Revisiting ecological integrity 30 years later: non‐native species and the misdiagnosis of freshwater ecosystem health

Abstract

Assessing the ecological integrity of freshwater ecosystems has become a priority to protect the threatened biodiversity they hold and secure future accessibility to the services they provide. Some of the most widespread applications of biological indicators are fish-based indices. These have mostly mirrored the approach proposed by Karr 30 years ago (Index of Biotic Integrity; IBI), based on the comparison of observed and expected composition and structure of local fish assemblages in the absence of major perturbations, using the so-called reference condition approach. Despite the notable success of the implementation of fish-based indices, most of them overlook non-native species as a source of ecosystem degradation, and evaluations are focused on the physico-chemical condition of freshwater ecosystems and their effects on freshwater biodiversity. Almost 90% of 83 reviewed IBIs did not consider non-native species when defining reference conditions. Most IBIs used non-native species in conjunction with native ones to construct the metrics that conform to the index. The response of the IBI to the effect of non-native species has hardly ever been tested. When developing and evaluating IBIs, attention was mostly directed to ensuring the correct response of the index to physicochemical parameters, which could otherwise be characterized more effectively using alternative methods. Current application of IBIs entails a misuse of biological indicators by overlooking some types of degradation that cannot be otherwise evaluated by traditional methods. This constrains the capacity to adequately respond to one of the most challenging and common threats to the conservation of freshwater fish diversity.

Assessing the causal relationships of ecological integrity: a re‐evaluation of Karr's iconic Index of Biotic Integrity

“…Integrity assessments, originally based on physico‐chemical water quality parameters, have moved toward the use of biological indicators in the last 30 yr (Hermoso and Clavero ). In fact, in the original development of the IBI, it had been claimed that the careful monitoring of fish alone would serve to assess the health of water resources (Karr ).…”

“…Although much attention has been given to distinguishing native and exotic species in conservation (Speziale et al. , Buckley and Catford ), almost all of the applications of IBIs in ecology do not consider exotic species (Hermoso and Clavero ).…”

Re‐envisioning State and Tribal Collaboration in Fishery Assessment and Restoration

“…However, we found that participants described natural function quite differently; some tribal participants described it as minimal change in structure from a precolonial reference condition, whereas some DNR participants described moderate changes from a prior condition with ecosystem function intact. This finding seems important in a global perspective as well, because many indigenous societies worldwide assess ecosystem and community health using precolonization reference conditions because of their interrelated and interdependent heritage (Salmon 2000;Lerma 2012), and there is current debate in the scientific community regarding whether nonnative species should be viewed as an ecosystem degradation (Hermoso and Clavero 2013). How the tribes would gauge success of a project on the status of native or nonnative species should be further understood and would strengthen participants' views that prior to restoration, clear objectives be set collectively.…”

Full Issue PDF Volume 39, Issue 7

“…The abundance or presence/absence of common sensitive fishes often contributes to Index of Biological Integrity (IBI) scores (Harris 1995), which are successfully applied to help identify impaired ecosystems and should therefore serve as early warning signs of broadscale population decline for sensitive species. However, unitless IBI scores inherently mask the status of individual populations 297 and the presence of environmentally sensitive nonnative fishes may result in higher IBI scores (Hermoso and Clavero 2013). Given the acute sensitivity of many fishes to urbanization and multivariate nature of IBI systems, a moderately impacted stream could retain a high IBI score and thus fail to signal an alarm bell for one or more particularly sensitive native species.…”