Social Organization and Dominance Interactions
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| Food and Predation |
| Habitat and Foraging |
| Social Spacing |
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Permission by C. Allen Morgan
Social organization
Kangaroo rats of all species exhibit little to no social organization and kangaroo rats are generally solitary animals. The burrows of the kangaroo rat are spaced to allow for adequate food sources within reasonable traveling distances for each rat. Spacing of mounds will also vary according to the abundance of food (Howard 1994).Sometimes feeding situations can cause kangaroo rats to cluster in the same area. If kangaroo rats are even in groups they are in aggregations or colonies (Howard 1994). There does not seem to be any incidences of helpers, kin selection or kin altruism.
Why Solitary?
The benefits to living alone for a kangaroo rat are that they do not have the increased conspicuousness of a group to predators. Kangaroo rats use their locomotive speed and nocturnal lifestyle to avoid predators so they do not need group defense for survival. They also have less competition to food since they forage alone. Since seeds do not take a group to gather, or hunt like predators of larger prey, it is more beneficial for kangaroo rats to forage alone so that they have sole access to any patch they find. Finally there is less competition for mates because they do not have a social system and they avoid possible cuckoldry. Cannibalism and spread of disease are also avoided by solitary living.
Dominance
Dominance interactions are important to the social system of kangaroo rats. Since kangaroo rats are solitary animals and males must compete for mating opportunity with females, the ability to gain dominance can determine a kangaroo rats reproductive success (Newmark and Jenkins, 2000). When kangaroo rats fight, they do so by leaping in the air and striking their competitor with their strong hind feet (Vorhies 1922). Kangaroo rats will only use biting as a secondary means of combat (Vorhies 1922).
While male kangaroo rats are constantly more aggressive and therefore more dominant than female kangaroo rats kangaroo rats in general have a high degree of aggressiveness in comparison to other rodents which may be an adaptation to fit this need for dominance. Female kangaroo rats tolerate each other more upon encounter than male kangaroo rats and engage in nonagonistic encounters more frequently than males do. This may be largely due to the fact that the female home ranges in kangaroo rats overlap less than male home ranges so agonistic encounters are not as necessary (Newmark and Jenkins, 2000).
Newmark and Jenkins conducted a study to determine if kangaroo rats have a linear dominance hierarchy. Many studies of kangaroo rats have shown that there are clear dominance relationships between kangaroo rats, but the degree of permanency was unknown (Newmark and Jenkins, 2000). In their study Newmark and Jenkins found that that there is a distinct linear hierarchy among male kangaroo rats. However, the researchers were unable to determine if the females had a linear dominance hierarchy . Their findings also showed that the winner of agonistic encounters were not necessarily the larger kangaroo rats or the kangaroo rats that were able to store more seeds or larderhoard more (Newmark and Jenkins, 2000). They believe that the variable that are most likely to affect dominance rank in male kangaroo rats was their activity level (or percentage of body mass lost during the course of dominance trials). The kangaroo rats that invest more in the agonistic encounters are those that gain dominance. However, I believe that since the kangaroo rats live solitarily we cannot define them as a dominance hierarchy because dominance interactions and rank are not continually reinforced, they only occur when an encounter occurs.
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