Diet of two sympatric Pheidole spp. ants in the central Monte desert: implications for seed–granivore interactions

Ants of the genus Pheidole are important seed consumers in several desert ecosystems. In South American deserts, although several Pheidole spp. have been characterized as seed harvesters, studies on their diet and ecological role are still missing. Pheidole spininodis (Mayr) and Pheidole bergi (Mayr) are capable of removing seeds in the central Monte desert. The aim of this study was to quantify and compare the diet of these species and to interpret the results in the context of seed–granivore interactions. Diet was estimated during mid-summer by collecting items brought back to the nest by foragers in ten colonies per species. While P. spininodis was mainly granivorous, P. bergi was mainly insectivorous. However, they both collected ~40% of other types of items. Among seeds, the diet of P. spininodis included mostly grass seeds, whereas the diet of P. bergi was mainly made up of shrub and tree seeds, usually retrieved cooperatively. This behavior allowed P. bergi to carry larger seeds, resulting in diet partitioning in terms of seed size. However, diet of P. spininodis is very similar to that of three sympatric Pogonomyrmex species. Thus, specialized harvester ants remove large quantities of grass seeds in the central Monte desert during the summer, potentially affecting their abundance in the soil seed bank. P. bergi directs its feeding pressure to shrub and tree seeds, and although seeds constitute ~10% of its diet, its high colony density and high activity levels, added to the lower proportion of large seeds in the soil seed bank, indicate that their importance as seed consumers cannot be ruled out.     

红火蚁与两种本地蚂蚁间的干扰竞争

为了探讨重大入侵生物红火蚁Solenopsis invicta Buren与本地蚂蚁的竞争机制以及红火蚁成功入侵的机理, 本研究以红火蚁和2种本地蚂蚁黑头酸臭蚁Tapinoma melanocephalum (Fabricius)及亮红大头蚁Pheidole fervida Smith为材料, 室内测定了红火蚁分别与黑头酸臭蚁、亮红大头蚁之间在个体水平和种群水平上的攻击性和攻击强度。一对一攻击试验结果表明：红火蚁和黑头酸臭蚁之间攻击级别多集中在Ⅲ级, 即竞争优势明显的红火蚁对黑头酸臭蚁缺乏激烈的攻击, 只是在相互攻击时多摆出威胁姿势; 红火蚁与亮红大头蚁之间攻击性较强, 尤其是红火蚁中型和小型工蚁与亮红大头蚁兵蚁之间的攻击性（3.35和3.30）显著强于红火蚁大型工蚁与亮红大头蚁兵蚁的攻击性（2.70）。群体攻击试验结果表明：与黑头酸臭蚁群体攻击的红火蚁各处理组合中, 无死亡红火蚁出现, 而黑头酸臭蚁死亡率为31.80%; 而与亮红大头蚁群体攻击中, 红火蚁死亡率为0.20%~12.00%, 而亮红大头蚁平均死亡率为49.91%。可见, 红火蚁的群体攻击能力强于黑头酸臭蚁和亮红大头蚁, 其中红火蚁与亮红大头蚁间的相互攻击程度激烈, 死亡率较高, 而与黑头酸臭蚁间的攻击程度较弱, 可能由于黑头酸臭蚁化学防御对本身起到一定的保护作用, 这为进一步加强红火蚁发生区本地蚂蚁优势种--黑头酸臭蚁的保护利用提供理论基础。     

Noise improves collective decision-making by ants in dynamic environments

Recruitment via pheromone trails by ants is arguably one of the best-studied examples of self-organization in animal societies. Yet it is still unclear if and how trail recruitment allows a colony to adapt to changes in its foraging environment. We study foraging decisions by colonies of the ant Pheidole megacephala under dynamic conditions. Our experiments show that P. megacephala, unlike many other mass recruiting species, can make a collective decision for the better of two food sources even when the environment changes dynamically. We developed a stochastic differential equation model that explains our data qualitatively and quantitatively. Analysing this model reveals that both deterministic and stochastic effects (noise) work together to allow colonies to efficiently track changes in the environment. Our study thus suggests that a certain level of noise is not a disturbance in self-organized decision-making but rather serves an important functional role.     

When trade-offs interact: balance of terror enforces dominance discovery trade-off in a local ant assemblage

1. Trade-offs underpin local species coexistence. Trade-offs between interference and exploitative competitive ability provie a mechanism for explaining species coexistence within guilds that exploit overlapping resources. 2. Omnivorous, leaf litter ants exploit a shared food base and occur in species-rich assemblages. In these assemblages, species that excel at usurping food items from other species are poor at finding food items first. In assemblages where some members are attacked by phorid fly parasitoids, host species face an additional trade-off between defending themselves against parasitic attack and maximizing their competitive abilities. Host species thus face two trade-offs that interact via the trait-mediated indirect interaction generated by phorid defence behaviour. 3. In this study we test for the existence of these trade-offs and evaluate the predictions of a model for how they interact in an assemblage of woodland ants in which two behaviourally dominant members are attacked by phorid fly parasitoids as they attempt to harvest food resources. 4. The major findings are that unparasitized species in the assemblage follow a dominance-discovery trade-off curve. When not subject to attack by phorid flies, host species violate that trade-off by finding resources too quickly for their level of behavioural dominance. In contrast, when attacked by their phorid parasitoids, the host species dominance drops such that they fall into the assemblage trade-off. 5. These results match the predictions of the balance of terror model, which derives the optimal host response to parasitism, indicating that the host species balance the competing fitness costs of reduced competitive dominance and loss of workers to parasitism. This result supports the view that understanding the structure of ecological communities requires incorporating the indirect effects created by trait plasticity.     

大头金蝇幼虫油脂对小鼠的降血脂作用

用健康昆明种小鼠建立高脂血症模型,同时用不同剂量的大头金蝇Chrysomyia megacepha la (Fabricius)幼虫油脂灌胃5周,摘除眼球取血,用试剂盒检测血脂值,光学显微镜观察小鼠肝脏病理变化。结果表明：大头金蝇幼虫油脂处理组小鼠血清胆固醇(TC)、甘油三酯（TG）、低密度脂蛋白胆固醇(LDL-C)水平显著降低,低剂量、中剂量和高剂量油脂处理组小鼠TG的浓度较高脂模型组小鼠分别下降20.70%、48.98%和56.06%;高脂模型组小鼠血清TC高达4.59 mmol/L,低剂量、中剂量和高剂量油脂处理组小鼠TC浓度较高脂模型组小鼠分别下降16.99%、23.52%和25.49%;高密度脂蛋白胆固醇（HDL-C）升高明显,低剂量、中剂量和高剂量油脂处理组小鼠HDL-C较高脂模型组小鼠升高11.74%、18.04%和18.95%,并呈现一定的剂量-效应关系;连续饲喂大头金蝇幼虫油脂对小鼠肝细胞有一定保护作用。提示大头金蝇幼虫油脂具有治疗小鼠高脂血症的作用。     

四川西部丽蝇科4蝇种昼夜活动节律的研究

首次记录四川西部雅安市丽蝇科(Calliphoridae)4蝇种昼夜活动节律的初步研究,结果表明,蝇类这一具有白昼活动、夜间蛰伏的生物生态特性的昆虫群体,对光照度和光照时间表现出异常敏感的行为反应;在地理生态环境中,对于影响蝇类行为活动诸因素如气温、光照、晴、阴、雨等气候现象,文中予以讨论。     

大头艾纳香化学成分的研究

利用硅胶柱色谱、Sephadex LH-20柱色谱等手段从大头艾纳香(Blumea megacephala(Randeria)Chang etTseng)全草中分离得到13个化合物,根据化合物的理化性质和光谱数据分别鉴定为无羁萜(1)、小麦黄素(2)、豆甾醇二十六烷酸酯(3)、豆甾醇十八烷酸酯(4)、α-香树脂醇(5)、α-香树脂醇乙酸酯(6)、β-香树脂醇乙酸酯(7)、β-谷甾醇(8)、豆甾醇(9)、β-胡萝卜苷(10)、二十七烷醇(11)、十六烷酸(12)和二十四烷酸(13)。所有化合物均为首次从大头艾纳香中分离得到。     

Direct and indirect top‐down effects of previous contact with an enemy on the feeding behavior of blowfly larvae

We investigated the addition of a trophic level to a simple food web. Direct and indirect effects caused by the presence of a new species in the food web were quantified by estimating survival and consumption rates on the basal resource. We focused on a blowfly intraguild prey–predator system with various ecological interactions taking place during the larval period. The experiments were designed to set Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae) as the intraguild prey and Chrysomya albiceps (Wiedemann) as the intraguild predator and/or cannibal. The generalist pupal parasitoid Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae) was introduced into the system during a non‐susceptible life stage of the interacting blowfly species. The cascading parasitoid effects induced behavioral changes in the blowfly larvae, increasing the impact of intraguild predation and cannibalism on blowfly survival. The results suggest that blowfly larvae can change their feeding behavior in response to the presence of a parasitoid.     

Floral visitation patterns of two invasive ant species and their effects on other hymenopteran visitors

Abstract.  1. Floral nectar of the native Hawaiian 'ōhi'a tree, Metrosideros polymorpha , is an important food source for several native honeycreepers and yellow-faced bees, Hylaeus spp., but is also attractive to invasive ants.
2. I undertook this study to compare floral visitation patterns of two widespread invasive ants, the Argentine ant, Linepithema humile , and the big-headed ant, Pheidole megacephala , and to determine their effects on nectar volume and floral hymenopteran visitors.
3. In the first year of the study, Argentine ants visited inflorescences more frequently than big-headed ants at mid-day and in the afternoon, but did not occur in higher densities than big-headed ants at any time of day. In the following year, Argentine ants visited inflorescences both more frequently and in higher densities than big-headed ants. Argentine ant density had a stronger association with nectar concentration than big-headed ant density.
4. Nectar volume did not differ between ant-excluded and ant-visited inflorescences for either ant species. However, ant density was negatively associated with nectar volume for both species.
5.  Hylaeus spp. never visited inflorescences with big-headed ants, while non-native honeybees visited inflorescences with and without ants of either species in equal frequency.
6. Most studies of the effects of invasive ants on native arthropods have focused on interactions on the ground. Flowers should not be overlooked as microhabitats from which native arthropods may be displaced by invasive ants.