Thresholds for impaired species recovery

Area of Science:

• Conservation Biology
• Population Ecology
• Marine Ecology

Background:

• Research in conservation biology predominantly focuses on small and declining populations, using frameworks like the small-population and declining-population paradigms.
• These paradigms primarily address extinction risks and the causes/consequences of population depletion, but offer limited insight into population recovery dynamics.
• Allee effects, which describe a positive relationship between population size and per capita growth rate, provide a basis for identifying thresholds where population recovery becomes uncertain.

Purpose of the Study:

• To critique existing studies on Allee effects.
• To quantify minimum population sizes and recovery trajectories for marine fish populations after threat mitigation.
• To propose a 'recovering population paradigm' to improve research and management of population recovery.

Main Methods:

• Critically reviewed literature on Allee effects.
• Quantified population-size minima and subsequent recovery trajectories for marine fish species.
• Compared recovery thresholds across marine fishes, terrestrial vertebrates, and marine mammals using life-history analyses.

Main Results:

• Threat mitigation alone is often insufficient for population recovery when populations are depleted below 10% of maximum abundance (N(max)) and remain so for extended periods.
• Recovery thresholds for impaired recovery appear to be lower for marine fishes compared to marine mammals.
• Life-history traits influence population-size thresholds for recovery.

Conclusions:

• A new 'recovering population paradigm' is needed to focus research on recovery thresholds and dynamics.
• Identifying generic impaired recovery thresholds across species can enhance conservation efforts.
• Clarifying terminology and distinguishing patterns from causes/consequences in Allee effect research will improve practical conservation outcomes.