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Ponds are among the most biodiverse and ecologically important freshwater habitats globally and may provide a significant opportunity to mitigate anthropogenic pressures and reverse the decline of aquatic biodiversity. Ponds also provide important contributions to society through the provision of ecosystem services. Despite the ecological and societal importance of ponds, freshwater research, policy, and conservation have historically focused on larger water bodies, with significant gaps remaining in our understanding and conservation of pond ecosystems. In May 2019, pond researchers and practitioners participated in a workshop to tackle several pond ecology, conservation, and management issues. Nine research themes and 30 research questions were identified during and following the workshop to address knowledge gaps around: (1) pond habitat definition; (2) global and long-term data availability; (3) anthropogenic stressors; (4) aquatic-terrestrial interactions; (5) succession and disturbance; (6) freshwater connectivity; (7) pond monitoring and technological advances; (8) socio-economic factors; and (9) conservation, management, and policy. Key areas for the future inclusion of ponds in environmental and conservation policy were also discussed. Addressing gaps in our fundamental understanding of pond ecosystems will facilitate more effective research-led conservation and management of pondscapes, their inclusion in environmental policy, support the sustainability of ecosystem services, and help address many of the global threats driving the decline in freshwater biodiversity.

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1. Root hemiparasites are common components of many ecosystems and can affect both the biomass and the nutritional quality of the plants they infect. The consequences of these modifications for the preference and performance of three herbivore feeding guilds sharing a host with the hemi-parasite were examined. \ud \ud 2. It was predicted that as the hemiparasite increased in biomass its impact on the host would increase, as would the indirect impacts on the herbivores. It was also predicted that herbivores from different feeding guilds would respond differently to the presence of the hemiparasite, reflecting the extent to which they utilise resources disrupted by the parasite and hence are in competition with it. \ud \ud 3. The preference and performance of phloem-feeding aphids, xylem-feeding spittle bugs, and leaf-feeding grasshoppers were measured on the host grass species, Holcus lanatus L. (Poaceae), with and without attachment from the hemi-parasite, Rhinanthus minor L. (Orobanchaceae). \ud \ud 4. The effects of R. minor on the host were dependent on the hemiparasite's stage of growth, being most pronounced when it was at peak biomass. At this stage it caused a significant reduction in the biomass, water content, and total nitrogen content of the host plants. \ud \ud 5. Overall, herbivores benefited from, or preferred, shared host plants more than uninfected plants. The aphid benefited from sharing a host with R. minor, showing increased population growth on, and preference for, parasitised plants. The spittle bug also showed a preference for parasitised plants. The grasshopper, Chorthippus brunneus Thunberg (Orthoptera: Acrididae), did not show a preference for, or a performance response to, parasitised hosts, but it consumed significantly more plant material when caged on parasitised plants. \ud \ud 6. These data support the prediction that invertebrate herbivores responded to changes in host plant traits driven by the hemiparasite, and strongly suggest that these indirect interactions could impact on population and community processes within natural communitie

1. Climatic warming has induced marked shifts in the geographical distribution and seasonal phenology of many species, although the impacts of climatic changes on the interactions between species across trophic levels are far less well known. 2. Freshwater microcosms were used to test the effect of temperature on the life history traits of a prey species, the fairy shrimp Chirocephalus diaphanus (Anostraca), the abundance of a predator, the microcrustacean Heterocypris incongruens (Ostracoda), and on the interaction between them. 3. When reared in the absence of predators, C. diaphanus survival was low at the highest temperature (25°C) and greatly reduced at the lowest temperature (5°C). It was reproductively most successful at an intermediate temperature (20°C), suggesting that it may benefit from the increase in temperature predicted under future climate change scenarios. In the absence of other species, temperature would have to increase dramatically to affect C. diaphanus adversely. 4. Heterocypris incongruens was more abundant and its predation on C. diaphanus greatest at higher temperatures, partially offsetting the positive effect of raised temperature on prey observed when the predator was absent. The net effect was that the optimal temperature for C. diaphanus when coexisting with its predator was lower than when it was in isolation. This means that currently predicted increases in temperature ultimately may be detrimental to C. diaphanus. 5. Predation rates were generally enhanced by high temperature, prey size and prey density, with significant interaction between them. Thus, the positive effects of raised temperature on predation rate were additionally dependent upon prey characteristics, being strongest when prey were large and at high density and weakest when prey were small and at low density. 6. Interactions with a natural enemy, in this case a predator, may alter how species respond to raised temperatures; prey size and density further modify the outcome of this interaction. This context dependency in the response of both predators and prey to temperature suggests that the ecological impacts of future climate change on trophic interactions may be difficult to predict.

Summary1. Individual plants are often simultaneously consumed by many different organisms and mediate important indirect interactions between their consumers, even when their consumers are phylogenetically distant and feed on different parts of the plant. 2. We examined the effects on two xylem feeders of sharing a plant host in greenhouse pot trials and outdoor mesocosms. The spittle bug Neophilaenus lineatus, which feeds on grass shoots, and a hemiparasitic angiosperm, Rhinanthus minor, which attaches to the roots, were added separately or together on grass host plants growing in pots or in model grassland swards. 3. We found strong asymmetric competition between the hemiparasite and the insect. In greenhouse experiments, sharing a grass host with R. minor significantly increased mortality of N. lineatus, but R. minor performance was unaffected. 4. Mortality of N. lineatus was also increased on swards containing R. minor in model communities grown in the field. R. minor was more sensitive to sharing a host with N. lineatus in these communities, and experienced a modest (non-significant) reduction in flower production. 5. The hemiparasite was the stronger competitor for xylem resources, possibly because of its ability to extract resources from the plant roots, and because of its significant ability to appropriate the xylem stream via its strong transpirational pull. 6. We believe these are the first experiments to demonstrate competition between insect herbivores and hemiparasitic plants mediated via a shared host plant. The consequences for the invertebrate population were potentially highly significant and we propose that future research should further explore the role of this asymmetric relationship in structuring invertebrate communities.

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