Final answer:
Male desertion in St. Peter's fish is influenced by offspring survival chances. Female sandpipers fight for territories, indicating a polyandrous mating system, while male lion competition is exemplary of a polygynous system. Both cases involve competition for limited resources, an element of natural selection.
Step-by-step explanation:
The male desertion in mouth-brooding St. Peter's fish is most likely influenced by offspring survival chances. This is because in species where males exhibit such parental investment, the decision to stay with the offspring is typically driven by the likelihood of those offspring surviving to adulthood. If the chances are high, males may commit to parental care, which will ensure greater success of those offspring, as opposed to seeking additional mating opportunities.
In the context of female spotted sandpipers, their aggressive competition for resource-rich territories indicates a polyandrous mating system. This is because in polyandrous systems, females often compete with each other to attract multiple males, ensuring a greater likelihood of successful rearing of their offspring due to an abundance of resources within their controlled territories.
Male lions, showcasing intense competition for mating rights, is consistent with a polygynous mating system, as typically one male ends up having exclusive mating rights with several females within his territory. Both scenarios exemplify the competition for limited resources, a fundamental concept of natural selection along with the variation of traits among individuals and the fact that more offspring are produced than can survive.