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36 results for “competition and facilitation”
Adult facilitation becomes competition as juvenile soapberry bugs age
<p>Intraspecific interactions can change from facilitative to competitive depending on the organism's ontogeny. In plant-feeding insects, host plant defenses can be strengthened or weakened by insect feeding, and can therefore be important for determining whether two insects feeding on the same plant help or harm each other's fitness. Here I conducted two experiments looking at the direct effect of a physical seed defense and the role of intraspecific facilitation in reducing the effects of that defense for juveniles of the red-shouldered soapberry bug. I demonstrate that juveniles are severely inhibited by the tough seed coat of their host plant, leading to high mortality early in development. Adults, in contrast, can create holes through which younger individuals could potentially feed. I manipulated whether or not seeds were fed on by adults on two host plant species: a well-defended native host and a poorly defended introduced host. Survival in the first week of development was dramatically improved by prior adult feeding and this facilitation was stronger on the well-defended host plant. However, the benefits of prior adult feeding ceased after the first week of development and shifted to having a negative effect on survival, development time, and body size. These results indicate that ontogeny is a key factor determining the effects of plant defenses and the strength and direction of intraspecific interactions across multiple host plant species.</p>
Impact of larval high density on the performance of Anastrepha ludens: competition or feeding facilitation?
<p>A critical point in diet management is maximizing density as a strategy for reducing costs. Artificial diets elaborated with large particle sizes have increased volume, possess high porosity and aeration capacity, are more penetrable and facilitate the movement of larvae, and increase the bioavailability of nutrients. The present experiment consisted in demonstrating that the bulking agent facilitates feeding and could have more capacity to support a high density of larvae with a minimal effect of competition on the life-history traits of <em>Anastrepha ludens</em>. The results indicate that density affected larval and pupal weight, but not pupation at 24 h, adult emergence, and flier percentage, which remained unchanged. However, there was an increase in yield and bioconversion. Larvae in high density conditions aggregated to increase the effect of regurgitation of amylases and proteases as a strategy to metabolize the food prior to ingestion through enzymes secreted in the saliva, contributing thus to feeding facilitation and the uptake of ingested food, which decreased the negative impact of competition in high density conditions. High density leads to an increase in food consumption and a consequent increase in digestive enzyme activity, contributing to the bioavailability of macronutrients ─ proteins, carbohydrates, and lipids ─ in the diet.</p> <p>Identifying the properties of bulking agents and other ingredients and their interaction under high-density conditions is essential to develop novel artificial diets and improve the mass-rearing strategies for the SIT.</p> <p> </p>
Adult facilitation becomes competition as juvenile soapberry bugs age
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Data from: A meta-analysis of plant interaction networks reveals competitive hierarchies as well as facilitation and intransitivity
The extent to which competitive interactions and niche differentiation structure communities has been highly controversial. To quantify evidence for key features of plant community structure, I recharacterized published data from interaction experiments as networks of competitive and facilitative interactions. I measured the network structure of 31 woody and herbaceous communities, including the intensity, distribution, and diversity of interactions at the species-pair and community level to determine the generality of competition, winner-loser relationships, and unequal interaction allocation. I developed novel methodology using meta-analysis to incorporate interaction uncertainty into estimates of structural metrics among independent networks. Plant communities were competitive, but intraspecific interactions were sometimes more intense than interspecific interactions. On the whole, interactions were imbalanced and communities were transitive. However, facilitation, balanced interactions, and intransitivity were common in individual communities. Synthesizing network metrics using meta-analysis is an original approach with which to generalize community structure in a systematic way.
Overgrowth competition or facilitation from cushion plants: Implication for the role of plant-plant interactions
<p>Our data reports the annual growth and age of the shrub <em>Caragana versicolor</em> overgrown or free of the cushion plant <em>Thylacospermum ceaspitosum</em>.<span> The observations and sampling were performed at ~5000 m.a.s.l., on the East facing slope of the Korzok range, on the North-Eastern side of Lake Tso Moriri above Korzok village (4522 m a.s.l.). </span><span>Our study demonstrates that the growth of </span><em>Caragana versicolor</em> is repressed by the competitive effect of the cushion plant <em>Thylacospermum ceaspitosum</em>, and shows no evidence of facilitation between the two co-occurring species.</p>
Facilitation and competition shape a geographical mosaic of flower colour polymorphisms
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Data from: A meta-analysis of plant interaction networks reveals competitive hierarchies as well as facilitation and intransitivity
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Interplay of competition and facilitation in grazing succession by migrant Serengeti herbivores
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Overgrowth competition or facilitation from cushion plants: Implication for the role of plant-plant interactions
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Shift from short-term competition to facilitation with drought stress is due to a decrease in long-term facilitation
Disentangling short- and long-term neighbour effects, using both removal and observational methods within a single experiment, has strongly improved our understanding of the driving mechanisms of plant-plant interactions. However, there has been no attempt to assess two important underlying processes of their changes along gradients, environmental-severity (changes in target performance without neighbours) and neighbour-traits (changes in performance with neighbours) effects, the former previously shown in alpine communities to be involved in competition and the latter in facilitation. We addressed this goal in an experiment conducted in continental saline depressions (sebkhas) from the Mediterranean arid climate of central Tunisia. We quantified short- and long-term effects of dominant shrubs, transplanting three target grass species in open, nurse and removed-nurse microhabitats of two habitats of different salinity levels in height sebkhas. The design extended geographically from central Tunisia to the Libyan border, 500km southeastward. We used the Relative Interaction Index to calculate short- and long-term effects of neighbours on target species before and after the dry summer seasons and to disentangle environmental-severity from neighbour-trait effects. Short-term effects were slightly negative and long-term effects strongly positive before the dry summer season in the two habitats. Short-term effects switched to positive with increasing drought stress, due to increasing environmental severity (decrease in the response without neighbours), whereas long-term effects decreased due to decreasing environmental mitigation (decrease in the response with neighbours). Soil moisture measurements showed that both changes were due to vanishing shrub soil engineering-effects during the summer drought. We conclude that an increase in short-term facilitation with increasing drought stress through time, apparently supporting the Stress-Gradient-Hypothesis, might be due to a decrease in long-term facilitation. Our study highlights that assessing the effects of neighbours with both the removal and observational methods is crucial for understanding the driving processes of plant-plant interactions in arid systems.
Data from: Food and habitat provisions jointly determine competitive and facilitative interactions among distantly related herbivores
1. Interactions between distantly related herbivores exert powerful influences on ecosystems, but most studies to date have only considered unidirectional effects. Few have simultaneously examined the mutual effects that vertebrate herbivores and insect herbivores have on one another. 2. We conducted a set of manipulative experiments to evaluate the potential competition and facilitation between two pairs of distantly related herbivore taxa: an insect caterpillar (Gynaephora alpherakii) and two large vertebrate herbivores, yak (Bos grunniens) and Tibetan sheep (Ovis aries tibetica). 3. We found that these large herbivores consistently increased the density of caterpillars likely by improving the habitat for caterpillars. The caterpillars, in turn, decreased yak but increased Tibetan sheep foraging time and intake bites by differently changing available food resources of the two large herbivores. Diet preferences of herbivores modified the habitat and food resources, thereby causing a diet-mediated competition between yak and caterpillars, and facilitation between sheep and caterpillars. The vertebrate herbivores non-feeding upon Lamiophlomis rotata and Gentiana straminea, the caterpillars preferred habitat, increased densities of the two plant species, thus favoring the caterpillars. In turn, the caterpillar preference for Kobresia pygmaea, significantly reduced food resources for yak, while promoted food resources (multiple forbs) for sheep. 4. Synthesis. Our study indicates that two different mechanisms (the changes in habitat and food availability) induced by herbivore foraging jointly determine competitive and facilitative interactions between distantly related herbivore species. We also suggest that examining the bidirectional effects between herbivores offers a better understanding of competition and facilitation in terrestrial animal communities.
Data from: The shift from plant–plant facilitation to competition under severe water deficit is spatially explicit
The stress-gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta-analysis to compare temporal differences of species diversity and productivity under a nurse plant (Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plants in situ during a year with below-average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss.
Data from: Field manipulations of resources mediate the transition from intraspecific competition to facilitation
1. Population density affects individual performance, though its effects are often mixed. For sessile species, increases in population density typically reduce performance. Still, cases of positive density dependence do occur in these systems and demand explanation. The stress gradient hypothesis (SGH) predicts that under stressful conditions, positive effects of facilitation may outweigh the negative effects of competition. 2. While some elements of the SGH are well studied, its potential to explain intraspecific facilitation has received little attention. Further, there have been questions regarding whether the SGH holds if the stressor is a resource. Most studies of interactions between the environment and intraspecific facilitation have relied on natural environmental gradients; manipulative studies are much rarer. 3. To test the effects of intraspecific density and resources, we manipulated resource availability over natural population densities for the marine bryozoan Watersipora subtorquata. 4. We found negative effects of density on colony performance in low resource environments, but mainly positive density-dependence in high resource environments. By adding resources, competition effects were reduced and the positive effects of facilitation were revealed. 5. Our results suggest that resource availability mediates the relative strength of competition and facilitation in our system. We also suggest that intraspecific facilitation is more common than may be appreciated and that environmental variation may act as mediators to the balance between negative and positive density-dependence.
Data from: Size and density mediate transitions between competition and facilitation
Species simultaneously compete with and facilitate one another. Size can mediate transitions along this competition-facilitation continuum, but the consequences for demography are unclear. We orthogonally manipulated the size of a focal species, and the size and density of a heterospecific neighbour, in the field using a model marine system. We then parameterised a size-structured population model with our experimental data. We found that heterospecific size and density interactively altered the population dynamics of the focal species. Size determined whether heterospecifics facilitated (when small) or competed with (when large) the focal species, while density strengthened these interactions. These size-mediated interactions also altered the pace of the focal's life history. We provide the first demonstration that size and density mediate competition and facilitation from a population dynamical perspective. We suspect such effects are ubiquitous, but currently underappreciated. We reiterate classic cautions against inferences about competitive hierarchies made in the absence of size-specific data.
Data for: Interspecific competition and facilitation coexist in mixed-species bird flocks of montane coniferous forests in Taiwan
<p><span>Besides competition, positive interactions also play an important role in shaping the social structure of mixed-species bird flocks. This study aimed to illuminate the interspecific interactions of competition and facilitation in mixed-species bird flocks. We recorded the foraging behavior and microhabitat use of flocking species in montane coniferous forests of Taiwan under different social contexts. Foraging niche breadth and niche-overlap with other flocking species were compared between individuals inside and outside of mixed flocks. For the three microhabitat variables (foraging locations, vertical strata, and horizontal strata), relationships between niche-overlaps of heterospecific pairs of these flocking species and their corresponding interspecific associations were determined using a simple linear regression. While in mixed flocks, two understory species, Taiwan Fulvetta <em>Fulvetta formosana</em> and Yellowish-bellied Bush-Warbler <em>Horornis acanthizoides</em>, shifted their foraging from shrubs upwards into coniferous trees. Meanwhile, Flamecrests (<em>Regulus goodfellowi</em>) moved downwards vertically within the canopy, and Black-throated Tits (<em>Aegithalos concinnus</em>) spread out horizontally along branches. In addition, Flamecrests applied many more sally-hovers inside of mixed flocks than outside of flocks. All four species are insectivores which might find it more difficult to obtain sufficient food during the colder winters when food resources become scarcer. Therefore, they may be using the increased vigilance afforded by the flock to expand their foraging niches and thus to increase their foraging opportunities inside mixed flocks. Furthermore, niche-overlaps of heterospecific pairs of the 11 common flocking species were positively correlated with their corresponding interspecific associations on all three microhabitat variables. These results indicate that a greater foraging niche-overlap between two flocking species would result in higher coexistence of the two species in mixed flocks. Consequently, facilitative interactions occurred in these mixed-species flocks in addition to competitive interactions.</span></p>
The higher species richness of calcareous than siliceous communities is explained by lower competition in grasslands but higher facilitation in forests
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Data from: Fatal diseases and parasitoids: from competition to facilitation in a shared host.
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Data from: Size and density mediate transitions between competition and facilitation
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Competition and facilitation among fungal plant parasites affect their life-history traits
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Shift from short-term competition to facilitation with drought stress is due to a decrease in long-term facilitation
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