Territorial Behavior in Pinnipeds
Mate frequency and LRF of successfully territorial males:
The peak frequency of interspecific aggression occurs during mating seasons, or, in other words, when territories are being and have been established. Aggression in male pinnipeds towards other males allows for the establishment of dominance and for more successful acquisition of territories. This in turn results in higher chance of successful reproduction. During a breeding season, a majority of the females are impregnated by a small number of males. Besides males that spontaneously leave their territories or claim abandoned territories within the CBA, males that exhibit the most territorial behavior are the most successful at defending territories against invasive males and are able to mate with a higher number of females which results in a greatly increased lifetime reproductive fitness (Bartholomew, 1970).
Zalophus californianus fighting over valuable pier space. (Image courtesy of Ingrid Taylar)
Male aggression and territoriality is heavily dependent on female breeding behaviors since females typically spend most of their time within the CBA, and also adjust their behaviors based on and due to male limitations in their ability to breed, reproduce, and maintain a territory. For females, polygyny and the establishment of male territories focused within one area results in females not having to compete for the males’ sexual attention and resources for protection. If a male that a female previously bore a pup to is suddenly preoccupied with other females, the female can migrate a short distance to a neighboring territory to mate or seek other resources from a different male (Bartholomew, 1970).
Temperature has an effect on the ability for successful reproduction, with dominant males residing within the CBA running the risk of their testes becoming too warm to produce functional sperm in addition to already low sperm counts due to high female:male sex ratios. Northern elephant seal females adjust to this risk by rejecting mounts at the time within reproductive cycle in which they are most likely to become pregnant, therefore any subordinate males will have a higher likelihood of being interrupted by a more dominant male if attempting to mate with an aggressive female. Then towards the end of that period of high fertility, the female is more accepting of mounts, resulting in subordinate males -- who live on the peripheries near the water, and do not have trouble with low sperm count due to overheating -- being able to complete copulation with less chance of interruption from dominant males (Renouf, 2012).
Advantages and Disadvantages of Aquatic vs. Terrestrial Breeding:
Terrestrial mating makes it easier for the males to secure a mate, as it is more likely for there to be available females in the proximity of the male’s territory. On the other hand, there are also many more males, leading to much more intersexual competition amongst the males as they fight over territory and mates. That being said, this increased competition provides a benefit for the females in that they get a greater degree of mate choice as there is more opportunity for direct comparison.
Aquatic mating gives more room for each male to establish a territory, but it must be held in different ways. Additionally, it is easier for females to escape when in the water due to the simple fact that pinnipeds are very heavily specialized in favor aquatic locomotion as opposed to terrestrial locomotion.