摘要:

Reproductive success in relation to egg size was studied in European Starlings (Sturnus vulgaris) by swapping whole clutches between nests at the stare of the incubation period. Egg size did not reflect parental quality as no measure of reproductive success was correlated with the foster mothers' mean egg size. There was a significant positive relationship between the mean size of the cross—fostered egg and the subsequent mean size of hatchlings. The mean size of cross—fostered eggs did not affect hatching success or nestling growth rates, and initial nestling size differences between broods with large and small eggs persisted for<1 wk. No effect of mean egg size on mean nestling survival could be detected. Furthermore, a partial cross—fostering experiment, where nestlings were swapped between nests the day after hatching, failed to demonstrate any lasting effect of egg size on nestling size. It is suggested that mean egg size may only influence reproductive success during particularly inferior environmental conditions.

ISSN:0012-9658    

DOI:10.2307/1940626

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

I used published data to test three possible relationships between the allocation of energy to growth (P) and respiration (R) in chicks: (1) a negative relationship stemming from a trade—off between increased allocation for one purpose, resulting in a reduced proportion of energy available for other purposes; (2) a lack of relationship between P and R; and (3) a positive relationship reflecting functional metabolic coupling of P and R. I restricted my analysis to three periods of the chick's postembryonic development, during which the conflict between allocation of energy to P vs. R is most likely to occur: (a) when the greatest proportion of assimilated energy is allocated to growth; (b) when growth rate (in grams per day), or (c) energy allocated to growth (in kilojoules per day) are at absolute maxima. I analyzed the correlation between P and R after accounting for differences in body mass, costs of biosynthesis, mode of development, breeding latitude, and phylogeny. Under assumption of production efficiency of 0.75, the correlations were negative for periods (a) and (b), and statistically insignificant for period (c). When production efficiency of 0.9 was assumed, the correlation remained negative only for period (c), and became statistically insignificant for the other two. I also found that the positive correlation between growth rate and metabolic rate reported by Klaasen and Drent (1991) becomes insignificant when the effect of breeding latitude is removed from their data set. Thus, the results of all analyses support (1) or (2), rather than (3). I conclude that predictions stemming from (1—3) can often be difficult to distinguish, which may account for the inconsistency between the results of different studies in which the relationship between P and R was analyzed.

ISSN:0012-9658    

DOI:10.2307/1940627

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

In many colonial waterbirds, reproductive success is affected by water levels around the colonies. In a study of the Greater Flamingo (Phoenicopterus ruber roseus) in the Camargue, southern France, we examined annual variation in water levels around the breeding colony site between 1984 and 1991 in relation to (1) the number of breeding pairs, (2) colony productivity (fledglings per breeding pair), and (3) physical condition of fledglings. The number of breeding pairs each year was highly variable and was positively correlated with high water levels during the March—July period. There was no significant relationship between the number of breeding pairs and the number of chicks fledged. Although the productivity of the colony was not affected by water levels during the chick—raising period, fledglings were heavier in years with high water levels. There was no relationship between colony productivity or the absolute number of chicks fledged and the average body condition of chicks in the creche. Differences between the 1984 and 1985 cohorts in the frequency of young birds making breeding attempts (i.e., ages 5 and 6 yr) suggested that body condition at fledging may have important life history consequences. Estimation of reproductive performance in colonial waterbirds, usually limited to the average nest productivity, could be improved by considering average body condition of chicks at fledging as well.

ISSN:0012-9658    

DOI:10.2307/1940628

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

To study the hierarchy of variables involved in the year—to—year dynamics in the distribution of Neotropical migratory birds, we compared observed numbers of local extinctions and recolonizations to those expected under six hypothetical mechanisms of settlement by returning spring migrants. These mechanisms were (1) random dispersal among forest fragments; (2) passive sampling of spring migrants according to fragment area; (3) dispersal among fragments between years according to the distance to the nearest fragment occupied the 1st yr; (4) resettlement of spring migrants according to the vertical structure of the vegetation in the fragments; (5) site fidelity of experienced breeders; (6) a combination of mechanisms 2, 3, 4, and 5. We selected four target species: Wood Thrush (Hylocichla mustelina), Black—and—white Warbler (Mniotilta varia), Ovenbird (Seiurus aurocapillus), and Scarlet Tanager (Piranga olivacea). In 50 fragments of mature deciduous forest (3.0—129.8 ha, median = 11.8 ha) within a 10 ° 10 km square, we recorded the presence of any target species and an abundance index in two successive breeding seasons. Absences were validated using song playbacks. Except for the random dispersal model, each hypothetical mechanism was simulated using logistic regressions on empirical data. Frequencies of population turnovers (local extinctions + recolonizations) were 16—28% between the two breeding seasons, varying with species. Observed numbers of population turnovers were best approximated by the combination model (model 6). Expected numbers of population turnovers were consistently higher than observed numbers for models 1—4, suggesting that between—year dynamics were constrained by some process(es). Our simulations suggest that site fidelity might be an important constraint on the distributional dynamics of these species, even when effects of fragment area and habitat on site fidelity are factored out. This finding has important implications for the response of Neotropical migrant birds to the fragmentation of their habitat.

ISSN:0012-9658    

DOI:10.2307/1940629

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

Comparative demographic studies of terrestrial vertebrates have included few samples of species from tropical forests. We analyzed 9 yr of mark—recapture data and estimated demographic parameters for 25 species of birds inhabiting lowland forests in central Panama. These species were all songbirds (Order Passeriformes) ranging in mass from 7 to 57 g. Using Jolly—Seber stochastic models for open populations, we estimated annual survival rate, population size, and recruitment between sampling periods for each species. We then explored relationships between these parameters and attributes such as body size, phylogenetic affiliation, foraging guild, and social behavior. Larger birds had comparatively long life—spans and low recruitment, but body size was not associated with population size. After adjusting for effects of body size, we found no association between phylogenetic affiliation and any demographic trait. Ecological attributes, especially foraging guild, were more clearly associated with interspecific variation in all demographic traits. Ant—followers had comparatively long life—spans, but species that participate in flocks did not live longer than solitary species. The allometric associations we observed were consistent with those demonstrated in other studies of vertebrates; thus, these relationships appear to be robust. Our findings that ecological factors were more influential than phylogenetic affiliation contrasts with comparative studies of temperate—zone birds and suggests that the relative importance of environmental vs. historical factors varies geographically.

ISSN:0012-9658    

DOI:10.2307/1940630

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

Stocking of the dominant planktivore of Castle Lake (rainbow trout) was discontinued to examine the impact of food web interactions on zooplankton communities and inter— and intra—annual dynamics of ecosystem properties (light penetration, primary productivity). Dynamics of zooplankton and ecosystem processes were examined for 3 yr following the manipulation and compared to 2—3 yr of premanipulation data. Sampling of vertebrate and invertebrate planktivores documented shifts in other members of the zooplanktivore guild as rainbow trout declined. Reduction of rainbow trout densities led to compensatory responses in other components of the Castle Lake fish assemblage as brook trout and golden shiners increased in abundance. This compensation resulted in increased rates of vertebrate planktivory on daphnids within 2 yr after trout stocking was discontinued. Zooplankton shifts in response to discontinuance of trout stocking were more rapid, particularly an immediate increase in a previously rare invertebrate predator (Diacyclops thomasi). Other limnological parameters also responded rapidly following the manipulation: water transparency declined and primary productivity (PPr) increased. In addition, intra—annual patterns (i.e., seasonal development) and the vertical distribution (shallow vs. deep) of PPr appeared to be affected by the food web manipulation. Our results indicate that complexities of real food webs complicate the prediction of the outcome of food web perturbations. Reduction of the previously dominant planktivore (rainbow trout) led to increases in other zooplanktivores (Diacyclops, golden shiners, brook trout) that resulted in enhanced predation pressure on zooplankton herbivores. Our results also indicated that alterations in water quality parameters (transparency, PPr) in response to food web alterations need not necessarily be mediated through changes in the abundance of Daphnia, as strong limnological responses preceded reductions in Daphnia by a year. We hypothesize an alternative mechanism for food—web—induced changes in lake ecosystem dynamics: changes in water clarity and productivity can result when cyclopoid predation strongly affects micrograzers.

ISSN:0012-9658    

DOI:10.2307/1940631

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

In size—structured populations, interactions are strongly dependent on size—specific foraging and anti—predator capacities of the organism. Conflicting size—specific selection pressures over the ontogeny often have different effects on different species leading to asymmetries in competitive and predator—prey interactions. Habitat complexity is likely to affect such asymmetric interactions due to species/size—specific competitive abilities in different habitats and due to the fact that habitat structural complexity may act differently as a prey refuge for different species. We experimentally analyzed the impact of a piscivorous predator (adult perch, Perca fluviatilis) on performance of juvenile perch and roach (Rutilus rutilus) at different levels of structural complexity (no structure, structure forming a partial refuge, and structure forming a complete refuge) in enclosures in an experimental pond. We measured predator diet and growth, prey fish habitat use, survival, diet and growth, and prey resource levels in different habitats. Prey fish (perch and roach) were found in the diet of piscivorous perch in no refuge and partial refuge treatments. Growth rate of the piscivorous perch decreased with increased refuge efficiency. Juvenile perch increased their proportional use of the structurally complex refuges in the presence of piscivorous perch and the survival increased with increased refuge efficiency (from partial to complete refuge). The diet of juvenile perch changed from predominantly cyclopoid copeponds in the absence of predators to predominantly macroinvertebrates in the presence of predators. There was no effect of predator—induced habitat restriction on growth of juvenile perch. Roach survival also increased with increased refuge efficiency in the presence of predators, and roach survival in the refuge treatments did not differ from each other or from the treatments with predators absent. Predator—induced habitat restriction in roach was associated with a decreased growth of roach. Our results suggest that, compared to juvenile roach, juvenile perch may compensate more for lost foraging opportunity in the open water via increased exploitation of structure—associated prey in refuges. As a result, predation—induced habitat shifts by juvenile perch and roach may alter competitive interactions between the species. On the other hand, structural complexity may form an almost complete refuge for juvenile roach from predators and thereby affect the predator—prey relationships between piscivorous perch and juvenile perch and roach to the advantage of juvenile roach. The demonstrated effects of structural complexity on competitive and predator—prey interactions between perch and roach can be related to the two species' distributions in lakes with different degrees of structural complexity.

ISSN:0012-9658    

DOI:10.2307/1940632

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

Divergent Natural selection for efficient exploitation of alternative resources is thought to be a primary cause of adaptive radiation. I transplanted two recently diverged stickleback species (Gasterosteus sp.) and their Hybrids between habitats to test three predictions of this hypothesis: (1) the form of natural selection on feeding traits should differ between resource environments; (2) fitness trade—offs should occur between morphs specialized for different resources; (3) feeding efficiency should be the basis of fitness differences between morphs. Growth rate was used as a surrogate component of fitness. All three predictions were upheld. The larger of the two species (the Benthic), which has a larger mouth, deeper body, and fewer, shorter gill rakers than the second species (the Limnetic), had a twofold growth advantage in the littoral zone of the lake. This pattern was reversed in the open—water habitat, where the Limnetic species grew at double the rate of the Benthic. Hybrids, which are morphologically intermediate, tended to be intermediate in growth in both habitats. Growth rates were closely predicted by earlier laboratory measurements of feeding efficiency of the three forms in the same habitats, thus linking growth (and probably fitness) with feeding performance and morphology. I compare the strengths of the present approach with other methods that have been used to test the role of resources in adaptive radiation. I also argue that steep trade—offs in fitness along the littoral—open—water habitat gradient have two further consequences. First, they may cause Hybrids to have low fitness, allowing Benthics and Limnetics to coexist in the absence of perfect premating isolation between them. Second, they may promote ecological character displacement. Steep trade—offs may thus help explain why divergence along the littoral—open—water gradient is so common in fish that have colonized low—diversity lakes.

ISSN:0012-9658    

DOI:10.2307/1940633

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

Costs and benefits to group living in animals may affect the fitness of individual group members and also demography of the population. The effects of grouping on the growth, survival, and attainment of maturity of juveniles of an Hawaiian coral—reef damselfish (Dascyllus albisella) were evaluated from 1987 through 1989. In this species, pelagic larvae settle (at °14 mm total length) on coral heads, joining temporary groups of up to 15 juveniles. Groups members establish a dominance hierarchy based on size, and fish leave these groups upon reaching mature size (70 mm total length) to enter the nearby adult population. Previously, I had demonstrated that larvae preferentially join larger groups and I expected to find clear advantages to group membership. Survival, especially of smaller fish, was enhanced in large groups, but growth, especially by individuals of low social status, was reduced. Consequently, the time to reach maturity increased with group size in both years of the study, suggesting a more rapid entry into the adult population of fish in smaller groups or living alone. However, the probability of reaching mature size (a function of size—specific growth and survival) increased with group size in 1988 but not in 1987, thus indicating a benefit to group living during only one of the two years of the study. Although this study demonstrated density—dependent juvenile growth and survival, with consequent fitness effects of group living, it has also highlighted considerable inter— and intra—annual variability in these relationships. Such variability will have major consequences for predictions of the effects of juvenile ecology on the demography of organisms.

ISSN:0012-9658    

DOI:10.2307/1940634

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY

摘要:

Diterpene alcohols produced by the brown seaweed Dictyota menstrualis deter feeding by numerous species of abundant herbivores. Here we show that these same compound also may prevent fouling organisms from colonizing the surface of this alga. In the field, Dictyota menstrualis plants were less frequently and less heavily fouled than any of the other common seaweed species investigated. In laboratory assays, larvae of the common fouling bryozoan Bugula neritina failed to settle on Dictyota even though they contacted its surface as often as they contacted the surface of a preferred host alga. Rejection occurred only after direct contact with the alga's surface. Rejection of Dictyota was not mediated by water—borne chemical cues or by surface wettability (a physical property of the surface that can affect fouling). The lipid—soluble extract from surface rubbings of Dictyota inhibited larval settlement when placed on other surfaces and contained the diterpene alcohols pachydictyol A and dictyol E. Larvae exposed to these compounds experienced mortality, abnormal development, or reduced rates of development. Although the potential for chemically mediated coevolution between plants and herbivores has been the focus of scores of previous investigations, such coevolution will depend on selection altering the chemical defenses of the plant following the evolution of resistance by herbivores. Such a reciprocal response will be constrained if compounds play multiple roles that are ecologically important. Dictyota produces secondary metabolites that are broadly defensive against a wide variety of consumers and fouling organisms. Although certain consumers may evolve resistance to these metabolites, it is unclear that feeding by these consumers will result in reciprocal responses from the plant. We suggest that coevolved interactions may be uncommon, and that many interactions that appear to be coevolved may result from fortuitous and opportunistic preadaptations.

ISSN:0012-9658    

DOI:10.2307/1940635

出版商:Ecological Society of America    

年代:1995

数据来源: WILEY