Revealing the hidden effects of anthropogenic disturbance on the spatiotemporal dynamics of animal populations

Globally, natural ecosystems are under threat due to the ever increasing pressures imposed by human activities. Many ecosystems are becoming fragmented or are being eroded at the edges while the effects of human disturbance are being felt even at the core of protected areas. Often, the impact of human activity or human-altered environments is obvious: when natural habitats are destroyed animals that can't escape will perish; humans directly harvest wild animals through poaching, hunting or fishing; infrastructure, such as wind turbines or roads, lead to collisions that kill animals; while diseases can spread from livestock and decimate wild populations. Beyond these direct impacts, much research has shown how humans can have more subtle effects on animals. For example, human activities can induce avoidance behaviour and restrict access to vital foraging areas, increase stress and vigilance levels, and interfere with sensory mechanisms by introducing noise and light into environments. While not as obvious, these indirect effects can have large impacts since many animals operate at the edge of their physiological limits whereby their energetic demands are finely balanced with resource availability, and weakened individuals can quickly succumb to predators, parasites, or disease. This means that even subtle impacts of human activity can significantly reduce the probability that an animal will survive and reproduce, which in turn can translate to large and sudden declines in the population.

In this research we will investigate the effects of increased human pressures on the migratory population of wildebeest, a keystone species that inhabit the Greater Serengeti ecosystem in East Africa. We will assess how human disturbance is changing how animals move, how much time they spend consuming resources as opposed to being vigilant, and how these factors are affecting their body condition. We will test if these effects alter the survival probability of individuals and the chance that they have viable offspring.

To evaluate the effects of human disturbance on movement and activities, we will use GPS devices and activity sensors mounted on collars that we will deploy on migratory wildebeest, combined with a comprehensive description of the distribution of resources (vegetation and soil nutrient maps) and risks (location of human infrastructure, tourism, illegal hunting activities, and natural predation). The GPS collars and sensors will allow us to track animals and determine how they respond to these environmental features, both in terms of how they move around in space, and how much time they allocate to different activities. To assess how body condition affects survival and reproduction we will analyse metabolites that get deposited in wildebeest tail hair as it grows. We will firstly calibrate our analysis on animals of known body condition, and then use this method to assess the body condition of animals that have died of different causes. This will allow us to estimate how poor body condition reduces a wildebeest's probability of survival. Using a similar analysis we will determine whether animals have reproduced and use field surveys to measure calf survival rates.

To understand how indirect effects of humans scale-up to impact the resilience of the population, we will use Integral Projection Models, a framework that will allow us to use data at the individual level to predict what will happen at the population level. By combining empirical data collection with mathematical models that link individual vital rates with population dynamics, we can ask what happens to the population abundance if human activities increase in specific areas, or if climate change leads to different distributions of resources. This research will be one of the most detailed assessments of the effects of humans on an ecosystem and will provide scientists and managers with vital information about how to keep ecosystems resilient in the future.