Data from: Partner switching can favor cooperation in a biological market

Intraspecific cooperation and interspecific mutualisms can be promoted by
mechanisms that reduce the frequency with which cooperative organisms are
exploited by unhelpful partners. One such mechanism consists of changing
partners after interacting with an uncooperative individual. I used
McNamara et al.'s (Nature, 451, 2008, 189) partner switching model as
a framework to examine whether this mechanism can select for increased
cooperative investment by house sparrows (Passer domesticus) collaborating
to rear offspring; previous research on this species has shown that
substantial cooperative investments by both pair members are required to
achieve high pay-offs from collaborating. I found that the poorer the
outcome of a breeding attempt relative to the number of eggs the female
invested, the greater the likelihood of partner switching. The incidence
of partner switching changed seasonally, with peak switching coinciding
with an increase in the number of alternative partners available to
females. After females switched partners, their breeding outcomes rose to
match those of females that remained with the same partner; this was not
the case for males that switched partners. Consistent with the
model's prediction, males in stable partnerships achieved over 25%
higher than average reproductive success, which was attributable to both
persistently good breeding outcomes and their older partners' high
fecundity. These results provide empirical support for the hypothesis that
partner switching favours increased cooperative investment levels, and
they demonstrate that variation in the relative value of by-product
benefits can enhance that process.