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Indirect Facilitation (indirect + facilitation)
Selected AbstractsIndirect facilitation of an anuran invasion by non-native fishesECOLOGY LETTERS, Issue 4 2003Michael J. Adams Abstract Positive interactions among non-native species could greatly exacerbate the problem of invasions, but are poorly studied and our knowledge of their occurrence is mostly limited to plant-pollinator and dispersal interactions. We found that invasion of bullfrogs is facilitated by the presence of co-evolved non-native fish, which increase tadpole survival by reducing predatory macroinvertebrate densities. Native dragonfly nymphs in Oregon, USA caused zero survival of bullfrog tadpoles in a replicated field experiment unless a non-native sunfish was present to reduce dragonfly density. This pattern was also evident in pond surveys where the best predictors of bullfrog abundance were the presence of non-native fish and bathymetry. This is the first experimental evidence of facilitation between two non-native vertebrates and supports the invasional meltdown hypothesis. Such positive interactions among non-native species have the potential to disrupt ecosystems by amplifying invasions, and our study shows they can occur via indirect mechanisms. [source] Indirect facilitation and competition in tree species colonization of sub-Mediterranean grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 3 2006Georges Kunstler Abstract: Questions: In the absence of herbivores, what is the importance of shrub facilitation for the colonization of grasslands by Fagus sylvatica and Quercus pubescens? Is there an indirect facilitative effect of shrubs on tree seedlings by limiting herb competition? Location: Causse du Larzac, southern Massif Central, France. Methods: We conducted field experiments on the facilitative role of shrubs in seedling emergence and survival, in relation to potential negative effects of shading and the presence of herbs. The effects of shade and herbs on allocation and root morphology were analysed in a pot experiment. Results: According to these experiments, the establishment of both tree species was facilitated by shrubs, but the two species differed in the processes underlying this facilitation. Shade directly facilitates the emergence rate of both species. Shade also indirectly facilitates Fagus survival by limiting herb competition. No indirect facilitation of Quercus survival was detected. These differences reflect variation in the tolerance of herb competition by seedlings of the two species. The tolerance of herb competition by Quercus seedlings allows regeneration over a wide area under each shrub and some regeneration events in grasslands at low grazing intensity. In contrast, for Fagus, only a narrow area under each shrub is suitable; regeneration is zero in grassland. The high tolerance of herb competition by Quercus seedlings may result from the avoidance of root competition. Conclusions In grasslands with severe drought stress, and almost obligatory shrub facilitation for tree seedling regeneration, the tolerance of herb competition may alter the precise role of facilitation in the colonization process. [source] Subtle top-down control of a freshwater meiofaunal assemblage by juvenile fishFRESHWATER BIOLOGY, Issue 9 2010GERARD DINEEN Summary 1. Top-down control of prey assemblages by fish predators has been clearly demonstrated in lakes (for zooplankton prey) and rivers (for macroinvertebrate prey). Fish predation can have a significant impact on the body size of prey assemblages; often large-bodied prey are reduced in abundance, and indirect facilitation of small-bodied prey occurs potentially initiating a trophic cascade. 2. Benthic communities in aquatic ecosystems also include a numerous and functionally important meiofaunal-sized component, but in freshwaters the impact of fish predation on meiofaunal assemblages is unknown. We used a laboratory microcosm study to explore the impact of juvenile fish predation on the abundance and size structure of a riverine meiofaunal assemblage. 3. The presence of fish in our microcosms had no significant effect on overall meiofaunal (temporary and permanent) abundance. However, for the Copepoda, we found the first evidence of top-down control of freshwater meiofaunal assemblages; in microcosms with juvenile fish, the abundance of large-bodied Copepoda was significantly reduced, whereas small-bodied Copepoda were significantly more abundant suggesting indirect facilitation. 4. We conclude that predation by juvenile fish can alter the structure of freshwater meiofaunal assemblages, although we do not yet know whether these relatively subtle changes are overwhelmed by large-scale events such as flow disturbances. [source] A test of the indirect facilitation model in a temperate hardwood forest of the northern French AlpsJOURNAL OF ECOLOGY, Issue 6 2003Jean-Philippe Pages Summary 1We tested the hypothesis that the more frequent occurrence of tree seedlings below the adult trees than in canopy openings might be explained by indirect facilitation. In a temperate hardwood forest, we compared the performance of five target tree seedlings (Picea abies, Abies alba, Fagus sylvatica, Acer pseudoplatanus and Quercus petraea), transplanted with or without a herbaceous competitor (Molinia caerulea), either within the forest or into experimentally created gaps. 2We quantified changes in understorey biomass, light penetration and available forms of soil nitrogen during three growing seasons. 3Photosynthetic photon flux density and total biomass of Molinia were significantly higher in the gap treatment than within the forest. Total available nitrogen was higher in the gaps in the absence of Molinia, but higher in the forest in the presence of Molinia. 4Quercus survival was very low within the forest because of fungal infection, whereas survival was very high for the four other tree species in all combinations of the two treatments. 5Although the competitive effect of Molinia on the growth of the tree seedlings was much greater in the gap treatment, seedling growth was lower within the forest. We conclude that the tree canopy imposed strong light competition, and that this direct negative influence was much greater than any indirect positive effect of increased availability of nutrients to tree seedlings, due to reduced nutrient uptake by Molinia. 6Target species responses to treatments were similar, despite strong differences in nitrogen requirements between species. This may be due to the overwhelming negative influence of the tree canopy in our experiment. [source] Indirect facilitation and competition in tree species colonization of sub-Mediterranean grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 3 2006Georges Kunstler Abstract: Questions: In the absence of herbivores, what is the importance of shrub facilitation for the colonization of grasslands by Fagus sylvatica and Quercus pubescens? Is there an indirect facilitative effect of shrubs on tree seedlings by limiting herb competition? Location: Causse du Larzac, southern Massif Central, France. Methods: We conducted field experiments on the facilitative role of shrubs in seedling emergence and survival, in relation to potential negative effects of shading and the presence of herbs. The effects of shade and herbs on allocation and root morphology were analysed in a pot experiment. Results: According to these experiments, the establishment of both tree species was facilitated by shrubs, but the two species differed in the processes underlying this facilitation. Shade directly facilitates the emergence rate of both species. Shade also indirectly facilitates Fagus survival by limiting herb competition. No indirect facilitation of Quercus survival was detected. These differences reflect variation in the tolerance of herb competition by seedlings of the two species. The tolerance of herb competition by Quercus seedlings allows regeneration over a wide area under each shrub and some regeneration events in grasslands at low grazing intensity. In contrast, for Fagus, only a narrow area under each shrub is suitable; regeneration is zero in grassland. The high tolerance of herb competition by Quercus seedlings may result from the avoidance of root competition. Conclusions In grasslands with severe drought stress, and almost obligatory shrub facilitation for tree seedling regeneration, the tolerance of herb competition may alter the precise role of facilitation in the colonization process. [source] Acer negundo invasion along a successional gradient: early direct facilitation by native pioneers and late indirect facilitation by conspecificsNEW PHYTOLOGIST, Issue 3 2010Patrick Saccone Summary ,Here, we analysed the role of direct and indirect plant interactions in the invasion process of Acer negundo along a natural successional gradient in the Middle Rhone floodplain (France). We addressed two questions: What are the responses of the invasive Acer seedlings to native communities' effects along the successional gradient? What are the effects of the invasive Acer adult trees on the native communities? ,In the three communities (Salix, Acer and Fraxinus stands) we transplanted juveniles of the invasive and juveniles of the natives within the forest and in experimental gaps, and with and without the herb layer. We also quantified changes in understory functional composition, light, nitrogen and moisture among treatments. ,Acer seedlings were directly facilitated for survival in the Salix and Acer communities and indirectly facilitated for growth by adult Acer through the reduction of the abundance of highly competitive herbaceous competitors. ,We conclude that direct facilitation by the tree canopy of the native pioneer Salix is very likely the main biotic process that induced colonization of the invasive Acer in the floodplain and that indirect facilitation by adult conspecifics contributed to population establishment. [source] | ||||||||||