Publications

Many biological, hydrological, and geological processes are interactively linked in ecosystems. These ecological phenomena normally vary within bounded ranges, but rapid, nonlinear changes to markedly different conditions can be triggered by even small differences if threshold values are exceeded. Intrinsic and extrinsic ecological thresholds can lead to effects that cascade among...

The epidemic potential of a disease is traditionally assessed using the basic reproductive number, R0. However, in populations with social or spatial structure a chronic disease is more likely to invade than an acute disease with the same R0, because it persists longer within each group and allows for more host movement between groups. Acute diseases ‘perceive’ a more structured host...

Spawning Yellowstone cutthroat trout (Oncorhynchus clarki) provide a source of highly digestible energy for grizzly bears (Ursus arctos) that visit tributary streams to Yellowstone Lake during the spring and early summer. During 1985–87, research documented grizzly bears fishing on 61% of the 124 tributary streams to the lake. Using track measurements, it was estimated that a minimum of...

Amphibian life histories are exceedingly sensitive to temperature and precipitation, and there is good evidence that recent climate change has already resulted in a shift to breeding earlier in the year for some species. There are also suggestions that the recent increase in the occurrence of El Niño events has caused declines of anurans in Central America and is linked to elevated...

The Amphibian Research and Monitoring Initiative (ARMI) began in 2000 as an attempt by the United States Geological Survey to determine the status and trends of amphibians on federal lands in the United States and its territories. ARMI research focuses on determining causes of declines, if observed, developing new techniques to sample populations and analyze data, and disseminating...

The balance of nature in any strict sense has been upset long ago…The only option we have is to create a new balance objectively determined for each area in accordance with the intended use of that area.” --Aldo Leopold, 1927, in a letter to the Superintendent of Glacier National Park The planning and management staff of state/national parks and protected areas face a complex set of...

We evaluate the efficacy of single-pass electrofishing without blocknets as a tool for collecting spatially continuous fish distribution data in headwater streams. We compare spatial patterns in abundance, sampling effort, and length-frequency distributions from single-pass sampling of coastal cutthroat trout (Oncorhynchus clarki clarki) to data obtained from a more precise multiple-pass...

The amount, chemical composition, and source of dissolved organic carbon (DOC), together with in situ ultraviolet (UV-B) attenuation, were measured at 1–2 week intervals throughout the summers of 1999, 2000, and 2001 at four sites in Rocky Mountain National Park (Colorado). Eight additional sites, four in Sequoia and Kings Canyon National Park/John Muir Wilderness (California) and four...

The use of noninvasive genetic sampling (NGS) for surveying wild populations is increasing rapidly. Currently, only a limited number of studies have evaluated potential biases associated with NGS. This paper evaluates the potential errors associated with analysing mixed samples drawn from multiple animals. Most NGS studies assume that mixed samples will be identified and removed during...

Global losses of amphibian populations are a major conservation concern and their causes have generated substantial debate. Habitat fragmentation is considered one important cause of amphibian decline. However, if fragmentation is to be invoked as a mechanism of amphibian decline, it must first be established that dispersal is prevalent among contiguous amphibian populations using formal...

We used radiotelemetry and population modeling techniques to examine factors related to population establishment of black bears (Ursus americanus) reintroduced to Felsenthal National Wildlife Refuge (NWR), Arkansas. Our objectives were to determine whether settling (i.e., establishment of a home range at or near the release site), survival, recruitment, and population viability were...

The Rocky Mountain Region of the United States Geological Survey's Amphibian Research and Monitoring Initiative is conducting monitoring of the status of amphibians on a transect that extends along the Continental Divide from Canada to Colorado and comprises four National Parks. Monitoring uses visual encounter surveys to determine site occupancy, with multiple visits to a subset of...