Abstract
The environment is currently undergoing changes at both global (e.g., climate change) and local (e.g., tourism, pollution, habitat modification) scales that have the capacity to affect the viability of animal and plant populations. Many of these changes, such as human disturbance, have an anthropogenic origin and therefore may be mitigated by management action. To do so requires an understanding of the impact of human activities and changing environmental conditions on population dynamics. We investigated the influence of human activity on important life history parameters (reproductive rate, and body condition, and growth rate of neonate pups) for California sea lions (Zalophus californianus) in the Gulf of California, Mexico. Increased human presence was associated with lower reproductive rates, which translated into reduced long-term population growth rates and suggested that human activities are a disturbance that could lead to population declines. We also observed higher body growth rates in pups with increased exposure to humans. Increased growth rates in pups may reflect a density dependent response to declining reproductive rates (e.g., decreased competition for resources). Our results highlight the potentially complex changes in life history parameters that may result from human disturbance, and their implication for population dynamics. We recommend careful monitoring of human activities in the Gulf of California and emphasize the importance of management strategies that explicitly consider the potential impact of human activities such as ecotourism on vertebrate populations.
Highlights
Increasing rates of human population growth and anthropogenic impacts on a global scale have left few populations of plants and animals undisturbed
In this study we explored how reproductive rate, pup body condition, and pup growth rate were affected by frequency of human activity in several breeding colonies of the California sea lion (Zalophus californianus) in Mexico (Figure 1)
Reproductive rate We examined frequency of human exposure and its relationship to reproductive rates and estimates of pup growth and condition in several colonies of the California sea lion in the Gulf of California, Mexico
Summary
Increasing rates of human population growth and anthropogenic impacts on a global scale have left few populations of plants and animals undisturbed. Human interactions with plants and animals may be among the most pressing issues in developing sustainable approaches to mitigating anthropogenic impacts. There is increasing evidence that vertebrate populations are stressed when exposed to humans, which is manifested by changes in behavior and physiology. Williams et al [2] found that human disturbance increased energetic costs as a result of behavioral modifications in killer whales (Orcinus orca). Human disturbance alters individual spatial distribution [4,5] and behavior [6] of animal populations. Behavioral and energetic changes are likely coupled with physiological alterations in the organism [7]
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