Trait shifts in bird communities from primary forest to human settlements in Mexican seasonal forests. Are there ruderal birds?

Abstract

Agriculture, cattle grazing, and human settlements negatively affect bird biodiversity, driving the loss of ecologically specialized species and favoring the dominance of generalists. Because ecological pressures define organisms’ success by acting on their intrinsic traits, biodiversity loss due to anthropization might cause directional trait shifts. Here, we use a trait-based approach to find empirical evidence of trait-shifts in bird communities across an anthropization gradient in seasonal forests in central Mexico. We performed point-count bird surveys within a region of tropical deciduous and seasonal oak forests considering three degrees of anthropization: primary forest, secondary growth, and human settlements. A multivariate analysis (PCA) showed similar trait-covariation patterns for both forest types; in the anthropized habitat the bird communities exhibited shorter life-cycles, higher fecundity, and broader ecological niches (diet, foraging habitat, and nesting resources) than those in the primary forests. Our finding of directional trait shifts resembles Evolutionary Ecological Strategies Theory (EES) predictions for successful organisms within highly disturbed anthropized habitats, which are known as a “ruderal adaptative strategy” in the EES framework. The use of trait-based approaches could improve ecological generalizations in bird communities, leading to a better understanding of avian biodiversity's responses to anthropization.

Keywords

• Anthropization
• Ecological strategies
• Functional ecology
• Tropical dry forest