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1. Higher bee abundance, but not pest abundance, in landscapes with more agriculture on a late-flowering legume crop in tropical smallholder farms

   https://doi.org/10.7717/peerj.10732  

   Vogel, Cassandra ; Chunga, Timothy L. ; Sun, Xiaoxuan ; Poveda, Katja ; Steffan-Dewenter, Ingolf ( January 2021 , PeerJ)

   Background Landscape composition is known to affect both beneficial insect and pest communities on crop fields. Landscape composition therefore can impact ecosystem (dis)services provided by insects to crops. Though landscape effects on ecosystem service providers have been studied in large-scale agriculture in temperate regions, there is a lack of representation of tropical smallholder agriculture within this field of study, especially in sub-Sahara Africa. Legume crops can provide important food security and soil improvement benefits to vulnerable agriculturalists. However, legumes are dependent on pollinating insects, particularly bees (Hymenoptera: Apiformes) for production and are vulnerable to pests. We selected 10 pigeon pea (Fabaceae: Cajunus cajan (L.)) fields in Malawi with varying proportions of semi-natural habitat and agricultural area within a 1 km radius to study: (1) how the proportion of semi-natural habitat and agricultural area affects the abundance and richness of bees and abundance of florivorous blister beetles (Coleoptera: Melloidae ), (2) if the proportion of flowers damaged and fruit set difference between open and bagged flowers are correlated with the proportion of semi-natural habitat or agricultural area and (3) if pigeon pea fruit set difference between open and bagged flowers in these landscapes was constrained by pest damage or improved bymore »bee visitation. Methods We performed three, ten-minute, 15 m, transects per field to assess blister beetle abundance and bee abundance and richness. Bees were captured and identified to (morpho)species. We assessed the proportion of flowers damaged by beetles during the flowering period. We performed a pollinator and pest exclusion experiment on 15 plants per field to assess whether fruit set was pollinator limited or constrained by pests. Results In our study, bee abundance was higher in areas with proportionally more agricultural area surrounding the fields. This effect was mostly driven by an increase in honeybees. Bee richness and beetle abundances were not affected by landscape characteristics, nor was flower damage or fruit set difference between bagged and open flowers. We did not observe a positive effect of bee density or richness, nor a negative effect of florivory, on fruit set difference. Discussion In our study area, pigeon pea flowers relatively late—well into the dry season. This could explain why we observe higher densities of bees in areas dominated by agriculture rather than in areas with more semi-natural habitat where resources for bees during this time of the year are scarce. Therefore, late flowering legumes may be an important food resource for bees during a period of scarcity in the seasonal tropics. The differences in patterns between our study and those conducted in temperate regions highlight the need for landscape-scale studies in areas outside the temperate region.« less
2. Salinity Influences Plant–Pest–Predator Tritrophic Interactions

   https://doi.org/10.1093/jee/toab133  

   Ali, M P ; Rahman, M S ; Nowrin, Farzana ; Haque, S S ; Qin, Xinghu ; Haque, M A ; Uddin, M M ; Landis, Douglas A ; Howlader, M T ( July 2021 , Journal of Economic Entomology)

   Eigenbrode, Sanford (Ed.)

   Abstract Climate change-induced salinity intrusion into agricultural soils is known to negatively impact crop production and food security. However, the effects of salinity increase on plant–herbivore–natural enemy systems and repercussions for pest suppression services are largely unknown. Here, we examine the effects of increased salinity on communities of rice (Oryza sativa), brown planthopper (BPH), Nilaparvata lugens, and green mirid bug (GMB), Cyrtorhinus lividipennis, under greenhouse conditions. We found that elevated salinity significantly suppressed the growth of two rice cultivars. Meanwhile, BPH population size also generally decreased due to poor host plant quality induced by elevated salinity. The highest BPH density occurred at 2.0 dS/m salinity and declined thereafter with increasing salinity, irrespective of rice cultivar. The highest population density of GMB also occurred under control conditions and decreased significantly with increasing salinity. Higher salinity directly affected the rice crop by reducing plant quality measured with reference to biomass production and plant height, whereas inducing population developmental asynchrony between BPH and GMB observed at 2 dS/m salinity and potentially uncoupling prey–predator dynamics. Our results suggest that increased salinity has harmful effects on plants, herbivores, natural enemies, as well as plant–pest–predator interactions. The effects measured here suggest that the bottom-up effects ofmore »predatory insects on rice pests will likely decline in rice produced in coastal areas where salinity intrusion is common. Our findings indicate that elevated salinity influences tritrophic interactions in rice production landscapes, and further research should address resilient rice insect pest management combining multipests and predators in a changing environment.« less
3. Nutrient levels and trade-offs control diversity in a serial dilution ecosystem

   https://doi.org/10.7554/eLife.57790  

   Erez, Amir ; Lopez, Jaime G ; Weiner, Benjamin G ; Meir, Yigal ; Wingreen, Ned S ( September 2020 , eLife)

   In most environments, organisms compete for limited resources. The number and relative abundance of species that an ecosystem can host is referred to as ‘species diversity’. The competitive-exclusion principle is a hypothesis which proposes that, in an ecosystem, competition for resources results in decreased diversity: only species best equipped to consume the available resources thrive, while their less successful competitors die off. However, many natural ecosystems foster a wide array of species despite offering relatively few resources. Researchers have proposed many competing theories to explain how this paradox can emerge, but they have mainly focused on ecosystems where nutrients are steadily supplied. By contrast, less is known about the way species diversity is maintained when nutrients are only intermittently available, for example in ecosystems that have seasons. To address this question, Erez, Lopez et al. modeled communities of bacteria in which nutrients were repeatedly added and then used up. Depending on conditions, a variety of relationships between the amount of nutrient supplied and community diversity could emerge, suggesting that ecosystems do not follow a simple, universal rule that dictates species diversity. In particular, the resulting communities displayed a higher diversity of microbes than the limit imposed by the competitive-exclusion principle.more »Further observations allowed Erez, Lopez et al. to suggest guiding principles for when diversity in ecosystems will be maintained or lost. In this framework, ‘early-bird’ species, which rapidly use a subset of the available nutrients, grow to dominate the ecosystem. Even though ‘late-bird’ species are more effective at consuming the remaining resources, they cannot compete with the increased sheer numbers of the ‘early-birds’, leading to a ‘rich-get-richer’ phenomenon. Oceanic plankton, arctic permafrost and many other threatened, resource-poor ecosystems across the world can dramatically influence our daily lives. Closer to home, shifts in the microbe communities that live on the surface of the human body and in the digestive system are linked to poor health. Understanding how species diversity emerges and changes will help to protect our external and internal environments.« less
4. Urban specialization reduces habitat connectivity by a highly mobile wading bird

   https://doi.org/10.1186/s40462-020-00233-7  

   Teitelbaum, Claire S. ; Hepinstall-Cymerman, Jeffrey ; Kidd-Weaver, Anjelika ; Hernandez, Sonia M. ; Altizer, Sonia ; Hall, Richard J. ( December 2020 , Movement Ecology)

   Abstract Background Mobile animals transport nutrients and propagules across habitats, and are crucial for the functioning of food webs and for ecosystem services. Human activities such as urbanization can alter animal movement behavior, including site fidelity and resource use. Because many urban areas are adjacent to natural sites, mobile animals might connect natural and urban habitats. More generally, understanding animal movement patterns in urban areas can help predict how urban expansion will affect the roles of highly mobile animals in ecological processes. Methods Here, we examined movements by a seasonally nomadic wading bird, the American white ibis ( Eudocimus albus ), in South Florida, USA. White ibis are colonial wading birds that forage on aquatic prey; in recent years, some ibis have shifted their behavior to forage in urban parks, where they are fed by people. We used a spatial network approach to investigate how individual movement patterns influence connectivity between urban and non-urban sites. We built a network of habitat connectivity using GPS tracking data from ibis during their non-breeding season and compared this network to simulated networks that assumed individuals moved indiscriminately with respect to habitat type. Results We found that the observed network was less connected thanmore »the simulated networks, that urban-urban and natural-natural connections were strong, and that individuals using urban sites had the least-variable habitat use. Importantly, the few ibis that used both urban and natural habitats contributed the most to connectivity. Conclusions Habitat specialization in urban-acclimated wildlife could reduce the exchange of propagules and nutrients between urban and natural areas, which has consequences both for beneficial effects of connectivity such as gene flow and for detrimental effects such as the spread of contaminants or pathogens.« less
5. Soaring like a bird via reinforcement learning in the field

   Reddy, G. ( October 2018 , 07 Nature)

   Soaring birds often rely on ascending thermal plumes in the atmosphere as they search for prey or migrate across large distances. The landscape of convective currents is turbulent and rapidly shifts on timescales of a few minutes as thermals constantly form, disintegrate, or are transported away by the wind. How soaring birds find and navigate thermals within this complex landscape is unknown. Reinforcement learning can be used to find an effective navigational strategy as a sequence of decisions taken in response to environmental cues. Reinforcement learning was applied to train gliders in the field to autonomously navigate atmospheric thermals. Gliders of two-meter wingspan were equipped with a flight controller that enabled an on-board implementation of autonomous flight policies via precise control over their bank angle and pitch. Learning is severely challenged by a multitude of physical effects and the unpredictability of the natural environment. A navigational strategy was determined solely from the experiences collected over several days in the field using exploratory behavioral policies. Bird-like performance was achieved and several viable biological mechanosensory cues were identified for soaring birds, which are also directly applicable to the development of autonomous soaring vehicles.