why are species where they are?
...and not where they are not?
Using coral reefs as a model system, my team works to understand the diversity and distribution of life on Earth through three key themes outlined below. To link small scale processes that take place at the level of individuals to global biodiversity patterns, we use a blend of fieldwork, statistics and state-of-the-art simulation modelling. This framework allows strong tests of macroecological theory that are focused on understanding the action of underlying processes. If we better understand why species are where they are, we can enhance predictions of how this will change into the future and contribute to solutions for the grand environmental challenges of our time.
1. SPECIES INTERACTIONS & BEHAVIOUR
Ample evidence suggests that gradients in environmental conditions influence the distribution of species. However, our understanding of the role for animal behaviour, including species interactions (e.g., competition, mutualism, predation), is extremely limited and constitutes a critical knowledge gap. Whilst there is strong support at small spatial scales that one species can cause exclusion of another through competition for a shared resource, the importance of this interaction and other behavioural processes at large biogeographic scales is unresolved. Therefore, one of my research themes concentrates on revealing the role for behaviour in determining diversity and distributions of biodiversity at large spatial scales.
Collection of community scale primary data across a large geographic extent designed to test macroecological theory is rare but essential to move beyond weak inference of process from patterns and towards direct tests of hypothesised processes. A major project, funded by the Villum Foundation (4 million DKK), aimed to determine their influence on species geographic range limits more explicitly.
We have collected behavioural and abundance data across the central Indo-Pacific aimed at answering biogeographical and ecological questions, including how and why do species interactions change through space and time? Can competitive “tournaments” can maintain high diversity systems? Do individual interactions scale-up to influence global biodiversity patterns?
I have recently become very interested in the role for behavioural flexibility in the potential for animals to adapt to a changing world. Ecological predictions of how species will shift their geographical distributions under climate change generally fail to consider that individuals make active behavioural decisions that mediate ecological dynamics. I am currently working on ways to pursue this new and fascinating research area so it can incorporated into our understanding of biogeographical patterns.
2. REPRODUCTION & DISPERSAL
Many processes that influence the distribution and abundance of a species occur at early life history stages, such as natal dispersal and density-dependent recruitment. These processes might be particularly important in the marine realm because many habitat-forming species (e.g., corals, macroalgae) do not move as adults. My research consistently identifies dispersal and establishment of propagules as key processes underlying geographic distributions in both temperate and tropical ecosystems.
Most recently, we have been developing a greater understanding for the timing of coral reproductive events. Working with a large team of collaborators from eight countries (led by Andrew Baird, JCU, Australia) who assembled an unprecedented data set of the spawning times for >60,000 individual coral colonies across 99 species from 34 reefs, we found that rapid seasonal rises in ocean temperatures provide a generalisable proximate environmental cue that initiates synchronised coral mass spawning events across the Indian and Pacific Oceans.
We are now trying to figure out if and how coral phenology will be impacted by climate change and what that means for diversity and distributions, how these data can improve biophysical models of coral dispersal, and what are the relative roles for dispersal and establishment in determining biodiversity patterns.
3. BIOGEOGRAPHIC HISTORY
Multiple processes operate in synchrony to determine species geographical range limits and the importance of each process varies according to the spatial and temporal scale of interest. We found that geological history and its influence on macroevolutionary processes appear to be particularly important for understanding the generation and maintenance of global biogeographic provinces for coral reefs. One way we are exploring this further is through simulations of dispersal, extinction and speciation at large spatial scales using a process-based model.
In the oceans, vertical depth distribution limits are also evident, analogous to elevational limits on land. Unfortunately, knowledge of depth distributions is severely limited because data collection at depth is difficult. Working with Ed Roberts (JCU, Australia), who is currently collecting the largest existing primary data set on coral depth distributions in the world that includes >10,000 coral colonies, we are progressing understanding of patterns and drivers of depth distributions for corals.