摘要:

Quantitative analysis of original land survey data was used to study the presettlement vegetation of a 681—km2watershed at a forest—savanna ecotone in the Driftless Area of southwestern Wisconsin. Five vegetation types were found: mesic forest, white oak—pine forest, oak—aspen forest, white oak woodland, and oak savanna. Existence of the five types was attributed to gradients of fire and climate, and the discrete boundaries between the types of topographically imposed discontinuities in the gradients. The mesic forest of the study area was at the northern limit of a mesic forest "island" in the extensive oak savannas of southwestern Wisconsin. The mesic forest island is a geologically controlled meteorological island, which experiences a combination of relatively high annual rainfall and cool summer temperatures. The presence of the mesic forest is attributed to this mesoclimate. Structural analysis of the mesic forest data and other evidence suggest a climatic change in the area at °430 BP

ISSN:0012-9658    

DOI:10.2307/1936853

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Demography, home range size, and sexual dimorphism of the common deermouse (Peromyscus maniculatus) were examined in three xeric communities of the West and Pacific Northwest. In heterogeneous communities, female mice inhabited the more favorable, moist microhabitats. Males were found in the less favorable, more exeric areas. The intersexual difference in home range size and body weight is positively correlated with habitat heterogeneity. Differential sex distribution with female dominance is a strategy that maximizes reproductive effort and survival of the young.

ISSN:0012-9658    

DOI:10.2307/1936854

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Small—volume samples of bactivorous ciliates were collected from a small pond. Qualitative (presence—absence) data were obtained from a set of 230 samples collected over all seasons during 3 yr and quantitative data were obtained from 81 samples collected during one summer. Analyses of these data demonstrate that apart from a segregation of taxa between aerobic and anaerobic benthic habitats, taxa were essentially independent in their distribution among samples. There was some indication of a net association in the qualitative samples, possibly due to seasonal and annual variations in ciliate abundance. There was little tendency for faunistically similar samples to be collected from the same site, at the same time, or form visually similar microhabitats. The frequency of samples containing different numbers of individuals and the ranked species abundance lists for samples taken at the same time and site are compatible with the species undergoing a stochastic pure birth and death process with rates linearly dependent on population size. The relative commonness of species is compatible with the hypothesis that the total number of occurrences is randomly partitioned among the species. Although communities of protozoa are thought to possess a complex structure maintained by interspecific interactions, the bactivorous ciliates in the pond appear to be an assemblage of essentially independent species undergoing density—independent growth processes and generally conforming to simple, neutral models of community structure.

ISSN:0012-9658    

DOI:10.2307/1936855

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Candida humicola, a parasitic yeast occuring in the gut of Green frog (Rana clamitans) tadpoles, enhanced the growth of tadpoles of this species under certain conditions. Low concentrations of C. humicola (1—10 cells per millilitre) increased the growth rate of tadpoles relative to siblings raised under identical conditions but without C. hunicola cells. Furthermore, the impact of a given concentration of C. humicola cells varied inversely with the size of the tadpole. Candida humicola appears to act as a mutualistic symbiont of the larger tadpoles and as a parasite of the small ones. Because larger tadpoles are more likely than their smaller siblings to metamorphose and reproduce, the mutualism benefits those individuals which are most likely to contribute to the continuation of the Green frog population. For this reason, resistance to the parasitism is not likely to develop. The parasite may act to regulate the adult Green frog population size by altering the probability of metamorphosis of individual tadpoles.

ISSN:0012-9658    

DOI:10.2307/1936856

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Plant litter was collected in traps from 8 to 10 replicates each of Ambarosia dumosa. Ephedra nevadensis, Krameria parvifolia, Larrea tridentata, Lycium andersonii, and Lycium pallidum in Rock Valley, southern Nevada, USA. Collections were made at biweekly to monthly intervals from 1975 to 1977 and handsorted into leaves, stems, flowers, and fruits. Lycium pallidum produced the most litter, with annual means ranging from 52 to 173 g per shrub. Annual means per shrub for other species ranged from 39 to 89 g (Lycium andersonii), 27 to 77 g (Larrea tridentata), 20 to 29 g (E. nevadensis), 6 to 18 g (K. parvifolia), and 3 to 21 g (A. dumosa). Litter fall was generally correlated with annual rainfall, which was low in 1975 (62 mm), high in 1976 (223 mm), and close to the long—term mean in 1977 (141 mm). Leaves were generally the largest litter category, followed by stems, fruits, and flowers. Large sample variations were found, particularly for reproductive parts. Aboveground litter fall from the six species, which comprise °82% of perennial plant biomass and °81% of shrub cover in Rock Valley, was about 117 kg/ha in 1975 and 318 kg/ha in 1976. Total aboveground litter fall for Rock Valley (all perennial and annual plants) was estimated to be 194 kg/ha in 1975 and 530 kg/ha in 1976. Distinct litter fall patterns occurred for shrub species and litter categories. Most litter fell during the summer months, with individual species peaks reflecting particular phenologies. Significant amounts of live aboveground biomass were shed as litter. Amounts of litter from the six species ranged from 7 to 83% of their respective live aboveground biomass.

ISSN:0012-9658    

DOI:10.2307/1936857

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Mark—recapture studies were conducted on a low (1675 m) and high (2542 m) altitude population of Sceloporus jarrovi in southeastern Arizona, USA from 1973 through 1976. Average age—specific mortality rates differed between altitudes only in the 0—1 yr age class. The increased mortality of neonates are low altitude was correlated with an increased number of potential predators and a significantly greater frequency of natural tail—breaks. Tail—break frequency did not differ between sites for older age classes. Survivorship and age at maturity were greater at high altitude. Low—altitude females mature in their first reproductive season. Transfer of neonates between altitudes indicate that high—altitude females do not mature in their first season even if raised at low altitude. Age at maturity appears to be adaptively adjusted by the demographic environment. Fertility schedules indicate that °40% of the replacement of low—altitude populations results from reproduction by 1st yr animals. There was a greater variation in replacement rate and population size at low than at high altitude.

ISSN:0012-9658    

DOI:10.2307/1936858

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Populations of goldenrods (Solidago canadensis) were sampled to determine the effects of three stem gall insects, Gnorimoshema gallaesolidaginis (Gelechiidae), Eurosta solidaginis (Tephritidae), and Rhopalomyia solidaginis (Cecidomyiidae) on resource allocation patterns in the plants. Gall infestations were as high as 38.5% and the dominant gall insect differed from site to site. The gall insects caused significant and highly specific effects on the plants. Each of the three gall types increased stem production, decreased current rhizome production, and lowered seed reproductive allocation as measured both by inflorescence production and propagule production. Vegetative reproductive allocation (the proportion of biomass allocated to new rhizome) was unaffected. With the exception of ball gall—beaing ramets, the number of new rhizomes produced was unaffected by the presence of galls. Growth of the elliptical gall significantly reduced shoot height and significantly increased lateral branching and propagule weight. Formation of the ball significantly reduced propagule weight and the number of new rhizomes produced. Thus gall insect—plant interactions may play an important role in the evolution of plant life history patterns in certain taxa. Future studies are needed to determine the effects of galls on entire clones (genets) and the implications of gall infestation on future growth, survivorship, and reproduction.

ISSN:0012-9658    

DOI:10.2307/1936859

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

Energy budgets are developed for two goldenrod stem gall insects: Eurosta solidaginis (Diptera: Tephritidae) and Gnorimoshema gallaesolidaginis (Lepidoptera: Gelechiidae). Energy budgets are also constructed for the parasitoid guilds associated with each of the gall insects. Over 25 kJ or °7% of mean ramet production were used in formation of these falls and support of the insects. If the gall insects were parasitized, only 15—20 kJ were used in gall and insect production. The ecological efficiencies of energy transfer between the gall insects and their parasites on a square—metre basis were 10 and 8% for Eurosta and Gnorimoshema, respectively. These insect energetics are then related to Harnett and Abrahamson's (1979) results for the effects of the two stem gall insects on resource allocation patterns in goldenrod, where gall—bearing ramets compared to non—gall—bearing ramets showed decreases of 45% (Eurosta) and 28% (Gnorimoshema) in ramet porgagule production. The energy lost form the ramet by having a ball gall is greater than is accounted for by energy flow into the gall, and the presence of either gall can have an appreciable impact on plant fitness.

ISSN:0012-9658    

DOI:10.2307/1936860

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

A model is given for multiple recapture studies on closed populations which allows capture probabilities to vary among individuals. The capture probability of each individual is assumed to be constant over time. Based on this model we give a nonparametric estimation procedure for population size. The estimator involves selecting one of a sequence of estimators which are each linear combinations of the capture frequencies. The individual estimators are derived from the generalized jackknife method. We also give a goodness of fit test for the model's assumption that individual capture probabilities do not change during the study. The robustness of this estimation procedure is investigated with a simulation study. By virtue of this study, and the theoretical nature of the estimator, it is judged to be robust to moderate variations in individual capture probabilities which may occur in commonly used short—term livetrapping studies.

ISSN:0012-9658    

DOI:10.2307/1936861

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY

摘要:

The dynamics of Northofagus forests in the near—timberline zone of south—central Chile are interpreted from structural analyses of pure stands, of Northofagus pumilio (Poepp. et Endl.) Krasser and mixed stands of N. betuloides (Mirb.) Bl. and N. pumilio. Nested quadrat pattern analyses suggest that the spatial distributions of these tree species are greatly affected by massive disturbances which periodically create conditions favorable for their regeneration. Their spatial distributions are also significantly affected by intra— and interspecific plant interactions. For example, as a stand ages, initially clustered distributions of saplings become regular or random as a consequence of the relatively large canopy space required by the shade—intolerant Northafagus. Strong community control of vegetation is also indicated by the inhibition of tree regeneration by the abundant understory bamboo, Chusquea tenuiflora Phil. In general, in the near—timberline Northofagus forests tree regeneration depends either on periodic, massive disturbance (by mass movements, volcanic ash desposition, avalanches, or large treefalls) or on the synchronous flowering and subsequent mass die—off of the local population of C. tenuiflora.

ISSN:0012-9658    

DOI:10.2307/1936862

出版商:Ecological Society of America    

年代:1979

数据来源: WILEY