Are insect pollinators more generalist
than insect herbivores?
Colin Fontaine1,*, Elisa The ´bault1and Isabelle Dajoz2
1NERC Centre for Population Biology, Division of Biology, Imperial College London,
Silwood Park Campus, Ascot, Berkshire SL5 7PY, UK
2Bioge ´ochimie et Ecologie des Milieux Continentaux, UMR 7618, Universite ´ Paris 7,
46 rue d’Ulm F-75230, Paris Cedex 05, France
Recent community-level studies have acknowledged that generalist species are more widespread than
previously thought and highlighted their preponderant impact on community functioning and evolution.
It is suggested that the type of interaction, trophic versus mutualistic, should affect species generalization
level; however, no direct comparison has been made yet. Here, we performed such a comparison using 44
plant–insect networks describing either pollination or herbivory communities. Our analysis shows that
the type of interaction does indeed have an impact on various aspects of species generalism, from the
distribution of generalism in the community to the phylogenetic diversity of the plants with which a
given insect species interacts. However, the amplitude of the observed differences depends on the
aspect of species generalism studied. While the non-quantitative and quantitative measures of generalism
suggest that pollinators interact with more plant species and more evenly than herbivores, phylogenetic
measures clearly show that herbivores interact with plant species far more closely related to each other
than pollinators. This comparative approach offers a promising perspective to better understand the
functioning and evolution of multispecies assemblages by pointing out some fundamental singularities
of communities depending on the type of interaction considered.
Keywords: generalism; herbivory; interaction web; mutualistic; pollination; trophic
Interactions among species are one of the most important
drivers of the ecology and evolution of species. Although
historically studies in terrestrial plant–animal interactions
have focused on direct pairwise interactions, it is now
acknowledged that generalization in interactions among
species is more widespread than previously thought. This
relatively high prevalence of generalist species has been
highlighted in both mutualistic (Waser et al. 1996) and
trophic (Novotny & Basset 2005) interaction networks.
Species generalism has some important consequences on
the functioning and evolution of ecological systems, and
the way we study them. Indeed, from an evolutionary per-
spective, the long-standing interest in coevolution between
pairs of species is now challenged by the concept of diffuse
coevolution, where selection pressures caused by one
species change in the presence of other species (Janzen
1980; Fox 1988; Inouye & Stinchcombe 2001; Strauss &
Irwin 2004). In the same way, from an ecological per-
spective, studies on the ecological dynamics of simple
prey–predator systems are now replaced by multispecies
systems and network approaches in which indirect effects
among species via shared interacting partners can be as
strong as the direct effects between interacting species (Lau &
Strauss 2005; van Veen et al. 2006). Thus, generalism is
clearly an important species property from both functional
and evolutionary perspectives. But interestingly, the views
on species generalization are different between the two
research areas concerned, respectively, with mutualistic
plant–pollinator systems and trophic plant–phytophagous
In plant–pollinator studies, network approaches have
been used to identify general patterns in community
organization. It has been proposed that the distribution
of species generalism follows power law family distri-
butions (Jordano et al. 2003); but see Okuyama (2008).
This implies that there is a higher proportion of specialist
species and some higher generalist species than expected
from a random distribution. These findings generate great
interest in the internal structure of pollination webs with
much emphasis on the importance of highly generalist
species in the functioning and resistance to perturbations
of pollination webs (Memmott et al. 2004; Fortuna &
vore studies, the interest mainly focused on the proportion
of extreme specialist species in a community. This is
directly related to the controversy surrounding global
estimates of arthropod species richness (Erwin 1982;
Novotny et al. 2002) that range from 2 to 80 million
species according to the percentage of specialist species
(Thompson 1994). Whereas recent studies have shown
that insect herbivores consume more species than
previously thought (Novotny & Basset 2005), it has been
proposed that these herbivores are often genus specialists,
i.e. thatthe hostplant rangemainlylieswithin plantgenera
rather than within plant species or family (Novotny et al.
2002; Novotny & Basset 2005).
These different current views on insect generalism
may simply arise for historical reasons. The scientific
* Author for correspondence (firstname.lastname@example.org).
Electronic supplementary material is available at http://dx.doi.org/10.
1098/rspb.2009.0635 or via http://rsbl.royalsocietypublishing.org.
Proc. R. Soc. B (2009) 276, 3027–3033
Published online 10 June 2009
Received 15 April 2009
Accepted 13 May 2009
This journal is q 2009 The Royal Society
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