Introduction to the Concept of Index of Native Fish Integrity
M. G. Sullivan, August 2006
The cumulative effects of human development and access can be pervasive and,
particularly in sensitive northern areas, entire ecosystems may be affected (Schneider et
al. 2003). A result of widespread development on ecosystems can be the alteration of the
integrity of the biological community. Biotic integrity has been defined as the ability to
support and maintain “a balanced, integrated, adaptive community of organisms having a
species composition, diversity, and functional organization comparable to that of natural
habitat of the region” (Karr and Dudley 1981). Monitoring every component of biological
communities, however, is far too complex, while focusing on a single indicator species
(often selected as being charismatic rather than an effective indicator) usually fails to
adequately address widespread changes (Landres et al. 1988; Cantebury et al. 2000).
An effective compromise between these extremes has been to use a carefully
selected group of indicators as an index of biotic integrity (IBI). Karr (1981; 1997)
developed and refined a system of metrics based on fish community composition and
health that has become very widely used to measure and communicate the effects of
disturbance on aquatic ecosystems (see review by Davis et al. 1996). Modifications of
this index have also been used to rank the status of disturbance on invertebrate, bird and
mammal communities (Plotnikoff and Ehinger 1997; Canterbury et al. 2000; Baynes et
al. 2004). In each case, a series of metrics such as number of native species, number of
predator species, percent of tolerant and intolerant species, and incidence of physical
anomalies is used to derive a single numeric value ranks the study site along a scale of
undisturbed to heavily disturbed. Although this summary metric may mask specific
cause-and effect responses (and consequently has lost favour amongst many basic
researchers), the IBI has proven to be a useful tool to communicate the broad status of
ecosystems to decision-makers, bureaucrats, and stakeholders (Teels 2003).
Aquatic ecosystems in boreal regions, such as Alberta, have characteristics of low
productivity with low biological diversity. For example, a typical Alberta lake may have
8 or 10 fish species, with streams often containing only 3 or 4 resident species (Nelson
and Paetz 1992; Joynt and Sullivan 2003). In contrast, typical IBI surveys were initially
developed and conducted in richly diverse areas such as streams in the Upper Mississippi
basin (Karr 1981; Niemela and Feist 2002) or Carolina coastal streams (Paller 1995)
where over 20 species may be present. Responses to human-induced disturbances in these
rich systems can be dramatic changes in species composition (Leonard and Orth 1986;
Hughes and Gammon 1987). Species richness in low diversity systems, however, cannot
change as markedly as can abundance and size structure of the few resident species. The
basic principle of monitoring the community structure and its function, however, remains
valid, but must be correspondingly modified to detect meaningful changes in these low
diversity systems.
Fishes in most Alberta aquatic communities may be classified into five general
groups, based both on their resilience to human-induced changes and their role in
defining and shaping the community function (Table 1).
Table 1. Functional groups of Alberta fish, ranked in terms of relative resilience to
human-induced stresses and importance to aquatic community function.
Fish Group
Resilience Community Function
Rare fish
Very low
Apex predators
low
Common
specialists
Exotics /
irruptives
moderate
Common
generalists
Very high
high
Examples
Boreal lakes
Minor role in community, major Lake trout
role in evolutionary process of
each species
Keystone species, major role as Walleye
community shapers
Moderate role in community
Lake
function and definition
whitefish
Replacement species, or
Yellow
dominant responder to trophic
perch
cascade
Minor role in defining
White
community
suckers
Examples
Prairie rivers
Lake sturgeon
Walleye
Goldeye
Brook
sticklebacks
White suckers
An index of native fish integrity (INFI) based on these guilds or functional groups
should focus on these categories of fish as those both most likely to change in response to
human-induced effects and also most likely to be a strong signal of meaningful changes
in community structure and function. Changes in these groups will not likely be the loss
of a species, but will be as major changes in abundance from the undisturbed condition.
Reference sites (spatial comparisons) or historical records (temporal comparisons) are
therefore necessary to allow comparisons of present abundance of species to the
undisturbed condition.
Perhaps the greatest utility of a single measure such as the INFI is its simplicity in
describing the effects of large-scale landscape disturbances on community integrity. By
correlating site-specific INFI values to surrounding measures of human disturbance,
dose-response curves can be easily developed. These curves can be directly integrated
into simulation models to forecast potential effects of landscape development on fish
communities. These curves can also be readily presented to stakeholders and decisionmakers as a basis to explain complex ecological interactions.
Similar to the Index of Biotic Integrity (IBI) as described by Karr (1997) and the
Index of Mammalian Integrity (IMI) for Alberta (Boutin and Baynes 2005), the INFI is
intended to be a quantified index of the integrity of a native animal community in the
boreal Alberta ecosystem. This index can be summarized into a single, easily understood
value for communication to decision-makers such as politicians, bureaucrats, and
stakeholders. The data validating the index must also be composed of the detailed
information needed to scientifically analyse probable cause-and-effect mechanisms for
the changes in the fish community.
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