Range fragmentation in the spectacled bear Tremarctos ornatus in the northern Andes

Abstract

This paper addresses the conservation status of the spectacled bear Tremarctos ornatus in the northern Andes (Venezuela, Colombia and Ecuador) by analysing the degree of range fragmentation and estimating habitat availability. From satellite images we constructed maps of remnant habitat blocks, consisting of Andean forest and páramo (high elevation shrublands and grassland) ecosystems. This information was overlain with a road map to determine potential isolation of populations, and a human accessibility model was used to estimate the core area of each block. This analysis revealed that the species' range is fragmented by landscape transformation and roads into 113 blocks >100 km2, representing 42% of the original extent of the bear's distribution. Forty percent of the blocks are <500 km2, and only nine are >5,000 km2. However, taking into account only core area, 56% of the blocks are <500 km2 and only six are >5,000 km2. In addition, many blocks have internal patches of colonization, further reducing habitat quality. This effect is more severe in smaller fragments, where internal disturbances constitute a high proportion of the block area. We used a high population density estimate of 0.25, a medium density of 0.11 and a low density of 0.04 bears per km2 to estimate population sizes. Twenty-nine populations are likely to have >500 individuals with the high estimate, but only nine with the medium and one with the low estimate (largest estimated population was 9,048 bears). These estimates are much lower if only the core area of blocks is used. Hunting has been identified as a major threat for many bear populations. Our analyses indicate that a regional conservation strategy for spectacled bear should focus on maintaining or increasing habitat availability in larger blocks, and reducing human-induced mortality across the region.