Heterospecific Individuals Research Articles

The response of the terrestrial slug Deroceras laeve to the mucus and air-borne odours of con- and heterospecifics (Pulmonata: Agriolimacidae)

Gastropods produce mucus for a number of reasons. 1 One of these is attracting potential mates through (volatile) metabolites that are released in the mucus. 2,3 Hence, mucus may to a greater or lesser extent be responsible for influencing the behaviour of conspecific and even related heterospecific individuals. Moreover, interference competition through mucus of conspecifics and related heterospecifics may reduce growth rates and reproduction in individuals, thus affecting their fitness.4‐6 We tested the response of the terrestrial land slug Deroceras laeve on the mucus of unstressed and stressed con- and heterospecifics, and on air-borne odours of conspecifics. D. laeve (Muller) individuals were obtained from a laboratory culture. D. reticulatum (Muller) and D. panormitanum (Lessona & Pollonera) were used for trials with heterospecifics. All individuals were kept isolated in plastic containers with a piece of sponge and damp paper towel. Dried cat food and poplar leaves were given as food. Animals were kept in a climate room at a constant temperature of 18°C and a 16 h light/8 h dark rhythm. Only equally sized adult individuals were used. Individuals that were used to obtain stressed mucus were not used in the trials. Individuals were only used once in each experiment. All experiments were carried out in complete darkness. After each trial, all experimental equipment was cleaned with water and detergent to remove all mucus. In a first experiment we tested the response of D. laeve on mucus of unstressed conspecifics using two different set-ups. In the first set-up, we used 12 � 17-cm plastic boxes that were surrounded with copper foil to prevent slugs from escaping. Half the surface of a box was lined with untreated damp paper towel and poplar leaves. The other half of a box was lined with damp paper towel and poplar leaves containing mucus from unstressed conspecifics. Unstressed mucus was obtained by letting three slugs move for 30 min in complete darkness in a 12 � 8.5-cm plastic box surrounded with copper foil. The bottom of the box was covered with damp paper towel and poplar leaves. The paper and leaves with the mucus were transferred to the larger experimental box. At the beginning of each trial one experimental animal was placed at the contact line of the two surfaces. The behavioural response of 30 slugs was filmed for one hour with a Sony DLRTRV 130 E digital handycam attached to a VHS videorecorder in a climate room at 18°C. The ‘super nightshot’ option of the handycam allowed filming in complete darkness. Each time, two experimental boxes were filmed at the same time with a different orientation of the treated surface to avoid any bias from movements towards a certain direction. After 1 h we recorded the position of each slug, calculated the time that was spent on each surface and calculated the time that the individual was active on each surface. Activity was expressed as: (total time an individual was crawling in area/total time spent in area) � 100% and arcsin square root transformed to meet the parametric assumptions of normality. 7 Individuals that showed no activity within 10 min of the start of the experiment were excluded from the analysis. The preference for one of the two areas was tested with a � 2 test. Differences in the time spent on the two areas and differences in activity on the two areas were tested with a paired Student’s t-test. There was a tendency for individuals at the end of an hour to be on areas with mucus of conspecifics rather than on areas without mucus although the difference was not significant (� 2 = 3.33; df = 1;

Genetic, ecological, and behavioural divergence between two sibling snapping shrimp species (Crustacea: Decapoda: Alpheus).

Examination of genetic and ecological relationships within sibling species complexes can provide insights into species diversity and speciation processes. Alpheus angulatus and A. armillatus, two snapping shrimp species with overlapping ranges in the north-western Atlantic, are similar in morphology, exploit similar ecological niches and appear to represent recently diverged sibling species. We examined phylogenetic and ecological relationships between these two species with: (i) sequence data from two mitochondrial genes (16S rRNA and COI); (ii) data on potential differences in microhabitat distribution for A. armillatus and A. angulatus; and (iii) data from laboratory experiments on the level of reproductive isolation between the two species. DNA sequence data suggest A. armillatus and A. angulatus are sister species that diverged subsequent to the close of the Isthmus of Panama, and that haplotype diversity is lower in A. armillatus than in A. angulatus. Both species are distantly related to A. heterochaelis and A. estuariensis, two species with which A. angulatus shares some similarities in coloration. Ecological data on the distribution of A. angulatus and A. armillatus from two locations revealed differences in distribution of the two species between habitat patches, with each patch dominated by one or the other species. However, there was no apparent difference in distribution of the two species within habitat patches with respect to microhabitat location. Ecological data also revealed that heterospecific individuals often occur in close proximity (i.e. within metres or centimetres) where sympatric. Behavioural data indicated that these species are reproductively isolated, which is consistent with speciation in transient allopatry followed by post-divergence secondary contact. Our data further resolve taxonomic confusion between the sibling species, A. armillatus and A. angulatus, and suggest that sympatry in areas of range overlap and exploitation of similar ecological niches by these two recently diverged species have selected for high levels of behavioural incompatibility.

Home Range Size of Sympatric Squirrel Species Inhabiting a Lowland Dipterocarp Forest in Malaysia1

Home range sizes and spatial overlap of four sympatric squirrel species were investigated in a lowland dipterocarp forest in Malaysia using a radio-tracking method. The population density of Callosciurus caniceps was highest and C. notatus was next highest, while C. nigrovittatus and Lariscus insignis were scarce. C. caniceps was larger than C. nigrovittatus and C. notatus while L. insignis was extremely small. For females, home range size was smaller in L. insignis than Callosciurus spp., which may support the body weight hypothesis: larger species have larger home ranges. Among the three Callosciurus species, female C. caniceps had the smallest home range. These differences were accounted for by habitat characteristics rather than by density or body weight; C. caniceps was dominant in bushy areas and used crowded small trees while C. notatus and C. nigrovittatus used large trees in the forest. In this study, home range size did not change seasonally; this differs from studies in temperate regions, possibly because food availability is much less variable among seasons in tropical rain forest. Home range overlap among heterospecific individuals was common but different species seemed to partition space by using different vertical levels of the forest. Consequently, the home range size and spatial overlap of sympatric squirrel species may be affected by habitat diversity in tropical rain forest.

Similarity in the qualities of individual odors among kin and species in Turkish (Mesocricetus brandti) and golden (Mesocricetus auratus) hamsters.

In this investigation, the authors used habituation techniques to explore similarities and differences in the qualities of individual odors from hamsters. In Experiment 1, male Turkish hamsters (Mesocricetus brandti) treated flank-gland odors of 2 males from 1 litter as similar compared with the odor of a male from another litter, whether the odor donors were familiar or unfamiliar. At the same time, the Turkish hamsters discriminated between the subtle differences in the individual odors of their familiar brothers. In Experiment 2, male Turkish and golden hamsters (Mesocricetus auratus) treated the flank-gland odors of 2 unfamiliar, unrelated conspecifics as similar compared with the flank odor of a heterospecific individual. The results suggest that similarities in individual odors are related to genetic similarity of the odor donors. These similarities could provide a basis for different types of social recognition, including kin and species recognition.

Bird Tolerance to Human Intrusion in Wyoming Montane Forests

Human intrusion can be a serious problem for birds because it can cause displacement, prevent access to resources, and reduce reproduction and survival. The factors that influence avian tolerance to intrusion are poorly understood. We studied passerine responses to intrusion in Wyoming montane forests during the breeding season by using two indices of intrusion tolerance: detectability period, the amount of time that a bird remains near its initial flush point; and approach distance, how close one can get to a bird before it flushes. A solitary observer experimentally approached focal individuals and recorded detectability period, approach distance, the seasonal and daily timing of intrusion, number of nearby conspecifics, number of nearby heterospecific individuals, and surrounding vegetation conditions. Using data from the literature, we also assessed influences of migratory status, body mass, conspicuousness, and height above the ground at which species are active during the breeding season. Detectability period was significantly shorter, indicating intrusion tolerance was lower, when fewer conspecifics were nearby. Approach distance was significantly longer, indicating tolerance was lower, for more-conspicuous species and for species that are active closer to the ground. Effects of other variables studied were not significant. These results demonstrate that social and biological factors can influence tolerance to intrusion. Intrusion-induced behaviors such as nest abandonment and decreased nest attentiveness have led to reduced reproduction and survival in species that are intolerant of intrusion. With knowledge of factors that influence tolerance, the risk of disturbing birds that are sensitive to intrusion could be reduced.

Aggregate Dispersion of Birds after Encountering a Predator: Experimental Evidence

Animals may join flocks to gain protection against predation. In this experiment we investigated how predation risk affects the spatial distribution of forest birds during breeding time. We manipulated the perceived risk of predation by showing stuffed avian predators and by playing the warning signals of some of the passerine species in experimental areas. The spatial distribution of the bird individuals in both experimental and control areas was investigated by censusing birds and marking the locations of all individuals on maps both before and after the simulated appearance of a predator. We predicted that the distances between heterospecific individuals would be reduced in the experimental areas compared with those in control plots because of a perceived increased risk of predation. After predator presentation individuals in experimental areas were closer to heterospecifics than in control areas. Predation risk is one possible cause of clumped distribution of species and mixed-species foraging flocks in boreal breeding bird communities.

DIFFERENCES IN RESTING-SITE PREFERENCE IN TWO COEXISTING LAND SNAILS, ARIANTA ARBUSTORUM AND ARIANTA CHAMAELEON (HELICIDAE), ON ALPINE SLOPES

Resting-site preference and patterns of spatial distribution were examined in the sympatric land snails Arianta arbustorum and A. chamaeleon on two opposite slopes in the south-eastern Alps, Austria. The two slopes did not differ in proportion of A. arbustorum and A. chamaeleon (74.4% vs. 25.6% on the NNE-exposed slope and 68.3% vs. 31.7% on the SSW-exposed slope). Individuals of both species showed aggregated dispersion patterns. The nearestneighbour method indicated that in both species snail aggregations predominantly consisted either of A. arbustorum or A. chamaeleon on the NNEexposed slope with a mosaic of rocks and distinct patches of different plants. On the SSW-exposed slope, which was less variable in vegetation cover, snail aggregations consisted of conspecific and heterospecific individuals. Juvenile and adult A. arbustorum preferred to rest attached to leaves of Adenostyles alliariae, but avoided rock surfaces and patches of grass on the NNE-exposed slope. In contrast, juvenile and adult A. chamaeleon preferentially rested on rock surfaces, and also avoided grass patches. Juvenile and adult A. chamaeleon did not differ in resting-site preference, whereas small differences in resting sites were observed between juvenile and adult A. arbustorum. Differences in resting-site preference is one way of niche differentiation which may allow individuals of the two Arianta species to coexist.

Laboratory experiments on spatial use and aggression in three sympatric species of shrew in Hokkaido, Japan.

Aggression and the use of vertical and horizontal space in the presence of con- or hetero-specific individuals were investigated in laboratory for Sorex unguiculatus, S. caecutiens, and S. gracillimus in Hokkaido, Japan. S. unguiculatus frequently used the below floor strata of experimental cages or subterranean burrows as their main area of activity, whereas S. caecutiens and S. gracillimus mainly used the cage floor or the ground surface. The presence of con- or hetero-specific individuals led to no changes in any of the three species in the use of space, or in behavioral patterns (active/inactive ; underground/resting/ moving on the ground surface). When two individual shrews were introduced into two interconnected cages, they tended to remain in separate cages, with the exception of S. gracillimus with a conspecific. Dominance rank was highest in S. unguiculatus, intermediate in S. caecutiens, and lowest in S. gracillimus. S. caecutiens attacked S. gracillimus most frequently and S. gracillimus received attacks from S. caecutiens most frequently. The implication of this research is that severe interference competition may occur in the field between S. caecutiens and S. gracillimus.

IS DECREASED FREQUENCY OF MATING AMONG CONSPECIFICS A COST OF SYMPATRY IN SALAMANDERS?

Reproductive interactions among species in areas of and contact zones have long fascinated evolutionary biologists. Much interest and fierce debate has centered on the potential for natural selection to prevent interspecific mating between species in cases in which the progeny from such unions exhibit reduced fitness (see papers in Otte and Endler 1989). The potential risk of interspecific mating may be regarded as an important cost of sympatry for many species. Other reproductive costs of may exist even for species that are sexually incompatible and thus never engage in interspecific mating. For example, individuals of different species may use similar resources necessary for successful mating. In odonates, this may result in lost mating opportunities with conspecifics because of courtship misdirected toward heterospecific females (Singer 1990). Negative interspecific interactions also may arise during the process of mate attraction in the form of signal interference, an unintended by-product of two or more species broadcasting signals in the same sensory modality while in close physical proximity. Anuran choruses are prime examples of situations in which interspecific acoustic interference may result in a decreased probability of encounters between conspecifics (e.g., Schwartz and Wells 1983). Levels of sexual incompatibility typically are high among sympatric species of plethodontid salamanders ofthe genus Desmognathus, and thus the risk of interspecific mating probably is not a reproductive cost of for contemporary populations (Maksymovitch and Verrell 1993). Nevertheless, the presence of a heterospecific individual could still exert a negative influence on

Cache dispersion by grey jays sequentially exploiting adjacent sources

Food caching is a behaviour used by a variety of birds and mammals and can be an essential strategy for surviving food-scarce periods. Ensuring that cached food remains available for later recovery is critical to the fitness of caching individuals. Cache robbers, conspecific or heterospecific individuals that remove and consume food stored by the original cacher, present a unique threat to food-caching individuals. Accordingly, caching species have evolved a variety of cache protection strategies to limit the potential risk of cache robbery. We assessed these cache protection strategies in Canada jays, year-round residents of Canada and the western United States that rely on cached food to survive food-scarce winters. We evaluated caching behaviour and movement patterns of captive Canada jays in caching contexts that varied in potential risk of cache robbing: presence versus absence of a model cache robber and visual cover from the cache robber. We found that depending on perceived risk, Canada jays flexibly used a variety of nonmutually exclusive cache protection strategies including cache depression, out-of-sight caching and spacing. These cache protection strategies likely reduce the risk of cache robbing and increase the probability of caches remaining available for recovery and consumption.

Cross‐species Discrimination of Individual Odors by Hamsters (Muridae: Mesocricetus auratus, Phodopus campbelli)

AbstractGolden hamsters, Mesocricetus auratus, and Djungarian hamsters, Phodopus campbelli, Muridae, were tested for the ability to discriminate between individual odors from both their own species and the other species. Hamsters were tested using an habituation technique, in which differences in time spent investigating familiar and novel scents indicate discrimination of individual differences. Both species showed similar patterns of results when tested with flank gland scents from golden hamsters and ventral gland scents from Djungarian hamsters: The duration of investigation of samples from the same indivídual scent donor declined over trials, indicating recognition of this scent, but then increased when a scent from a novel individual was presented, indicating discrimination of individual differences. Thus, the capacity and tendency to respond differentially to signals from different individuals is not confined to a single species, suggesting the lack of species‐specificity in the signals and perceptual mechanisms involved in individual recognition by scent. This capacity may be common in mammals, and if so suggests the possibility for considerable knowledge of heterospecific individuals.

Faecal pellets as burrow markers: intra- and interspecific odour recognition by western plethodontid salamanders

Chemical communication is widespread among plethodontid salamanders (Caudata: Plethodontidae), but little information exists on the role of odours in interspecific competition in general and among species in western North America in particular. The present study examined the potential of faecal odours for intra- and interspecific communication among sympatric plethodontids in two-choice tests in the laboratory. In experiment 1, Plethodon vehiculum and Aneides ferrus from Vancouver Island, B.C., Canada, were presented with two burrows marked with (1) a faecal pellet of male P. vehiculum versus a control clay pellet, and (2) a faecal pellet of male A. ferreus versus a control pellet. In experiment 2, responses of P. vehiculum, P. dunni and P. vandykei from Washington, U.S.A., were tested towards faecal pellets of conspecific males and females, and towards pellets of congeneric males. Both P. vehiculum and P. dunni distinguished odours of conspecific males and females, based on their behavioural responses towards faecal and control pellets. Only P. dunni, however, avoided burrows marked with faeces of conspecific individuals. In contrast, neither A. ferreus nor P. vandykei appeared to distinguish faecal odours of conspecific salamanders from control pellets. In tests with odours of heterospecific individuals, P. dunni and P. vehiculum distinguished odours of each other, and P. vandykei distinguished odours of P. vehiculum. The data from these two experiments suggest that P. dunni use faecal pellets as territorial markers both in intraspecific communication and in interspecific encounters with P. vehiculum.

Faecal pellets as burrow markers: intra- and interspecific odour recognition by western plethodontid salamanders

Chemical communication is widespread among plethodontid salamanders (Caudata: Plethodontidae), but little information exists on the role of odours in interspecific competition in general and among species in western North America in particular. The present study examined the potential of faecal odours for intra- and interspecific communication among sympatric plethodontids in two-choice tests in the laboratory. In experiment 1, Plethodon vehiculum and Aneides ferrus from Vancouver Island, B.C., Canada, were presented with two burrows marked with (1) a faecal pellet of male P. vehiculum versus a control clay pellet, and (2) a faecal pellet of male A. ferreus versus a control pellet. In experiment 2, responses of P. vehiculum, P. dunni and P. vandykei from Washington, U.S.A., were tested towards faecal pellets of conspecific males and females, and towards pellets of congeneric males. Both P. vehiculum and P. dunni distinguished odours of conspecific males and females, based on their behavioural responses towards faecal and control pellets. Only P. dunni, however, avoided burrows marked with faeces of conspecific individuals. In contrast, neither A. ferreus nor P. vandykei appeared to distinguish faecal odours of conspecific salamanders from control pellets. In tests with odours of heterospecific individuals, P. dunni and P. vehiculum distinguished odours of each other, and P. vandykei distinguished odours of P. vehiculum. The data from these two experiments suggest that P. dunni use faecal pellets as territorial markers both in intraspecific communication and in interspecific encounters with P. vehiculum.

Competition and Coexistence among Panorpa Scorpionflies (Mecoptera: Panorpidae)

The ecological and behavioral interactions of adults of nine species of Panorpa scorpionflies were studied during 1971—1974 at eight woodland sites in southeastern Michigan, USA. The species overlap considerably in habitat use, diurnal foraging time and location, and diet. All species inhabit primarily the herb stratum of moist forests. Soft—bodied dead arthropods comprise from 88.5 to 100% of the diets of the different species. Panorpa scorpionflies are very aggressive around food. The species can be ranked linearly in relation to their ability to dominate heterospecific individuals at food. The aggressive dominance ranking of the species is related to increasing size (r = .78, P = .04). The study sites vary in Panorpa species richness from three to eight. Panorpa species clearly interact. Mark—recapture data reveal that at the site where only three species occur adults of P. banksi live longer and move less than adults of the same species at a site where six species occur. The adult seasonal distributions of the three species at the site where only three species occur are extended in comparison to the seasonal distributions of the same species at other sites with greater Panorpa species richness. Species or species groups partition the season to some extent by successional emergence. Seasonal overlap, however, is sufficient to result in competitive interactions between some species. Analyses of the seasonalities of the species reveal that the numbers of individuals and species of Panorpa present during a species' adult seasonal period inversely influence the duration of that period. The durations of the adult seasonal period of the more aggressive species are primarily influenced by the number of conspecific individuals present, whereas the durations of the adult seasonal periods of the less aggressive species are primarily influenced by the number of individuals of heterospecific and more aggressive species present. Very aggressive species cause less aggressive species to feed above the herb stratum; this may result in increased exposure to predators and to reduced longevity of the less aggressive species. I suggest that the emergence times of the species allow coexistence and have been selected in the context of interspecific competition for food. The emergence times of the species in relation to each species' aggressive dominance appears consistent with this hypothesis. The variation in species richness between sites is probably not due to the extinction of certain species because of competition, but is the result of different amounts of Panorpa habitat destruction at the sites in the past.