Journal articles
Sanders D, Frago E, Kehoe R, Patterson C, Gaston K (In Press). A meta-analysis of biological impacts of artificial light at night. Nature Ecology and Evolution
Sanders D, Kehoe R, Cruse D, Van Veen F, Gaston KJ (In Press). Low levels of artificial light at night strengthen top-down control in insect food web. Current Biology
Gaston K, Ackermann S, Bennie J, Cox D, Phillips B, Sanchez De Miguel A, Sanders D (In Press). Pervasiveness of biological impacts of artificial light at night. Integrative and Comparative Biology
Tougeron K, Sanders D (2023). Combined light pollution and night warming as a novel threat to ecosystems.
Trends Ecol Evol,
38(8), 701-704.
Abstract:
Combined light pollution and night warming as a novel threat to ecosystems.
Artificial light at night (ALAN) and night-time warming (NW) are a combined threat altering the night-time environment and the behaviour and physiology of organisms. Impacts on fitness and the nocturnal niche have knock-on effects for ecosystem structure and function. Understanding the way both stressors interact is critical for making ecological predictions.
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Sanders D, Hirt MR, Brose U, Evans DM, Gaston KJ, Gauzens B, Ryser R (2023). How artificial light at night may rewire ecological networks: concepts and models.
Philos Trans R Soc Lond B Biol Sci,
378(1892).
Abstract:
How artificial light at night may rewire ecological networks: concepts and models.
Artificial light at night (ALAN) is eroding natural light cycles and thereby changing species distributions and activity patterns. Yet little is known about how ecological interaction networks respond to this global change driver. Here, we assess the scientific basis of the current understanding of community-wide ALAN impacts. Based on current knowledge, we conceptualize and review four major pathways by which ALAN may affect ecological interaction networks by (i) impacting primary production, (ii) acting as an environmental filter affecting species survival, (iii) driving the movement and distribution of species, and (iv) changing functional roles and niches by affecting activity patterns. Using an allometric-trophic network model, we then test how a shift in temporal activity patterns for diurnal, nocturnal and crepuscular species impacts food web stability. The results indicate that diel niche shifts can severely impact community persistence by altering the temporal overlap between species, which leads to changes in interaction strengths and rewiring of networks. ALAN can thereby lead to biodiversity loss through the homogenization of temporal niches. This integrative framework aims to advance a predictive understanding of community-level and ecological-network consequences of ALAN and their cascading effects on ecosystem functioning. This article is part of the theme issue 'Light pollution in complex ecological systems'.
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Zhong Z, Li G, Sanders D, Wang D, Holt RD, Zhang Z (2022). A rodent herbivore reduces its predation risk through ecosystem engineering.
Curr Biol,
32(8), 1869-1874.e4.
Abstract:
A rodent herbivore reduces its predation risk through ecosystem engineering.
Predator-prey interactions are ubiquitous and powerful forces that structure ecological communities.1-3 Habitat complexity has been shown to be particularly important in regulating the strength of predator-prey interactions.4-6 While it is well established that changes in habitat structure can alter the efficacy of predatory and anti-predatory behaviors,7-9 little is known about the consequences of engineering activity by prey species who modify the external environment to reduce their own predation risk. Using field surveys and manipulative experiments, we evaluated how habitat modification by Brandt's voles (Lasiopodomys brandtii) influences predation risk from a principal avian predator (shrike; Lanius spp.) in a steppe grassland, located in Inner Mongolia, China. We found that voles actively modify habitat structure by cutting down a large, unpalatable bunchgrass species (Achnatherum splendens) in the presence of shrikes, a behavior that disappeared when these avian predators were excluded experimentally. The damage activities of these voless dramatically decreased the volume of unpalatable grasses, which in turn reduced visitations by shrikes and thus mortality rates. Our study shows that herbivorous prey that act as ecosystem engineers can directly reduce their own predation risk by modifying habitat structure. Given the ubiquity of predation risks faced by consumers, and the likely ability of many consumers to alter the habitat structure in which they live, the interplay between predation risk and ecosystem engineering may be an important but unappreciated mechanism at play in natural communities.
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Newbury A, Dawson B, Klümper U, Hesse E, Castledine M, Fontaine C, Buckling A, Sanders D (2022). Fitness effects of plasmids shape the structure of bacteria-plasmid interaction networks.
Proc Natl Acad Sci U S A,
119(22).
Abstract:
Fitness effects of plasmids shape the structure of bacteria-plasmid interaction networks.
Antimicrobial resistance (AMR) genes are often carried on broad host range plasmids, and the spread of AMR within microbial communities will therefore depend on the structure of bacteria–plasmid networks. Empirical and theoretical studies of ecological interaction networks suggest that network structure differs between communities that are predominantly mutualistic versus antagonistic, with the former showing more generalized interactions (i.e. species interact with many others to a similar extent). This suggests that mutualistic bacteria–plasmid networks—where antibiotics are present and plasmids carry AMR genes—will be more generalized than antagonistic interactions, where plasmids do not confer benefits to their hosts. We first develop a simple theory to explain this link: fitness benefits of harboring a mutualistic symbiont promote the spread of the symbiont to other species. We find support for this theory using an experimental bacteria–symbiont (plasmid) community, where the same plasmid can be mutualistic or antagonistic depending on the presence of antibiotics. This short-term and parsimonious mechanism complements a longer-term mechanism (coevolution and stability) explaining the link between mutualistic and antagonistic interactions and network structure.
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Sanders D, Baker DJ, Cruse D, Bell F, van Veen FJF, Gaston KJ (2022). Spectrum of artificial light at night drives impact of a diurnal species in insect food web.
Sci Total Environ,
831Abstract:
Spectrum of artificial light at night drives impact of a diurnal species in insect food web.
Artificial light at night (ALAN) has become a profound form of global anthropogenic environmental change differing in from natural light regimes in intensity, duration, distribution and spectra. It is clear that ALAN impacts individual organisms, however, population level effects, particularly of spectral changes, remain poorly understood. Here we exposed experimental multigenerational aphid-parasitoid communities in the field to seven different light spectra at night ranging from 385 to 630 nm and compared responses to a natural day-night light regime. We found that while aphid population growth was initially unaffected by ALAN, parasitoid efficiency declined under most ALAN spectra, leading to reduced top-down control and higher aphid densities. These results differ from those previously found for white light, showing a strong impact on species' daytime performance. This highlights the importance of ALAN spectra when considering their environmental impact. ALAN can have large impacts on the wider ecological community by influencing diurnal species.
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Kehoe R, Sanders D, van Veen FJ (2022). Towards a mechanistic understanding of the effects of artificial light at night on insect populations and communities.
Curr Opin Insect Sci,
53Abstract:
Towards a mechanistic understanding of the effects of artificial light at night on insect populations and communities.
Artificial light at night (ALAN) is markedly changing the night-time environment with many studies showing single-species responses. Exposure to ALAN can lead to population declines that should have consequences for the functioning and stability of ecological communities. Here, we summarise current knowledge on how insect communities are affected by ALAN. Based on reported effects of ALAN on the interactions between species, and what has been demonstrated for similar effects in other contexts, we argue that direct effects of ALAN on a few species can potentially propagate through the network of species interactions to have widespread effects in ecological communities. This can lead to a shift in community structure and simplified communities. We discuss the diversity of ALAN as a pressure and highlight major gaps in the research field. In particular, we conclude that landscape level impacts on populations and communities are understudied.
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Li X, Risch AC, Sanders D, Liu G, Prather C, Wang Z, Hassan N, Gao Q, Wang D, Zhong Z, et al (2021). A facilitation between large herbivores and ants accelerates litter decomposition by modifying soil microenvironmental conditions.
FUNCTIONAL ECOLOGY,
35(8), 1822-1832.
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Kehoe R, Frago E, Sanders D (2021). Cascading extinctions as a hidden driver of insect decline.
Ecological Entomology,
46(4), 743-756.
Abstract:
Cascading extinctions as a hidden driver of insect decline
1. The decline in insect abundance and diversity observed in many ecosystems is of major concern because of the long-term consequences for ecosystem function and stability. 2. Species in ecological communities are connected through interactions forming complex networks. Therefore, initial extinctions can cause further species losses through co-extinctions and extinction cascades, where single extinctions can lead to waves of secondary extinctions. Such knock-on effects can multiply the initial impact of disturbances, thereby largely adding to the erosion of biodiversity. However, our knowledge of their importance for the current insect decline is hampered because secondary extinctions are challenging to both detect and predict. 3. In this review, we bring together theory and knowledge about secondary extinctions in the light of the main drivers of insect decline. We evaluate potential and evidence for cascading extinction for the different drivers and identify major pathways. By providing selected examples we discuss how habitat loss, pollution, species invasions, climate change and overexploitation can cause cascading extinctions. We argue that habitat loss and pollution in particular have the largest potential for such extinctions by changing community structure, the physical environment, and community robustness. 4. Overall, cascading extinction are part of an ecosystems' response to anthropogenic drivers but are so far not explicitly measured in their contribution when evaluating biodiversity loss. This knowledge is necessary to predict biodiversity loss and find strategies to buffer against the devastating long-term impact of habitat loss, pollution, species invasions, and climate change.
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Zhong Z, Li X, Sanders D, Liu Y, Wang L, Ortega YK, Pearson DE, Wang D (2021). Soil engineering by ants facilitates plant compensation for large herbivore removal of aboveground biomass.
Ecology,
102(5).
Abstract:
Soil engineering by ants facilitates plant compensation for large herbivore removal of aboveground biomass.
The interplay between top-down and bottom-up processes determines ecosystem productivity. Yet, the factors that mediate the balance between these opposing forces remain poorly understood. Furthering this challenge, complex and often cryptic factors like ecosystem engineering and trait-mediated interactions may play major roles in mediating the outcomes of top-down and bottom-up interactions. In semiarid grasslands of northeastern China, we conducted a large-scale, three-year experiment to evaluate how soil engineering by ants and plasticity in plants independently and jointly influenced the top-down effects of grazing by a ubiquitous herbivore (cattle) on aboveground standing biomass of the dominant perennial grass, Leymus chinensis. Herbivory had strong top-down effects, reducing L. chinensis AB by 25% relative to baseline levels without cattle or ants. In contrast, soil engineering by ants facilitated weak bottom-up effects in the absence of herbivory. However, in the presence of herbivory, soil engineering effects were strong enough to fully offset herbivore removal of aboveground biomass. This outcome was mediated by L. chinensis's plasticity in reallocating growth from below- to aboveground biomass, a result linked to additive effects of engineers and herbivores increasing soil N availability and engineering effects improving soil structure. Soil engineering increased soil N by 12%, promoting aboveground biomass. Herbivores increased soil N by 13% via defecation, but this increase failed to offset their reductions in aboveground biomass in isolation. However, when combined, engineers and herbivores increased soil N by 26% and engineers improved soil bulk density, facilitating L. chinensis to shift resource allocations from below- to aboveground biomass sufficiently to fully offset herbivore suppression of aboveground biomass. Our results demonstrate that soil engineering and trait-mediated effects of plant plasticity can strongly mediate the outcome of top-down and bottom-up interactions. These cryptic but perhaps ubiquitous processes may help to explain the long-debated phenomenon of plant compensatory responses to large grazers.
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Hesse E, O'Brien S, Lujan AM, Sanders D, Bayer F, Veen EM, Hodgson DJ, Buckling A (2021). Stress causes interspecific facilitation within a compost community.
ECOLOGY LETTERS,
24(10), 2169-2177.
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Kehoe R, Sanders D, Cruse D, Silk M, Gaston KJ, Bridle JR, van Veen F (2020). Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host–parasitoid interaction strength.
Journal of Animal Ecology,
89(11), 2508-2516.
Abstract:
Longer photoperiods through range shifts and artificial light lead to a destabilizing increase in host–parasitoid interaction strength
Abstract
Many organisms are experiencing changing daily light regimes due to latitudinal range shifts driven by climate change and increased artificial light at night (ALAN). Activity patterns are often driven by light cycles, which will have important consequences for species interactions.
We tested whether longer photoperiods lead to higher parasitism rates by a day‐active parasitoid on its host using a laboratory experiment in which we independently varied daylength and the presence of ALAN. We then tested whether reduced nighttime temperature tempers the effect of ALAN.
We found that parasitism rate increased with daylength, with ALAN intensifying this effect only when the temperature was not reduced at night. The impact of ALAN was more pronounced under short daylength. Increased parasitoid activity was not compensated for by reduced life span, indicating that increased daylength leads to an increase in total parasitism effects on fitness.
To test the significance of increased parasitism rate for population dynamics, we developed a host–parasitoid model. The results of the model predicted an increase in time‐to‐equilibrium with increased daylength and, crucially, a threshold daylength above which interactions are unstable, leading to local extinctions.
Here we demonstrate that ALAN impact interacts with daylength and temperature by changing the interaction strength between a common day‐active consumer species and its host in a predictable way. Our results further suggest that range expansion or ALAN‐induced changes in light regimes experienced by insects and their natural enemies will result in unstable dynamics beyond key tipping points in daylength.
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Sanders D, Gaston KJ (2018). How ecological communities respond to artificial light at night.
J Exp Zool a Ecol Integr Physiol,
329(8-9), 394-400.
Abstract:
How ecological communities respond to artificial light at night.
Many ecosystems worldwide are exposed to artificial light at night (ALAN), from streetlights and other sources, and a wide range of organisms has been shown to respond to this anthropogenic pressure. This raises concerns about the consequences for major ecosystem functions and their stability. However, there is limited understanding of how whole ecological communities respond to ALAN, and this cannot be gained simply by making predictions from observed single species physiological, behavioral, or ecological responses. Research needs to include an important building block of ecological communities, namely the interactions between species that drive ecological and evolutionary processes in ecosystems. Here, we summarize current knowledge about community responses to ALAN and illustrate different pathways and their impact on ecosystem functioning and stability. We discuss that documentation of the impact of ALAN on species interaction networks and trait distributions provides useful tools to link changes in community structure to ecosystem functions. Finally, we suggest several approaches to advance research that will link the diverse impact of ALAN to changes in ecosystems.
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Perkins MJ, Inger R, Bearhop S, Sanders D (2018). Multichannel feeding by spider functional groups is driven by feeding strategies and resource availability.
Oikos,
127(1), 23-33.
Abstract:
Multichannel feeding by spider functional groups is driven by feeding strategies and resource availability
Multichannel feeding, whereby consumers feed across resource channels such as upon herbivore and detritivore resources, acts to link discrete compartments of a food web with implications for ecosystem functioning and stability. Currently however, we have little understanding which feeding strategies of consumers underlie multichannel feeding. We therefore link spider functional group and resource density-dependent or density-independent feeding strategies to multichannel feeding by quantifying not only consumer diet, but also the relative availability of resources. Here we analysed herbivore (green) and detritivore (brown) prey use by spider communities in grasslands, and tested if available prey biomass proportions were linked to observed spider dietary proportions. Different spider functional groups each linked green and brown resource channels, but while green prey were always consumed in proportion to their relative biomass, brown prey were consumed independently of proportion by some functional groups. Additionally, we found greater intraguild predation by cursorial spiders when green resources were relatively scarcer, suggesting green prey was preferred, and needed to be compensated for when rare. Overall, we observed a stronger consumer connection to the green than brown resource channel, yet this green connection was more variable due to greater range in green resource availability across grasslands and density-dependent consumption on green prey. Consequently, multichannel feeding by spiders was determined by density-dependent and density-independent feeding strategies that varied by spider functional group and across resources channels. Our results demonstrate that the role of multichannel feeding by spiders in linking separate food web compartments is a dynamic component of food web structure in these wild grasslands.
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Li X, Zhong Z, Sanders D, Smit C, Wang D, Nummi P, Zhu Y, Wang L, Zhu H, Hassan N, et al (2018). Reciprocal facilitation between large herbivores and ants in a semi-arid grassland.
Proc Biol Sci,
285(1888).
Abstract:
Reciprocal facilitation between large herbivores and ants in a semi-arid grassland.
While positive interactions have been well documented in plant and sessile benthic marine communities, their role in structuring mobile animal communities and underlying mechanisms has been less explored. Using field removal experiments, we demonstrated that a large vertebrate herbivore (cattle; Bos tarurs) and a much smaller invertebrate (ants; Lasius spp.), the two dominant animal taxa in a semi-arid grassland in Northeast China, facilitate each other. Cattle grazing led to higher ant mound abundance compared with ungrazed sites, while the presence of ant mounds increased the foraging of cattle during the peak of the growing season. Mechanistically, these reciprocal positive effects were driven by habitat amelioration and resource (food) enhancement by cattle and ants (respectively). Cattle facilitated ants, probably by decreasing plant litter accumulation by herbivory and trampling, allowing more light to reach the soil surface leading to microclimatic conditions that favour ants. Ants facilitated cattle probably by increasing soil nutrients via bioturbation, increasing food (plant) biomass and quality (nitrogen content) for cattle. Our study demonstrates reciprocal facilitative interactions between two animal species from phylogenetically very distant taxa. Such reciprocal positive interactions may be more common in animal communities than so far assumed, and they should receive more attention to improve our understanding of species coexistence and animal community assembly.
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Kehoe RC, Cruse D, Sanders D, Gaston KJ, van Veen FJF (2018). Shifting daylength regimes associated with range shifts alter aphid-parasitoid community dynamics.
Ecology and Evolution,
8(17), 8761-8769.
Abstract:
Shifting daylength regimes associated with range shifts alter aphid-parasitoid community dynamics
With climate change leading to poleward range expansion of species, populations are exposed to new daylength regimes along latitudinal gradients. Daylength is a major factor affecting insect life cycles and activity patterns, so a range shift leading to new daylength regimes is likely to affect population dynamics and species interactions; however, the impact of daylength in isolation on ecological communities has not been studied so far. Here, we tested for the direct and indirect effects of two different daylengths on the dynamics of experimental multitrophic insect communities. We compared the community dynamics under “southern” summer conditions of 14.5-hr daylight to “northern” summer conditions of 22-hr daylight. We show that food web dynamics indeed respond to daylength with one aphid species (Acyrthosiphon pisum) reaching much lower population sizes at the northern daylength regime compared to under southern conditions. In contrast, in the same communities, another aphid species (Megoura viciae) reached higher population densities under northern conditions. This effect at the aphid level was driven by an indirect effect of daylength causing a change in competitive interaction strengths, with the different aphid species being more competitive at different daylength regimes. Additionally, increasing daylength also increased growth rates in M. viciae making it more competitive under summer long days. As such, the shift in daylength affected aphid population sizes by both direct and indirect effects, propagating through species interactions. However, contrary to expectations, parasitoids were not affected by daylength. Our results demonstrate that range expansion of whole communities due to climate change can indeed change interaction strengths between species within ecological communities with consequences for community dynamics. This study provides the first evidence of daylength affecting community dynamics, which could not be predicted from studying single species separately.
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Sanders D, Kehoe R, Thebault E, Van Veen FJF (2018). Trophic redundancy reduces vulnerability to extinction cascades. Proceedings of the National Academy of Sciences
Zhong Z, Li X, Pearson D, Wang D, Sanders D, Zhu Y, Wang L (2017). Ecosystem engineering strengthens bottom-up and weakens top-down effects via trait-mediated indirect interactions.
Proc Biol Sci,
284(1863).
Abstract:
Ecosystem engineering strengthens bottom-up and weakens top-down effects via trait-mediated indirect interactions.
Trophic interactions and ecosystem engineering are ubiquitous and powerful forces structuring ecosystems, yet how these processes interact to shape natural systems is poorly understood. Moreover, trophic effects can be driven by both density- and trait-mediated interactions. Microcosm studies demonstrate that trait-mediated interactions may be as strong as density-mediated interactions, but the relative importance of these pathways at natural spatial and temporal scales is underexplored. Here, we integrate large-scale field experiments and microcosms to examine the effects of ecosystem engineering on trophic interactions while also exploring how ecological scale influences density- and trait-mediated interaction pathways. We demonstrate that (i) ecosystem engineering can shift the balance between top-down and bottom-up interactions, (ii) such effects can be driven by cryptic trait-mediated interactions, and (iii) the relative importance of density- versus trait-mediated interaction pathways can be scale dependent. Our findings reveal the complex interplay between ecosystem engineering, trophic interactions, and ecological scale in structuring natural systems.
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Sanders D, Kehoe R, van Veen FF, McLean A, Godfray HCJ, Dicke M, Gols R, Frago E (2016). Defensive insect symbiont leads to cascading extinctions and community collapse.
Ecol Lett,
19(7), 789-799.
Abstract:
Defensive insect symbiont leads to cascading extinctions and community collapse.
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.
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Turrini T, Sanders D, Knop E (2016). Effects of urbanization on direct and indirect interactions in a tri-trophic system.
Ecological Applications,
26(3), 664-675.
Abstract:
Effects of urbanization on direct and indirect interactions in a tri-trophic system
© 2016 by the Ecological Society of America. While effects of urbanization on species assemblages are receiving increasing attention, effects on ecological interactions remain largely unexplored. We investigated how urbanization influences the strength of direct and indirect trophic interactions in a tritrophic system. In a field experiment including five cities and nearby farmed areas, we used potted Vicia faba plants and manipulated the presence of Megoura viciae aphids and that of naturally occurring aphid predators. When predators could access aphids, they reduced their abundance less in the urban than in the agricultural ecosystem. Compared to aphid abundance on plants without predator access, abundance on plants with predator access was 2.58 times lower in urban and 5.27 times lower in agricultural areas. This indicates that urbanization limited top-down control of aphids by predators. In both ecosystems, plant biomass was negatively affected by herbivores and positively affected by predators, but the positive indirect predator effect was weaker in cities. Compared to aphid-infested plants without predator access, plants with predator access were 1.89 times heavier in urban and 2.12 times heavier in agricultural areas. Surprisingly, differences between ecosystems regarding the indirect predator effect on plants were not explained by the differentially strong herbivore suppression. Instead, the urban environment limited plant biomass per se, thereby mitigating the scope of a positive predator effect. Our results show that urbanization can influence direct and indirect trophic interactions through effects on biotic top-down forces and on plant growth. In order to understand how urbanization affects biodiversity and ecosystem functioning, it is fundamental to not only consider species assemblages, but also species interactions.
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Kehoe R, Frago E, Barten C, Jecker F, van Veen F, Sanders D (2016). Nonhost diversity and density reduce the strength of parasitoid–host interactions.
Ecology and Evolution,
6(12), 4041-4049.
Abstract:
Nonhost diversity and density reduce the strength of parasitoid–host interactions
The presence of nonprey or nonhosts is known to reduce the strength of consumer– resource interactions by increasing the consumer's effort needed to find its resource. These interference effects can have a stabilizing effect on consumer–resource dynamics, but have also been invoked to explain parasitoid extinctions. To understand how nonhosts affect parasitoids, we manipulated the density and diversity of nonhost aphids using experimental host–parasitoid communities and tested how this affects parasitation efficiency of two aphid parasitoid species. To further study the behavioral response of parasitoids to nonhosts, we tested for changes in parasitoid time allocation in relation to their host-finding strategies. The proportion of successful attacks (attack rate) in both parasitoid species was reduced by the presence of nonhosts. The parasitoid Aphidius megourae was strongly affected by increasing nonhost diversity with the attack rate dropping from 0.39 without nonhosts to 0.05 with high diversity of nonhosts, while Lysiphlebus fabarum responded less strongly, but in a more pronounced way to an increase in nonhost density. Our experiments further showed that increasing nonhost diversity caused host searching and attacking activity levels to fall in A. megourae, but not in L. fabarum, and that A. megourae changed its behavior after a period of time in the presence of nonhosts by increasing its time spent resting. This study shows that nonhost density and diversity in the environment are crucial determinants for the strength of consumer–resource interactions. Their impact upon a consumer's efficiency strongly depends on its host/prey finding strategy as demonstrated by the different responses for the two parasitoid species. We discuss that these trait-mediated indirect interactions between host and nonhost species are important for community stability, acting either stabilizing or destabilizing depending on the level of nonhost density or diversity present.
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Sanders D, Moser A, Newton J, van Veen FJF (2016). Trophic assimilation efficiency markedly increases at higher trophic levels in four-level host-parasitoid food chain.
Proc Biol Sci,
283(1826).
Abstract:
Trophic assimilation efficiency markedly increases at higher trophic levels in four-level host-parasitoid food chain.
Trophic assimilation efficiency (conversion of resource biomass into consumer biomass) is thought to be a limiting factor for food chain length in natural communities. In host-parasitoid systems, which account for the majority of terrestrial consumer interactions, a high trophic assimilation efficiency may be expected at higher trophic levels because of the close match of resource composition of host tissue and the consumer's resource requirements, which would allow for longer food chains. We measured efficiency of biomass transfer along an aphid-primary-secondary-tertiary parasitoid food chain and used stable isotope analysis to confirm trophic levels. We show high efficiency in biomass transfer along the food chain. From the third to the fourth trophic level, the proportion of host biomass transferred was 45%, 65% and 73%, respectively, for three secondary parasitoid species. For two parasitoid species that can act at the fourth and fifth trophic levels, we show markedly increased trophic assimilation efficiencies at the higher trophic level, which increased from 45 to 63% and 73 to 93%, respectively. In common with other food chains, δ(15)N increased with trophic level, with trophic discrimination factors (Δ(15)N) 1.34 and 1.49‰ from primary parasitoids to endoparasitic and ectoparasitic secondary parasitoids, respectively, and 0.78‰ from secondary to tertiary parasitoids. Owing to the extraordinarily high efficiency of hyperparasitoids, cryptic higher trophic levels may exist in host-parasitoid communities, which could alter our understanding of the dynamics and drivers of community structure of these important systems.
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Sanders D, Kehoe R, Tiley K, Bennie J, Cruse D, Davies TW, Frank van Veen FJ, Gaston KJ (2015). Artificial nighttime light changes aphid-parasitoid population dynamics.
Sci Rep,
5Abstract:
Artificial nighttime light changes aphid-parasitoid population dynamics.
Artificial light at night (ALAN) is recognized as a widespread and increasingly important anthropogenic environmental pressure on wild species and their interactions. Understanding of how these impacts translate into changes in population dynamics of communities with multiple trophic levels is, however, severely lacking. In an outdoor mesocosm experiment we tested the effect of ALAN on the population dynamics of a plant-aphid-parasitoid community with one plant species, three aphid species and their specialist parasitoids. The light treatment reduced the abundance of two aphid species by 20% over five generations, most likely as a consequence of bottom-up effects, with reductions in bean plant biomass being observed. For the aphid Megoura viciae this effect was reversed under autumn conditions with the light treatment promoting continuous reproduction through asexuals. All three parasitoid species were negatively affected by the light treatment, through reduced host numbers and we discuss induced possible behavioural changes. These results suggest that, in addition to direct impacts on species behaviour, the impacts of ALAN can cascade through food webs with potentially far reaching effects on the wider ecosystem.
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Sanders D, Kehoe R, van Veen FJF (2015). Experimental Evidence for the Population-Dynamic Mechanisms Underlying Extinction Cascades of Carnivores.
Curr Biol,
25(23), 3106-3109.
Abstract:
Experimental Evidence for the Population-Dynamic Mechanisms Underlying Extinction Cascades of Carnivores.
Species extinction rates due to human activities are high, and initial extinctions can trigger cascades of secondary extinctions, leading to further erosion of biodiversity. 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. 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. 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.
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Sanders D, Vogel E, Knop E (2015). Individual and species-specific traits explain niche size and functional role in spiders as generalist predators.
Journal of Animal Ecology,
84(1), 134-142.
Abstract:
Individual and species-specific traits explain niche size and functional role in spiders as generalist predators
Summary: the function of a predator within a community is greatly based on its trophic niche, that is the number and the strength of feeding links. In generalist predators, which feed on a wide range of prey, the size and position of the trophic niche is likely determined by traits such as hunting mode, the stratum they occur in, their body size and age. We used stable isotope analyses (13C and 15N) to measure the trophic niche size of nine spider species within a forest hedge community and tested for species traits and individual traits that influence stable isotope enrichment, niche size and resource use. The spiders Enoplognatha, Philodromus, Floronia, and Heliophanus had large isotopic niches, which correspond to a more generalistic feeding behaviour. In contrast, Araneus, Metellina and Agelena, as top predators in the system, had rather narrow niches. We found a negative correlation between trophic position and niche size. Differences in trophic position in spiders were explained by body size, hunting modes and stratum, while niche size was influenced by hunting mode. In Philodromus, the size of the trophic niche increased significantly with age. Fitting spiders to functional groups according to their mean body size, hunting mode and their habitat domain resulted in largely separated niches, which indicates that these traits are meaningful for separating functional entities in spiders. Functional groups based on habitat domain (stratum) caught the essential functional differences between the species with species higher up in the vegetation feeding on flying insects and herb and ground species also preying on forest floor decomposers. Interestingly, we found a gradient from large species using a higher habitat domain and having a smaller niche to smaller species foraging closer to the ground and having a larger niche. This shows that even within generalist predators, such as spiders, there is a gradient of specialism that can be predicted by functional traits.
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Sanders D, Vogel E, Knop E (2015). Individual and species-specific traits explain niche size and functional role in spiders as generalist predators.
J Anim Ecol,
84(1), 134-142.
Abstract:
Individual and species-specific traits explain niche size and functional role in spiders as generalist predators.
The function of a predator within a community is greatly based on its trophic niche, that is the number and the strength of feeding links. In generalist predators, which feed on a wide range of prey, the size and position of the trophic niche is likely determined by traits such as hunting mode, the stratum they occur in, their body size and age. We used stable isotope analyses ((13)C and (15)N) to measure the trophic niche size of nine spider species within a forest hedge community and tested for species traits and individual traits that influence stable isotope enrichment, niche size and resource use. The spiders Enoplognatha, Philodromus, Floronia, and Heliophanus had large isotopic niches, which correspond to a more generalistic feeding behaviour. In contrast, Araneus, Metellina and Agelena, as top predators in the system, had rather narrow niches. We found a negative correlation between trophic position and niche size. Differences in trophic position in spiders were explained by body size, hunting modes and stratum, while niche size was influenced by hunting mode. In Philodromus, the size of the trophic niche increased significantly with age. Fitting spiders to functional groups according to their mean body size, hunting mode and their habitat domain resulted in largely separated niches, which indicates that these traits are meaningful for separating functional entities in spiders. Functional groups based on habitat domain (stratum) caught the essential functional differences between the species with species higher up in the vegetation feeding on flying insects and herb and ground species also preying on forest floor decomposers. Interestingly, we found a gradient from large species using a higher habitat domain and having a smaller niche to smaller species foraging closer to the ground and having a larger niche. This shows that even within generalist predators, such as spiders, there is a gradient of specialism that can be predicted by functional traits.
Abstract.
Author URL.
Sanders D, Jones CG, Thébault E, Bouma TJ, van der Heide T, van Belzen J, Barot S (2014). Integrating ecosystem engineering and food webs.
Oikos,
123(5), 513-524.
Abstract:
Integrating ecosystem engineering and food webs
Ecosystem engineering, the physical modification of the environment by organisms, is a common and often influential process whose significance to food web structure and dynamics is largely unknown. In the light of recent calls to expand food web studies to include non-trophic interactions, we explore how we might best integrate ecosystem engineering and food webs. We provide rationales justifying their integration and present a provisional framework identifying how ecosystem engineering can affect the nodes and links of food webs and overall organization; how trophic interactions with the engineer can affect the engineering; and how feedbacks between engineering and trophic interactions can affect food web structure and dynamics. We use a simple integrative food chain model to illustrate how feedbacks between the engineer and the food web can alter 1) engineering effects on food web dynamics, and 2) food web responses to extrinsic environmental perturbations. We identify four general challenges to integration that we argue can readily be met, and call for studies that can achieve this integration and help pave the way to a more general understanding of interaction webs in nature. Synthesis all species are affected by their physical environment. Because ecosystem engineering species modify the physical environment and belong to food webs, such species are potentially one of the most important bridges between the trophic and non-trophic. We examine how to integrate the so far, largely independent research areas of ecosystem engineering and food webs. We present a conceptual framework for understanding how engineering can affect food webs and vice versa, and how feedbacks between the two alter ecosystem dynamics. With appropriate empirical studies and models, integration is achievable, paving the way to a more general understanding of interaction webs in nature. © 2014 the Authors.
Abstract.
Sanders D, Jones CG, Thébault E, Bouma TJ, van der Heide T, van Belzen J, Barot S (2014). Integrating ecosystem engineering and food webs. Oikos
Knop E, Zünd J, Sanders D (2014). Interactive prey and predator diversity effects drive consumption rates.
Oikos,
123(10), 1244-1249.
Abstract:
Interactive prey and predator diversity effects drive consumption rates
The positive relationship between biodiversity and ecosystem functioning is mainly derived from studies concerning primary producers, whereas a generalization of this relationship for higher trophic levels is more difficult. Furthermore, most evidence of the biodiversity-ecosystem functioning relationship is derived from experiments manipulating only one trophic level and, as a consequence, interactive diversity effects at multiple trophic levels have mostly been ignored. Here, we performed a mesocosm experiment in which we manipulated functional group diversity at two trophic levels (primary and secondary consumers) applying a full-factorial design. More specifically, we asked whether 1) predator functional diversity affects prey mortality rates, 2) prey functional diversity affects prey mortality rates, 3) whether there are interactive effects of simultaneous diversity changes at both trophic levels. For each trophic level we used two functional groups, i.e. organisms belonging to two different habitat domains: at the higher trophic position 1) a ground foraging spider species and 2) a spider species foraging in the vegetation canopy and at the lower trophic position 3) a ground living cricket species and 4) leafhoppers living in the vegetation canopy. Increasing predator functional group diversity increased prey mortality by 53%, and increasing prey functional group diversity increased prey mortality by 24%. Further, prey mortality was highest at the uppermost level of functional group diversity (142% increase in prey mortality compared to single prey and predator functional diversity), most likely due to resource partitioning between the predators. This finding demonstrates that a multi-trophic perspective is necessary, and that previous studies focusing on only one trophic level have most likely underestimated the strength of the relationship between biodiversity and ecosystem functioning.
Abstract.
Knop E, Zünd J, Sanders D (2014). Interactive prey and predator diversity effects drive consumption rates.
OikosAbstract:
Interactive prey and predator diversity effects drive consumption rates
The positive relationship between biodiversity and ecosystem functioning is mainly derived from studies concerning primary producers, whereas a generalization of this relationship for higher trophic levels is more difficult. Furthermore, most evidence of the biodiversity-ecosystem functioning relationship is derived from experiments manipulating only one trophic level and, as a consequence, interactive diversity effects at multiple trophic levels have mostly been ignored. Here, we performed a mesocosm experiment in which we manipulated functional group diversity at two trophic levels (primary and secondary consumers) applying a full-factorial design. More specifically, we asked whether 1) predator functional diversity affects prey mortality rates, 2) prey functional diversity affects prey mortality rates, 3) whether there are interactive effects of simultaneous diversity changes at both trophic levels. For each trophic level we used two functional groups, i.e. organisms belonging to two different habitat domains: at the higher trophic position 1) a ground foraging spider species and 2) a spider species foraging in the vegetation canopy and at the lower trophic position 3) a ground living cricket species and 4) leafhoppers living in the vegetation canopy. Increasing predator functional group diversity increased prey mortality by 53%, and increasing prey functional group diversity increased prey mortality by 24%. Further, prey mortality was highest at the uppermost level of functional group diversity (142% increase in prey mortality compared to single prey and predator functional diversity), most likely due to resource partitioning between the predators. This finding demonstrates that a multi-trophic perspective is necessary, and that previous studies focusing on only one trophic level have most likely underestimated the strength of the relationship between biodiversity and ecosystem functioning. © 2014 the Authors.
Abstract.
van Veen FJF, Sanders D (2013). Herbivore identity mediates the strength of trophic cascades on individual plants.
ECOSPHERE,
4(5).
Author URL.
Eggs B, Sanders D (2013). Herbivory in Spiders: the Importance of Pollen for Orb-Weavers.
PLOS ONE,
8(11).
Author URL.
Sanders D, Sutter L, van Veen FJF (2013). The loss of indirect interactions leads to cascading extinctions of carnivores.
Ecology Letters,
16(5), 664-669.
Abstract:
The loss of indirect interactions leads to cascading extinctions of carnivores
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. © 2013 Blackwell Publishing Ltd/CNRS.
Abstract.
Sanders D, Sutter L, van Veen FJF (2013). The loss of indirect interactions leads to cascading extinctions of carnivores.
Ecol Lett,
16(5), 664-669.
Abstract:
The loss of indirect interactions leads to cascading extinctions of carnivores.
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.
Abstract.
Author URL.
Sanders D, Van Veen FJF (2012). Indirect commensalism promotes persistence of secondary consumer species.
Biology Letters,
8(6), 960-963.
Abstract:
Indirect commensalism promotes persistence of secondary consumer species
Local species extinctions may lead to, often unexpected, secondary extinctions. To predict these, we need to understand how indirect effects, within a network of interacting species, affect the ability of species to persist. It has been hypothesized that the persistence of some predators depends on other predator species that suppress competitively dominant prey to low levels, allowing a greater diversity of prey species, and their predators, to coexist. We show that, in experimental insect communities, the absence of one parasitoid wasp species does indeed lead to the extinction of another that is separated by four trophic links. These results highlight the importance of a holistic systems perspective to biodiversity conservation and the necessity to include indirect population dynamic effects in models for predicting cascading extinctions in networks of interacting species. © 2012 the Royal Society.
Abstract.
Platner C, Piñol J, Sanders D, Espadaler X (2012). Trophic diversity in a Mediterranean food web—Stable isotope analysis of an ant community of an organic citrus grove. Basic and Applied Ecology, 13(7), 587-596.
Sanders D, van Veen FJF (2011). Ecosystem engineering and predation: the multi-trophic impact of two ant species. Journal of Animal Ecology, 80(3), 569-576.
Sanders D, Schaefer M, Platner C, Griffiths GJK (2011). Intraguild interactions among generalist predator functional groups drive impact on herbivore and decomposer prey.
Oikos,
120(3), 418-426.
Abstract:
Intraguild interactions among generalist predator functional groups drive impact on herbivore and decomposer prey
Different functional groups of generalist predators may complement each other in controlling prey populations; but intraguild interactions, common among generalist predators, may also reduce the strength of top-down control. In natural communities greater alterations to ecosystem function are expected if a whole functional group declines in abundance or is lost. Therefore studying functional group diversity is important for predicting effects of predator loss. We studied the top-down impact of web-building spiders, hunting spiders and ants, which are highly abundant generalist predators in most terrestrial ecosystems, on prey from the herbivore and decomposer system of a grassland food web. The density of the three predator groups was manipulated by continuous removal in a three-factorial designed field experiment, which was carried out for two years. We found no positive effect of increasing predator functional group richness on prey control. However there was evidence for strong composition effects between the functional groups. The presence of ants in predator assemblages reduced the prey suppression through mostly trait-mediated intraguild interactions, while hunting and web-building spiders contributed additively to prey suppression and reduced the density of herbivore and decomposer prey by 50-60%. A trophic cascade on plant biomass triggered by web-builders and hunting spiders was diminished at levels of higher predator group diversity. In conclusion, our experiments showed that intraguild interactions strongly influence the strength of top-down control by generalist predators. Among spiders there was evidence for a positive relation between functional group richness and prey suppression but the overall outcome strongly depended on the occurrence of interference, driven by trait-mediated indirect interactions. © 2011 the Authors. Oikos © 2011 Nordic Society Oikos.
Abstract.
Sanders D, Entling MH (2011). Large variation of suction sampling efficiency depending on arthropod groups, species traits, and habitat properties.
Entomologia Experimentalis et Applicata,
138(3), 234-243.
Abstract:
Large variation of suction sampling efficiency depending on arthropod groups, species traits, and habitat properties
Suction sampling is widely used to estimate arthropod abundance and diversity. To test the reliability of abundance data derived from suction sampling, we examined sampling efficiency across a wide range of arthropod groups and tested for effects of species traits, vegetation density, and differences between sites. Suction sampling efficiency was quantified by vacuuming an enclosed meadow area and subsequent removal of the turf, which was treated with heat extraction to collect the remaining arthropods. We obtained 250 pairs of suction and turf samples from seven grasslands with variable vegetation density. High suction sampling efficiencies between 49 and 86% were obtained for Auchenorrhyncha, Heteroptera, Araneida, Curculionoidea, Hymenoptera, and Diptera. In contrast, efficiencies were below 30% for Aphidae, Thysanoptera, Staphylinidae and other Coleoptera, and for soil arthropods such as Collembola, Isopoda, Diplopoda, and Formicidae. Efficiency varied significantly among habitats (sites) for most groups, often more than two-fold. Surprisingly, sampling efficiency for Hymenoptera, Diplopoda, and Collembola increased with vegetation density, probably because aboveground activity of these taxa was higher in dense vegetation. Suction sampling was nearly twice as efficient for spiders living in the vegetation than for spiders living near the soil surface, and cursorial and large-bodied spider species were more efficiently sampled than web-builders and small species. Depending on the sampling effort, suction sampling missed between 49% (one sample) and 31% (250 samples) of the spider species present. Suction sampling efficiency varied more strongly among sites and among arthropod groups than previously recognized. Abundance data derived from suction sampling are strongly underestimated, especially for arthropods living near the soil surface. Thus, comparisons of abundance and diversity between sites should be restricted to vegetation-dwelling species of the most efficiently sampled groups. The positive relationship of sampling efficiency with vegetation density demonstrates that variation in efficiency is mediated by arthropod behaviour. © 2011 the Authors. Entomologia Experimentalis et Applicata © 2011 the Netherlands Entomological Society.
Abstract.
Sanders D, van Veen FJF (2010). The impact of an ant–aphid mutualism on the functional composition of the secondary parasitoid community.
Ecological Entomology,
35(6), 704-710.
Abstract:
The impact of an ant–aphid mutualism on the functional composition of the secondary parasitoid community
1. Mutualistic and antagonistic interactions, although often studied independently, may affect each other and food web dynamics are likely to be determined by the two processes working in concert.
2. The structure, and hence dynamics, of food webs depends on the relative abundances of generalist and specialist feeding guilds. Secondary parasitoids of aphids can be divided into two feeding guilds: (i) the more specialised endoparasitoids, which attack the primary parasitoid larvae in the still living aphid, and (ii) the generalist ectoparasitoids, which attack the pre-pupa of the primary or secondary parasitoid in the mummified aphid.
3. We studied the effect of an ant-aphid mutualism on the relative abundance of these two functional groups of secondary parasitoids. We hypothesised that generalists will be negatively affected by the presence of ants, thus leading to a greater dominance of specialists.
4. We manipulated the access of ants (Lasius niger) to aphid colonies in which we placed parasitized aphids. Aphid mummies were collected and reared to determine the levels of endo- and ecto-secondary parasitism.
5. When aphids were attended by L. niger the proportion of secondary parasitism by ectoparasitoids dropped from 26% to 8 %, with Pachyneuron aphidis most strongly affected, while endoparasitoids as a group did not respond. Among these Syrphophagus mamitus profited from ant attendance becoming the dominant secondary parasitoid, while parasitization rates of Alloxysta and Phaenoglyphus declined.
6. The shift to S. mamitus as dominant secondary parasitoid in ant-attended aphid colonies is likely due to the behavioural plasticity of this species in response to ant aggression, and a release from tertiary parasitism by generalist ectoparasitoids.
7. The reduction of secondary parasitism by generalist ectoparasitoids reduces the potential for apparent competition among primary parasitoids with consequences for the dynamics of the wider food web.
Abstract.
Sanders D, Nickel H, Grützner T, Platner C (2008). Habitat structure mediates top–down effects of spiders and ants on herbivores. Basic and Applied Ecology, 9(2), 152-160.
Schuch S, Platner C, Sanders D (2008). Potential positive effect of the ant species Lasius niger on linyphiid spiders. Journal of Applied Entomology, 132(5), 375-381.
Sanders D, Platner C (2006). Intraguild interactions between spiders and ants and top-down control in a grassland food web. Oecologia, 150(4).
