title: Range expansions transition from pulled to pushed waves as growth becomes more cooperative in an experimental microbial population.
abstract: Range expansions are becoming more frequent due to environmental changes and rare long-distance dispersal, often facilitated by anthropogenic activities. Simple models in theoretical ecology explain many emergent properties of range expansions, such as a constant expansion velocity, in terms of organism-level properties such as growth and dispersal rates. Testing these quantitative predictions in natural populations is difficult because of large environmental variability. Here, we used a controlled microbial model system to study range expansions of populations with and without intraspecific cooperativity. For noncooperative growth, the expansion dynamics were dominated by population growth at the low-density front, which pulled the expansion forward. We found these expansions to be in close quantitative agreement with the classical theory of pulled waves by Fisher [Fisher RA (1937) Ann Eugen 7(4):355-369] and Skellam [Skellam JG (1951) Biometrika 38(1-2):196-218], suitably adapted to our experimental system. However, as cooperativity increased, the expansions transitioned to being pushed, that is, controlled by growth and dispersal in the bulk as well as in the front. Given the prevalence of cooperative growth in nature, understanding the effects of cooperativity is essential to managing invading species and understanding their evolution.
authors.affiliation: Physics of Living Systems Group, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Saurabh R
authors.identifier: 0000-0002-3630-0393
authors.initials: SR
authors.lastname: Gandhi
authors.affiliation: Physics of Living Systems Group, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139;
authors.forename: Eugene Anatoly
authors.initials: EA
authors.lastname: Yurtsev
authors.affiliation: Department of Physics, Boston University, Boston, MA 02215; Graduate Program in Bioinformatics, Boston University, Boston, MA 02215 korolev@bu.edu gore@mit.edu.
authors.forename: Kirill S
authors.initials: KS
authors.lastname: Korolev
authors.affiliation: Physics of Living Systems Group, Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139; korolev@bu.edu gore@mit.edu.
authors.forename: Jeff
authors.initials: J
authors.lastname: Gore
mesh_terms: D005075:Biological Evolution; D004463:Ecology; D008954:Models, Biological; D011157:Population Dynamics; D011158:Population Growth
keywords: Allee effect; Fisher wave; biological invasion