Ultimate and proximate mechanisms underlying the occurrence of bears close to human settlements: review and management implications

Abstract

ABSTRACT1. Large carnivores (LCs), such as bears (Ursidae), are commonly believed to occur near human settlements because they have a learned tolerance of humans (human habituation) and because they associate humans with accessible highquality foods (food conditioning). Young bears and females with cubs are often overrepresented among 'problem' bears near settlements. 2. We review the mechanisms underlying the occurrence of brown and black bears (Ursus arctos, Ursus americanus, Ursus thibetanus) near settlements, and consider four hypotheses designed to separate ultimate and proximate mechanisms. 3. Increased occurrence of bears near people or settlements can be explained by (i) the human habituation hypothesis; increased use of human-derived foods can be explained by (ii) the food-conditioning hypothesis. However, both mechanisms are proximate, because they can only apply if bears have earlier experience of people and/or human-derived food. 4. A lack of human experience can explain the increased occurrence of younger bears near people or settlements: (iii) the naivety hypothesis. This is a proximate mechanism, because movements of naive bears are typically triggered by aggression and/or competition among conspecifics. 5. We conclude that the disproportionate occurrence of bears in certain sex, age and reproductive classes near people or settlements can only be explained by predation avoidance and/or interference competition, i.e. by (iv) the despotic distribution hypothesis. Therefore, a despotic distribution must be an ultimate mechanism causing the proximate mechanisms of habituation or conditioning. Thus, bears using settlements as predation refuges should not be considered 'unnatural' , but rather as exhibiting an adaptive behaviour, because of the despotic distribution among conspecifics. 6. Management of LCs includes attractant management, to counteract food conditioning, but failure to consider despotic behaviour among conspecifics may lead to treating only the symptom, e.g. habituation or conditioning. The ultimate cause of attraction to specific settlements may be identified by considering the type of bear involved; the occurrence of large solitary bears near settlements suggests attractive habitat or food shortage in remote areas, whereas subadults and females with cubs suggest lower-quality habitat.

Dispersal of male bears into peripheral habitats inferred from mtDNA haplotypes

“…In particular, the opportunistic nature of both species can cause them to take advantage of anthropogenic foods, thus altering their tendencies to avoid people (Baker and Timm 1998;Timm and Baker 2007;Beckmann and Lackey 2008). Wild animals living near the borders between wildlands and developed areas have frequent contact with humans, vehicles, and settlements, and this increases their chances of learning from these interactive experiences in both rural and urban areas (Naughton- Treves et al 1998;Mazur and Seher 2008;Donaldson et al 2012;Elfström et al 2014). The inadvertent enticing of animals closer to human settlements by providing human-derived resources is likely to be the first step toward these animals becoming habituated to human presence (Bateman and Fleming 2012).…”

“…These landscapes are called "attractive sinks" or "evolutionary traps" (Delibes et al 2001;Schlaepfer et al 2002). The spatial distribution of individuals in a population is an ideal despotic distribution when there is a social hierarchy in the population, whereby dominant individuals are predicted to exploit habitats of high quality (in terms of food or security, or both) more often than do their subordinate conspecifics (Fretwell and Lucas 1969;Elfström et al 2014). In cases where habitats in or near urban areas became attractive sinks, spatial redistribution occurs and the socially dominant individuals select these habitats on the basis of this despotic distribution.…”

“…The increased prevalence of American black bears in Nevada has been viewed as an overall increase in population size by local government and by the public, without recognition of the possibility that nearby wildlands have been partially or mostly depopulated (Beckmann and Berger 2003a). In the case of brown bears, these two different possibilities could be distinguished by determining whether the increased sightings are of subordinate subadult males or females with dependent young or of dominant adult males (Sato et al 2011;Elfström et al 2014;Sato et al 2014). A change in the landscape in and near an urban area to an attractive sink for carnivores would lead to an undesirable increase in HWCs, including the potential risk of attacks on humans and of increased mortality for carnivores.…”

“…1) can be explained by the population increase in the western Ishikari population (Hokkaido 2015) and a subsequent expansion in distribution (Japan Bear Network 2014) through colonization process by dispersing individuals (Elfström et al 2014). Invasions of the city center by brown bears are still rare and can be considered as temporary incursions by socially subordinate sex-or age-class individuals (i.e., subadult males and females with dependent young), not because of their attachment to resources or conditions in the city center but simply because of occasional straying (Sapporo City, unpublished data).…”

“…In cases where the numbers of problem animals in urban areas increase along with population expansion as a result of the redistribution of socially subordinate animals in an ideal despotic distribution manner (as referred to by Elfström et al 2014), lethal control would be effective in preventing settling of the subordinate animals in the urban areas. In some cases, however, lethal control can increase conflict.…”