Geology Reports⌕ Search

Geology topics

Peter J. Gogan

Publications and source records attributed to Peter J. Gogan.

16 recordsLinked to original sources
USGS2013

Pregnancy rates in central Yellowstone bison

Plains bison ( Bison b. bison ) centered on Yellowstone National Park are chronically infected with brucellosis ( Brucella abortus ) and culled along the park boundaries to reduce the probability of disease transmission to domestic livestock. We evaluated the relationship between pregnancy rates and age, dressed carcass weight, and serological status for brucellosis among bison culled from the central Yellowstone subpopulation during the winters of 1996&ndash;1997, 2001&ndash;2002, and 2002&ndash;2003. A model with only dressed carcass weight was the best predictor of pregnancy status for all ages with the odds of pregnancy increasing by 1.03 (95% CI&thinsp;=&thinsp;1.02&ndash;1.04) for every 1-kg increase in weight. We found no effect of age or the serological status for brucellosis on pregnancy rates across age classes; however, we did find a positive association between age and pregnancy rates for bison &ge;2 years old. Bison &ge;2 years old had an overall pregnancy rate of 65% with markedly different rates in alternate ages for animals between 3 and 7 years old. Pregnancy rates were 0.50 (95% CI&thinsp;=&thinsp;0.31&ndash;0.69) for brucellosis positive and 0.57 (95% CI&thinsp;=&thinsp;0.34&ndash;0.78) for brucellosis negative 2- and 3-year-olds and 0.74 (95% CI&thinsp;=&thinsp;0.60&ndash;0.85) in brucellosis positive and 0.69 (95% CI&thinsp;=&thinsp;0.49&ndash;0.85) in brucellosis negative bison &ge;4 years old. Only 1 of 21 bison <2 years old was pregnant. Our findings are important to accurately predict the effects of brucellosis on Yellowstone bison population dynamics. We review our results relative to other studies of Yellowstone bison that concluded serological status for brucellosis influences pregnancy rates.

Wyoming↗
USGS2013

Re-introduction of tule elk to Point Reyes National Seashore, California, USA

Tule elk (Cervus elaphus nannodes), a subspecies endemic to California, was historically found in large herds throughout much of central and coastal California. Market hunting during the California Gold Rush decimated these herds, and by 1895, only two to 10 elk remained. This remnant group was protected and served as the source for early relocation efforts (McCullough, 1971). Early efforts were generally unsuccessful but did establish a herd in California’s Owens Valley, outside their historical range, in 1933. The herd grew rapidly and supported six controversial hunts between 1943 and 1969. In an effort to limit hunting, concerned preservationists formed the Committee for the Preservation of Tule Elk in 1960. Public pressure resulted in the California State Legislature passing a law in 1971 that halted hunting until either state-wide numbers reached 2,000, or no further unoccupied elk habitat existed. This law prompted the California Department of Fish and Game to begin reintroducing tule elk throughout their former range. In 1976, the U.S. Congress passed a resolution that concurred with state law and directed federal agencies to make lands available for reintroductions within the subspecies’ historical range. Point Reyes National Seashore was identified as a potential translocation site.

California↗
USGS2012

Genetic population substructure in bison at Yellowstone National Park

The Yellowstone National Park bison herd is 1 of only 2 populations known to have continually persisted on their current landscape since pre-Columbian times. Over the last century, the census size of this herd has fluctuated from around 100 individuals to over 3000 animals. Previous studies involving radiotelemetry, tooth wear, and parturition timing provide evidence of at least 2 distinct groups of bison within Yellowstone National Park. To better understand the biology of Yellowstone bison, we investigated the potential for limited gene flow across this population using multilocus Bayesian clustering analysis. Two genetically distinct and clearly defined subpopulations were identified based on both genotypic diversity and allelic distributions. Genetic cluster assignments were highly correlated with sampling locations for a subgroup of live capture individuals. Furthermore, a comparison of the cluster assignments to the 2 principle winter cull sites revealed critical differences in migration patterns across years. The 2 Yellowstone subpopulations display levels of differentiation that are only slightly less than that between populations which have been geographically and reproductively isolated for over 40 years. The identification of cryptic population subdivision and genetic differentiation of this magnitude highlights the importance of this biological phenomenon in the management of wildlife species.

Journal of Heredity↗
USGS2012

Estimating survival rates with time series of standing age‐structure data

It has long been recognized that age‐structure data contain useful information for assessing the status and dynamics of wildlife populations. For example, age‐specific survival rates can be estimated with just a single sample from the age distribution of a stable, stationary population. For a population that is not stable, age‐specific survival rates can be estimated using techniques such as inverse methods that combine time series of age‐structure data with other demographic data. However, estimation of survival rates using these methods typically requires numerical optimization, a relatively long time series of data, and smoothing or other constraints to provide useful estimates. We developed general models for possibly unstable populations that combine time series of age‐structure data with other demographic data to provide explicit maximum likelihood estimators of age‐specific survival rates with as few as two years of data. As an example, we applied these methods to estimate survival rates for female bison ( Bison bison ) in Yellowstone National Park, USA. This approach provides a simple tool for monitoring survival rates based on age‐structure data.

Ecology↗
USGS2012

Aerial survey estimates of fallow deer abundance

Reliable estimates of the distribution and abundance of an ungulate species is essential prior to establishing and implementing a management program. We used ground surveys to determine distribution and ground and aerial surveys and individually marked deer to estimate the abundance of fallow deer (Dama dama) in north-coastal California. Fallow deer had limited distribution and heterogeneous densities. Estimated post-rut densities across 4 annual surveys ranged from a low of 1.4 (SE=0.2) deer/km 2 to a high of 3.3 (se=0.5) deer/km 2 in a low density stratum and from 49.0 (SE=8.3) deer/km 2 to 111.6 deer/km 2 in a high density stratum. Sightability was positively influenced by the presence of white color-phase deer in a group and group size, and varied between airial and ground-based observers and by density strata. Our findings underscore the utility of double-observer surveys and aerial surveys with individually marked deer, both incorporating covariates to model sightability, to estimate deer abundance.

California↗
USGS2010

Spatial population structure of Yellowstone bison

Increases in Yellowstone National Park, USA, bison ( Bison bison ) numbers and shifts in seasonal distribution have resulted in more frequent movements of bison beyond park boundaries and development of an interagency management plan for the Yellowstone bison population. Implementation of the plan under the adaptive management paradigm requires an understanding of the spatial and temporal structure of the population. We used polythetic agglomerative hierarchical cluster analysis of radiolocations obtained from free-ranging bison to investigate seasonal movements and aggregations. We classified radiolocations into 4 periods: annual, peak rut (15 Jul–15 Sep), extended rut (1 Jun–31 Oct), and winter (1 Nov–31 May). We documented spatial separation of Yellowstone bison into 2 segments, the northern and central herds, during all periods. The estimated year-round exchange rate (4.85–5.83%) of instrumented bison varied with the fusion strategy employed. We did not observe exchange between the 2 segments during the peak rut and it varied during the extended rut (2.15–3.23%). We estimated a winter exchange of 4.85–7.77%. The outcome and effectiveness of management actions directed at Yellowstone bison may be affected by spatial segregation and herd affinity within the population. Reductions based on total population size, but not applied to the entire population, may adversely affect one herd while having little effect on the other. Similarly, management actions targeting a segment of the population may benefit from the spatial segregation exhibited.

Wyoming↗
USGS2010

A simple solar radiation index for wildlife habitat studies

Solar radiation is a potentially important covariate in many wildlife habitat studies, but it is typically addressed only indirectly, using problematic surrogates like aspect or hillshade. We devised a simple solar radiation index (SRI) that combines readily available information about aspect, slope, and latitude. Our SRI is proportional to the amount of extraterrestrial solar radiation theoretically striking an arbitrarily oriented surface during the hour surrounding solar noon on the equinox. Because it derives from first geometric principles and is linearly distributed, SRI offers clear advantages over aspect-based surrogates. The SRI also is superior to hillshade, which we found to be sometimes imprecise and ill-behaved. To illustrate application of our SRI, we assessed niche separation among 3 ungulate species along a single environmental axis, solar radiation, on the northern Yellowstone winter range. We detected no difference between the niches occupied by bighorn sheep ( Ovis canadensis ) and elk ( Cervus elaphus; P = 0.104), but found that mule deer ( Odocoileus hemionus ) tended to use areas receiving more solar radiation than either of the other species ( P < 0.001). Overall, our SRI provides a useful metric that can reduce noise, improve interpretability, and increase parsimony in wildlife habitat models containing a solar radiation component.

Wyoming↗
USGS2009

Survey of ungulate abundance on Santa Rosa Island, Channel Islands National Park, California, March 2009

Reliable estimates of elk (Cervus elaphus) and deer (Odocoileus hemionus) abundance on Santa Rosa Island, Channel Islands National Park, California, are required to assess the success of management actions directed at these species. We conducted a double-observer aerial survey of elk on a large portion of Santa Rosa Island on March 19, 2009. All four persons on the helicopter were treated as observers. We used two analytical approaches: (1) with three capture occasions corresponding to three possible observers, pooling the observations from the two rear-seat observers, and (2) with four capture occasions treating each observer separately. Approach 1 resulted in an estimate of 483 elk in the survey zone with a 95-percent confidence interval of 479 to 524 elk. Approach 2 resulted in an estimate of 489 elk in the survey zone with a 95-percent confidence interval of 471 to 535 elk. Approximately 5 percent of the elk groups that were estimated to have been present in the survey area were not seen by any observer. Fog prevented us from collecting double-observer observations for deer as intended on March 20. However, we did count 434 deer during the double-observer counts of elk on March 19. Both the calculated number of elk and the observed number of deer are minimal estimates of numbers of each ungulate species on Santa Rosa Island as weather conditions precluded us from surveying the entire island.

California↗
USGS2007

Historic distribution and challenges to bison recovery in the northern Chihuahuan Desert

Ecologists and conservationists have long assumed that large grazers, including bison ( Bison bison ), did not occur in post-Pleistocene southwestern North America. This perception has been influential in framing the debate over conservation and land use in the northern Chihuahuan Desert. The lack of an evolutionary history of large grazers is being used to challenge the validity of ranching as a conservation strategy and to limit the protection and reintroduction of bison as a significant component of desert grassland ecosystems. Archeological records and historical accounts from Mexican archives from AD 700 to the 19th century document that the historic range of the bison included northern Mexico and adjoining areas in the United States. The Janos-Hidalgo bison herd, one of the few free-ranging bison herds in North America, has moved between Chihuahua, Mexico, and New Mexico, United States, since at least the 1920s. The persistence of this cross-border bison herd in Chihuahuan Desert grasslands and shrublands demonstrates that the species can persist in desert landscapes. Additional lines of evidence include the existence of grazing-adapted grasslands and the results of experimental studies that document declines in vegetation density and diversity following the removal of large grazers. The Janos-Hidalgo herd was formed with animals from various sources at the turn of the 19th century. Yet the future of the herd is compromised by differing perceptions of the ecological and evolutionary role of bison in the Desert Grasslands of North America. In Mexico they are considered native and are protected by federal law, whereas in New Mexico, they are considered non-native livestock and therefore lack conservation status or federal protection. Evidence written in Spanish of the presence of bison south of the accepted range and evidence from the disciplines of archaeology and history illustrate how differences in language and academic disciplines, in addition to international boundaries, have acted as barriers in shaping comprehensive approaches to conservation. Bison recovery in the region depends on binational cooperation.

Arizona, Chihuahua, Coahuila, Durango, New Mexico,↗
USGS2007

Second chance for the plains bison

Before European settlement the plains bison ( Bison bison bison ) numbered in the tens of millions across most of the temperate region of North America. Within the span of a few decades during the mid- to late-1800s its numbers were reduced by hunting and other factors to a few hundred. The plight of the plains bison led to one of the first major movements in North America to save an endangered species. A few individuals and the American Bison Society rescued the remaining animals. Attempts to hybridize cattle and bison when bison numbers were low resulted in extensive cattle gene introgression in bison. Today, though approximately 500,000 plains bison exist in North America, few are free of cattle gene introgression, 96% are subject to anthropogenic selection for commodity production, and only 4% are in herds managed primarily for conservation purposes. Small herd size, artificial selection, cattle-gene introgression, and other factors threaten the diversity and integrity of the bison genome. In addition, the bison is for all practical purposes ecologically extinct across its former range, with multiple consequences for grassland biodiversity. Urgent measures are needed to conserve the wild bison genome and to restore the ecological role of bison in grassland ecosystems. Socioeconomic trends in the Great Plains, combined with new information about bison conservation needs and new conservation initiatives by both the public and public sectors, have set the stage for significant progress in bison conservation over the next few years.

Biological Conservation↗
USGS2007

Where the buffalo roam: The role of history and genetics in the conservation of bison on U.S. federal lands

As an emblem of the Great Plains, American Indians, and wildlife conservation, the American bison ( Bison bison ) is one of the most visible and well-known of wildlife species in North America (fig. 1, above). Species of the genus Bison originally entered the continent via the Bering land bridge from northern Eurasia in the Illinoian glacial period of the Pleistocene epoch (125,000&ndash;500,000 years ago). Bison are the largest species in North America to have survived the late Pleistocene&ndash;early Holocene megafauna extinction period (around 9,000&ndash;11,000 years ago), but likely experienced a dramatic population reduction triggered by environmental changes and increased human hunting pressures around this time (Dary 1989; McDonald 1981). The modern American bison species ( Bison bison ) emerged and expanded across the grasslands of North America around 4,000&ndash;5,000 years ago (McDonald 1981). As the major grazer of the continent, bison populations ranged from central Mexico to northern Canada and nearly from the east to west coasts ( fig. 2; McDonald 1981), with 25&ndash;40 million bison estimated to have roamed the Great Plains prior to the 19th century (Flores 1991; McHugh 1972; Shaw 1995).

Park Science↗
USGS2004

What limits the Serengeti zebra population?

The populations of the ecologically dominant ungulates in the Serengeti ecosystem (zebra, wildebeest and buffalo) have shown markedly different trends since the 1960s: the two ruminants both irrupted after the elimination of rinderpest in 1960, while the zebras have remained stable. The ruminants are resource limited (though parts of the buffalo population have been limited by poaching since the 1980s). The zebras' resource acquisition tactics should allow them to outcompete the ruminants, but their greater spatial dispersion makes them more available to predators, and it has been suggested that this population is limited by predation. To investigate the mechanisms involved in the population dynamics of Serengeti zebra, we compared population dynamics among the three species using demographic models based on age-class-specific survival and fecundity. The only major difference between zebra and the two ruminants occurred in the first-year survival. We show that wildebeest have a higher reproductive potential than zebra (younger age at first breeding and shorter generation time). Nevertheless, these differences in reproduction cannot account for the observed differences in the population trends between the zebra and the ruminants. On the other hand, among-species differences in first-year survival are great enough to account for the constancy of zebra population size. We conclude that the very low first-year survival of zebra limits this population. We provide new data on predation in the Serengeti and show that, as in other ecosystems, predation rates on zebras are high, so predation could hold the population in a "predator pit". However, lion and hyena feed principally on adult zebras, and further work is required to discover the process involved in the high mortality of foals.

Serengeti↗
USGS2001

Ecological studies of bison in the Greater Yellowstone Area: Development and implementation

Bison (Bison bison) of the Greater Yellowstone Area (GYA) are perhaps best known to the scientific community from the classic study of Meagher (1973) that reviewed their ecological status and management from the time of establishment of Yellowstone National Park in 1872 through the last National Park Service (NPS) removals of bison within the park in 1966. Since cessation of herd reductions in the park, bison numbers within Yellowstone increased (Dobson and Meagher 1996), as did range use (Meagher 1989b), including increased frequency and magnitude of movements beyond the park boundaries in winter (Meagher 1989a; Pac and Frey 1991; Cheville et al. 1998).

Wyoming↗
USGS2001

Control of ungulate numbers in a protected area

Successful long-term control of ungulate numbers within a protected area requires continuous review and refinement of management practices. Insights gained may have application to other sites. We evaluated management objectives and actions to control populations of exotic axis deer (Axis axis) and fallow deer (Dama dama) at Point Reyes National Seashore, California. Using records of numbers of each species culled from 1968 to 1996 and demographic data, we modeled each population's potential response to management actions and to the cessation of control in 1996. These simulations indicated that control measures hold numbers of both populations below ecological carrying capacity (K) and that populations of fallow and axis deer may have reached K within 5 to 13 years of ceasing control, respectively. We also simulated each population's response to removal of actual numbers of males killed but no females and actual numbers of females killed but no males from 1968 to 1996. Removing males only resulted in both populations reaching K. Removing females only led to the extirpation of both populations. Cessation of control activities prior to removal of all females resulted in recovery of both populations. A team of personnel expended an average of 1.75 work-hours/deer to remove 1,182 exotic deer of both species from 1984 to 1994. The work effort to kill each deer increased 2-fold from 1984 to 1994. The work effort required to remove s2 deer/day reached as great as 20 hours/deer. Elimination of the axis deer population is feasible and likely a more cost-effective management alternative than continued population control. Elimination of fallow deer is potentially more difficult but may be more costeffective than continuing control actions indefinitely. We recommend similar assessments of management alternatives to those charged with controlling ungulate numbers in protected areas.

California↗