Final answer:
The three-spined stickleback evolved from a saltwater fish to a freshwater fish, and further speciation occurred due to the use of different feeding micro niches in freshwater lakes. Evolutionary changes within species like the stickleback can have significant impacts on their ecosystems, as seen in their effects on nutrient availability and the growth of algae.
Step-by-step explanation:
The three-spined stickleback (Gasterosteus aculeatus) is an exemplary species to understand evolution. About 10,000 years ago, these fish made a significant evolutionary leap: they adapted from living in saltwater to freshwater environments. Once isolated in different freshwater lakes, sticklebacks underwent further evolutionary changes. Depending on the specific lake, they either remained as one species or differentiated into two species. This speciation was driven by the exploitation of distinct micro niches within the lakes for feeding.
Environmental changes, including those impacted by sticklebacks' feeding habits, influence the survival of other organisms, particularly photosynthetic species. Dr. Luke Harmon's work highlights how the evolution of species like the stickleback can directly affect the ecosystem's environment.
In some cases, the presence of two stickleback species led to the consumption of all nutrients in the water, preventing the growth of algae. This dynamic interaction showcases the reciprocal effects between environment and evolution, which can now be integrated into simulation models to predict ecosystem changes.