International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.1, 26-33 http://ecoevopublisher.com/index.php/ijmeb 30 plant seeds rather than artificial food sources in cities. Meanwhile, the colors and feathers of rural sparrows may also adapt to more natural environments to reduce the risk of being preyed upon by natural enemies. Fish in aquatic environments also exhibit differences in selective constraints across different ecological niches. Fish in freshwater and seawater environments also experience different selective constraints, leading to differences in physiological and behavioral adaptability. In marine environments, fish face multiple challenges from salinity, water temperature, and food availability. To address these challenges, some marine fish have developed highly salt tolerant humoral regulation abilities to maintain normal internal salinity. In addition, they may have a highly streamlined body shape to adapt to the water flow and predation in seawater. Freshwater fish typically live in environments with relatively stable salinity, but may face different challenges such as temperature changes and seasonal changes in food resources. Therefore, their fluid regulation ability may not be as strong as that of marine fish, but they may exhibit adaptability to low temperatures. In addition, the body size and dietary choices of freshwater fish may also vary to adapt to different freshwater ecological niches and food resources. 3.3 How ecological niche characteristics affect the performance of selective constraints Niche characteristics play a crucial role in the selective constraint performance of different niches. These characteristics include resource availability, food types, degree of competition, and habitat complexity (Yu et al., 2022). Taking birds as an example, there are significant differences in ecological niche characteristics among carnivorous bird populations residing in different geographical regions. In resource scarce desert niches, the red bellied Whistler in Australia has undergone significant adaptive changes in its mouth shape and feeding habits to more effectively capture scarce insect food. Their mouths become longer and thinner, helping to catch flying insects in the air. In resource rich niches, such as the rainforests of South America, there are different populations of carnivorous birds, such as the Pitta sordida (Figure 3). The ecological niche characteristics of these birds are significantly different from those of the red bellied thrush. Due to the abundance of insects in rainforest environments, their mouth shapes may be more suitable for hunting different types of insects, such as butterflies and beetles. These different ecological niche characteristics reflect differences in resource availability and food types, which have a significant impact on the performance of selective constraints. Figure 3 The mouth shape of the green breasted eight colored thrush can prey on different types of insects The degree of competition and habitat complexity also play a crucial role in selectively constraining the ecological niche. In highly competitive niches, species may experience stronger selective constraints, leading to more significant adaptive changes. The complexity of habitats, such as the vegetation structure in forests, can also affect
RkJQdWJsaXNoZXIy MjQ4ODYzNA==