Pilger T. J.,Kansas State University |
Gido K. B.,Kansas State University |
Propst D. L.,Conservation Services Division
Ecology of Freshwater Fish | Year: 2010
Abstract - The upper Gila River basin is one of the few unimpounded drainage basins west of the Continental Divide, and as such is a stronghold for endemic fishes in the region. Nevertheless, multiple nonindigenous fishes potentially threaten the persistence of native fishes, and little is known of the trophic ecology of either native or nonnative fishes in this system. Gut contents and stable isotopes ( 13C and 15N) were used to identify trophic relationships, trophic niche overlap and evaluate potential interactions among native and nonnative fishes. Both native and nonnative fishes fed across multiple trophic levels. In general, adult native suckers had lower 15N signatures and consumed more algae and detritus than smaller native fish, including juvenile suckers. Adult nonnative smallmouth bass (Micropterus dolomieu), yellow bullhead (Ameiurus natalis) and two species of trout preyed on small-bodied fishes and predaceous aquatic invertebrates leading to significantly higher trophic positions than small and large-bodied native fishes. Thus, the presence of these nonnative fishes extended community food-chain lengths by foraging at higher trophic levels. Although predation on juvenile native fishes might threaten persistence of native fishes, the high degree of omnivory suggests that impacts of nonnative predators may be lessened and dependent on environmental variability. © 2010 John Wiley & Sons A/S.
Novellie P.,Conservation Services Division |
Gaylard A.,Conservation Services Division
Koedoe | Year: 2013
We examined a heavily grazed plant community dominated by creeping grass species with the aim of, (1) determining its response to the exclusion of grazing and (2) its long-term persistence. This plant community was particularly favoured by wild ungulate species that prefer short grasses - blesbok (Damaliscus dorcas phillipsi), springbok (Antidorcas marsupialis) and black wildebeest (Connochaetes gnou). Exclusion of grazing by large herbivores by means of fencing resulted in the virtual disappearance of the creeping grasses and their replacement by tall tufted species. On plots that remained unfenced, the plant species composition was found to be little changed after an interval of more than 20 years. The number large stock unit equivalents (LSU) per ha carried by the plant community was used as a proxy for grazing intensity. Monitored for approximately 2 years at the start of the study, LSU per ha was found to greatly exceed levels recommended for commercial livestock production. This plant community conforms to a recently published definition of a grazing lawn, in that intense grazing promotes palatable, grazing-tolerant grass species. Conservation implications: The positive association between grazers and grazing-tolerant grass species evidently persisted for more than 20 years and there was no evidence of an increase in abundance of unpalatable plant species. Despite the small size of the park, which limited the extent of large herbivore movements, localised heavy grazing did not lead to range degradation. © 2013. The Authors.
Propst D.L.,University of New Mexico |
Gido K.B.,Kansas State University |
Whitney J.E.,Kansas State University |
Gilbert E.I.,Conservation Services Division |
And 6 more authors.
River Research and Applications | Year: 2015
Native fish faunas throughout the American Southwest have declined dramatically in the past century, mainly a consequence of habitat alteration and alien species introductions. We initiated this 6-year study to evaluate the efficacy of mechanical removal of nonnative predaceous rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta, yellow bullhead Ameiurus natalis and smallmouth bass Micropterus dolomieu from an open 4.6-km reach of West Fork Gila River in southwest New Mexico, USA. Removal efforts involved intensive sampling with a 10- to 12-person crew using backpack electrofishers and seines to capture fish over a 4- to 5-day period each year. Additionally, two reference sites were sampled with similar methods to compare temporal changes in species mass in the absence of a removal effort. Results were mixed. Mass of yellow bullhead, rainbow trout and brown trout declined in the removal reach from 2007 through 2012, but there was no change in smallmouth bass. Concurrently, mass of Rainbow trout, yellow bullhead and smallmouth bass did not change at reference sites, but brown trout mass declined, indicating factors other than removal were driving abundance of brown trout. Occurrence of several large flathead catfish Pylodictis olivaris in the removal reach in 2012 changed what would have been a decline in overall nonnative mass to no change over the course of the study. Spikedace Meda fulgida was the only native species positively responding to predator removal. Results of this study suggest that with moderate effort and resources applied systematically, mechanical removal can benefit some native fish species, but movement of problem species from surrounding areas into removal reaches necessitates continued control efforts. Copyright © 2014 John Wiley & Sons, Ltd.