Geology topics

David D. Gustine

Publications and source records attributed to David D. Gustine.

26 records · Page 2Linked to original sources

USGS2014

Isotopic nitrogen in fecal fiber as an indicator of winter diet in caribou and muskoxen

RATIONALE: The ratios of stable nitrogen isotopes (δ 15 N values) in excreta have been used to examine aspects of trophic and nutritional ecology across taxa. Nitrogen fractions in feces of herbivores include endogenous (e.g., sloughed intestinal cells, unresorbed digestive secretions, and microbial debris) and dietary sources. For animals such as large herbivores, that have diets and feces with high concentrations of indigestible ﬁber, endogenous 15 N may constrain the use of fecal δ 15 N values to estimate dietary δ 15 N values and reconstruct diets. METHODS: We compared two techniques (detergent and detergent-free) to isolate fractions of plant ﬁbers in the forages of caribou ( Rangifer tarandus ) and muskoxen ( Ovibos moschatus ); estimated the discrimination factors between the δ 15 N values of fecal ﬁber residues and of the diets of captive animals; and used the more effective isotopic tracer of dietary δ 15 N values to examine the relationships between the δ 15 N values of fecal residues and diet composition in several populations of wild caribou and muskoxen throughout North America in winter. RESULTS: The detergent-based approach contaminated the fractions of plant ﬁbers in forages and feces with 14 N, whereas the detergent-free method was a good proxy to estimate δ 15 N values of plant ﬁbers (r 2 = 0.92) and provided a better estimate of the fecal-ﬁber to diet discrimination factor for both species (caribou = 3.6‰; muskoxen = 2.8‰). In wild populations, the δ 15 N values of fecal ﬁbers reﬂected diet composition in muskoxen (adjusted R 2 = 0.43) but not caribou (adjusted R 2 = 0.06). CONCLUSIONS: Contamination from detergent residues prohibited the use of detergent extraction in isolating forage 15 N from endogenous 15 N in the feces of herbivores. Although δ 15 N values in fecal ﬁbers can be used to track dietary δ 15 N values in wild herbivores, discrimination between fecal extracts and diet may vary with the contribution of endogenous nitrogen (N), and, therefore, residual endogenous 15 N in feces may limit dietary reconstructions from fecal δ 15 N values for some large herbivores.

Alaska↗

USGS2014

Capturing migration phenology of terrestrial wildlife using camera traps

Remote photography, using camera traps, can be an effective and noninvasive tool for capturing the migration phenology of terrestrial wildlife. We deployed 14 digital cameras along a 104-kilometer longitudinal transect to record the spring migrations of caribou ( Rangifer tarandus ) and ptarmigan ( Lagopus spp.) in the Alaskan Arctic. The cameras recorded images at 15-minute intervals, producing approximately 40,000 images, including 6685 caribou observations and 5329 ptarmigan observations. The northward caribou migration was evident because the median caribou observation (i.e., herd median) occurred later with increasing latitude; average caribou migration speed also increased with latitude (r 2 = .91). Except at the northernmost latitude, a northward ptarmigan migration was similarly evident (r 2 = .93). Future applications of this method could be used to examine the conditions proximate to animal movement, such as habitat or snow cover, that may influence migration phenology.

Alaska↗

USGS2014

Changing Arctic ecosystems: resilience of caribou to climatic shifts in the Arctic

The U.S. Geological Survey (USGS) Changing Arctic Ecosystems (CAE) initiative strives to inform key resource management decisions for Arctic Alaska by providing scientific information and forecasts for current and future ecosystem response to a warming climate. Over the past 5 years, a focal area for the USGS CAE initiative has been the North Slope of Alaska. This region has experienced a warming trend over the past 60 years, yet the rate of change has been varied across the North Slope, leading scientists to question the future response and resilience of wildlife populations, such as caribou ( Rangifer tarandus ), that rely on tundra habitats for forage. Future changes in temperature and precipitation to coastal wet sedge and upland low shrub tundra are expected, with unknown consequences for caribou that rely on these plant communities for food. Understanding how future environmental change may affect caribou migration, nutrition, and reproduction is a focal question being addressed by the USGS CAE research. Results will inform management agencies in Alaska and people that rely on caribou for food.

Alaska↗

USGS2014

Historical and contemporary imagery to assess ecosystem change on the Arctic coastal plain of northern Alaska

The Arctic Coastal Plain of northern Alaska is a complex landscape of lakes, streams, and wetlands scattered across low-relief tundra that is underlain by permafrost. This region of the Arctic has experienced a warming trend over the past three decades leading to thawing of on-shore permafrost and the disappearance of sea ice at unprecedented rates. The U.S. Geological Survey’s (USGS) Changing Arctic Ecosystems (CAE) research initiative was developed to investigate and forecast these rapid changes in the physical environment of the Arctic, and the associated changes to wildlife populations, in order to inform key management decisions by the U.S. Department of the Interior and other agencies. Forecasting future wildlife responses to changes in the Arctic can benefit greatly from historical records that inform what changes have already occurred. Several Arctic wildlife and plant species have already responded to climatic and physical changes to the Arctic Coastal Plain of northern Alaska. Thus, we located historical aerial imagery to improve our understanding of recent habitat changes and the associated response to such changes by wildlife populations. In this report, we describe and make available a set of 61 georectified aerial images of the Arctic Coastal Plain (taken from 1948 to 2010) that were obtained by the USGS to inform research objectives of the USGS CAE Initiative. Here, we describe the origins, metadata, and public availability of these images that were obtained within four main study areas on the Arctic Coastal Plain: Teshekpuk Lake Special Area, Chipp River, the Colville River Delta, and locations along the Dalton Highway Corridor between the Brooks Range and Deadhorse. We also provide general descriptions of observable changes to the geomorphology of landscapes that are apparent by comparing historical and contemporary images. These landscape changes include altered river corridors, lake drying, coastal erosion, and new vegetation communities. All original and georectified images and metadata are available through the USGS Alaska Science Center Portal (search under ‘Project Name’ using title of this report) or by contacting ascweb@usgs.gov .

Alaska↗

USGS2012

Diversity of nitrogen isotopes and protein status in caribou: implications for monitoring northern ungulates

Nutritional condition is an important determinant of productivity and survival in caribou (Rangifer tarandus). We used samples of excreta (n = 1,150) to estimate diet composition from microhistology and 2 isotopic proxies of protein status for 2 ecotypes of caribou in 4 herds in late winter (2006–2008). Isotopes of nitrogen (δ 15 N in parts per thousand [‰]) from excreta samples (urea, diet, and body N) were used to estimate indexes of protein status: the proportion of urea N derived from body N (p-UN) and the difference between the δ15N of the body and urinary urea (Δbody-urea). We examined dietary and terrain characteristics, δ 15 N, p-UN, and Δ body-urea by ecotype, herd, year, and foraging site. Multiple regression and an information-theoretic approach were used to evaluate correlates of protein status at each foraging site. The dietary and terrain characteristics of foraging sites did not vary by ecotype or herd (P > 0.108); diets were dominated by lichens (68% ± 14.1% SD). The δ 15 N of urea, diet, body N, p-UN, and Δ body-urea varied among foraging sites within each herd (P < 0.001). Although highly variable, the δ 15 N of urinary urea was typically low (−4.68‰ ± 2.67‰ SD). Dietary N also had low δ 15 N (−4.18‰ ± 0.92‰ SD), whereas body N was generally heavier in 15 N (2.20‰ ± 1.56‰ SD) than urinary urea or the diet. Both measures of protein status were similarly diverse between ecotypes and among herds, which limited their applicability to monitor protein status at the population level. Although we observed limitations to interpreting estimates of p-UN from highly vagile ungulates, the Δbody-urea may prove to be a useful index of protein status at smaller spatial and temporal scales. Indeed, a portion of the observed variance (r 2 = 0.26) in Δbody-urea at each foraging site was explained by the proportion of shrubs in the winter diet. There remains potential in using δ 15 N in excreta as a noninvasive tool for evaluating protein status in northern ungulates; however, considerable analytical and sampling challenges remain for applying these isotopic approaches at large scales.

Alaska↗

USGS2012

Changing Arctic ecosystems - measuring and forecasting the response of Alaska's terrestrial ecosystem to a warming climate

The Arctic Coastal Plain of northern Alaska is a complex landscape of lakes, streams, and wetlands scattered across low relief tundra that is underlain by permafrost. This region of the Arctic has experienced a warming trend over the past three decades, leading to thawing of on-shore permafrost and the disappearance of sea ice at an unprecedented rate. The loss of sea ice has increased ocean wave action, leading to higher rates of erosion and salt water inundation of coastal habitats. Warming temperatures also have advanced the overall phenology of the region, including earlier snowmelt, lake ice thaw, and plant growth. As a result, many migratory species now arrive in the Arctic several days earlier in spring than in the 1970s. Predicted warming trends for the future will continue to alter plant growth, ice thaw, and other basic landscape processes. These changes will undoubtedly result in different responses by wildlife (fish, birds, and mammals) and the food they rely upon (plants, invertebrates, and fish). However, the type of response by different wildlife populations and their habitats-either positively or negatively-remains largely unknown.

Alaska↗

USGS2011

Characteristics of foraging sites and protein status in wintering muskoxen: insights from isotopes of nitrogen

Identifying links between nutritional condition of individuals and population trajectories greatly enhances our understanding of the ecology, conservation, and management of wildlife. For northern ungulates, the potential impacts of a changing climate to populations are predicted to be nutritionally mediated through an increase in the severity and variance in winter conditions. Foraging conditions and the availability of body protein as a store for reproduction in late winter may constrain productivity in northern ungulates, yet the link between characteristics of wintering habitats and protein status has not been established for a wild ungulate. We used a non‐invasive proxy of protein status derived from isotopes of N in excreta to evaluate the influence of winter habitats on the protein status of muskoxen in three populations in Alaska (2005–2008). Multiple regression and an information‐theoretic approach were used to compare models that evaluated the influence of population, year, and characteristics of foraging sites (components of diet and physiography) on protein status for groups of muskoxen. The observed variance in protein status among groups of muskoxen across populations and years was partially explained (45%) by local foraging conditions that affected forage availability. Protein status improved for groups of muskoxen as the amount of graminoids in the diet increased (−0.430 ± 0.31, β± 95% CI) and elevation of foraging sites decreased (0.824 ± 0.67). Resources available for reproduction in muskoxen are highly dependent upon demographic, environmental, and physiographic constraints that affect forage availability in winter. Due to their very sedentary nature in winter, muskoxen are highly susceptible to localized foraging conditions; therefore, the spatial variance in resource availability may exert a strong effect on productivity. Consequently, there is a clear need to account for climate–topography effects in winter at multiple scales when predicting the potential impacts of climatic shifts on population trajectories of muskoxen.

Oikos↗

USGS2011

An isotopic approach to measuring nitrogen balance in caribou

Nutritional restrictions in winter may reduce the availability of protein for reproduction and survival in northern ungulates. We refined a technique that uses recently voided excreta on snow to assess protein status in wild caribou ( Rangifer tarandus ) in late winter. Our study was the first application of this non‐invasive, isotopic approach to assess protein status of wild caribou by determining dietary and endogenous contributions of nitrogen (N) to urinary urea. We used isotopic ratios of N (δ 15 N) in urine and fecal samples to estimate the proportion of urea N derived from body N ( p ‐UN) in pregnant, adult females of the Chisana Herd, a small population that ranged across the Alaska‐Yukon border. We took advantage of a predator‐exclosure project to examine N status of penned caribou in April 2006. Lichens were the primary forage (>40%) consumed by caribou in the pen and δ 15 N of fiber tracked the major forages in their diets. The δ 15 N of urinary urea for females in the pen was depleted relative (−1.3 ± 1.0 parts per thousand [‰], ${\bar {x}}\pm {\rm SD}$ ) to the δ 15 N of body N (2.7 ± 0.7‰). A similar proportion of animals in the exclosure lost core body mass (excluding estimates of fetal and uterine tissues; 55%) and body protein (estimated by isotope ratios; 54%). This non‐invasive technique could be applied at various spatial and temporal scales to assess trends in protein status of free‐ranging populations of northern ungulates. Intra‐ and inter‐annual estimates of protein status could help managers monitor effects of foraging conditions on nutritional constraints in ungulates, increase the efficiency and efficacy of management actions, and help prepare stakeholders for potential changes in population trends.

Journal of Wildlife Management↗