Table 1.

Symbols and definitions.

Symbol	Definition
a	Intensity of local competition
e	Intensity of sunk cost selection
r	Coefficient of relatedness
pij, pi, p	Frequency of altruism allele (in individual ij, in group i, and in global metapopulation, respectively)
b	Maximum benefit of altruism
c	Direct effect of altruism
Wij, Wi, W	Fitness (of individual ij, mean of group i, and mean of global metapopulation, respectively)
fij, fi, f	Fecundity, i.e., the gross number of pre-regulation offspring produced (individual, mean group, and in absence of altruists, respectively)
f (t −1)	Mean fecundity of parents
vij, vi, v	Viability, i.e., resource-independent probability of survival to reproductive stage (individual, mean group, and in absence of altruists, respectively)
Si, S	Resource supply, i.e., per-consumer amount of resources available to a group (mean group, and in absence of altruists, respectively)
TD	Sunk cost parameter, i.e., the average proportion of total resources consumed by an individual before pre-reproductive death
kS,i, kS	Half-saturation constant, i.e., per-capita resource supply at which fitness is half its asymptotic value (mean group, and in absence of altruists, respectively)
ωi, ω	Coefficient of local crowding (in group i and in a group without altruists, respectively)
Ni, N	Number of founders of a deme (in group i and in a group without altruists, respectively)
x	Dummy variable used to modulate among Type I, II and III functional responses
y	As directly above, but can also be interpreted as the “handling time” of prey