摘要:

The population dynamics of five species of foliaceous corals (Agaricia agaricites forma purpurea, A. lamarcki, Leptoseris cucullata, Montastrea annularis, and Porites astreoides) was followed on Jamaican reefs using annual photographic censuses. Overall, population cover, size frequencies, and number of colonies were stable over the monitored period from 1977 to 1980. However, individual colonies were in turmoil: of the original 883 colonies, 315 were killed outright and 499 suffered partial colony mortality (injury) at least once during the 3 yr. Partial mortality generated an additional 189 colonies by fission, while larval recruitment added another 201, and fusion subtracted 40 colonies. The net result was a decrease of<10% in number of colonies. There was considerable variation among years and sites in measured life history parameters, as well as striking differences between species. The most stable populations were M. annularis and A. lamarcki, followed by P. astreoides, A. agaricites, and L. cucullata. Rates of partial— and whole—colony mortality were strongly dependent on colony size for all species. Typically, small colonies either were unharmed, or were killed outright, while most large colonies survived but were injured each year, often by extensive amounts. The amount of tissue lost from a population through injuries was usually much greater than through the death of whole colonies, even in a year which included a major winter storm. Frequently, large corals were split asunder by partial mortality to produce several daughter colonies, which presumably were of identical genotype. Therefore counts of physically separate colonies exceeded the number of genetically distinct individuals (genets), by at least 20%. Individual genets, measured as the lateral extent of known daughter colonies, were frequently up to 5 m across, and for M. annularis and A. lamarcki were certainly several centuries old. Colony extension rates measured in situ were very weakly dependent on depth from —10 to —55 m, and were independent of colony size. Small colonies showed much faster relative changes in area, although even the largest corals continued to grow if they avoided major injuries. Within a size—class, the fates of colonies were diverse because of differential rates of growth and shrinkage, so that size was a very poor indicator of age. Differences in the life history and "mobility" between species are reflected in the taxonomic and morphological composition of coral communities over the reef. Shallow—water assemblages of foliaceous corals are composed of more dynamic, delicately built species, while many deeper water communities are dominated by slower growing, robust species. Ironically, disturbance on coral reefs often seems to favor the organisms most vulnerable to damage.

ISSN:0012-9615    

DOI:10.2307/1942555

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The objectives of this study were to measure larval growth and mortality rates in a butterfly population and to determine how these rates vary locally in space and time. The survivorship and growth rates of 1353 Papilio polyxenes larvae, placed on natural food plants in typical habitats, were followed during both generations of 1973 and 1974. In each year and generation, cohorts of first instar larvae were set out on three commonly used host—plant species and at two elevations. Larvae reaching the fifth instar were returned to the laboratory, where the surviving pupae gave rise to 87 adults. Together with estimates of egg mortality in the field (50%) and the sex ratio of emerging adults (50/50), this result indicates that females must lay at least 60 eggs, on average, to replace themselves once in the next generation. Stage—specific mortality rates (qx) averaged 0.59, 0.33, 0.35, and 0.41 for the first four instars, respectively, approximating a Type II survivorship curve (constant mortality rate). Both the shapes of survivorship curves and the probability of reaching the fifth instar were highly variable from one treatment to another, however, providing a heterogeneous pattern of survivorship in space and time Survivorship was greater in 1973 than in 1974, probably due to different weather conditions; it was greater at high—elevation than at low—elevation sites; and it was greater on wild carrot, Daucus carota, and on parsnip, Pastinaca sativa, than on poison hemlock, Conium maculatum. Survivorship of larvae placed artificially did not differ from that of larvae hatching from wild—laid eggs on the same host species at the same time and place. Arthropod predators attacking larvae included spiders as well as hemipterans of the families Nabidae, Reduviidae, Coreidae, and Pentatomidae. Parasitoids emerging from larvae or pupae belonged to the families Phoridae, Tachinidae, Ichneumonidae, and Braconidae. Our results, supplemented by predator—exclusion experiments in 1977, indicate that predation is the major source of larval mortality, small (arthropod) predators having the greatest impact on younger larvae and large (vertebrate) predators the greatest impact on older stages. Larvae grew faster in 1973 than in 1974, probably because of more favorable weather in 1973. Growth was faster at low— than at high—elevation sites and markedly faster on poison hemlock than on wild carrot or parsnip. Unpredictability of larval survivorship in space and time is likely to favor widely spaced oviposition by P. polyxenes females. Such behavior may also be favored by variability in larval growth rates, since adult emergence times may be crucial to the reproductive success of surviving male progeny.

ISSN:0012-9615    

DOI:10.2307/1942556

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

A stratigraphic study was undertaken to determine the historic role of watershed and sea—level changes on the development of Fresh Pond Marsh on Long Island's north shore. Pollen analytic, radiometric, and macrofossil techniques were aimed at differentiating among marsh, watershed, and regional changes over the last 1000 yr. A study of surface pollen distribution was conducted to determine pollen source and tidal influences on pollen deposition and to evaluate comparability of fossil pollen records from various intertidal environments. Regional and local inputs along a transect that included several tidal regimes were identified. Pollen counts from these different environments were comparable and proved useful for marsh reconstructions. Pollen analyses from the coastal marsh and a nearby lake distinguished changes in upland vegetation and cultural patterns within the watershed from those occurring regionally. Records of local pollen, foraminifera, macrofossils, rhizomes, and lithology indicated that the history of Fresh Pond Marsh has included periods of both tidal and freshwater conditions. Close dating control provided by210Pb measurements and historically documented changes in indicator pollen taxa identified marsh responses to external influences, including dynamics of a baymouth bar, land clearing, agriculture, mosquito ditching, and sea—level fluctuations. Results showed that (1) tidal marsh sections can provide sensitive records of both upland and marsh vegetation histories, (2) pollen and macrofossil records can be closely linked to tide—gauge records and are responsive to short—term changes in sea level with a high degree of temporal resolution, and (3) upland influences can play an important role in determining the course of plant succession in the intertidal environment. Pollen provides the most sensitive record of marsh and upland development, as long as pollen source is accounted for.

ISSN:0012-9615    

DOI:10.2307/1942557

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The object of this study was to determine whether interspecific competition modified local geographic distribution, after taking into account the effect of habitat structure. The tendencies for 14 passerine birds to have positive or negative associations were examined, using 7861 sample points in seven native forests on the islands of Hawaii, Maui, and Kauai. All birds were at least partly insectivorous and were fairly common in forested areas, although some fed chiefly on nectar or fruit. Species—pairs were classified as primary or secondary potential competitors based on general dietary similarity. To evaluate the association between species and to account for the effect of individual species habitat preferences, partial correlations were computed for each species—pair in a study area from the simple correlations between the species and 26 habitat variables plus two quadratic terms to represent nonlinearity. The partial correlations represented a short—term ("instantaneous") assessment of the strength of competitive interactions, and did not reflect the accumulation of competitive displacement through time. Of 170 partial correlations in the analysis, only 10 indicated significant negative association. The general pattern was of positive association (76 significantly positive partials), which probably resulted from flocking and from attraction of birds to areas of resource superabundance. Two species showed consistent patterns of negative partial correlations over several adjacent study areas, the Japanese White—eye/Iiwi in montane Hawaii, and the Japanese White—eye/Elepaio in windward Hawaii; both patterns could be reasonably attributed to direct competition. Species—pairs were grouped by the native or exotic status of the component species. Native/exotic pairs had a significantly greater proportion of negative partial correlations (37%) than either native/native pairs (8%) or exotic/exotic pairs (0%). This pattern was consistent across the seven study areas and appeared to reflect the occurrence of interspecific competition along a broad and diffuse ecological "front" between a co—evolved native avifauna and recently introduced exotic species. The role of competition in the pattern was corroborated by the significantly higher proportion of negative partial correlations among species—pairs of primary potential competitors than among those of secondary potential competitors. Our results suggested that °47% of the primary potential competitors among native/exotic species—pairs may experience at least small depressions in local population density due to competition. Although the negative correlations were for the most part small (average negative r = 0.06), one species could eventually replace another as spatial displacement accumulated through time. The Japanese White—eye appeared to have a principal role in native/exotic interactions, with 62% of the partial correlations between it and native primary potential competitor species being negative. Noteworthy implications were that (1) it was important to account for the habitat responses of individual species when studying the role of interspecific competition in modifying small—scale geographic distribution; (2) competition was frequently sporadic in its geographic occurrence and in the species affected, thus supporting Wiens' (1977) theory of competition; and (3) as a consequence, the role of interspecific competition in modifying distribution may be difficult to detect statistically with small data sets.

ISSN:0012-9615    

DOI:10.2307/1942558

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The postglacial history of the forest—tundra zone in Labrador is inferred from the pollen stratigraphy of sediment cores from four lakes which differ considerably in the size and relative relief of their hydrologic catchments. Local pollen—assemblage zones are established independently for each pollen sequence by numerical methods. The relative pollen stratigraphies, interpreted through multivariate statistical comparison with modern pollen spectra from the region, show an overall increase in the tundra component of the forest—tundra vegetation since °3000 BP. Decreasing absolute frequencies of Picea pollen in the sediments are interpreted as evidence of the decline in tree numbers within the lake catchments, and therefore as a potential record of lowering of the altitudinal tree limit. The records show diachronous changes between sites because of differences in catchment elevation and relief. Tree limit has apparently fallen at least 40 m between 3000 and 1000 BP. A further fall of 30 m may have taken place by 250 BP. High ground in northern Laborador makes it unlikely that any equivalent southward displacement of latitudinal tree line can be identified.

ISSN:0012-9615    

DOI:10.2307/1942559

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY