Demographic performance of coral populations in changing environments

Understanding how populations respond to climate-induced stressors is essential for predicting their future trajectories under continued climate change, and for inferring how the collective dynamics of interacting populations shape the resilience of ecological communities. Species experience environmental pressures unevenly across their distributional range, as local conditions can mediate both the severity of stress and result in response variation among populations, but it remains unclear how climate change will affect populations differentially in such contrasting environments. Environmental gradients across a species’ geographical distribution thus create natural contrasts in exposure to stressors, allowing population dynamics to be examined across space and time.
This thesis investigates demographic performance under contrasting environmental contexts by examining population dynamics across spatial and taxonomic scales, with a particular focus on latitudinal gradients as natural laboratories for exploring differential responses to environmental stress in coral populations. I first investigate whether there is a general pattern in demographic performance among different realms and different taxa across a latitudinal gradient. I illustrate how demographic performance across animal and plant populations does not fully correspond to latitudinal contrasts, but may be affected by micro-climate and within-population intrinsic factors. Next, to understand how genetic identities influence demographic performance and at which taxonomic resolution provides sufficient ecological relevance, I investigate vital rates of different coral taxa from coarse to fine-scale taxonomic resolution, to find that genus-scale categorisation provides the most ecological relevance in a coral demographic context. Finally, I explore the demographic performance of coral populations along environmental gradients and project how they will respond to future climate change across three paired tropical accreting reefs and cooler-marginal assemblages. I evaluate spatial patterns and the impact of environmental variability on the long-term performance of coral populations across coral taxa. Using an integral projection model framework, I show how tropical communities are affected by warming more severely compared to their subtropical counterparts, which, despite slower growth and lower reproductive activity, may serve as potential refugia for conspecifics under continued climate change.
Overall, this thesis advances understanding of demographic processes in coral communities that experience contrasting environments and demonstrates how both intrinsic and extrinsic factors interact to shape population trajectories. By integrating demographic data with genetic resolution and climate projections, I highlight the limitations of coarse ecological indicators such as coral cover, while underscoring the value of size-based and taxonomically resolved approaches. In the face of intensifying climate change, the demographic approaches I present in this thesis will be essential for assessing and forecasting population viability and persistence.