Geoscience Reference
In-Depth Information
VIII. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
166
A. The Determinants of Fundamental Niche . . . . . . . . . . . . . . . . . .
166
B. The Determinants of Realised Niche . . . . . . . . . . . . . . . . . . . . . .
169
C. Future Research Avenues and the Effect of Spatio-Temporal
Variation in Host-Parasitoid Networks . . . . . . . . . . . . . . . . . . . .
172
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
ABSTRACT
Recent studies of the allometric scaling of metabolism, resource handling and
space use have provided a mechanistic understanding of how interactions
within ecological networks are arranged. Especially, the 'allometric diet
breadth model' (ADBM), which considers the association between consumer
size, resource availability and handling costs, has shown that food webs are
predictably shaped according to the body-size relationships of the organisms
within them. However, size-based models of network structure are more
applicable to predator-prey webs than to insect host-parasitoid networks
because the relationship between body size and host use appears to be less
straightforward in host-parasitoid interactions. Herein, we describe the
structuring of host-parasitoid networks using frameworks that are based
not only upon parasitoid body-size considerations but also upon the life-
history characteristics that are commonly used to describe variation among
hymenopteran parasitoids: the degree of ovigeny, idio/koinobosis and endo/
ectoparasitism. We compare these frameworks with those suggested by the
ADBM and elucidate upon why it has been unable to successfully predict
host-parasitoid network structure. For instance, body-size constraints upon
foraging capability are a stronger determinant of whether an interaction is
possible in predator-prey webs than they are in host-parasitoid networks
because the ultimate determinant of host suitability is its phylogeny. Further,
the degree to which the taxonomic host range of a parasitoid is constrained
by phylogeny is largely determined by parasitoid life history, for example,
whether the larva develops as an endo- or ectobiont. In addition, we describe
how parasitoid life history influences host-choice decisions, which
are expected to be tailored towards the optimal allocation of scarce
resources, through the determination of how species are limited in their
reproductive success. To conclude, we describe some fruitful avenues for
future research and highlight the importance of considering how temporal
or spatial variation in the characteristics of parasitoids or their hosts affects
how networks are structured.
