Which of the following is true about complex life cycles in species?

Complex life cycles, characterized by multiple distinct life stages that may include changes in structure, function, and habitat, often occur in a variety of environments. This flexibility allows species with complex life cycles to take advantage of different ecological niches and resources available in both terrestrial and aquatic ecosystems. For instance, many insects and amphibians exhibit complex life cycles wherein larval stages thrive in water while adult forms may transition to land. This adaptability to various environments is a key feature of complex life cycles, supporting the reasoning for the correct answer.

The other options present specific statements that do not accurately reflect the nature of complex life cycles, such as the requirement for environmental changes or limitations to certain animal groups. While some complex life cycles do involve metamorphosis, not all exhibit this characteristic, indicating that there's diversity in how these life cycles manifest across different species.