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The transition from sink to source status is one of the key events in leaf development. When a leaf is about half grown, it stops importing phloem-mobile nutrients from the rest of the plant and begins to export its own products of photosynthesis. This shift in transport direction, which is largely irreversible, involves major changes in the way metabolites are transported to and from the mesophyll through plasmodesmata and via transporters. The import of nutrients ceases when plasmodesmata in large veins are lost or narrowed, preventing phloem unloading. Export begins when the minor veins mature and begin to load sugars and other compounds into the phloem. The unidirectional nature of loading is a consequence of sucrose transporter orientation in the plasma membrane of phloem cells, or of the trapping of raffinose-family sugars in those species that load through plasmodesmata.
We used a spatially explicit population model of wolves (Canis lupus) to propose a framework for defining rangewide recovery priorities and finer-scale strategies for regional reintroductions. The model predicts that Yellowstone and central Idaho, where wolves have recently been successfully reintroduced, hold the most secure core areas for wolves in the western United States, implying that future reintroductions will face greater challenges. However, these currently occupied sites, along with dispersal or reintroduction to several unoccupied but suitable core areas, could facilitate recovery of wolves to 49% of the area in the western United States that holds sufficient prey to support wolves. That percentage of the range with recovery potential could drop to 23% over the next few decades owing to landscape change, or increase to 66% owing to habitat restoration efforts such as the removal of some roads on public lands. Comprehensive habitat and viability assessments such as those presented here, by more rigorously defining the Endangered Species Act's concept of “significant portion of range,” can clarify debate over goals for recovery of large carnivores that may conflict with human land uses.
The network of experimental forests and ranges administered by the US Department of Agriculture Forest Service consists of 77 properties that are representative of most forest cover types and many ecological regions in the nation. Established as early as 1908, these sites maintain exceptional, long-term databases on environmental dynamics and biotic responses. Early research at these sites focused on silviculture, ecosystem restoration, and watershed management. Over time, many of the properties have evolved into a functional network of ecological observatories through common large-scale, long-term experiments and other approaches. Collaboration with other institutions and research programs fosters intersite research and common procedures for managing and sharing data. Much current research in this network focuses on global change and interdisciplinary ecosystem studies at local to global scales. With this experience in developing networks and compiling records of environmental history, the experimental forests and ranges network can contribute greatly to formation of new networks of environmental observatories.
In 1999, the first phase of a multiyear program was initiated at the National Oceanic and Atmospheric Administration's National Marine Mammal Laboratory and Pacific Marine Environmental Laboratory to advance the use of passive acoustics for the detection and assessment of large whales in offshore Alaskan waters. To date, autonomous recorders have been successfully deployed in the Gulf of Alaska (1999–2001), the southeastern Bering Sea (2000–present), and the western Beaufort Sea (2003–2004). Seasonal occurrences of six endangered species (blue, fin, humpback, North Pacific right, bowhead, and sperm whales) have been documented on the basis of call receptions in these remote ocean regions. In addition, eastern North Pacific gray whale calls were detected in the western Beaufort Sea from October 2003 through May 2004. Here we provide an overview of this suite of research projects and suggest the next steps for applying acoustic data from long-term recorders to the assessment of large whale populations.
As the fields of ecology and conservation biology increasingly rely on models to address pertinent questions, there has been greater sharing of models among scientists. However, many models lack comprehensive documentation, especially in a format that is easy to use and to understand. Also, modelers lack a framework they can use when evaluating a model for its potential use. Here we outline how ecologists and conservation biologists can begin to establish a culture of good practice for model sharing. We offer suggestions on how model developers, model users, user communities, and journal editors can contribute to the appropriate sharing of ecological models.
To promote higher-order thinking in college students, we undertook an effort to learn how to assess critical-thinking skills in an introductory biology course. Using Bloom's taxonomy of educational objectives to define critical thinking, we developed a process by which (a) questions are prepared with both content and critical-thinking skills in mind, and (b) grading rubrics are prepared in advance that specify how to evaluate both the content and critical-thinking aspects of an answer. Using this methodology has clarified the course goals (for us and the students), improved student metacognition, and exposed student misconceptions about course content. We describe the rationale for our process, give detailed examples of the assessment method, and elaborate on the advantages of assessing students in this manner.