Interspecific Contacts Research Articles

Population Structure as a Predictor of Spatial Association between Sigmodon hispidus and Microtus ochrogaster

Terman's (1974) model of interspecific competition based on the frequency of interspecific contact (FIC) predicted that the degree of spatial association between cotton rats and prairie voles could be determined from characteristics of the cotton rat population. To test Terman's model, annual changes in cotton rat population structure were examined for correlations with spatial association between voles and cotton rats. Coefficients of association varied systematically with changes in cotton rat population density, numbers of adults, and numbers of reproductive adults. The results tend to support Terman's general model based on FIC. However, the relationships between cotton rat population structure and spatial association were not linear.

Neighbour relationships in grass–legume communities. I. Interspecific contacts in four grassland communities near London, Ontario

A survey of four old grasslands near London, Ontario, showed that different legumes formed consistent relationships with different grass species. Each legume was strongly associated with a particular combination of grass species. It is suggested that each legume–grass combination is selected through the ability of the combination to utilize the soil environment more efficiently than random combinations of species. The ability of species to combine as well as compete is an important factor in maintaining the dynamic stability of grasslands.

An experimental study of movement in natural populations of Mus musculus, microtus pennsylvanicus , and Microtus pinetorum

distribution of natural populations of Microtus pinetorum, Microtus pennsylvanicus, and Mus musculus through removal and return of individuals of these species from a natural field community over a three month period. The movements of neighboring animals concurrent with and subsequent to these manipulations were analysed to determine both their extent and variability. These three species are known to use the same runways (BENTON, 1955; GENTRY, 1966) and it can be assummed that interspecific contacts very likely occur. Previously, CALHOUN (1968) presented an elaborate theoretical system of the intra-and interspecific use of space in which he proposed the existence of effective means of communication both within and between species. The present study was designed, not to determine the nature of mechanisms of communication that may exist, but to obtain evidence of the presence or absence of such communication. The objectives of this study were: 1. To measure the movements (immigration, emigration) of animals in the field in response to removal and return of individuals from the natural community. 2. To determine if the species varied in movement patterns associated with the manipulation of removal and return. 3. To evaluate movement patterns relative to the ecological characteristics of each species.

Effets de lésions précoces de l'amygdale sur le développement de l'agressivité interspécifique du rat

Bilateral amygdaloid lesions made at the age of 7–8 days entail a marked increase in the proportion of rats that display mouse-killing behavior when adult (90% killer-rats in a group sustaining extensive and symmetrical destruction of the amygdala, 65% killer-rats in a group sustaining more limited amygdaloid lesions, as compared to 9% killer-rats in the sham-operated group). Amygdaloid lesions that include the centromedial region are more efficient with regard to initiation of mouse-killing behavior than lesions that spare the central and medial nuclei. When performed at the age of 25 days, amygdaloid lesions also increase the proportion of killer-rats (62%, as compared to 17% in the sham-operated group). Amygdaloid lesions made at the age of 8 days clearly reduce the efficiency of early interspecific social contacts in preventing initiation of mouse-killing behavior (72% killer-rats among animals reared with mice from weaning). The efficiency of intraspecific social interactions in preventing initiation of mouse-killing behavior following removal of the olfactory bulbs is also reduced when bilateral amygdaloid lesions are combined with the bulbectomy at the age of 25 days (59% killer-rats, as compared to 7% killer-rats in a group of non-amygdalectomized bulbectomized animals). Intraspecific social interactions remain efficient in bulbectomized rats following a bilateral destruction of the dorsomedial thalamus.

Behavioral Interactions between Microtus and Sigmodon: A Model for Competitive Exclusion

An alleged negative interaction between Microtus ochrogaster and Sigmodon hispidus was examined in the laboratory. Sigmodon proved to be the dominant animal, and excluded Microtus from confined areas except when dense cover was provided. Movements of Microtus were reduced by a free-ranging Sigmodon but not by a confined one. Frequency of interspecific contact apparently was responsible for negative interactions. A model that emphasizes frequency of interspecific contact (FIC) explains the probable relationship between Microtus ochrogaster and Sigmodon hispidus ; a variation of this model might explain the phenomenon of competitive exclusion in all myomorph rodents.

Notes on conflict between elephants and some bovids and on other inter-specific contacts in Yankari Game Reserve, N.E. Nigeria

Notes on conflict between elephants and some bovids and on other inter-specific contacts in Yankari Game Reserve, N.E. Nigeria

Ecological Isolation and Competitive Exclusion in Two Crayfish (Orconectes Virilis and Orconectes Immunis)

The two crayfish, Orconectes virlis and O. immunis, have similar ranges but are ecologically isolated within these ranges; the former species inhabits streams and lake margins, the latter inhabits ponds and sloughs. Field and experimental data suggest that the stream species, O. virilis, is excluded from ponds by summer drying and periodic low oxygen periods of those ponds. It is not as competent a burrower as O. immunis nor is its as tolerant of low oxygen levels. Neither current nor substratum excludes the pond species, O. immunis, from the stream. But both field and laboratory observations strongly indicate a competitive exclusion of O. immunis by O. virilis. The latter was demonstrated to be intrinsically more aggressive in interspecific contacts, and in other experiments, evicted O. immunis from crevices in the substratum.

Intra‐ vs. Interspecific Aggression in Pygmy Nuthatch Flocks

Pygmy Nuthatches, White—breasted Nuthatches, and Mountain Chickadees travel in mixed flocks in winter in Colorado. The species exhibited different by overlapping foraging niches. Both intra— and interspecific aggression occurred, supporting the idea of niche overlap. The ratio of intra— to interspecific encounters was higher than expected if encounters were in proportion to flock composition, indicating that niche overlap was not complete. At artificial feeding stations, where found niches were identical for all species, the level of interspecific aggression initially was higher than in nature. However, the dominance of Pygmy Nuthatches at the feeders soon resulted in a "competitive exclusion" of the other birds and a lessening of interspecific contact.

Ethological Isolation between Peromyscus maniculatus and Peromyscus polionotus

Social behavior of Peromyscus maniculatus rufinus and P. polionotus leucocephalus was observed in mixed groups of three mice each to determine the degree of ethological isolation and to observe be- havior patterns which might contribute to the isolation noted between the two species. Ten categories of behavior were selected as indicators of ethological isolation, and the amount of interspecific and intraspecific contacts observed are presented. Behavioral patterns of the two species are similar. Mice of each species directed most of the sexual behavior to animals of the same species; however, there was less restriction of some other types of social behavior to mice of the same species. It is estimated the ethological isolation would prevent interbreeding between the two species if they were to become sympatric. INTRODUCTION Ethological isolating mechanisms are usually the most important in restricting interbreeding between closely related animal species (Mayr, 1963), including species of the genus of cricetid rodents, Peromyscus. Closely related species of Peromyscus may be crossed in the laboratory, but in areas of sympatry the natural populations fail to interbreed due to ecological and ethological isolating mechanisms (Dice, 1940). Peromyscus maniculatus and P. polionotus are classi- fied in the same species group (Osgood, 1909), and although they have completely allopatric distributions, there is evidence that they would fail to interbreed if natural populations ever became sympatric. Laboratory crosses between the two species result in some fertile ofi- spring (Liu, 1953); however, Blair and Howard (1944), found evi- dence of ethological isolation between them. Ethological isolating mechanisms are based on restriction of the direction of sexual behavior by an animal to another animal that provides the specific stimuli characteristic of that species. Reinforcement could strengthen iso- lating mechanisms by narrowing the range of stimuli to which an animal will respond, or by resulting in avoidance of stimuli associated with another sympatric species. However, reinforcement is not neces- sary for the development of ethological isolation between two species (Godfrey, 1958). Observations of the behavior of mixed groups of mice were made in the laboratory to determine the degr ee of ethological isolation between the two species and to observe particular behavior sequences or differences in behavior that might contribute to the ethological isolation noted between the two species. I am indebted to Dr. W. F. Blair for his assistance and encouragement during this research project. The study was supported by NSF Graduate Fellowships 20200 and 31116.