Geoscience Reference
In-Depth Information
Increasing cost of handling hosts
Utilise available host
Forego available host
Profit from finding new host
Figure 9
Diagram illustrating the effects of searching and handling time limitations
on host profitability and parasitoid foraging strategy. Parasitoid foragers can be
limited in their reproductive success by time limitation, that is, they will die before
they deposit their eggs. This can manifest in two ways (i) they are limited by the time
required to find new hosts, which will result in a high cost to finding a new host, and
thus will reduce the profit associated with foregoing an available host in search of a
host of better quality; (ii) conversely, the parasitoid can be limited because there is a
large handling time associated with attacking an available host, in this case, the
forager is limited in the number of hosts that it can attack in its lifetime, analogously
to egg-limited foragers, so it should maximise the quality of each host that it
parasitizes.
study of two parasitoid wasps of the genus Aphidius determined that the
species with longer handling time constraints (A. picipes) was significantly
less likely to attack an already parasitized host, analogous to low quality,
than the species less constrained by handling time (A. rhopalosiphi;
van
Baaren et al., 2004
). Similarly as with egg-limitation, we would expect
parasitoid species that forage electively, because of handling time limitations,
to structure their realised niche according to host characteristics and not
encounter rate.
These ideas are supported by theories related to functional responses and
density-dependent foraging. Where functional responses determine the fit-
ness returns associated with increasing host encounter rate, which in turn
determines whether parasitoid forage in a density-dependent manner (
Corley
et al., 2010; Wajnberg, 2006
). High handling time limitations on foraging
parasitoids result in a saturating response of oviposition rate to host density.
With a decelerating (saturating) oviposition rate response to host availabili-
ty, there is a possibility that host populations can reach a density where
oviposition rate of an individual is no longer density dependent because it
