore, the influence of environmental conditions strongly constrained the genetic structure of these bears.