Facilitative Effects (facilitative + effects)

Distribution by Scientific Domains


Selected Abstracts


Positive diversity,stability relationships in forest herb populations during four decades of community assembly

ECOLOGY LETTERS, Issue 10 2010
Martin Dov
Ecology Letters (2010) Abstract It is suggested that diversity destabilizes individual populations within communities; however, generalizations are problematic because effects of diversity can be confounded by variation attributable to community type, life history or successional stage. We examined these complexities using a 40-year record of reassembly in forest herb communities in two clearcut watersheds in the Andrews Long-term Ecological Research Site (Oregon, USA). Population stability was higher among forest than colonizing species and increased with successional stage. Thus, life history and successional stage may explain some of the variability in diversity,stability relationships found previously. However, population stability was positively related to diversity and this relationship held for different forest communities, for species with contrasting life histories, and for different successional stages. Positive relationships between diversity and population stability can arise if diversity has facilitative effects, or if stability is a precursor, rather than a response, to diversity. [source]


Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift

ECOLOGY LETTERS, Issue 8 2004
F. Ludwig
Abstract Under large East African Acacia trees, which were known to show hydraulic lift, we experimentally tested whether tree roots facilitate grass production or compete with grasses for below-ground resources. Prevention of tree,grass interactions through root trenching led to increased soil water content indicating that trees took up more water from the topsoil than they exuded via hydraulic lift. Biomass was higher in trenched plots compared to controls probably because of reduced competition for water. Stable isotope analyses of plant and source water showed that grasses which competed with trees used a greater proportion of deep water compared with grasses in trenched plots. Grasses therefore used hydraulically lifted water provided by trees, or took up deep soil water directly by growing deeper roots when competition with trees occurred. We conclude that any facilitative effect of hydraulic lift for neighbouring species may easily be overwhelmed by water competition in (semi-) arid regions. [source]


Facilitation research in marine systems: state of the art, emerging patterns and insights for future developments

JOURNAL OF ECOLOGY, Issue 6 2009
Fabio Bulleri
Summary 1. Positive species interactions are increasingly recognized as important drivers of community structure and ecosystem functioning. Although the literature on facilitative interactions in terrestrial environments has been reviewed and emerging patterns have been synthesized, comparable attempts are lacking for the marine realm. 2. By means of a quantitative survey of the literature, I provide a critical summary of current knowledge on positive species interactions in marine environments. In particular, I (i) assess how marine facilitation research compares to that carried out in terrestrial environments in terms of focus and philosophical approach; (ii) illustrate the mechanisms by which facilitation takes place in different habitats; (iii) assess whether benefactor and beneficiary species are more likely to belong to the same or to a different trophic level; and (iv) provide examples of how including facilitation into ecological theory might advance our understanding of the mechanisms that regulate ecosystem functioning. 3. Except for some studies in intertidal habitats, few studies in marine environments have been framed within mainstream facilitation theory (e.g. the Stress Gradient Hypothesis) and research does not seem to be organized in a self-contained theme. Amelioration of physical conditions appears to be the most common mechanism of facilitation in intertidal habitats, whilst associational defence predominates in the subtidal. 4. In contrast to the terrestrial literature, dominated by plant,plant interactions, marine benefactors and beneficiary species often belong to different trophic levels. This might imply little overlapping of resource niches or a differential response to environmental conditions or consumer pressure, with implications for the persistence of facilitative effects at the extreme ends of stress gradients. 5. Recent research shows that facilitation can enhance temporal variability and invasibility of marine communities and emphasizes the central role of positive species interactions in regulating the functioning of natural ecosystems. 6.Synthesis. Studies encompassing a wide variety of life histories and environmental conditions are central to achieving a unified facilitation theory. Research in marine environments can provide new insights into the mechanisms underlying variations in the strength and direction of species interactions, but this will require greater awareness and consideration of facilitation. [source]


Effects of resource competition and herbivory on plant performance along a natural productivity gradient

JOURNAL OF ECOLOGY, Issue 2 2000
René Van Der Wal
Summary 1,The effects of resource competition and herbivory on a target species, Triglochin maritima, were studied along a productivity gradient of vegetation biomass in a temperate salt marsh. 2,Transplants were used to measure the impact of grazing, competition and soil fertility over two growing seasons. Three parts of the marsh were selected to represent different successional stages; Triglochin reached local dominance at intermediate biomass of salt-marsh vegetation. At each stage, three competition treatments (full plant competition, root competition only, and no competition) and three grazing treatments (full grazing, no grazing on Triglochin, and no grazing on Triglochin or neighbours) were applied to both seedlings and mature plants. 3,Competition and herbivory reduced biomass and flowering of Triglochin. The impact of grazing was strongest at the stage with the lowest biomass, while both herbivory and competition had a significant impact at the stage with the highest biomass. When plants were protected from direct herbivory, competition operated at all three successional stages. 4,Grazing reduced light competition when vegetation biomass was low or intermediate, but at high biomass there was competition for light even when grazing occurred. Herbivore exclusion increased the effects of plant competition. Except at low biomass, the negative impact of plant competition on Triglochin performance was greater than the positive effect of not being grazed. 5,Grazing played a minor role in seedling survival and establishment which were largely controlled by competitive and facilitative effects. 6,Once established, the persistence of Triglochin will be determined largely by grazing. Intense grazing in the younger marsh and increasing competition for light in the older marsh will restrict the distribution to sites with intermediate biomass. [source]