Bears and Other
Carnivores

There has been a large-scale shift in ecology from single-species studies to a focus on holistically understanding multispecies interactions. Bears move through landscapes that are heavily dominated by humans and interact with other large carnivores in the ecosystem, all of which can affect their behavior, including predation patterns and subsequent prey population trends (1, 2). Bears are generally not very effective predators of adult ungulates, such as moose, although they do occasionally prey on them. However, bears are incredible efficient scavengers. For example, they will eat the remains of animals that died during winter, remains of hunter-killed ungulates, and will also steal kills from subordinate carnivores (3). Thus, bears may compete with other predators in two main ways: directly (e.g., by stealing kills or excluding them from a resource, also known as interference competition) and indirectly (by competing for shared food sources, also known as exploitation competition) (4). The majority of research on interactions between bears and other predators has largely focused on wolves. However, we also put into context interactions with the other large carnivores on the Scandinavian Peninsula: lynx and wolverine.

Wolves

Brown bears and wolves are both apex predators in Scandinavia that compete directly and indirectly for food (4). Moose are the primary prey for both bears and wolves in Scandinavia (5-7). Bears primarily prey on newborn moose during the weeks surrounding calving season and rarely kill adults (5, 8), while wolves prey on both adults and young, but select for young of the majority of the year (6, 7). For example, newborn moose comprise the great majority (~90%) of wolf diet during the moose calving season and wolves continue to select for young of the year as they age through the season, right up until calving season when the pattern begins anew (6, 7).

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In Scandinavia, it appears that two types of competition occur between wolves and bears. Interference competition occurs when bears first emerge from their dens and wolves are hunting larger calves from the previous year (4). During this time, bears can scavenge from wolf kills and potentially limit wolf access to kills, although to what degree this occurs remains unknown (4). Exploitation competition occurs during the calving season when wolves and bears share the same prey (4). During this time, bears and wolves prey on newborn calves, successively depleting the supply of shared food (4). The ultimate result of this is that competition from bears decreases wolf kill rates, which might result in fitness consequences for the wolf population (3). On the other hand, bears may benefit from wolves as they provide them food subsidies (9). Theft of wolf-killed prey often happens during spring when wolves are preying on larger bodied prey (e.g., last year’s calves and adults). Bears visit at least 50% of the wolf kills in central Sweden, yet the visitation rate is lower during spring-early summer when both bears and wolves are preying on neonate moose that provide little left for scavenging (10).

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Competition might be such that it slowed down the expansion of wolves into core bear habitat between 1990 and 2012 in Scandinavia (11), i.e., the probability of wolf pack establishment was negatively related to bear density (11, 12). Where bears and wolf populations do overlap, the two species segregate more at a fine scale then would be expected by chance, meaning, they seem to avoid each other (13). Compared to bears, wolves selected more for young forest, rugged terrain, and moose occurrence, although both wolves and bears avoid humans, especially during daytime (13).

Lynx

Lynx in southern and central Scandinavia primarily prey on roe deer (14-16), and have little diet overlap with bears, thus little potential for exploitation competition. However, lynx in other areas depend mainly on reindeer, and partly sheep, as a prey (17, 18). Thus the probability of bears and lynx interacting is greater in areas where they share habitat (19) as well as prey. Lynx are not avid scavengers; thus, they likely do not show up at bear killed prey very often. However, bears may scavenge lynx kills, as documented elsewhere. Research in other systems has shown that brown bears can steal up to 50% of lynx kills in areas where bear densities are high (20). Although it likely occurs to some extent, this does not appear to be a common phenomenon in Scandinavia. For example, a lynx study conducted in Northern Sweden, in and around Sarek, found that only 5% (5 of 95) lynx-killed reindeer were visited by brown bears, even though bears were relatively common in the area (21).

Wolverine

There is not much known about direct interactions between wolverines and bears, but they are both efficient scavengers and attracted to similar resources. Wolverines have been observed feeding at bear kills in Scandinavia, albeit rarely, which means there is potential for exploitation competition between the two in the form of depleted carrion (22). It is also possible that bears might scavenge from wolverine kills, although this remains unknown. Black bears have been observed killing wolverines in North America, suggesting the potential for direct interference competition between bears species and wolverine (23). A study from south-eastern Norway, showed that wolverine tend to use more high-elevation open rugged terrain than bears, who more commonly use rugged forested terrain at lower elevations (19). This suggested that bears and wolverine occupied slightly different niches and had less chance for direct and indirect interactions (19). However, as the wolverines have increased in areas of lowland forest habitat since then (24), there is an increasing potential for competition between wolverines and bears in accessing carcasses to scavenge in areas where they co-occur.