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Ecological network

About: Ecological network is a(n) research topic. Over the lifetime, 2029 publication(s) have been published within this topic receiving 86604 citation(s).

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Open accessJournal ArticleDOI: 10.1890/04-0922
D. U. Hooper1, F. S. Chapin2, John J. Ewel3, Andy Hector4  +12 moreInstitutions (14)
Abstract: Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the re- lationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are struc- tured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain.

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  • FIG. 7. Potential patterns of effects of intensification of agricultural practices on diversity of nontarget species. Letters a–f on the x-axis refer to increasing states of management intensity, with ‘‘a’’ being an unmanaged ecosystem and ‘‘f’’ being intensive, industrialized agriculture. Intensification tends to reduce diversity of associated taxa, although the patterns could follow a variety of trajectories, including the potential for initial increases in species richness for some taxa under the assumptions of the intermediate disturbance hypothesis (Giller et al. 1997). Losses of associated diversity may thereby affect ecosystem services related to agricultural production, although the effects often depend on the details of the relationships among the species and services in question (see Section III). The figure is modified from Vandermeer et al. (2002).
    FIG. 7. Potential patterns of effects of intensification of agricultural practices on diversity of nontarget species. Letters a–f on the x-axis refer to increasing states of management intensity, with ‘‘a’’ being an unmanaged ecosystem and ‘‘f’’ being intensive, industrialized agriculture. Intensification tends to reduce diversity of associated taxa, although the patterns could follow a variety of trajectories, including the potential for initial increases in species richness for some taxa under the assumptions of the intermediate disturbance hypothesis (Giller et al. 1997). Losses of associated diversity may thereby affect ecosystem services related to agricultural production, although the effects often depend on the details of the relationships among the species and services in question (see Section III). The figure is modified from Vandermeer et al. (2002).
  • FIG. 2. Theoretical examples of how changing species diversity could affect ecosystem properties. Lines show average response, and points show individual treatments. (A) Selection effect for a dominant species: average ecosystem properties increase with increasing species richness, but maximal response is also achievable with particular combinations even at low diversity. The increase in average response results from the greater probability of including the most effective species as species richness increases. The figure illustrates results for productivity as change in aboveground biomass. (B) Complementarity and/or positive interactions among species, illustrated for plant cover as an index of aboveground primary productivity in a system with all new aboveground growth each year. Once there is at least one of each different type of species or functional type, effects of increasing species richness on ecosystem properties should begin to saturate; adding more species at that point would have progressively less effect on process rates (Tilman et al. 1997b, Loreau 2000). Where the relationship saturates depends on the degree of niche overlap among species (Petchey 2000, Schwartz et al. 2000). The figures are from Tilman (1997b).
    FIG. 2. Theoretical examples of how changing species diversity could affect ecosystem properties. Lines show average response, and points show individual treatments. (A) Selection effect for a dominant species: average ecosystem properties increase with increasing species richness, but maximal response is also achievable with particular combinations even at low diversity. The increase in average response results from the greater probability of including the most effective species as species richness increases. The figure illustrates results for productivity as change in aboveground biomass. (B) Complementarity and/or positive interactions among species, illustrated for plant cover as an index of aboveground primary productivity in a system with all new aboveground growth each year. Once there is at least one of each different type of species or functional type, effects of increasing species richness on ecosystem properties should begin to saturate; adding more species at that point would have progressively less effect on process rates (Tilman et al. 1997b, Loreau 2000). Where the relationship saturates depends on the degree of niche overlap among species (Petchey 2000, Schwartz et al. 2000). The figures are from Tilman (1997b).
  • FIG. 6. Anticipated effects of diversity on ecosystem properties (plant net primary productivity is shown) across increasing scales. As habitat heterogeneity, temporal variation in conditions, and response to disturbance are included, more species are needed to saturate ecosystem properties. If species are selected at random, rather than chosen according to their adaptations, ecosystem properties may saturate even more slowly. ‘‘Zone accessible to intensive management’’ reflects agronomic ecosystems where very high productivity may be achieved at very low species richness, but at the cost of substantial inputs of time, energy, fertilizers, pesticides, and/or water resources, often with concurrent off-site impacts and trade-offs with other ecosystem services. The figure is modified from Field (1995).
    FIG. 6. Anticipated effects of diversity on ecosystem properties (plant net primary productivity is shown) across increasing scales. As habitat heterogeneity, temporal variation in conditions, and response to disturbance are included, more species are needed to saturate ecosystem properties. If species are selected at random, rather than chosen according to their adaptations, ecosystem properties may saturate even more slowly. ‘‘Zone accessible to intensive management’’ reflects agronomic ecosystems where very high productivity may be achieved at very low species richness, but at the cost of substantial inputs of time, energy, fertilizers, pesticides, and/or water resources, often with concurrent off-site impacts and trade-offs with other ecosystem services. The figure is modified from Field (1995).
  • FIG. 3. Variation in effects of plant species richness and composition on plant productivity. (A) Experiments in the tropics. Treatments ran for five years and included four monocultures (two rotations [1st and 2nd] of maize [Zea mays], one rotation of cassava [Manihot esculenta], and one rotation of a tree, Cordia alliodora); a diverse (.100 plant species) natural succession following clearing and burning of original vegetation; a species-enriched (;120 species) version of natural succession; and an imitation of succession that mimicked the plant life forms in the natural succession treatment, but with different species. Monocultures were timed to coincide with growth phases of natural succession: maize during the initial herbaceous stage, cassava during the shrub-dominated stage, and C. alliodora during the tree-dominated stage. Note that the maize monoculture had both the highest and lowest overall productivity, and that the productivity of the successional vegetation was not increased by further increases in species richness. This figure is modified from Ewel (1999). (B) The pan-European BIODEPTH experiment. At several sites, plant productivity increased with increasing species richness, although the pattern of response varied in individual location analyses. Five of the sites had either non-saturating or saturating patterns (on a linear scale). At two sites significant differences across different levels of diversity (ANOVA) provided a better model than a linear regression. One site (Greece, dotted line) showed no significant relationship between aboveground plant productivity and species richness. Even where there are strong trends in the diversity effect, there is also variation within levels of richness resulting in part from differences in composition. Points are individual plot biomass values, and lines are regression curves or join diversity level means (squares for Ireland and Silwood). The figure is after Hector et al. (1999).
    FIG. 3. Variation in effects of plant species richness and composition on plant productivity. (A) Experiments in the tropics. Treatments ran for five years and included four monocultures (two rotations [1st and 2nd] of maize [Zea mays], one rotation of cassava [Manihot esculenta], and one rotation of a tree, Cordia alliodora); a diverse (.100 plant species) natural succession following clearing and burning of original vegetation; a species-enriched (;120 species) version of natural succession; and an imitation of succession that mimicked the plant life forms in the natural succession treatment, but with different species. Monocultures were timed to coincide with growth phases of natural succession: maize during the initial herbaceous stage, cassava during the shrub-dominated stage, and C. alliodora during the tree-dominated stage. Note that the maize monoculture had both the highest and lowest overall productivity, and that the productivity of the successional vegetation was not increased by further increases in species richness. This figure is modified from Ewel (1999). (B) The pan-European BIODEPTH experiment. At several sites, plant productivity increased with increasing species richness, although the pattern of response varied in individual location analyses. Five of the sites had either non-saturating or saturating patterns (on a linear scale). At two sites significant differences across different levels of diversity (ANOVA) provided a better model than a linear regression. One site (Greece, dotted line) showed no significant relationship between aboveground plant productivity and species richness. Even where there are strong trends in the diversity effect, there is also variation within levels of richness resulting in part from differences in composition. Points are individual plot biomass values, and lines are regression curves or join diversity level means (squares for Ireland and Silwood). The figure is after Hector et al. (1999).
  • FIG. 5. Increasing stability with increasing species richness in ecological experiments. In both cases, the overall patterns are as predicted from theory, but the underlying mechanisms may coincide only in part (see Section II.B.2). (A) Temporal variability (coefficient of variation, CV) in aboveground plant biomass (correlated with productivity in these Minnesota grasslands) in response to climatic variability (the figure is from Tilman [1999]). The gradient in species richness results from different levels of nutrient addition, so that the stability response may result from differences in species composition instead of, or in addition to, compensatory responses among species (Givnish 1994, Huston 1997). (B) Standard deviation (SD) of net ecosystem CO2 flux in a microbial microcosm (the figure is from McGrady-Steed et al. [1997]). The decrease in variability with increasing diversity may result from both decreased temporal variability and increased compositional similarity among replicates. See also Morin and McGrady-Steed (2004). Composite figure after Loreau et al. (2001).
    FIG. 5. Increasing stability with increasing species richness in ecological experiments. In both cases, the overall patterns are as predicted from theory, but the underlying mechanisms may coincide only in part (see Section II.B.2). (A) Temporal variability (coefficient of variation, CV) in aboveground plant biomass (correlated with productivity in these Minnesota grasslands) in response to climatic variability (the figure is from Tilman [1999]). The gradient in species richness results from different levels of nutrient addition, so that the stability response may result from differences in species composition instead of, or in addition to, compensatory responses among species (Givnish 1994, Huston 1997). (B) Standard deviation (SD) of net ecosystem CO2 flux in a microbial microcosm (the figure is from McGrady-Steed et al. [1997]). The decrease in variability with increasing diversity may result from both decreased temporal variability and increased compositional similarity among replicates. See also Morin and McGrady-Steed (2004). Composite figure after Loreau et al. (2001).
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Topics: Ecosystem services (65%), Ecosystem health (64%), Ecological network (63%) ...read more

6,315 Citations


Journal ArticleDOI: 10.1086/281792
Abstract: In recent years the attention of experimental evolutionists has been increasingly directed toward polymorphism as furnishing desirable plasticity to a species. In particular, attention has been directed toward polymorphism with a known genetic basis. The best studied case is that of two alleles showing balanced polymorphismn: that is, the heterozygote has a higher adaptive value in a certain environment or range of environments than either homozygote. Such balanced polymorphism is the only way a pair of alleles can remain in equilibrium within a single environment (or ecological niche), if we ignore mutation pressure and migration from the outside. Onthe other hand, it would seem that the existence of several ecological niches, with one allele favored in one niche and the other allele favored in another, might increase the possibilities for attainment of equilibrium with both alleles present in substantial proportions. Recently the question arose of whether it was in fact possible to have equilibrium without the heterozygote being superior to both homozygotes in any single niche. It is shown below that under certain assumptions the answer is yes. The model here proposed is as follows: Let there be alleles A and A' with gene frequencies of q and 1 q respectively, and let mating be at random over the whole population, so that the initial zygotic frequencies are q2AA, 2q(1 -q)AA'j and (1 q)2AA'. After fertilization the zygotes settle down at random in large numbers into each of the niches, and are thereafter immobile. There is then differential mortality ending with a fixed number of individuals in each niche. After selection the relative frequencies of AA, AA', and A'A'will be Wjq2:2q(1 ~-q):Vj(1 -q)3 in niche 1, W2q2:2q(1-q):V2(1 -q)a in the second niche, etc., where W1l and V1 are the adaptive values of AA and A'A'individuals relative to AA'in the i-th niche. We need consider only intra-niche comparisons and not the absolute viabilities in the different niches. If we disregard drift and consider only the force of selection, the absolute number of survivors in the different niches is also irrelevant and we may work with the numbers cl, where ci is the proportion of the total survivors to be found in the i-th niche, and =ci = 1. To complete the model, we suppose that at the time of reproduction the survivors leave the niches, and that mating is at random in the entire population. If we denote by q'the frequency of A in this mating popu-

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Topics: Ecological niche (74%), Environmental niche modelling (69%), Niche segregation (68%) ...read more

1,245 Citations


Open accessJournal ArticleDOI: 10.1073/PNAS.0706375104
Abstract: In natural communities, species and their interactions are often organized as nonrandom networks, showing distinct and repeated complex patterns. A prevalent, but poorly explored pattern is ecological modularity, with weakly interlinked subsets of species (modules), which, however, internally consist of strongly connected species. The importance of modularity has been discussed for a long time, but no consensus on its prevalence in ecological networks has yet been reached. Progress is hampered by inadequate methods and a lack of large datasets. We analyzed 51 pollination networks including almost 10,000 species and 20,000 links and tested for modularity by using a recently developed simulated annealing algorithm. All networks with >150 plant and pollinator species were modular, whereas networks with <50 species were never modular. Both module number and size increased with species number. Each module includes one or a few species groups with convergent trait sets that may be considered as coevolutionary units. Species played different roles with respect to modularity. However, only 15% of all species were structurally important to their network. They were either hubs (i.e., highly linked species within their own module), connectors linking different modules, or both. If these key species go extinct, modules and networks may break apart and initiate cascades of extinction. Thus, species serving as hubs and connectors should receive high conservation priorities.

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1,178 Citations


Journal ArticleDOI: 10.1126/SCIENCE.1188321
13 Aug 2010-Science
Abstract: Research on the relationship between the architecture of ecological networks and community stability has mainly focused on one type of interaction at a time, making difficult any comparison between different network types. We used a theoretical approach to show that the network architecture favoring stability fundamentally differs between trophic and mutualistic networks. A highly connected and nested architecture promotes community stability in mutualistic networks, whereas the stability of trophic networks is enhanced in compartmented and weakly connected architectures. These theoretical predictions are supported by a meta-analysis on the architecture of a large series of real pollination (mutualistic) and herbivory (trophic) networks. We conclude that strong variations in the stability of architectural patterns constrain ecological networks toward different architectures, depending on the type of interaction.

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Topics: Ecological network (59%)

1,101 Citations


Open accessJournal ArticleDOI: 10.1111/J.1469-185X.2012.00235.X
Mary S. Wisz1, Julien Pottier2, W. Daniel Kissling1, Loïc Pellissier2  +21 moreInstitutions (9)
01 Feb 2013-Biological Reviews
Abstract: Predicting which species will occur together in the future, and where, remains one of the greatest challenges in ecology, and requires a sound understanding of how the abiotic and biotic environments interact with dispersal processes and history across scales. Biotic interactions and their dynamics influence species' relationships to climate, and this also has important implications for predicting future distributions of species. It is already well accepted that biotic interactions shape species' spatial distributions at local spatial extents, but the role of these interactions beyond local extents (e.g. 10 km2 to global extents) are usually dismissed as unimportant. In this review we consolidate evidence for how biotic interactions shape species distributions beyond local extents and review methods for integrating biotic interactions into species distribution modelling tools. Drawing upon evidence from contemporary and palaeoecological studies of individual species ranges, functional groups, and species richness patterns, we show that biotic interactions have clearly left their mark on species distributions and realised assemblages of species across all spatial extents. We demonstrate this with examples from within and across trophic groups. A range of species distribution modelling tools is available to quantify species environmental relationships and predict species occurrence, such as: (i) integrating pairwise dependencies, (ii) using integrative predictors, and (iii) hybridising species distribution models (SDMs) with dynamic models. These methods have typically only been applied to interacting pairs of species at a single time, require a priori ecological knowledge about which species interact, and due to data paucity must assume that biotic interactions are constant in space and time. To better inform the future development of these models across spatial scales, we call for accelerated collection of spatially and temporally explicit species data. Ideally, these data should be sampled to reflect variation in the underlying environment across large spatial extents, and at fine spatial resolution. Simplified ecosystems where there are relatively few interacting species and sometimes a wealth of existing ecosystem monitoring data (e.g. arctic, alpine or island habitats) offer settings where the development of modelling tools that account for biotic interactions may be less difficult than elsewhere.

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Topics: Non-trophic networks (64%), Species richness (62%), Ecological network (61%) ...read more

1,100 Citations


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No. of papers in the topic in previous years
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20221
2021191
2020163
2019158
2018140
2017147

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