Biological Integrity

Fish communities are a key element in fluvial ecosystems Their position in the top of the food chain and their sensitivity to a whole range of impacts make them a clear objective for ecosystem conservation and a sound indicator of biological integrity. The UE Water Framework Directive includes fish community composition, abundance and structure as relevant elements for the evaluation os biological condition. Several approaches have been proposed for the evaluation of the condition of fish communities, from the bio-indicator concept to the IBI (Index of biotic integrity) proposals. However, the complexity of fish communities and their ecological responses make this evaluation difficult, and we must avoid both oversimplified and extreme analytical procedures. In this work we present a new proposal to define reference conditions in fish communities, discussing them from an ecological viewpoint. This method is a synthetic approach called SYNTHETIC OPEN METHODOLOGICAL FRAMEWORK (SOMF) th...

The Chapada Diamantina National Park (Bahia State, Brazil) was created with the intention of protecting beautiful mountain scenery and important water resources, but its boundaries had to be drawn within the context of a highly human-modified landscape. The resulting reserve has a very irregular shape, a low area/perimeter ratio, limited core areas, and excludes neighbouring ecosystems. GIS techniques and extensive field work identified nine distinct areas contiguous with the park boundaries that were subsequently evaluated for potential annexation to the reserve, based on: (1) the lack of significant human habitation or economic use of the land; (2) the biological integrity of these sites, derived by considering the percentage of their land area degraded under four categories of anthropogenic alteration and the time required for natural recuperation; and (3) an enhancement factor that objectively evaluates the ecological benefits of any modification of the reserve. These techniques offered the possibility for re-evaluating the entire region surrounding the park, together with the capacity to precisely delineate new boundaries with high ecological gains for the reserve but with low potential for generating serious conflicts with established human populations. Three areas were recommended for incorporation into the Park, and six for off-reserve conservation management.

1. Welsh & Hodgson (2008) argued that stream-associated amphibians (Ascaphus truei, Dicamptodon tenebrosus and Rhyacotriton variegatus) are reliable indicators of ecosystem health in the Pacific Northwest (PNW), U.S.A. We demonstrate that their assertions rely on circular reasoning as well as logical and empirical assumptions that have not received rigorous evaluation.2. Welsh & Hodgson (2008) based their arguments on data collected in northwestern California, U.S.A. However, all three taxa occur across a wide range of environmental gradients in the PNW, and other research results suggest that the taxa respond differentially to environmental perturbations across their geographical distribution. Hence, differences in abundance are not always reliable indicators of the state of an ecosystem, as population numbers can be influenced by factors that may not be associated with habitat quality (e.g. predation and disease).3. Welsh & Hodgson (2008) present indices (rather than estimates) of abundance, which contain an unquantifiable amount of uncertainty not reliably attributable to either environmental or management factors. Evaluating parameters such as reproductive success and survival are more likely to provide strong inference about factors influencing population size than correlative studies that associate some measure of relative abundance with individual habitat features.4. We argue that direct measurement of physical features (water temperature, sediment and wood), for which Welsh & Hodgson (2008) suggest using amphibians as surrogates, is more accurate, efficient and cost effective compared with monitoring cryptic species with methods that are unable to quantify spatial and temporal uncertainty in biological responses.5. Headwater streams are critical components of catchments in the PNW, and all three amphibian taxa show strong associations with low-order streams. However, we think research and monitoring of headwater streams should be guided by hypotheses that evaluate causal mechanisms, rather than relying on descriptive patterns that are limited in geographical scope and which support only weak inference about ecosystem processes. Other studies provide direct links between physical features and responses of target populations (i.e. fish). Adding a second correlative link (i.e. amphibians) provides no added benefit, and increases uncertainty in the association between management actions and changes in population size.