摘要:

Effective management of the Amazon's commercial fish populations requires an understanding of the factors controlling their production. A fundamental step in the investigation of fish production is to identify the plant groups that contribute energy to fish foodwebs. Stable isotope data for plants and 35 fish species were used to identify autotrophic carbon sources for the central Amazon fish community. Adult fish, aquatic macrophytes, tree parts, periphyton, and phytoplankton were collected in lakes and other flooded environments along the central Amazon floodplain and analyzed for carbon stable isotope composition (°13C) by mass spetroscopy. °13C values for plants ranged from —39.4 to —11.9% with averages of —33.3, —28.8, —27.6, —26.2, and —12.8% for phytoplankton, flooded forests trees, C3aquatic macrophytes, periphyton, and C4macrophytes, respectively. The average for all C3plants (phytoplankton, trees, C3 macrophytes, and Periphyton) was —29.1%, while the average for C4plants (mainly C4macrophytes) was —12.8%. Mean °13C values for adult fish ranged from —37.0 to —19.8% with an average of —28.8%. Fish and plant data were used in an isotope mixing model to estimate the relative contribution of different plant groups to fish carbon. C4macrophytes, which contributed over half of the primary production on the floodplain, accounted on average for only 2.5—17.6% (minimum to maximum) of the carbon in fish. The C3plants, as a group, were the primary carbon source for 34 fish species, and accounted for an average of 82.4—97.5% of the carbon in all species. Phytoplankton, a minor C3producer, accounted for a minimum of 36.6% of fish carbon on average, and was the principal carbon source for the commercially important characiform detritivores. Several alternative hypothese are proposed to explain the apparent selective transfer of C3carbon through Amazon fish foodchains.

ISSN:0012-9658    

DOI:10.2307/1940793

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Phosphorous fertilization of a pristine tundra river for four consecutive summers dramatically changed biological processes and populations at all trophic levels. At the primary producer level, both algal biomass and productivity increased and cholorophyll accumulated on the river bottom in the first two summers. Diatom community composition changed little in spite of large chorophyll changes. However, an increase in grazing insects prevented chlorophyll buildup in the third and fourth summers. Some microbial processes were also stimulated by the increased photosynthesis caused by fertilization. Total respiration of the epilithon, acetate uptake, and decomposition of lignin monomers were all stimulated but only in light—grown epilithon. When epilithon was grown in the dark in the fertilized region of the river, there was no increased respiration. Also, phosphorous did not stimulate the decompostition of Carex litter. Although insects grew more rapidly in the fertilized section of the river, there were community interactions that kept total insect production from appreciable change. The four most abundant large insects did increase their growth rates in response to phosphorus addition and there were increases in populations of Baetis lapponicus and Brachycentrus americanus. These increases were offset by the decline in abundance of the dominant species, the black fly Prosimulium martini, perhaps caused by competition for space from Brachycentrus. Growth of both young—of—the—year and adult grayling (Thymallus arcticus) was strongly stimulated by phosphorus addition in years 3 and 4 (not tested in years 1 and 2). Carbon and nitrogen stable isotope tracers indicated that the measured increases in insect and fish growth were largely attributable to increases in the production of epilithic algae. Overall, the results indicate a strong "bottom—up" response of the riverine food web to additions of the limiting nutrient, phosphorus. The response was modified in later years, however, by a strong "top—down" feedback of insects grazing on epilithic algae and by competitive exclusion of black flies caddisflies.

ISSN:0012-9658    

DOI:10.2307/1940794

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Life history data for three unexploited populations of brook trout, Salvelinus fortinalis, were used to test the predictions of life history theory that, relative to juveniles, (1) high adult survival favors low reproductive effort and delayed reproduction, and (2) increased juvenile growth rate favors high effort and early reproduction. Field data supported both predictions. The population having the highest adult—to—juvenile survival ratio expended the least effort, reproduced latest in life, and experienced the lowest survival cost of reproduction. Among populations a high juvenile—to—adult growth rate was associated with early reproduction, high reproductive effort, and high reproductive cost. Early reproduction was also associated with increased growth within populations. The adaptive significance of interpopulation variation in life history was assessed by comparing the fitness, r, of observed life histories with those of potentially alternative strategies. Empirically derived fitness functions supported the hypothesis that population differences in life history were adptive. Observed combinations of age—specific survival and fecundity were those that maximized fitness. Within populations the fitness advantages associated with reproducing early in life favored reduced age at reproduction for the fastest—growing individuals. The results are consistent with the predictions of life history theory and demonstrate empirically how survival and growth rate can independently and interactively influence life history evolution.

ISSN:0012-9658    

DOI:10.2307/1940795

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

We constructed an energetic model to determine the optimal focal point current velocity (i.e. microhabitat) for rainbow trout (Oncorhynchus mykiss) and rosyside dace (Clinostomus funduloides) in Coweeta Creek, a fifth—order stream in North Carolina, USA. Energetic costs were evaluated by quantifying the metabolic expenditure associated with swimming at a given velocity. We estimated bebefits by measuring potential energetic gains of feeding at a given velocity. This included estimates of the ability of the fish to capture prey at different current velocities as well as etimates of the frequency and the energy content of drifting prey at various velocities. We derived separate models for small (53—70 mm SL [standard length]) and medium (71—125 mm SL) trout, and medium (47—52 mm SL) and large (53—70 mm SL) dace for all seasons, deriving net energy gain as a function of current velocity. We predicted fishes would occupy velocities at which net energy gain was maximized. Predicted velocities were compared with those utilized by fishes inhabiting Coweeta Creek. Optimal velocities predicted by energetic models ranged from 7.7 to 22.1 cm/s, and closely matched actual velocity use (average deviation = 2.6 cm/s). Prey capture success appeared to be the most important component in the models. Consequently, we constructed models based solely upon aspects of capture success; the average deviation from veolocity use with these models was only 1.8 cm/s. Thus, the ability of dace and trout to capture prey at varying velocities appears to be the dominant factor affecting microhabitat selection in these species.

ISSN:0012-9658    

DOI:10.2307/1940796

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

I examined habitat use efficiencies of two morphologically distinct threespine sticklebacks (Gasterosteus spp.). The species make up one of several coexisting pairs that apparently formed in the past 13 000 yr in coastal British Columbia lakes. Previous comparative work has shown that morphology and habitat use are correlated within and among populations. Sticklebacks occurring alone in lakes are intermediate in morphology and habitat use, suggesting that differences between the sympatric species result from ecological character displacement. I tested two hypotheses to explain these patterns, and which are implicit in general views of the causes of adaptive radiation: (1) Each resource (habitat) subjects its species to unique selection pressures, owing to the advantages of certain combinations of traits for foraging; (2) Phenotypes intermediate between habitat specialists suffer a competitive disadvantage. These hypotheses were evaluated by measuring the foraging rates of the two species and their interspecific hybrids in the two main habitats (benthos and open water) provided in the laboratory. Efficiencies of habitat exploitation matched obeserved morphological differences. In the benthic habitat the larger, deeper bodies species (having also a wide mouth and few short gill rakers) was superior to the smaller, more slender species (having a narrow mouth and many long gill rakers). Success of hybrids was intermediate. This rank order of species efficiencies was reversed in the open water habitat. These results support the hypothesis that different traits are favored in different habitats, and that adaptation to one habitat has occurred at the expense of feeding rate in the other. Average foraging success of hybrids in the two habitats fell near to below the average of the two parental species, suggesting natural selection against intermediate phenotypes. Foraging efficiency in open water was greatest in the smaller size classes of fish, hinting that small size of the open water species is the result of selection for high foraging efficiency. However, size could not explain most differences in feeding efficiency between species, and it is likely that many traits contribute.

ISSN:0012-9658    

DOI:10.2307/1940797

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

The isopod Caecidotea intermedius serves as the intermediate host for the acanthocephalan Acanthocephalus dirus. C. intermedius is preyed upon by the northern creek chub, Semotilus atromaculatus, which also serves as the definitive host for A. dirus. The effects of the parasite on the antipredator behavior of C. intermedius were examined. We tested the hypothesis that behavioral changes induced in C. intermedius by the parasite are by—products of increased energy demands induced by the parasite (i.e., increased hunger). Infected and uninfected C. intermedius were placed in a divided aquarium with 0, 1, or 2 creek chubs. Leaf discs provided both a food source and a refuge from the predator. In the presence of the creek chubs, uninfected C. intermedius avoided the predator, and were found more frequently in refugia as the number of creek chubs increased. However, infected C.intermedius were associated with the side of aquarium containing the predator, and spent significantly more time out in the open away from the refuge regardless of the number of creek chubs. These data show that the antipredator behavior exhibited by C. intermedius is altered by A. dirus, and that such alterations are unlikely to be simply products of increased energy demands. Parasite—induced behavioral changes appear to increase C. intermedius' vulnerability to predation, thereby increasing the likelihood of A. dirus completing its life cycle. We find little evidence for greater foraging need as the mechanism indicating changes in antipredator behavior.

ISSN:0012-9658    

DOI:10.2307/1940798

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

A sampling view of the colonization of small habitat fragments by birds is based on the assumption that individual birds acquire territories in the fragments randomly, and their occurrence frequencies follow from abundances in the regional species pool. We tested the following predictions of this view using birds census data from a fragment "arhchipelago" in the southern Finnish taiga: (1) the location of breeding pairs varies randomly among the fragments from year to year, and (2) the pattern of species accrual with increasing sample size is similar to radom sampling. The data agreed with the predictions. For most species the distribution of pairs in the fragments agreed with the Poisson prediction. The pattern of species turnover in single fragments agreed with the sampling view so that an average fragment had about 10 pairs of 7 species in a single breeding season, and about 40 pairs of 13 species over the 4—yr period. The sampling model is a "null" assumption that should be considered when assessing the occurrence of birds in small habitat fragments. This requirement defines methodological imperatives that have often been violated in ornithological studies; we discuss such methodological problems. The sampling model implies that local turnover in small fragments may be mechanical reflection of change in territory location from year to year and disconnected from population dynamics. In such case, apparent "extinctions" and "recolonizations" in single fragments are ecologically trivial. Assessing the interface between sampling colonization and genuine metapopulation dynamics is an urgent challenge for conservation ecology, particularly in temperate and boreal areas.

ISSN:0012-9658    

DOI:10.2307/1940799

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

In most mathemetical models of population dynamics in ecological communities, the death rate of prey species is a linearly increasing function of the density of their predator(s). If antipredator behavior is incorporated into such models it becomes very unlikely that prey death rate is a linear function of predator density. In addition, it is possible for the prey death rate to decrease, rather than increase, as a function of the population density of its predator. Decreasing predation rates may be common when the prey organism is attempting to accumulate resources for growth or reproduction. Decreasing predation rates are less likely when the prey organism is attempting to minimize mortality. These results are earlier ones on indirect effects generated by optimal foraging (Abrams 1984, 1991a, b) suggest that higher order ineractions shoyld be extremely common in natural communities.

ISSN:0012-9658    

DOI:10.2307/1940800

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

The conventional ecological approach to predation provides a limited framework for understanding perceptual and tactical mechanisms of search and detection and their dynamical consequences. In constrast, models developed to guide naval search operations are "spatiotemporal dynamic interaction models," analogous to those developed in plant population ecology. Our application of these modes to foraging sparrows indicates that perceptual and tactical constraints play a critical role in the allocation of search effort across habitat patches, in the choice of tactics within patches, and in the predation dynamics that emerge over time. Sparrows search where prey are most detectable rather than where they are most abundant, and they tune search tactics to preceptual operating conditions. The approach describes and predicts details of search and detection, cumulative harvest rates, and selectivities more accurately than the conventional search—efficiency approach.

ISSN:0012-9658    

DOI:10.2307/1940801

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Clutch predation is generally considered a selective force in nest site selection by gound—nesting birds. We examined characteristics of vegetation and cover around nest sites and inter—nest spacing for Willow Ptarmigan (Lagopus lagopus) to determine whether choice of nest location influenced probability of predation. Types of vegetation around successful and depredated nests and random points were similar. However, hens chose sites that had more lateral and overhead cover than that found at random points. Amount of cover was similar for successful and depredated nests. We Suggest that hens choose cover to deter predation on themselves or to reduce energy costs of incubation. Inter—nest distances were larger and nests were located closer to the centroid of the territory than if nest sites had been selected at random. Hens that renested placed their nests farther from their first nests but not farther from neigboring nests than expected if they had located them at random. Probability of a clutch being preyed upon was not related to its distance from a clutch that had previously been depredated. We conclude that, for the breeding densities that we encountered, nests were spaced far enough apart to deter area—restricted search by predators. Predation may have been a factor causing over—dispersion of nests in the past, but current selection may be masked by other factors such as the hen's behavior or stochasticity.

ISSN:0012-9658    

DOI:10.2307/1940802

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY