Are urban habitats safer even when humans are around? Predation risk in house finches using multiple indicators of risk.

摘要

One of the current ecological paradigms is that urbanization decreases species diversity, but it increases the abundance of certain species with high tolerance to human activities. The safe-habitat hypothesis tries to explain this pattern through a decrease in the abundance of native predators, which reduces predation risk in highly urbanized habitats. However, this hypothesis does not consider the potential negative effects of human disturbance (e.g., pedestrians, dogs). My goal was to assess the degree of perceived predation risk in house finches (Carpodacus mexicanus) through field studies and semi-natural experiments in areas with different levels of urbanization using multiple indicators (flock size, flight initiation distance, vigilance and foraging behavior). Field studies showed that house finches in more urbanized habitats formed larger flocks, and flushed at larger distances than in less urbanized habitats. In the semi-natural experiment, I found that individuals spent a greater proportion of time in the refuge patch and increased the instantaneous pecking rate in the more urbanized habitat with pedestrians. Vigilance parameters were influenced in different ways depending on habitat type and distance to flock-mates. Contrary to the predictions of the safe-habitat hypothesis, my results suggest relatively higher perceived predation risk in more urbanized habitats with high levels of human activity, despite the lower abundance of native predators. I suggest that 2 processes, sensitization and availability of alternative suitable habitats, could explain the higher perceived predation risk of house finches in highly urbanized areas.