| 1. |
- Berg, Sofia, et al.
(author)
-
Rare but important: perturbations to uncommon species have disproportionately large impact on ecological communities
-
Other publication (other academic/artistic)abstract
- The majority of species in the ecosystems of the world are rare. Because the contributions to community biomass and productivity of many of these species are small it has been suggested that loss of rare species should have relatively small ecological consequences. However, the extent to which rare species affect the structure and stability of ecosystems is largely unknown. Using a theoretical approach, based on analytical methods, we here investigate how perturbations to rare as well as common species affect the structure (distribution of equilibrium abundances of species) and resilience (recovery rate) of complex ecological communities. We show that, contrary to expectation, resilience and structure of ecological communities are generally more sensitive to perturbations to rare than to common species. We find the explanation for this to lie in the cause of rarity: rare species tend to interact strongly, on a per capita basis, with other species. Our results suggest that many rare species are likely to fill important ecological roles in ecosystems.
|
|
| 2. |
- Hauzy, Céline, et al.
(author)
-
Confronting the Paradox of Enrichment to the Metacommunity Perspective
- 2013
-
In: PLOS ONE. - San Francisco, CA United States : Public Library of Science. - 1932-6203. ; 8:12, s. e82969-
-
Journal article (peer-reviewed)abstract
- Resource enrichment can potentially destabilize predator-prey dynamics. This phenomenon historically referred as the "paradox of enrichment" has mostly been explored in spatially homogenous environments. However, many predator-prey communities exchange organisms within spatially heterogeneous networks called metacommunities. This heterogeneity can result from uneven distribution of resources among communities and thus can lead to the spreading of local enrichment within metacommunities. Here, we adapted the original Rosenzweig-MacArthur predator-prey model, built to study the paradox of enrichment, to investigate the effect of regional enrichment and of its spatial distribution on predator-prey dynamics in metacommunities. We found that the potential for destabilization was depending on the connectivity among communities and the spatial distribution of enrichment. In one hand, we found that at low dispersal regional enrichment led to the destabilization of predator-prey dynamics. This destabilizing effect was more pronounced when the enrichment was uneven among communities. In the other hand, we found that high dispersal could stabilize the predator-prey dynamics when the enrichment was spatially heterogeneous. Our results illustrate that the destabilizing effect of enrichment can be dampened when the spatial scale of resource enrichment is lower than that of organismss movements (heterogeneous enrichment). From a conservation perspective, our results illustrate that spatial heterogeneity could decrease the regional extinction risk of species involved in specialized trophic interactions. From the perspective of biological control, our results show that the heterogeneous distribution of pest resource could favor or dampen outbreaks of pests and of their natural enemies, depending on the spatial scale of heterogeneity.
|
|
| 3. |
- Hauzy, Céline, et al.
(author)
-
Density-dependent dispersal and relative dispersal affect the stability of predator-prey metacommunities
- 2010
-
In: Journal of Theoretical Biology. - : Elsevier BV. - 0022-5193 .- 1095-8541. ; 266:3, s. 458-469
-
Journal article (peer-reviewed)abstract
- Although density-dependent dispersal and relative dispersal (the difference in dispersal rates between species) have been documented in natural systems, their effects on the stability of metacommunities are poorly understood. Here we investigate the effects of intra- and interspecific density-dependent dispersal on the regional stability in a predator-prey metacommunity model. We show that, when the dynamics of the populations reach equilibrium, the stability of the metacommunity is not affected by density-dependent dispersal. However, the regional stability, measured as the regional variability or the persistence, can be modified by density-dependent dispersal when local populations fluctuate over time. Moreover these effects depend on the relative dispersal of the predator and the prey. Regional stability is modified through changes in spatial synchrony. Interspecific density-dependent dispersal always desynchronizses local dynamics, whereas intraspecific density-dependent dispersal may either synchronize or desynchronize it depending on dispersal rates. Moreover, intra- and interspecific density-dependent dispersal strengthen the top-down control of the prey by the predator at intermediate dispersal rates. As a consequence the regional stability of the metacommunity is increased at intermediate dispersal rates. Our results show that density-dependent dispersal and relative dispersal of species are keys to understanding the response of ecosystems to fragmentation.
|
|
| 4. |
- Hauzy, Celine, et al.
(author)
-
Spatial heterogeneity and functional response: an experiment in microcosms with varying obstacle densities
- 2010
-
In: Oecologia. - : Springer Science Business Media. - 0029-8549 .- 1432-1939. ; 163:3, s. 625-636
-
Journal article (peer-reviewed)abstract
- Spatial heterogeneity of the environment has long been recognized as a major factor in ecological dynamics. Its role in predator-prey systems has been of particular interest, where it can affect interactions in two qualitatively different ways: by providing (1) refuges for the prey or (2) obstacles that interfere with the movements of both prey and predators. There have been relatively fewer studies of obstacles than refuges, especially studies on their effect on functional responses. By analogy with reaction-diffusion models for chemical systems in heterogeneous environments, we predict that obstacles are likely to reduce the encounter rate between individuals, leading to a lower attack rate (predator-prey encounters) and a lower interference rate (predator-predator encounters). Here, we test these predictions under controlled conditions using collembolans (springtails) as prey and mites as predators in microcosms. The effect of obstacle density on the functional response was investigated at the scales of individual behavior and of the population. As expected, we found that increasing obstacle density reduces the attack rate and predator interference. Our results show that obstacles, like refuges, can reduce the predation rate because obstacles decrease the attack rate. However, while refuges can increase predator dependence, we suggest that obstacles can decrease it by reducing the rate of encounters between predators. Because of their opposite effect on predator dependence, obstacles and refuges could modify in different ways the stability of predator-prey communities.
|
|
| 5. |
|
|
| 6. |
- Kaneryd, Linda, et al.
(author)
-
Species-rich ecosystems are vulnerable to cascading extinctions in an increasingly variable world
- 2012
-
In: Ecology and Evolution. - : Wiley-Blackwell. - 2045-7758. ; 2:4, s. 858-874
-
Journal article (peer-reviewed)abstract
- Global warming leads to increased intensity and frequency of weather extremes. Such increased environmental variability might in turn result in increased variation in the demographic rates of interacting species with potentially important consequences for the dynamics of food webs. Using a theoretical approach, we here explore the response of food webs to a highly variable environment.We investigate how species richness and correlation in the responses of species to environmental fluctuations affect the risk of extinction cascades. We find that the risk of extinction cascades increases with increasing species richness, especially when correlation among species is low. Initial extinctions of primary producer species unleash bottom-up extinction cascades, especially in webs with specialist consumers. In this sense, species-rich ecosystems are less robust to increasing levels of environmental variability than species-poor ones. Our study thus suggests that highly speciesrich ecosystems such as coral reefs and tropical rainforests might be particularly vulnerable to increased climate variability.
|
|
| 7. |
- Mueller, Johann P, et al.
(author)
-
Ingredients for protist coexistence: competition, endosymbiosis and a pinch of biochemical interactions
- 2012
-
In: Journal of Animal Ecology. - : Wiley-Blackwell. - 0021-8790 .- 1365-2656. ; 81:1, s. 222-232
-
Journal article (peer-reviewed)abstract
- 1. The interaction between mutualism, facilitation or interference and exploitation competition is of major interest as it may govern species coexistence. However, the interplay of these mechanisms has received little attention. This issue dates back to Gause, who experimentally explored competition using protists as a model [Gause, G.F. (1935) Verifications experimentales de la theorie mathematique de la lutte pour la vie. Actualites Scientifiques et Industrielles, 277]. He showed the coexistence of Paramecium caudatum with a potentially allelopathic species, Paramecium bursaria. less thanbrgreater than less thanbrgreater than2. Paramecium bursaria hosts the green algae Chlorella vulgaris. Therefore, P. bursaria may benefit from carbohydrates synthesised by the algae. Studying endosymbiosis with P. bursaria is possible as it can be freed of its endosymbiont. In addition, C. vulgaris is known to produce allelochemicals, and P. bursaria may benefit also from allelopathic compounds. less thanbrgreater than less thanbrgreater than3. We designed an experiment to separate the effects of resource exploitation, endosymbiosis and allelopathy and to assess their relative importance for the coexistence of P. bursaria with a competitor that exploits the same resource, bacteria. The experiment was repeated with two competitors, Colpidium striatum or Tetrahymena pyriformis. less thanbrgreater than less thanbrgreater than4. Results show that the presence of the endosymbiont enables the coexistence of competitors, while its loss leads to competitive exclusion. These results are in agreement with predictions based on resource equilibrium density of monocultures (R*) supporting the idea that P. bursarias endosymbiont is a resource provider for its host. When P. bursaria and T. pyriformis coexist, the density of the latter shows large variation that match the effects of culture medium of P. bursaria. Our experiment suggests these effects are because of biochemicals produced in P. bursaria culture. less thanbrgreater than less thanbrgreater than5. Our results expose the hidden diversity of mechanisms that underlie competitive interactions. They thus support Gausess speculation (1935) that allelopathic effects might have been involved in his competition experiments. We discuss how a species engaged both in competition for a resource and in costly interference such as allelopathy may counterbalance these costs with a resource-provider endosymbiont.
|
|
| 8. |
- Robinson, Kathryn M, et al.
(author)
-
Relative impacts of environmental variation and evolutionary history on the nestedness and modularity of tree-herbivore networks
- 2015
-
In: Ecology and Evolution. - : Wiley-Blackwell. - 2045-7758. ; 5:14, s. 2898-2915
-
Journal article (peer-reviewed)abstract
- Nestedness and modularity are measures of ecological networks whose causative effects are little understood. We analyzed antagonistic plant-herbivore bipartite networks using common gardens in two contrasting environments comprised of aspen trees with differing evolutionary histories of defence against herbivores. These networks were tightly connected owing to a high level of specialization of arthropod herbivores that spend a large proportion of the life cycle on aspen. The gardens were separated by ten degrees of latitude with resultant differences in abiotic conditions. We evaluated network metrics and reported similar connectance between gardens but greater numbers of links per species in the northern common garden. Interaction matrices revealed clear nestedness, indicating subsetting of the bipartite interactions into specialist divisions, in both the environmental and evolutionary aspen groups, although nestedness values were only significant in the northern garden. Variation in plant vulnerability, measured as the frequency of herbivore specialization in the aspen population, was significantly partitioned by environment (common garden) but not by evolutionary origin of the aspens. Significant values of modularity were observed in all network matrices. Trait-matching indicated that growth traits, leaf morphology, and phenolic metabolites affected modular structure in both the garden and evolutionary groups, whereas extra-floral nectaries had little influence. Further examination of module configuration revealed that plant vulnerability explained considerable variance in web structure. The contrasting conditions between the two gardens resulted in bottom-up effects of the environment, which most strongly influenced the overall network architecture, however, the aspen groups with dissimilar evolutionary history also showed contrasting degrees of nestedness and modularity. Our research therefore shows that, while evolution does affect the structure of aspen-herbivore bipartite networks, the role of environmental variations is a dominant constraint.
|
|
