Mate-finding Allee effects can be exacerbated or relieved by sexual cannibalism

Area of Science:

• Ecology
• Evolutionary Biology
• Population Dynamics

Background:

• Allee effects decrease survival and reproduction in small or sparse populations.
• Mate-finding difficulties at low densities are a primary driver of Allee effects.
• Sexual cannibalism, where females consume males, can exacerbate mate-finding Allee effects.

Purpose of the Study:

• To investigate how sexual cannibalism influences mate-finding Allee effects.
• To identify conditions where sexual cannibalism detrimentally impacts population viability.
• To assess the role of cannibalism-derived fecundity benefits on extinction risk.

Main Methods:

• Developed an individual-based model tracking female reproductive success.
• Measured extinction risk and per capita growth rate to quantify Allee effect strength.
• Varied founder population size and mate encounter rates to isolate mechanisms.

Main Results:

• Sexual cannibalism significantly increased extinction risk, particularly with pre-copulatory cannibalism, small founder populations, and low encounter rates.
• Post-copulatory cannibalism reduced extinction risk if it substantially increased female fecundity.
• Strong threshold effects were observed, where minor changes in encounter rate drastically altered extinction risk.

Conclusions:

• Sexual cannibalism generally negatively impacts population survival as population size and mate encounter rates decline.
• These effects can be worsened by declining male quality and increasing female hunger.
• Findings have implications for top invertebrate predators and suggest other reproductive strategies can also cause Allee effects.