摘要:

The persistence and structure of a small but morphologically diverse fish assemblage of a California stream was examined to see if it had the characteristics of a deterministically regulated or stochastically regulated community. We evaluated persistence by monitoring the fish populations for 5 yr and examined resource use by measuring summer microhabitats and diets of each species. We also compared the microhabitats and diets of the juveniles and adults of each species to investigate the hypothesis that in stream fish assemblages at low diversity, juvenile fishes essentially function ecologically as separate species. Species composition in each of four stream sections was persistent over the 5—yr period, which included extreme flood conditions. Differences in species composition among sections reflected differences in their physical characteristics. The most abundant species were segregated by habitat, microhabitat, and/or diet. In addition, in all but one species, young—of—year were ecologically segregated from the adults; this increased the functional complexity of the assemblage. The observed fish assemblage thus appears to have the characteristics of a highly structured community, as expected under Connell's “niche diversification hypothesis.” The structure observed is probably characteristic of fish assemblages in cold—water streams throughout North America that contain the same or similar species.

ISSN:0012-9658    

DOI:10.2307/1941301

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Two herbivorous, interspecifically territorial West Indian damselfishes, the beaugregory (Eupomacentrus leucostictus) and the three—spot damselfish (E. planifrons), both inhabit the back—reef area of coral reefs in a narrow depth band. A survey of coral heads in this habitat revealed that beaugregories utilize all types of heads, while three—spots are found only on branching or creviced heads with relatively complex internal structure. Translocations of individual fish and heterospecific pairs were performed to determine whether this differential microhabitat utilization is the result of differences in microhabitat preference between the two species, or aggressive interactions between them, or both. As indicated by duration of residence of translocated fish on experimental heads, three—spot damselfishes showed significant preference for heads with complex internal structure, while beaugregories showed no preference. In translocations of heterospecific pairs, three—spots won aggressive contests more often on internally complex heads, and beaugregories won more often on heads without internal structure, then would be expected on a random basis. Since this difference fell just short of significance (P = .053), translocations of heterospecific pairs were also done in aquaria with artificial heads. In these more controlled conditions, the preponderance of wins by three—spots on complex heads and beaugregories on simple heads reappeared as a significant difference, with occasional co—occupation of the complex head by both species. The observed differences in microhabitat utilization are thus due both to different preferences and aggressive interaction. It is probable that the aggressive interactions, a form of interference competition, and responsible for the evolution of the different habitat preferences. However, for both the three—spot damselfish and the beaugregory, it has been shown that a principal function of aggressive interspecific territoriality is the protection of food resources from exploitation competition.

ISSN:0012-9658    

DOI:10.2307/1941302

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Seasonal divergences of planktonic copepod communities in a marine eelgrass bed and adjacent unvegetated channel habitats were associated with increases in predator abundance in the littoral habitat. During midsummer, when planktivorous silversides, Menidia menidia, were abundant in the eelgrass bed, pelagic copepod densities were significantly reduced in the eelgrass bed, relative to channel abundances. Differences declined overnight, when fish were not feeding, and were reestablished after dawn. In late winter, coincident with the arrival of large numbers of postlarval fish in the eelgrass bed, there was selective reduction of juvenile Centropages spp. in the eelgrass bed, relative to channel abundances. Field and laboratory experiments indicate that these differences were due to intense predation by planktivorous fish. However, the littoral copepod Pseudodiaptomus coronatus appeared unaffected by the intense predation in the eelgrass bed. Laboratory experiments demonstrated that its epibenthic habit and cryptic coloration allow P. coronatus to utilize refuges in the littoral habitat, and that prey selection by two fish species differed due to differences in foraging behavior.

ISSN:0012-9658    

DOI:10.2307/1941303

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The colonial ascidian—algal symbiosis Didemnum molle Herdman occurs in large numbers (densities of>100 colonies/m2) on shallow patch reefs in the lagoon at Lizard Island, Australia. Shallow—water currents in the lagoon are driven unidirectionally by the southeast trade winds most of the year. The patch reefs are several hundred metres apart and are separated by sand flats. The largest populations of D. molle occur on the upstream ends of the patch reefs. D. molle larvae, followed underwater, dispersed invariably downstream in the direction of the water current at °1—2 m/min. Although larvae were capable of swimming for up to 2 h, they generally settled in 10—15 min when given a suitable substratum such as a dark surface. Larvae experimentally denied a suitable substratum for 40 min settled rapidly when provided with a dark surface, suggesting that when larvae encounter a reef after drifting over sand flats, they probably settle immediately. A qualitative model of larval dispersal was developed to predict the settlement pattern of D. molle in the lagoon at Lizard Island. Three predictions of the model were tested by measuring larval recruitment upstream and downstream of an experimental patch reef for 1 wk before, then 1 wk after denuding the reef of all reproductive D. molle colonies. The results agree with the model, indicating that larval recruitment of D. molle in the lizard Island lagoon is a highly predictable process. The settlement pattern that results from the dispersal model describes the upstream distribution of adult D. molle colonies on patch reefs in the Lizard Island lagoon.

ISSN:0012-9658    

DOI:10.2307/1941304

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Field surveys at Enewetak Atoll, Marshall Islands, show that coral density and diversity is much lower beneath Acropora table corals than in adjacent unshaded areas. Additionally, the understory community is predominantly composed of massive and encrusting species, while branching Acropora and Pocillopora predominate in unshaded areas. Results of experiments in which coral fragments were transferred to the shade of table Acropora and to adjacent unshaded areas show that shading slows the growth and leads to higher mortality of branching species, while massive and encrusting species are unaffected. Light measurements made beneath table Acropora show that illumination and irradiance values fall to levels at which most hermatypic corals do not occur. The fast—growing but fragile table Acropora are abundant in a wide variety of atoll habitats and grow rapidly to form a canopy °50 cm above the substrate. However, table Acropora also have high mortality rates, so that there is continuous production of unshaded areas. The growth and death of tables thus create local disturbances, and the resulting patchwork of recently shaded and unshaded areas may enhance coral diversity in areas of high coral cover.

ISSN:0012-9658    

DOI:10.2307/1941305

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

We introduce a demographic model for a local population of sessile marine invertebrates that have a pelagic larval phase. The processes in the model are the settling of larvae onto empty space, and the growth and mortality of the settled organisms. The rate of settlement per unit of unoccupied space is assumed to be determined by factors outside of the local system. The model predicts the number of animals of each age in the local system through time. The model is offered in both discrete and continuous—time versions. The principal result is that the growth of the settled organisms is destabilizing. In the model, there is always a state where recruitment balances mortality. However, growth can interfere with recruitment and can destabilize this steady state, provided also that the settlement rate is sufficiently high. The model suggests that two qualitatively distinct pictures of population structure result, depending on the settlement rate. In the high settlement limit, the intertidal landscape is a mosaic of cohorts, punctuated with occasional gaps of vacant substrate. In the low settlement limit, the intertidal landscape has vacant space and organisms of all ages mixed together and spatial variation in abundance is caused by microgeographic variation in settlement and mortality rates.

ISSN:0012-9658    

DOI:10.2307/1941306

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

During summer and fall, depth profiles of zooplankton community grazing were determined in situ during day and night in the Schohsee, a small eutrophic lake. Labeled algae of two different sizes were mixed with the natural suspension of phytoplankton in a grazing chamber. A small blue—green alga (Synechococcus, I μm) was labeled with32P; a larger green alga (Scenedesmus, 4—15 μm)was labeled with14C. Grazing and vertical migration of zooplankton were strongly coupled. During summer, grazing in the upper 5 m was negligible during day but strong at night. Hence, algae grow relatively unimpeded by grazing during daytime but are harvested at night. Vertical and diel differences in grazing rates disappeared when the vertical migration ceased in fall. Selectivity of grazing was controlled by the zooplankton species composition. Eudiaptomus showed a strong preference for Scenedesmus (electivity index D = 0.9). Daphnia showed a slight preference for Scenedesmus, but Ceriodaphnia preferred Synechococcus. Cyclopoid copepodites did not ingest the small blue—green. Because Daphnia and Eudiaptomus were dominant, grazing rates on larger cells were usually higher than grazing rates on the small cells. Negative electivity indices for Scenedesmus occurred only when the biomass of large crustaceans was extremely low (near the surface, during day). Zooplankton biomass was the main factor controlling both vertical and seasonal variations in grazing. Highest grazing rates (65%/d) were measured during fall when zooplankton abundance was high. Differences between day and night in the grazing activity per unit biomass were not statistically significant. Laboratory experiments showed considerable losses of tracer from preserved animals, and loss rates differed for the two radioisotopes. Because such differential losses can produce substantial errors in the results, it was necessary to process the samples on the boat immediately after collection, without preservation.

ISSN:0012-9658    

DOI:10.2307/1941307

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Experiments were used to study the mechanisms underlying the persistence of beds of the surfgrass Phyllospadix scouleri, a prominent feature on horizontal benches in rocky intertidal areas ranging from British Columbia to Baja California. The stability of P. scouleri beds was investigated by: (1) quantifying structure and persistence, (2) experimentally removing P. scouleri, and (3) measuring rates of recovery from disturbance. At two Oregon study sites P. scouleri not only occupied more space than any other species but also persisted through all seasons for 3 yr. Differences between the two sites seem related to their disturbance patterns; although new free space was rarely created at either site (0.13 and 0.04% of the area per year), P. scouleri occupies much more space at the site where it is less often disrupted. Experimental removals of P. scouleri (0.25—m2plots) resulted in significant increases in algal cover and in upright—plant diversity, suggesting that it preempts space from other species. These invading algal species dominated the experimental plots for the remainder of the study. During the 3—yr experiment only nine surfgrass seedlings recruited into 28 plots and occupied<1% cover. Mapped seedlings in a 28—m2area experienced 93% mortality in 7 mo. Rhizomes of surrounding P. scouleri plants grew into experimental plots at a maximum increase in rhizome length of 6 cm/yr. The slow recovery makes even the rare disturbances that occur in these communities important. Therefore, P. scouleri beds have high persistence stability, despite their slow recovery. They owe this persistence mainly to their high preemptive ability. These characteristics appear common to many species with escapes from herbivores.

ISSN:0012-9658    

DOI:10.2307/1941308

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

Systems of differential equations exhibiting complex periodic or chaotic behavior can sometimes be associated with one—dimensional mappings (difference equations) which encapsulate the properties of the attractor governing the full n—dimensional system. Recent advances make it possible to reconstruct the underlying attractor, and hence the one—dimensional map, from time—series data for a single state variable (species). The present paper illustrates this technique with reference to a hypothetical system consisting of a single predator species and two species of victims. Trapping records for Canadian lynx suggest that the method may have application to real—world populations.

ISSN:0012-9658    

DOI:10.2307/1941309

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY

摘要:

The jackknife estimation procedure is used to estimate Brillouin's and Simpson's indices of diversity when sampling is done by selecting quadrats. Using simulated data, a sampling plan is set up to study effects of quadrat size, sample size, and sampling area. The estimates are evaluated by estimating bias, standard error, and mean square error, and by comparing expected 95% confidence interval coverage with observed 95% confidence interval coverage. Smaller quadrats tend to give less biased and smaller variance estimates of Brillouin's index. The jackknife estimate of Simpson's index is unbiased using quadrat samples, but the estimates of standard error appears to be an overestimate for large samples, causing overcoverage (>95%) for observed confidence intervals.

ISSN:0012-9658    

DOI:10.2307/1941310

出版商:Ecological Society of America    

年代:1985

数据来源: WILEY