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Microhabitat Use and Reproductive Success of the California Red-legged Frog (Rana Aurora Draytonii) and Bullfrog (Rana Catesbeiana) in an Ephemeral Marsh
No full textI undertook a study of the habitat use, distribution. and factors influencing the reproductive success of the threatened California red-legged frog (Rana aurora draytonii) and introduced bullfrog (Rana catesbeiana) at Ledson Marsh, Sonoma County, California. Ledson Marsh is a seasonal marsh encompassing approximately 11 ha at its maximum size and is typically dry by late fall. This human-constructed marsh supports on abundant population of red-legged frogs and has been invaded by non-native bullfrogs. The bullfrog has been implicated as a predator and competitor of native amphibians, including the red-legged frog.\ud
The availability of microhabitats and their locations in the marsh changed markedly with the seasons, and frogs were associated with microhabitats at each season. Both species of frog showed distribution patterns in the marsh that were related to seasonal changes in habitat and their social behavior, and both were most active during their respective breeding periods. Important microhabitat features for all seasons included vegetative cover at the water's surface and water depth. Dead spikerush in shallow water (mean=39 cm) was the primary microhabitat used by frogs early in the season but it only covered 13.7% of the marsh in the winter of 1996. In spring through fall, frogs were most associated with smartweed. a dominant microhabitat type in the marsh. Frogs typically avoided open water and occasionally used bulrush, but both microhabitat types became more important late in the season.\ud
Water depths used by both species of frog did not differ significantly throughout the year, except during spring, but the marsh water levels changed substantially. The marsh water depths were highest in the winter and rapidly receded in summer. Maximum water depth of the marsh was approximately 150 cm. Both species were distributed in vegetative cover usually with depths between 30-40 cm, but spring was the exception when bullfrogs used deeper water for breeding. In summer, smartweed was a dominant microhabitat type used by frogs, and it occurs in the deepest remaining water.The breeding schedule, egg mass locations. and microhabitat used at oviposition sites differed substantially between species of frog. Resource partitioning of microhabitat types between the red~legged frog and bullfrog was evident during their breeding periods although substantial habitat overlap occl1lTed during all seasons. Habitat types used by one species where generally unavailable during the breeding period of the other species. The breeding periods of the two species were separated by approximat.ely two months. Red-legged frog egg masses were significantly associated with dead spikerush in shallow water (mean=32.8 cm), while bullfrog egg masses were significantly associated with smartweed in deeper water (mean=63.1 ern). There was no significant evidence that temperature differences were responsible for the selection of shallow water for ovipostion sites by the red-legged frog. Dead spikerllsh and cattail were common attachment sites for red-legged frog egg masses, while bulrush was never used.\ud
The relative successes of the red-legged frog and bullfrog are largely related to their strategies for reproduction and how well these match the ephemeral nature of Ledson Marsh. The seasonality of the marsh limits the possible duration of breeding and requires a high rate of embryonic development and tadpole metamorphosis prior to the marsh drying. Only post-metamorphic frogs can survive the fall dry period. Red-legged frog tadpoles metamorphosed by mid-summer, several months before the marsh dried in midOctober. Most bullfrog tadpoles were unable to metamorphose prior to the dry-down. The survival rate of red-legged frog eggs to metamorphosis was estimated at 1.9%, while the bullfrog rate was 0.0001 %.\ud
The dry-down of the marsh by a third of its area ill the summer and the observed concentration of both species suggests that the rate of predation by bullfrogs on redlegged frogs is highest during summer from the increased chance of interspecific encounters. The remains of three red-legged frog tadpoles were found in the stomachs of eight bullfrogs examined in the spring and summer.\ud
The ephemeral nature of Ledson Marsh favors the reproductive success of red-legged frogs, while hindering tadpole survival of bullfrogs. Designing and maintaining ephemeral habitats is an important consideration in managing populations of red-legged frogs. However, other factors should be examined, such as local climatic conditions, proximity to bullfrog source populations and frog dispersal rates, and the susceptibility of habitats to invasion by other non-native predators
Correlati neurobiologici del Disturbo di Ansia di Separazione nell'Infanzia e nell'Età Adulta
No full textAn investigation into the electrochemical properties of nanostructured metals and their application as amperometric biosensors
No full textEThOS - Electronic Theses Online ServiceGBUnited Kingdo
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Baches of Raglan
Full text linkThis is a book about Raglan’s older baches. Many were built in the “boom years” of the 50s and 60s when thousands of Kiwis invested in a bit of land by the sea; others are much older and have been handed down through families with long connections to the Raglan community.
Built of wood, concrete or fibrolite with iron roofs, they remain largely unaltered. Their owners have no interest in granite bench tops, polished concrete floors and tinted glass. They have a greater affection for a deckchair, a dinghy and sculptures made of driftwood. The book tells the stories of people who have “a place at the beach” and an affection for a simple life
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