USGS Science⌕ Search

Geology topics

Research about Isle Royale National Park

Source-linked reports with geographic coverage including Isle Royale National Park.

9 recordsLinked to original sources
USGS2019

Negative frequency-dependent foraging behaviour in a generalist herbivore (Alces alces) and its stabilizing influence on food-web dynamics

1. Resource selection is widely appreciated to be context‐dependent and shaped by both biological and abiotic factors. However, few studies have empirically assessed the extent to which selective foraging behaviour is dynamic and varies in response to environmental conditions for free‐ranging animal populations. 2. Here, we assessed the extent that forage selection fluctuated in response to different environmental conditions for a free‐ranging herbivore, moose (Alces alces), in Isle Royale National Park, over a 10‐year period. More precisely, we assessed how moose selection for coniferous versus deciduous forage in winter varied between geographic regions and in relation to (a) the relative frequency of forage types in the environment (e.g. frequency‐dependent foraging behaviour), (b) moose abundance, (c) predation rate (by grey wolves) and (d) snow depth. These factors are potentially important for their influence on the energetics of foraging. We also built a series of food‐chain models to assess the influence of dynamic foraging strategies on the stability of food webs. 3. Our analysis indicates that moose exhibited negative frequency dependence, by selectively exploiting rare resources. Frequency‐dependent foraging was further mediated by density‐dependent processes, which are likely to be predation, moose abundance or some combination of both. In particular, frequency dependence was weaker in years when predation risk was high (i.e. when the ratio of moose to wolves was relatively low). Selection for conifers was also slightly weaker during deep snow years. 4. The food‐chain analysis indicates that the type of frequency‐dependent foraging strategy exhibited by herbivores had important consequences for the stability of ecological communities. In particular, the dynamic foraging strategy that we observed in the empirical analysis (i.e. negative frequency dependence being mediated by density‐dependent processes) was associated with more stable food web dynamics compared to fixed foraging strategies. 5. The results of this study indicated that forage selection is a complex ecological process, varying in response to both biological (predation and moose density) and abiotic factors (snow depth) and over relatively small spatial scales (between regions). This study also provides a useful framework for assessing the influence of other aspects of foraging behaviour on the stability of food web dynamics.

Michigan↗
USGS2017

Modelling moose–forest interactions under different predation scenarios at Isle Royale National Park, USA

Loss of top predators may contribute to high ungulate population densities and chronic over-browsing of forest ecosystems. However, spatial and temporal variability in the strength of interactions between predators and ungulates occurs over scales that are much shorter than the scales over which forest communities change, making it difficult to characterize trophic cascades in forest ecosystems. We applied the LANDIS-II forest succession model and a recently developed ungulate browsing extension to model how the moose population could interact with the forest ecosystem of Isle Royale National Park, USA, under three different wolf predation scenarios. We contrasted a 100-yr future without wolves (no predation) with two predation scenarios (weak, long-term average predation rates and strong, higher than average rates). Increasing predation rates led to lower peak moose population densities, lower biomass removal rates, and higher estimates of forage availability and landscape carrying capacity, especially during the first 40 yr of simulations. Thereafter, moose population density was similar for all predation scenarios, but available forage biomass and the carrying capacity of the landscape continued to diverge among predation scenarios. Changes in total aboveground live biomass and species composition were most pronounced in the no predation and weak predation scenarios. Consistent with smaller-scale studies, high browsing rates led to reductions in the biomass of heavily browsed Populus tremuloides, Betula papyrifera , and Abies balsamea , and increases in the biomass of unbrowsed Picea glauca and Picea mariana , especially after the simulation year 2050, when existing boreal hardwood stands at Isle Royale are projected to senesce. As a consequence, lower predation rates corresponded with a landscape that progressively shifted toward dominance by Picea glauca and Picea mariana , and lacking available forage biomass. Consistencies with previously documented small-scale successional shifts, and population estimates and trends that approximate those from this and other boreal forests that support moose provide some confidence that these dynamics represent a trophic cascade and therefore provide an important baseline against which to evaluate long-term and large-scale effects of alternative predator management strategies on ungulate populations and forest succession.

Isle Royale National Park↗
USGS2005

Conservation genetics of the endangered Isle Royale gray wolf

The small group of wolves on Isle Royale has been studied for over three decades as a model of the relationship between large carnivores and their prey. During the last ten years the population declined from 50 individuals to as few as 12 individuals. The causes of this decline may be food shortages, disease, or reduced genetic variability. We address the issues of genetic variability and relationships of Isle Royale wolves using allozyme electrophoresis, mtDNA restriction-site analysis, and multilocus hypervariable minisatellite DNA analysis (genetic fingerprinting). Our results indicate that approximately 50% of the allozyme heterozygosity has been lost in the island population, a decline similar to that expected if no immigration had occurred from the mainland. The genetic fingerprinting data indicate that the seven sampled Isle Royale wolves are as similar as captive populations of siblings. Surprisingly, the Isle Royale wolves have an mDNA genotype that is very rare on the mainland, being found in only one of 144 mainland wolves ThFF suggests that the remaining Isle Royale wolves areprobably derived from a single female founder.

Michigan↗
USGS2003

Bedrock, soil, and lichen geochemistry from Isle Royale National Park, Michigan

Isle Royale National Park, Michigan, is a large island in northeastern Lake Superior that became a national park in 1940 and was designated as a wilderness area in 1976. The relative isolation of Isle Royale (Figure 1), 25 kilometers out in Lake Superior from the Canadian mainland, its generally harsh climate, and its status as a wilderness national park have minimized human influence on the geochemical evolution of its landscape. USGS sampling on Isle Royale began in 1996 as part of a larger project on the geology of the Midcontinent rift in the Lake Superior region and continued through 2000. Sampling began with collecting bedrock samples to characterize the geochemistry of the volcanic rocks that make up the much of the island, as well as samples representative of the minor native copper mineralization found on the island. Preliminary results from the bedrock study indicated, among other findings, that basaltic bedrock on the island had no detectable mercury, but that there was an association between native copper mineralization and trace amounts of mercury (Cannon and Woodruff, 1999). This finding and the recognition by the National Park Service that 6 of 32 inland lakes on Isle Royale have mercury levels in game fish that exceed State of Michigan acceptable levels for human consumption (Kallemeyn, 2000) resulted in renewed sampling on the island focused more on environmental issues. To evaluate atmospheric inputs of mercury and other elements to soil geochemistry, regionally distributed samples of both soils and lichens were collected as paired samples across the entire island. At each soil sample site, three epiphytic (grows in trees) lichen species, Evernia mesomorpha , Hypogymnia plysodes , and Parmelia sucata , were always collected. At some sites Cladina rangiferina , a lichen that grows on bare bedrock and soil surfaces, was also collected. The occurrence of Cladina rangiferina on the island is somewhat limited, and so this lichen species was not collected at all sites. A high density of soil samples was collected within three individual watersheds (Sargent Lake, Lake Wagejo, and Lake Richie) for a localized study that evaluated the terrestrial distribution of mercury and other elements of environmental concern. These lakes were chosen using data from Kallemeyn (2000) that showed that Sargent Lake and Lake Wagejo have high mercury in fish, whereas Lake Richie, which is similar in size to Sargent Lake, does not. As part of this study on the terrestrial contribution of mercury to lakes, long cores of lake sediments were recovered from Sargent Lake and Lake Richie using a modified Livingston piston sampler. For an ancillary study that evolved from the study on the distribution of mercury in certain watersheds, some soil samples were collected to evaluate the impact of forest fire on soil geochemistry, deliberately sampling within and outside areas on the island that burned in severe forest fires in 1936. To complete bedrock sampling on the island, rock samples from the Copper Harbor Formation, a sedimentary unit that occurs on the southeastern part of the island were collected in 1999. This report presents all the geochemical data from samples collected by the USGS during this period (Figures 1 and 2). A number of reports presenting data interpretation are in preparation

Michigan↗
USGS2002

Management practices that concentrate visitor activities: Camping impact management at Isle Royale National Park, USA

This study assessed campsite conditions and the effectiveness of campsite impact management strategies at Isle Royale National Park, USA. Protocols for assessing indicators of vegetation and soil conditions were developed and applied to 156 campsites and 88 shelters within 36 backcountry campgrounds. The average site was 68 m 2 and 83% of sites lost vegetation over areas less than 47 m 2 . We believe that management actions implemented to spatially concentrate camping activities and reduce camping disturbance have been highly successful. Comparisons of disturbed area/overnight stay among other protected areas reinforces this assertion. These reductions in area of camping disturbance are attributed to a designated site camping policy, limitation on site numbers, construction of sites in sloping terrain, use of facilities, and an ongoing program of campsite maintenance. Such actions are most appropriate in higher use backcountry and wilderness settings.

Isle Royale National Park↗
USGS1995

Abnormal chemical element concentrations in lichens of Isle Royale National Park

Lichens have been used for many years to monitor changes in deposited airborne chemical elements in many areas, but few studies have focused on areas suspected of experiencing slightly elevated pollution. Detection of subtle patterns of slightly elevated pollutants calls for developing several lines of evidence as opposed to single line studies used in heavily polluted areas. This study of two lichen species, Hypogymnia physodes and Evernia mesomorpha , in Isle Royale National Park, Michigan compares the concentrations and ranks of elements with the concentrations and ranks of the elements in the earth's crust, changes in element concentrations over a nine year period, and the geography of element concentrations in the park. S, Zn, Pb, Cd and Se were elevated in both species and higher in rank compared to the concentrations and ranks in the earth's crust. Toxic elements increased 123% in Hypogymnia and 62% in Evernia over 9 years, compared to increases of 45% and 59% for non-toxic elements in each species, respectively. Geographically, the lichens at certain localities with higher exposures experienced higher than average element concentrations. Finally, tissue concentrations of Mn, S and Se at some localities were above levels known to be either toxic or similar to those found in polluted areas. These four lines of evidence suggest that Isle Royale National Park is experiencing the onset of chronic air pollution stress from a number of sources.

Michigan↗
USGS1975

The geologic story of Isle Royale National Park

Isle Royale is an outstanding example of relatively undisturbed northwoods lake wilderness. But more than simple preservation of such an environment is involved in its inclusion in our National Park System. Its isolation from the mainland provides an almost untouched laboratory for research in the natural sciences, especially those studies whose very nature depends upon such isolation. One excellent example of such research is the intensive study of the predator-prey relationship of the timber wolf and moose, long sponsored by the National Park Service and Purdue University. In probably no other place in North America are the necessary ecological conditions for such a study so admirably fulfilled as on Isle Royale. The development of a natural laboratory with such conditions is ultimately dependent upon geologic processes and events that although not unique in themselves, produced in their interplay a unique result, the island archipelago as we know it today, with its hills and valleys, swamps and bogs the ecological framework of the plant and animal world. Even the most casual visitor can hardly fail to be struck by the fiordlike nature of many of the bays, the chains of fringing islands, the ridge-and-valley topography, and the linear nature of all these features. The distinctive topography of the archipelago is, of course, only the latest manifestation of geologic processes in operation since time immemorial. Fragments of geologic history going back over a billion years can be read from the rocks of the island, and with additional data from other parts of the Lake Superior region, we can fill in some of the story of Isle Royale. After more than a hundred years of study by man, the story is still incomplete. But then, geologic stories are seldom complete, and what we do know allows a deeper appreciation of one of our most naturally preserved parks and whets our curiosity about the missing fragments.

Michigan↗