Sexual cannibalism and population viability

Abstract

Some behaviours that typically increase fitness at the individual level may reduce population persistence, particularly in the face of environmental changes. Sexual cannibalism is an extreme mating behaviour which typically involves a male being devoured by the female immediately before, during or after copulation, and is widespread amongst predatory invertebrates. Although the individual‐level effects of sexual cannibalism are reasonably well understood, very little is known about the population‐level effects. We constructed both a mathematical model and an individual‐based model to predict how sexual cannibalism might affect population growth rate and extinction risk. We found that in the absence of any cannibalism‐derived fecundity benefit, sexual cannibalism is always detrimental to population growth rate and leads to a higher population extinction risk. Increasing the fecundity benefits of sexual cannibalism leads to a consistently higher population growth rate and likely a lower extinction risk. However, even if cannibalism‐derived fecundity benefits are large, very high rates of sexual cannibalism (>70%) can still drive the population to negative growth and potential extinction. Pre‐copulatory cannibalism was particularly damaging for population growth rates and was the main predictor of growth declining below the replacement rate. Surprisingly, post‐copulatory cannibalism had a largely positive effect on population growth rate when fecundity benefits were present. This study is the first to formally estimate the population‐level effects of sexual cannibalism. We highlight the detrimental effect sexual cannibalism may have on population viability if (1) cannibalism rates become high, and/or (2) cannibalism‐derived fecundity benefits become low. Decreased food availability could plausibly both increase the frequency of cannibalism, and reduce the fecundity benefit of cannibalism, suggesting that sexual cannibalism may increase the risk of population collapse in the face of environmental change.

Ecology of female mating failure/lifelong virginity: a review of causal mechanisms in insects and arachnids

“…High rates of precopulatory cannibalism are obviously maladaptive for males, and also for females because they induce male-biased sex ratios by consuming receptive mating partners without accessing their sperm. Strong selection against precopulatory cannibalism is expected to reduce its incidence in nature (Gav ın-Centol et al, 2017;Fisher et al, 2018).…”

Relatedness modulates density‐dependent cannibalism rates in Drosophila

“…Cannibalism can be a significant source of mortality and has evolved in species across many taxonomic groups, including fish (Pereira et al., 2017), amphibians (Pfennig et al., 1994), insects (Fisher, Holwell, et al., 2020; Hopper et al., 1996) and spiders (Elgar, 1991). Cannibalism can also drive the evolution of phenotypic traits such as size variation (Elgar, 1991; Pfennig et al., 1994; Wilder & Rypstra, 2008) and can have a large impact at the population level by stabilising population fluctuations and affecting extinction risk (Fisher et al., 2018; Fisher, Cornell, et al., 2020; Ricker, 1954; Via, 1999). Hypotheses for the adaptive function of cannibalism are diverse and range from cannibalism as a foraging strategy (Barry et al., 2008; Petersen et al, 2010) to cannibalism as a mechanism of mate choice (Prenter et al., 2006).…”

Dispersal reduces interspecific competitiveness by spreading locally harmful traits

“…This competition can take the form of intraspecific interference (Ziemba & Collins, 1999) or exploitative competition (Wacker & Von Elert, 2008) and can ultimately reduce population size and increase extinction risk (Matsuda & Abrams, 1994). The importance of self‐serving behaviour can be seen in cannibalism, which is common and widespread (Fox, 1975; Pereira et al., 2017) despite negatively affecting population viability (Fisher et al., 2018). Beyond cannibalism, traits that impede the survival or fecundity of conspecifics can lower population densities (Boström‐Einarsson et al., 2013), making them more susceptible to stochastic extinction.…”