Evolution has shaped all ecological communities. It has tested their resilience in experiments we could never perform. Now can it help us identify what characteristics make a community resilient or vulnerable to external forces?
Anthropogenic influences such as invasive species, climate change, and urbanization pressure ecosystems everywhere on the planet. Some collapse suddenly, others appear remarkably resilient. What makes some systems more vulnerable, and how could we identify them? Ecologists have long sought to understand the factors most influencing this stability, but the scale is immense and the problem complex – making controlled experimentation difficult and limited.
Rapid developments in sequencing technology & computational capacity have recently enabled us to reconstruct the ancestral links of many species. Phylogeneticists have demonstrated how this data can be combined with morphologies we observe today to reconstruct their evolutionary history and patterns. Can we use this information to understand how ecological communities assemble and change? Can phylogenetic relationships reveal the results of evolutionary experiments we could never perform?
Community ecologists have recently turned to phylogenetic data to shed more light on ecosystem stability. For instance, ecologists have long thought that diversity is an important correlate of stability for a community, and have now begun to quantify phylogenetic diversity as a possible metric of this. Others have considered whether patterns of trait similarity reflect or diverge from patterns of phylogenetic relatedness as a measure of niche conservatism. Such approaches are an important start, but they ignore the much richer picture of trait evolution that recent advances in both methods and available data have made possible.
My research would offer a new approach to this problem. My work in comparative phylogenetics has developed approaches to identify major evolutionary regime shifts - points in history where the pattern of evolution in some functional trait has changed dramatically. This may change the strength of selection, the location or emergence of a fitness peak, or the rate of change in a trait. These evolutionary shifts can serve as experiments in community stability, perturbations on a scale of space and time that we could not create experimentally.
In applying this approach to ecological communities, I must bring to bear information about geographical ranges of the species involved and a biomechanical understanding of how morphological traits correspond to ecological niches. Biogeography determines which species may interact and which may be isolated, and will also vary over the evolutionary history. Recent methods estimate biogeographical history using the phylogeny, and could be leveraged here to determine which species could potentially interact at a given time. The evolutionary regime shift step identifies which traits in which species experience a sudden shift, while the biogeography identifies which species are potentially present in the same community at that time, allowing us to identify which communities have experienced those shifts and which have been more stable.
Ecological stability is a distant frontier for phylogenetic methods, and is fraught with challenges. Reconstructions of evolutionary biogeography, phylogeny, and functional traits are each burdened with their own challenges and uncertainty. The patterns left on what we observe in present-day species from evolutionary transitions will be faint, but the scale and variety of data we can bring to bear on these problems is rapidly increasing. A robust method should be able to quantify the uncertainty of the inference and make it clear when phylogenetics is potentially informative of the community dynamics and when we have reached the limits of such approaches, which is natural for the model-based statistical approaches used here.
Though these evolutionary transitions are shrouded in the past, by developing methods that can draw on different lines of evidence such as traits, geography, and phylogeny we may better triangulate what happened and when. Identifying shifts in the evolutionary patterns of different communities offers a window into history which can expand our picture of what makes a community a stable or responsive to sudden shifts.