Treesearch

Wild-type house mice were used to test the effect of intrauterine position on anogenital distance (AGD) and to verify whether crowding stress would masculinize female pups, developing at all intrauterine positions, as has been demonstrated in CF-1 mice stressed by restraint, heat, and light. Stress of crowding was documented by comparing aggressive behavior, litter birth weights, and plasma corticosterone levels among females in different densities. AGDs were recorded from pups born to females housed from day 12 to 19 of gestation either individually with their mate (nonstressed) or in one...

Differences in hormone levels influence sexual differences in aggression. survival, home-range size and dispcrsal in rodents. The role oftestosterone in establishing some of these differences in wild house mice was examined. Females treated with either 0·5 mg of testosterone enanthate (TE-treated) or oil (control), and an equal number of untreated males, were released onto three 'highway islands' and periodically recaptured over the following 7 weeks. Tbe islands are segments of highway cloverleafs enclosed by entrance and exit lanes that reduce emigration. Competition was encouraged by...

Preparing for planting conifer seedlings reduces competition for site resources but creates poor range conditions. bare soil, low plant cover, adn little forage do not support forest grazing programs. At Boyd Hill on the Modoc National Forest, in California, several regeneration sites were prepared in 1988. Early in 1989 they were planted with ponderosa pine (Pinus ponderosa) seedlings. On five plantations that summer, live plant cover averaged just 2.5 percent. Except for shrubs, which covered 1.4 percent of the surface, cover values for plant groups (perennial grasses, annual grasses,...

We review and reinterpret major events in the evolution of pines and their stem rusts using information from their taxonomy, genetics, biogeography, and fossil history. Understanding of pine evolution has been significantly revised in the last 20 years. Pines appear to have evolved early in the Mesozoic and to have diversified and migrated throughout middle latitudes in the Northern Hemisphere supercontinent, Laurasia, by the end of the Mesozoic. By this time, the major subgenera had appeared (subgenus Strobus, oldest) as well as several early subsections, probably including at least...

Variation at 32 allozyme loci in nine disjunct populations of Part-Orford-cedar (POC) from the California floristic region was measured to estimate the amount and pattern of genetic variability in natural stands. Variation in electrophoretically detectable loci was moderately high, with mean number of alleles per locus = 1.9, 64.9% polymorphic loci, and observed heterozygosity = 0.13. Diversity was highest in the seven populations from the coastal mountains and lowest in the two populations from the inland portion of POC's distribution. The Sacramento River population in the inland group...

There's no doubt about it. Planting trees has caught the attention of the American public. In his 1990 State of the Union address, President Bush proposed planting a billion Fees annually for the next ten years. Inspired by the potential for trees to reduce greenhouse gases and mitigate global climate change, tree-planting programs such as Treepeople and Global ReLeaf are organizing campaigns at the local and national levels for a massive re-greening of America.

Why is a chapter on widespread species appearing in a volume on rare species? One answer to that is another question: Why focus on species in the first place? Granted, species do have a unique status. They are more or less closed units genetically, and species extinction signals the end of an evolutionary lineage that may have begun millions of years ago. By contrast. individuals and populations within species are lost and replaced all the time.

Data from the annual Christmas Bird Count between 1939 and 1989, around Honolulu, on the island of Oahu during late December, were analyzed to discover the annual rates of change and possible competitive interactions of introduced and native land bird species. Both total number of species and total number of individuals increased over the period. The proportion of species that were rare dropped, rose, and dropped again during the 50-year period, probably as a result of new introductions. Two species held steady, while 12 increased (about 9 linearly and 3 logarithmically). The higher rates...

Sediment transport occurring after spawning can cause scour of incubating embryos and infiltration of fine sediment into spawning gravel, decreasing intergravel flow and preventing hatched fry from emerging from the gravel. Documentation of these effects requires measuring gravel conditions before and after high flow periods and combining methods to record scour and fill and sediment infiltration by different grain sizes at different depths in the streambed. Scour and fill is best measured with scour chains, which can record the depth of maximum scour that occurs during high flow. Repetitiv...

Factors contributing to poor establishment of blue oak (Quercus douglasii) and valley oak (Q. lobata) in California oak-grassland savannas were studied in a series of acorn seeding experiments initiated in 1985. Exclusion of large herbivores permitted examination of herbaceous interference and small mammal and insect depredation. Herbaceous interference was the most important factor. Average emergence in all blue oak seedings with and without herb control was 45 percent and 29 percent, respectively. The respective values for all valley oak seedings were 60 percent and 46 percent. Average...