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Harvesting in seasonal environments
Cailin Xu1, Mark S Boyce, Daryl J Daley
1Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. cailin@ualberta.ca
Journal of Mathematical Biology
|December 23, 2004
Summary
Harvesting strategies in seasonal environments significantly impact population persistence and maximum annual yield (M.A.Y.). Optimal strategies depend on population growth rate and seasonality, with pulse harvesting sometimes exceeding maximum sustainable yield (M.S.Y.).
Area of Science:
- Ecology
- Population Dynamics
- Conservation Biology
Background:
- Traditional harvest theory often assumes stable environments, neglecting the pervasive influence of environmental seasonality on population dynamics.
- Understanding population responses to harvesting under fluctuating environmental conditions is crucial for effective resource management.
Purpose of the Study:
- To investigate the effectiveness of five common harvest strategies in seasonal environments, focusing on maximum annual yield (M.A.Y.) and population persistence.
- To determine how intrinsic growth rate and the magnitude of seasonality influence optimal harvest strategies.
Main Methods:
- Simulated logistic population growth under varying degrees of environmental seasonality.
- Evaluated five distinct harvest strategies, including open/closed harvest and pulse harvest.
- Analyzed the impact of harvest timing on annual yield for time-dependent strategies.
Main Results:
- Optimal harvest strategy is highly dependent on the population's intrinsic growth rate and the degree of environmental seasonality.
- For populations with high growth rates and low seasonality, constant, linear, and time-dependent harvest strategies achieve M.A.Y. close to M.S.Y.
- Pulse harvest can exceed M.S.Y. in seasonal environments due to dynamic population fluctuations relative to carrying capacity.
- For low growth rates and high seasonality, M.A.Y. is significantly lower than M.S.Y. for all tested strategies.
Conclusions:
- Environmental seasonality fundamentally alters the effectiveness of population harvesting strategies.
- Harvest timing is critical for time-dependent strategies, with optimal timing linked to seasonal declines in carrying capacity.
- Further research is needed to develop effective strategies for populations with low growth rates facing significant seasonality and for populations with complex dynamics (e.g., age structure, predation).