Isle Royale National Park Research Articles

Large herbivores and aquatic–terrestrial links in southern boreal forests

1. Concurrent measurement of population dynamics and associated spatio-temporal patterns of resource flow across aquatic-terrestrial boundaries are rare, yet necessary to understand the consequences of cross-habitat resource flux. Long-term study of the moose Alces alces (L.) population in Isle Royale National Park (Lake Superior, USA) provides an opportunity to examine the patterns of resource flux from aquatic to terrestrial habitats over approximately50 years. 2. We analysed the spatio-temporal dynamics of aquatic-derived nitrogen (N) that moose transfer to terrestrial systems by using excretion models, foraging parameters, moose densities, and moose carcass locations (n = 3616) collected from 1958-2005. 3. Results suggest that moose transfer significant amounts of aquatic-derived N to terrestrial systems, which likely increases terrestrial N availability in riparian zones. A seasonal increase in terrestrial N availability when moose are foraging on N-rich aquatic macrophytes would contrast with the depression of soil N mineralization previously attributed indirectly to moose. 4. Aquatic foraging by moose and moose carcass locations are significantly clustered at multiple scales, indicating that grey wolves Canis lupus (L.) and moose can create concentrated areas of resource transfer due to clustered predation and foraging patterns. 5. This study shows that patterns of faunal-mediated resource transfer can depend significantly on predator-prey dynamics, and that large predators in this system influence herbivore-controlled resource transfer between ecosystems. Given the circumpolar extent of moose, they constitute an important, unquantified aquatic-terrestrial resource vector in boreal systems.

Mercury, lead and lead isotope ratios in the teeth of moose (Alces alces) from Isle Royale, U.S. Upper Midwest, from 1952 to 2002

Assessing the effect of recent reductions in atmospheric pollution on metal concentrations in wildlife in North America has been difficult because of the sparse availability of historical samples with which to establish a "pre-regulation" baseline, and because many ecosystems may be affected by local point sources which could obscure broader-scale trends. Here we report a recent 50 yr annual record of Hg, Pb and Pb isotope ratios in the teeth of a resident population of moose (Alces alces) in Isle Royale National Park, a relatively remote island in Lake Superior, Michigan, USA. During the early 1980s, concentrations of tooth Hg abruptly declined by approximately 65% compared to the previous 30 years (p<0.001), similar to a previous study of Hg in herring gull eggs in the Great Lakes region. Lead declined at the same time, and by 2002 Pb in adult moose teeth was approximately 80% lower than it had been prior to the early 1980s (p<0.001). These trends were unaffected by normalization against the geogenic elements La and Sr, which indicates that the trends in Hg and Pb had an anthropogenic cause. Temporal patterns of Pb isotope ratios suggested that the primary sources of Pb at different times in the moose were combustion of U.S. coal and leaded gasoline. Reductions in emissions from coal combustion might explain the co-incident reductions of Hg and Pb in Isle Royale moose, with elimination of alkyl Pb additives also playing a role in the continued tooth Pb reductions after 1983.

Using LiDAR to detect cultural resources in a forested environment: an example from Isle Royale National Park, Michigan, USA

AbstractThis article discusses the use of light detecting and ranging (LiDAR) technology as an effective remote sensing tool for the location of cultural resources. Its use, particularly in Europe, has proven successful in the identification of archaeological sites obscured by dense vegetation or surface disturbances. This study used LiDAR‐derived imagery to detect pre‐ and post‐European contact sites, and their related features, in densely forested environments on Isle Royale, Michigan, USA. LiDAR bare‐Earth models were used to ‘see through’ the vegetation in an effort to: (i) identify cultural features prior to the implementation of a pedestrian reconnaissance survey; (ii) aid in the development of a more informed survey strategy; and (iii) produce an overall safer, more efficient and more cost‐effective research design. Three study areas were selected for investigation. Within these three study areas, a total of seven investigation locales containing 32 separate features were identified using LiDAR‐derived imagery. Eighteen of the 32 features were found to have been previously recorded. Of the remaining 14 features, seven were confirmed in the field as being cultural features and were recorded for the first time as a result of this investigation. The remaining seven could not be located on the ground or were found to be non‐cultural. The results of this study support the use of LiDAR as a viable method for the detection of cultural resources, particularly in remote and heavily forested environments. Despite its positive contributions, there is a limited range of archaeological (surface) features that can be detected using this technology. As applied to archaeology, LiDAR is not an exclusive investigatory technique. It must be part of a comprehensive research strategy that integrates field, laboratory and archival investigation in order to achieve the best possible interpretation of the archaeological record. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Carnivore-specific stable isotope variables and variation in the foraging ecology of modern and ancient wolf populations: case studies from Isle Royale, Minnesota, and La Brea

We use carbon and nitrogen isotope data collected from two North American gray wolf ( Canis lupus L., 1758) populations (Isle Royale and northern Minnesota) to both calculate carnivore-specific isotopic variables and investigate wolf foraging ecology. The isotopic enrichments of13C and15N that occur between mammalian carnivores and their prey have not been well defined in modern populations. We use bone collagen from the Isle Royale National Park wolf, moose ( Alces alces (L., 1758)), and beaver ( Castor canadensis Kuhl, 1820) populations to determine trophic enrichment factors of 1.3‰ ± 0.6‰ for δ13C and 4.6‰ ± 0.7‰ for δ15N. We apply these carnivore-specific fractionation factors to a case study from the fossil record, and reconstruct the diets of late-Pleistocene dire wolves ( Canis dirus (Leidy, 1858)) from the La Brea tar pits. We use the Minnesota wolf tissue (collagen, hair, muscle) isotopic data to estimate carnivore population subsample sizes needed to replicate the mean values of the whole population within one standard deviation. Finally, we compare the Isle Royale and Minnesota collagen and hair isotopic data to published δ13C and δ15N values for North American gray wolf populations. We find that interpopulation differences in isotope variances provide insight into wolf foraging ecology.

Computer Simulation as a Tool for Planning and Management of Visitor Use in Protected Natural Areas

The United Nations Environment Programme’s Principles on Implementation of Sustainable Tourism suggest that implementing sustainable tourism must include monitoring visitor use of protected natural areas and directing it to areas where the environmental and social impacts of tourism are minimised. Thus, sustainable tourism management requires information about the spatial and temporal flow of visitor use in protected natural areas to help identify potential tourism-related threats to the natural and cultural resources of an area and the quality of visitors’ experiences. Recent research has identified at least four ways in which simulation modelling of visitor use can facilitate more informed planning and management of sustainable tourism in protected natural areas, including (1) describing existing visitor use flows; (2) monitoring the condition of ‘hard to measure’ indicator variables; (3) testing the effectiveness of alternative visitor use management practices; and (4) guiding the design of research on public attitudes. The purpose of this paper is to demonstrate, using findings from studies conducted in the Inyo National Forest and Isle Royale National Park, USA, each of these four potential contributions of computer simulation to sustainable tourism management and planning. The paper concludes with an assessment of the limitations of existing applications of computer simulation to nature-based tourism and recommendations for future research.

Genetic diversity and distribution ofSarracenia purpurea(Sarraceniaceae) in the western Lake Superior basin

Restoring plant populations requires an understanding of plant morphological adaptation to site locations and population genetic diversity and relatedness. This study examined the genetic and morphological diversity of Sarracenia purpurea L. within the natural fragmentation of western Lake Superior. Populations of S. purpurea were compared among three locations: Isle Royale National Park, the Keweenaw Peninsula, Michigan, USA, and Sleeping Giant Provincial Park, Ontario, Canada. Analysis of genetic and demographic data showed Canadian populations to be less robust with smaller plant sizes. Canadian populations were also slightly distinct genetically. Overall genetic diversity appears moderate (H = 0.30–0.36) and populations genetically similar. Analysis of molecular variance showed only 3.83% of variation among the three locations (p = 0.0049). Fragmentation did not have a distinguishable effect on genetic diversity and morphological characters but the limestone bedrock geology of the Canadian region may be starting to influence plant morphology and genetic differentiation. This indicates that restoration can take place within the western basin of Lake Superior using a variety of seed sources but regional geology may influence observed plant morphology.

Methyl and total mercury in precipitation in the Great Lakes region

Methylmercury (MeHg) and total mercury (THg) concentrations were measured in precipitation collected from five US sites in the Great Lakes region: three sites on the southern shore of Lake Superior (Brule River, WI, Eagle Harbor, MI, and Tahquamenon Falls, MI), one at Isle Royale National Park (MI), and one in southern Wisconsin (Devil's Lake), between May 1997 and December 2003. MeHg and THg concentrations at these sites were compared to MeHg and THg concentrations in precipitation collected at the Experimental Lakes Area (ELA) in north-western Ontario, Canada. Detectable MeHg concentrations (>0.01 ng L −1) were found in the majority of rain and snow samples collected from all sites (range=0.01–0.85 ng L −1). In general, the lowest MeHg concentrations were observed in samples taken at Tahquamenon Falls and the ELA, and the highest MeHg concentrations in precipitation were observed in samples collected from Brule River and Eagle Harbor. Total Hg concentrations in precipitation were generally between 10 and 60 ng L −1, exceeding 60 ng L −1 in one precipitation event sampled from each of Brule River, Isle Royale, Tahquamenon Falls, and Devil's Lake. The proportion of THg that was MeHg (%MeHg), was less than 6% at all sites, with the exception of seven events at Tahquamenon Falls and two events at the ELA that were between 6% and 18% MeHg. Generally, the highest MeHg concentrations were found in low-volume precipitation events (<100 mL). At Tahquamenon Falls, meteorological analysis indicated that events with higher MeHg concentrations and %MeHg exceeding 6% were generally associated with lake effect precipitation and weak local winds.

The wolves of Isle Royale display scale‐invariant satiation and ratio‐dependent predation on moose

Summary 1 The importance of two features of the predator functional response (satiation and predator dependence) is investigated in the wolf–moose interaction on Isle Royale National Park (Michigan, USA). This is done by fitting and comparing nine different functional response models to the observed kill rates. 2 Three different observational scales (the whole island, the wolf packs, or a ‘mixed’ scale) are used to assess the sensitivity of the detected properties with respect to these spatial scales. 3 Independently of the observational scale and of statistical assumptions on data structure, strong predator dependence and satiation of the wolf functional response are found. The ‘mixed’ scale gives the most consistent results, suggesting that predation should be measured for each pack, but that packs share all moose on the island. On this scale, the functional response is clearly ratio-dependent.

Lichens of the U. S. National Parks

Over 26,100 records of lichens present in 144 U.S. national park units were assembled from various sources into a database and analyzed. Within these 144 park units 2,435 species and 375 genera are reported, representing 63% and 74% of the North American flora, respectively. The park units are located in 41 states and Washington, D.C. The average number of species in a park is 104, but the median is 60, indicating there are many parks with a small number of species and a few with high numbers. Isle Royale National Park has the most species, 611, and twelve parks have only one species reported. The number of records of lichens present ranged from one for 25 parks, to 1,623 for Isle Royale. Physcia aipolia is the most frequently observed species, being found in 65 parks. One fourth of the park units are classified cultural resource parks, while the remainder are considered natural resource parks. This study was based on 453 sources, including literature citations, park reports and collections in the University of Minnesota Herbarium.

Wolf homesite attendance patterns

Adult gray wolves, Canis lupus L., 1758, frequent den and rendezvous sites (homesites) during summer to bring food to pups and to ensure security of the pups. We monitored homesite attendance of several adult wolves from a single pack in Isle Royale National Park, Michigan, for 6 years. Pack size, number of pups, and prey density varied during the period of monitoring. Given the effect of prey density on wolf behavior, we predicted that wolf homesite attendance patterns would vary with prey density. We also examined the effects of varying pack size, social status, and number of pups on homesite attendance. Contrary to our expectations, prey density did not appear to be a significant predictor of homesite attendance statistics such as hours per day at the homesite or length of absence from the homesite. Furthermore, when prey density and social status remained the same, homesite attendance (hours/day) of individual wolves monitored for multiple years varied substantially. Our results show homesite attendance to be highly variable and not well predicted by prey density.

The Holocene vegetation history of Isle Royale National Park, Michigan, U.S.A.

A vegetation history for Isle Royale National Park, Michigan, U.S.A., is reconstructed using pollen and spores extracted from two lake sediment cores. Lily Lake is on the southwestern end of the main island of Isle Royale surrounded by northern hardwoods forest. Lake Ojibway is on the northeastern end of the main island surrounded by boreal forest. Pollen and spore records were analyzed using pollen percentage diagrams, nonmetric multidimensional scaling ordination, and modern analog analysis. Squared chord distances for temporally paired subsamples from each site were calculated to determine palynological dissimilarities between the sites through time. These analyses revealed an overall vegetation history that is consistent with other regional reconstructions. High percentages of spruce pollen, indicating a cool climate, are present in the early Holocene, whereas high percentages of pine pollen, indicating a dry climate, occur in the mid-Holocene. The pollen records from the two sites diverge with increased precipitation during the late Holocene. At this time, birch-dominated forest is established near Lily Lake on till-derived soils. At Lake Ojibway, a mixed birch, pine, spruce, and fir forest is established on bedrock-derived soils. The divergence in forest composition is most pronounced within the last 500 years, and this divergence is tentatively attributed to the response of taxa on different substrates to increasing precipitation. Other possible explanations for the recent divergence include changing microclimates or disturbance regimes.

Factors affecting enhanced mercury bioaccumulation in inland lakes of Isle Royale National Park, USA

We investigated factors causing mercury (Hg) concentrations in northern pike to exceed the consumption advisory level (>500 ng/g) in some inland lakes of Isle Royale National Park. Using Hg-clean techniques, we collected water, zooplankton, macro invertebrates, and fishes in 1998 and 1999 from one advisory lake, Sargent Lake, for analysis of total mercury (Hg T) and methylmercury (MeHg). For comparison, samples were also collected from a non-advisory lake, Lake Richie. Concentrations of Hg T in northern pike were significantly higher in Sargent Lake ( P<0.01). Counter to expectations, mean concentrations of both Hg T and MeHg in open water samples were slightly higher in Lake Richie. However, zooplankton in Sargent Lake contained higher average concentrations of Hg T and MeHg than in Lake Richie. Mercury concentrations in macro invertebrates were similar between lakes, but different between taxa. The two lakes exhibited similar Hg T concentrations in age-1 yellow perch and adult perch but concentrations in large adult perch (>160 mm) in Sargent Lake were twice the concentrations in Lake Richie. Analysis of stable isotopes (δ 13C and δ 15N) in biota showed that pike from the two lakes are positioned at the same trophic level (4.2 and 4.3), but that the food web is more pelagic-based in Sargent and benthic-based in Richie. Factors causing concentrations in large pike to be higher in Sargent Lake may include higher bioavailability of methylmercury and a food web that enhances bioaccumulation.

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 68m2 and 83% of sites lost vegetation over areas less than 47m2. 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.

Compensatory bone remodelling in moose: a study of age, sex, and cross‐sectional cortical bone dimensions in moose at Isle Royale National Park

AbstractWe studied interrelationships among age, sex, and cross‐sectional cortical bone dimensions using quantitative computed tomography (QCT) scans of metatarsal bones of 180 moose (Alces alces) that died in Isle Royale National Park, Michigan. As a large‐bodied quadruped with demanding ecological constraints on movement and behaviour, a moose experiences different weight‐bearing and mechanical stressors than humans, to whom most existing studies of mechanical adaptations of bone pertain. In moose, both sexes showed significant subperiosteal expansion and an increase in medullary area, with an overall increase in cortical bone area over time. Female moose did not exhibit cortical thinning or reduction in cross‐sectional area with age, rather they showed an increase in cortical bone area with periosteal apposition exceeding endosteal resorption, similar to the males. We also found that moose undergo changes in bone geometry through remodelling of bone similar to humans, suggesting a compensatory mechanism for increasing bone strength under conditions of decline in bone mineral density with age. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Survey of Angling in Lake Superior Waters at Isle Royale National Park, 1998

Abstract An on-site direct-contact creel survey was conducted in the Lake Superior waters of Isle Royale National Park during June–August 1998 to estimate fishing effort, sport catch, sport harvest, and residency of noncharter boaters. The sport harvest of lake trout Salvelinus namaycush and coaster brook trout S. fontinalis was of particular concern. Estimates were based on boat counts from air flights and from the ferry vessel Voyageur II, as well as from interviews of boating parties at Isle Royale, Michigan, ports; at Grand Portage, Minnesota; and onboard the ferry vessel Ranger III. Total boating effort at Isle Royale National Park during June–August was 29,273 h, of which 696 h (2%) involved charter fishing boats, 19,340 h (66%) noncharter fishing boats, and the remaining 9,237 h (32%) nonfishing boats. Most boaters were from Minnesota and Michigan, which together accounted for 95% of the noncharter anglers and 70% of the nonfishing boaters. Total angler hours for the period were 62,232. Lake trout ...

Mercury concentrations in deer mouse ( Peromyscus maniculatus) tissues from Isle Royale National Park

We used deer mice ( Peromyscus maniculatus) to investigate variation in mercury exposure across the terrestrial ecosystem of Isle Royale National Park (Michigan, USA). Although previous work suggested that mercury (Hg) levels may be higher inside the Sargent Lake watershed of Isle Royale than outside the watershed, Hg concentrations in livers were higher outside the Sargent Lake watershed (100.13 ng Hg/g dry tissue) than inside the watershed (35.50 ng Hg/g dry tissue; P=0.06). Mercury levels in kidneys did not differ significantly ( P=0.57) between samples collected outside (443.23 ng Hg/g dry tissue) and inside (360.62 ng Hg/g dry tissue) the Sargent Lake watershed. Mean Hg concentrations in the livers of mice at some sites in Isle Royale are not significantly lower ( P=0.62) than Hg concentrations considered by some government agencies to be unhealthy for human consumption. Although Hg concentrations in mouse tissues were not remarkably high (compared to heavily polluted sites), concern is warranted because: (1) Isle Royale National park is a protected area in a remote location; (2) any exposure in deer mice represents a path for biomagnification in the terrestrial food web; and (3) the source of this mercury remains unidentified.

Atmospheric Transport, Deposition, and Fate of Triazine Herbicides and Their Metabolites in Pristine Areas at Isle Royale National Park

Trace concentrations of triazine herbicides, used in the Midwestern United States, are being transported atmospherically hundreds of kilometers and deposited by precipitation onto pristine areas, such as Isle Royale National Park (Lake Superior). Atrazine, deethylatrazine, deisopropylatrazine, and cyanazine were detected in Isle Royale rainfall from mid-May to early July (1992−1994) at concentrations of less than 0.005 to 1.8 μg/L. Analysis of predominant wind direction indicated that the herbicides originated from the upper Midwestern United States. The annual mass of herbicides deposited by rainfall varied between years, from 13.4 μg/m2/yr for 1992, 3.7 μg/m2/yr for 1993, and 54 μg/m2/yr for 1994. Atrazine and deethylatrazine were found also in concentrations of less than 5−22 ng/L in lakes across Isle Royale. Concentrations of atrazine in the surface layer of the lakes increased during deposition periods and decreased later in the year. The fate of triazines in shallow lakes suggests faster degradation...

Polychlorinated Naphthalenes and Polychlorinated Biphenyls in Fishes from Michigan Waters Including the Great Lakes

Polychlorinated naphthalene (PCN) and polychlorinated biphenyl (PCB) congeners were measured in whole body and fillet of fishes collected from Michigan waters, including the Great Lakes, during 1996−1997. PCNs were found in all the fishes analyzed including those from Siskiwit Lake, a remote lake located near the southern shoreline of Isle Royale National Park in Lake Superior. Concentrations of total PCNs in fishes ranged from 19 to 31 400 pg/g, wet wt, and varied depending on sampling location and species. Fishes from the Detroit River contained the greatest concentrations of both PCNs and PCBs. Concentrations of total PCNs in fishes from Michigan waters were significantly correlated with the concentrations of PCBs. As with total PCN concentrations, the profiles of PCN isomer/congener distribution in fishes varied among sampling locations and species. Fishes from the Detroit River contained PCN profile similar to that of Halowax 1014, whereas those from Siskiwit Lake and Lake Superior contained greater ...

WOLF–MOOSE INTERACTION ON ISLE ROYALE: THE END OF NATURAL REGULATION?

Long-term population fluctuations of wolves and moose in Isle Royale National Park, Michigan, are used to evaluate a central tenet of the “natural regulation” concept commonly applied by the National Park Service (NPS) in the United States, namely, that wild cervid populations exhibit density dependence which, even in the absence of large predators, will stabilize population growth. This tenet, restated as a hypothesis, is rejected based on moose population response to a chronic wolf decline. In 1980–1996 with wolf numbers down, partly due to introduced disease, moose numbers increased to a historic high level. There was insufficient density dependence in moose reproduction and mortality to stabilize moose numbers. In 1996 moose suffered a crash; 80% died, primarily from starvation. These fluctuations, along with the possibility that the highly inbred wolf population may become extinct, will challenge NPS policy. The long-standing NPS management tradition of nonintervention may not be compatible with the current policy that stresses maintenance of natural ecological processes, such as a predator–prey system.

Population Limitation and the Wolves of Isle Royale

Population regulation for gray wolves in Isle Royale National Park, Michigan, was examined in 1987–1995 when wolves were in chronic decline following a crash of the population in 1981–1982. Canine parvovirus (CPV-2) was probably influential during the crash, but it disappeared by the late 1980s. High mortality abruptly ceased after 1988, but low recruitment in the absence of disease and obvious shortage of food prevented recovery of the wolf population. In 1983–1995, with a comparable number of moose ≥10 years old as potential prey, wolves were only half as numerous as in 1959–1980. A simulation of annual fluctuations in effective population size ( N e ) for wolves on Isle Royale suggests that their genetic heterozygosity has declined ca. 13% with each generation and ca. 80% in the 50-year history of this population. Inbreeding depression and stochastic demographic variation both remain possible explanations for recent low recruitment.