Michael R. Bower

An introduced and a native vertebrate hybridize to form a genetic bridge to a second native species

The genetic impacts of hybridization between native and introduced species are of considerable conservation concern, while the possibility of reticulate evolution affects our basic understanding of how species arise and shapes how we use genetic data to understand evolutionary diversification. By using mitochondrial NADH dehydrogenase subunit 2 (ND2) sequences and 467 amplified fragment-length polymorphism nuclear DNA markers, we show that the introduced white sucker (Catostomus commersoni) has hybridized with two species native to the Colorado River Basin—the flannelmouth sucker (Catostomus latipinnis) and the bluehead sucker (Catostomus discobolus). Hybrids between the flannelmouth sucker and white sucker have facilitated introgression between the two native species, previously isolated by reproductive barriers, such that individuals exist with contributions from all three genomes. Most hybrids had the mitochondrial haplotype of the introduced white sucker, emphasizing its pivotal role in this three-way hybridization. Our findings highlight how introduced species can threaten the genetic integrity of not only one species but also multiple previously reproductively isolated species. Furthermore, this complex three-way reticulate (as opposed to strictly bifurcating) evolution suggests that seeking examples in other vertebrate systems might be productive. Although the present study involved an introduced species, similar patterns of hybridization could result from natural processes, including stream capture or geological formations (e.g., the Bering land bridge).

Influences of Fragmentation on Three Species of Native Warmwater Fishes in a Colorado River Basin Headwater Stream System, Wyoming

Abstract We investigated the effects of constructed instream structures on movements and demographics of bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta in the upstream portion of Muddy Creek, an isolated headwater stream system in the upper Colorado River basin of Wyoming. Our objectives were to (1) evaluate upstream and downstream movements of these three native species past a small dam built to divert irrigation water from the stream and a barrier constructed to prevent upstream movements of nonnative salmonids and (2) describe population characteristics in stream segments created by these structures. Our results indicated that upstream and downstream movements of the three target fishes were common. Fish of all three species moved frequently downstream over both structures, displayed some upstream movements over the irrigation diversion dam, and did not move upstream over the fish barrier. Spawning migrations by some fish into an intermittent...

Precision of Hard Structures Used to Estimate Age of Riverine Catostomids and Cyprinids in the Upper Colorado River Basin

Abstract Understanding the population dynamics of native and nonnative fishes is critical for guiding and evaluating management activities, but obtaining information on population dynamics is often dependent on identifying structures that provide precise estimates of age. We examined age estimation using various hard structures for native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta, and nonnative white suckers C. commersonii, creek chub Semotilus atromaculatus, white sucker × bluehead sucker hybrids, and white sucker × flannelmouth sucker hybrids in a small headwater stream of the upper Colorado River basin (UCRB) in Wyoming. We evaluated between-reader precision (i.e., between two readers) and agreement of otolith age estimates with estimates from scales, fin rays, cleithra, and opercular bones. Exact agreement between readers was highest for otoliths (66–96% among species) and fin rays (61–92%) and lowest for opercles (25–69%), cleithra (21...

Summer food habits and trophic overlap of roundtail chub and creek chub in Muddy Creek, Wyoming

Abstract Native fishes of the Upper Colorado River Basin have experienced substantial declines in abundance and distribution, and are extirpated from most of Wyoming. Muddy Creek, in south-central Wyoming (Little Snake River watershed), contains sympatric populations of native roundtail chub (Gila robusta), bluehead sucker, (Catostomus discobolus), and flannelmouth sucker (C. latipinnis), and represents an area of high conservation concern because it is the only area known to have sympatric populations of all 3 species in Wyoming. However, introduced creek chub (Semotilus atromaculatus) are abundant and might have a negative influence on native fishes. We assessed summer food habits of roundtail chub and creek chub to provide information on the ecology of each species and obtain insight on potential trophic overlap. Roundtail chub and creek chub seemed to be opportunistic generalists that consumed a diverse array of food items. Stomach contents of both species were dominated by plant material, aquatic and terrestrial insects, and fishes, but also included gastropods and mussels. Stomach contents were similar between species, indicating high trophic overlap. No length-related patterns in diet were observed for either species. These results suggest that creek chubs have the potential to adversely influence the roundtail chub population through competition for food and the native fish assemblage through predation.

Random versus Fixed-Site Sampling When Monitoring Relative Abundance of Fishes in Headwater Streams of the Upper Colorado River Basin

Abstract Native fishes of the upper Colorado River basin (UCRB) have declined in distribution and abundance due to habitat degradation and interactions with nonnative fishes. Consequently, monitoring populations of both native and nonnative fishes is important for conservation of native species. We used data collected from Muddy Creek, Wyoming (2003–2004), to compare sample size estimates using a random and a fixed-site sampling design to monitor changes in catch per unit effort (CPUE) of native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, roundtail chub Gila robusta, and speckled dace Rhinichthys osculus, as well as nonnative creek chub Semotilus atromaculatus and white suckers C. commersonii. When one-pass backpack electrofishing was used, detection of 10% or 25% changes in CPUE (fish/100 m) at 60% statistical power required 50–1,000 randomly sampled reaches among species regardless of sampling design. However, use of a fixed-site sampling design with 25–50 reaches greatly...

Habitat Features Affect Bluehead Sucker, Flannelmouth Sucker, and Roundtail Chub across a Headwater Tributary System in the Colorado River Basin

ABSTRACT We assessed the distributions of three species of conservation concern, bluehead sucker (Catostomus discobolus), flannelmouth sucker (Catostomus latipinnis), and roundtail chub (Gila robusta), relative to habitat features across a headwater tributary system of the Colorado River basin in Wyoming. We studied the upper Muddy Creek watershed, Carbon County, portions of which experience intermittent flows during late summer and early fall. Fish and habitat were sampled from 57 randomly-selected, 200-m reaches and 416 habitat units (i.e., pools, glides, or runs) during the summer and fall of 2003 and 2004. Among reaches, the occurrences of adults and juveniles of all three species were positively related to mean wetted width and the surface area of pool habitat, and the occurrences of adult bluehead sucker and roundtail chub were also positively related to the abundance of rock substrate. Only juvenile bluehead sucker appeared to be negatively influenced by the proportion of a reach that was dry at the time of sampling. Within individual pools, glides, and runs, the occurrences of adults and juveniles of all three species were positively related to surface area and maximum depth, and occurrences of bluehead sucker and flannelmouth sucker juveniles were more probable in pools than in glides or runs.

An integrated data model to estimate spatiotemporal occupancy, abundance, and colonization dynamics

Ecological invasions and colonizations occur dynamically through space and time. Estimating the distribution and abundance of colonizing species is critical for efficient management or conservation. We describe a statistical framework for simultaneously estimating spatiotemporal occupancy and abundance dynamics of a colonizing species. Our method accounts for several issues that are common when modeling spatiotemporal ecological data including multiple levels of detection probability, multiple data sources, and computational limitations that occur when making fine-scale inference over a large spatiotemporal domain. We apply the model to estimate the colonization dynamics of sea otters (Enhydra lutris) in Glacier Bay, in southeastern Alaska.

Morphometric and Meristic Differences among Bluehead Suckers, Flannelmouth Suckers, White Suckers, and Their Hybrids: Tools for the Management of Native Species in the Upper Colorado River Basin

Abstract Hybridization with nonnative fishes is a major factor influencing the status of native catostomids in the Colorado River basin. In Wyoming, hybridization with nonnative white suckers Catostomus commersonii is a particular concern in the conservation of native bluehead suckers C. discobolus and flannelmouth suckers C. latipinnis. The purpose of this study was to describe the meristic and morphometric characteristics of bluehead suckers, flannelmouth suckers, white suckers, and their hybrids from Muddy Creek, Wyoming, for which genotypic data were available to verify the classification of individual fish as pure species or hybrids. We also sought to develop discriminant function models that can be used in the field. Bluehead suckers and flannelmouth suckers had more lateral line scales, shorter and narrower heads, and narrower caudal peduncles than white suckers. Bluehead suckers and bluehead sucker × white sucker hybrids had a cartilaginous biting ridge in their mouth. Important characteristics fo...

Spatial Patterns of Fish Assemblage Structure in a Tributary System of the Upper Colorado River Basin

ABSTRACT This study was conducted to describe the distributions of both native and nonnative fishes and to identify spatial patterns in fish assemblage structure of Muddy Creek in the upper Colorado River basin of Wyoming using data collected from 77 reaches during 1999–2004. Fish assemblages in high-elevation reaches were characterized by brook trout (Salvelinus fontinalis) and represented a coldwater faunal zone. Reaches at lower elevations were characterized by warmwater fish species. The upper segment of the warmwater faunal zone contained four native (i.e., bluehead sucker [Catostornus discobolus], flannelmouth sucker [C. latipinnis], speckled dace [Rhinichthys osculus], roundtail chub [Gila robusta]) and two nonnative (i.e., white sucker [C. commersoni] and creek chub [Semotilus atromaculatus]) species. The lower segment of the warmwater faunal zone included species present in upstream segments and three additional nonnative species (i.e., common carp [Cyprinus carpio], redside shiner [Richardsonius baleatus], and fathead minnow [Pimephales promelas]). Differences in fish assemblage structure between coldwater and warmwater faunal zones were likely due to physiological constraints of species adapted for either coldwater or warmwater habitats. Changes in fish assemblages over the warmwater faunal zone are due to introduction and naturalization of nonnative fishes and anthropogenic barriers preventing upstream movements and colonization by some of these species.

Estimating occupancy and abundance using aerial images with imperfect detection

Summary 1.Species distribution and abundance are critical population characteristics for efficient management, conservation, and ecological insight. Point process models are a powerful tool for modeling distribution and abundance, and can incorporate many data types, including count data, presence-absence data, and presence-only data. Aerial photographic images are a natural tool for collecting data to fit point process models, but aerial images do not always capture all animals that are present at a site. Methods for estimating detection probability for aerial surveys usually include collecting auxiliary data to estimate the proportion of time animals are available to be detected. 2.We developed an approach for fitting point process models using an N-mixture model framework to estimate detection probability for aerial occupancy and abundance surveys. Our method uses multiple aerial images taken of animals at the same spatial location to provide temporal replication of sample sites. The intersection of the images provide multiple counts of individuals at different times. We examined this approach using both simulated and real data of sea otters (Enhydra lutris kenyoni) in Glacier Bay National Park, southeastern Alaska. 3.Using our proposed methods, we estimated detection probability of sea otters to be 0.76, the same as visual aerial surveys that have been used in the past. Further, simulations demonstrated that our approach is a promising tool for estimating occupancy, abundance, and detection probability from aerial photographic surveys. 4.Our methods can be readily extended to data collected using unmanned aerial vehicles, as technology and regulations permit. The generality of our methods for other aerial surveys depends on how well surveys can be designed to meet the assumptions of N-mixture models. This article is protected by copyright. All rights reserved.