Geoscience Reference
In-Depth Information
I. AN INTRODUCTION TO ECOLOGICAL NETWORK
THEORY AND HOST-PARASITOID NETWORKS
A. Ecological Networks and Their Role in Ecology
Ecological networks document the interactions among organisms within an
ecosystem, such as predators feeding upon prey or insects pollinating plants
(
Ings et al., 2009; Woodward et al., 2005, 2010b
). Networks are generally
resolved at the species level, where each species forms a node within the
network and a link demarks which pairs of species have been observed (or are
assumed) to be interacting (
Oleson et al., 2010; Woodward et al., 2005
),
although more recent work has emphasised the role of individual-level inter-
actions (
Gilljam et al., 2011; Woodward et al., 2010a
). Although ecological
networks have been perceived to be difficult to compile and analyse, the
study of how species interact has taken a central role in investigating key
aspects of ecological theory, such as the complexity-stability debate (the
ongoing debate as to whether biodiversity promotes long-term ecological
stability;
McCann, 2000
), and the debate as to which species should receive
priority in the global conservation effort (i.e. either rare, endemic species
most at risk of extinction or those that are integral to the stability of
ecosystems;
Ings et al., 2009
). Further, the investigation of the properties
and structure of ecological networks has been shown to be a powerful tool
for use in applied ecology, such as assessing the impact of biological pertur-
bations within ecosystems (e.g. invasion of an ecosystem by an alien species
or a biological control) and determining the effectiveness of conservation
programmes (
Friberg et al., 2011; Memmott, 2009; Mulder et al., 2011
).
Because of the wide-spread importance of networks within the field of
ecology, understanding the mechanisms by which interactions within net-
works are structured has been highlighted as a priority for future research
(
Ings et al., 2009; Woodward et al., 2010b
).
Most published ecological networks belong to one of three categories,
which are defined by the nature of the interactions between the individuals
within the network (
Ings et al., 2009; Oleson et al., 2010
). Most commonly
studied are food webs, which depict antagonistic interactions that transfer
energy across trophic levels, focused particularly upon predator-prey and
primary consumer-basal resource relationships (
Hall and Raffaelli, 1993;
Ings et al., 2009
). Host-parasitoid networks also depict antagonistic interac-
tions, but they are typically focused on a particular guild of insect herbivores
and their specialist parasitoid enemies (
Hawkins, 1992
). Mutualistic net-
works consist of beneficial interactions between species, such as plant-
pollinator interactions. While much of the pioneering work on ecological
networks was carried out in terrestrial host-parasitoid systems, the recent
