Data from: The role of male body size in mating success and male-male competition in a false widow spider

In many animals, body size is correlated with reproductive success.
Selection sometimes generates striking differences in body size between
males and females (i.e., sexual size dimorphism, SSD). SSD is common in
spiders (Araneae), and is typically explained by selection for larger,
more fecund females, and rapidly maturing, and consequently smaller males.
Within a species males and females also often vary in body size. 
In the false widow spider (Steatoda grossa), females are larger than males
and males trade off body size for rapid development and early maturation.
Moreover, males exhibit considerable variation in body size, suggesting
that under certain conditions there may be advantages to large size. Here,
we tested the role of male body size on mating success under
non-competitive and competitive mating conditions (i.e., male-male
competition) in S. grossa. We found that body size did not influence
mating success or copulation duration under non-competitive conditions,
but that larger males were more successful at obtaining access to females
under competitive mating conditions. Additionally, we found that total
copulation duration was significantly lower when a rival male was present.
Our results show a large male advantage under male-male competition, which
we suggest may contribute to the high variation in male body size observed
in S. grossa. We further suggest that the reduced copulation duration
observed under competitive mating conditions may have potential
ramifications for male and female reproductive success, and discuss how
patterns of selection acting on male body size might limit the extent of
SSD in this species.