Predators reverse the direction of density dependence for juvenile salmon mortality

Area of Science:

• Ecology
• Population Dynamics
• Conservation Biology

Background:

• Predator-prey interactions critically influence population stability.
• Density-dependent mortality is key for stable prey populations, but predator saturation can reverse this effect.
• Juvenile salmon are vulnerable to predators, yet the demographic impact of predators on them remains unclear.

Purpose of the Study:

• To investigate the interactive effects of predators and population density on juvenile Atlantic salmon mortality.
• To determine if slimy sculpins alter density dependence in juvenile salmon mortality.

Main Methods:

• Controlled releases of newly hatched juvenile Atlantic salmon at three density treatments.
• Experimental streams with and without slimy sculpin (Cottus cognatus) as predators.
• Replicated study across six streams over two summers.

Main Results:

• In streams without sculpin, juvenile salmon mortality was density dependent.
• In streams with abundant sculpin, juvenile salmon mortality became inversely density dependent.
• Predator presence reversed the natural density-dependent mortality patterns of juvenile salmon.

Conclusions:

• Predator-mediated inverse density dependence can destabilize prey populations, increasing extinction risk.
• This phenomenon poses significant challenges for the persistence of rare prey populations and the restoration of depleted ones.
• Understanding predator-prey dynamics is crucial for effective wildlife conservation and population management.