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651.
Victoria J. Allison Tara K. Rajaniemi Deborah E. Goldberg Donald R. Zak 《Plant Ecology》2007,190(1):53-69
Environmental perturbations can alter the composition of plant communities, either directly, by altering growth of some species
more than others, or indirectly, by altering the strength of interspecific interactions among species. The relative importance
of direct and indirect effects is not at all well known. We used an experimental approach to quantifying direct and indirect
effects of fungicide on the composition of a plant community. To separate the direct and indirect impacts of fungicide we
grew plant species in monoculture and mixed communities, and with and without the systemic fungicide benomyl. We predicted
that direct effects of fungicide would be important at low but not high nutrient availability, while indirect effects would
be more important at high nutrient availability. After 3 years there was little impact of fungicide on arbuscular mycorrhizal
fungal colonization, and on soil microbial community composition assessed as the relative abundance of different phospholipid
fatty acids. Like fertilizer, fungicide increased plant biomass. However, in contrast to fertilizer, this did not result in
a decline in species evenness. Although not significant, the direct effects of fungicide tended to oppose the indirect effects
of both fungicide and interspecific interactions on plant community composition. Experiments relying on fungicide treatments
must be interpreted extremely cautiously, because the impact of fungicide is potentially the integrated response of plants
to multiple factors, including arbuscular mycorrhizal fungi, pathogenic and saprophytic fungi, and nutrient inputs. 相似文献
652.
653.
We analyzed the impact of interspecific interactions between two ecologically and morphologically distinct Puerto Rican lizards,
Anolis gundlachi and A. evermanni, in an experimental design consisting of six 20 × 20 m plots divided into three blocks, each consisting of a pair of experimental
and control plots. We removed A. gundlachi from experimental plots and monitored the response of A. evermanni. The reduction in the number of A. gundlachi resulted in a significant increase in the abundance of both adult and juvenile A. evermanni. We found no evidence for a shift in structural habitat use in A. evermanni in experimental plots. Two possible mechanisms, interspecific competition and intraguild predation, could explain the increase
in abundance of A. evermanni after the removal of A. gundlachi. These results make clear that interactions still occur between A. gundlachi and A. evermanni even given their morphological and ecological differences.
Received: 14 November 1997 / Accepted: 4 May 1998 相似文献
654.
Seven species of freshwater algae were grown in defined media in monoalgal and mixed cultures, to test whether species interactions and community efficiency were predictable on the basis of ecological theory. Results supported the prediction of competitive interactions, although no differences were detectable in the strength of competition in two and three species mixed cultures, nor was the severity of competitive effects predictable on the basis of relatedness at the level of phyla. On a community level, cultures with two and three species fixed a greater proportion of available carbon than cultures with only one species, implying a more efficient overall use of available resources. Implications for the design of artificial closed ecosystems are discussed. 相似文献
655.
Summary Recurrent or introgressive backcrossing of Phaseolus vulgaris — P. acutifolius hybrids with either P. vulgaris or P. acutifolius increased fertility, as measured by pollen stainability and seed per pod from non-manipulated flowers, while invariably resulting in loss of traits from the non-recurrent parent. When hybrids were backcrossed with each of the parent species in alternate generations (congruity backcrossing), fertility decreased in early generations but gradually increased in later generations. By the fourth or fifth generation, congruity-backcross hybrids produced numbers of seeds per pod from non-manipulated flowers comparable to those of parent species, although the percent of stainable pollen tended to be lower. Congruity-backcross hybrids were intermediate to parent species when pedigrees contained equal representation of parents but favored the majority parent when pedigrees were unbalanced. Individuals exhibiting symptoms of developmental incongruity, such as abnormal leaflet number, foliar variagation, or unusual growth patterns, occurred in each generation. However, completely new characteristics appeared after the second backcross generation, presumably due to recombination. Backcrossing to both parent species in alternate generation reversed incongruity, allowing selection for fertility without loss of traits from one of the parent species.Scientific Journal Series Paper Number 15, 671 of the Minnesota Agricultural Experimental Station 相似文献
656.
Nobuhiko Suzuki 《Ecological Research》1986,1(3):259-268
Field experiments were conducted in order to investigate the mode of exploitation of food resources and the mechanism of coexistence
of mixed larval populations of the two chrysomelids,Gastrophysa atrocyanea andGalerucella vittaticollis, under limited food resource conditions. The larval survival rates seemed high enough to assure coexistence when hatchlings
of the two species were released in 1∶1 and 1∶3 ratios on a host plant. However, the survival rate became almost nil for both
species when a 3∶1 ratio was employed, suggesting asymmetrical interspecific competition.
Wasted food consumption was much higher inG. atrocyanea larvae. The population ofG. atrocyanea seemed to be regulated more by intraspecific competition, while on the other hand, the population ofG. vittaticollis was considered to be more likely affected by the interspecific competition withG. atrocyanea, depending on the initial ratio and density of the two species. 相似文献
657.
J. Nagaraju M. S. Jolly 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(2):269-273
Summary A rare case of interspecific hybridization between the Indian oak feeding silkworm Antheraea roylei (n=31) and Chinese oak feeding silkworm A. pernyi (n=49) yielding fertile and vigorous offspring is reported. The F1 and the backcross (A. roylei X A. pernyi X A. pernyi male individuals of the above cross and the F23 and F32 male offspring derived from an earlier cross between another race of A. roylei (n=30) and A. pernyi (n=49) were cytogenetically analysed in order to study their chromosome dynamics. The F1 hybrids showed 18 trivalents and 13 bivalents in the first meiotic prophase and metaphase. The backcross individuals possessed either 9 trivalents and 31 bivalents or 49 bivalents, in Metaphase I cells. The F23 and F32 individuals were karyotypically alike and exhibited 49 bivalents. The following conclusions were drawn from the above observations: (a) in spite of allopatry and karyotypic divergence in number, a high degree of homology exists between the chromosomal complements of the two species; (b) A. pernyi possibly evolved from A. roylei, during the course of which 18 chromosomes of the latter underwent fission to give rise to the 36 chromosomes of the former. This is demonstrated by trivalent formation and pairing affinities in F1 hybrids; (c) selection has favoured the elimination of large A. roylei chromosomes which participated in trivalent formation in successive generations of inbred hybrids to establish a stable Karyotype like that of A. pernyi. 相似文献
658.
We investigated the effect of water potential (WP) on the growth of, and interaction between, two ophiostomatoid fungi, Grosmannia clavigera and Ophiostoma montium, associated with the mountain pine beetle (Dendroctonus ponderosae). The WP of malt extract agar was amended by adding potassium chloride (KCl) or sucrose. Growth of both fungi decreased with WP on KCl-amended media. Growth of G. clavigera also decreased with WP on sucrose-amended media, although growth was stimulated on these media compared to unamended treatments. Growth of O. montium remained relatively constant on sucrose-amended media, confounding the effect of WP on this species. Both fungi were able to colonize media occupied by the other species, but at a slower rate than on unoccupied media, indicating competition. In most treatments, G. clavigera grew faster than O. montium and colonized a greater area when the two fungi were inoculated concurrently but distant to one another on a Petri dish. However, when each fungus was inoculated adjacent to a 10-d-old well-established colony of the other species, O. montium colonized occupied media more effectively than G. clavigera considering the growth rate of each species alone. Thus, G. clavigera dominated primary (uncolonized) resources on most media, whereas O. montium was more effective in colonizing secondary (occupied) resources. The differential response of the two fungi to sucrose indicates that they may use different carbon sources, or use different carbon sources at different rates, in the tree. Fine-scale resource partitioning, differences in primary and secondary resource capture abilities, and the non-equilibrium dynamics in an attacked tree over time, could all act to promote the co-existence of two unit-restricted dispersers on a discontinuous resource. 相似文献
659.
Aggregations of predators on food patches have been documented for both terrestrial and marine animals. Here, we documented for the first time, and investigated, non-predatory aggregations occurring between humpback whales (Megaptera novaeangliae) and killer whales (Orcinus orca) while feeding on wintering Norwegian spring spawning herring (Clupea harengus) in Andfjord, northern Norway. Observational data were collected during 109 opportunistic surveys through three seasons 2013–2016. Killer whales were observed feeding on 59 occasions, with one to three humpback whales involved in 47 of these feeding events (79.7%), and there was an increased probability of finding feeding humpback whales when feeding killer whales also were observed. With killer whales identified as the initiating species in 94.4% of the feeding aggregations for which the first species was known, and with humpback whales joining and feeding on the fish ball afterwards, we suggest that humpback whales may benefit more from these aggregations than the opposite. 相似文献
660.
Theory suggests that body size is an important factor in determining interspecific competition and, ultimately, in structuring
ecological communities. However, there is a lack of pragmatic studies linking body size and interspecific competition to patterns
in ecological communities. The objective of the present study was to determine the effect of body size (mass) on competitive
interactions between bird pairs and to investigate the influence of food guilds. Point-counts were carried out in nine sites
every month from November 2002 to November 2003 in the Cuetzalan Region, Mexico, and we used presence/absence and abundance
data for the analyses. To calculate the strength of competition we used the Angle Frequency Method to extract form factors
from 20 pairwise interactions. A prototype competition interaction and random pairs were also constructed. We used clustering
techniques (PCA) to calculate the dissimilarity scores (distances, D) of each of the pairwise interactions to the prototype competition and random pairs and one-way ANOVA to test for differences
between the means of the random and competitive pairs. The ratio in body mass (lnBM) for each of the interacting pairs was
calculated, and the association between the lnBM ratio and the strength of competition (D) was tested using a Pearson product-moment correlation coefficient. To test for the influence of foraging guilds we used
a univariate general linear model. Our results demonstrate a significant negative relationship between bird body mass ratio
and competition strength – i.e. competition strength increased when the body masses of the birds became more similar. We did
not find a significant influence of foraging guild on the relationship between body mass ratio and competition strength. On
the basis of these results, we suggest that high variation in body sizes amongst sympatric species promotes coexistence in
communities. 相似文献