Skip to main content
Advanced Search

Filters: Tags: competition (X) > Types: Journal Citation (X)

26 results (166ms)   

View Results as: JSON ATOM CSV
Interspecific interactions of herbivores sharing a host plant may be important in structuring herbivore communities. We investigated host plant-mediated interactions of root (Hylobius transversovittatus) and leaf herbivores (Galerucella calmariensis), released to control purple loosestrife (Lythrum salicaria) in North America, in field and potted plant experiments. In the potted plant experiments, leaf herbivory by G. calmariensis reduced H. transversovittatus larval survival (but not larval development) but did not affect oviposition preference. Root herbivory by H. transversovittatus did not affect either G. calmariensis fitness or oviposition preference. In field cage experiments, we found no evidence of interspecific...
The alien grass Bromus tectorum dominates stable annual-plant communities that have replaced native shrub-perennial grass communities over much of the semi-arid western United States. We conducted field competition experiments between B. tectorum and a native grass, Elymus elymoides, on two sites to determine the effects of B. tectorum competition on perennial grasses, and the role of B. tectorum competition in the stability of B. tectorum-dominated communities. B. tectorum competition acting on seedling-stage E. elymoides plants greatly reduced first-year relative growth rates and biomass which, in turn, reduced second-year survival, biomass, and flowering. However, B. tectorum competition acting on older E. elymoides...
• Theoretical and empirical research has supported the hypothesis that plant–plant interactions change from competition to facilitation with increasing abiotic stress. However, the consistency of such changes has been questioned in arid and semiarid ecosystems. • During a drought in the semiarid south-western USA, we used observations and a field experiment to examine the interactions between juveniles of a foundation tree (Pinyon pine, Pinus edulis ) and a common shrub (Apache plume, Fallugia paradoxa ) in replicated areas of high and low stress. • The presence of F. paradoxa reduced P. edulis performance at low-stress sites, but had the opposite effect at high-stress sites. However, the intensity of the...
thumbnail
The relative competitive abilities of Agropyron desertorum and Agropyron spicatum under rangeland conditions were compared using Artemisia tridentata ssp. wyomingensis transplants as indicator plants. We found A. desertorum to have substantially greater competitive ability than A. spicatum as manifested by the responses of Artemisia shrubs that were transplanted into nearly monospecific stands of these grass species. The Artemisia indicator plants had lower survival, growth, reproduction, and late-season water potential in the neighborhoods dominated by A. desertorum than in those dominated by A. spicatum. In similar, essentially monospecific grass stands, neutron probe soil moisture measurements showed that stands...
Distributional patterns and species diversity of benthic insects in an alpine stream in Gunnison County, Colorado, USA were investigated on several levels of spatial scale, from faunal replacement over 1,000 vertical m to microdistribution within the stony substratum. Ecotones including zonation in terrestrial vegetation and in trout distribution did not appear to affect faunal replacement. Competition among congeners accounted for 7-30% of the cases, while in the majority of species, faunal replacement appeared to be associated with gradual changes in the physical gradient. Trout zonation may affect total numbers of insects, however, as the trout-free headwaters had two to six times higher insect densities. Microdistribution...
thumbnail
Seedlings of the succulent crassulacean acid metabolism (CAM plant Agave deserti in the northwestern Sonoran Desert were found only in sheltered microhabitats, nearly all occurring under the canopy of a desert bunchgrass, Hilaria rigida. Apparently because soil surface temperatures can reach 71@?C in exposed areas, seedlings were generally located near the center or on the northern side of this nurse plant. Both species have shallow root systems, about half of the roots of H. rigida and all those for seedlings of A. deserti occurring above soil depths of 0.08 m. To examine competition for water between the nurse plant and an associated seedling, a three-dimensional model for root water uptake was developed. The...
I investigated the individual and joint effects of simulated herbivory and interspecific competition on survival of Coleogyne ramosissima Torr. (blackbrush) seedlings. Seeds of C. ramosissima and Bromus rubens L. (red brome grass) were collected at mid-elevations (1220 to 1770 m) of the Spring Mountains in southern Nevada. A pot trial experiment was conducted for six months (27 wk) in a controlled environmental greenhouse. This trial experiment, consisting of a 2 � 2 factorial design with simulated rodent herbivory and interspecific competition with B. rubens as the main effects, resulted in four treatments. Herbivory on C. ramosissima by heteromyid and non-heteromyid species of rodents was simulated by clipping...
Invasion of natural ecosystems by exotic plant species is a major threat to biodiversity. Disturbance to native plant communities, whether natural or management induced, is a primary factor contributing to successful invasion by exotic plant species. Herbivory by both wild and domestic ungulates exerts considerable impact on structure and composition of native plant communities. Intensive herbivory by ungulates can enhance exotic plant invasion, establishment, and spread for three reasons: (1) many exotic plants are adapted to ground disturbances such as those caused by ungulate feeding, trampling, and movements; (2) many exotic plants are adapted for easy transport from one area to another by ungulates via endozoochory...
The primary hypothesis for the astonishing success of many exotics as community invaders relative to their importance in their native communities is that they have escaped the natural enemies that control their population growth ? the `natural enemies hypothesis'. However, the frequent failure of introduced biocontrols, weak consumer effects on the growth and reproduction of some invaders, and the lack of consistent strong top-down regulation in many natural ecological systems indicate that other mechanisms must be involved in the success of some exotic plants. One mechanism may be the release by the invader of chemical compounds that have harmful effects on the members of the recipient plant community (i.e., allelopathy)....
The demographic consequences of a severe drought year were examined for two experimental plantings of the herbaceous desert perennial Cryptantha flava(Boraginaceae) in northeastern Utah, United States. A total of 6680 nutlets were planted individually or in clusters of four both under shrubs and in open microhabitats within two natural populations. Survival, growth, and flowering as a function of density and microhabitat were followed for 7 years, including 1 year when precipitation just before and during the growing season was 74.5% below normal. The design permitted assessment of how intraspecific density and shrub cover affect demographic response to drought. Mortality increased and flowering decreased dramatically...
1 A 3-year field study examined the physiological and demographic consequences of resource pulse use by an herbaceous, aridland perennial, Cryptantha flava, as well as potential competitive and facilitative interactions with larger shrubs. 2 We applied a pulse of urea and faecal pellets, simulating Mule deer excretions, to plants growing between and under Sagebrush and Rabbitbrush canopies. 3 We hypothesized that C. flava would show strong positive responses to N pulses in open microhabitats, and such plants had approximately 50% increases in leaf N concentrations within days of pulse application, accompanied by increased photosynthetic rates. Over the next year, higher rates of growth and reproduction were found...
thumbnail
In annual plants, increased competitive advantage has often been attributed to rapid germination and early establishment. In contrast, many annual species exhibit some degree of delayed germination (i.e., seed dormancy) that results in the formation of age structure within the seed population. Delayed germination can be an effective bet-hedging strategy in variable or unpredictable environments as a seed bank can buffer against years with reproductive failures and reduce the probability of local extinction. However, there has been little consideration of the direct effects of aging within the seed pool although the potential demographic costs of such a strategy (e.g., mortality in the seed bank or delayed reproduction)...
If plants cannot simultaneously acclimate to shade and drought because of physiological trade-offs, then plants are expected to be less tolerant to shading under drier conditions. One observation that, at first sight, seems incompatible with this idea is the fact that the establishment of new plants in dry areas is often restricted to shady sites under the canopy of other plants, called “nurse plants.� We use a graphical model to resolve this paradox. The model visualizes how facilitative patterns can be understood from the simultaneous effects of plant canopies on microsite light and moisture, and the growth responses of establishing seedlings to those factors. The approach emphasizes the fact that positive...
Circumstantial evidence suggests that Artemisia tridentata may out?compete Pinus ponderosa and P. jefferyi for water at ecotones between shrub steppe and montane forest vegetation in the Great Basin. Other studies indicate that within the shrub steppe Artemisia may act as a nurse plant for a third species of pine, P. monophylla. We used field experiments to study these contrasting effects of Artemisia on P. ponderosa and P. monophylla within the context of the distributional patterns in western Nevada of all three species on andesite, and on sites where hydrothermal activity has altered the andesite. At intermediate elevations in the Great Basin Artemisia and P. monophylla are restricted to unaltered desert soils,...
Broom snakeweed (snakeweed) is a native range shrub found throughout semiarid rangelands of the western United States, which increases and dominates plant communities after disturbances such as overgrazing, drought, or wildfire. The objective of this study was to compare the ability of selected grass species and prostrate kochia to restrict establishment and growth of snakeweed seedlings in potted-plant and replicated field studies within two sagebrush ecological sites. In the potted-plant studies, single snakeweed seedlings were grown with seedlings (seedling neighbor study) and established plants (established neighbor study) of three cool-season grasses (crested, pubescent, and bluebunch wheatgrass), prostrate...
Altered hydrology of southwestern United States rivers has led to a decline in native cottonwood (Populus deltoides). Areas historically dominated by cottonwood have been replaced by invasive saltcedar (Tamarix chinensis). Restoration of historic hydrology through periodic flooding of riparian areas has been a means of restoring native species. However, due to similarity in germination requirements of cottonwoods and saltcedars, flooding may create an unwanted increase in the number of saltcedar seedlings. Therefore, we evaluated competitive aspects of these co-occurring species in an extant riparian habitat in the arid southwestern US. We measured effects of competition between cottonwood and saltcedar seedlings...
Invasion by cheatgrass and the associated high fire frequency can displace native plant communities from a perennial to an annual grass driven system. Our overall objective of this study was to determine the potential to favor desired native perennial bunchgrasses over annual grasses by altering plant available mineral nitrogen (N). In the first study, we grew cheatgrass and three native bunch grasses (native grasses were combined in equal proportions) in an addition series experimental design and applied one of three N treatments (0, 137, and 280 mg N/kg soil). Regression models were used to derive the effects of intra- and interspecific competition on individual plant yield of cheatgrass and the native bunch grasses...
Using 18 years of census data from permanent quadrats, we examined the interactions between spatially coexisting but temporally segregated winter and summer ephemeral plant communities in the Chihuahuan Desert. The ability of winter and summer annuals to achieve nearly complete temporal segregation by partitioning the bimodal annual rainfall permits the coexistence of a diverse flora of annual (and perennial) plants in this unproductive arid environment. Despite the differences in their biogeographical affinities and temporal segregation, long-term data indicated that at the scales of both the entire 20-ha study site and small 0.25-m2 sample quadrats, abundances of plants were never high in two successive growing...
The “evolution of increased competitive ability� (EICA) hypothesis predicts that exotic species will adapt to reduced herbivore pressure by losing costly defenses in favor of competitive ability. Previous studies often support the prediction that plants from exotic populations will be less well defended than plants from native populations. However, results are mixed with respect to the question of whether plants from exotic populations have become more competitive. In a common-garden experiment involving plants from two native and two exotic populations of 14 different invasive species, we tested whether exotic plants generally grow larger than conspecific native plants, and whether patterns of relative growth...
Behavior of focal individuals of two potentially competing sympatric stonefly species, Megarcys signata and Kogotus modestus (Perlodidae), was videotaped in flow-through plexiglass arenas placed in the East River, Gunnison County, Colorado. Focal individuals were observed alone and in pairs with conspecifics and allospecifics at four prey (Baetis bicaudatus, Baetidae, Ephemeroptera) densities to determine whether competitors and prey resource levels affected prey capture rates. Presence of conspecific or allospecific competitors reduced stonefly prey capture rates, especially for Kogotus, the smaller of the two species, due to a significant decline in predator-prey encounter rates with competitors present. This...
map background search result map search result map Competitive Ability Is Linked to Rates of Water Extraction. A Field Study of Two Aridland Tussock Grasses Interactions Between Seedlings of Agave Deserti and the Nurse Plant Hilaria Rigida Seed aging, delayed germination and reduced competitive ability in Bromus tectorum Interactions Between Seedlings of Agave Deserti and the Nurse Plant Hilaria Rigida Competitive Ability Is Linked to Rates of Water Extraction. A Field Study of Two Aridland Tussock Grasses Seed aging, delayed germination and reduced competitive ability in Bromus tectorum