Effects of food limitation on social grouping and foraging in a fission-fusion species.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Social groups form when the benefits of group association outweigh the costs. In fission-fusion societies, groups change in response to current local conditions rather than being fixed as seen in stable groups. This flexibility allows individuals to counterbalance the negative consequences of grouping by splitting into small groups but then aggregate again when it is beneficial. The composition may also be in constant flux, resulting in changing group composition and, sometimes, sexual segregation. Furthermore, individuals form associations within groups, such that social costs and benefits may be experiences not only in relationship to group size or composition but by the identity of a close neighbour, which could be a better representation of social effects within a group. Harassment by males, usually related to mating, is a one common behaviour that had a negative influence on individuals and causes changes to behaviour, which could be altered by group composition or near neighbour.
Male harassment occurs in giraffe due to their polygynous and asynchronous breeding, and they exhibit fission-fusion groups, so that they can respond to costs and benefits of grouping. They also show a degree of sexual segregation throughout the year. Furthermore, due to their large body size, they require a large amount of food, and may be particularly sensitive to food limitation. In addition, giraffe are currently undergoing what has been termed a ‘silent extinction’, with numbers from falling 155 000 to 97 000 over 30 years. Up until recently there has been little research conducted on giraffe, therefore, we need a better understanding of their ecology and behaviour to be able to stem the loss in numbers and develop more effective management plans for the conservation of the species. It is important to know more about environmental variability, especially with common events like drought, so we can improve management responses to such events.
In this thesis I tested if giraffe females change their foraging behaviour in relation to their immediate social group and their nearest neighbours. I found that female giraffe change their foraging efficiency if a large male is present, therefore there is a foraging cost to being near large males. My research shows that giraffe are influenced by their close neighbours and this may influence their behaviour more than group composition as a whole. I found that seasonal variation alters these behavioural patterns. I also test if foraging behaviour is changed with food availability. After periods of drought there is less food available and female giraffe become more tolerant to the presence of male close neighbours as there are fewer foraging options. I test if there is sexual segregation in giraffe populations and found the degree of segregation changes with environmental and food availably differences. I tested a range of sexual segregation hypotheses and found that sexual segregation is caused by a combination of different factors including social influences and by physical differences caused by distinct sexual dimorphism in giraffe.
Food limitation effects social interactions in giraffe populations and knowledge of environmental conditions that can alter food availability is important for conservation efforts for this species. By looking at close neighbour effects in a fission-fusion species we can better understand the costs and benefits of grouping and how these groups are formed and maintained.