Food resource and temporal partitioning amongst a guild of predatory agroecosystem-inhabiting ant species

Prey diversity and temporal foraging patterns of six abundant,predatory ant species were investigated seasonally in an agroecosystem with two main vegetable crops.Pheidole sp.demonstrated the highest predation success and therefore appears to be the dominant species while Tapinoma melanocephalum showed the lowest success under the natural field conditions.Investigation of prey diversity and temporal activity patterns with the null model tests of niche overlap revealed a significant overlap indicating that the activity periods and prey diversity may not be solely influenced by interactions among the co-existing ant species.However,niche partitioning in the daily peak activity periods was demonstrated during all the three seasons(summer,rainy and winter)particularly between Pheidole sp.and T.melanocephalum.Pheidole sp.exhibited a high intensity,broadly extended mono-modal foraging pattern.Camponotus compressus and C.paria showed bi-modality in their foraging activity during the rainy season and mono-modal patterns during summer and winter seasons.Pachycondyla tesserinoda,Tetramorium sp.and T.melanocephalum exhibited peak foraging activities in the morning hours during the summer and rainy seasons.The activity profiles of C.compressus and T.melanocephalum were skewed towards late afternoon hours during the winter season indicating avoidance of foraging activity during the favourable periods when the more aggressive Pheidole sp.is active.In the sponge gourd agroecosystem,the ants captured predominantly hymenopteran,orthopteran and coleopteran insects.While Pheidole sp.hunted mainly the large orthopteran prey,other ant species captured worker ants in the sponge gourd agroecosystem.In the cauliflower agroecosystem,while other species captured prey chiefly belonging to six orders,i.e.,Lepidoptera,Hymenoptera,Coleoptera,Hemiptera,Isoptera and Diptera,Pheidole sp.and P.tesserinoda were the only species to also hunt many orthopteran prey.The agroecosystem-inhabiting ant species prey on a large number and wide variety of insect herbivores as evident from the differences in the peak foraging times and the proportion of each type of prey hunted.Overall,our results indicate that the structure of agroecosystem-inhabiting ant assemblage may be influenced by a variety of factors including competition,temporal heterogeneities,prey availability and its characteristics such as size and mobility.

Hourly and monthly variations in the surface activity patterns of Hemilepistus reaumurii in arid environments of Tunisia

Life in desert ecosystems drives animals to adapt their surface locomotor activity according to environmental conditions. In this study, the hourly and monthly variations in the surface activity patterns of the terrestrial crustacean Hemilepistus reaumurii were investigated. The surface activity of H. reaumurii at the population scale was observed by collecting the hourly active individuals from the sunrise to the sunset of the studied day in each month of 2013 in the Bchachma locality, Tunisia. The collected active individuals were put in perspex boxes（on which we labeled the hourly time interval in which the individuals were collected） in the field and then transported to the laboratory for analysis. Individuals were counted, sexed, and measured in the laboratory. Despite desert conditions in the studied site, H. reaumurii was characterized by a diurnal surface activity, showing a bimodal pattern during the warm months（i.e., May to October）. However, it exhibited a unimodal surface activity pattern in the cold months（i.e., February, March, and November）. The surface activity was significantly correlated with sunrise and sunset. Moreover, a significant quadratic effect of temperature on the surface activity of H. reaumurii was observed. Furthermore, the study showed that the most important surface activity was recorded in March. The daily exploitation of the temporal niches was significantly different as a function of months. The body size of males was larger than that of females, and the body size of active individuals changed with months. All these behavioural changes in the surface activity represent an adaptive strategy of life in the arid environment.

Timing is everything:does early and late germination favor invasions by herbaceous alien plants?

Aims Plant invasions represent a unique opportunity to study the mechanisms underlying community assembly rules and species distribution patterns.While a superior competitive ability has often been proposed as a major driver of successful plant invasions,its significance depends crucially on the timing of any competitive interaction.We assess whether a mismatch in germination phenology can favor the establishment of alien species,allowing them to exploit vacant niches where competition is low.As well as having important effects on the survival,growth and fitness of a species,asymmetric competition and potential soil legacies resulting from early or late germination can also impact on species recruitment.However,early or late germination comes at a cost,increases the risks of exposure to unfavorable conditions and requires an enhanced abiotic resistance if it is to lead to successful establishment.Important Findings While there are several anecdotal accounts of early and late ger-mination for invasive species,there are limited comparative data with resident species growing under natural conditions.Available evidence from grassland communities indicates that a short-term germination advantage or priority(few days/weeks)provides inva-sive species with a strong competitive advantage over native species and is a critical factor in many invasions.While the exploitation of periods of low competition is a plausible mechanism for the suc-cessful establishment of many invasive plants,direct evidence for this strategy is still scarce.This is particularly true with regard to the exploitation of late germination niches.Consequently,long-term comparative monitoring of the germination phenology of invasive and native plants in situ is needed to assess its significance in a range of ecosystems and its impact on community dynamics.

Shifts in hydropower operation to balance wind and solar will modify effects on aquatic biota

To avoid negative consequences to freshwater biota from climate change,society must complete the transition from fossil to renewable electricity sources.However,temporal patterns in hydropower generation(and flow releases that affect aquatic biota)may change with increased wind and solar penetration.We used power cost modeling to characterize current and future within-day and seasonal patterns in hydropower generation across the Eastern Interconnection in a wet and a dry year.Compared to the baseline,future hydropower generation across the grid decreased during the day and increased before dawn and after dusk.At a project level,such a pattern would suggest‘double peaking’operation(up-and down-ramping before dawn and after dusk,with lower releases midday).Variation in generation was higher in wet years than dry years,foreshadowing possible flow constraints on hydropower flexibility.At the grid scale,projected ramping rates were higher in all seasons.A review of the ecological literature suggests that these changes would shift the timing of invertebrate drift and elevate the risk of nest scouring during up-ramping and the risk of stranding or dewatering during down ramping.Thermal conditions may be moderated by increased ramping.Strategies for adapting to future shifts in the renewable portfolio range from re-regulation in reservoir cascades to providing flow refuge(structures and vegetation)below individual projects.Coordinated basin-scale operation can distribute peaking operation to maintain grid support while restricting local ramping at critical ecological times.In addition,research to design hybrid renewable systems that add battery storage is needed to understand how we can mitigate future risks to aquatic communities while promoting the use of renewable energy.This study,which is among the first to examine ecological side-effects of the shift to renewable energy in freshwater ecosystems,lays out a path toward understanding and navigating changes to flow regimes under the energy transition.