Abstract
The use of species traits to characterize the functional composition
of benthic invertebrate communities has become well established in
the ecological literature. This approach holds much potential for
predicting changes of both species and species assemblages along
environmental gradients in terms of traits that are sensitive to
local environmental conditions. Further, in the burgeoning field
of biomonitoring, a functional approach provides a predictive basis
for understanding community-level responses along gradients of environmental
alteration caused by humans. Despite much progress in recent years,
the full potential of the functional traits-based approach is currently
limited by several factors, both conceptual and methodological. Most
notably, we lack adequate understanding of how individual traits
are intercorrelated and how this lack of independence among traits
reflects phylogenetic (evolutionary) constraint. A better understanding
is needed if we are to make the transition from a largely univariate
approach that considers single-trait responses along single environmental
gradients to a multivariate one that more realistically accounts
for the responses of many traits across multiple environmental gradients
characteristic of most human-dominated landscapes. Our primary objective
in this paper is to explore the issue of inter-trait correlations
for lotic insects and to identify opportunities and challenges for
advancing the theory and application of traits-based approaches in
stream community ecology. We created a new database on species-trait
composition of North American lotic insects. Using published accounts
and expert opinion, we collected information on 20 species traits
(in 59 trait states) that fell into 4 broad categories: life-history,
morphological, mobility, and ecological. First, we demonstrate the
importance of considering how the linkage of specific trait states
within a taxon is critical to developing a more-robust traits-based
community ecology. Second, we examine the statistical correlations
among traits and trait states for the 311 taxa to identify trait
syndromes and specify which traits provide unique (uncorrelated)
information that can be used to guide trait selection in ecological
studies. Third, we examine the evolutionary associations among traits
by mapping trait states onto a phylogentic tree derived from morphological
and molecular analyses and classifications from the literature. We
examine the evolutionary lability of individual traits by assessing
the extent to which they are unconstrained by phylogenic relationships
across the taxa. By focusing on the lability of traits within lotiv
genera of Ephemeroptera, Plecoptera, and Trichoptera, taxa often
used as water-quality indicators, we show how a traits-based approach
can allow a priori expectations of the differential response of these
taxa to specific environmental gradients. We conclude with some ideas
about how specific trait linkages, statistical correlations among
traits, and evolutionary lability of traits can be used in combination
with a mechanistic understanding of trait response along environmental
gradients to select robust traits useful for a more predictive community
ecology. We indicate how these new insights can direct the research
in statistical modeling that is necessary to achieve the full potential
of models that can predict how multiple traits will respond along
multiple environmental gradients.
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