Let's stay together? Intrinsic and extrinsic factors involved in pair bond dissolution in a recolonizing wolf population

Abstract

Summary For socially monogamous species, breeder bond dissolution has important consequences for population dynamics, but the extent to which extrinsic or intrinsic population factors causes pair dissolution remain poorly understood, especially among carnivores.Using an extensive life‐history data set, a survival analysis and competing risks framework, we examined the fate of 153 different wolf (Canis lupus) pairs in the recolonizing Scandinavian wolf population, during 14 winters of snow tracking and DNA monitoring.Wolf pair dissolution was generally linked to a mortality event and was strongly affected by extrinsic (i.e. anthropogenic) causes. No divorce was observed, and among the pair dissolution where causes have been identified, death of one or both wolves was always involved. Median time from pair formation to pair dissolution was three consecutive winters (i.e. approximately 2 years). Pair dissolution was mostly human‐related, primarily caused by legal control actions (36·7%), verified poaching (9·2%) and traffic‐related causes (2·1%). Intrinsic factors, such as disease and age, accounted for only 7·7% of pair dissolutions. The remaining 44·3% of dissolution events were from unknown causes, but we argue that a large portion could be explained by an additional source of human‐caused mortality, cryptic poaching.Extrinsic population factors, such as variables describing the geographical location of the pair, had a stronger effect on risk of pair dissolution compared to anthropogenic landscape characteristics. Population intrinsic factors, such as the inbreeding coefficient of the male pair member, had a negative effect on pair bond duration. The mechanism behind this result remains unknown, but might be explained by lower survival of inbred males or more complex inbreeding effects mediated by behaviour.Our study provides quantitative estimates of breeder bond duration in a social carnivore and highlights the effect of extrinsic (i.e. anthropogenic) and intrinsic factors (i.e. inbreeding) involved in wolf pair bond duration. Unlike the effects of intrinsic and extrinsic factors that are commonly reported on individual survival or population growth, here we provide quantitative estimates of their potential effect on the social unit of the population, the wolf pair.

Mating patterns in an inbred Arctic carnivore

“…Hence, the temporal changes in social structure may be a consequence of inbreeding avoidance that occurs with a one-year time lag in response to increased number of relatives. Connected to this, Milleret et al (2017) recorded that inbreeding coefficient contributed to a decrease in pair duration (i.e. lowered pair bond stability) in the Scandinavian grey wolf (Canis lupus).…”

“…For instance, in species with long-term pair bonds, random mating can be prevented by existence of already established pair bonds. Furthermore, high levels of inbreeding can influence the duration of social structures such as pair bonds (Milleret et al 2017).…”

“…Milleret et al 2017). The Scandinavian Arctic fox (Vulpes lagopus) was an abundant tundra species until the late 19th century when fur harvesting almost drove the population to extinction ).…”

Couch potatoes do better: Delayed dispersal and territory size affect the duration of territory occupancy in a monogamous mammal

“…We have evidence that individuals of unknown fate were forced out by an intruding individual of the same sex that took over the territory (Mayer et al., ). Alternatively, human‐caused mortality might be more common as observed, due to unreported cases of hunting or poaching, for example, shown in wolves ( Canis lupus ) (Liberg et al., ; Milleret et al., ). After the loss of its territory, an individual could have died, it could have become a floater, or it could have managed to establish in a new territory with a new mate.…”

The evolution of intraspecific variation in social organization

“…For example, in pair‐living species, if one of the two breeders dies, the other individual automatically becomes solitary living (Figure ). The death of a single individual in pair‐living Scandinavian wolves often results in temporarily solitary individuals (Milleret et al., ). Individuals might then respond adaptively to this imposed change, such as by re‐pairing as reported in beavers ( Castor fiber ; Mayer, Künzel, Zedrosser, & Rosell, ).…”