9780521861724htl 1..2

CHAPTER FIVE

Body size in streams: macroinvertebrate

community size composition along

natural and human-induced

environmental gradients

COLIN R.TOWNSEND

University of Otago, New Zealand

ROSS M.THOMPSON

Monash University, Australia

Introduction
Communities contain a diversity of species and a spectrum of life forms.
A consequence of evolutionary processes is that lists of species from different
communities tell us almost nothing about how similar they are ecologically. On
the other hand, by quantifying the life-history traits represented, we can discern
similarities and differences among communities and gain an understanding of
the functional relationships between traits and habitats. In response to
Southwood’s ( 1977 ) contention that habitat provides the templet upon which
evolution forges characteristic life-history strategies, we are interested in the
extent to which life-history traits of macroinvertebrates can be directly mapped
onto stream habitat axes. More recently, stream researchers have used the
metaphor of environmental filters (Poff, 1997 ) that can eliminate certain traits
and produce similar trait compositions in similar habitats (Statzner, Dole ́dec &
Hugueny, 2004 ). Trait-specific selective forces along environmental gradients
may act over evolutionary time, as Southwood (1977) contended, or over an
ecological time scale, selecting for successful strategists from the potential pool
of colonists.
The earliest categorization of species traits in stream ecology related to
trophic role. Cummins ( 1974 ) identified grazer-scrapers, fine particle collectors
(gatherers or filterers), large particle shredders and predators. Stream ecologists
now use this trophic categorization to focus on the similarities and differences
of communities in different parts of the world (e.g. Winterbourn, Rounick &
Cowie, 1981 ; Thompson & Townsend,2000; Fenoglio, Bo & Cucco, 2004 ), in
different parts of the river continuum (e.g. Vannoteet al., 1980; Grubaugh,
Wallace & Houston, 1996 ) and in different kinds of terrestrial setting (e.g.
Thompson & Townsend, 2000 ; Woodward & Hildrew, 2002 ).

Body Size: The Structure and Function of Aquatic Ecosystems, eds. Alan G. Hildrew, David G. Raffaelli and
Ronni Edmonds-Brown. Published by Cambridge University Press.#British Ecological Society 2007.