We examined allelic variation at nuclear-encoded microsatellites and sequences of mitochondrial (mt)DNA in 10 geographic samples representing 6 nominal species of the cyprinid genus Dionda. Species of Dionda are found in springs and spring-fed headwaters in the southwestern United States and Mexico and are of particular interest to conservation and management, in part because of their limited distribution and habitat specificity, and in part as indicator species of habitat quality. All 10 samples examined appear to be discrete, demographically independent populations, with greater observed F_ST values between or among samples within species (0.123–0.280) than threshold values above which demographic independence is indicated. All 10 exhibited microsatellite and mtDNA variation comparable to or lower than that found in other cyprinids considered to be threatened or endangered; across microsatellites, average number of alleles across populations ranged from of 2.09 to 9.76, allelic richness from 2.24 to 8.45, and gene diversity from 0.0211 to 0.606; for mtDNA, the number of haplotypes across populations ranged from 1 to 14. Estimates of historical and present-day genetic demography indicated that all 10 populations have experienced order-of-magnitude declines in effective population size, with lower bounds of time intervals for the declines in 9 of the populations ranging from 6 to 65 years. Estimates of average long-term effective population size (536 in Dionda argentosa from San Felipe Creek to 2335 in D. texensis) and effective number of breeders (22 in D. flavipinnis from Fessenden Spring to 555 in D. diaboli from Devils River) also indicated recent declines in effective size, and at least 5 of the populations appear to have undergone recent, severe bottlenecks (mean M_c range 0.806–0.848, P value range 0.000–0.0350). The observation that all 10 populations are demographically independent indicates that local extirpations likely would not be replaced by new migrants and that loss of any of the populations would represent loss of a unique genetic entity. Conservation recommendations for each of the populations are briefly discussed.

Vegetation surveys at Zion National Park (Zion), Utah, have contributed to our understanding of plant community patterns and their relationship to environmental factors. Previous authors used vegetation plot data to characterize vegetation types at Zion following conventional procedures that emphasize spatial discreteness and dominant species. We developed and applied an alternative approach for community characterization that emphasizes nondiscrete presence-absence patterns and is compatible with the individualistic concept. We reanalyzed existing plot data from Zion using coalition clustering, an algorithm that identifies groups of positively-associated species referred to as coalition groups. Each species and plot in the data set was linked to each coalition group via an “affinity” value obtained through weighted averaging. Affinity values were used to characterize environmental affinities of coalition groups through regression tree modeling and predictive mapping. We also identified species that frequently co-occurred with coalition groups (affiliate species) and those that frequently co-occurred with high cover (dominant-affiliates), viewing these as alternatives to conventional prevalent and dominant species. Following this approach, we identified 10 coalition groups at Zion that overlapped compositionally and spatially to differing degrees. Mesic environments on a gradient from low-elevation riparian zones through mid-elevation narrow canyons to high-elevation plateaus were represented by 3 overlapping groups. Two groups occupying slickrock and sand environments were detected on the Navajo Sandstone, as well as 2 on mesa tops above it. At lower elevations, 3 intergrading xeric coalition groups were distinguished. When previously classified associations of the National Vegetation Classification were clustered based on shared affinities to coalition groups, the arrangement differed from existing classification schemes but was environmentally interpretable. Although these patterns are contingent on conditions at the time of data collection, they provide a baseline that could be used for evaluating and predicting plant community change in the park. With proper attention to sampling and analysis issues, our community characterization approach could be applied in other settings as an alternative or supplement to conventional vegetation classification.