No abstract

No abstract

No abstract

Reference criteria are needed for wetland monitoring and assessment programs. We used field-collected vegetation data from non-forested wetland sites in the south-central United States to establish preliminary criteria for identifying reference-quality wetlands in future surveys. Our analysis included three parts: (1) preliminary reference verification and metric ranking using boxplots and standardized effect size, (2) updating the putative reference sample and metric selection using Test Site Analysis, and (3) establishing reference criteria from best-metric confidence intervals and indicator species combinations. The Floristic Quality Assessment Index most clearly distinguished the reference wetlands; an index value of at least 20 is recommended for future reference designations in the study region. Other potential reference criteria include a maximum of 3-5 % bare ground in the 100 m buffer, a moderately sensitive species assemblage (mean conservatism>5.0), a small percentage (<10 %) of tolerant species (coefficient of conservatism≤2), and high native richness (>22 species). Five single species, four pairs, and one triplet combination were extracted as potential indicators of reference sites from 70,375 combinations of 75 candidate species, offering an efficient alternative to sampling entire vegetation communities. The analysis framework in this case study could be useful for similar projects in other regions.

Summary Species occurrences have multiple ecological states that may strongly influence community analysis and inference. This may be especially true in freshwater systems where many animals have complex life cycles with adult dispersal and juvenile resident stages. The effects of ecological state variation on standard empirical approaches are largely unknown. Here, we analysed the effects of natal resident versus non‐natal immigrant species occurrence on community‐level environmental gradient modelling and spatial–environmental hypothesis testing using adult dragonflies and damselflies as model taxa. Resident and total (resident + immigrant) occurrences of these taxa responded to different sets of environmental variables and resident occurrences reduced model selection uncertainty in 75% of test cases. Effects of environmental gradients, spatial gradients or both were observed in residents but not immigrants, and supported predictions of dispersal limitation and niche‐based species sorting often implicated for structuring freshwater communities. These results indicate that resident‐only analysis of the dispersal stage should improve multi‐model inference and detection of spatial–environmental effects in freshwater community ecology. The species resident–immigrant dichotomy neglects population dynamics and individual variation yet apparently marks an ecologically significant boundary that scales up to influence community‐level occurrence patterns.