Geoscience Reference
In-Depth Information
Parasitoid A
Foragers should maximise the
number of offspring that they
produce, realised niche structure is
determined by the relative
abundances of each host-species.
Searching time costs are
greater than handling
time costs *
5.
3.
7.
Time limited
1.
1
2
3
4
Host
4.
Handling time costs are
greater than searching
time costs *
Parasitoid life-
history
6.
Foragers are highly elective and
realised niche structure is deter-
mined by traits that relate to host
quality; such as size.
1(b)
Parasitoid B
8.
2.
Egg limited
6.
1
2
3
4
Host
Figure 13
Life history and realised niche structure in host-parasitoid networks. (1 and 2) Life-history traits, such as the degree of
ovigeny, determine whether a parasitoid is more likely to experience egg or time limitation because these characteristics determine the
availability of eggs at any given time, the lifespan of the parasitoid and the rate of parasitism (
Rosenheim et al., 2008
). (3 and 4) Time
limited parasitoids must optimally allocate their time in order to maximise reproductive success. Parasitoids that are limited because they
cannot find enough hosts to utilise all their eggs experience searching time limitation of reproductive success, while those that are limited
in their parasitism rate because they cannot handle hosts fast enough experience handling time limitation of reproductive success. The
likelihood of either of these limitations occurring is determined by both parasitoid characteristics, such as wing venation, and how host
choice is constrained by life history (e.g. idiobiont hyperparasitoids must attack their hosts during the mummy stage and have long
handling times) as well as by host characteristics, such as abundance (
Sanders and Van Veen, 2010
). (5) When time costs are most
incurred during the process of searching for hosts, parasitoids should utilise all viable hosts that they encounter. (6) When the costs to the
currency that must be allocated optimally, which can be time or eggs, are most incurred through utilising hosts, hosts utilised should be
of optimal quality, so as to gain the greatest fitness benefits from using limited resources (
Minkenberg et al., 1992
). (7 and 8) The realised
niche of a parasitoid species is constructed from multiple host-choice decisions made by each parasitoid species within an ecosystem.
Each decision consists of whether to use an available host or not, and the likelihood of either decision is determined by a foragers degree
of electivity. (7) Foragers that are not very elective, and attack every viable host that they encounter, have a realised niche constructed
according to the relative abundances of the different host species within the ecosystem. (8) In foragers that are highly elective, the relative
interaction strengths between the parasitoid and the available hosts are determined by the characteristics of the host.
