Timescale reverses the relationship between host density and infection risk
Tara E Stewart Merrill1,2, Carla E Cáceres2,3, Samantha Gray3
1Coastal and Marine Laboratory, Florida State University, St. Teresa, FL 32358, USA.
Proceedings. Biological Sciences
|August 3, 2022
Summary
Host density impacts disease risk differently over time. Initially, higher host numbers offer
Area of Science:
- Ecology
- Epidemiology
- Parasitology
Background:
- Host density influences disease dynamics through competing mechanisms.
- Safety in numbers' can reduce infection risk at high host densities.
- Density-dependent transmission' can increase infection risk with more hosts.
Purpose of the Study:
- To investigate the theoretical proposal that host density's effect on infection risk changes over time.
- To test if short-term risk reduction is followed by long-term risk amplification.
- To examine the role of parasite reproduction in density-dependent disease dynamics.
Main Methods:
- Laboratory experiments using a zooplankton-disease model.
- Field observations to validate experimental findings.
- Analysis of infection risk across different host densities and timescales.
Main Results:
- Observed negative density-risk relationships ('safety in numbers') in the short term.
- Demonstrated a reversal of this relationship to positive density-dependence ('density-dependent transmission') within two host generations.
- Confirmed that parasite numerical responses mediate the shift in risk.
Conclusions:
- Host density effects on infection risk are time-dependent.
- Short-term 'safety in numbers' can transition to increased long-term risk due to parasite reproduction.
- Ecological timescales are critical for understanding host-parasite population dynamics and disease management.
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