Explain the difference between r-selected and K-selected species.

R-selected and K-selected species are terms used in ecology to describe two different strategies of reproduction and survival that are observed in nature.

1. R-selected species: These species are characterized by high growth rates, typically exploit less-crowded ecological niches, and produce many offspring, each of which has a relatively low probability of surviving to adulthood. They are often referred to as "opportunistic" because they take advantage of quick changes in the environment. Examples of r-selected species include bacteria, rodents, and insects.

2. K-selected species: On the other hand, K-selected species are characterized by slower growth rates, live at densities close to the carrying capacity (K), and invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood. They are often larger organisms that live longer and have fewer offspring, but invest more time and energy into ensuring those offspring reach reproductive age. Examples of K-selected species include humans, elephants, and whales.

In summary, the main difference between r-selected and K-selected species is the way they reproduce and survive. R-selected species produce many offspring with a low survival rate, while K-selected species produce fewer offspring but invest more resources into ensuring their survival.