摘要:

Population dynamics, energy budgets, and nutrient concentrations were used to develop a compartment model for evaluating energy flow and nutrient fluxes in the spider and orthopteran components of an eastern Tennessee grassland ecosystem. The arthropod community consisted of; herbivores–Melanoplus sanguinipes (Acrididae), Conocephalus fasciatus (Tettigoniidae), and several of the Homoptera—Hemiptera; omnivore–Pteronemobius fasciatus (Gryllidae); and predators–Lycosa spp. (Lycosidae). Weekly estimates of arthropod density and biomass and monthly estimates of vegetation biomass were made during the 1965—69 growing season. Supporting studies included: (1) determination of caloric equivalents; (2) measurements of arthropod metabolism; (3) determination of whole—body concentrations of Na, Ca, and K; (4) estimation of biological turnover rates of these nutrients with radioactive analogues; and (5) field studies of arthropod feeding habits and food consumption. Total net primary production of the grassland ecosystem was 1,274 kcal/m2; 89% of this total was by grass species (Festuca arundinacea and Andropogon virginicus) and 11% by green forbs. Herbivores and omnivores consumed 9.6% (122.9 kcal/m2) of net primary production. Annual net secondary production by the insect community was 32.05 kcal/m2. Total net tertiary production by spiders was 2.26 kcal/m2. Total annual energy flow (= total assimilation) through the community was 75.6 kcal/m2. Herbivores accounted for 79.8% of this total, omnivores 12.2%, and predators 8.1%. Whole—body concentrations of sodium increased with higher trophic position in the food chain: vegetation (0.43 mg/g ash free dry wt = AFDW), prey (1.18 mg/g AFDW), and predators (1.94 mg/g AFDW). Calcium concentrations decreased from vegetation (5.82 mg/g AFDW) to prey (0.85 mg/g AFDW) and remained constant to predators (0.88 mg/g AFDW). Potassium concentrations were much higher in vegetation (14.28 mg/g AFDW) than in either the prey (1.87 mg/g AFDW) or predators (1.96 mg/g AFDW), which were essentially the same. Sodium and potassium behaved similarly in their movement through arthropod food chains. The low concentrations of calcium in arthropod trophic levels and the rapid elimination of this element from each trophic level suggest that calcium is not as limiting as are sodium and potassium in this arthropod community. Herbivores, the dominant members of the arthropod fauna, attained a maximum standing crop of 927 mg/m2(Melanoplus = 705 mg/m2, Conocephalus = 200 mg/m2, and the Homoptera—Hemiptera = 22 mg/m2). This trophic level was responsible for 85% of the sodium turnover, 76% of the calcium turnover, and 78% of the potassium turnover by the arthropod component of the ecosystem. The omnivore Pteronemobius fed equally well on fresh vegetation and on litter. It reached a maximum biomass of 194 mg/m2and utilized 10% of the sodium, 22% of the calcium, and 20% of the potassium which passed through the arthropod community. The predator (Lycosa spp.) biomass reached a maximum of 146 mg/m2in late fall and was responsible for 5% of the sodium, 2% of the calcium, and 2% of the potassium utilized by the arthropod component of the ecosystem. Wolf spiders consumed 21% of total net secondary production. Absence of other predator species in collections from the arthropod community suggests that Lycosa was the dominant invertebrate predator in this grassland ecosystem.

ISSN:0012-9615    

DOI:10.2307/1942433

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

Extensive sampling of chaparral with 10—m line intercepts in the San Gabriel and San Bernardino Mountains of southern California revealed site—oriented vegetative characteristics and successional patterns. Of the 78 species encountered, few were widespread and abundant; most were local and infrequent. The most widespread and abundant species were long—lived rootcrown sprouters. Adenostoma fasciculatum (chamise), the most frequently encountered shrub, occurred on 71.4% of the sites and composed one—fifth of all shrubs in the study. The second most common species, Quercus dumosa (scrub oak), appeared on 32% of the sites sampled. Many non—sprouting subshrubs and woody species were restricted to elevations below 3,000 ft (ca. 900 m), sunny exposures, and young stands. Chaparral succession, both in composition and rate of change, is influenced most by aspect, particularly north— and south—facing slopes. Next in importance is the influence of coastal and desert exposure. Elevation is a factor that may compensate for coastal—desert exposure or aspect. Percentage of slope is least important. The rate of succession after fire in coastal chaparral is slowest on south—facing slopes below 3,000 ft. Early stages of shrub succession are characterized by a mixture of chaparral seedlings, resprouts, and seedlings of coastal sage subshrubs. Most of the present—day chaparral on south—facing slopes is a coastal sage—chaparral subclimax due to frequent fire. On fire—free sites a chamise—chaparral climax community develops within 30 years after fire. The fastest succession rate is in coastal chaparral on north—facing slopes above 3,000 ft. The profusion of coastal sage subshrubs is missing, and vigorous, tall—growing sprouting species are abundant. The death of large, short—lived species in stands older than 25 years allows pockets of seral species to develop in the climax scrub oak—chaparral. Chaparral succession is not a series of vegetational replacements, but a gradual ascendance of long—lived species present in the pre—fire stand. The pattern of chaparral succession on desert exposures differs from that on coastal exposures. Slope aspect is less important, but proximity to the Pacific Ocean is more important than on coastal exposures. Fire favors the sprouting species of chaparral over woodland and forest communities bordering the chaparral communities. Fewer chaparral species occur on desert exposures than on coastal ones. Seedling and mature shrub mortality rates are lower in desert than in coastal chaparral. Succession after fire in desert chaparral is slow, and the climax community is composed of large shrub specimens with subshrubs clustered around their skirts and a canopy broken by intershrub spaces. Chaparral stands older than 60 years often are decadent, especially chamise—chaparral. Old stands are characterized by a high proportion of dead wood, little annual growth, and no new seedling development. Various phytotoxic substances may account for the loss of vitality and lack of regeneration. Maintenance of vigorous chamise—chaparral is shown to be dependent on fire. A re—evaluation of current fire—exclusion and suppression practices is needed. The present fire—exclusion policy is probably the least desirable one to insure the perpetuation of chamise—chaparral.

ISSN:0012-9615    

DOI:10.2307/1942434

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

To investigate experimentally the relationship between dispersal and population regulation in small mammals, voles were removed continuously from two plots in southern Indiana for 2 years. Three control populations of two Microtus species were monitored over the same period, and animals dispersing onto the experimental areas were compared with resident control animals for the following characteristics: (1) age, weight, and sex; (2) genotype for two polymorphic plasma proteins, leucine aminopeptidase (LAP) and transferrin (Tf); and (3) exploratory, aggressive, and general activity behavior of males. Dispersal was most common during the fall and winter, and in the phase of population increase 59% of male and 69% of female Microtus pennsylvanicus loss from two control populations could be accounted for by dispersal. In contrast, little of the high loss during the population decline could be associated with dispersal. In the late peak and decline periods male M. pennsylvanicus of the Tf—E and LAP—S phenotypes were more common among dispersing animals. In Microtus ochrogaster males the very rare Tf—F type was found only in dispersing ales. Young females were more common in dispersing populations of both species, and sexual maturation and dispersal were related in both vole species. However, dispersal by adults was only common. Dispersing males tended to be less active than males of resident populations. During a period of peak population density, dispersing male M. pennsylvanicus were more aggressive. As population density increased, "intolerant" animals moved into less densely populated areas. The genetic differences between dispersing and resident populations tend to support Howard's hypothesis that a genetic polymorphism influences the tendency to disperse. The association between increasing populations and abundant dispersal agrees with Lidicker's theory of population regulation by emigration and Chitty's hypothesis that a behavioral polymorphism regulates population density.

ISSN:0012-9615    

DOI:10.2307/1942435

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY

摘要:

A general theory of distribution suggests that the microhabitat, habitat, and geographic distribution of Psephenus herricki is related to water turbulence. The different life stages typically occur in stream riffles. Adults are found in riffles because they are "attracted" to the moist wave—splashed rocks that stick out of the water. These same rocks provide a mating site and give the female access to the subsurface materials for oviposition. The microdistribution of eggs is a function of the distribution of wave—splashed rocks during oviposition and female oviposition behavior. Oviposition initially accounts for the large numbers of larvae in riffles, but larvae live about 2 years giving them sufficient time to disperse into the runs and pools. Dispersion, however, is negligible due to a thigmokinesis that inhibits vagility when they are wedged in the interstitial spaces of the substrate. This and the distribution of algae on rocks seems to determine the microdistribution of larvae. Riffles contain an abundance of these interstitial crevices due to sorting by stream turbulence. Turbulence and physiography, governing the geographic distribution of riffles, directly influence the geographic distribution of the species.

ISSN:0012-9615    

DOI:10.2307/1942436

出版商:Ecological Society of America    

年代:1971

数据来源: WILEY