Intraspecific Effects Research Articles

Competitive interactions between co-occurring herbivorous gastropods

The competitive interactions between two species of limpet, Patelloida alticostata (Angas), and Cellana tramoserica (Sowerby) were investigated at two sites; a low-lying intertidal platform and an adjacent subtidal reef located in southeastern Australia, during 1977 and 1982. C. tramoserica was relatively more abundant and larger in shell length than P. alticostata at the intertidal site, but P. alticostata was the more abundant species subtidaily. Fences were used to enclose various combinations of the two species to compare both intra- and inter-specific interactions. By repeating this design at two different, but adjacent sites, it was possible to test the generality of any interactions, and to investigate whether the nature of these could explain the observed differences in the relative abundances between the two sites. Intraspecific increases in density affected C. tramoserica more than P. alticostata at both sites. These effects were manifested both lethally (increased mortality at the intertidal site) and sublethally (as decreased growth and tissue weight at the subtidal site). Interspecific comparisons were asymmetrical, but were similar at both sites: C. tramoserica affected P. alticostata more than P. alticostata affected C. tramoserica. These latter effects were, however, only similar, or minor in comparison with the strong intraspecific effect that C. tramoserica had on itself. This suggests that, as has been found in some previous studies, competitive exclusion of the subordinate species (P. alticostata) is unlikely because of the greater intraspecific effects on the superior competitor (C. tramoserica). Furthermore, because there was little difference in the relative competitive abilities of the two species in the two habitats, competition between the species was probably not responsible for the different relative abundances between the two adjacent areas.

Vertical and seasonal patterns in competition for microalgae between intertidal gastropods.

Grazing by the snail Nerita atramentosa and the limpet Cellana tramoserica caused similarly great reductions in abundance of microalgae - measured by direct counts and by estimation of chlorophyll analyses. A smaller snail, Bembicium nanum, caused smaller reductions of microalgal resources, compared with ungrazed areas. These results were consistent with the competitive abilities of these three species. Chlorophyll concentrations in samples of grazed rocks were reliable estimates of the nature and abundance of food available to the grazers.Inter- and intra-specific competition amongst Nerita and Cellana were investigated at various densities in experimental cages. To examine the effects of different availability of food resources, the experiments were repeated at three heights on the shore (abundance of food decreases with height) and during autumn/winter and spring/summer periods of the year (less food is available during summer).Density-dependent mortality of Cellana was caused by the presence of other limpets, or of Nerita. Mortality was greatest at higher levels and during the spring/summer and was significantly, negatively correlated with mean chlorophyll concentration in the experimental cages. The only exception was that all limpets suddenly died in cages at the highest level during the summer period, which cannot be explained solely by competitive interactions. Nerita showed no density-dependent mortality during the short periods of these experiments. Tissue-weights of Nerita declined with increased density, but the effect of Cellana was not as great as the intraspecific effect of Nerita. Snails retained weight better at lower than at higher levels, and during the autumn/winter which is consistent with the availability of food. Tissue weights of both Nerita and Cellana were positively correlated with chlorophyll concentrations inside the cages in both seasons investigated.These experimental results demonstrate that intensity of competition will vary from place to place and time to time according to the densities and mixtures of the grazers, and according to the availability of microalgal food.

The Influence of Recruitment, Competition, and Benthic Predation on Spatial Distributions of Three Species of Kelp Forest Gastropods (Trochidae: Tegula)

Factors influencing the bathymetric segregation of three species of turban snails (Tegula) were examined in Monterey Bay, California. Two of the three species are abundant: Tegula brunnea occurs in shallow water (0—6 m), and T. pulligo occurs in deep water (7—12 m). Tegula montereyi occurs at intermediate and deep depths but is relatively rare. I examined the effects of larval recruitment, interspecific competition, and benthic predation on the maintenance of these patterns. The distribution of recently settled juvenile snails coincides closely with adult distribution, indicating that planktonic larvae of the three species may settle differentially to different depths. Juveniles of the two abundant species occur in different microhabitats at the extremes of their adult ranges: juvenile Tegula brunnea occur in the low—intertidal/shallow—subtidal zone on algae—covered rock substrate, and juvenile T. pulligo occur in deep water (11—12 m) on shell—fragment rubble. T. montereyi juveniles are less abundant than those of the other two species, depth and microhabitat distributions are similar to those of T. pulligo. Competition among the three species is not strong; neither food nor space limitation appears to occur in nature. The effects of competition on patterns of movement and habitat use in the field and on growth and reproductive development in the laboratory showed that interspecific and intraspecific effects were not significantly different. In addition, densities at which competition would have a strong effect are probably much higher than those that occur naturally. It is unlikely that competition is responsible for the bathymetric segregation of the three species. The major predators of Tegula are benthic invertebrates and demersal fishes. Tegula have two spatial refuges predators: kelp plants (which allow snails to stay off the primary substratum and away from predators) and dense benthic vegetation (predators cannot detect and capture snails as easily in areas of dense vegetation). Benthic predation pressure increases with increasing substrate depth because (1) the cover of protective benthic vegetation decreases significantly, and (2) predators are more abundant in deeper water. Higher predation pressure in deeper water limits adult Tegula brunnea to shallower depths. Individual T. brunnea spend more time on the kelp forest floor than do individuals of the other two species causing them to be killed at a disproportionately higher rate in deeper water. Benthic predation is also responsible for the concentration of T. pulligo on kelp plants in deeper depths, but cannot explain why this species is not more abundant in shallow depths. The rarity of T. montereyi is not caused by predation, since this species is the best defended of the three against starfish. For both species, patterns and intensities of larval settlement may be of primary importance. Further information on the larval biology of these species is needed.

Consequences of competition on the time budgets, growth and distributions of three species of terrestrial slugs

SummaryThe behavioural time budgets of two non‐aggressive slugs and one aggreessive species were evaluated in monocultures or in 2‐way combinations in field cages. The seasonal time budgets of L. maximus, A. ater and A. columbianus in monoculture were remarkably similar despite their strong differences in physiological resource allocation. Similarity in physical design and resource utilization appeared to be more important determinants of behaviour.The time budgets showed distinct seasonal patterns associated with underlying physiological demands for reserve accumulation, sperm acquisition and oviposition. A. ater and L. maximus displayed a definite dispersal phase associated with femalephase maturation.In combination, A. ater and A. columbianus had no detectable effect on one another's time budgets. L. maximus disrupted nearly every category of behaviour in these non‐aggressive species, but its own time budget was not significantly different in the monoculture or in the two combinations, except for minor effects on resting and sexual behaviour. L. maximus appeared to be adapted to maximize behavioural disturbance of interspecific competitors while minimizing intraspecific effects.

Insect territoriality

Territorial behavior has been reported in many orders of insects, particularly among the Odonata, Orthoptera, Hemiptera, Coleoptera, Hymenoptera, Lepidoptera, and Diptera. Although territoriality has been recognized among immature stages as well as in both sexes of adult insects, most of the published reports deal with the reproductive consequences of aggressive interactions among territorial males. Some dominance hierarchies have been described, particularly among cockroaches and megachilid and halictid bees. Lek behavior has also been reported among dragonflies, butterflies, and Hawaiian drosophilids. In all the species studied, territorial behavior spreads males through a habitat, minimizing intruder interference with courtship and mating, and increasing the probability that females will be mated. Besides these intraspecific effects, however, aggressive behavior towards unrelated species may reverberate through the larger community. For example, repeated attacks by aggressive files may cause pollinating bees and aphidophagous predators to change their foraging routes, and thus prevent them from servicing particular habitats.

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

Species Removal Effects on Movements of Sigmodon hispidus and Reithrodontomys fulvescens

The effects of interspecific interactions on movements of hispid cotton rats (Sigmodon hispidus) and fulvous harvest mice (Reithrodontomys fulvescens) were examined by experimental removal of species. For both Sigmodon and Reithrodontomys, the average distance moved by individuals (AvD,) was greater for males than females. The average distance moved by the population within trap periods (AvD,) was negatively correlated with Sigmodon density only in a field with low resource abundance whereas the AvDp for Reithrodontomys was negatively correlated with density in all fields. Species removal did not affect AvDp of either species. Seasonal differences in AvDp for R. fulvescens suggested an intraspecific effect on movement. Reithrodontomys used the vertical component of the habitat to a significantly greater extent when Sigmodon was present. There was no difference between experimental and control fields in vertical habitat structure, suggesting an interspecific effect of Sigmodon upon movement of Reithrodontomys. Variation in movement may result from differences in available habitat for Sigmodon, but not for Reithrodontomys.

Distribution of acid-soluble phosphates in the erythrocytes of selected species of amphibians

1. 1. Enzymatic, colorimetric and/or ion-exchange Chromatographic analyses of amphibian erythrocytic organic phosphates (EOPs) were performed to: (1) explore interspecific diversity; (2) determine the intraspecific effects of temperature, photoperiod and body size; and (3) correlate interspecific EOP similarities with the behavioral and physiological capabilities. 2. 2. The types and concentrations of EOPs ranged from reptilian to mammalian in character, and responded weakly to temperature and photoperiod. 3. 3. Inositol polyphosphate was detected in five species, but never exceeded 5% of the total acid-soluble phosphate. 2,3-Diphosphoglycerate (DPG) was the major EOP in 18 species and was present in all species examined. DPG: hemoglobin (Hb) molar ratios ranged from 0.07 to 1.9. Nucleoside triphosphate (NTP) was the major EOP in 12 species. NTP: Hb molar ratios ranged from 0.32 to 1.8. 4. 4. Analysis of similarity among species based on body mass, [Hb], hematocrit, [NTP] and [DPG] revealed three clusters of amphibians. EOP: Hb molar ratios of 1.0 or larger in bufonids and Scaphiopus correlated with a high dependence on aerobic activity metabolism. EOP: Hb molar ratios less than one in ranids correlated with a dependence on anaerobic activity metabolism.

Inter-and intraspecific effects of density manipulations upon females of two orb-weaving spiders (araneae: araneidae).

A field experiment was conducted to establish whether or not inter-and intraspecific competition occurs between two syntopic species of orb-weaving spiders. Replicated single-species and mixed-species adult populations of the basilica spider, Mecynogea lemniscata, and the labyrinth spider, Metepeira labyrinthea, were established at a range of densities on open experimental units in the species' natural habitat. Each experimental unit was a 4mx1.6mx1m wood frame supporting branches upon which introduced spiders built webs. Survival and reproduction on the units were monitored from 1 August through 1 November 1978,There were no significant negative interspecific effects of density upon either survival or reproduction, which indicates that interspecific competition was not occurring during the experiment. There was statistically significant evidence of intraspecific competition between females for both species, but the negative density effects were small. They explained 5% of the variance in Mecynogea web height, 2% of the variance in Metepeira survival, and 1% of the variation in number of eggs per sac for Mecynogea.Hence inter-and intraspecific competition was either absent or weak in 1978, despite the fact that a field experiment conducted the previous year (Wise 1979) demonstrated that prey abundance was limiting the egg production of both species. Evidence of food limitation in 1977 followed by only weak competitive interactions the following year suggests that the significance of resource limitation and competition may vary temporally for the basilica and labyrinth spiders.

The distribution of cestodes within the spiral intestine of Raja naevus Muller & Henle

The three tetraphyllidean cestodes Acanthobothrium quadripartitum, Phyllobothrium piriei and Echeneibothrium sp. occur in most parts of the spiral intestine of R. naevus with peak infections in tiers 2 and 3, Echinobothrium harfordi (Diphyllidea) is restricted to anterior tiers, and Grillotia erinaceus (Trypanorhyncha) shows litlle attachment site specificity. Details of the distribution patterns can be correlated with the dorsoventral orientation of the gut in the body cavity, the internal anatomy of the spiral intestine and associated pathways of food movement, the surface topography of the mucosa, acidity, sugar gradients and intraspecific effects at high intensities of infection. The distribution of the larger (‘mature’) cestodes does not depend on the settling pattern of the larvae.

Competitive relationships existing between two closely related species of Argemone living in the same area.

The present paper deals with the reaction of two closely related species of Argemone L., A. mexicana L. and A. ochroleuca Sweet, to its own density in pure stands and a comparison of this with its reaction to the density of the associated species. The results of the pure culture studies indicate that whilst each of the two species reacted to an increase in its own density by higher mortality and a striking reduction in vegetative and reproductive growth, A. mexicana was more susceptible to intraspecific effect than A. ochroleuca. On the other hand, mixed culture studies indicated that A. mexicana was more successful when in competition with A. ochroleuca. Further, that species which was in a majority in the mixture suffered most compared to the minority species. Such a density dependent differential behaviour in pure stands and frequency dependent differential behaviour in mixed cultures along with the reversal in superiority of the two species in pure and mixed cultures was considered to be responsible for the cohabitation of the two species and their relative population sizes in nature.