Ecological studies on the population of isaza,Chaenogobius Isaza Tanaka,in Lake Biwa,with special reference to the effects of population density upon its growth

1. In order to get the knowledge on the age composition of “isaza” population in Lake Biwa and the effect of population density on growth, monthly distribution of mean body length and mean body weight has been analyzed on the basis of monthly haul by “isazabiki” trawl during 1949 to 1953 and also 1960 to 1965.
2. There is no apparent sex difference in the growth in the first and second years of life.
3. “Isaza” population is composed of two age groups, age 0 and 1 groups (1+fish), the latter occupying by far the greater part in commercial catch.
4. During the growth season fishes of both ages feed mainly on zooplankton, though in winter frequently take chironomid larvae, gammaridae and others in volume.
5. The growth season falls in the period from April to October in both age groups.
6. A considerable yearly variation occurring in growth is in close connection with the fluctuation of population density of all ages.
7. The influence affected by the density of age 1 group is larger than that by age 0 group.

     

Growth related to behaviour of ayu,Plecoglossus altivelis,reared under low density

1. Three groups of ayu, each populated by 6 fish, were reared in three concrete ponds of same size (1×4×0.3 m). Growth of all individuals was measured on total length, and behaviour of all individuals marked by vinyl ribbon was observed at some intervals during the experiment of about 40 days in August and September, 1960.
2. Averaged growth of fish did not vary significantly among the groups. But the growth of individual whether in the size attained or its rate varied considerably, and the variation well corresponded to the social construction in which they participted.
3. Within each group, individual behaviour which was well expressed in the strength of chasing action (competition) and territory formation correlated positively to the growth of fish. The correlation as such is believed to exist not only in ayu but also in many other species of fish possessing competitive or territorial behaviour.
4. The different social structures formulated by the three groups of fish under low population density may not be adequately explained at this moment leaving further studies to be carried out.
5. It was assumed that the ayu population of low density as experimented here has not presented natural social structure of the species, thus, resulted diversity. Nonetheless, the experiment is believed to approve the writer's concept-density dependent growth of fish will be resulted through the medium of differential behaviour of associated member.

     

Population studies based on relative abundance of five different life history stages of Ayu,Plecoglossus altivelis (Pisces,Plecoglossidae), in Lake Biwa

1. Comparison of relative abundance of each two successive life history stages was made for studying population dynamics of ayu, Plecoglossus altivelis, in Lake Biwa.
2. Number of eggs spawned is proportional primarily to the size of biomass of spawner population although spawning success plainly depends on presence or absence of heavy rain in the spawning period.
3. Although density of fry tends to be proportional to that of egg, yearly fluctuation of the fry mortality may be caused by changes in density of food organisms but is not in compensatory way.
4. From the fry stage to the juvenile one the rate of mortality and/or of growth seem to fluctuate in compensatory way which is supposed to be related to a shortage of food.
5. Yearly fluctuation of mortality of adult stage is caused by an artificial factor as changes of fishing intensity.
6. Necessity of studying actual events at each stage of the life history process separately in relation with environmental conditions is discussed through the result of the present analysis.

     

Aging alters interspecific competition between two sympatric insect–parasitic nematode species

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When to cut your losses: Dispersal allocation in an asexual filamentous fungus in response to competition

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Competitive interactions are mediated in a sex‐specific manner by arbuscular mycorrhiza in Antennaria dioica

• Plants usually interact with other plants, and the outcome of such interaction ranges from facilitation to competition depending on the identity of the plants, including their sexual expression. Arbuscular mycorrhizal (AM) fungi have been shown to modify competitive interactions in plants. However, few studies have evaluated how AM fungi influence plant intraspecific and interspecific interactions in dioecious species.
• The competitive abilities of female and male plants of Antennaria dioica were examined in a greenhouse experiment. Females and males were grown in the following competitive settings: (i) without competition, (ii) with intrasexual competition, (iii) with intersexual competition, and (iv) with interspecific competition by Hieracium pilosella – a plant with similar characteristics to A. dioica. Half of the pots were grown with Claroideoglomus claroideum, an AM fungus isolated from the same habitat as the plant material. We evaluated plant survival, growth, flowering phenology, and production of AM fungal structures.
• Plant survival was unaffected by competition or AM fungi. Competition and the presence of AM fungi reduced plant biomass. However, the sexes responded differently to the interaction between fungal and competition treatments. Both intra‐ and interspecific competition results were sex‐specific, and in general, female performance was reduced by AM colonization. Plant competition or sex did not affect the intraradical structures, extraradical hyphae, or spore production of the AM fungus.
• These findings suggest that plant sexual differences affect fundamental processes such as competitive ability and symbiotic relationships with AM fungi.

     

Interspecific competition between insect herbivores: asymmetric competition between cinnabar moth and the ragwort seed-head fly

ABSTRACT.

• 1 Removal field experiments and observational studies have been undertaken to determine whether feeding by cinnabar moth Tyria jacobaeae L. on the flower heads of ragwort Senecio jacobaea L. affects the abundance of the fly Pegohylemyia seneciella (Meade) that feeds in the flower heads as a larva.
• 2 Correlations between the population density of cinnabar moth and the population density of the fly were suggestive of habitat separation, but provided little evidence of exploitation competition.
• 3 Removal of cinnabar moth by hand from replicated plots over two years shows that, in years when ragwort flower production is consumed by cinnabar moth caterpillars, the fly may show no recruitment at all.
• 4 Fly populations persist in refugia, exploiting ragwort plants that grow in areas where there are no cinnabar moth.
• 5 Recruitment of ragwort is not seed limited, so the reduction in seed production caused by P. seneciella (maximum about 30%) has no impact on ragwort abundance, or on the abundance of cinnabar moth.
• 6 We conclude that there is strong interspecific competition between these two species, and that the competition is highly asymmetric. The cinnabar moth had a substantial effect on the recruitment of the fly in 1986, but the fly has no measurable impact on the recruitment of the moth. In six years out of seven in our long-term study, cinnabar moth reduced flower production to levels comparable to those measured in 1986, and we infer that strong competition with the fly was likely in six years out of seven.
• 7 One reason why there are so few published examples of asymmetric interspecific competition may be simply that the experiments are thought too obvious to be worth doing. We argue that this is not a good reason for eschewing manipulative field experiments, and that few processes in ecology are at all obvious when investigated in detail.

     

Variable effects of wolves on niche breadth and density of intraguild competitors

1. The parallel niche release hypothesis (PNR) indicates that reduced competition with dominant competitors results in greater density and niche breadth of subordinate competitors and which may support an adaptive advantage.
2. We assessed support for the PNR by evaluating relationships between variation in niche breadth and intra‐ and interspecific density (an index of competition) of wolves (Canis lupus) coyotes (C. latrans), and bobcats (Lynx rufus).
3. We estimated population density (wolf track surveys, coyote howl surveys, and bobcat hair snare surveys) and variability in space use (50% core autocorrelated kernel density home range estimators), temporal activity (hourly and overnight speed), and dietary (isotopic δ¹³C and δ¹⁵N) niche breadth of each species across three areas of varying wolf density in the Upper Peninsula of Michigan, USA, 2010–2019.
4. Densities of wolves and coyotes were inversely related, and increased variability in space use, temporal activity, and dietary niche breadth of coyotes was associated with increased coyote density and decreased wolf density supporting the PNR. Variability in space use and temporal activity of wolves and dietary niche breadth of bobcats also increased with increased intraspecific density supporting the PNR.
5. Through demonstrating decreased competition between wolves and coyotes and increased coyote niche breadth and density, our study provides multidimensional support for the PNR. Knowledge of the relationship between niche breadth and population density can inform our understanding of the role of competition in shaping the realized niche of species.

     

Key factors and related principles in the conservation of large African carnivores

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Effects of past and projected river discharge variability on freshwater production in an anadromous fish

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Interspecific competition in Arabidopsis thaliana: root hairs are important for competitive effect, but not for competitive response

Background and aims

The role of root hairs in intraspecific competition for Phosporus (P) is well examined, but their importance during interaction with other plant species is unknown, as is the differential meaning for competitive effect and response. This study aims to fill this gap of knowledge.

Methods

Competitive abilities of Arabidopsis thaliana wildtype and mutants with aberrant root hair phynotypes (root hair deficient, rhd2-1 or excessive root hair density, prc1-1) were examined in a pot-experiment with P-deficient sand. Competitive effects on a phytometer (Hieracium pilosella) or on A. thaliana itself were assessed as well as competitive responses to species mixtures.

Results

In intraspecific interaction, the competitive effect of wildtype was superior to that of rhd2-1 or prc1-1. This was much less pronounced in interspecific interaction. Competitive response was entirely uniform between Arabidopsis root phenotypes.

Conclusions

The notion that root hairs are important for competition for P should be differentiated. With A. thaliana root hairs less important in inter- than in intraspecific interaction and with root hairs entirely unimportant for competitive response, functional mechanisms of competition for P appear quite complex. Such differential importance of root traits in different facets of competition might well be more common than previously thought.     

The competition amongDrosophila larvae in different growth stages

1. The experiment was conducted in order to examine the influence of the difference in the growth stage of the competitors on the intraspecific competition. Drosophila melanogaster, “wild” and its mutant “ebony” were used as materials.
2. The earlier developed or older larvae have considerable advantage, such as the increase of the body weight of flies, and of the total weight of flies from one vial, and high constant emerging percentage, while the younger competitors received the opposite influence in addition to the increase of the larval-pupal duration.
3. The grand total yields (the yield of “wild” plus that of “ebony”) from one vial were almost constant even the difference in the growth stage between competitors is changed.

     

The spatial pattern in a natural population of goldenrod (Solidago altissima L.), with particular reference to its change during the shoot growth

In a natural population of Solidago altissima L., the changes in the spatial pattern of shoots in the course of growth were studied. The results obtained were summarized as follows:

1. The spatial pattern changed from clumped to random distribution as plants grew. The change seemed to be resulted from some density-dependent process acting at a small spatial scale, probably the competition for space.
2. Large plants tended to distribute themselves more uniformly over the space than the small ones but at the mature stage of growth such a difference was not obviously recognized. The process of appearance of the small-sized plants during successive periods also seemed to be dependent on local density.
3. Large plants at the early stage of growth tended to survive better, and there was a positive correlation between initial size and the size at maturity.
4. From these results, it is inferred that the change of spatial pattern from clumped to random distribution is largely due to the elimination of small shoots as the result of competition for space among individual shoots.

     

Studies on interspecies competition between the azuki bean weevil and the southern cowpea weevil

Experimental studies was made on the interspecies competition between the azuki bean weevil, Callosobruchus chinensis and the southern cowpea weevil, C. macultatus. And the following results were obtained.

1. The reverse result of competition between the two species observed under the air-tight condition and the air-free one. That is, the population of the azuki bean weevils destroyedby that of the southern cowpea weevils under the former condition and vice versa under the latter. It is thought that such a reversal is due to the difference of sensibility of each species to the air-tight condition.
2. Under the air-free condition, change of the time interval of food-supplying had no effect on the result of competition within the limits of this experiment. The population of the southern cowpea weevils was always destroyed by that of the azuki bean weevils. But there was a certain degree of correlation between the duration of co-existence and the interval of food-supplying.
3. From the results, it is possible to say that by changing the degree of air-tightness, or the time interval of food-supplying, the co-existence period and the final result of competition can be changed.
4. The different mechanism of competition between two species in the present experiment from the experiments ofUtida (1952) andYoshida (1957) were discussed.
5. A difference in the mechanism of interspecies competition and intraspecies competition was expected from the level of total population numbers of two species and the individual weight of C. chinensis.

     

Facultative predation and scavenging by mammalian carnivores: seasonal,regional and intra‐guild comparisons

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Studies on interspecies competition between the azuki bean weevil,Callosobruchus chinensis,and the southern cowpea weevil,C. maculatus II. Competition under different environmental conditions

The experimental studies was done on the interspecies competition between the azuki bean weevil, Callosobruchus chinensis, and the southern cowpea weevil, C. maculatus, under the different environmental conditions.

1. At 30°C, 70% R. H., the change of food replenishment interval had no influence upon the competition results, and the competition always ended in the extinction of C. maculatus. But there was a tendency for the period of co-existence to be elongated as the interval of replenishment lengthened.
2. At 30°C, 70% R. H., there were no differences in the competition processes and results between the competition using the dry bean (water content about 11%) or the normal one (about 15%).
3. At 32°C, 64% R. H., the competition result was reversed from that at 30°C, 70% R. H. This is thought to be due to the differences of the developmental rates and the numbers of eggs oviposited between the two species at these conditions.
4. In some cases the competition result could be understood from the point of the phenomena of single species populations of both species, but in other cases, the results were in conflict with the expectation from those phenomena. To analyze the competition mechanism, it is necessary to investigate the interaction between species.

     

Aspects of interspecific interaction betweenReithrodontomys megalotis andMicrotus montanus in one acre enclosures

1. Two one acre enclosures were cleared of all resident rodents, and then, one enclosure was seeded with founder populations of Reithrodontomys megalotis (grid M) and the other with Reithrodontomys megalotis plus Microtus montanus (grid I). Founder populations consisted of eight animals for each species introduced and a sex ratio of 1∶1.
2. Five parameters were measured for a period of one year. Data collection was started in September 1971, and ended in September 1972; enumeration was conducted twice a month for three days.
3. The five parameters measured were: (1) population density through time and individual growth rates; (2) reproduction; (3) survival of age and sex classes; (4) sex ratio; and (5) sizes of home ranges.
4. There were no significant differences in three out of the five parameters studied. Density estimates along with individual growth rates were not significantly different between the grids. Reproduction, including breeding season and efficiency of reproductive effort, showed no or very little variation due to interspecific interaction. Home range sizes did not appear to be significantly different between the grids. Survival of juvenile males on grid I seemed lower and juvenile males from grid I were significantly smaller although possibly younger than those of grid M. The sex ratio of grid I was significantly different from the expected 1∶1 ratio.
5. It is postulated that Reithrodontomys megalotis may regulate their density by alteration of their sex ratios.

     

Competition from sea to mountain: Interactions and aggregation in low‐diversity monogenean and endohelminth communities in twospot livebearer Pseudoxiphophorus bimaculatus (Teleostei: Poeciliidae) populations in a neotropical river

1. The role of interspecific interactions in structuring low‐diversity helminth communities is a controversial topic in parasite ecology research. Most parasitic communities of fish are species‐poor; thus, interspecific interactions are believed to be unimportant in structuring these communities.
2. We explored the factors that might contribute to the richness and coexistence of helminth parasites of a poeciliid fish in a neotropical river.
3. Repeatability of community structure was examined in parasitic communities among 11 populations of twospot livebearer Pseudoxiphophorus bimaculatus in the La Antigua River basin, Veracruz, Mexico. We examined the species saturation of parasitic communities and explored the patterns of species co‐occurrence. We also quantified the associations between parasitic species pairs and analyzed the correlations between helminth species abundance to look for repeated patterns among the study populations.
4. Our results suggest that interspecific competition could occur in species‐poor communities, aggregation plays a role in determining local richness, and intraspecific aggregation allows the coexistence of species by reducing the overall intensity of interspecific competition.

     

Reproductive strategy and interspecific competition in the Lake-living gobiid fish isaza,Chaenogobius isaza

Isaza,Chaenogobius isaza, is a small gobiid fish endemic to Lake Biwa. It lives offshore throughout almost the entire year, showing a remarkable diel vertical migration. In early spring, males and females migrate to lake shore to spawn under stones. Spawning season is limited to a very short span of time in early spring, late April to early May. During this short spawning season, the male is supposed to have only 2 brood cycles at maximum. At each brood cycle, the male is strictly monogynous, never accepting additional females. Males therefore show a marked mate choice, choosing a larger female regardless of the size of the male himself. Females also choose larger males. However, males are supposed to not waste time in male-male fighting in the natural spawning area. That this very short spawning season and its occurrence in early spring is primarily to avoid interspecific competition with another littorally reproducing goby Yoshinobori,Rhinogobius brunneus, is experimentally demonstrated.     

Optimal foraging by an aphid parasitoid affects the outcome of apparent competition

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