Effects Of Interspecific Interactions Research Articles

Growth depends on neighbours: experiments with three Sphagnum L. species

Our aim was to search for reasons why some peat mosses (Sphagnum), despite having wide distribution areas, consistently occur in small and distantly scattered populations. The effect of interspecific interactions was proposed as the main hypothesis. Three Sphagnum species exhibiting different distribution frequencies (S. wulfianum Girg., S. teres (Schimp.) Ångstr., and S. magellanicum Brid.) were selected, and two experiments in controlled conditions were established. In the first experiment, the peat mosses were grown in mono-species, two-species, and three-species mixtures. Only the growth of the species with the most restricted distribution (S. wulfianum) responded significantly to the presence of the other Sphagnum species. In the second experiment, shoots of S. wulfianum were watered with the exudates and extracts of the other two species. Significant effects were observed on the growth of S. wulfianum. We conclude that neighbour species can suppress the growth of some bryophyte species and possibly limit their natural distribution.

Predicting the interactions between “ecologically equivalent” indigenous and nonindigenous brachyurans

Predictive models used to determine the impacts of nonindigenous brachyurans on their “ecological equivalents” in marine ecosystems are sorely lacking. Determining the spatial and temporal extent and magnitude of such impacts by nonindigenous species is difficult because of the broad range of qualitative and quantitative criteria currently used to describe their effects. Forecasting potential impacts requires the development of predictive models that incorporate the effects of interspecific interactions and the mechanisms that give rise to these interactions. Successful validation of such models requires improved techniques for measuring and estimating the functional responses on bioenergetic processes across species compositions, abundances, and environmental conditions. Species-specific information used to support predictive modeling of nonindigenous brachyurans is currently heavily biased towards (i) estimating per capita consumption and growth rates in laboratory conditions and (ii) incorporating the effects of abiotic and biotic factors on these measures. Robust predictive models require repetitive experimentation that advances the understanding of species’ interactions (beyond consumption alone) across variable densities and considers their effects across different spatial and temporal scales.

Competitive Interactions of Garlic Mustard (Alliaria petiolata) and Damesrocket (Hesperis matronalis)

AbstractCompetitive interactions between native plants and nonnative, invasive plant species have been extensively studied; however, within degraded landscapes, the effect of interspecific interactions among invasive plants is less explored. We investigated a competitive interaction between two sympatric, invasive mustard species that have similar life history strategies and growth forms: garlic mustard and damesrocket. Greenhouse experiments using a full range of reciprocal density ratios were conducted to investigate interspecific competition. Garlic mustard had a negative effect on the final biomass, number of leaves, and relative growth rate in height of damesrocket. Survival of damesrocket was not negatively affected by interspecific competition with garlic mustard; however, garlic mustard showed higher mortality because of intraspecific competition. These results indicated that although garlic mustard has been observed to be the dominant species in this landscape, it may not completely outcompete damesrocket in all situations. Studies of invasive species in competition are important in degraded landscapes because this is the common situation in many natural areas.

The impact of alternative harvesting strategies in a resource–consumer metapopulation

Summary1. The majority of our knowledge of harvested populations has been drawn from studies on single‐species occupying continuous landscapes. Population dynamics in spatially structured landscapes are markedly different from those in continuous habitats. We investigate the effects of several harvesting strategies on the metapopulation dynamics of the bruchid beetle Callosobruchus maculatus and its parasitoid Anisopteromalus calandrae, when locally extinction prone populations of bruchids were harvested. By harvesting the resource in this closed resource–consumer interaction, we could examine the scenario where humans and natural predators share a common resource.2. Using population‐level models in single and coupled‐patch systems, simulations were run to estimate sustainable harvesting levels for each harvesting strategy. These harvesting levels were then implemented in experimental metapopulation microcosms. Experiments were run for multiple generations and long‐term time series of population size and harvest yield were collected.3. Controversially, harvesting resulted in larger regional population sizes in harvested metapopulations than in unharvested metapopulations. Similarly, conservative harvesting strategies such as fixed escapement harvesting and harvesting with refuges resulted in smaller population sizes than fixed quota or fixed proportion harvesting strategies. Fixed proportion harvesting gave rise to the largest population sizes, fewest local extinctions and largest yields. Assuming both species are of ecological importance, fixed proportion is therefore the optimal harvesting strategy for this model system.4. Synthesis and applications. We demonstrate that, under certain conditions, increasing local mortality can increase population sizes. This ‘hydra effect’ may be caused by the advantage of higher rates of local population turnover for dispersive species in patchy landscapes, or due to the interruption of overcompensatory density‐dependence in the host populations. These results are of particular relevance both in the development of sustainable harvesting policies in multi‐species communities or, conversely, the control of pest species inhabiting spatially structured landscapes. We have shown that predictive models can be a useful tool in the estimation of sustainable harvesting limits where no a priori knowledge of the system exists. We also demonstrate that spatial structure, the effects of interspecific interactions and knowledge of density‐dependent population dynamics must be included in the generation of sustainable harvesting theory.

Transgenic Control of Vectors: The Effects of Interspecific Interactions

The control of insect vectors through conventional sterile insect or transgenic technologies (e.g., RIDL®) is an intense focus of research in the combat against vector-borne disease. While the population dynamic implications of these control strategies are reasonably well-established, the effects of interspecific competition between different vectors and control strategies have not previously been explored. Different control intervention methods can affect the interaction and potential coexistence of vector species. By altering the shape of the zero net growth isoclines, conventional and transgenic control can affect patterns of vector coexistence and/or exclusion through Allee effects and transient dynamics. Further, transgenic control methods can mediate coexistence between target and non-target species and this can have important consequences for the persistence of disease and community ecological interactions.

Interspecific Interactions Among Three Entomopathogenic Nematodes, <I>Steinernema carpocapsae</I> Weiser, <I>S. feltiae</I> Filipjev, and <I>Heterorhabditis bacteriophora</I> Poinar, with Different Foraging Strategies for Hosts in Multipiece Sand Columns

Abstract Multipiece sand columns were used to study the dispersal and interspecific interactions at different depths among three nematode species with different foraging strategies. Steinernema carpocapsae Weiser, strain ‘NY001’, an ambusher nematode, Heterorhabditis bacteriophora Poinar, strain ‘Oswego’, a cruiser nematode, and S. feltiae Filipjev, strain ‘Valko’, an intermediate nematode were applied to multipiece sand columns in single-, two-, and three-species combinations 7 d before host introduction. The effect of interspecific interactions on nematode performance was estimated by comparing the percent host infected by a nematode species at specified depths when applied alone to the performance of the same nematode species when applied in combination with other nematode species. All three nematodes were capable of infecting some proportion of hosts down to the 32.5-cm depth when applied singly. In nematode combinations, interspecific competition occurred, but negative impacts of competition on nemat...

Population and microhabitat effects of interspecific interactions on the endangered Andalusian toothcarp (Aphanius baeticus)

The Andalusian toothcarp, Aphanius baeticus, is a critically endangered cyprinodontid species, with only nine known extant populations. Although not yet studied in the field, the distribution and abundance of Andalusian toothcarp are thought to be strongly influenced by interspecific interactions. We analysed the abundance and microhabitat use of Andalusian toothcarp in two water courses, one in which several other fish species occurred (sympatric site) and one hypersaline stream in which toothcarp was the only species present (allopatric site). Fish were sampled using plastic minnow traps and results were analysed separately for three size categories. Toothcarps were clearly more abundant in the allopatric population than in the sympatric one, though the difference was less apparent in the smallest size category. In coexistence with other species, toothcarp occupied shallower microhabitats, but in both sites in the absence of shelter fish selected deeper positions than in its absence. While in the sympatric site sheltered microhabitats were used predominately by small individuals, in the allopatric ones they were used by larger ones. Observed patterns strongly suggest that predation is the main mechanism involved in the differences in abundance and microhabitat use between sites. Our results confirm that the presence or absence of coexisting species is an important habitat feature for Andalusian toothcarp populations.

Increase of laccase activity during interspecific interactions of white-rot fungi

White-rot fungi are of interest due to their ability to degrade lignin. Lignin-degrading enzymes such as laccase can also degrade xenobiotic compounds. The effects of interspecific interactions between white-rot fungi and other microorganisms on laccase activity was studied in laboratory cultures. Laccase activity in cultures of Trametes versicolor and Pleurotus ostreatus increased significantly after the introduction of soil fungi, bacteria and yeasts or after contact with nonsterile soil. Addition of Trichoderma harzianum to cultures of T. versicolor increased laccase activity more than 40 fold, whereas addition of other soil fungi or bacteria resulted in 2–25 fold increases and the addition of soil or soil extracts led to 10–15 fold increases. No laccase induction was detected after addition of heat or filter-sterilized microbial cultures, soil or soil extract. Increased decolorization of the synthetic dye Remazol Brilliant Blue R occurred in mixed cultures. When T. versicolor was cocultured with other soil microorganisms, the number of colony forming units of the other soil microbes decreased. This effect could not be shown to be caused by laccase. In 16 of 24 species of white-rot fungi tested, laccase increased following the addition of T. harzianum. The increase was only absent in species with no or low laccase production. Co-inoculation of P. ostreatus and T. versicolor resulted in an increase of laccase in the mixed culture.

The effect of breeding-habitat patch size on bird population density

An individual-based simulation model was used to study the effect of the relative location of food and nest sites in the landscape on the relationship between the breeding habitat patch size and bird population density. The model predicted that when both food and nest sites are located exclusively in the breeding habitat patches, larger patches tend to harbor higher population densities. But when food starts to be added to the `matrix' habitat and taken out of the breeding habitat the advantageous effect of larger patches diminishes and eventually the trend reverses, with small patches having higher population densities. This pattern arises from the combined effect of the existence of an extended foraging area around patches and an intrinsic advantage of large habitat patches associated with the concentration of food resources and potential colonizers. The effects of interspecific interactions and the management implications of the model are discussed.

THE IMPORTANCE OF COMPETITION IN REGULATING PLANT SPECIES ABUNDANCE ALONG A SALINITY GRADIENT

Current theories differ in their predictions concerning the effects of interspecific interactions on species growth and distribution along environmental gradients. In this study, we examined the influence of competition on species composition across a salinity gradient. This work involved three common fresh and brackish marsh species. The three species, Spartina patens, Sagittaria lancifolia, and Panicum hemitomon, differ in salt tolerances but are commonly found in overlapping zones across coastal marsh gradients in the southeastern United States. Plants were grown in a greenhouse under four salinity treatments (0, 2, 4, and 8 g/kg), in monocultures and in three-species mixtures. Data from the monocultures and mixtures were used to examine the importance of competition in regulating community composition and species' growth. Results for individual species were significantly different when grown in monoculture vs. the three-species mixture. While with increasing salinity community dominance shifted toward the most salt-tolerant species, Spartina patens, competition was found to alter community composition equally over all salinities. However, the responses of individual species demonstrated a very different pattern; the relative importance of competition in influencing individual growth differed substantially depending on the salinity tolerances of species. These results support the contention that, as abiotic stress increases, competition becomes less of a limiting factor in regulating the abundance of a species. However, the role of competition at the community level is the sum of the individual species' responses and may or may not vary with the level of abiotic stress.

Burrow systems made by Aporrectodea nocturna and Allolobophora chlorotica in artificial cores: morphological differences and effects of interspecific interactions

Burrow systems of earthworms contained in artificial cores were analysed through X-ray computed tomography and 3D skeleton reconstructions. Gas diffusion experiments were carried out on these cores to characterize soil transfer properties associated with the different burrow systems. Three types of cores were studied: cores in which Aporrectodea nocturna, an anecic earthworm was introduced (treatment 1), cores in which Allolobophora chlorotica, an endogeic earthworm was introduced (treatment 2) and cores that contained both species (treatment 3). Comparisons of the characteristics of the burrow systems of treatment 1 and 2 show important differences: the burrow system of A. nocturna comprises fewer burrows, which are longer, less branched, more vertical and have a lower sinuosity. The burrow system of A. chlorotica is characterized by lower continuity, which however did not result in a lower soil diffusivity. To study the burrow systems made by the two species in the same core (treatment 3), a separation that was based on differences in pore diameter between the two species and that takes into account the burrow orientation was designed. This separation was proven to be efficient since it resulted in low percentages of errors (around 10%) when applied to the burrow systems of treatments 1 and 2. Comparison of the burrow systems from treatments 1 and 3 demonstrated that the burrow system of A. nocturna was influenced by the presence of A. chlorotica: in treatment 3, A. nocturna made burrows that were smaller, more vertical and less branched. However, these interactions have to be confirmed under natural conditions.

Magnitude of within‐patch variation in seagrass Halophila ovalis growth affected by adjacent Thalassia hemprichii vegetation

Seagrass beds in South‐east Asia sometimes consist of a mosaic of different species in monospecific patches. We examined whether the magnitude of within‐patch variation in the seagrass Halophila ovalis is affected by the presence or absence of surrounding vegetation consisting of another seagrass species Thalassia hemprichii in an intertidal flat in Thailand waters. We measured biomass and growth rates of H. ovalis at the edges and centers of two different types of patches: (i) H. ovalis patches adjoining T. hemprichii vegetation (HT patches), and (ii) H. ovalis patches adjoining unvegetated sand flats (HS patches). Furthermore, we examined the possible effects of interspecific interactions on the growth of H. ovalis by experimentally removing adjoining T. hemprichii at the edges of HT patches. The biomass of H. ovalis was greater at the patch centre than the patch edge in both types of patches. For the growth rate of H. ovalis, significant interactions were detected between patch types and positions in patches. The difference in growth was significant and more than 4‐fold between edges and centers of the HS patches, whereas the growth was not significantly different between edges and centers of the HT patches. The removal of T. hemprichii did not significantly affect the growth rate of H. ovalis at the edge of the HT patches. These findings demonstrate that the magnitude of within‐patch variation in H. ovalis growth is affected by the conditions of adjoining habitats. However, any effects of local competition with T. hemprichii on H. ovalis growth were not evident in this short‐term manipulative experiment.

The effects of interspecific interactions on resource use and behavior in a desert ant.

We examined how interspecific competition in ants affects resource use and behavior. To test how neighboring Myrmecocystus colonies influence the desert ant Aphaenogaster cockerelli, we placed temporary enclosures around Myrmecocystus spp. colonies and recorded the resources collected by A. cockerelli and the numbers of A. cockerelli ants engaged in various tasks outside the nest. When neighbors were enclosed, A. cockerelli colonies collected a significantly higher proportion of termites and significantly less plant matter than when neighbors were active. The numbers of A. cockerelli ants engaged in foraging behavior and nest maintenance work increased when Myrmecocystus colonies were enclosed. Interspecific interactions thus can affect the behavior and resource use of A. cockerelli colonies and may influence colony fitness.

Fine-scale biogeographic differences in the crustacean fauna of a cave system in West Virginia, USA

We examined the distribution patterns of four amphipod and one isopod crustaceans in 23 cave stream segments within a subterranean drainage basin. The patterns indicate that invasion history is a strong determinant of the species' distributions. One set of species likely has invaded the cave system from the zone of interstitial water, and thus is distributed mainly in headwater streams throughout the drainage. One species probably invaded through upstream migration from the resurgence of the cave system, and thus is strongly associated with the larger, higher-order streams. The effect of interspecific interactions on the patterns of distribution is not apparent at our scale of analysis.

PATTERNS OF DIVERSITY IN THE CANADIAN INSECT FAUNA

AbstractThe diversity of the Canadian insect fauna decreases and its composition (at all taxonomic levels) changes as climates become progressively more harsh toward the north. This climatic trend dominates patterns of diversity, but many other factors interact to produce the observed patterns. In the arctic, species richness is greatest in the west. Farther south, overall species richness is greatest in the west (especially British Columbia), associated with coastal and cordilleran habitats, and to a somewhat smaller degree in the southeast (especially Ontario), associated with deciduous forests and particularly with transitional forests which occupy a large area of southeastern Canada. However, certain taxa are better represented in the west or in the east, depending on present-day habitats and on historical factors. These conclusions, based chiefly on a sample of taxa of different types, are possible only because basic systematic work has been carried out to distinguish and map the species. Preliminary data on numerical patterns, such as the numbers of species relative to different potential resources such as host plants in different zones, tend to suggest that the occurrence of species in the north may depend so heavily on climatic factors that potential resources are not fully exploited and the effects of interspecific interactions on diversity are reduced.

Effects of species interactions on community organization along a trampling gradient

Abstract. Effects of interspecific interactions on the organization of two trampled communities, Eragrostio ferrugineae ‐ Plantaginetum asiaticae (EP) and Eleusino indicae ‐ Digitarietum violascentis (ED), were examined by 4‐yr field experiments. We compared changes in the relative abundance of the main component species of the communities in monoculture and mixed culture along a trampling gradient. At no trampling in mixed culture, Ambrosia artemisiifolia var. elatior and Erigeron annuus (roadside herbs, RH) predominated and excluded the trampled community species. Severe trampling markedly reduced the predominance of these roadside herbs, promoted Eragrostis ferruginea (a perennial grass of EP), but suppressed Eleusine indica (an annual grass of ED). These results suggest that the differentiation of trampled and roadside herb communities under heavy trampling are caused by asymmetric competition between their main species.Several species pairs showed a constant rank order of relative cover at high trampling levels. Pennisetum alopecuroides (a perennial grass of both RH and EP) and Eragrostis coexisted, indicating symmetric competition. Eragrostis and Plantago asiatica (a perennial herb of EP) or Poa annua (a winter‐annual grass of both EP and ED) coexisted through separation in phenology. Eragrostis promoted the survival of Plantago by moderating unpredictable drought (commensalistic positive interaction). This suggests that community composition is maintained by several interspecific interactions.

An Experimental Study of Habitat Use in an Assemblage of Ozark Minnows

The underlying causes of habitat use in an assemblage of six Ozark minnow species were investigated in an experimental laboratory study. An earlier field study had shown that the assemblage was segregated in pools primarily by a single habitat variable, vertical position in the water column. Although the field study indicated that interspecific interactions affected species' use of vertical position, a lack of control over species' combinations and densities prevented determination of the relative contribution of habitat selection vs. interspecific interactions in affecting habitat—use patterns. In the laboratory experiments in the present study, 75—L aquaria were used to simulate pool habitat. A series of selection experiments determined the preferred vertical distribution of each species; only three species preferred distributions distinct from other species. A series of multispecies experiments determined the effect of interspecific interactions on vertical distributions. A response was considered an association if a species' distribution shifted significantly from its preferred distribution toward that of the heterospecific, and was considered a dissociation if it shifted away from the heterospecific. Of 45 possible interactions, 34 were significant and were composed of 18 associations and 16 dissociations. Species—pairs interactions appeared to be species specific and could be observed across multispecies experiments. Mean pairwise overlaps for preferred distributions and multispecies experiments were very similar, but mean overlaps for associative interactions were larger than those in dissociative interactions. The near—balance of the two types of interactions explains the lack of reduction in mean overlap in the multispecies combinations. In the three— and four—species experiments, interactions were complex; a strong interaction between one species pair buffered interactions between other pairs and determined the overall segregational pattern. The similarity of segregrational patterns in the four—species experiments and the field study suggests that multispecies interactions contribute to habitat—use patterns in the assemblage. The ability of each species to modify its (preferred) vertical distribution in response to heterospecifics indicates that assemblage members are relatively flexible in their use of stream habitats and also explains the variability of habitat use observed in the field.

The Effects of Interspecific Interactions Upon Male Reproductive Success in Two Sympatric Sticklebacks, Gasterosteus Aculeatus and G. Wheatlandi

1. Two closely related sticklebacks nest together in tide pools along the southern shore of the St. Lawrence estuary. 2. We tested the hypothesis that interspecific interactions limit male reproductive success by manipulating both fish density and species abundance ratios. The index of male reproductive success used was the number of eggs per nest and the per cent of males building nests. 3. There was no significant relationship between reproductive success and density or abundance ratios. 4. The data of the present study (sympatric populations) were compared to a previous study (allopatric populations). A higher per cent of G. aculeatus bred in the sympatric than in the allopatric pools while the opposite was true for G. wheatlandi. There were no differences in the number of eggs per nest for either species between the allopatric and sympatric situations. 5. We conclude that interspecific interactions between G. aculeatus and G. wheatlandi may lower the reproductive success of G. wheatlandi when both species breed in sympatry.

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.

Visual and acoustical social displays by the grasshopper Chortophaga viridifasciata (Acrididae: Oedipodinae)

Univoltine northern populations of Chortophaga viridifasciata (De Geer) are usually separated seasonally and by habitat preference from other acridids, whereas southern populations usually are bi- or tn-voltine. potentially interacting with many acridid species seriatim. This series of populations affords an opportunity to lest quantitatively the effects of interspecific interaction on the communication system. Field and laboratory analyses of a population from northern Illinois clarify several aspects of the communication system. As a member of the Oedipodinae, Chortophaga possesses several primitive-appearing morphological characteristics associated with signalling, for example, a variable stridulatory apparatus present only in the male, relatively uncolored and unhanded hindwings, and a lack of contrasting colors or markings associated with the metathoracic legs which are used as a semaphore signalling device. In addition, behavioral analyses reveal signals (e.g., the fast flick) intermediate between those used for agonistic and courtship behavior, and provide evidence which may support extant hypotheses regarding the origin of communication systems in the Oedipodinae. It remains uncertain, however, whether these features are truly primitive or the result of relaxed selection pressure for maintenance of a more precise communication system,