Geology topics

Joseph J. Fontaine

Publications and source records attributed to Joseph J. Fontaine.

25 records · Page 2Linked to original sources

USGS2015

Masked expression of life-history traits in a highly variable environment

Differing life-history strategies may act as a constraint on reproductive expression that ultimately limits the ability of individual species to respond to changes in the magnitude or frequency of environmental variation, and potentially underlies the variation often inherent in phenotypic and evolved responses to anthropogenic change. Alternatively, if there are environmental cues that predict reproductive potential, differential expression of life-history strategies may represent differences in the adaptive capacity to optimize current reproductive value given variation in environmental conditions. We compared several aspects of walleye Sander vitreus spawning ecology at two reservoirs that differ in environmental variability (i.e., annual water-level fluctuation) to identify the capacity of phenotypic expression and the corresponding association with age. Despite significant differences in female body and liver masses between reservoirs that differ in environmental variability, we found no difference in reproductive investment measured by egg size and fecundity. Walleye in a highly variable environment appear to exhibit reproductive traits more typical of a short-lived life-history strategy, which may be resultant from the interaction of environmental and anthropogenic pressures. This finding emphasizes the need to identify the degree to which life-history expression represents physiological constraints versus ecological optimization, particularly as anthropogenic change continues to alter environmental conditions.

Great Plains Research↗

USGS2014

Assessing landscape constraints on species abundance: Does the neighborhood limit species response to local habitat conservation programs?

Landscapes in agricultural systems continue to undergo significant change, and the loss of biodiversity is an ever-increasing threat. Although habitat restoration is beneficial, management actions do not always result in the desired outcome. Managers must understand why management actions fail; yet, past studies have focused on assessing habitat attributes at a single spatial scale, and often fail to consider the importance of ecological mechanisms that act across spatial scales. We located survey sites across southern Nebraska, USA and conducted point counts to estimate Ring-necked Pheasant abundance, an economically important species to the region, while simultaneously quantifying landscape effects using a geographic information system. To identify suitable areas for allocating limited management resources, we assessed land cover relationships to our counts using a Bayesian binomial-Poisson hierarchical model to construct predictive Species Distribution Models of relative abundance. Our results indicated that landscape scale land cover variables severely constrained or, alternatively, facilitated the positive effects of local land management for Ring-necked Pheasants.

Nebraska↗

USGS2013

Choosing a DIVA: a comparison of emerging digital imagery vegetation analysis techniques

Question: What is the precision of five methods of measuring vegetation structure using ground-based digital imagery and processing techniques? Location: Lincoln, Nebraska, USA Methods: Vertical herbaceous cover was recorded using digital imagery techniques at two distinct locations in a mixed-grass prairie. The precision of five ground-based digital imagery vegetation analysis (DIVA) methods for measuring vegetation structure was tested using a split-split plot analysis of covariance. Variability within each DIVA technique was estimated using coefficient of variation of mean percentage cover. Results: Vertical herbaceous cover estimates differed among DIVA techniques. Additionally, environmental conditions affected the vertical vegetation obstruction estimates for certain digital imagery methods, while other techniques were more adept at handling various conditions. Overall, percentage vegetation cover values differed among techniques, but the precision of four of the five techniques was consistently high. Conclusions: DIVA procedures are sufficient for measuring various heights and densities of standing herbaceous cover. Moreover, digital imagery techniques can reduce measurement error associated with multiple observers' standing herbaceous cover estimates, allowing greater opportunity to detect patterns associated with vegetation structure.

Nebraska↗

USGS2013

Great gray owls ( Strix nebulosa ) in Yosemite National Park: on the importance of food, forest structure, and human disturbance

We studied great gray owls (Strix nebulosa Forster) in Yosemite National Park, California, measuring variables that could potentially influence patterns of occurrence and conservation of this stateendangered species. We found that owl presence was closely tied to habitat (red fir (Abies magnified A. Murray) and the abundance of meadows), prey, and snags across the landscape. We also found that indicators of human recreational activities negatively influenced owl distribution and habitat use. Great gray owls appear to prefer mid-elevation red fir forest with meadows that are drier and more productive in terms of small mammal populations. That these areas also have the highest human activity presents a paradox, both for individual owls and for the future conservation and management of this California endangered species. The extent to which human recreation in natural areas affects animal behavior, species distribution, and productivity is a growing issue in natural area management. We present information that will allow land managers to better understand how existing natural resources, coupled with human recreation, influence the distribution and habitat use of the great gray owl.

California↗

USGS2011

Nest predation and circulating corticosterone levels within and among species

Variation in the risk of predation to offspring can influence the expression of reproductive strategies both within and among species. Appropriate expression of reproductive strategies in environments that differ in predation risk can have clear advantages for fitness. Although adult-predation risk appears to influence glucocorticosteroid levels, leading to changes in behavioral and life-history strategies, the influence of offspring-predation risk on adult glucocorticosteroid levels remains unclear. We compared total baseline corticosterone concentrations in Gray-headed Juncos (Junco hyemalis dorsalis) nesting on plots with and without experimentally reduced risk of nest predation. Despite differences in risk between treatments, we failed to find differences in total baseline corticosterone concentrations. When we examined corticosterone concentrations across a suite of sympatric species, however, higher risk of nest predation correlated with higher total baseline corticosterone levels. As found previously, total baseline corticosterone was negatively correlated with body condition and positively correlated with date of sampling. However, we also found that corticosterone levels increased seasonally, independent of stage of breeding. Nest predation can alter the expression of birds' reproductive strategies, but our findings suggest that total baseline corticosterone is not the physiological mechanism regulating these responses.

The Condor↗

USGS2009

Spatial and temporal variation in climate change: A bird’s eye view

Recent changes in global climate have dramatically altered worldwide temperatures and the corresponding timing of seasonal climate conditions. Recognizing the degree to which species respond to changing climates is therefore an area of increasing conservation concern as species that are unable to respond face increased risk of extinction. Here we examine spatial and temporal heterogeneity in the rate of climate change across western North America and discuss the potential for conditions to arise that may limit the ability of western migratory birds to adapt to changing climates. Based on 52 years of climate data, we show that changes in temperature and precipitation differ significantly between spring migration habitats in the desert southwest and breeding habitats throughout western North America. Such differences may ultimately increase costs to individual birds and thereby threaten the long-term population viability of many species.

Climatic Change↗

USGS2009

A neotropical migrant bird's dilemma: where to stop for a good meal

To learn how migrating birds determine where to stop and find food, scientists from the U.S. Geological Survey, Northern Arizona University, and The University of Arizona studied the behavior of 28 species of neotropical migrant songbirds - warblers, flycatchers, tanagers, and vireos - along the lower Colorado River from 2001 to 2004. They found that, like interstate travelers greeted by restaurant billboards, songbirds flying over Cibola National Wildlife Refuge, Arizona, relied on the flowering of honey mesquite (Prosopis glandulosa) to detect the availability of insects that they prey on. Understanding where and why migrant birds stop will help land managers better protect key habitats used by these tiny travelers.

Fact Sheet↗