摘要:

The bottomland forest on Horseshoe Lake Island, located on the Mississippi alluvial plain in Alexander County, Illinois in comprised of 2 stands, one relatively undisturbed and the other which is recovering from disturbance in the late 1800s or early 1900s. In both stands vegetational structure, gradient relationships, diversity and size—class characteristics were studied. In the old—growth stand, 35 soil—site variables were measured or estimated for interpretation of vegetational patterns and species distributions. Both direct and indirect gradient analyses were evaluated for use in floodplain forest studies and ultimately the indirect approach with multiple regression interpretation was used to construct a gradient model of the vegetation. Basal area and density of the old—growth and floristic composition of both stands are typical of much of the original Southern Floodplain Forest. The coenocline was divided into 3 segments, mesic, transition and wet with the first and last corresponding to the ridge and hardwood bottoms described by Braun (1950). The important species on the ridge bottoms are Acer saccharum, Asimina triloba, Liquidambar styraciflua, Ulumus rubra, Quercus rubra and Tilia americana and are associated with well—drained soils and infrequent flooding. The transitional segment is dominated by Asimina triloba, Liquidambar styraciflua, Quercus michauxii, Quercus muhlenbergii and Ulmus americana with Quercus pagodaefolia and Quercus shumardii as associates on moderately heavy and poorly drained soils with intermediate flooding. The hardwood bottom sites are dominated by Acer rubrum, Fraxinus pennsylvanica, Liquidambar styraciflua and Ulmus americana and may be flooded for several months each year and have heavy textured, poorly drained soils. Multiple regression analysis with ridge regression revealed that Fraxinus americana and Acer saccharum have wider tolerances to flooding and poor aeration than previously reported. Importance Values of several species were related to duration and depth of flooding, soil mottling and soil texture indicating that distributions are affected by a site—inundation, soil drainage—aeration complex. Diversity of the tree stratum is comparable with that found in some of the mixed mesophytic forests elsewhere. Due to competition from Asimina triloba and Aesculus discolor and possibly some environmental limitations due to the northern location of the stands, the shrub—sapling stratum is depauperate. Along the coenocline from mesic to wet sites density and equitability decrease while basal area increases. Size—class analysis indicates that both the negative power and negative exponential functions fit the size—class distribution for the 2 stands but that neither is entirely appropriate. The old—growth stand is characterized by 3 groups of individuals each with different mortality rates which give a plateaued deviation from each model. The secondary stand is more balanced and does not exhibit a well developed plateau. A comparison of individual species reveals that various regeneration patterns are present which range from uneven—aged (sized) in the case of Acer saccharum to even—aged for Fagus grandifolia, Quercus rubra and Ulmus rubra. The plateaued pattern in the old—growth stand does not reflect past disturbance but apparently is a characteristic of this forest. The principal mode of regeneration in this stand is gap—phase replacement.

ISSN:0012-9615    

DOI:10.2307/2937230

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

At Monteverde, Costa Rica, 10 successional plant species used 14 hummingbird species for pollination. Displacement among flowering seasons suggests that the plants influenced hummingbirds to abandon another. There was no evidence that the flowering of one plant influenced hummingbirds to abandon another Pollination is simultaneously flowering plants likely suffered nonetheless, since birds tended to move indiscriminately among flowers of different species and could lose much pollen between successive visits to conspecific plants. This may have led to scatter in flowering peaks by favoring the quick establishment of plant colonists with unique flowering seasons over colonists whose flowering seasons coincided with those of established species. The continuous supply of nectar provided by staggered flowering peaks maintained a continuous supply of hummingbirds competing for nectar. Even inconspicuous plants with few flowers received sufficient hummingbird visits for moderate to high potential rates of outbreeding. At large, flower—laden trees and shrubs, hummingbirds defending feeding territories evidently effected much inbreeding, but movements of intruders between territories kept inbreeding from becoming absolute. Nectar secretion rates varied widely among flowers of each of the 5 plant species in which nectar volume was measured. Many flowers produced little or no nectar, while a few secreted quite copious volumes. This "bonanza" pattern may benefit plants by reducing caloric expenditures on nectar while increasing the duration of hummingbirds' foraging bouts. The latter possibility was tested and verified experimentally with artificial flowers exposed to a free—living hummingbird on Trinidad, West Indies. When pollinators are abundant, plants with "bonanza" patterns can attract consistent visitors and rare, inconspicuous plants can count on consistent service. At Monteverde, the unspecialized, opportunistic nature of both plants and birds assured abundant hummingbirds and resulted in a well—integrated complex of plants and pollinators despite the transient nature of the successional habitats.

ISSN:0012-9615    

DOI:10.2307/2937231

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

Fish communities associated with model and natural reef patches were studied to determine the effects of heterogeneity, area, and isolation on the number of fish species in these systems. The effects of season and succession on the structure of these communities were also examined. Species turnover was estimated to determine if numbers of fish species on small reefs can be viewed as a balance between immigration and local extinction. Interspace size diversity, one facet of reef heterogeneity, was not positively correlated with the number of fish species on either model or natural reefs. In addition, interspace size diversity had no significant effects on species composition. In most of the cases examined reef height, another aspect of reef heterogeneity, was positively correlated with the number of fish species and species diversity, H', on natural reefs. Observations of selected fish species inhabiting model reefs support the hypothesis that vertical zonation is a means of resource partitioning in these fish communities. A negative correlation was found between reef isolation and number of fish species on patch reefs. This correlation was strongest during periods when fish population sizes were lowest. Season had more of an effect on the structure of fish communities on model reefs than did succession. Immigration and local extinction of fish species occurred on model reefs throughout the study. Patterns of immigration and extinction approximated the predictions of the MacArthur—Wilson equilibrium model of insular zoogeography when species turnover was highest.

ISSN:0012-9615    

DOI:10.2307/2937232

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

The coefficients of variation of daily discharge and the logarithm of daily discharge were calculated from long term records in 15 river systems, including runoff—fed prairie rivers in Illinois and Missouri, groundwater— and spring—fed upland rivers in Southern Ohio, Southern Illinois and the Missouri Ozarks, and the snowmelt—fed Powder River in Wyoming. In almost all cases variability was lower in downstream sections. The patterns of temporal variability were consistent with the hydrology of the basins, with source of flow and size important determinants. Diversity patterns of fishes were tabulated for the same rivers from literature records. In all rivers, diversity increased rapidly from upstream to downstream sections, almost entirely the result of addition of new species with little replacement of the upstream fauna. Maximal species richness was usually in the lowest sections (order VI or greater). Headwater diversity was lowest in the rivers with the most variable headwaters, the increase in diversity downstream steepest for those rivers with the steepest decrease in variability, and the number of species in downstream sections was greater in rivers with more constant downstream sections. Longitudinal replacement rates were very low in all rivers studied, but were generally larger in the most temporally constant rivers. Literal replacement was moderate between small tributaries, but was low between major tributaries. The diversity gradients of individual feeding groups were similar to the gradient for all species, with an increase in richness from headwaters downstream in all groups with intermediate maxima sometimes seen. Piscivores showed consistently steeper diversity increases. These observations were related to hypotheses of factors controlling stream fish distributions. They are most consistent with hypotheses relating control to extermination—recolonization dynamics or the interspecific competition mediated by temporal variability and habitat structure.

ISSN:0012-9615    

DOI:10.2307/2937233

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

With the exception of a recently discovered rare species, the gastropod genus Conus is represented only by Conus miliaris at Easter Island, and isolated outpost of the Indo—West Pacific (IWP) marine biota probably<2.5 million yr old. Throughout most of the IWP region. C. miliaris co—occurs with 4—23 congeners on marine benches and coral reefs. Compared with these central populations, Easter Island C. miliaris (1) is more abundant in favorable habitats, (2) utilizes different habitat and food resources, and (3) is ecologically released with respect to food and probably depth range, but not microhabitat. Most striking, the major prey species (Onuphis sp.; 31% of the diet) belongs to a family of polychaetes not known to be exploited by any Conus species elsewhere. In all, 6 species of polychaetes eaten rarely or not at all by C. miliaris elsewhere comprise 77% of its diet at Easter Island. Sixteen prey species are eaten at Easter Island (vs. 2—8 in central IWP localities) and prey species diversity measured by the H' statistic is 2.0 vs. 0.2—1.3. Shifts to larger prey species with increasing size of C. miliaris account for some of the high prey diversity, but analysis of multiple feedings revealed that 68% of such individuals had eaten polychaetes of 2 or more species. Several polychaete species that C. miliaris preys on the Easter Island but not elsewhere are important components of the diets of other Conus species in the central IWP. Some of the ecological expansion of C. miliaris at Easter Island is thus directed toward resources that absent congeners would be expected to utilize were they present, or if they should colonize the island in the future. It is suggested that the virtual absence of congeneric species and increased intraspecific competition in dense populations at Easter Island have selected for the observed ecological expansion.

ISSN:0012-9615    

DOI:10.2307/2937234

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY

摘要:

This paper concerns the growth of 2 predator species competing exploitatively for the same prey population. The prey population grows logistically in the absence of predation, and the predators feed on the prey with a saturating functional response to prey density. Specifically, we assume that Michaelis—Menten kinetics or the Holling "disc" model describe how feeding rates and birth rates change with increasing prey density. We focus on the question of which predator species will survive and which will not, given the growth parameters of the prey and the functional response parameters of the 2 predators. Which predator wins or loses depends critically on the relative magnitude of the prey carrying capacity, K, and the λ parameters of the 2 predators. °irepresents the prey density at which the ith predator "breaks even" (equal birth and death rates). This prey density is defined by the product of the predator's half—saturation (Michaelis—Menten) constant times the ratio of the predator's death rate to its intrinsic rate of increase. Coexistence is also possible for a wide range of parameters, but only as a periodic solution. A primary conclusion is that coexistence is possible only if the predator with the smaller half—saturation constant also has the smaller birth—rate—to—death—rate ratio. This necessary constraint is the mechanistic equivalent to requiring that 1 predator be an "r—strategist" and the other be a "K—strategist." This condition is insufficient to guarantee coexistence, however. If the prey carrying capacity, K, is "too small" the K—strategist wins, and if K is "too large," the r—strategist wins. The bounded region of intermediate K values permitting coexistence is defined by the functional response parameters of the 2 predator species. The greater the disparity between the half—saturation constants of the 2 predators, the larger the region of K permitting coexistence.

ISSN:0012-9615    

DOI:10.2307/2937235

出版商:Ecological Society of America    

年代:1978

数据来源: WILEY