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Bayview, CA, United States

Wolfe J.D.,Pacific Southwest Research Station | Wolfe J.D.,Louisiana State University | Ryder T.B.,Smithsonian Institution | Pyle P.,Institute for Bird Populations
Journal of Field Ornithology | Year: 2010

Accurately differentiating age classes is essential for the long-term monitoring of resident New World tropical bird species. Molt and plumage criteria have long been used to accurately age temperate birds, but application of temperate age-classification models to the Neotropics has been hindered because annual life-cycle events of tropical birds do not always correspond with temperate age-classification nomenclature. However, recent studies have shown that similar molt and plumage criteria can be used to categorize tropical birds into age classes. We propose a categorical age-classification system for tropical birds based on identification of molt cycles and their inserted plumages. This approach allows determination of the age ranges (in months) of birds throughout plumage succession. Although our proposed cycle-based system is an improvement over temperate calendar-based models, we believe that combining both systems provides the most accurate means of categorizing age and preserving age-related data. Our proposed cycle-based age-classification system can be used for all birds, including temperate species, and provides a framework for investigating molt and population dynamics that could ultimately influence management decisions. ©2010 The Author(s). Journal compilation ©2010 Association of Field Ornithologists. Source

Cocking M.I.,Humboldt State University | Varner J.M.,Humboldt State University | Knapp E.E.,Pacific Southwest Research Station
Ecological Applications | Year: 2014

We studied vegetation composition and structure in a mixed conifer-oak ecosystem across a range of fire severity 10 years following wildfire. Sample plots centered on focal California black oaks (Quercus kelloggii) were established to evaluate oak and neighboring tree and shrub recovery across a gradient of fire severity in the southern Cascade Range, USA. Shrub and oak resprouting was strongest around focal oaks where conifer mortality was greatest. Linear modeling revealed negative relationships between California black oak sprout height or basal area and residual overstory tree survival, primarily white fir (Abies concolor). The two dominant competing species, California black oak and white fir, showed opposite responses to fire severity. Sprouting California black oak and associated shrubs dominated in severely burned areas, while surviving, non-sprouting white fir maintained dominance by its height advantage and shading effects in areas that burned with low fire severity. Our results indicate that high-severity fire promotes persistence and restoration of ecosystems containing resprouting species, such as California black oak, that are increasingly rare due to widespread fire exclusion in landscapes that historically experienced more frequent fire. We present a conceptual model based on our results and supported by a synthesis of postfire resprouting dynamics literature. Our results and conceptual model help illuminate long-term postfire vegetation responses and the potential ability of fire to catalyze formation of alternate vegetation community structures that may not be apparent in studies that evaluate postfire effects at shorter time-since-fire intervals or at coarser scales. © 2014 by the Ecological Society of America. Source

Powell R.A.,North Carolina State University | Zielinski W.J.,Pacific Southwest Research Station
PLoS ONE | Year: 2012

Translocations are frequently used to restore extirpated carnivore populations. Understanding the factors that influence translocation success is important because carnivore translocations can be time consuming, expensive, and controversial. Using population viability software, we modeled reintroductions of the fisher, a candidate for endangered or threatened status in the Pacific states of the US. Our model predicts that the most important factor influencing successful re-establishment of a fisher population is the number of adult females reintroduced (provided some males are also released). Data from 38 translocations of fishers in North America, including 30 reintroductions, 5 augmentations and 3 introductions, show that the number of females released was, indeed, a good predictor of success but that the number of males released, geographic region and proximity of the source population to the release site were also important predictors. The contradiction between model and data regarding males may relate to the assumption in the model that all males are equally good breeders. We hypothesize that many males may need to be released to insure a sufficient number of good breeders are included, probably large males. Seventy-seven percent of reintroductions with known outcomes (success or failure) succeeded; all 5 augmentations succeeded; but none of the 3 introductions succeeded. Reintroductions were instrumental in reestablishing fisher populations within their historical range and expanding the range from its most-contracted state (43% of the historical range) to its current state (68% of the historical range). To increase the likelihood of translocation success, we recommend that managers: 1) release as many fishers as possible, 2) release more females than males (55-60% females) when possible, 3) release as many adults as possible, especially large males, 4) release fishers from a nearby source population, 5) conduct a formal feasibility assessment, and 6) develop a comprehensive implementation plan that includes an active monitoring program. Source

Railsback S.F.,Humboldt State University | Harvey B.C.,Pacific Southwest Research Station
Trends in Ecology and Evolution | Year: 2013

Many ecologists believe that there is a lack of foraging theory that works in community contexts, for populations of unique individuals each making trade-offs between food and risk that are subject to feedbacks from behavior of others. Such theory is necessary to reproduce the trait-mediated trophic interactions now recognized as widespread and strong. Game theory can address feedbacks but does not provide foraging theory for unique individuals in variable environments. 'State- and prediction-based theory' (SPT) is a new approach that combines existing trade-off methods with routine updating: individuals regularly predict future food availability and risk from current conditions to optimize a fitness measure. SPT can reproduce a variety of realistic foraging behaviors and trait-mediated trophic interactions with feedbacks, even when the environment is unpredictable. © 2012 Elsevier Ltd. Source

Davidson J.M.,Pacific Southwest Research Station | Davidson J.M.,University of Hawaii at Manoa | Patterson H.A.,University of California at Davis | Wickland A.C.,University of California at Davis | And 2 more authors.
Phytopathology | Year: 2011

The transmission ecology of Phytophthora ramorum from bay laurel (Umbellularia californica) leaves was compared between mixed-evergreen and redwood forest types throughout winter and summer disease cycles in central, coastal California. In a preliminary multisite study, we found that abscission rates of infected leaves were higher at mixedevergreen sites. In addition, final infection counts were slightly higher at mixed-evergreen sites or not significantly different than at redwood sites, in part due to competition from other foliar pathogens at redwood sites. In a subsequent, detailed study of paired sites where P. ramorum was the main foliar pathogen, summer survival of P. ramorum in bay laurel leaves was lower in mixed-evergreen forest due to lower recovery from infected attached leaves and higher abscission rates of infected leaves. Onset of inoculum production and new infections of bay laurel leaves occurred later in mixed-evergreen forest. Mean inoculum levels in rainwater and final infection counts on leaves were higher in redwood forest. Based on these two studies, lower summer survival of reservoir inoculum in bay laurel leaves in mixed-evergreen forest may result in delayed onset of both inoculum production and new infections, leading to slower disease progress in the early rainy season compared with redwood forest. Although final infection counts also will depend on other foliar pathogens and disease history, in sites where P. ramorum is the main foliar pathogen, these transmission patterns suggest higher rates of disease spread in redwood forests during rainy seasons of short or average length. © 2011 The American Phytopathological Society. Source

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