Publications by year
In Press
van Veen FJF, Godfray HCJ (In Press). Consequences of trait changes in host-parasitoid interactions in insect communities. In Ohgushi T, Schmitz O, Holt RD (Eds.)
Interaction Richness and Complexity: Ecological and Evolutionary Aspects of Trait-Mediated Indirect Interactions, Cambridge University Press.
Abstract:
Consequences of trait changes in host-parasitoid interactions in insect communities
Abstract.
Henri DC, Van Veen FJF (In Press). Link flexibility: evidence for environment-dependent adaptive foraging in a food web time-series.
Abstract:
Link flexibility: evidence for environment-dependent adaptive foraging in a food web time-series
Temporal variability in the distribution of feeding links in a food web can be an important stabilising factor for these complex systems. Adaptive foraging and prey choice have been hypothesised to cause this link flexibility as organisms adjust their behaviour to variation in the prey community. Here, we analyse a 10-year time series of monthly aphid-parasitoid-secondary parasitoid networks and show that interaction strengths for polyphagous secondary parasitoids are generally biased towards the larger host species within their fundamental niche; however, in months of higher competition for hosts, size-based biases are reduced. The results corroborate a previous hypothesis stating that host-selectivity of parasitoids should be correlated to the relative likelihood of egg-limitation vs time-limitation. Our results evince adaptation of foraging behaviour to varying conditions affects the distribution of host-parasitoid link-strengths, where link-rewiring may be integral to stability in complex communities.
Abstract.
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
Henri DC, Jones O, Tsiattalos A, Thebault E, Seymour CL, Van Veen FJF (In Press). Natural vegetation benefits synergistic control of the three main insect and pathogen pests of fruit crop in southern Africa.
Journal of Applied EcologyAbstract:
Natural vegetation benefits synergistic control of the three main insect and pathogen pests of fruit crop in southern Africa
1 Most studies of the potential for natural habitat to improve agricultural productivity have been conducted in transformed, temperate regions, but little is known of the importance of agroecosystem services in biodiverse developing countries.
2. Natural vegetation may promote the density and/or diversity of natural enemies of crop pests, but the strength of the effect varies, and few studies directly measure concurrent impacts on pest density. Considering multiple pest species within the same agroecosystem may help explain why some pests are more affected than others by landscape complexity. Here, we investigated multiple pest species (leaf-galling flies, three species of Tephritidae fruit fly and pathogenic fungi Fusarium spp.) and their enemies in cultivated mango Mangifera indica, in North-Eastern South Africa.
3. The density of generalist Tephritidae fruit flies increased with distance from natural vegetation during harvesting months, and predation rate of pupae sharply decreased from ~50% at the edge with natural vegetation to 0% at 250m into the crop. Parasitism rates of the cryptic, gall-forming fly increased with proximity to natural vegetation but pest density was unrelated to distance from natural vegetation. Incidence of the fungal pathogen disease increased with distance from natural vegetation, possibly due to decreased predation of commensal mites.
4 Although the relationship with distance to natural vegetation was significant for all species considered, the strength of this relationship varied across pest species and type of natural enemy studied, suggesting the benefits of natural vegetation depends on each natural enemy species’ ability to disperse into the agricultural environment.
5. Syntheses and applications. Our results suggest that natural vegetation is a net source of natural enemies in a region of South Africa that still contains much of its natural biodiversity. However, the decline in natural enemies, and increase in pests, with distance from natural habitat indicates that this biocontrol is limited by natural enemy dispersal. In landscapes like these that are still dominated by natural habitat, conservation biocontrol can still be improved by management aimed at providing corridors of key plants and habitat elements into to the crops, to facilitate natural enemy dispersal.
Abstract.
2023
Davies-Barnard T, Catto JL, Harper AB, Imron MA, Frank van Veen FJ (2023). Future fire risk under climate change and deforestation scenarios in tropical Borneo.
Environmental Research Letters,
18(2), 024015-024015.
Abstract:
Future fire risk under climate change and deforestation scenarios in tropical Borneo
Abstract
. Fire in the tropical peatland forests of Borneo is an environmental issue interactioning with climate change and deforestation, and the consequences have local and global implications. While research has shown that fire severity and frequency are expected to increase with climate change, there is conflicting model and observational data as to the effect of deforestation on precipitation, which is a key metric for fire risk. To better understand the changes in fire risk from deforestation and climate change we ran simulations of the climate scenario RCP8.5 with and without total deforestation using regional climate model RegCM4. The output was then used for calculations of the fire weather index. We find that annual temperature change from deforestation at elevations above 500 m is 53% of the change over the 21st century in RCP8.5. Fire risk is significantly affected by both climate change and deforestation, despite some increases in precipitation from deforestation. While the multi model dry season (June–August) mean increases in fire risk are larger from elevated atmospheric carbon dioxide, the increases in maximum fire risk are larger from deforestation. The altitude is a good predictor of fire risk change, with larger increases at more densely populated lower elevations where the peatlands are concentrated and smaller increases at higher elevations. Therefore, while deforestation generally causes a smaller increase in climate-related fire risk than climate change, its local control and heterogeneous effects compared to global carbon emissions makes it critical for climate mitigation policy. These high-resolution simulations provide a guide to the most vulnerable areas of Borneo from climatic increases in fire risk.
Abstract.
2021
Kawatsu K, Ushio M, van Veen FJF, Kondoh M (2021). Are networks of trophic interactions sufficient for understanding the dynamics of multi-trophic communities? Analysis of a tri-trophic insect food-web time-series.
Ecol Lett,
24(3), 543-552.
Abstract:
Are networks of trophic interactions sufficient for understanding the dynamics of multi-trophic communities? Analysis of a tri-trophic insect food-web time-series.
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.
Abstract.
Author URL.
Thurstan R, Hockings K, Hedlund J, Bersacola E, Collins C, Early R, Harrison M, Kaiser-Bunbury C, Nuno A, Van Veen F, et al (2021). Envisioning a resilient future for biodiversity conservation in the wake of the COVID-19 pandemic. People and Nature
2020
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.
2019
Knox A, Markx J, How E, Azis A, Hobaiter C, van Veen FJF, Morrogh-Bernard H (2019). Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo.
International Journal of Primatology,
40(3), 393-416.
Abstract:
Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo
Research on captive and wild great apes has established that they employ large repertoires of intentional gestural signals to achieve desired goals. However, gestural research has focused on African great apes, with orang-utan data limited to a few captive studies. We address this gap by describing gesture use in wild Southwest Bornean orang-utan (Pongo pygmaeus wurmbii) mother and offspring pairs. We conducted focal follows on 16 individuals in the Sabangau peat-swamp forest in Borneo, Indonesia. The resulting 681 h of video footage yielded 1299 communicative signals: 858 vocal signals and 441 gestural signals. Eleven vocal signal types and 21 gesture types met the criteria for inclusion in the repertoire; however, the gestural repertoire did not approach asymptote and further gesture types will likely be identified in the future. Signalers used gestures of any modality in higher frequency when the recipient was paying visual attention, and took the recipient’s visual attention into account when selecting gesture modalities. Orang-utans employed hands and arms more than legs and feet in gesturing, but were more flexible in their choice of limb than chimpanzees using the same gestures. Orang-utans were highly responsive to gestural requests, using them to achieve eight goals and, where successful, responding either before gesturing ended or in
Abstract.
2018
Karp DS, Chaplin-Kramer R, Meehan TD, Martin EA, DeClerck F, Grab H, Gratton C, Hunt L, Larsen AE, Martinez-Salinas A, et al (2018). Crop pests and predators exhibit inconsistent responses to surrounding landscape composition.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA,
115(33), E7863-E7870.
Author URL.
Simba LD, Foord SH, Thébault E, van Veen FJF, Joseph GS, Seymour CL (2018). Indirect interactions between crops and natural vegetation through flower visitors: the importance of temporal as well as spatial spillover.
Agriculture, Ecosystems and Environment,
253, 148-156.
Abstract:
Indirect interactions between crops and natural vegetation through flower visitors: the importance of temporal as well as spatial spillover
As the Anthropocene advances, understanding the complex web of interactions between species has become a central theme in the maintenance of biodiversity, ecosystem functions, and agricultural systems. Plant-flower visitor networks yield insights into how natural vegetation supports crop pollination. Although crops themselves also support pollinators, the importance of spillover of flower-visiting pollinators from natural vegetation into croplands is increasingly appreciated. Natural vegetation not only provides forage and nesting sites, but can also support crop flower visitors when the crop is not flowering. We evaluated indirect effects between mango (the dominant tropical fruit crop globally) and wild plant species in neighbouring vegetation, and the factors determining these indirect effects, by constructing flower visitor networks. We constructed these networks for transects that included mango fields and neighbouring natural vegetation in north-eastern South Africa. Surveys were conducted before, during and after mango flowering, to allow evaluation of the importance of pollinator support when the crop was not in flower. Network analysis showed that potential indirect effects of other plant species on mango increased with flower abundance of those species, although this increase was less marked for species growing in natural vegetation. The cumulative (total, i.e. indirect effects summed) effect of natural vegetation on mango flower visitation was greater both during mango flowering and when it was not flowering. This is likely because of the greater plant diversity in natural systems, and because the combination of these species provided flowers over a protracted period. These positive indirect effects among plants flowering over extended periods of time have to date rarely been considered in crop pollination studies. Given the rapid expansion of high-intensity, high-yield monoculture plantings, such effects warrant further investigation.
Abstract.
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.
Abstract.
Sanders D, Kehoe R, Thebault E, Van Veen FJF (2018). Trophic redundancy reduces vulnerability to extinction cascades. Proceedings of the National Academy of Sciences
2017
Moxley C, Lammers W, van Veen FJF, Thébault E, Esler KJ, Seymour CL (2017). A major subtropical fruit pest accumulates in crop fields and spills over to a wild host.
Agriculture, Ecosystems and Environment,
242, 102-109.
Abstract:
A major subtropical fruit pest accumulates in crop fields and spills over to a wild host
Wild plant species are often considered a source of crop pests in mixed landscapes but this view rarely considers pest spillover in the opposite direction (from crop fields to natural vegetation), or spatiotemporal variability in resources between crop and wild habitats. We investigate how infestation of mango crop (Mangifera indica, Anacardiaceae) and a related wild host (marula, Sclerocarya birrea, Anacardiaceae) by a major subtropical fruit crop pest (Ceratitis cosyra, Diptera: Tephritidae) varies with distance from the boundary between crop and natural vegetation. We determined how infestation of marula is associated with proximity to mango crops at field and landscape scales over two fruiting seasons on three farms in north-eastern South Africa. This is one of few studies to date to consider pest spillover from crop fields to natural vegetation and the only one performed in a biodiverse region with relatively little habitat transformation. Over three sampling periods, C. cosyra infestation of marula always decreased with distance from mango fields. At the landscape scale, marula alongside crop fields were 30 times more likely to be infested than in distant vegetation (1.3–6 km from mango), suggesting that spillover occurs from crop fields to natural vegetation. During late mango and marula fruiting, twice as many flies infested marula than mango. However, over the two months post-mango fruiting, up to 25 times more C. cosyra were trapped in mango fields than in bordering natural vegetation. Although pests spillover from crop fields into natural vegetation to use marula as an alternate host, biological control in the natural vegetation may eliminate this habitat as a pest reservoir outside the crop season. Other nearby crops may be more important than wild hosts for maintaining C. cosyra out of mango season. Landscape planning should consider proximity and arrangement of fields containing crops that host shared pests at different times of the year.
Abstract.
Hansen S, Roets F, Seymour CL, Thébault E, van Veen FJF, Pryke JS (2017). Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks. Diversity and Distributions, 24(1), 58-68.
Forshage M, Bowdrey J, Broad GR, Spooner BM, van Veen F (2017). Checklist of British and Irish Hymenoptera - Cynipoidea.
Biodiversity Data Journal,
5(1).
Abstract:
Checklist of British and Irish Hymenoptera - Cynipoidea
Background the British and Irish checklist of Cynipoidea is revised, considerably updating the last complete checklist published in 1978. Disregarding uncertain identifications, 220 species are now known from Britain and Ireland, comprising 91 Cynipidae (including two established non-natives), 127 Figitidae and two Ibaliidae. New information One replacement name is proposed, Kleidotoma thomsoni Forshage, for the secondary homonym Kleidotoma tetratoma Thomson, 1861 (nec K. tetratoma (Hartig, 1841)).
Abstract.
Cheyne SM, Capilla BR, Van Veen FJF, Boyd N, Adul, Husson SJ, Harrison ME, Morrogh-Bernard HC, Maimunah S (2017). Conserving Non-Protected Primate Habitat: the Rungan River Conservation Programme of the Borneo Nature Foundation, Indonesia.
Author URL.
Morgan WH, Thébault E, Seymour CL, van Veen FJF (2017). Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid.
BioControl,
62(2), 175-184.
Abstract:
Density dependence and environmental factors affect population stability of an agricultural pest and its specialist parasitoid
Host–parasitoid dynamics are intrinsically unstable unless the risk of parasitism is sufficiently heterogeneous among hosts. Spatial aggregation of parasitoids can contribute to this heterogeneity, stabilising host–parasitoid population dynamics and thereby reducing pest outbreaks. We examined the spatial distribution of mango gall fly (Procontarinia matteiana, Kiefer and Cecconi), a non-native pest of South African mango orchards, which is controlled by a single parasitoid (Chrysonotomyia pulcherrima, Kerrich). We assessed whether spatial aggregation of parasitoids is associated with proximity to natural vegetation and/or to host density-dependent and host density-independent factors at three spatial scales. We found evidence for higher parasitism rates near natural vegetation at the field scale, and inverse host-density dependent and density-independent parasitoid aggregation at both the leaf scale and field scale. Therefore, we conclude that natural vegetation plays a role in promoting stabilising aggregation of parasitoids, possibly through provision of non-host resources (nectar, pollen), in this system.
Abstract.
Nel L, Pryke JS, Carvalheiro LG, Thébault E, van Veen FJF, Seymour CL (2017). Exotic plants growing in crop field margins provide little support to mango crop flower visitors.
Agriculture, Ecosystems and Environment,
250, 72-80.
Abstract:
Exotic plants growing in crop field margins provide little support to mango crop flower visitors
Introduced plant species integrate into native trophic networks, often disrupting flower-visitation patterns. Although non-native invasive plants frequently occur in disturbed natural vegetation bordering crop fields, their impact on crop pollination has not been studied. We investigated whether an invasive plant (Lantana camara) influences flower visitation to mango (Mangifera indica), a pollinator-dependent crop, and whether the invasive supports mango pollinators when mango is not flowering. We surveyed insect flower-visitation in mango orchards bordering natural vegetation and within adjacent natural vegetation, with and without L. camara present, before, during and after mango flowering. We used these data to calculate the indirect effect of L. camara on mango through shared flower visitors before, during and after mango flowering, and the effects of the invasive on crop productivity. Lantana camara had a positive effect on mango flower visitation at low to medium mango flower density, but not at high mango flower densities. Although L. camara and mango shared flower visitor species, the frequency with which these flower visitor species visited the crop and the invasive differed markedly before, during and after mango flowering. Furthermore, the potential indirect effect of L. camara on mango via shared visitors was greatest when mango was flowering, but significantly lower before and after mango flowering, suggesting that the invasive is unimportant in the diet of mango flower visitors when the crop is not flowering. Contrary to findings in previous studies using native species in mango fields, there was a trend (not significant) for lower mango fruit production in fields with L. camara. This suggests that Lantana does not contribute to an increase in successful pollination of mango. Although our focal alien invasive plant species facilitated flower visitation of crops, it had no effect on mango production, and provided little support to mango flower visitor species that live longer than the crop's flowering period. Given that L. camara is detrimental to grazing and was not associated with increased mango production, the removal of this invasive is advisable.
Abstract.
2016
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.
Abstract.
Author URL.
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.
Abstract.
Geslin B, Oddie M, Folschweiller M, Legras G, Seymour CL, van Veen FJF, Thébault E (2016). Spatiotemporal changes in flying insect abundance and their functional diversity as a function of distance to natural habitats in a mass flowering crop.
Agriculture, Ecosystems and Environment,
229, 21-29.
Abstract:
Spatiotemporal changes in flying insect abundance and their functional diversity as a function of distance to natural habitats in a mass flowering crop
To meet the dietary requirements of a burgeoning human population, the demand for animal-dependent crops continues to grow. To meet the demand, intensive farming practices are used. The gains in food production associated with agricultural intensification may be offset by its detrimental effects on pollinator populations through natural habitat fragmentation and pesticide use. Abundance and species richness of pollinators have been found to decrease with increasing distance to natural habitat in agroecosystems, reducing crop yields. A key aspect of crop pollination lies in the diversity of functional traits (functional diversity, FD) of flower-visitor communities within crop fields. Higher FD allows improved pollination success through complementarity between flower-visitors' morphology, phenology and behaviour. Many studies reported negative effects of increasing distance to natural habitats on the abundance and richness of flower-visitor communities, but the link between FD and natural habitat isolation is less well understood. Also, a more complete understanding of the functional traits of flower-visitor communities within crops should consider potential variations through time. Differences in resources availability between seasons are important in tropical areas and could modify ecological responses of flower-visitor communities to isolation. In this study, we surveyed the Hymenoptera and Diptera communities within mango orchards of South Africa using pan traps at 100 m, 200 m and at the maximal distance possible from any natural habitat. We measured the response of insect abundance, wing span and body size as well as functional diversity to habitat isolation during mango flowering (dry season), and during the wet season (after mango fruit harvest). Flying insect abundance decreased with increasing distance to natural habitat during mango flowering, but no effect was detected during the wet season. FD of flying insects declined with increasing distance to natural habitat in both sampling periods. Insects captured during mango flowering were smaller but had higher wing length/body length ratios than those caught during the wet season. This study highlights that mango orchards are more inhospitable for flying insects during mango flowering. This effect might be due to low palatability of mango flowers, or pesticide use in mango fields. In order to maintain a high FD of flower-visiting species, and reduce the detrimental effects of habitat isolation to ultimately ensure better crop pollination, we propose establishment of patches of resource-rich habitats combined with judicious use of pesticides within orchards.
Abstract.
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.
Abstract.
Author URL.
2015
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.
Abstract.
Author URL.
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.
Abstract.
Author URL.
Henri DC, Jones O, Tsiattalos A, Thébault E, Seymour CL, van Veen FJF (2015). Natural vegetation benefits synergistic control of the three main insect and pathogen pests of a fruit crop in southern Africa.
Journal of Applied Ecology,
52(4), 1092-1101.
Abstract:
Natural vegetation benefits synergistic control of the three main insect and pathogen pests of a fruit crop in southern Africa
Summary: Most studies of the potential for natural habitat to improve agricultural productivity have been conducted in transformed, temperate regions, but little is known of the importance of agroecosystem services in biodiverse developing countries. Natural vegetation may promote the density and/or diversity of natural enemies of crop pests, but the strength of the effect varies, and few studies directly measure concurrent impacts on pest density. Considering multiple pest species within the same agroecosystem may help explain why some pests are more affected than others by landscape complexity. Here, we investigated multiple pest species (three species of Tephritidae fruit fly, leaf galling flies and pathogenic fungi Fusarium spp.) and their enemies in cultivated mango Mangifera indica, in north-eastern South Africa. The density of generalist Tephritidae fruit flies increased with distance from natural vegetation during harvesting months, and predation rate of pupae sharply decreased from ~50% at the edge with natural vegetation to 0% at 250 m into the crop. Parasitism rates of the cryptic, gall-forming fly increased with proximity to natural vegetation, but pest density was unrelated to distance from natural vegetation. Incidence of the fungal pathogen disease increased with distance from natural vegetation, possibly due to decreased predation of commensal mites. Although the relationship with distance to natural vegetation was significant for all species considered, the strength of this relationship varied across pest species and type of natural enemy studied, suggesting the benefits of natural vegetation depend on each natural enemy species' ability to disperse into the agricultural environment. Synthesis and applications. Our results suggest that natural vegetation is a net source of natural enemies in a region of South Africa that still contains much of its natural biodiversity. However, the decline in natural enemies, and increase in pests, with distance from natural habitat indicates that this biocontrol is limited by natural enemy dispersal. In landscapes like these that are still dominated by natural habitat, conservation biocontrol can still be improved by management aimed at providing corridors of key plants and habitat elements into the crops, to facilitate natural enemy dispersal. Our results suggest that natural vegetation is a net source of natural enemies in a region of South Africa that still contains much of its natural biodiversity. However, the decline in natural enemies, and increase in pests, with distance from natural habitat indicates that this biocontrol is limited by natural enemy dispersal. In landscapes like these that are still dominated by natural habitat, conservation biocontrol can still be improved by management aimed at providing corridors of key plants and habitat elements into the crops, to facilitate natural enemy dispersal.
Abstract.
Van Veen FJF (2015). Plant-modified trophic interactions.
Current Opinion in Insect ScienceAbstract:
Plant-modified trophic interactions
Plants can modify the interactions between herbivorous insects and their natural enemies in various ways. Chemical defences from the plants against herbivores may in fact harm the latter's natural enemies, thereby weakening the trophic interaction. On the other hand, volatile chemicals produced by the plant in response to herbivory may attract natural enemies, thereby strengthening the interaction. Recent research shows that effects of plants on insect interactions are not curious phenomena confined to a few specialist species but rather that they are ubiquitous in terrestrial ecosystems and often involve complex interactions among many species. The major challenge now is to study how the commonly reported short-term effects of plants affect long term dynamics of insect interactions in the context of complex natural communities.
Abstract.
Ehlers Smith YC, Ehlers Smith DA, Seymour CL, Thébault E, Van Veen FJF (2015). Response of avian diversity to habitat modification can be predicted from life-history traits and ecological attributes.
Landscape EcologyAbstract:
Response of avian diversity to habitat modification can be predicted from life-history traits and ecological attributes
Context: Habitat conversion for agriculture is a major driver of global biodiversity loss, partly because of homogeneity within agri-ecosystems. Anthropogenic landscapes can also increase habitat heterogeneity and primary productivity, however, augmenting regional biodiversity, as species that exploit resources associated with human activities expand their ranges into novel ecological regions.
Abstract.
2014
Perkins MJ, McDonald RA, van Veen FJF, Kelly SD, Rees G, Bearhop S (2014). Application of nitrogen and carbon stable isotopes (δ(15)N and δ(13)C) to quantify food chain length and trophic structure.
PLoS One,
9(3).
Abstract:
Application of nitrogen and carbon stable isotopes (δ(15)N and δ(13)C) to quantify food chain length and trophic structure.
Increasingly, stable isotope ratios of nitrogen (δ(15)N) and carbon (δ(13)C) are used to quantify trophic structure, though relatively few studies have tested accuracy of isotopic structural measures. For laboratory-raised and wild-collected plant-invertebrate food chains spanning four trophic levels we estimated nitrogen range (NR) using δ(15)N, and carbon range (CR) using δ(13)C, which are used to quantify food chain length and breadth of trophic resources respectively. Across a range of known food chain lengths we examined how NR and CR changed within and between food chains. Our isotopic estimates of structure are robust because they were calculated using resampling procedures that propagate variance in sample means through to quantified uncertainty in final estimates. To identify origins of uncertainty in estimates of NR and CR, we additionally examined variation in discrimination (which is change in δ(15)N or δ(13)C from source to consumer) between trophic levels and among food chains. δ(15)N discrimination showed significant enrichment, while variation in enrichment was species and system specific, ranged broadly (1.4‰ to 3.3‰), and importantly, propagated variation to subsequent estimates of NR. However, NR proved robust to such variation and distinguished food chain length well, though some overlap between longer food chains infers a need for awareness of such limitations. δ(13)C discrimination was inconsistent; generally no change or small significant enrichment was observed. Consequently, estimates of CR changed little with increasing food chain length, showing the potential utility of δ(13)C as a tracer of energy pathways. This study serves as a robust test of isotopic quantification of food chain structure, and given global estimates of aquatic food chains approximate four trophic levels while many food chains include invertebrates, our use of four trophic level plant-invertebrate food chains makes our findings relevant for a majority of ecological systems.
Abstract.
Author URL.
Ferrer-Suay M, Janković M, Selfa J, Van Veen FJF, Tomanović Ž, Kos K, Rakhshani E, Pujade-Villar J (2014). Qualitative analysis of aphid and primary parasitoid trophic relations of genus Alloxysta (Hymenoptera: Cynipoidea: Figitidae: Charipinae).
Environmental Entomology,
43(6), 1485-1495.
Abstract:
Qualitative analysis of aphid and primary parasitoid trophic relations of genus Alloxysta (Hymenoptera: Cynipoidea: Figitidae: Charipinae)
Charipinae hyperparasitoids affect effectiveness of the primary parasitoids of aphids by decreasing their abundance and modifying their behavior. As a result, increase of aphid populations can cause severe yield losses in some crops. Therefore, ecological studies on the subfamily Charipinae have a great economical and biological importance. Host specificity of these hyperparasitoids is still under debate and for many Charipinae species very little is known about their trophic relations. Here, we give a comprehensive overview of the trophic relationships between the Charipinae species of the genus Alloxysta Förster and their aphid and primary parasitoids hosts, worldwide. Within this subfamily, Alloxysta arcuata (Kieffer), Alloxysta brevis (Thomson), Alloxysta fuscicornis (Hartig), and Alloxysta victrix (Westwood) are the most generalist species sharing many aphid hosts, while for primary parasitoid hosts these are A. arcuata, A. brevis, Alloxysta pleuralis (Cameron), and A. victrix. Alloxysta citripes (Thomson), Alloxysta halterata (Thomson), Alloxysta leunisii (Hartig), and Alloxysta ramulifera (Thomson) appear, up to now, as the most specialized in relation to the primary parasitoid hosts. Primary parasitoids of the genera Aphidius Nees, Lysiphlebus Förster, Praon Haliday, and Trioxys Haliday are the most common hosts for Alloxysta species, and the common host aphid species belong to the genera Aphis L. Uroleucon Mordvilko, Myzus Passerini, and Sitobion Mordvilko. Host range is analyzed for each Alloxysta species, as well as the extent of overlap between them. We used Jaccard's distance and a hierarchical cluster analysis to determine the host range dissimilarity. A permutation test has been applied to analyze if the host range dissimilarity is significantly different from what is expected by chance. We have calculated additional qualitative measures that complement well the Alloxysta niche overlap analysis and evaluated their host specificity using different indices and bipartite networks.
Abstract.
2013
Elias M, Fontaine C, Van Veen FJF (2013). Evolutionary history and ecological processes shape
a local multilevel antagonistic network.
Current Biology,
23, 1-5.
Abstract:
Evolutionary history and ecological processes shape
a local multilevel antagonistic network
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.
Abstract.
Elias M, Fontaine C, Frank Van Veen FJ (2013). Evolutionary history and ecological processes shape a local multilevel antagonistic network.
Current Biology,
23(14), 1355-1359.
Abstract:
Evolutionary history and ecological processes shape a local multilevel antagonistic network
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. © 2013 Elsevier Ltd.
Abstract.
van Veen FJF, Sanders D (2013). Herbivore identity mediates the strength of trophic cascades on individual plants.
ECOSPHERE,
4(5).
Author URL.
Perkins MJ, Mcdonald RA, van Veen FJF, Kelly SD, Rees G, Bearhop S (2013). Important impacts of tissue selection and lipid extraction on ecological parameters derived from stable isotope ratios.
Methods in Ecology and Evolution,
4(10), 944-953.
Abstract:
Important impacts of tissue selection and lipid extraction on ecological parameters derived from stable isotope ratios
Summary: the nitrogen (δ15N) and carbon (δ13C) isotope ratios of animal tissues can help identify the composition of diets and open up a myriad of ecological applications. However, consumers do not ingest or assimilate all components of food items, and it is not well understood how sampling different tissues of sources and consumers may affect isotopic values ascribed, and thereby how such variation affects derived ecological measures. Utilizing a simple prey-predator feeding relationship in insects, we examined isotopic differences in soft, exoskeleton and whole tissues using samples with and without lipid extraction. As a derived ecological measure, we calculated trophic discrimination factors, changes in δ15N or δ13C between source and consumer, for the different prey-predator tissue combinations. Lipid extraction did not affect δ15N values, and we found significant tissue differences in δ15N that varied between prey and predator. Lipid extraction enriched δ13C values in most instances, and it was only after extraction of lipids that we observed consistent depletion of δ13C in exoskeleton relative to soft tissues in prey and predator. Isotopic differences between tissue types propagated marked variation in derived ecological parameters. Common sampling practice using whole tissue for prey and predator (whole/whole) resulted in a trophic discrimination factor of 0·48‰ for δ15N, compared with correct factors of 0·97‰ (soft/whole) and 2·18‰ (soft/soft) using prey soft tissue actually ingested by the predator. For δ13C, variation across discrimination factors was less, with whole/whole tissue of -0·14‰, whilst correct factors were -0·55‰ (soft/whole) and -0·04‰ (soft/soft). Our results indicate that tissue selection and preparation are important considerations for isotopic studies using arthropods. Lipid extraction is necessary to derive accurate δ13C values based on proteins, whilst consequences of tissue selection are likely context-dependent: in poorly defined systems where sources are isotopically similar or have larger variance, our results indicate that tissue selection within sources is important to avoid significant error, whether estimating trophic positions or dietary proportions using mixing models. In such cases, we strongly recommend exclusion of source materials not assimilated in consumers. © 2013 British Ecological Society.
Abstract.
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.
2012
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.
Rand TA, van Veen FJF, Tscharntke T (2012). Landscape complexity differentially benefits generalized fourth, over specialized third, trophic level natural enemies.
Ecography,
35, 97-104.
Abstract:
Landscape complexity differentially benefits generalized fourth, over specialized third, trophic level natural enemies
The differential loss of higher trophic levels in the face of natural habitat loss can result in the disruption of important trophic interactions, such as biological control. Natural enemies of herbivorous pests in cropping systems often benefit from the presence of natural habitats in surrounding landscapes, as they provide key resources such as alternative hosts. However, any benefits from a biological control perspective may be dampened if this also enhances enemies at the fourth trophic level. Remarkably, studies of the influence of landscape structure on diversity and interactions of fourth trophic-level natural enemies are largely lacking. We carried out a large-scale sampling study to investigate the effects of landscape complexity (i.e. the proportion of non-crop habitat in the landscapes surrounding focal study areas) on the parasitoid communities of aphids in wheat and on an abundant extra-field plant, stinging nettle. Primary parasitoid communities (3rd trophic level) attacking the cereal aphid, Sitobion avenae, had little overlap with the communities attacking the nettle aphid, Microlophium carnosum, while secondary parasitoids (4th trophic level) showed high levels of species overlap across these two aphids (25 vs 73% shared species respectively), resulting in significantly higher linkage density and lower specialization for secondary than primary parasitoid webs. In wheat, parasitoid diversity was not related to landscape complexity for either primary or secondary parasitoids. Rates of primary parasitism were generally low, while secondary parasitism rates were high (37–94%) and increased significantly with increasing landscape complexity, although this pattern was driven by a single secondary parasitoid species. Overall, our results demonstrate that extra-field habitats and landscape complexity can differentially benefit fourth, over third, trophic level natural enemies, and thereby, could dampen biological control. Our results further suggest that fourth trophic-level enemies may play an important, yet understudied, role in linking insect population dynamics across habitat types.
Abstract.
Henri DC, Seager D, Weller T, van Veen FJF (2012). Potential for climate effects on the size-structure of host-parasitoid indirect interaction networks.
Philosophical Transactions of the Royal Society B: Biological Sciences,
367(1605), 3018-3024.
Abstract:
Potential for climate effects on the size-structure of host-parasitoid indirect interaction networks
Communities of insect herbivores are thought to be structured mainly by indirect processes mediated by shared natural enemies, such as apparent competition. In host-parasitoid interaction networks, overlap in natural enemy communities between any pair of host species depends on the realized niches of parasitoids, which ultimately depend on the foraging decisions of individuals. Optimal foraging theory predicts that egg-limited parasitoid females should reject small hosts in favour of future opportunities to oviposit in larger hosts, while time-limited parasitoids are expected to optimize oviposition rate regardless of host size. The degree to which parasitoids are time- or egglimited depends in part on weather conditions, as this determines the proportion of an individual's lifespan that is available to foraging. Using a 10-year time series of monthly quantitative host-parasitoid webs, we present evidence for host-size-based electivity and sex allocation in the common secondary parasitoid Asaphes vulgaris. We argue that this electivity leads to body-sizedependent asymmetry in apparent competition among hosts and we discuss how changing weather patterns, as a result of climate change, may impact foraging behaviour and thereby the size-structure and dynamics of host-parasitoid indirect interaction networks. © 2012 the Royal Society.
Abstract.
2011
von Burg S, van Veen FJF, Álvarez-Alfageme F, Romeis J (2011). Aphid-parasitoid community structure on genetically modified wheat.
Biology Letters,
7(3), 387-391.
Abstract:
Aphid-parasitoid community structure on genetically modified wheat
Since the introduction of genetically modified (GM) plants, one of the main concerns has been their potential effect on non-target insects. Many studies have looked at GM plant effects on single non-target herbivore species or on simple herbivore-natural enemy food chains. Agro-ecosystems, however, are characterized by numerous insect species which are involved in complex interactions, forming food webs. In this study, we looked at transgenic disease-resistant wheat (Triticum aestivum) and its effect on aphid-parasitoid food webs. We hypothesized that the GM of the wheat lines directly or indirectly affect aphids and that these effects cascade up to change the structure of the associated food webs. Over 2 years, we studied different experimental wheat lines under semi-field conditions. We constructed quantitative food webs to compare their properties on GM lines with the properties on corresponding non-transgenic controls. We found significant effects of the different wheat lines on insect community structure up to the fourth trophic level. However, the observed effects were inconsistent between study years and the variation between wheat varieties was as big as between GM plants and their controls. This suggests that the impact of our powdery mildew-resistant GM wheat plants on food web structure may be negligible and potential ecological effects on non-target insects limited.
Abstract.
Henri DC, van Veen FJF (2011). Body Size, Life History and the Structure of Host-Parasitoid Networks.
Adv. Ecol. Res.,
45, 135-180.
Abstract:
Body Size, Life History and the Structure of Host-Parasitoid Networks
Recent studies of the allometric scaling of metabolism, resource handling and space use have
provided a mechanistic understanding of how interactions within ecological networks are
arranged. Especially, the ‘allometric diet breadth model’ (ADBM), which considers the
association between consumer size, resource availability and handling costs, has shown that
food webs are predictably shaped according to the body-size relationships of the organisms
within them. However, size-based models of network structure are more applicable to
predator-prey webs than to insect host-parasitoid networks because the relationship between body-size and host use appears to be less straightforward in host-parasitoid interactions.
Herein, we describe the structuring of host-parasitoid networks using frameworks that are
based not only upon parasitoid body-size considerations, but also upon the life-history
characteristics that are commonly used to describe variation among hymenopteran
parasitoids: the degree of ovigeny, idio/koinobosis and endo/ectoparasitism. We compare these frameworks with those suggested by the ADBM and elucidate upon why it has been
unable to successfully predict host-parasitoid network structure. For instance, body-size
constraints upon foraging capability are a stronger determinant of whether an interaction is
possible in predator-prey webs than they are in host-parasitoid networks because the ultimate
determinant of host-suitability is its phylogeny. Furthermore, the degree to which the
taxonomic host range of a parasitoid is constrained by phylogeny is largely determined by
parasitoid life-history, e.g. whether the larva develops as an endo- or ecto-biont. In addition,
we describe how parasitoid life-history influences host-choice decisions, which are expected to be tailored towards the optimal allocation of scarce resources, through the determination of
how species are limited in their reproductive success. To conclude, we describe some fruitful
avenues for future research and highlight the importance of considering how temporal or
spatial variation in the characteristics of parasitoids or their hosts affect how networks are structured.
Abstract.
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.
Jones TS, Allen E, Haerri SA, Krauss J, Mueller CB, van Veen FJF (2011). Effects of genetic diversity of grass on insect species diversity at higher trophic levels are not due to cascading diversity effects.
Oikos,
120(7), 1031-1036.
Abstract:
Effects of genetic diversity of grass on insect species diversity at higher trophic levels are not due to cascading diversity effects
Genetic diversity in plant populations has been shown to affect the species diversity of insects. In grasses, infection with fungal endophytes can also have strong effects on insects, potentially modifying the effects of plant genetic diversity. We manipulated the genetic diversity and endophyte infection of a grass in a field experiment. We show that diversity of primary parasitoids (3rd trophic level) and, especially, secondary parasitoids (4th trophic level) increases with grass genetic diversity while there was no effect of endophyte infection. The increase in insect diversity appeared to be due to a complementarity effect rather than a sampling effect. The higher parasitoid diversity could not be explained by a cascading diversity effect because herbivore diversity was not affected and the same herbivore species were present in all treatments. The effects on the higher trophic levels must therefore be due to a direct response to plant traits or mediated by effects on traits at intermediate trophic levels.
Abstract.
Fontaine F, Guimaraes PRJ, Kefi S, Loeuille N, Memmott J, van der Putten WH, van Veen FJF, Thebault E (2011). The ecological and evolutionary implications of merging different types of networks.
Ecology Letters,
14, 1170-1181.
Abstract:
The ecological and evolutionary implications of merging different types of networks
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.
Abstract.
2010
Woodward G, Benstead JP, Beveridge OS, Blanchard J, Brey T, Brown LE, Cross WF, Friberg N, Ings TC, Jacob U, et al (2010). Ecological Networks in a Changing Climate. In (Ed) Advances in Ecological Research, Elsevier, 71-138.
Woodward G, Benstead JP, Beveridge OS, Blanchard J, Brey T, Brown LE, Cross WF, Friberg N, Ings TC, Jacob U, et al (2010). Ecological Networks in a Changing Climate.
Advances in Ecological Research,
42(C), 71-138.
Abstract:
Ecological Networks in a Changing Climate
Attempts to gauge the biological impacts of climate change have typically focussed on the lower levels of organization (individuals to populations), rather than considering more complex multi-species systems, such as entire ecological networks (food webs, mutualistic and host-parasitoid networks). We evaluate the possibility that a few principal drivers underpin network-level responses to climate change, and that these drivers can be studied to develop a more coherent theoretical framework than is currently provided by phenomenological approaches. For instance, warming will elevate individual ectotherm metabolic rates, and direct and indirect effects of changes in atmospheric conditions are expected to alter the stoichiometry of interactions between primary consumers and basal resources; these effects are general and pervasive, and will permeate through the entire networks that they affect. In addition, changes in the density and viscosity of aqueous media could alter interactions among very small organisms and disrupt the pycnoclines that currently compartmentalize many aquatic networks in time and space. We identify a range of approaches and potential model systems that are particularly well suited to network-level studies within the context of climate change. We also highlight potentially fruitful areas of research with a view to improving our predictive power regarding climate change impacts on networks. We focus throughout on mechanistic approaches rooted in first principles that demonstrate potential for application across a wide range of taxa and systems. © 2010 Elsevier Ltd.
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.
Holt RD, Holdo RM, Van Veen FJF (2010). Theoretical Perspectives on Trophic Cascades: Current Trends and Future Directions. In Terborgh J, Estes J (Eds.) The Science of Trophic Cascades, Island Press, 301-318.
2009
van Veen FJF, Brandon CE, Godfray HCJ (2009). A positive trait-mediated indirect effect involving the natural enemies of competing herbivores.
OECOLOGIA,
160(1), 195-205.
Author URL.
Ings TC, Montoya JM, Bascompte J, Bluethgen N, Brown L, Dormann CF, Edwards F, Figueroa D, Jacob U, Jones JI, et al (2009). Ecological networks - beyond food webs.
JOURNAL OF ANIMAL ECOLOGY,
78(1), 253-269.
Author URL.
van Veen FJF (2009). Food webs. Current Biology, 19, R281-R283.
Jones TS, Godfray HCJ, van Veen FJF (2009). Resource competition and shared natural enemies in experimental insect communities.
OECOLOGIA,
159(3), 627-635.
Author URL.
2008
Bukovinszky T, van Veen FJF, Jongema Y, Dicke M (2008). Direct and indirect effects of resource quality on food web structure.
SCIENCE,
319(5864), 804-807.
Author URL.
Traugott M, Bell JR, Broad GR, Powell W, Van Veen FJF, Vollhardt IMG, Symondson WOC (2008). Endoparasitism in cereal aphids: Molecular analysis of a whole parasitoid community.
Molecular Ecology,
17(17), 3928-3938.
Abstract:
Endoparasitism in cereal aphids: Molecular analysis of a whole parasitoid community
Insect parasitoids play a major role in terrestrial food webs as they are highly diverse, exploit a wide range of niches and are capable of affecting host population dynamics. Formidable difficulties are encountered when attempting to quantify host-parasitoid and parasitoid-parasitoid trophic links in diverse parasitoid communities. Here we present a DNA-based approach to effectively track trophic interactions within an aphid-parasitoid food web, targeting, for the first time, the whole community of parasitoids and hyperparasitods associated with a single host. Using highly specific and sensitive multiplex and singleplex polymerase chain reaction, endoparasitism in the grain aphid Sitobion avenae (F) by 11 parasitoid species was quantified. Out of 1061 aphids collected during 12 weeks in a wheat field, 18.9% were found to be parasitized. Parasitoids responded to the supply of aphids, with the proportion of aphids parasitized increasing monotonically with date, until the aphid population crashed. In addition to eight species of primary parasitoids, DNA from two hyperparasitoid species was detected within 4.1% of the screened aphids, with significant hyperparasitoid pressure on some parasitoid species. In 68.2% of the hyperparasitized aphids, identification of the primary parasitoid host was also possible, allowing us to track species-specific parasitoid-hyperparasitoid links. Nine combinations of primary parasitoids within a single host were found, but only 1.6% of all screened aphids were multiparasitized. The potential of this approach to parasitoid food web research is discussed. © 2008 the Authors.
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