Extreme ecological specialization in a rainforest mammal, the Bornean tufted ground squirrel,Rheithrosciurus macrotis

Abstract

The endemic Bornean tufted ground squirrel, Rheithrosciurus macrotis , has attracted great interest among biologists and the public recently. Nevertheless, we lack information on the most basic aspects of its biology. Here we present the first empirical data on the feeding ecology of tufted ground squirrels, and use data from 81 sympatric mammalian and avian vertebrates to place it within a broad comparative context. R. macrotis is a dedicated seed predator and shows much more extreme ecological specialization than any other vertebrate, feeding on a far smaller subset of available plant foods and demonstrating a greater reliance on a single plant species– Canarium decumanum– than any other vertebrate taxon. Our results suggest that R. macrotis plays an important, previously unknown role in the ecology of Bornean lowland forests, and highlight how much we have yet to learn about the fauna inhabiting some of the most diverse, and most severely threatened, ecosystems on the planet.

Stratified activity: Vertical partitioning of the diel cycle by rainforest mammals in Borneo

“…Horse‐tailed squirrels S. hippurus were most active in the early morning at both ground‐ and canopy‐level (Figure 3), which may be linked to competitor avoidance. This small‐bodied rodent specializes in consuming hard‐shelled nuts, and likely competes with the arboreal giant squirrel R. affinis and the predominantly terrestrial tufted ground squirrel Rheithrosciurus macrotis , both of which have similar diets (Marshall et al, 2020) but are larger and more strongly diurnal (Figure 2). As the latter two species mainly utilize different strata, they are unlikely to directly compete with each other, whereas the semi‐arboreal horse‐tailed squirrel could conceivably compete with both and, due to its smaller size, be at a disadvantage.…”

“…Horse-tailed squirrels S. hippurus were most active in the early morning at both groundand canopy-level (Figure 3), which may be linked to competitor avoidance. This small-bodied rodent specializes in consuming hardshelled nuts, and likely competes with the arboreal giant squirrel R. affinis and the predominantly terrestrial tufted ground squirrel Rheithrosciurus macrotis, both of which have similar diets (Marshall et al, 2020) but are larger and more strongly diurnal (Figure 2).…”