Boom-Bust Cycles Constrain Host-Parasite Dynamics, Suppress Parasite Spread, and Drive Parasites Extinct

Area of Science:

• Ecology
• Epidemiology
• Theoretical Biology

Background:

• Host-parasite theory traditionally assumes equilibrium population dynamics.
• Many host populations exhibit dynamic "boom-bust" life histories or range expansions with bottlenecks.
• Dynamic host density can alter density-dependent processes like parasite transmission and reproduction.

Purpose of the Study:

• To investigate how recurring host population bottlenecks, simulating boom-bust dynamics, affect disease spread.
• To compare disease dynamics in non-equilibrium boom-bust systems with traditional equilibrium models.
• To explore the implications for horizontally transmitted symbionts.

Main Methods:

• A simple compartment model was developed.
• The model was subjected to recurring host population bottlenecks to simulate boom-bust life histories.
• The impact of bottleneck frequency and severity on disease spread was analyzed.

Main Results:

• Recurring bottlenecks suppressed disease spread by allowing host populations to recover faster than parasites could transmit.
• Increased bottleneck frequency and/or severity led to significant reductions in disease transmission.
• Parasite extinction was highly probable under frequent and/or severe bottleneck conditions.

Conclusions:

• Dynamic host density in boom-bust systems generates unique ecological and epidemiological behaviors not observed in equilibrium models.
• The findings are generalizable to other horizontally transmitted symbionts, including mutualists and commensals.
• Accurate prediction of disease and symbiont dynamics requires explicit modeling of boom-bust life histories.