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L. C. Zeigenfuss

Publications and source records attributed to L. C. Zeigenfuss.

7 recordsLinked to original sources
USGS2008

Role of patch size, disease, and movement in rapid extinction of bighorn sheep

The controversy (Berger 1990, 1999; Wehausen 1999) over rapid extinction in bighorn sheep ( Ovis canadensis ) has focused on population size alone as a correlate to persistence time. We report on the persistence and population performance of 24 translocated populations of bighorn sheep. Persistence in these sheep was strongly correlated with larger patch sizes, greater distance to domestic sheep, higher population growth rates, and migratory movements, as well as to larger population sizes. Persistence was also positively correlated with larger average home-range size ( p = 0.058, n = 10 translocated populations) and home-range size of rams ( p = 0.087, n = 8 translocated populations). Greater home-range size and dispersal rates of bighorn sheep were positively correlated to larger patches. We conclude that patch size and thus habitat carrying capacity, not population size per se, is the primary correlate to both population performance and persistence. Because habitat carrying capacity defines the upper limit to population size, clearly the amount of suitable habitat in a patch is ultimately linked to population size. Larger populations (250+ animals) were more likely to recover rapidly to their pre-epizootic survey number following an epizootic ( p = 0.019), although the proportion of the population dying in the epizootic also influenced the probability of recovery ( p = 0.001). Expensive management efforts to restore or increase bighorn sheep populations should focus on large habitat patches located ≥23 km from domestic sheep, and less effort should be expended on populations in isolated, small patches of habitat.

Conservation Biology↗
USGS2002

Influence of trophy hunting and horn size on mating behavior and survivorship of mountain sheep

We conducted a study of the effects of horn sizes and trophy hunting on mating behavior and survival of rams in hunted and unhunted populations of Dall sheep ( Ovis dalli ), Rocky Mountain bighorn ( O. canadensis canadensis ), and desert bighorn ( O. c. nelsoni ) sheep. Mating success was positively correlated with horn size in Dall sheep ( P = 0.03) and Rocky Mountain bighorns ( P = 0.05), but not in the desert bighorn ( P > 0.05) taxa. Group sizes, rams per rut group, and competition between rams were lowest in desert bighorn sheep. There were indications of greater harassment of ewes by young rams in trophy-hunted populations. In hunted populations, compared with unhunted, ewes ran away more often from approaching rams, ewes moved farther away from courting young rams ( P = 0.003), younger rams performed fewer courtship displays ( P = 0.042) and more aggressive displays to ewes, and sheep interacted 27% more of the time. Ram-to-ewe interaction times per individual ewe did not differ for any of the taxa ( P > 0.05), and, apparently as a consequence of this, we found no discernable effects of trophy hunting on survivorship of ewes, ewe fecundity, or recruitment of young ( P > 0.05). There were greater energy expenditures by young rams in the heavily hunted Dall sheep population versus the paired Dall sheep unhunted population, but not in the lightly hunted Rocky Mountain and desert bighorn populations when compared with unhunted populations. This was consistent with evidence for depressed survivorship of rams too young or too small to be hunted (approximately ages 4–6) in the heavily hunted Dall sheep population ( P = 0.0001), but not in the bighorn sheep populations ( P > 0.05).

Journal of Mammalogy↗
USGS2002

Influences of herbivory and water on willow in elk winter range

Elimination of large predators and reduced hunter harvest have led to concerns that an increasing elk ( Cervus elaphus ) population may be adversely affecting vegetation on the low-elevation elk winter range of Rocky Mountain National Park, Colorado, USA. Beaver ( Castor canadensis ) and their impoundments also have declined dramatically (94%) in the same area over the past 50 years coincident with a 20% decline in willow ( Salix spp.) cover. From 1994 to 1998, we studied vegetation production responses of willow communities to elk herbivory and water availability. We estimated willow production by measuring current annual growth of shrubs in 9.3-m2 circular plots, and we measured herbaceous production by clipping vegetation within 0.25-m2 circular plots. Elk herbivory suppressed willow heights, leader lengths, annual production, and herbaceous productivity of willow communities. Water impoundment had a positive effect on herbaceous plant production, but little effect on shrubs, possibly because water tables were naturally high on the study sites even without beaver dams. Nevertheless, the winter range environment previously included more riparian willow habitat because of more stream area (47-69%) due to larger beaver populations. Elk herbivory appears to be the dominant force determining vegetation productivity in willow sites, but the effects may be exacerbated by lowered water tables. Fewer elk or protection from browsing, and water enhancement for <10 years along with management to encourage elk movement away from willow communities, could possibly work as strategies to reestablish sustainable willow communities.

Colorado↗
USGS2002

Sustainability of vegetation communities grazed by elk in Rocky Mountain National Park

Current management of the worlds' grazing lands in either based on changes in plant species composition or on other management evaluation programs that emphasize changes in net aboveground production. Management is based solely on changes in aboveground production has been criticized as too limited in view, because it ignores root production, nitrogen pools, nutrient processes, and the long-term sustainability of the ecosystem. The purpose of this study was to compare the effects of elk ( Cervus elaphus ) grazing on aboveground production, internal nitrogen (N) fluxes, N pools and inputs, and elk nutrient transfers across the landscape in different vegetation types in Rocky Mountain National Park (RMNP), Colorado. Nitrogen processes and possibly N pools were significantly reduced in the willow community, but not in the upland grass/shrub community. Nitrogen mineralization rates were lower in grazed versus ungrazed short willow sites (P = 0.07; n = 4 sites), as were nitrate (NO3) pools (P = 0.10), but not in tall willow sites (P > 1.10 n = 4 sites) after 4 years. There was about half the annual N inputs to the soil surface in grazed willow sites (5.79g N/m 2 /yr = annual herbaceous biomass a?? offtake + litterfall + elk urine and feces) compared to ungrazed sites (9.66 g N/m 2 /yr = annual herbaceous biomass + litterfall), suggesting elk herbivory and movement led to a net loss of N in the willow vegetation type. Elk substantially reduced the annual growth of willows (Salix spp.) by 98% after 35 years and 66% after 4 years of treatment. Thus, height and canopy and N yield of willows were reduced as well as willow litter biomass (65 g/m2/yr in ungrazed versus 33 g/m2/yr in grazed), and N yield of willows was 64% less in grazed plots. Elk grazing had no significant effect on other soil N pools (NH4) or litter decomposition rates in either of the two willow types, nor on any nitrogen process rates or pools in the upland grass/shrub type (P > 0.10). Nitrogen concentrations in plant tissue were not influenced for the most part by elk grazing (increased N concentration found in only 4 of 13 species). Elk apparently also transported N away from aspen at an even higher rate (N inputs were 1.65 g N/m2/yr in grazed sites vs. 3.79 g N/m 2 /yr ungrazed). CENTURY modeling supported these observations. This soil N model predicted almost no change (0.5$ - 2% less) in N or carbon (C) pools in 50 years in the upland grass/shrub vegetation type, but greater losses in the willow type. If elk population levels were increased to carrying capacity in the ecosystem (about 25% more consumption) projected losses after 50 years were greater, but still <4% for soil C and 1% for spoil N in the upland type, and 6% for soil C and 2% for soil N in the willow type. Total shrub C was projected to decline 10% in 50 years in the willow type at current elk densities. We recommend conservative management of elk numbers and grazing until additional years of measures are gathered on the lower mineralization rates in the short willow type and until the projected declines in N pools can be verified.

Report↗
USGS2001

Test of a modified habitat suitability model for bighorn sheep

Translocation of bighorn sheep ( Ovis canadensis ) is time, labor, and cost intensive and, therefore, high levels of success are desirable. We tested a widely used habitat suitability model against translocation success and then modified it to include additional factors which improved its usefulness in predicting appropriate translocation sites. The modified Smith habitat suitability model for bighorn sheep was 64% accurate in predicting success or failure of 32 translocations of bighorn sheep into the Rocky Mountains, Colorado Plateau desert, and prairie-badlands of six states. We had sheep location data for 13 populations, and the modified habitat model predicted the areas used by bighorn sheep with greater than 90% accuracy in eight populations, greater than 55% accuracy in four populations, and less than 55% accuracy in one population. Translocations were more successful when sheep were placed into discrete habitat patches containing a high proportion of lambing period habitat (>10% of suitable habitat, p = 0.05), where animals had a migratory tendency ( p = 0.02), no contact with domestic sheep ( p = 0.02), or greater distance to domestic sheep (>23 km, p = 0.02). Rate of population growth was best predicted by area of lambing period habitat, potential area of winter range, and distance to domestic sheep. We retested the model using these refined criteria and the refined model then predicted success or failure of these 32 translocated populations with 82% accuracy.

Restoration Ecology↗
USGS2001

Population growth, fecundity, and survivorship in recovering populations of bighorn sheep

The single greatest obstacle to the restoration of large, healthy, populations of bighorn sheep ( Ovis canadensis ) in the western United States is epizootic outbreaks of bronchopneumonia that may kill 20–100% of the animals in populations. Although the species is capable of rapid initial growth rates following restoration into new habitat (λ = 1.23–1.30 have been observed), these rates of increase are typical only a few years following the release of a population, and then most populations either decline to extirpation or remnant status (<30 animals) or remain at <100 individuals. We studied the fecundity and survivorship of three increasing, and three declining and suspected diseased, populations of bighorn sheep (the latter were subjected to outbreaks of bronchopneumonia) located in or near several large national parks in the western United States from 1991 to 1996. Titers verified both population categories were exposed to the bacteria Pasteurella haemolytica serotypes 3; 4; and 3, 4, 10; Moraxella sp., and parainfluenza-3 and bluetongue (BT) viruses. Pregnancy rates of adult ewes were not different in increasing or decreasing populations (pooled rate = 0.93; p = 0.57), but pregnancy rates of yearlings were lower (0.00 for decreasing vs. 0.33 for increasing populations), initial production of lambs and annual recruitment of lambs was lower (0.14, decreasing vs. 0.66, p < 0.05). Adult survival was lower during the first year of an epizootic, 0.62, in one population, but recovered to 0.85 by the second and subsequent years. Survival of adult rams was variable in diseased populations; in two populations rams appeared to be disproportionately impacted, but in a third population rams survived better during the epizootic. In all the increasing park (unhunted) populations, adult ram survival (0.94 ± 0.01) was higher than adult ewe survival (0.89 ± 0.02) ( p = 0.10), in contrast to published information from hunted populations where ram survival was lower. Removal of about 20% of one population for restorations severely impacted one declining population. Removals of 12–20% appeared to be excessive and were not readily compensated for in the Canyonlands National Park desert bighorn population. Disease was a significant limiting factor to restoration of bighorn sheep in the study areas; six of 11 total recovering populations we monitored closely were negatively influenced by apparent disease at some time during our observations.

Restoration Ecology↗