Ecology Letters (2011) 14: 1170–1181
Interactions among species drive the ecological and evolutionary processes in ecological communities. These interactions are effectively key components of ...biodiversity. Studies that use a network approach to study the structure and dynamics of communities of interacting species have revealed many patterns and associated processes. Historically these studies were restricted to trophic interactions, although network approaches are now used to study a wide range of interactions, including for example the reproductive mutualisms. However, each interaction type remains studied largely in isolation from others. Merging the various interaction types within a single integrative framework is necessary if we want to further our understanding of the ecological and evolutionary dynamics of communities. Dividing the networks up is a methodological convenience as in the field the networks occur together in space and time and will be linked by shared species. Herein, we outline a conceptual framework for studying networks composed of more than one type of interaction, highlighting key questions and research areas that would benefit from their study.
Current species extinction rates are at unprecedentedly high levels. While human activities can be the direct cause of some extinctions, it is becoming increasingly clear that species extinctions ...themselves can be the cause of further extinctions, since species affect each other through the network of ecological interactions among them. There is concern that the simplification of ecosystems, due to the loss of species and ecological interactions, increases their vulnerability to such secondary extinctions. It is predicted that more complex food webs will be less vulnerable to secondary extinctions due to greater trophic redundancy that can buffer against the effects of species loss. Here, we demonstrate in a field experiment with replicated plant-insect communities, that the probability of secondary extinctions is indeed smaller in food webs that include trophic redundancy. Harvesting one species of parasitoid wasp led to secondary extinctions of other, indirectly linked, species at the same trophic level. This effect was markedly stronger in simple communities than for the same species within a more complex food web. We show that this is due to functional redundancy in the more complex food webs and confirm this mechanism with a food web simulation model by highlighting the importance of the presence and strength of trophic links providing redundancy to those links that were lost. Our results demonstrate that biodiversity loss, leading to a reduction in redundant interactions, can increase the vulnerability of ecosystems to secondary extinctions, which, when they occur, can then lead to further simplification and run-away extinction cascades.
Resource–consumer interactions are considered a major driving force of population and community dynamics. However, species also interact in many non‐trophic and indirect ways and it is currently not ...known to what extent the dynamic coupling of species corresponds to the distribution of trophic links. Here, using a 10‐year data set of monthly observations of a 40‐species tri‐trophic insect community and nonlinear time series analysis, we compare the occurrence and strengths of both the trophic and dynamic interactions in the insect community. The matching between observed trophic and dynamic interactions provides evidence that population dynamic interactions reflect resource–consumer interactions in the many‐species community. However, the presence of a trophic interaction does not always correspond to a detectable dynamic interaction especially for top‐down effects. Moreover a considerable proportion of dynamic interactions are not attributable to direct trophic interactions, suggesting the unignorable role of non‐trophic and indirect interactions as co‐drivers of community dynamics.
It has not been known to what extent the dynamic coupling of species corresponds to the distribution of trophic links in nature. A 10‐year observations of a 40‐species tri‐trophic insect community and nonlinear time series analysis reveal that trophic interactions would not be sufficient for understanding the dynamics of multi‐trophic communities.
Artificial light has transformed the nighttime environment of large areas of the earth, with 88% of Europe and almost 50% of the United States experiencing light-polluted night skies 1. The ...consequences for ecosystems range from exposure to high light intensities in the vicinity of direct light sources to the very widespread but lower lighting levels further away 2. While it is known that species exhibit a range of physiological and behavioral responses to artificial nighttime lighting e.g., 3–5, there is a need to gain a mechanistic understanding of whole ecological community impacts 6, 7, especially to different light intensities. Using a mesocosm field experiment with insect communities, we determined the impact of intensities of artificial light ranging from 0.1 to 100 lux on different trophic levels and interactions between species. Strikingly, we found the strongest impact at low levels of artificial lighting (0.1 to 5 lux), which led to a 1.8 times overall reduction in aphid densities. Mechanistically, artificial light at night increased the efficiency of parasitoid wasps in attacking aphids, with twice the parasitism rate under low light levels compared to unlit controls. However, at higher light levels, parasitoid wasps spent longer away from the aphid host plants, diminishing this increased efficiency. Therefore, aphids reached higher densities under increased light intensity as compared to low levels of lighting, where they were limited by higher parasitoid efficiency. Our study highlights the importance of different intensities of artificial light in driving the strength of species interactions and ecosystem functions.
•Artificial light at night, at varying intensities, is globally widespread•Intensity of artificial light determines the community response in an insect food web•Impacts of artificial light on interactions between species may be very common
Sanders et al. demonstrate how different intensities of artificial light at night change interactions in experimental insect food webs between aphids and parasitoid wasps as their natural enemies. Major food web parameters such as parasitism rate, aphid abundance, and plant biomass were correlated with light intensity, highlighting that outcomes for ecological communities depend very much on the intensity of this widespread human impact.
Uncovering the processes that shape the architecture of interaction networks is a major challenge in ecology. Studies have consistently revealed that more closely related taxa tend to show greater ...overlap in interaction partners, fuelling the idea that interactions are phylogenetically conserved 1–8. However, local ecological processes such as exploitative or apparent competition (indirect interactions) might instead cause a decrease in overlap in interacting partners. Because of the taxonomic and geographic coarseness of existing studies 2–5, 7, the structuring effect of such processes has been overlooked. Here, we assess the relative importance of phylogeny and ecological processes in a local, highly resolved, four-level antagonistic network. Across all network levels we consistently find that phylogenetic relatedness among resource species is correlated with consumer overlap but that phylogenetic relatedness among consumer species is not or negatively correlated with resource overlap. This pervasive pattern indicates that the antagonistic network has been shaped by both phylogeny on resource range and by exploitative competition limiting resource overlap among closely related consumer species. Intriguingly, the strength of phylogenetic signal varies in a consistent way across the network levels. We discuss the generality of our findings and their implications in a changing world.
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•Related “resource” species tend to be consumed by the same “consumer” species•Related consumer species tend to consume different resource species•The strength of this pattern varies consistently across antagonistic networks•Such networks are shaped by phylogeny and exploitative competition
The diversity and complexity of food webs (the networks of feeding relationships within an ecological community) are considered to be important factors determining ecosystem function and stability. ...However, the biological processes driving these factors are poorly understood. Resource quality affects species interactions by limiting energy transfer to consumers and their predators, affecting life history and morphological traits. We show that differences in plant traits affect the structure of an entire food web through a series of direct and indirect effects. Three trophic levels of consumers were influenced by plant quality, as shown by quantitative herbivore-parasitoid-secondary parasitoid food webs. We conclude, on the basis of our data, that changes in the food web are dependent on both trait- and density-mediated interactions among species.
Ecological networks -beyond food webs INGS, Thomas C; MONTOYA, José M; LAURIDSEN, Rasmus B ...
The Journal of animal ecology,
2009, 2009-Jan, 20090101, Letnik:
78, Številka:
1
Journal Article
Recenzirano
1. A fundamental goal of ecological network research is to understand how the complexity observed in nature can persist and how this affects ecosystem functioning. This is essential for us to be able ...to predict, and eventually mitigate, the consequences of increasing environmental perturbations such as habitat loss, climate change, and invasions of exotic species. 2. Ecological networks can be subdivided into three broad types: 'traditional' food webs, mutualistic networks and host-parasitoid networks. There is a recent trend towards cross-comparisons among network types and also to take a more mechanistic, as opposed to phenomenological, perspective. For example, analysis of network configurations, such as compartments, allows us to explore the role of co-evolution in structuring mutualistic networks and host-parasitoid networks, and of body size in food webs. 3. Research into ecological networks has recently undergone a renaissance, leading to the production of a new catalogue of evermore complete, taxonomically resolved, and quantitative data. Novel topological patterns have been unearthed and it is increasingly evident that it is the distribution of interaction strengths and the configuration of complexity, rather than just its magnitude, that governs network stability and structure. 4. Another significant advance is the growing recognition of the importance of individual traits and behaviour: interactions, after all, occur between individuals. The new generation of high-quality networks is now enabling us to move away from describing networks based on species-averaged data and to start exploring patterns based on individuals. Such refinements will enable us to address more general ecological questions relating to foraging theory and the recent metabolic theory of ecology. 5. We conclude by suggesting a number of 'dead ends' and 'fruitful avenues' for future research into ecological networks.
Animals often engage in mutualistic associations with microorganisms that protect them from predation, parasitism or pathogen infection. Studies of these interactions in insects have mostly focussed ...on the direct effects of symbiont infection on natural enemies without studying community‐wide effects. Here, we explore the effect of a defensive symbiont on population dynamics and species extinctions in an experimental community composed of three aphid species and their associated specialist parasitoids. We found that introducing a bacterial symbiont with a protective (but not a non‐protective) phenotype into one aphid species led to it being able to escape from its natural enemy and increase in density. This changed the relative density of the three aphid species which resulted in the extinction of the two other parasitoid species. Our results show that defensive symbionts can cause extinction cascades in experimental communities and so may play a significant role in the stability of consumer‐herbivore communities in the field.
Species extinctions are biased towards higher trophic levels, and primary extinctions are often followed by unexpected secondary extinctions. Currently, predictions on the vulnerability of ecological ...communities to extinction cascades are based on models that focus on bottom‐up effects, which cannot capture the effects of extinctions at higher trophic levels. We show, in experimental insect communities, that harvesting of single carnivorous parasitoid species led to a significant increase in extinction rate of other parasitoid species, separated by four trophic links. Harvesting resulted in the release of prey from top‐down control, leading to increased interspecific competition at the herbivore trophic level. This resulted in increased extinction rates of non‐harvested parasitoid species when their host had become rare relative to other herbivores. The results demonstrate a mechanism for horizontal extinction cascades, and illustrate that altering the relationship between a predator and its prey can cause wide‐ranging ripple effects through ecosystems, including unexpected extinctions.
Species extinction rates due to human activities are high 1–3, and initial extinctions can trigger cascades of secondary extinctions, leading to further erosion of biodiversity 4. A potential major ...mechanism for secondary extinction cascades is provided by the long-standing theory that the diversity of consumer species is maintained due to the positive indirect effects that these species have on each other by reducing competition among their respective resource species 5–7. This means that the loss of one carnivore species could lead to competitive exclusion at the prey trophic level, leading to extinctions of further carnivore species. Evidence for these effects is difficult to obtain due to many confounding factors in natural systems, but extinction cascades that could be due to this mechanism have been demonstrated in simplified laboratory microcosms 8. We established complex insect food webs in replicated field mesocosms and found that the overharvesting of one parasitoid wasp species caused increased extinction rates of other parasitoid species, compared to controls, but only when we manipulated the spatial distribution of herbivore species such that the potential for interspecific competition at this level was high. This provides clear evidence for horizontal extinction cascades at high trophic levels due to the proposed mechanism. Our results demonstrate that the loss of carnivores can have widespread effects on other species at the same trophic level due to indirect population-dynamic effects that are rarely considered in this context.
•Initial carnivore extinctions can trigger extinctions of other carnivore species•An experiment shows that these effects are transmitted by competition among hosts/prey•These population-dynamic processes can be major drivers of extinction cascades
Sanders et al. demonstrate the mechanisms for horizontal extinction cascades at high trophic levels in a field experiment. They show that the loss of carnivores can increase extinction rates of other species at the same trophic level due to indirect population-dynamic effects that are rarely considered in this context.
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