Body Size, Life History and the Structure of Host–Parasitoid Networks - Advances in Ecological Research - page 146

III. LIMITATIONS ON HOST RANGE
A. Fundamental Niches in Host-Parasitoid Networks
An ecologically important difference between food webs and host-parasitoid
networks concerns 'host range or diet breadth' ( Memmott et al., 2000; van
Veen et al.,2008 ), which refers to the range of host/prey species with which
each parasitoid/predator species interacts in their respective networks. For
food webs, this is species consumed ( Gilljam et al., 2011; Memmott et al.,
2000; Petchey et al., 2008 ), whereas in host-parasitoid networks, it is the
number of host species in which a parasitoid oviposits ( van Veen et al., 2008 ).
Diet breadth is determined by the range of species with which a forager can
successfully interact, that is, the fundamental niche. In parasitoids, this is
species from which offspring can complete juvenile development ( van Veen
et al., 2008 ). Parasitoids are generally more specialist than predators and thus
have narrower diet breadths, due to the physiological constraints associated
with the parasitoid life history, such as over-coming host defences, success-
fully recognising viable hosts and ensuring the larvae has access to host
biomass ( Mackauer et al., 1996; Quicke, 1997; Whitfield, 1998 ). These con-
straints are opposed to the idea presented in food webs, where the diet
breadths of predators are thought to scale allometrically, and as a result, so
does their trophic level ( Arim et al., 2010; Brose et al., 2006; Gilljam et al.,
2011; Petchey et al., 2008 ).
Fundamental niche constraints result in generalised differences between
host-parasitoid networks and food webs. For example, a greater reliance on
fewer host species for nutrition results in high levels of trait-matching be-
tween parasitoids and their hosts ( Ings et al., 2009; Memmott et al., 2000; van
Veen et al., 2008 ). Further, a narrower 'diet breadth' results in many strong
interactions between species, and networks that consist mostly of strongly
interacting species are prone to reduced stability ( O'Gorman and Emmerson,
2009; van Veen et al., 2008 ). The strong interactions between the components
of host-parasitoid networks have been suggested to be an important aspect
of the effectiveness of parasitoid biological control programmes ( Mills and
Wajnberg, 2008 ).
B. The Role of Phylogeny in Host-Parasitoid Network
Structure
Due to the intimacy of the interaction between host and parasitoid, host
defences and parasitoid counter-offenses are highly specialised. This may
lead one to expect that diet breadth and network structure in these systems