Abstract
Accurate establishment of baseline conditions is critical to successful management and habitat restoration. We demonstrate the ability to robustly estimate historical fish community composition and assess the current status of the urbanized Barton Creek watershed in central Texas, U.S.A. Fish species were surveyed in 2008 and the resulting data compared to three sources of fish occurrence information: (i) historical records from a museum specimen database and literature searches; (ii) a nearly identical survey conducted 15 years earlier; and (iii) a modeled historical community constructed with species distribution models (SDMs). This holistic approach, and especially the application of SDMs, allowed us to discover that the fish community in Barton Creek was more diverse than the historical data and survey methods alone indicated. Sixteen native species with high modeled probability of occurrence within the watershed were not found in the 2008 survey, seven of these were not found in either survey or in any of the historical collection records. Our approach allowed us to more rigorously establish the true baseline for the pre-development fish fauna and then to more accurately assess trends and develop hypotheses regarding factors driving current fish community composition to better inform management decisions and future restoration efforts. Smaller, urbanized freshwater systems, like Barton Creek, typically have a relatively poor historical biodiversity inventory coupled with long histories of alteration, and thus there is a propensity for land managers and researchers to apply inaccurate baseline standards. Our methods provide a way around that limitation by using SDMs derived from larger and richer biodiversity databases of a broader geographic scope. Broadly applied, we propose that this technique has potential to overcome limitations of popular bioassessment metrics (e.g., IBI) to become a versatile and robust management tool for determining status of freshwater biotic communities.
Highlights
A reference condition is critical to the interpretation of bioassessment data and indicators of ecosystem health
Through the incorporation of these disparate and temporally diverse historical occurrence data with environmental variables accounting for only broad-scale physiological and biogeographical constraints, we propose that species distribution models (SDMs) used as described in this study provide a more robust and quantifiable estimation of historical habitat suitability than bioassessment techniques using variable quality reference conditions [24,25]
G. affinis is represented in 53% of historical collecting events, followed by C. venusta (35%), C. anomalum and L. auritus, and A. mexicanus and L. megalotis
Summary
A reference condition is critical to the interpretation of bioassessment data and indicators of ecosystem health. Over time, shifting baselines result in management for steadily decreasing biodiversity or habitat quality This process undermines our attempts to manage for sustainability into the future as managers rely on incomplete perspectives as to what a ‘‘natural’’ assemblage is for a given area and what factors shape it. This is especially acute in freshwater systems where historical data are relatively sparse compared with marine fisheries where shifting baselines were first documented, and where the dendritic nature of streams and rivers serve to aggregate stressors over large spatial and temporal scales, resulting in widespread effects [6,7,8] and difficulty in attributing causal mechanisms [9,10]. Modeling and historical reconstruction of community compositions prior to human alteration could help managers correctly set and maintain baselines
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