Effect of desiccation on mosquito oviposition site selection in Mediterranean temporary habitats

1. Hydroperiod duration has been identified as the main factor determining the faunal composition and structure of aquatic communities in temporary habitats. It is hypothesised that desiccation will positively affect mosquito oviposition habitat selection during the post-drought period due to the lack of antagonists. 2. An experiment was carried out in outdoor mesocosms to assess whether desiccation events have post-drought effects on community richness and mosquito oviposition. Three different treatments were randomly assigned to the mesocosms: (i) eight mesocosms were left dried for a week and then reflooded; (ii) eight mesocosms stayed dry for 4 weeks before they were reflooded; (iii) eight mesocosms were maintained at a constant water volume of 30 litres during the entire experiment as controls. Mosquito oviposition and invertebrate community richness were monitored in every mesocosm, along with environmental parameters [water temperature, pH, conductivity, dissolved oxygen, total suspended solids (TSS) and chlorophyll a concentration]. 3. Post-drought mosquito oviposition and larval abundance were higher in the short-drought and long-drought pools than in the control. Desiccation negatively affected the biomass of the filter feeder invertebrates in both desiccation treatments. Chlorophyll a concentrations were higher in the long-drought pools than in controls. The negative impact of desiccation on zooplankton led to a post-drought increase in algae, associated with an increase in mosquito oviposition. 4. Despite immediate negative effect on mosquitoes, pulsed disturbances can benefit mosquitoes as they favour oviposition during the post-disturbance recovery period due to a lower abundance of mosquito antagonists and higher food resources for their offspring.     

Effects of a fire-retardant on oviposition habitat selection and larval development of the mosquito Culiseta longiareolata

1. Fire retardants are composed of fertilising salts that are commonly used for fighting wildfires. These chemicals have various effects on individual arthropod species and aquatic communities. 2. This study investigated the effects of four treatments of a prevalent fire retardant [FR CROS 134 (FR), applied at concentrations of 0, 3.8 × 10², 7.6 × 10² and 11.4 × 10² mg litre⁻¹] on oviposition habitat selection (OHS) by Culiseta longiareolata and Culex laticinctus mosquitoes in an outdoor mesocosm. Additionally, larval development of C. longiareolata was examined in response to this fire retardant. 3. The results demonstrate that OHS increased in both species, whereas survivorship (0–86.7%) and time to metamorphosis (5.4–23.1 days) of C. longiareolata were not affected by any of the treatments. However, cyanobacterial biomass increased and heterotrophic bacteria decreased in response to the addition of FR. 4. It was found that FR applications can have unintended consequences which can increase OHS by female mosquitoes. The growing use of fire retardants worldwide, and especially in Israel, justify evidence-based assessment and environmental management of their use. This study is a first critical step in filling the knowledge gap with respect to the impact of FR on aquatic ecosystems.     

Oviposition habitat selection by the mosquito Culiseta longiareolata in response to risk of predation and conspecific larval density

Abstract. 1. Most female Culiseta longiareolata (Diptera: Culicidae) avoid ovipositing in pools that contain the predatory backswimmer Notonecta maculata . Such oviposition habitat selection has been suggested to reflect a trade-off between the risk of predation on larvae and potential density-dependent fitness costs. This putative trade-off was examined. In particular, evidence was sought in support of direct female response to local heterogeneity in habitat quality.
2. Three habitat types were established using artificial outdoor pools: predator pools, and non-predator pools with either low or high densities of Culiseta larvae. During each experimental night, females were offered one of the three possible pair-wise treatment combinations.
3. The majority (≈88%) of females oviposited in low-density pools rather than in the predator- or high-density pools. Furthermore, a substantially higher proportion of females oviposited in predator pools when faced with the high-density alternative, however this was due largely to fewer females ovipositing in high- vs low-density pools.
4. Females of a second mosquito species ( Culex laticinctus ), the larvae of which are at a lower risk of predation, were predicted to exhibit weaker aversion to N. maculata ; this prediction was supported only weakly.
5. Oviposition habitat selection by female C. longiareolata does not appear to involve a behavioural response that is based on individual assessment of local heterogeneity in relative pool quality, at least not at the spatial scale examined here; alternative explanations are discussed.     

Effects of Anisops sardea (Hemiptera: Notonectidae) on oviposition habitat selection by mosquitoes and other dipterans and on community structure in artificial pools

We investigated the effects of the predatory backswimmer, Anisops sardea, on oviposition habitat selection of mosquitoes and other dipterans, and on community structure in experimental pools. We predicted that those dipteran species whose larvae were shown to be highly vulnerable to predation by Anisops would avoid Anisops pools when choosing an oviposition site. We established the following treatments in plastic tubs: (1) Control (without Anisops); (2) Free Anisops (ten Anisops within pool but not caged); (3) Caged Anisops (ten Anisops in cage). The pools were open to colonization by insects. We added resting stages of crustaceans and first instar larvae of the mosquitoes Culiseta longiareolata and Culex laticinctus. Among the dipteran species, Culiseta longiareolata, Culex laticinctus, Chironomus riparius (Chironomidae) and Forcipomyia sp. (Ceratopogonidae), only Culisetalarvae were highly vulnerable to predation. As predicted, based on larval vulnerability, Culiseta, but not the other species, avoided Anisops pools when ovipositing. Free Anisops reduced taxon richness. This reduction resulted largely from the elimination of the cladoceran Ceriodaphniasp. and Culiseta in most free Anisops pools. Thus, Anisops sardea structures the community, both by a behavioral response of prey to its presence and by consumption of prey.     

Urban rain pools: seasonal dynamics and entomofauna in a park of Buenos Aires

We describe the seasonal variations of the insect community of the rain pools in a park of Buenos Aires during a 1-year period, based on a weekly sampling programme. We also analyse the relationships between the observed biotic patterns and some physical and meteorological variables. Four periods, fairly coincident with the seasons of the year, were graphically identified as functions of temperature, rainfall, flooded area, number of rain pools, depth and taxonomic richness. A total of 45 insect taxa was identified: 18 Coleoptera, 15 Diptera, 9 Heteroptera, 1 Ephemeroptera and 2 Odonata. Culicidae represented 76% of the pooled abundance of insects, probably related to their rapid development before the pools dry up. Taxonomic richness was maximum at the end of the summer (32), in coincidence with maximum rainfalls and temperatures. Inversely, the minimum richness (2) was recorded during the spring drought. Richness was positively correlated to the flooded area and to the number of pools on each sampling date. The species recorded throughout the study period were: Aedes albifasciatus, Culex eduardoi, Culex pipiens, Liodessus sp., Rhantus signatus signatus, Tropisternus setiger, Tropisternus lateralis limbatus and Sigara platensis. Some of the species recorded are considered pioneer in temporary habitats. Both coleopterans and heteropterans are likely to persist in the park through repeated colonisation from more permanent habitats. Habitat duration and flooded area were positively correlated to richness in each one of the rain pools.     

Comparison of adult mosquito community structure on various habitats

The community structure of adult mosquitoes was compared from New Jersey light trap collections in six different types of habitats in Citrus County, Florida, USA. From October 1998 to December 2000, mosquitoes were collected three times a week from the following habitats (swamps, swamps and freshwater marshes, pine fiat-woods, pine fiat-woods and scrub, salt marshes, and salt marshes and mangroves). Mosquito density was highest in the swamps and freshwater marshes habitat, with an average of 95.65 specimens per trap.Density was lowest in the flatwoods and scrub habitat, with an average of 14.38 specimens per trap. Species dominance differed among habitats. Salt marshes produced the greatest aggregation index, while pine flatwoods produced the lowest. Conversely, diversity analysis showed that pine flatwoods had the greatest diversity, while salt marshes the lowest diversity. Similarity indices indicated that the adult mosquito communities from pine flatwoods and pine flatwoods and scrub were very similar (0.8583). The adult mosquito community of salt marshes was different from that of swamps and freshwater marshes (the similar index was 0.0217).     

Microclimate,developmental plasticity and community structure in artificial temporary pools

Solar radiation, which influences temperature and hydroperiod, should strongly influence colonization, development rate, development strategies and survival in temporary pools. We assessed these hypotheses at two spatial microscales with varying microclimate. One scale, ca. 200 m, was opposing slopes of a canyon on MT Carmel, Israel, referred to as 'Evolution Canyon' (Nevo, 1995). Due primarily to differential solar radiation, the warmer and drier South-facing slope (SFS) supports a savanna-like open park forest while the cooler, moister North-facing slope (NFS) is heavily forested, primarily with live oak. Using artificial pools, we assessed how these close but contrasting environments may influence developmental plasticity in the frog, Hyla savignyi, and colonization of insects. As expected, hydroperiod was considerably longer on the NFS. Hyla tadpole development was significantly faster on the SFS, while size at metamorphosis was greater on the NFS. Insect species richness was higher in NFS pools. The most common species, Culex pipiens, oviposited significantly more in NFS pools than in SFS pools. In the second scale, we placed pools only meters apart, but varying in shade and thus maximum temperature at Haifa University Campus, MT Carmel. Species richness and maximum temperature among pools were not correlated during winter and early spring (cool to mild temperatures), but were strongly and negatively correlated during early summer (hot temperatures). Thermal tolerance in the laboratory of selected species matched their thermal spatial distribution in the field. These results indicate that temperature can play a strong role in affecting developmental strategies, species′ distributions and community structure in temporary pools over a very small spatial scale. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of flooding on a wetland bird community

The Lake Izunuma–Uchinuma was extensively flooded in 1998 and vast areas (approximately 200 ha) of rice fields were submerged for the first time since the land was reclaimed in 1963. When the numbers of birds in 1998 were compared with those in normal years (1995–1997), the numbers of black-crowned night herons (Nycticorax nycticorax L.), cattle egrets (Bubulcus ibis L.) and black kites (Milvus migrans Boddaert) increased during the flooding, and the numbers of ducks, especially dabbling ducks (seven species of 11 Anas spp.) were high even after the flooding, while the numbers of the little grebe Tachybaputus ruficollis Pallas were diminished by the flooding.     

Habitat stability and the larval mosquito community in treeholes and other containers on a temperate Island

The temporal fluctuation of water levels and the presence of mosquito larvae were investigated for four types of small container habitats (treeholes, bamboo stumps, cemetery stone vases, and cemetery stone vessels) on Kabeshima Island in Kyushu, southwestern Japan. The probability that containers held water was positively correlated with the quantity of the preceding rainfall and with the depth and volume of the containers. It was estimated that dehydration occurred more regularly in autumn and winter than in summer. The probability that mosquito larvae were present in each type of container was positively correlated with habitat stability in terms of the probability of the existence of standing water and the coefficient of variation of the water level. Twelve species of mosquito larvae, including two rare predators, were found. Species composition differed between the different types of container. Although 4 to 10 species used each type of container, the median number of species per container was two for treeholes and bamboo stumps, and one for the others. The dominant species wasTripteroides bambusa in treeholes and bamboo stumps,Aedes albopictus in stone vases, andA. japonicus in stone vessels. The larval mosquito community, which lacked major predators, possessed the following features that may facilitate the coexistence of many species: (1) niche segregation amongst species in terms of their selection of container types; (2) an aggregated distribution of the individual species among containers of the same type; (3) high intraspecific mean crowding (and hence probably intense intraspecific competition) in the dominant species in each type of container; (4) independent species associations within the same type of container; and (5) low interspecific mean crowding (and hence probablynot intense interspecific competition) between species in the same type of container.     

Effects of different vegetative substrates on algal composition in vernal mesocosms

We investigated the response of an algal assemblage to different vegetative substrates in controlled vernal mesocosms. Litter was collected from four vascular plant communities (Deciduous Forest, Macrophyte, Old Field and Pinus stands) and the litter was used to line the benthos of the vernal mesocosms. The development and response of the algal assemblage in treatment and control mesocosms was tracked biweekly for a period of 56 days. A repeated-measure MANOVA and Bonferroni (Dunn) post-hoc test indicated that the Pinus treatment produced a significantly greater biomass than all other treatments. The Pinus treatment mesocosms had acidic (4.5–4.7) water when sampled on day 42, which continued until the completion of the study. The greatest levels of species richness and diversity were recorded from the Deciduous Forest and Old Field treatments. Algal assemblage analyses indicated that there was much overlap in community structure between various litter treatments and algae alone (no litter). Most of the vernal mesocosm treatments were dominated by the filamentous chlorophytes Mougeotia, Oedogonium and Ulothrix. These results suggest that, in this study, the vegetative litter of vernal mesocosms (with the exception of Pinus) exhibits limited independent influence on the developmental trajectories of algal communities.     

Effects of habitat size and isolation on species immigration–extinction dynamics and community nestedness in a desert river system

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Oviposition habitat selection by the mosquito, Culiseta longiareolata: effects of conspecifics, food and green toad tadpoles

Abstract. 1. Ovipositing females should choose egg-laying sites which maximize the growth and survivorship of their offspring. Accordingly, they should avoid habitats with high densities of competitors and predators and should choose sites with adequate food. We tested experimentally the oviposition response of the mosquito, Culiseta longiareolata Macquart, to extra food and two species which are both potential competitors and predators of its offspring: conspecific larvae and green toad ( Bufo viridis ) tadpoles.
2. We conducted the experiment in outdoor artificial pools where wild C. longiareolata females were presented with choices of all combinations of the presence or absence of: (1) C.longiareolata larvae, (2) B.viridis tadpoles, and (3) extra food (a mixture of ground fish food and mouse chow).
3. Oviposition rates averaged approximately 4 times greater in response to extra food.
4. The presence of the tadpoles, particularly later in the experiment when they were larger, caused a significant reduction (approximately 50%) in oviposition rate.
5. We did not detect a statistically significant effect of conspecific larvae on oviposition habitat selection.
6. Our results indicate that Culiseta females choose habitats for oviposition based on food availability. They also tend to avoid habitats containing Bufo tadpoles, presumably to avoid predation and/or competition.     

洞庭湖区洪灾淹没区鼠类群落结构恢复的生态过程

在 1998年特大洪灾中被淹没 3个多月的湖南省安乡县安造大垸 ,经退水后连续 3a的观察 ,揭示了洪涝灾害对鼠类群落结构的影响以及群落演替或恢复的过程。当地的优势种黑线姬鼠是洪灾后农田区残留的主要鼠种 ,但密度极低 ;房舍区则以中型鼠褐家鼠与黄胸鼠为主 ,并保持较高的密度。在农田 ,灾后近 2 a时间内都仅捕获黑线姬鼠 ,而农房的鼠种组成很快变成与未被淹地区相似 ,不同的是在未被淹地区小家鼠的比例比灾区高。比较灾区与对照区群落的鼠种组成、群落优势度及优势集中性指数、群落的多样性与均匀性指数、群落相似性系数 ,发现随着群落的演替 ,灾区鼠群落逐步地与对照区趋于一致 ;仅有灾区的害鼠密度例外 ,仍维持在较高水平。由于房屋的顶层或楼房的 2层以上部分 ,在洪灾中未被淹没而成为害鼠的避难地 ,因此洪涝灾害对房舍区鼠群落结构的破坏比农田区的小 ,这从灾后的鼠密度和结构的变化可知 ,也是房舍区鼠类群落的恢复速度比农田区快的原因     

水淹干扰对水库水滨带植物群落稳定性与种间关系的影响

受城市化与人类活动等因素影响而退化的水滨带植被的恢复与重建是近年来生态环境的热点问题。植物群落的种间关系直接影响植被的演替与恢复。以南水北调中线一期工程通水前的丹江口水库原有水滨带植被为研究对象,对年均多于9个月（海拔142 m以下）、6-9个月（海拔142-147 m）、3-6个月（海拔147-151 m）和少于3个月（海拔151-157 m）的4种不同强度水淹干扰的水滨带植物群落的稳定性和种间关系进行分析,探讨不同水淹干扰强度对水库水滨带植物群落稳定性及种间关系的影响。采用M.Godron稳定性测定法对植物群落稳定性进行分析,通过方差比率（VR）、χ²检验、联结系数（AC）以及Spearman秩相关检验对不同水淹干扰强度下的植物群落优势种进行种间关联分析。结果表明：（1）水库水滨带植物群落稳定性从高到低依次为水淹时长3-6个月、水淹时长6-9个月、水淹时长少于3个月和水淹时长多于9个月。中度水淹干扰下的植物群落稳定性要好于重度和轻度水淹干扰的植物群落;（2）不同水淹干扰强度下水滨带植物群落总体性关联表现为显著正相关。随着水淹时间增加,群落中正联结种对占总对数的比例呈下降趋势,负联结种对比例呈增加趋势,正负联结比值降低,群落内种间联结强度逐渐降低,说明水淹干扰强度增加会导致水滨带植物群落种群间相互依存关系减弱或竞争关系加剧。在此基础上,探讨不同水淹干扰强度下物种的空间分布和生态习性,并提出针对不同水淹干扰强度的水滨带植被恢复的物种选择建议。     

龙眼园害虫群落结构与动态研究

研究结果表明,龙眼害虫群落包括8目38科62种,其中为害较严重的有10多种。荔枝蝽蟓、龙眼角颊木虱、荔枝蒂蛀虫、龙眼亥麦蛾、荔枝尖细蛾和三角新小卷蛾为害尤为严重,是龙眼害虫的关键物种。这些害虫直接影响龙眼的产量和质量,是生产上防治的重点。龙眼害虫群落的生物多样性指数全年变动范围为0．0919—2．2938,均匀度指数全年变动范围为0．0837—0．8273。总体上分析,龙眼害虫群落优势种的优势地位明显,生态优势度大,在药剂防治实践中,应该注意保护果园昆虫天敌和蜘蛛类等有益生物,保护果园生物多样性,达到害虫可持续控制目的。     

Temporal dynamics of an ephemeral plant community: species turnover in seasonal rock pools on Ivorian inselbergs

Inselbergs are monolithic, old and stable landscape elements with a worldwide distribution. On inselbergs, relatively old (i.e. hundreds of years old) rock pools form a unique habitat that offers locally wet conditions in an otherwise edaphically and microclimatically dry environment. They occur as seasonally water-filled depressions with a thin layer of soil, and are mainly inhabited by ephemerals and cryptogams. Even during the rainy season, they often become dry if precipitation is lacking for a few days. Between 1990 and 1999, about 200 rock pools in the Ivorian savanna zone were examined on a regular basis. Absolute and relative turnover rates were calculated: values ranged from 0.00 to 3.00 and 0 to 78%, respectively. Mean turnover was 0.19 (17%). The turnover in the SRPs increased significantly with soil depth and area. No correlation was found between turnover and species number of the pools, which increased significantly with area. The highest turnover was shown by the annual Cyanotis lanata. The turnover of therophytes was higher than those of other life-forms. Turnover and frequency of the species were only weakly correlated. In an environment of frequent stochasticity, climatic disturbances are the major driving force determining community dynamics (e.g. local extinctions and immigrations) of these habitat islands.     

Correlation between population dynamics of mosquito larvae and their habitat qualities

Surveillance of anopheline and culicine larvae was conducted fortnightly to determine population composition and density at seven sites in the area of the Mathura Refinery, Mathura, India during 2005–2006. The correlation between population of the vectors and their habitat quality was established. Temperature (0.978 and 0.85°C), pH (0.99 and 0.95), conductivity (0.98 and 0.98 mho) and calcium ion hardness (0.978 and 0.85 p.p.m.) were positively correlated with the populations of both larval species. In contrast, the correlation coefficients between the parameters total hardness, magnesium ion hardness, biochemical oxygen demand and chemical oxygen demand varied with the larval species. The anopheline larval population was dominant over the culicine population in the surveillance area. The distribution of anopheline mosquito larvae during the study period was found to be constant, and the average density of anopheline and culicine larvae was 84.70 and 15.30%, respectively, across all seven sites. Thus, the study demonstrated spatial and temporal population differences of mosquito larvae with respect to environmental factors, including water quality.