Public Defence: Rick Willem Heeres

Rick Willem Heeres is defending his dissertation for the degree philosophiae doctor (PhD) at the University of South-Eastern Norway.

He has completed the doctoral programme in ecology at the Faculty of Technology, Natural Sciences and Maritime Sciences.

You are invited to follow the trial lecture and the public defence.

Summery

Generally, species are classified as either social or non-social species. The classical assumption is that non-social species are solitary; spend their lives alone and only interact with other individuals for mating purposes. However, no species can be «non- or a-social» as they need to know their neighbours, build up relationships, and interact to reproduce.

Brown bears (Ursus arctos), a presumed «non-social» solitary carnivore, have a more nuanced and complex social system and interactions between individuals are not as scarce as previously thought. We found that individuals of either sex, are interacting with each other throughout the year and far more often than expected.

Furthermore, during the project we started to understand the importance of habitat and landscape features on brown bear reproductive behaviour. We have called it the «landscape of love», where pairs of bears (female and male) seem to primarily meet on clearcuts and young growth forest patches prior to mating events.

Sexually selected infanticide, the killing of unrelated offspring by males, is common in the Scandinavian brown bear population. From previous studies we know that females with offspring adapt their habitat use, but this time we looked closer at the fine-scale movement behaviour of females with offspring of all ages and found they are successfully avoiding males throughout the mating season.

However, female brown bears care for their offspring for about 2 to 3 years, and this also influences the movement behaviour of females prior and during the mating season. The mating season is also the period that families separate, and some females seem to make the «choice» to abandon their current offspring and focus on mating to have offspring the following year.

Lastly, human pressures (such as harvest) appear to influence the mating behaviour of males. We found that male bears potentially have three different tactics to mate successfully, namely: they either search for many mates throughout the mating season, actively guard or follow a female, and lastly sequester a female by limiting the females’ movements to reduce competition with other males. Besides that, the sequestering tactic is primarily used by young but relatively large males, however this tactic is not used when the local harvest is high. We also see that subdominant males (small and young), which normally have a low change of reproducing, gain mating opportunities when local harvest increases. Once again showing that human pressure changes social dynamics, reproductive behaviour, and is a potential evolutionary selective pressure.

We took the opportunity during this project to dive into many aspects that influence the social life of brown bears in south-central Sweden using various data collected over the last two decades (2003-2022) resulting in five manuscripts. We were able to use an extensive database including information such as GPS locations, individual characteristics, genetics, reproduction, and local harvest. This project provides new insights regarding the social life of solitary species. Also, it raises new questions and knowledge gaps about social complexity, mating systems, habitat use, and the role of human pressure in shaping animal behaviour and will hopefully be the foundation for many follow-up studies.