Exotic plants in early and late seral vegetation of fifteen northern Rocky Mountain environments (HTs)

We determined the capacity of exotic plants to invade major environmental types of the northern Rocky Mountains. We did this by observing their presence on disturbed and undisturbed sites in relatively well inoculated locations--corridors adjacent to highways--on transects across the mountains in Glacier National Park and Grand Teton National Park and on low-altitude sites between them. We draw 3 primary conclusions. First, of 29 exotics commonly found, the most dominant are intentionally introduced grasses ( Agrostis, Bromus, Dactylis , and especially Phleum pratense and Poa pratensis ) and legumes ( Melilotus, Medicago , and Trifolium ) rather than the forbs more often listed as noxious. Second, in the environmental types studied, disturbed sites are invasible, except in the alpine. Third, invasion of undisturbed sites declines from grasslands and open forests to alpine to moist forests. This gradient probably represents a decline in resource (light, water, nutrients) availability for herbs, except in the alpine, where a physical limitation is suggested by the poor performance of exotics on noncompetitive disturbed sites.     

A life history study of the Snake River plains endemic Lepidium papilliferum (Brassicaceae)

Lepidium papilliferum is an ephemeral species that occupies ""slick spot"" microhabitats in the matrix of sagebrush steppe vegetation of the southwestern Snake River plains, Idaho, USA. We related population demographic data collected from 1993 to 1996 to on-site precipitation data on the Orchard Training Area west of Boise. We also carried out field seed-retrieval and in situ seed bank studies. We found that L. papilliferum has a dual life history strategy. A fraction of each cohort sets seed as summer annuals, while the remaining plants remain vegetative and potentially biennial. Surviving biennials flower and set seed along with the annual cohort of the following year. The switch to flowering as an annual appears to be based on threshold rosette size. Probability of survival to flowering was much lower for biennials than for annuals of the same cohort, but surviving biennials sometimes had enhanced seed production. The summerdry environment of the Snake River plains combined with the slick spot habitat has apparently selected for a primarily summer annual life cycle for this species. Seeds were highly dormant at dispersal and were not responsive to dormancybreaking cues. Those from a given cohort of L. papilliferum remained viable in the soil for at least 11 years. This persistent seed bank provides a buffer against extinction in sequences of years when seed production is low or absent. Estimated seed bank size varied from near zero for a heavily disturbed site that formerly supported the species to 18 viable seeds · dm -2 for an extant population in high-quality habitat. Management for population preservation for L. papilliferum should focus on protecting the seed bank from destruction caused by livestock trampling and other anthropogenic disturbances.     

Biomass of fifty conifer forests and nutrient exports associated with their harvest

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Inhibition of angiotensin-converting enzyme by analogs of peptides fromBothrops jararaca venom

Zusammenfassung Nachweis mit Analogen der im Gifte vonBothrops jararaca gefundenen Peptide, dass die Inhihibition des Angiotensins «converting enzyme» von zwei eindeutigen Teilsequenzen dieser Peptide abhängig ist. Die hohe spezifische kompetitive Inhibition, hervorgerufen durch die Peptide vonBothrops jararaca, wird der Bindung ihrer Tripeptidreste vom Carboxyterminus mit dem aktiven Zentrum des Enzyms zugeschrieben, die in gleicher Weise wie die Peptidsubstrate mit dem Enzym gebunden werden. Die Wirksamkeit der Giftpeptide hängt von der Bindung eines zweiten Teiles der Peptide mit dem Enzym ab.     

Cyclic activity of the corpus allatum related to gonotrophic cycles in adult femalePeriplaneta americana

Zusammenfassung Durch Inkorporation von¹⁴C-Methionin in die Corpora allata vonPeriplaneta americana werden während des Eireifungszyklus zwei Aktivitätsmaxima festgestellt und diese als Juvenilhormonsynthese interpretiert.