Significant Interspecific Competition Research Articles

Interspecific Relationship Between Monochamus alternatus Hope and Arhopalus rusticus (L.) in Pinus thunbergii Affected by Pine Wilt Disease

Monochamus alternatus Hope and Arhopalus rusticus (L.) are important stem-boring pests that co-occur on weakened Pinus spp. Their larvae damage the xylem and phloem of the trunks and branches. At present, the consequences of the interspecific relationship between two longicorn beetles on the same host of Pinus trees are unclear. The population dynamics and spatial distribution of these two species on Pinus thunbergii trees were investigated to clarify the ecological niches and interspecific relationship of two longicorn beetles on the different degrees of decline in P. thunbergii trees. The results showed temporal niche overlap values from 0.02 ± 0.01 to 0.05 ± 0.02, suggesting a very high degree of temporal ecological niche segregation and no competition in temporal niche resources. There is significant interspecific competition between the two longicorn beetles in spatial distribution, and the spatial niche overlap values are 0.67 ± 0.11 and 0.61 ± 0.09 in the middle and late stages of the decline in P. thunbergii trees, respectively.

Growth and fecundity of Palmer amaranth escaping glufosinate in cotton with and without grass competition

Abstract Field experiments were conducted at Clayton and Rocky Mount, NC, during summer 2020 to determine the growth and fecundity of Palmer amaranth plants that survived glufosinate with and without grass competition in cotton. Glufosinate (590 g ai ha−1) was applied to Palmer amaranth early postemergence (5 cm tall), mid-postemergence (7 to 10 cm tall), and late postemergence (>10 cm tall) and at orthogonal combinations of those timings. Nontreated Palmer amaranth was grown in weedy, weed-free in-crop (WFIC) and weed-free fallow (WFNC) conditions for comparisons. Palmer amaranth control decreased as larger plants were treated; no plants survived the sequential glufosinate applications in both experiments. The apical and circumferential growth of Palmer amaranth surviving glufosinate treatments was reduced by more than 44% compared to the WFIC and WFNC Palmer amaranth in both experiments. The biomass of Palmer amaranth plants surviving glufosinate was reduced by more than 62% when compared with the WFIC and WFNC in all experiments. The fecundity of Palmer amaranth surviving glufosinate treatments was reduced by more than 73% compared to WFNC Palmer amaranth in all experiments. Remarkably, the plants that survived glufosinate were fecund as WFIC plants only in the Grass Competition experiment. The results prove that despite decreased vegetative growth of Palmer amaranth surviving glufosinate treatment, plants remain fecund and can be fecund as nontreated plants in cotton. These results suggest that a glufosinate-treated grass weed may not have a significant interspecific competition effect on Palmer amaranth that survives glufosinate. Glufosinate should be applied to 5 to 7 cm Palmer amaranth to cease vegetative and reproductive capacities.

How neighbourhood interactions control the temporal stability and resilience to drought of trees in mountain forests

Abstract Over the coming decades, the predicted increase in frequency and intensity of extreme events such as droughts is likely to have a strong effect on forest functioning. Recent studies have shown that species mixing may buffer the temporal variability of productivity. However, most studies have focused on temporal stability of productivity, while species mixing may also affect forest resilience to extreme events. Our understanding of mechanisms underlying species mixing effects on forest stability and resilience remains limited because we ignore how changes from intraspecific to interspecific interactions in the neighbourhood of a given tree might affect its stability and resilience to extreme drought (i.e. response during and after this drought). This is crucial to better understand forests’ response to climate change and how diversity may help maintain forest functioning. Here we analysed how local intra‐ or interspecific interactions may affect the temporal stability and resilience to drought of individual trees in French mountain forests, using basal area increment data over the previous 20 years for Fagus sylvatica, Abies alba and Quercus pubescens. We analysed the effect of interspecific competition on (a) the temporal stability and (b) the resilience to drought (resistance and recovery) of individual tree radial growth. We found no significant interspecific competition effect on temporal stability, but species‐specific effects on tree growth resilience to drought. There was a positive effect of heterospecific proportion on the drought resilience of Q. pubescens, a negative effect for A. alba and no effect for F. sylvatica. These differences may be related to interspecific differences in water use or rooting depth. Synthesis: In this study, we showed that stand composition influences individual tree growth resilience to drought, but this effect varied depending on the species and its physiological responses. Our study also highlighted that a lack of biodiversity effect on long‐term stability might hide important effects on short‐term resilience to extreme climatic events. This may have important implications in the face of climate change.

A comparison of species composition and stand structure between planted and natural mangrove forests in Shenzhen Bay, South China

Aims For assisting faster restoration of damaged or severely disturbed coastal ecosystems, selected mangrove species have been planted on previously mangrove-inhabited sites of the tropical and subtropical coasts of southern China. The objective of this study was to understand the stand dynamics of the planted mangroves and their functional traits in comparison with natural mangrove forests under similar site conditions. Methods Species composition, stand density, tree size distribution, and aboveground production were investigated along three transects in a 50year-old planted mangrove stand and three transects in an adjacent natural mangrove stand in Shenzhen Bay, South China. Measurements were made on tree distribution by species, stand structure, and aboveground biomass (AGB) distribution. Analyses were performed on the spatial patterns of tree size distribution and species association. Important Findings We found that the planted and natural mangrove stands did not differ in stand density, average diameter at breast height (DBH), species composition, and AGB. Spatial distribution of AGB and frequency at species level were also similar between the planted and natural stands. However, the traits in stand structure were more variable in the planted stand than in the natural stand, indicating higher spatiotemporal heterogeneity in the development and succession of planted mangroves. Geostatistical analyses show that both DBH and AGB were spatially auto-correlated within a specific range in the direction perpendicular to coastline. More than 60% of the variance in these attributes was due to spatial autocorrelation. The Ripley’s K-function analysis shows that the two dominant species, Kandelia obovata and Avicennia marina, clumped in broader scales in the natural stand than in the planted stand and displayed significant interspecific competition across the whole transect. It is suggested that interspecific competition interacts with spatial autocorrelation as the underlying mechanism shaping the mangrove structure. This study demonstrates that at age 50, mangrove plantations can perform similarly in stand structure, spatial arrangement of selected stand characteristics and species associations to the natural mangrove forests.

Nitrogen:sulphur ratio alters competition between Trifolium repens and Lolium perenne under cutting: Production and competitive abilities

Grasslands species, like others crops, no longer benefit from high atmospheric sulphur deposition. This may cause sulphur limitation and in turn may induce a shift in plant communities by altering species performance and competitive abilities. To test this hypothesis, a greenhouse pot experiment was designed to investigate the interacting effects of sulphur (S) and nitrogen (N) availability on production, morphology and competitive abilities of white clover ( Trifolium repens L.) and perennial ryegrass ( Lolium perenne L.). Plants were grown in monocultures and mixtures during 4 months. They were supplied with combinations of three levels of S and three levels of N and subjected to three defoliation events. Both S and N gradients altered plants performance and modulated competitive interactions. In L. perenne, above- and below-ground dry matter production, leaf and tiller number and contribution to mixture DM production were little affected by S, but highly by N. For T. repens, these traits were significantly increased by S, but only slightly by N. At establishment, T. repens was subjected to a significant interspecific competition at low N–low S and high N–high S. But at regrowth (cuts 2 and 3), T. repens was much more affected by intra- than interspecific competition. L. perenne was only sensitive to competition (intraspecific) when N supply was combined with no or moderate S supply. We conclude that N:S ratio of soil appears to drive species production, morphology and competitive abilities, which in turn affect leguminous–gramineous species ratio and grassland plant community structure. Since the growth of T. repens was significantly reduced in low S treatments, our results suggest that the drastic fall in atmospheric sulphur deposition could restrict leguminous species in high N soil conditions.

Competitive exclusion of a worldwide invasive pest by a native. Quantifying competition between two phytophagous insects on two host plant species

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.

Spatial population structure in forest voles of the genus Clethrionomys in the southern taiga of the Middle Irtysh region

A comparative analysis of spatial population structure in the northern red-backed vole (Clethrionomys rutilus Pall.) and large-toothed red-backed vole (Cl. rufocanus Sund.) has been performed in the middle taiga zone of the Middle Irtysh region (Omsk oblast). Populations of these species are represented by sets of territorial groups whose numbers and spatial distribution change from year to year depending on the ratio of these species in a biotope and their population density. There is no significant interspecific competition between cohabitant Cl. rutilus and Cl. rufocanus. In particular, this follows from the fact that the population density and distribution pattern of one species are independent of those of the other species. It has been found that the size of home ranges in Cl. rutilus inversely depends on its population density, with that in Cl. rufocanus remaining approximately the same at different population densities, and that the structure of the resident part of the population in both species changes during the season, as voles from neighboring habitats or dispersing voles settle in the study area.

Nutrient Removal from Simulated Wastewater Using Canna indica and Schoenoplectus validus in Mono- and Mixed-Culture in Wetland Microcosms

Emergent wetland plant species may exhibit different nutrient removal efficiencies when grown in monoculture and mixed stands in constructed wetlands for tertiary purification of wastewater. A glasshouse study was conducted to investigate the influence of mono- and mixed-culture between Canna indica Linn and Schoenoplectus validus (Vahl) A. Love & D. Love on their growth in, and nutrient removal from, simulated wastewater in the surface water of vertical-flow wetland microcosms. Plants were grown for 50 days before imposing nutrient treatments that simulated secondary-treated municipal wastewater effluent with either low (17.5 mg N and 10 mg P per litre) or high (35.0 mg N and 20 mg P per litre) nutrient concentrations. Treatment solutions were renewed in weekly intervals. After 65 days of nutrient and plant treatments, the total and above-ground biomass was significantly (P < 0.01) greater in the high compared with the low nutrient treatment, but there were no significant differences in below-ground biomass. Significant (P < 0.01) differences in above-ground and below-ground biomass were observed, but no significant difference in total biomass was detected among plant treatments. The highest below-ground biomass was in monoculture of C. indica, whereas the highest above-ground biomass was in the monoculture of S. validus. The biomass of mixed-culture was intermediate to that in the two monoculture treatments. There was significant interspecific competition between C. indica and S. validus in mixed-culture, with C. indica being the superior competitor. The concentrations of N and P in plant tissues (except P in above-ground tissues) were significantly (P < 0.01) higher in the high than in the low nutrient treatment. The accumulation of N and P in above- and below-ground tissues largely reflected patterns of biomass allocation. No significant difference was observed between the nutrient treatments in nutrient removal efficiencies. Plant uptake was the major nutrient removal pathway in the wetland microcosms. Nutrient removal from simulated wastewater in mixed-culture was not greater than in mono-cultures, due to interspecific competition. The results suggested that plant nutrient uptake was the major removal mechanism at the establishment stands in the constructed wetlands.

Competition between Hatchery‐Raised Rio Grande Cutthroat Trout and Wild Brown Trout

AbstractAn important problem for conservation of cutthroat trout Oncorhynchus clarkii is the presence of nonnative trout. We used eight 20‐m instream enclosures on the Rio Cebolla, New Mexico, to evaluate competition between hatchery‐raised Rio Grande cutthroat trout O. clarkii virginalis and similar‐sized wild, nonnative brown trout Salmo trutta. Four control enclosures each contained 20 fish of the same species; four treatment enclosures each contained equal numbers of like‐sized fish of the two species. Results indicated that wild brown trout were superior competitors to hatchery‐raised Rio Grande cutthroat trout. Significant interspecific competition was inferred from comparisons of treatment fish with their controls. Among Rio Grande cutthroat trout, control fish grew in length and body weight, whereas growth of fish confined in enclosures with brown trout was significantly lower than that of controls (P &lt; 0.001). In contrast, brown trout enclosed with Rio Grande cutthroat trout experienced significantly greater growth than did control brown trout (P &lt; 0.005). Rio Grande cutthroat trout in enclosures with brown trout had lower postmortem fat content and an elevated incidence of caudal fin damage than did control fish. Gut contents showed that control fish of both species fed most frequently on small larval caddisflies Lepidostoma spp. However, when the two species were confined together, more brown trout had food in the gut and the food items consumed by Rio Grande cutthroat trout shifted from Lepidostoma spp. to surface‐occurring invertebrates (terrestrial infall, water striders, water mites, and phaerate adult aquatic insects) and benthic‐associated invertebrates (oligochaetes, caddisflies (Limnephilidae and Helicopsyche spp.), and snails). Collectively, the results indicated interspecific competition that was mediated through elevated aggression by brown trout that altered foraging activity by both species. The results underscore the importance of minimizing contact with nonnative brown trout when using hatchery fish to restore cutthroat trout to suitable habitats.

Impact of the presence of Dicyphus tamaninii Wagner (Heteroptera: Miridae) on whitefly (Homoptera: Aleyrodidae) predation by Macrolophus caliginosus (Wagner) (Heteroptera: Miridae)

Abstract Macrolophus caliginosus (Wagner) is currently commercialized in Europe for the control of whiteflies in tomato greenhouses. Another mirid predator, Dicyphus tamaninii Wagner, spontaneously colonizes Mediterranean greenhouses. The impact of the presence of D. tamaninii on predation of the greenhouse whitefly ( Trialeurodes vaporariorum Westwood) by M. caliginosus was investigated in the laboratory on tomato plants during four days. No significant interspecific competition was recorded between mirid nymphs and no significant intraguild predation was observed. Higher level of predation of the whitefly populations was achieved by D. tamaninii alone, than by M. caliginosus alone. Predation by the heterospecific combination ( M. caliginosus + D. tamaninii ) was similar to the results obtained by conspecific treatments. No intraspecific competition was recorded with D. tamaninii , nor with M. caliginosus . Finally, the distribution of whitefly predation on the plant by the mirids changed according to the predator treatment. The heterospecific combination of both mirids had a higher predation rate on lower leaves of the plant than monospecific combinations. Overall, the presence of D. tamaninii did not disrupt whitefly predation by M. caliginosus and could even increase the level of predation.

What Determines the Distribution of Coastal Hydrobiid Mudsnails Within North‐Western Europe?

The three north‐west European species ofHydrobiaare often partially segregated along salinity gradients and/or sympatric in the nontidal eastern Danish waters and Baltic Sea, but are rarely sympatric and are confined either to nontidal coastal lagoons (Hydrobia ventrosaandHydrobia neglecta) or to the marine/estuarine intertidal zone (Hydrobia ulvae) along the macrotidal Atlantic and North Sea coasts. Significant interspecific competition has been found in Danish waters but not elsewhere in the Atlantic and North‐Sea Europe. The two nontidal species andH. ulvaealso possess contrasting reproductive strategies. The roles of life‐history strategy, interspecific competition and between‐habitat dispersal in restricting these mudsnails to their differing habitats are evaluated in the light of these and other findings. It is concluded that all are likely to be relevant, especially dispersal in maintaining and interspecific competition in opposing, mixed populations in the Kattegat‐Baltic, and life‐history strategy in maintaining the lagoonal versus intertidal dichotomy in the rest of north‐west Europe. This dichotomy prevents segregation of species along common salinity gradients outside the Baltic region and restricts potential interspecific competition to within lagoons, whereH. ulvaeis at a recruitment disadvantage.

Competition between three Chihuahuan desert species: evidence from plant size‐distance relations and root distribution

Abstract. Using size‐distance data we tested the intensity and importance of competition between Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a succulent) in the Chihuahuan desert. We also compared the vertical and horizontal distribution of roots to assess the potential degree of overlap in the use of soil resources. The relationships between sizes and distances of nearest‐neighbour plants suggested that intraspecific competition is generally more important than interspecific competition. However, evidence of stronger inter than intraspecific competition was found in some cases. Species combinations showing significant interspecific competition involved always Opuntia, whereas Larrea and Hilaria did not influence each other. The analysis of the symmetry of competition showed that Opuntia was adversely affected by the presence of Hilaria or Larrea.Although differences were found in the distribution of roots, the results of the size‐distance study support the idea that, (particularly) Opuntia, below‐ground niche differentiation is not sufficiently important to totally avoid the negative effects of plant competition.

Changes in growth of two C4 grasses (Schizachyrium scoparium and Paspalum plicatulum) in monoculture and mixture: influence of soil depth

The growth of Schizachyrium scoparium (Michx.) Nash (little bluestem) and Paspalum plicatulum Michx. (brownseed paspalum), two C4 grasses, was examined in monoculture and in mixed culture in three soil depths. Effects of soil depth and competition were both significant. Growth of both species increased as soil depth increased from 30 to 180 cm in pot experiments. However, P. plicatulum dry mass increased approximately four times more than S. scoparium as soil depth increased. Schizachyrium scoparium dry mass was always greater in monoculture while P. plicatulum dry mass was always greater in mixture. Significant interspecific competition was not measured in the shallow soil treatment (30 cm) suggesting equal competition. Significant interspecific competition was measured in the deeper soil treatments (90 and 180 cm), and P. plicatulum dry mass was clearly greater in mixtures in the two deeper soils. Paspalum plicatulum does not appear to prevent the growth of S. scoparium roots in the deeper soil, but seems able to exploit deeper soil resources by proliferating roots at depths where S. scoparium roots do not seem capable of growth.

Interspecific competition is not a major organizing force in many insect communities

Part of the current dogma in ecology is that competition between species for limited resources is not only common but also a major organizing force in many communities1,2 largely because studies on vertebrates, particularly birds, have played a major role in creating the traditional framework of niche theory and resource partitioning3–9. Other workers, particularly those studying insect communities, have suggested that significant interspecific competition is too rare and sporadic to be of major significance and have placed more emphasis on autecological processes10–13. Efforts to resolve the controversy have concentrated on the question of whether or not competition is common in nature1. Here we show that even where competition can be demonstrated, it need not have a major role in community organization.

Habitat Effects on Reproductive Success in the Coral Reef Fish, Acanthochromis Polyacanthus (Pomacentridae)

Current hypotheses advanced to account for the maintenance of the diversity of coral reef fishes differ fundamentally in the assumed role of competitive processes. The equilibrial hypothesis is based primarily upon an assumption of extensive competitive interactions and subsequent niche partitioning; the lottery hypothesis, instead, assumes populations limited to levels well below carrying capacity due to the high larval mortality, a large effect of chance patterns in larval recruitment, and few, if any, significant competitive interactions. To date, no direct evidence for or against the presence of such interactions has been produced, with the role of competition, if any, inferred from community characteristics. To obtain such data, reproductive success of pairs of the planktivorous reef fish Acanthochromis polyacanthus located on isolated habitat patches was recorded over a 2—yr period at One Tree Island, Great Barrier Reef. Correlations were sought between each of six measures of individual fitness and 20 physical and social characteristics of the inhabited reefs. Significant correlations were found with only four characteristics: the number of individuals of all species inhabiting the reefs, the presence of the dominant lagoonal piscivore, current strength, and, most often, the number of heterospecific planktivores inhabiting the reef. Increased numbers of these apparent food competitors correlated with delayed spawning, reduced initial brood size, and reduced adult (and possibly juvenile) rates of growth. Results of a brief series of experimental manipulations of community structure, involving selective of apparent food competitors, appear to support these observations. The results suggest that food abundance is a limiting resource for A. polyacanthus and that significant interspecific competition for food occurs. The potential therefore exists, despite possible external constraints on population size, for selection to favor niche partitioning and for resources in short supply to affect year—class success and, subsequently, community structure.

Ecology of Subtidal Algae on Seasonally Devastated Cobble Substrates off Ghana

The growth of subtidal algae on calcareous cobbles is restricted to a short (2—4 mo) growing season. Most algae are destroyed during rainy season storms due to surge and cobble tumbling; algal density is low throughout the year. Significant interspecific competition does not occur on cobbles, and no species/area relationship could be demonstrated. The number of species per cobble is correlated with cobble moment of inertia (resistance to tumbling) during the rainy season. Species diversity on cobbles is significantly higher than on neighboring rocky reefs. Available evidence suggests an annual floristic cycle, although biomass and diversity are closely related to short—term weather conditions. Ephemerals, annuals, pseudoannuals, and prennials appear sequentially during the growing season. Species with greater potential size reach peak abundance late in the growing season, although many never reach maximum size or reproduce on cobbles. These longevity and size trends cannot be said to constitute adaptive strategies on cobbles. The high species diversity observed on cobbles is adequately explained by seasonal disturbance.