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Target Plants (target + plant)
Selected AbstractsIntraspecific seed trait variations and competition: passive or adaptive response?FUNCTIONAL ECOLOGY, Issue 3 2009Cyrille Violle Summary 1The phenotype of offspring depends on the abiotic and biotic environment in which the parents developed. However, the direct effects of competition experienced by parent plants on single-seed traits are poorly documented despite their impact on plant fitness. 2We hypothesize that single-seed traits can differentially respond to the resource deficiencies of parent plants due to competition: seed quality may decrease as seed number does, magnifying the negative effects of competition for offspring (,passive response' hypothesis), or increase and then enhance offspring fitness to offset the reduction in offspring number (,adaptive response' hypothesis). Here we tested these hypotheses for four single-seed traits. We assessed the sensibility of their responses to changes in competition intensity due to species with different competitive effects and to contrasting soil nitrogen conditions. 3In a common-garden experiment, four single-seed traits related to fitness , seed mass, seed nitrogen concentration (SNC), germinability and the timing of germination , were measured on a phytometer species transplanted in 14 different neighbours grown in monoculture with and without soil nitrogen limitation. 4Under nitrogen-limiting conditions, the responses of SNC and of the timing of germination were passive and mainly related to the effects of neighbours on soil nitrogen availability, as shown by the increase in SNC with N-fixing neighbours. Within-individual seed mass variability decreased with increasing competition intensity, as an adaptive response to counterbalance the reduction in seed production. With nitrogen supplementation, competitors had no detectable effect on single-seed traits despite an overall increase in SNC and germination rate, confirming their nitrogen-dependent passive responses to competition. Germinability did not change among treatments. 5The impact of competition on single-seed traits depends on both phytometer trait identity and resource modulation by neighbours. The passive response of seed chemical composition to competitors may magnify the competitive effects on offspring. By contrast, the adaptive response of seed size variability may offset these competitive effects. As a consequence, experiments looking at the fitness consequences of competition should not only consider the effects on fitness parameters of a target plant but also on the offspring. [source] Measuring the components of competition along productivity gradientsJOURNAL OF ECOLOGY, Issue 2 2007MARK V. WILSON Summary 1Controversy surrounds the measurement of competition intensity. Moreover, when biomass varies systematically along productivity and other environmental gradients, common indices of competitive outcome mask important ecological interactions. 2This study presents two indices derived from how neighbours interact with target plants. The first, relative crowding, increases directly with the abundance of neighbours present and decreases inversely with the potential size and vigour of the target plant itself. The second, interaction strength, is the integral of suppression of the target by neighbours over the range of neighbour abundance. Relative crowding and interaction strength are derived independently, but when multiplied produce the commonly used relative competitive index, showing the biological underpinnings of the relative competition index in terms of crowding and strength of interaction. Since the new indices of relative crowding and interaction strength explicitly account for the amount of neighbour biomass, they serve as a valid method to track the effects of changing habitat conditions on the components of competition. 3The new indices are applied to three published data sets. In each case, relative crowding increased with standing crop. In one case competition was reported as unchanged along a productivity gradient, whereas the new indices show that relative crowding and interaction strength both had significant patterns, but their effects were counteracting. These results do not fit current theories of competition. Further empirical studies are needed to see if competition theory needs revision. 4Separating the mechanisms of competition into relative crowding and strength of interaction reveals previously hidden patterns that help bring to light underlying processes of competition along productivity gradients. [source] The benefits of being in a bad neighbourhood: plant community composition influences red deer foraging decisionsOIKOS, Issue 1 2009Jennie N. Bee Diet selection by mammalian herbivores is often influenced by plant community composition, and numerous studies have focused on the relationships between herbivore foraging decisions and food/plant species abundance. However, few have examined the role of neighbour palatability in affecting foraging of a target plant by large mammalian herbivores. We used a large-scale field dataset on diet selection by red deer Cervus elaphus in Fiordland National Park, New Zealand to: (1) estimate the palatability of native forest plant species to introduced deer from observed patterns of browse damage; and (2) examine whether intraspecific variation in browsing of plants can be related to variation in the local abundance of alternative forage species. Overall, 21 of the 53 forest species in our dataset were never browsed by deer. At a community level, plants were more likely to be browsed if they were in a patch of vegetation of high forage quality, containing high abundances of highly palatable species and/or low abundances of less-palatable species. Our findings suggest that deer make foraging decisions at both a coarse-grain level, selecting vegetation patches within a landscape based on the overall patch quality, and at a fine-grain level by choosing among individual plants of different species. [source] Herbivore-Mediated Competition between Defended and Undefended Plant Species: A Model to Investigate Consequences of Climate ChangePLANT BIOLOGY, Issue 5 2002C. F. Dormann Abstract: Optimal levels of anti-herbivore defence are determined not only by grazing pressure on the target plant, but also by the efficiency of the defence and by competitive interactions with neighbours. In the high Arctic on Svalbard, grazing by reindeer is a process that can be modelled without plant-to-herbivore feedback, as reindeer population sizes are not correlated with plant growth. However, growing conditions are extreme: a short season and low temperatures inhibit optimal growth. Therefore, it is possible to model anti-herbivore defence in competition in this system, assess how its optimum depends on grazing intensity and defence efficiency, and, finally, how global climate change will effect plant-plant interactions. This model, based on a Lotka-Volterra type competition and temperature-dependent growth, indicates that competition is of considerable importance even in extreme environments. Herbivory mediates displacement of the defended plant by releasing it from competition. This process is more pronounced under high grazing pressure than under low pressure. In other words, competition potentially magnifies the effect of herbivory. Elevated temperatures and a longer growing season have no qualitative impact on these processes, as the dominant defended plant profits most. [source] Herbivore and neighbour effects on tundra plants depend on species identity, nutrient availability and local environmental conditionsJOURNAL OF ECOLOGY, Issue 1 2008Anu Eskelinen Summary 1I performed a factorial transplant experiment to test the roles of plant,plant interactions, herbivory by mammal grazers and resource availability for plant performance in two contrasting habitat types in a mountain tundra environment. 2Three perennial dicot herbs, Solidago virgaurea, Erigeron uniflorus and Saussurea alpina, were used as target plants to study the effects of neighbour removal and grazer exclusion, and nutrient enrichment and liming on plant growth, survival and reproductive success. These treatments were replicated in two contrasting habitat types, infertile acidic and fertile non-acidic tundra heaths. 3The effects of plant,plant interactions on Saussurea varied from facilitation in infertile acidic habitats to competition in fertile non-acidic habitats and in nutrient-enriched conditions, while the overall performance of Saussurea was strongly negatively influenced by the presence of grazers, the effects being greater when plants were fertilized and in fertile non-acidic heaths. Erigeron performed better under nutrient-enriched conditions than in unfertilized plots, when neighbours had been removed. Solidago was negatively affected by grazing and this impact was greater in nutrient-enriched plots and in non-acidic heaths than in acidic heaths and for unfertilized controls. There were no interactions between neighbour removal and herbivory in any of the three species, indicating that these processes operated independently. 4Grazer-preferred tall plants are strongly limited by consumption by mammal herbivores in nutrient-enriched conditions and in inherently fertile habitats. By contrast, arctic,alpine specialists and species of low stature experience increased competition with neighbouring vegetation in fertile habitats and in enriched nutrient conditions. 5Synthesis. Overall, the results suggest that the strength and directions of plant,plant and plant,herbivore interactions depend on plant species identity and are modified by soil edaphic factors to govern vegetation processes in tundra plant communities. These findings have important implications for understanding the forces structuring vegetation in barren tundra ecosystems under a changing environment. [source] Measuring the components of competition along productivity gradientsJOURNAL OF ECOLOGY, Issue 2 2007MARK V. WILSON Summary 1Controversy surrounds the measurement of competition intensity. Moreover, when biomass varies systematically along productivity and other environmental gradients, common indices of competitive outcome mask important ecological interactions. 2This study presents two indices derived from how neighbours interact with target plants. The first, relative crowding, increases directly with the abundance of neighbours present and decreases inversely with the potential size and vigour of the target plant itself. The second, interaction strength, is the integral of suppression of the target by neighbours over the range of neighbour abundance. Relative crowding and interaction strength are derived independently, but when multiplied produce the commonly used relative competitive index, showing the biological underpinnings of the relative competition index in terms of crowding and strength of interaction. Since the new indices of relative crowding and interaction strength explicitly account for the amount of neighbour biomass, they serve as a valid method to track the effects of changing habitat conditions on the components of competition. 3The new indices are applied to three published data sets. In each case, relative crowding increased with standing crop. In one case competition was reported as unchanged along a productivity gradient, whereas the new indices show that relative crowding and interaction strength both had significant patterns, but their effects were counteracting. These results do not fit current theories of competition. Further empirical studies are needed to see if competition theory needs revision. 4Separating the mechanisms of competition into relative crowding and strength of interaction reveals previously hidden patterns that help bring to light underlying processes of competition along productivity gradients. [source] Lack of relationship between below-ground competition and allocation to roots in 10 grassland speciesJOURNAL OF ECOLOGY, Issue 4 2003James F. Cahill Jr Summary 1A field experiment in a native grassland in Central Alberta, Canada, tested whether plants alter relative allocation to roots vs. shoots in response to below-ground competition, and whether the mass of a species' root system accounts for interspecific differences in below-ground competitive response. 2Seedlings of each of 10 native species were transplanted into the naturally occurring vegetation in the field at the start of the growing season. Root interactions between the target plants and their neighbours were manipulated through the use of PVC root exclusion tubes, with target plants grown with or without potential root interactions with their neighbours. Neighbour shoots were also tied back, forcing any target,neighbour interactions to be below ground. 3Below-ground competition generally reduced plant growth, with its relative magnitude varying among species. 4An allometric analysis indicated that competition below ground did not result in an increase in the relative biomass allocated to roots for any of the 10 target species. This is counter to the growth-balance hypothesis (and optimal foraging theory). Below-ground competition did increase root : shoot ratios, but this was due to reduced plant size (small plants have larger root : shoot ratios), rather than adaptive plasticity. 5A species' below-ground competitive ability was not related to its root system size. Although this finding is counter to commonly made assumptions, it is supported by other work demonstrating below-ground competition to be generally size-symmetric. 6Despite the majority of plant,plant interactions in grasslands being below ground, our understanding of plant competition above ground is significantly more robust. Several wide-spread assumptions regarding below-ground competition are suspect, and more multispecies studies such as this are required to provide a fuller picture of how plants respond to, and compete for, soil resources. [source] Juvenile shrubs show differences in stress tolerance, but no competition or facilitation, along a stress gradientJOURNAL OF ECOLOGY, Issue 1 2000Lisa A. Donovan Summary 1,We investigated experimentally differences in abiotic stress tolerance and the effects of plant,plant interactions for two desert shrubs, Chrysothamnus nauseosus and Sarcobatus vermiculatus, along a soil salinity (NaCl) and boron (B) gradient at Mono Lake, California, USA. Based on differences in natural distribution, and the classical expectation of a trade-off between competitive ability and stress tolerance, we hypothesized that (i) Chrysothamnus would have greater competitive ability than Sarcobatus at the low salinity end of the gradient, and that (ii) Sarcobatus would be more stress tolerant than Chrysothamnus. 2,Juvenile target plants of Chrysothamnus and Sarcobatus were planted into four sites along the gradient. Biomass was determined by destructive harvests over two growing seasons. At each site, interspecific relative competitive ability was assessed as the effect of Sarcobatus neighbours on Chrysothamnus targets compared to the effect of Chrysothamnus neighbours on Sarcobatus targets. Stress tolerance was assessed as the ability of each species to survive and grow, in the absence of neighbours, at different sites along the gradient. 3,The two species did not differ in the relative strength of plant,plant interactions, providing no support for the expectation that Chrysothamnus had greater competitive ability than Sarcobatus. Furthermore, there was no evidence for competition or facilitation, either interspecific or intraspecific, at any site in either year of the study. However, fertilization treatments demonstrated nutrient limitations, soil water reached limiting levels and root systems of targets and neighbours overlapped substantially. It is therefore surprising that plant,plant interactions among juveniles apparently play little role in the growth and survival of shrubs in this saline desert habitat. 4,Sarcobatus was more stress tolerant than Chrysothamnus and the two species performed optimally at different sites along the gradient. Sarcobatus juveniles grew best at the two most saline sites and survived at all sites, whereas Chrysothamnus juveniles grew best at a low-salinity site and did not survive at the most saline site. The difference in site of optimal performance may be due to differences in nutrient limitations or to interactions between nutrient availability and sodium (Na) and B tolerance. [source] Vectoring of Pepino mosaic virus by bumble-bees in tomato greenhousesANNALS OF APPLIED BIOLOGY, Issue 2 2008J.L. Shipp Abstract Pepino mosaic virus (PepMV) has become an important viral disease of greenhouse tomatoes worldwide. The ability of bumble-bees (Bombus impatiens), used for pollination, to acquire and transmit PepMV was investigated, and the prevalence of PepMV in plants and bumble-bees in commercial tomato greenhouses was determined. PepMV infection in plants was determined using enzyme-linked immunosorbent assay, while in bumble-bees direct real-time PCR was used. In the first experiment, the bumble-bees were exposed for 14 days to PepMV-infected plants. After 14 days, almost all bumble-bees were PepMV positive both in the hive (78.5 ± 17.5%) and in the flowers (96.3 ± 3.6%). In the second experiment, bumble-bees were released into a greenhouse with both PepMV-infected source plants and healthy non-infected target plants for 14 days. At the end of the experiment, 61.0 ± 19.5% of the bees collected from the hive and 83.3 ± 16.7% of the bees sampled from the flowers were PepMV positive. Bumble-bees transmitted PepMV from the infected to the healthy non-infected tomato plants. Two weeks after bumble-bee release, the virus was detected in leaf, fruit and flower samples of formerly healthy plants. After 6 weeks, the percentage of PepMV positive samples from the target plants increased to 52.8 ± 2.8% of the leaves and 80.6 ± 8.4% of the fruits. In the control greenhouse without bumble-bees, the target plants did not become infected. Based on the infection levels in flowers, fruits and leaves, the PepMV infection occurred possibly first in the pollinated flowers, and then spread from the fruit that developed from the flowers to other parts of the plant. In commercial greenhouses where PepMV was present, 92,100% of the plants and 88,100% of the bumble-bees were PepMV positive. No infected plant samples were found in the control commercial greenhouse, but a small number of bumble-bees (10%) tested PepMV positive. [source] | ||||||||||||||||||||||