New findings from short-term experimental and simulated ecological studies [1, 2], and from molecular studies [3-5], demonstrate that neutral priority effects – whereby the order of arrival of organisms into an ecosystem influences final ecosystem structure [6-8] – can have extremely long-lasting impacts, and operate within species and across a vast range of spatial scales . Founding lineages are able to rapidly dominate the available niche space of newly-colonised territory, quickly reaching population densities that can effectively block colonisation by later arrivals . Such patterns can be maintained when local recruits substantially outnumber immigrants. Under these circumstances, density-blocking by founders can render subsequent dispersal by others, including conspecifics, almost entirely ineffective. Evidence is mounting that a substantial component of global biogeography can be explained by these non-adaptive processes, which will continue to shape ecosystems in the wake of anthropogenic environmental change. Thus, the ability to disperse, which we have long assumed to be a critical factor in a species’ evolutionary success, does not necessarily promote connectivity of disjunct populations, but rather allows species to wedge a proverbial foot in the door when a disturbance opens new opportunities for colonisation.
Density-blocking effects mean that the offspring of dispersing individuals have a far greater chance of colonisation if there are no established populations of conspecifics .
Recent work in this field [9, 11, 12] has emphasised the ubiquity and importance of these processes, but also raised a number of urgent questions that must be addressed for us to understand the critical roles of dispersal and disturbance in structuring ecosystems and global patterns of biodiversity.
In a new, broad project funded via a Future Fellowship from the ARC, my research group will address the following key questions:
Question 1: How is the strength of density-blocking effects influenced by organisms’ relative rates of dispersal versus reproduction?
I hypothesise that density blocking will be greatest for organisms that have high reproductive relative to dispersal rates, as the rate of arrival of new lineages will be less than the rate at which the founding lineage can reach high densities.
Question 2: What is the range of spatial scales across which density blocking operates?
I hypothesise that density blocking will play a role in spatial patterns of biodiversity at both fine (among individuals) and broad (among populations) scales.
Question 3: How is species turnover in ecosystems driven by both density blocking and disturbance?
I hypothesise that opportunities for new lineages to enter ecosystems require disturbance in the form of widespread destruction of existing lineage/s.
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9. Waters, J.M., C.I. Fraser, and G.M. Hewitt, Founder takes all: density-dependent processes structure biodiversity. Trends in Ecology & Evolution, 2013. 28: p. 78-85.
10. Hewitt, G., The genetic legacy of the Quaternary ice ages. Nature, 2000. 405(6789): p. 907-913.
11. Fraser, C.I., S.C. Banks, and J.M. Waters, Priority effects can lead to underestimation of dispersal and invasion potential. Biological Invasions, 2015. 17(1): p. 1-8.
12. Waters, J.M., et al., The founder space race: a reply to Buckley et al. Trends in Ecology & Evolution, 2013. 28: p. 190-191.