Landscape alteration and habitat modification: impacts on plant-pollinator systems

Insect pollinators provide an important ecosystem service to many crop species and underpin the reproductive assurance of many wild plant species. Multiple, anthropogenic pressures threaten insect pollinators. Land-use change and intensification alters the habitats and landscapes that provide food and nesting resources for pollinators. These impacts vary according to species traits, producing winners and losers, while the intrinsic robustness of plant-pollinator networks may provide stability in pollination function. However, this functional stability might be eroded by multiple, interacting stressors. Anthropogenic changes in pollinator-mediated connectivity will alter plant mating systems (e.g. inbreeding level), with implications for plant fitness and phenotypes governing trophic interactions. The degree to which plant populations can persist despite, or adapt to, pollination deficits remains unclear

From landscape to host-plant scales: Bottom-up heterogeneity affects invertebrate diversity and interactions

The influence of ecological heterogeneity on invertebrate diversity, trophic guild structure, and host-parasitoid interactions was assessed at landscape, habitat and host-plant scales. Variation in the cover of forest and spatial heterogeneity of six landscapes affected the diversity of epigeal beetles and soil fauna, indicating human land-use can structure communities that operate at fine spatial scales. Invertebrate taxon identity determined if species richness, abundance or both were affected by landscape structure and whether the relationship was linear or hump-shaped. Above-ground diversity positively correlated with soil fauna diversity, but worm and collembola diversity correlated with different plant functional groups. Using the presence of cattle grazing in birch woodlands the impact of disturbance to semi-natural habitat on invertebrate diversity and trophic interactions was studied. Grazing led to a reduction in the height of understorey vegetation, and concomitant increase in plant diversity. This grazing-dependent habitat heterogeneity was correlated with a decline in the diversity of generalist secondary consumers but left herbivores unaffected. A host-parasitoid interaction was affected by the presence of cattle in birch woods. Increased floral diversity in the grazed sward indirectly (via increases in host density) and directly increased parasitism rates, a rare example of a tertiary trophic level being positively affected by anthropogenic disturbance. Using this host-parasitoid system we examined the influence of habitat patch size and isolation on this antagonistic interaction. The largest patches supported the greatest herbivore densities, but the parasitoid was unaffected. This differential impact of habitat structure meant that parasitism was inversely density-dependent and the potential stability of the interaction (CV > 1) was reduced, providing a refuge from parasitism for the host. Bottom-up sources of heterogeneity at different scales affect diversity at higher trophic levels. Anthropogenic disturbance to plant communities can alter trophic guild structure and interactions between insect species

Managing farmed landscapes for pollinating insects

Increasing floral resources and improving habitat conditions can benefit pollinating insect species, wildflowers and crop production

Network size, structure and mutualism dependence affect the propensity for plant-pollinator extinction cascades

1. Pollinator network structure arising from the extent and strength of interspecific mutualistic interactions can promote species persistence and community robustness. However, environmental change may re-organise network structure limiting capacity to absorb or resist shocks and increasing species extinctions. 2. We investigated if habitat disturbance and the level of mutualism dependence between species affected the robustness of insect–flower visitation networks Following a recently developed Stochastic Co-extinction Model (SCM), we ran simulations to produce the number of extinction episodes (cascade degree), which we correlated with network structure in undisturbed and disturbed habitat. We also explicitly modelled whether a species’ intrinsic dependence on mutualism affected the propensity for extinction cascades in the network. 3. Habitat disturbance generated a gradient in network structure with those from disturbed sites being less connected, but more speciose and so larger. Controlling for network size (z-score standardisation against the null model) revealed that disturbed networks had disproportionately low linkage density, high specialisation, fewer insect visitors per plant species (vulnerability) and lower nestedness (NODF). 4. This network structure gradient driven by disturbance increased and decreased different aspects of robustness to simulated plant extinction. Disturbance decreased the risk that an initial insect extinction would follow a plant species loss. Although, this effect disappeared when network size and connectance were standardised, suggesting the lower connectance of disturbed networks increased robustness to an initial secondary extinction. 5. However, if a secondary extinction occurred then networks from disturbed habitat were more prone to large co-extinction cascades, likely resulting from a greater chance of extinction in these larger, speciose networks. Conversely, when species mutualism dependency was explicit in the SCM simulations the disturbed networks were disproportionately more robust to very large co-extinction cascades, potentially caused by non-random patterns of interaction between species differing in dependence on mutualism. 6. Our results showed disturbance altered the size and the distribution of interspecific interactions in the networks to affect their robustness to co-extinction cascades. Controlling for effects due to network size and the interspecific variation in demographic dependence on mutualism can improve insight into properties conferring the structural robustness of networks to environmental changes

Risks to pollinators and pollination from invasive alien species

Invasive alien species modify pollinator biodiversity and the services they provide that underpin ecosystem function and human well-being. Building on the Intergovernmental Science-Policy Platform for Biodiversity and Ecosystem Services (IPBES) global assessment of pollinators and pollination, we synthesize current understanding of invasive alien impacts on pollinators and pollination. Invasive alien species create risks and opportunities for pollinator nutrition, re-organize species interactions to affect native pollination and community stability, and spread and select for virulent diseases. Risks are complex but substantial, and depend greatly on the ecological function and evolutionary history of both the invader and the recipient ecosystem. We highlight evolutionary implications for pollination from invasive alien species, and identify future research directions, key messages and options for decision-making

Risk to pollinators from anthropogenic electro-magnetic radiation (EMR): evidence and knowledge gaps

Worldwide urbanisation and use of mobile and wireless technologies (5G, Internet of Things) is leading to the proliferation of anthropogenic electromagnetic radiation (EMR) and campaigning voices continue to call for the risk to human health and wildlife to be recognised. Pollinators provide many benefits to nature and humankind, but face multiple anthropogenic threats. Here, we assess whether artificial light at night (ALAN) and anthropogenic radiofrequency electromagnetic radiation (AREMR), such as used in wireless technologies (4G, 5G) or emitted from power lines, represent an additional and growing threat to pollinators. A lack of high quality scientific studies means that knowledge of the risk to pollinators from anthropogenic EMR is either inconclusive, unresolved, or only partly established. A handful of studies provide evidence that ALAN can alter pollinator communities, pollination and fruit set. Laboratory experiments provide some, albeit variable, evidence that the honey bee Apis mellifera and other invertebrates can detect EMR, potentially using it for orientation or navigation, but they do not provide evidence that AREMR affects insect behaviour in ecosystems. Scientifically robust evidence of AREMR impacts on abundance or diversity of pollinators (or other invertebrates) are limited to a single study reporting positive and negative effects depending on the pollinator group and geographical location. Therefore, whether anthropogenic EMR (ALAN or AREMR) poses a significant threat to insect pollinators and the benefits they provide to ecosystems and humanity remains to be established

Elevated atmospheric CO2 impairs aphid escape responses to predators and conspecific alarm signals

Research into the impact of atmospheric change on predator–prey interactions has mainly focused on density dependent responses and trophic linkages. As yet, the chemical ecology underpinning predator–prey interactions has received little attention in environmental change research. Group living animals have evolved behavioral mechanisms to escape predation, including chemical alarm signalling. Chemical alarm signalling between conspecific prey could be susceptible to environmental change if the physiology and behavior of these organisms are affected by changes in dietary quality resulting from environmental change. Using Rubus idaeus plants, we show that elevated concentrations of atmospheric CO2 (eCO2) severely impaired escape responses of the aphid Amphorophora idaei to predation by ladybird larvae (Harmonia axyridis). Escape responses to ladybirds was reduced by >50 % after aphids had been reared on plants grown under eCO2. This behavioral response was rapidly induced, occurring within 24 h of being transferred to plants grown at eCO2 and, once induced, persisted even after aphids were transferred to plants grown at ambient CO2. Escape responses were impaired due to reduced sensitivity to aphid alarm pheromone, (E)-β-farnesene, via an undefined plant-mediated mechanism. Aphid abundance often increases under eCO2, however, reduced efficacy of conspecific signalling may increase aphid vulnerability to predation, highlighting the need to study the chemical ecology of predator–prey interactions under environmental change

Top-down control by Harmonia axyridis mitigates the impact of elevated atmospheric CO2 on a plant-aphid interaction

1. The present study investigated the impact of elevated atmospheric CO2 (390 or 650 μmol/mol) on raspberry genotypes varying in resistance to the large raspberry aphid Amphorophora idaei and any subsequent impact on the coccinellid predator Harmonia axyridis. 2. CO2 enrichment promoted plant growth, ranging from 30% in the partially susceptible cultivar to a more than 100% increase for the susceptible cultivar. 3. Aphid abundance and colonization (presence–absence) on the susceptible cultivars were not influenced by CO2 enrichment. On the resistant cultivar, aphid colonisation increased from 14% in ambient CO2 to 70% in elevated CO2 with a subsequent increase in aphid abundance, implying a breakdown in resistance. Inclusion of the natural enemy on the resistant cultivar, however, suppressed the increase in aphid abundance at elevated CO2. 4. The present study highlights how crop genotypes vary in responses to climate change; some cultivars can become more susceptible to aphid pests under elevated CO2. We do, however, demonstrate the potential for top-down control to mitigate the effect of global climate change on pest populations

Habitat loss, predation pressure and episodic heat-shocks interact to impact arthropods and photosynthetic functioning of microecosystems

Ecosystems face multiple, potentially interacting, anthropogenic pressures that can modify biodiversity and ecosystem functioning. Using a bryophyte–microarthropod microecosystem we tested the combined effects of habitat loss, episodic heat-shocks and an introduced non-native apex predator on ecosystem function (chlorophyll fluorescence as an indicator of photosystem II function) and microarthropod communities (abundance and body size). The photosynthetic function was degraded by the sequence of heat-shock episodes, but unaffected by microecosystem patch size or top-down pressure from the introduced predator. In small microecosystem patches without the non-native predator, Acari abundance decreased with heat-shock frequency, while Collembola abundance increased. These trends disappeared in larger microecosystem patches or when predators were introduced, although Acari abundance was lower in large patches that underwent heat-shocks and were exposed to the predator. Mean assemblage body length (Collembola) was reduced independently in small microecosystem patches and with greater heat-shock frequency. Our experimental simulation of episodic heatwaves, habitat loss and non-native predation pressure in microecosystems produced evidence of individual and potentially synergistic and antagonistic effects on ecosystem function and microarthropod communities. Such complex outcomes of interactions between multiple stressors need to be considered when assessing anthropogenic risks for biota and ecosystem functioning

Root herbivores drive changes to plant primary chemistry, but root loss is mitigated under elevated atmospheric CO2

Above- and belowground herbivory represents a major challenge to crop productivity and sustainable agriculture worldwide. How this threat from multiple herbivore pests will change under anthropogenic climate change, via altered trophic interactions and plant response traits, is key to understanding future crop resistance to herbivory. In this study, we hypothesized that atmospheric carbon enrichment would increase the amount (biomass) and quality (C:N ratio) of crop plant resources for above- and belowground herbivore species. In a controlled environment facility, we conducted a microcosm experiment using the large raspberry aphid (Amphorophora idaei), the root feeding larvae of the vine weevil (Otiorhynchus sulcatus), and the raspberry (Rubus idaeus) host-plant. There were four herbivore treatments (control, aphid only, weevil only and a combination of both herbivores) and an ambient (aCO2) or elevated (eCO2) CO2 treatment (390 versus 650 ± 50 μmol/mol) assigned to two raspberry cultivars (cv Glen Ample or Glen Clova) varying in resistance to aphid herbivory. Contrary to our predictions, eCO2 did not increase crop biomass or the C:N ratio of the plant tissues, nor affect herbivore abundance either directly or via the host-plant. Root herbivory reduced belowground crop biomass under aCO2 but not eCO2, suggesting that crops could tolerate attack in a CO2 enriched environment. Root herbivory also increased the C:N ratio in leaf tissue at eCO2, potentially due to decreased N uptake indicated by lower N concentrations found in the roots. Root herbivory greatly increased root C concentrations under both CO2 treatments. Our findings confirm that responses of crop biomass and biochemistry to climate change need examining within the context of herbivory, as biotic interactions appear as important as direct effects of eCO2 on crop productivity