Question

Like Bear Paw Lake, nearby Kalmbach Lake is an Alaskan lake that historically had no native predatory fish. The Alaska Department of Fish and Game started introducing rainbow trout into Kalmbach Lake in 1982. Prior to these introductions, pelvic reduction was common in this stickleback population. The rainbow trout is known to prey on stickleback. What would you hypothesize has happened to the stickleback population in the more than 30 generations that have elapsed since the trout was introduced?

A) The population size of stickleback fish dropped dramatically, leaving only a few survivors, all of which have the absent pelvic phenotype.
B) Most stickleback fish in Kalmbach Lake now have pelvic spines.

Answer 1

The introduction of predatory rainbow trout to Kalmbach Lake likely resulted in a natural selection process that favored stickleback fish with developed pelvic spines, as these offered some protection from predation. Over 30 generations, this would mean most sticklebacks in the lake would now have pelvic spines, indicating an evolutionary response to the change in their environment.

Step-by-step explanation:

When examining the impact of predatory fish such as rainbow trout on native species like stickleback, a significant change in the population dynamics can be expected. The introduction of rainbow trout, a predatory species, to Kalmbach Lake, where there were no native predatory fish and where stickleback with reduced pelvic spines were common, likely led to a strong selective pressure on the stickleback population. Prior to the introduction of trout, the absence of the pelvic structure may have been advantageous in an environment with no predators, possibly due to energy savings associated with reduced skeletal structures.

However, with the introduction of rainbow trout, sticklebacks with reduced pelvic spines would have been more susceptible to predation, lacking a key defense mechanism against predators. Over 30 generations, natural selection would likely have favored sticklebacks with more developed pelvic spines, which offer some protection from predation. Hence, the hypothesized outcome would be that most stickleback fish in Kalmbach Lake now have pelvic spines, as this trait would increase their chances of survival and reproduction in the presence of the newly introduced predator.

It is important to note that environmental factors and fish stocking programs often have complex and sometimes unintended effects on ecosystems. The introduction of non-native species can result in drastic changes in native populations and ecosystem dynamics, as seen in other case studies where the introduction of non-native fish led to the decline of native fish populations and altered ecosystem balance. Therefore, while the specific changes to the Kalmbach Lake stickleback population since 1982 are not detailed here, they would reflect evolutionary responses to the selective pressure exerted by the predatory rainbow trout.