Phase-locking and environmental fluctuations generate synchrony in a predator–prey community

Abstract

Spatially synchronized fluctuations in system state are common in physical and biological systems ranging from individual atoms to species as diverse as viruses, insects and mammals. Although the causal factors are well known for many synchronized phenomena, several processes concurrently have an impact on spatial synchrony of species, making their separate effects and interactions difficult to quantify. Here we develop a general stochastic model of predator-prey spatial dynamics to predict the outcome of a laboratory microcosm experiment testing for interactions among all known synchronizing factors: (1) dispersal of individuals between populations; (2) spatially synchronous fluctuations in exogenous environmental factors (the Moran effect); and (3) interactions with other species (for example, predators) that are themselves spatially synchronized. The Moran effect synchronized populations of the ciliate protist Tetrahymena pyriformis; however, dispersal only synchronized prey populations in the presence of the predator Euplotes patella. Both model and data indicate that synchrony depends on cyclic dynamics generated by the predator. Dispersal, but not the Moran effect, 'phase-locks' cycles, which otherwise become 'decoherent' and drift out of phase. In the absence of cycles, phase-locking is not possible and the synchronizing effect of dispersal is negligible. Interspecific interactions determine population synchrony, not by providing an additional source of synchronized fluctuations, but by altering population dynamics and thereby enhancing the action of dispersal. Our results are robust to wide variation in model parameters representative of many natural predator-prey or host-pathogen systems. This explains why cyclic systems provide many of the most dramatic examples of spatial synchrony in nature.

Different types of synchrony in chaotic and cyclic communities

“…Instead, we found only short periods where there is phase locking. For the cyclic communities, our study confirms previous observations that migration between cyclic communities can lead to phase-locked dynamics and that the intrinsic cyclical behaviour persists 11,12,35,37 . Interestingly, we did not find the driver and response population cycling in-phase as has been shown in another experimental predator-prey system 11 , instead we found out-phase cycles.…”

“…To our knowledge, this is the first experimental study, comparing the synchronization behaviour in cyclic and chaotic communities. Previous experimental studies focused on cyclic communities and populations 11,34,35 . In general, synchronization is considered to arise from dispersal or migration between subpopulations, interactions with a mobile predator or parasite or by spatially correlated environmental variation 5,36 .…”

“…Synchronization between populations may be caused by migration or dispersal between populations, fluctuating abiotic parameters affecting multiple populations (Moran effect), or trophic interactions with synchronized predators or food resources 5 . Until now, synchronization has been observed for lynx 6,7 , voles 8 , measles 9,10 , microbes 11 and mussel populations 12 . Synchronization of biological phenomena, such as periodic dynamics of populations, physiological activities or reproductive behavior, have been shown and one principal conclusion of these studies is that synchronization and phase locking can have a fundamental role 11,13,14 .…”

“…Until now, synchronization has been observed for lynx 6,7 , voles 8 , measles 9,10 , microbes 11 and mussel populations 12 . Synchronization of biological phenomena, such as periodic dynamics of populations, physiological activities or reproductive behavior, have been shown and one principal conclusion of these studies is that synchronization and phase locking can have a fundamental role 11,13,14 . However, previous studies did not consider more complex dynamics such as chaos and quasiperiodicity that are predicted for complex systems with multi-species interactions as we find them in nature 15,16 .…”

“…Beside in-phase synchronization between spatially separated populations, where populations cycle in tune, a more subtle form, phase locking, has been suggested by ecological models for periodic and chaotically oscillating populations 7,11,[25][26][27] . Phase locking occurs when one (or more) oscillator influences a second oscillator in such a way that their phases oscillate in tune but that there is a constant difference in the phase of two oscillators 1,2 .…”