摘要:

Data collected on natural populations of Asarum caudatum in western Washington indicated that populations were polymorphic for growth rate, seed production, and palatability to a native slug. However, in habitats where slugs were not as abundant, populations of wild ginger were dominated by individuals allocating more energy to growth rate and seed production, and less to the production of an antiherbivore mechanism. On the basis of these data, I postulated that in the absence of grazing pressure, palatable, faster growing individuals would be at a competitive advantage over slower growing individuals that devote more energy to an antiherbivore mechanism. Under grazing pressure, however, fitness of the unpalatable individuals would be increased since smaller amounts of photosynthetic tissue would be consumed.

ISSN:0012-9658    

DOI:10.2307/1934969

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The wet tundra near Barrow, Alaska, is dominated by three species of graminoids: Dupontia fischeri, Carex aquatilis, and Eriophorum angustifolium. Root production, root turnover, and root distribution patterns of these three species were studied by direct observations of growing roots and by analysis of whole, interconnected tiller systems dug from the soil. Root weight per unit length and density of individual tillers were also measured in the field. Production of new roots was found to be strongly correlated with age of individual tillers, each species having a distinctive pattern and phenology. Root turnover rates also varied considerably; the range is from an annual turnover in E. angustifolium to 6—8(10) yr in C. aquatis. An estimated of root turnover on an ecosystem basis is about 100 g ° m—2° yr—2, or 25% of the live root biomass. Species with the shallowest and longest lived roots have the greatest weight per unit length of root, and vice versa. Each species has a characteristic root distribution pattern with depth and in relation to the progress of soil thaw.

ISSN:0012-9658    

DOI:10.2307/1934970

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Theoretical considerations and evidence from the literature suggest that early successional plant species should make a lesser commitment of resources to defense against herbivores, and should then provide better food sources for generalized herbivores than later successional and climax plants. Commitment to defense by plants is estimated by determining short—term palatabilities to two slug species; one native to western Washington, Ariolimax columbianus, and one introduced from Europe, Arion ater. Results of tests with 100 plant species of three growth forms and from different seral stages indicated that early successional annuals were significantly more palatable than early successional perennials which were significantly more palatable than later successional species. No correlation was found between palatability and evolutionary association of the herbivores with the plant species.

ISSN:0012-9658    

DOI:10.2307/1934971

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

Large single phytoplankton cells are likely to catabolize a smaller fraction of their biomass than do small phytoplankton cells. Under certain environmental conditions, this characteristic may be highly important in regulating the growth rates of large versus small phytoplankton. A model is developed incorporating experimental data on phytoplankton growth, respiration, and sinking rates as a function of cell size. Application of the model to specific oceanic regions shows that the net growth rate of large cells may exceed that of small cells when the mixed layer is relatively deep, despite the larger gross production rates characteristics of the smaller cells.

ISSN:0012-9658    

DOI:10.2307/1934972

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The energy content of eggs of 10 lizard species was determined and used as a measure of reproductive effort (ratio of clutch calories to body calories). Values for eggs ranged from 5.87 to 7.20 cal/mg ash—free dry weight (°=6.37). Species differences in calories going into reproduction during a breeding season, however, were primarily due to differences in clutch size and clutch frequency between species. Correlation analysis between three measures of reproductive effort, including the preceding, and a suite of demographic variables revealed only one significant correlation (negative) between clutch calories to body calories ratio and mean annual adult survivorship. The energy allocated to eggs in comparison to total annual energy expenditure was estimated for three of the species investigated. Sceloporus graciosus had the highest reproductive effort, with proportional values for first and older breeders about the same. The proportion of total energy expended on reproduction was slightly lower for UTA stansburiana, with first and older breeders exhibiting the same effort. Sceloporus jarrovi had the lowest reproductive effort, but showed an increasing effort with increasing age. These data suggest that the demographic environment may not be the primary selective pressure determining reproductive effort, and that reproductive effort may not be positively correlated with age in all species.

ISSN:0012-9658    

DOI:10.2307/1934973

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

An examination of selected ecological variables on the 18 low, sandy, non—disturbed islands of the northwestern Hawaiian Islands, and the vascular plants and birds, primarily seabirds, occurring there shows that species richness on low, sandy, oceanic islands is influenced by ecological diversity and is affected by variables similar to those on high, rocky islands. Species richness of vascular plants on these islands can be predicted by means of stepwise regression on the basis of area of vegetation, and to a lesser extent, elevation. In turn, variation in numbers of breeding species of seabirds, total species of seabirds, and total species of birds on these same islands can be predicted on the basis of number of species of vascular plants, and to a lesser extent, area of the island. Ecological diversity, although poor in quality, is of prime importance in regulating use of low, sandy, oceanic islands by any seabird. Although terrestrial bird use islands for obtaining food and for nesting whereas seabird use islands only as a nesting and roosting place, species of terrestrial birds and seabirds on islands are associated with similar ecological variables.

ISSN:0012-9658    

DOI:10.2307/1934974

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

To describe the thermal biology of Anolis marmoratus, a species living without congeners, we obtained 29 samples of air and body temperatures. Mean body temperatures (range 9.9°) differ from locality to locality, among habitats within localities, and during the day. Strong correlation of mean body with mean air temperatures among samples suggests that these lizards are routinely passive to ambient conditions. Indeed, short—term thermoregulatory behaviors such as basking and regulation of times of activity are rarely used by individuals in most populations. Nonetheless, evidence of habitat selection at one locality suggests that these anoles have long—term thermal preferences. The broad thermal niche of A. mamoratus seems primarily due to individual eurythermy rather than to populational differentiation. The general passivity of this and some other anoles may be an adaptation to life in tropical forests, where careful thermoregulation is disadvantageous.

ISSN:0012-9658    

DOI:10.2307/1934975

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

The disposal of secondary sewage effluent on a subalpine forest floor was investigated in terms of its relationship to nutrient discharge in a Tahoe basin watershed. Heavenly Valley Creek showed significant increases in NO3—1—N and ultraviolet absorbance downstream form a site that had been used for land disposal 5 yr prior to this study. These increases were traceable to subsurface discharge from the sprayed area. Evidence indicated that substances present in the spray area discharge and the streamwater are inhibitory to algal photosynthesis at in situ concentrations. This effect may be due in part to NO3—1—N which undoubtedly becomes stimulatory through dilution in the lake. Discharge from the spray area can be traced into Lake Tahoe by following patterns of UV absorbance which correlate closely with patterns of primary productivity. This correlation, combined with estimates of continuing heavy NO3—1—N loading of Lake Tahoe by Heavenly Valley Creek, reveals the long—term impact of land disposal of effluent on the ultra—oligotrophic lake.

ISSN:0012-9658    

DOI:10.2307/1934976

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

In southern New England Spartina alterniflora occurs as a tall grass (1.25—2m) within the intertidal zone and as a short form (0.3—0.4 m) within pannes on the high marsh. By means of electrophoretic comparisons of total soluble proteins and selected enzymes, along with reciprocal field transplants, an attempt was made to clarify the ecotype versus ecophene status of these different forms. All data obtained suggest that the tall and short forms are genetically indistinguishable and therefore merely reflect physiological responses to the environmental differences between the intertidal and panne sites.

ISSN:0012-9658    

DOI:10.2307/1934977

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY

摘要:

To establish plausible explanations of the factors determining patterns of local distribution and abundance of white—footed mice, Peromyscus leucopus, concurrent measures of habitat structure, plant species composition, and mouse density were performed in several seral stages at Point Pelee National Park, southern Ontario. Population density covaries with foliage profile structure among habitats in which P. leucopus occur, whereas floristic composition is unimportant. White—footed mouse distribution and restriction to nongrassland habitats may be due to a significant structural difference between grassland and nongrassland habitats.

ISSN:0012-9658    

DOI:10.2307/1934978

出版商:Ecological Society of America    

年代:1975

数据来源: WILEY