"Negative frequency-dependence is not a mechanism of coexistence in spatially fragmented populations"Devadhasan, AnushAcross scales of organization, understanding the mechanisms that shape and maintain diversity in a population remains a fundamental challenge and there exists a large literature in evolutionary biology describing the processes that can account for persistent coexistence within populations. At their core, the theoretical frameworks are grounded in balancing selection, including negative frequency-dependent (NFD) selection, spatial or temporal habitat heterogeneity, and heterozygote advantage. In particular, NFD selection, by favoring rare types, is often suggested as the main selective force for biodiversity and polymorphism in natural populations. In this talk I will describe an evolutionary model in which, unintuitively, the opposite occurs: NFD selection decreases coexistence relative to neutrality, for certain spatial population structures. We call this the spatial speedup effect and, using a combination of mathematical analysis and simulation, we find that the condition for this effect depends critically on the spatial arrangement of the population. We show that spatial speedup is specifically shaped by the algebraic connectivity of the population: a measure of “spatial fragmentation” that derives from spectral graph theory. I will discuss how spatial speedup in fragmented populations can significantly impact biodiversity over evolutionary and ecological timescales by analyzing fixation times and species richness as the respective proxies for coexistence. |
« back