The Role of Body Size in Complex Food Webs: A Cold Case - Advances in Ecological Research - page 181

analyzing relationships between trophic structure, body size and network
structure, the diversity of predatory species types needs to be considered in
future studies.
I. INTRODUCTION
Human activity is affecting ecosystems on a global scale to such an extent
that few, if any, pristine ecosystems remain. This begs the question as to what
characterises an undisturbed food web and how human induced disturbances
such as habitat destruction, overexploitation, introduction of alien species
and climate change might be expected to affect the structure and functioning
of ecosystems ( Dirozo and Raven, 2003 ). Indeed, there are growing concerns
that disturbances on ecosystems, via changes in species richness, species
composition and trophic structure will affect and seriously threaten impor-
tant ecosystem functions ( Thomas et al., 2004 ). In the light of these potential
threats, a key question ecologists must now answer is how will such losses
affect the diversity, structure and functioning of the world's ecosystems?
Attempting to answer this question has stimulated much of the interest in
understanding the relationships between biodiversity and ecosystem func-
tioning ( Schulze and Mooney, 1993 ) and has led to numerous experimental
studies over the past couple of decades ( Balvanera et al., 2006; Cardinale
et al., 2006; Loreau et al., 2001, 2002; Naeem et al., 1994; Petchey and
Gaston, 2006; Petchey et al., 2004a; Tilman, 1991 ). These and other studies
have shown that there is not necessarily a simple linear relationship between
biodiversity and ecosystem function and have led to a more recent focus on
functional diversity instead of species richness per se and on how to identify
and characterise functionally significant components of biodiversity ( D´az
and Cabido, 2001; Petchey et al., 2004b; Reiss et al., 2009 ).
Clearly, the effects of species loss ultimately have to be studied in natural
systems to understand the full range of possible responses within the com-
plex, multispecies networks of interacting taxa, such as described within the
context of food web research ( Reiss et al., 2009 ). Here, loss of a few species
can potentially trigger a cascade of extinctions and other marked changes in
food web structure ( Bascompte et al., 2005; Borer et al., 2005 ).
There is increasing evidence that unexpected cascades of species extinc-
tions and the pathways of restoration and recovery depend on the complex
nature of species-rich communities ( Bascompte and Stouffer, 2009; Dunne
et al., 2004 ). From a conservation perspective, information on species func-
tional roles is therefore desirable if we are to predict the likelihood of species
extinctions and their potential effects on structure and function of the entire
ecosystem ( Memmott, 2009 ).