The occurrence of fish species may be strongly influenced by a stream's thermal regime (magnitude, frequency, variation, and timing). For instance, magnitude and frequency provide information about sublethal temperatures, variability in temperature can affect behavioral thermoregulation and bioenergetics, and timing of thermal events may cue life history events, such as spawning and migration. We explored the relationship between thermal regimes and the occurrences of native Bull Trout Salvelinus confluentus and nonnative Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta across 87 sites in the upper Klamath River basin, Oregon. Our objectives were to associate descriptors of the thermal regime with trout occurrence, predict the probability of Bull Trout occurrence, and estimate upper thermal tolerances of the trout species. We found that each species was associated with a different suite of thermal regime descriptors. Bull Trout were present at sites that were cooler, had fewer high‐temperature events, had less variability, and took longer to warm. Brook Trout were also observed at cooler sites with fewer high‐temperature events, but the sites were more variable and Brook Trout occurrence was not associated with a timing descriptor. In contrast, Brown Trout were present at sites that were warmer and reached higher temperatures faster, but they were not associated with frequency or variability descriptors. Among the descriptors considered, magnitude (specifically June degree‐days) was the most important in predicting the probability of Bull Trout occurrence, and model predictions were strengthened by including Brook Trout occurrence. Last, all three trout species exhibited contrasting patterns of tolerating longer exposures to lower temperatures. Tolerance limits for Bull Trout were lower than those for Brook Trout and Brown Trout, with contrasts especially evident for thermal maxima. Our results confirm the value of exploring a suite of thermal regime descriptors for understanding the distribution and occurrence of fishes. Moreover, these descriptors and their relationships to fish should be considered with future changes in land use, water use, or climate. Received March 4, 2016; accepted July 27, 2016 Published online October 11, 2016
Mottled ducks Anas fulvigula are nonmigratory and primarily depend on habitats associated with coastal marshes of the Gulf Coast for their entire life cycle. Much of remaining available coastal marsh habitats of the Texas Gulf Coast are managed by state and federal agencies. The Texas Gulf Coast breeding population of mottled ducks has recently declined dramatically. To aid in development of management plans for breeding mottled ducks, we estimated the number of potential pair ponds available on the Texas Chenier Plain National Wildlife Refuge Complex relative to marsh type (fresh, intermediate, brackish, and saline), estimated occupancy, compared habitats of used and unused pair ponds, and evaluated pair pond selection relative to marsh type during spring 2004 and 2005. Greater than 18,000 ponds were recorded in >22,400 ha of coastal marsh with >74% of potential pair ponds in the intermediate marsh type. Average pond size of 425 randomly selected ponds across marsh types was 0.09 ha. Pond occupancy was estimated as 1.3% and 2.5% in 2004 and 2005, respectively, in 634 ponds surveyed for presence of mottled duck pairs. Mottled ducks selected for ponds in fresh marsh with short surrounding vegetation associated with recent cattle grazing, but avoided recently (<3 mo prior) burned areas. Pond area was greater with shallower water depth for used compared to unused ponds. The presence and coverage of submergent and emergent vegetation did not influence use of pair ponds by mottled ducks. Development of breeding habitat (pair ponds, nesting cover, brood habitat) in fresh marsh will benefit mottled ducks. Our results indicate development of breeding habitat on the Texas Gulf Coast, and vegetation management using cattle grazing timed for disturbance in fresh marsh during mid- to late winter and early spring will further attract breeding mottled ducks.
Recent studies have examined the effects oflivestock grazing, agriculture, and humanhabitation on nest predation and brood parasitismin riparian areas in the western United States.However, we know little about factors influencingnest success in riparian areas lacking suchanthropogenic influences, in part because theinfluences are so pervasive. We studied riparianbird communities in a 115 000 hawildlife refuge where livestock grazing wasdiscontinued >10 years ago, and which haslittle nearby agriculture or human habitation. Wemonitored nests on 24 aspen (Populustremuloides) and 10 willow(Salixspp.) plots. Brood parasitism rates weresubstantially lower than at other western sites anddid not differ between aspen and willow habitats.Nest success in aspen was relatively high comparedto that reported for other western sites and higherthan in willow. Predators may have been able tofind nests more efficiently in willow than in aspenbecause territory densities were higher in willow(40 versus 30 pairs per ha,respectively), because willow had lessstructural heterogeneity, or both. We did not findstrong evidence that nest success was influenced byaspen patch size or distance to riparian edge,indicating that even small aspen patches providevaluable nesting habitat. Weather was an importantcause of nest failure, particularly at higherelevations during late-spring snowstorms. Ourresults indicate that riparian areas without majoranthropogenic impacts, especially aspen stands,constitute high-quality breeding habitat andwarrant conservation focus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.