Temporal variability in host availability alters the outcome of competition between two parasitoid species

Variability in the availability of resources through time is a common
attribute in trophic interactions, but its effects on the fitness of
different consumer species and on interspecific competition between them
are not clearly understood. To investigate this, we allowed two parasitoid
species, Trichopria drosophilae and Pachycrepoideus vindemiae, to exploit
Drosophila host pupae under different temporal variability treatments,
either on their own or simultaneously. When tested individually (in the
absence of interspecific competition), both parasitoid species had lower
fitness when hosts were exposed for a short duration at high density than
when exposed for a long duration at low density. When both parasitoid
species exploited hosts simultaneously, interspecific competition
significantly decreased the number of offspring for both parasitoid
species. The outcome of this interspecific competition depended on host
temporal variability, with T. drosophilae or P. vindemiae dominating in
short and long host exposure treatments, respectively. These results can
be explained by the combination of host availability and egg load of
female adult parasitoids. When abundant hosts are provided for a short
period, the ample mature eggs of the proovigenic T. drosophilae enable
them to exploit hosts more efficiently than P. vindemiae, which is
synovigenic. However, P. vindemiae is an intrinsically superior competitor
and dominates when multiparasitism occurs. Multiparasitism is more
frequent when hosts are at low levels relative to the egg load of the
parasitoids. Our results clearly demonstrate that resource temporal
availability can alter the outcome of competition between consumers with
different reproductive traits.