The traits and characteristics in a life table that will affect an organism's ability to survive and reproduce determine that organism's life history. These traits result from natural selection to optimize fitness, which requires trade-offs between reproduction and survival. We'll examine some different reproductive strategies, starting with semelparity and iteroparity.

Semelparity, as demonstrated by salmon, involves having many offspring once, right before they die. In the strategy of semelparity, the reproductive effort the organism puts forth maximizes the offspring it produces and minimizes the offspring foregone due to other costs. On the other hand, iteroparity involves a reproductive strategy where an organism has offspring multiple times throughout its life, similar to humans. This strategy also focuses on maximizing the number of offspring while minimizing costs to achieve optimal reproductive effort.

Another perspective on reproductive strategies is K-selection and r-selection theories, which consider the trade-off between the quantity and quality of offspring. With K-selection, prevalent in humans and whales, the organism invests heavily in fewer offspring, increasing each offspring's probability of surviving to adulthood. K-selected species often live close to the carrying capacity of their environments in more stable conditions. These organisms require extensive parental care, usually have a longer maturation period, are generally larger, and tend to have longer lifespans.

In contrast, r-selection, exemplified by mice, emphasizes producing many offspring with a low probability of surviving to adulthood. These species invest less in each individual offspring and thrive in less stable environments where the ability to reproduce quickly is crucial. Mice, for instance, can reproduce several times a year, showing high fecundity and a short generation time. r-selected species tend to be smaller, have shorter lifespans, and the offspring mature quickly, reaching adulthood to reproduce in a short time.

Understanding these reproductive strategies helps us grasp the survival tactics in varied ecological niches. For example, humans are K-selected, focusing on quality over quantity of offspring, whereas frogs typically showcase r-selection strategies. With this understanding, we can now proceed to the next section of our discussion.