Geology topics

Sterling C. Keeley

Publications and source records attributed to Sterling C. Keeley.

4 recordsLinked to original sources

USGS1984

Seed predation due to the yucca moth symbiosis

All species of Yucca (Agavaceae) require the pollinator services of a species of moth in the genus Tegeticula ( Lepidoptera : Incurvariidae). These moths oviposit in the ovary of the plants and the larvae are entirely dependent upon Yucca seeds for food. The extent and distribution of larval seed predation was examined in nine Yucca species in the southwestern United States. The proportion of seeds destroyed by the yucca moth ranged from 3 % in Y. schidigera from coastal southern California to 45 % in one population of Y. angustissima from southern Utah. This sampling was done in 1979 at which time the Y. schidigera population averaged 0.6 larvae per fruit and the population of Y. angustissima averaged 9.3 larvae per fruit. A second sampling of these populations in 1982 averaged 0.5 for Y. schidigera and 5.6 for Y. angustissima . Several species showed significant differences between populations in the number of larvae per fruit. Contrary to expectation, based on the dogma that fruit production is dependent upon Tegeticula pollination (which is always followed by oviposition), a large number of fruits were found without larvae. The proportion varied greatly between populations but was as high as two thirds of all fruits in some populations. Observations suggested that these flowers had been pollinated by Tegeticula and the moths had oviposited in them but that the eggs failed to hatch.

American Midland Naturalist↗

USGS1984

Post-fire recovery of California coastal sage scrub

Postfire regeneration of the shrub and herb vegetation on eight coastal slopes of California coastal sage scrub was studied in the first two growing seasons after fire. All shrub species resprouted with the exception of the suffrutescent Lotus scoparius , though it is not known if this species was alive prior to the fire. It was estimated that 70% of the prefire shrub populations resprouted and these sprouts covered one third of the ground surface by the end of the second season. In contrast to chaparral, seedling establishment from soil-stored seed was low (∼ 102-103/ha) in the 1st postfire year. Resprouts of most major species ( Artemisia californica , Encelia californica , Haplopappus squarrosus , Eriogonum cinereum ) flowered and set seed in the 1st year. Seedling densities were ∼ 104-106/ha in the 2nd year. Herbs dominated the first postfire season vegetation in number of species, cover and biomass. The magnitude of the postfire herb flora was comparable to that in chaparral after fire and included many of the same species. On several slopes, "pyrophyte endemic" annuals ( Lupinus succulentus , Lotus salsuginosus , Phacelia parryi ) dominated the first season and were rare or absent in the 2nd year. One major distinction between these coastal sage sites and chaparral was that resprouting perennial herbs dominated some slopes in the first postfire season and most slopes in the second season in coastal sage. Seedling recruitment of perennial herbs was rare; 26 of the 28 species were present only as resprouts. Total herb cover was markedly lower in the 2nd year despite the fact that it was a wetter year. Between the 1st and 2nd years, shrub cover ∼ doubled, largely from resprouts, annual herb cover declined markedly and perennial herb cover remained relatively constant. The perennial bunchgrass Stipa lepida was an important component of the herb flora on all slopes and was the only species (herb or shrub) to exceed 1/m2 on all eight slopes.

California↗

USGS1981

Post-fire succession of the herbaceous flora in southern California chaparral

Postfire succesion of the temporary herbaceous and suffrutescent cover was studied after chaparral fires in San Diego County, California, USA. Four categories of species make up the temporary cover. (1) "Generalized herbaceous perennials" are present before and after fire. Populations of these herbs are sparse under the shrub canopy. They resprout after fire from bulbs or other underground parts and postfire populations are sparse. (2) "Generalized annuals" are present in openings before fire but produce their peak population size in the first few years after fire. (3) Specialized "fire—annuals" are more or less restricted to the 1st postfire yr. (4) Specialized "fire—perennials" (subshrubs) are uncommon before fire, establish from seed in the 1st postfire yr and reach maximum cover in the 3rd and 4th yr. Community—level changes in cover and diversity are interpreted in light of differences in population dynamics of the four groups. Specis richness was highest in the 1st yr after fire because this was the only time all four groups were present together. Throughout succession herbaceous species richness was positively related to herb cover, negatively related to elevation and unrelated to slope aspect. The number of annual species fluctuated greatly through succession at all sites, but the number of herbaceous perennials did not. Herb cover fluctuated markedly from year to year and was positively related to amount of annual precipitation and negatively related to subshrub or "fire—perennial" cover. Artificial seeding with annual rye grass Lolium multiflorum had not apparent effect on total herb cover since sites with poor Lolium establishment had as high or higher herb cover as sites with high Lolium establishment. Lolium success was at the expense of the native cover and this negative effect was greatest on the "fire annuals."

Ecology↗

USGS1977

Energy allocation patterns of a sprouting and nonsprouting species of Arctostaphylos in the California chaparral

The r- and K-selection theory was used to generate testable hypotheses about patterns of energy allocation in two chaparral shrubs of different reproductive strategies. Terminal-branchlet vegetative and reproductive biomass of the nonsprouting Arctostaphylos glauca and the sprouting A. glandulosa were sampled in a 23-year-old and a 90-year-old stand of chaparral to test the predictions that: (1) the terminal vegetative growth (g dry weight/m 2 of areal coverage) would be equal in the two species, in both stands; (2) oven dry weight (g) of reproductive parts/m 2 of areal coverage would be greater in A. glauca than in A. glandulosa in both aged populations; (3) allocation to reproductive parts by the shrubs in the 23-year-old stand would be greater than (or equal to) that of the 90-year-old shrubs. The amount of terminal vegetative growth was equal for both species in the 23-year-old and the 90-year-old stands. There was no statistically significant difference in the weight of fruits produced by the two species in the 23-year-old stand. However, fruit production by A. glauca was significantly greater than by A. glandulosa in the 90-year-old stand. Fruit production was also significantly greater for the older A. glauca shrubs than for those in the 23-year-old stand. The relationships of rainfall pattern and age of shrubs to fruit production are discussed.

California↗