Cyanobacteria in the Australian northern savannah detect the difference between intermittent dry season and wet season rain

This research was conducted in the northern Australian savannah at Boodjamulla National Park where cyanobacterial crusts dominate the soil and rock surfaces in between tussock grasses. It is widely accepted that terrestrial cyanobacteria are drought tolerant and rapidly recommence photosynthesis once moisture is available. Initial tests at the research site indicated that cyanobacteria did not respond to rehydration during the dry season, even after several days. We hypothesised that resurrection had not taken place and new growth from survival cells had to take place during the follow-up wet season. To further understand the desiccation–resurrection processes we tested photosystem II (PSII) responses both during the dry and wet seasons. In the 2009 dry season after 125 days without rain, crust samples were regularly rehydrated. Over the 10 day trial cyanobacteria did not recover PSII activity or CO₂-uptake. Although new colonies of Nostoc grew other cyanobacteria remained inactive, even though liverworts and lichens in the same crusts had responded within 24 h. Dry season cyanobacterial crusts were collected in 2010 then reintroduced into their natural environment and exposed to rainfall during the 2011 wet season. Within 24 h PSII in cyanobacteria from a range of crust types had resurrected and CO₂-uptake was verified, although different crust types responded at significantly different rates. These are the first studies that have demonstrated that PSII does not respond to rainfall during the dry season and cyanobacterial function appears controlled by other environmental conditions. It is likely that mass extracellular polysaccharide (EPS) production during the wet season, once dry, protects cyanobacteria from premature resurrection in the dry season. We propose that EPS regulates moisture penetration, thus the resurrection of PSII at the onset of the wet season, at which time moisture and humidity alters the rheological properties of EPS permitting rehydration.     

A comparison of ten rice-straw varieties grown at two different altitudes during a wet and a dry season,using the in vitro cumulative gas production technique

In vitro cumulative gas production was used to evaluate a series of rice straws for their fermentability. The straws comprised ten different varieties which had been grown at two locations (higher and lower altitudes), during two seasons (wet and dry). Curves were fitted, and the resulting parameters, DM loss and gas yield, were tested for significant differences by an analysis of variance using the Tukey test. Significant differences between the parameters of the fitted curves were found between the offered and refused straw, the material grown at different altitudes, the material from the wet and dry seasons, and between varieties. Significant interactions were found between the environmental factors and cultivar, for the offered and refused feeds.     

Breeding behaviour, home range and habitat selection in Rock Firefinches Lagonosticta sanguinodorsalis in the wet and dry season in central Nigeria

Knowledge of a species’ movement behaviour and habitat choice is a prerequisite for assessing its ecological requirements to plan successful conservation strategies. Little is known about these factors in the Rock Firefinch, a recently described species which is probably endemic to the Jos Plateau in central Nigeria. We investigated home range size, habitat use and breeding behaviour of the Rock Firefinch in Amurum forest reserve in central Nigeria during the wet (August–October) and the dry season (November–December) using radiotracking. Birds showed high site fidelity. They mainly moved alone or in pairs but did not have exclusive home ranges. Home range size tended to be larger during the dry season due to long movements to water sources. Birds generally preferred inselberg habitat and avoided farmland. During the dry season they additionally utilized gallery forests where water was readily available, and as a result of having to cross scrub savannah to get to water, scrub savannah was also more heavily used during the dry season. Birds bred between the late rainy (September–October) and the early dry season (November). Nest‐sites were associated with rocky boulders. Both sexes contributed to incubation. Daily egg survival rate calculated using the Mayfield method was 0.89 (0.83–0.95 95% confidence interval); no nests failed during the chick stage, but sample size was only four nests. Of all 14 nests found, 50% were depredated and only 29% of breeding attempts succeeded in producing Rock Firefinch chicks. A second breeding attempt was recorded when the first one failed. Chick production just about compensated adult mortality (measured in a separate study at the site) such that the population is probably stable at present. However, given the large uncertainty in our underlying assumptions, more data are needed to confirm this. We suggest that the presence of inselberg habitat in close proximity to water sources is the essential and limiting resource for this species.     

Divergent response of seasonally dry tropical vegetation to climatic variations in dry and wet seasons

Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO₂ growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p < 0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γ^int) and to precipitation (δ^int). γ^int is ~1% °C^?1 more negative and δ^int is ~8% 100 mm^?1 more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γ^int can be explained by background moisture and temperature conditions. Positive γ^int occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60 mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine‐learning algorithm applied to flux tower measurements, and nine process‐based carbon cycle models) were examined for the GPP–climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γ^int, while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis–climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.     

Eimeria azul sp. n. (protozoa: Eimeriidae) from the eastern cottontail, Sylvilagus floridanus, in Pennsylvania.

Eimeria azul sp. n. is described from the cottontail rabbit, Sylvilagus floridanus, in central Pennsylvania. The oval oocysts are 19.5--27.0 micrometer by 15.0--19.0 (mean - 22.9 X 16.7 micrometer). The fusiform sporocysts are 7.8--14.0 micrometer by 3.3--6.5 micrometer (mean = 11.8 X 5.8 micrometer). A Stieda Body is present. There is no micropyle, oocyst residuum or polar granule. The sporocyst has a residuum which is variable in appearance. The oocysts are characterized by a blue tint when viewed with an apochromatic objective lens.     

Lignocellulose pretreatment: A comparison of wet and dry ball attrition

Summary A comparison of wet and dry ball attrition of various lignocellulosic substrates indicates that terminal crystallinity index following enzymatic hydrolysis usually decreases after wet attrition and increases after dry attrition. Particle size was reduced to a greater extent in dry attrition in accordance with increased friability. Conversions favored neither wet nor dry pretreatment, indicating substrate specific requirements.     

Short dry spells in the wet season increase mortality of tropical pioneer seedlings

Variation in plant species performance in response to water availability offers a potential axis for temporal and spatial habitat partitioning and may therefore affect community composition in tropical forests. We hypothesized that short dry spells during the wet season are a significant source of mortality for the newly emerging seedlings of pioneer species that recruit in treefall gaps in tropical forests. An analysis of a 49-year rainfall record for three forests across a rainfall gradient in central Panama confirmed that dry spells of ≥10 days during the wet season occur on average once a year in a deciduous forest, and once every other year in a semi-deciduous moist and an evergreen wet forest. The effect of wet season dry spells on the recruitment of pioneers was investigated by comparing seedling survival in rain-protected dry plots and irrigated control plots in four large artificially created treefall gaps in a semi-deciduous tropical forest. In rain-protected plots surface soil layers dried rapidly, leading to a strong gradient in water potential within the upper 10 cm of soil. Seedling survival for six pioneer species was significantly lower in rain-protected than in irrigated control plots after only 4 days. The strength of the irrigation effect differed among species, and first became apparent 3–10 days after treatments started. Root allocation patterns were significantly, or marginally significantly, different between species and between two groups of larger and smaller seeded species. However, they were not correlated with seedling drought sensitivity, suggesting allocation is not a key trait for drought sensitivity in pioneer seedlings. Our data provide strong evidence that short dry spells in the wet season differentially affect seedling survivorship of pioneer species, and may therefore have important implications to seedling demography and community dynamics.     

A biometric and ecologic comparison between Artemia from Mexico and Chile

Background

A preliminary biometric and ecologic database for the brine shrimp Artemia from Mexico and Chile is presented. The area abounds in small and seasonal ponds and large inland lakes, the latter mainly located in Mexico, although relatively large and isolated lakes are found in complex hydrological settings in pre-high plateau areas of Chile. This paper summarizes research efforts aimed at the localization, characterization, and evaluation of the aquaculture potential of Artemia populations in Mexico and Chile, which exhibit great habitat diversity (ponds, salterns, coastal lagoons, sea arms, coastal and inland lakes), contrasting weather conditions and different levels of isolation and human intervention.

Results

This study covered locations between 29° north latitude (Baja California, Mexico) to 50° south latitude (Puerto Natales, Chile). Biological characteristics considered are species name, reproductive mode, cyst diameter, chorion thickness, and nauplius length, whereas ecological data include pond size, pH, salinity, temperature, and water ionic composition. Artemia franciscana is the only species found in Mexico, it exists together with A. persimilis in Chile, though separated geographically. Ecological differences in habitat exist between both regions but also within countries, a pattern particularly clear with regard to water composition. Surprisingly, a Mexican (Cuatro Ciénegas, A. franciscana) and a Chilean location (Torres del Paine, A. persimilis) share habitat characteristics, at least for the period when data were collected. The discriminat analysis for cyst diameter and nauplius length shows that Artemia from only one location match in cyst diameter with those from San Francisco Bay (SFB) (Point Lobos), and one (Marquez) is far apart from SFB and all the others. The Chilean locations (Pampilla, Cejar, Cahuil, Llamara, Yape) share cyst diameter, but tend to differ from SFB. The remaining Mexican locations (Juchitan, Ohuira, Yavaros) are well separated from all the others. With regard to nauplii length, populations tend to distribute in a relatively random manner, being Marquez the location differing the most in cyst diameter from SFB.

Conclusion

This database will contribute to the knowledge of radiation centers and serves as a baseline for further biogeographic studies, population characterization, management, and monitoring of Artemia biodiversity. Likewise, the impact of colonization and translocations for aquaculture purposes can be better assessed with a baseline for reference. Mexico and Chile exemplify the need to increase and further integrate regional information to tackle fundamental problems underlying practical utilization of Artemia.     

典型喀斯特流域旱雨季交替下溶解硅的输送特征

河流溶解硅（DSi）作为营养物质对维持陆地、河流及海洋生态系统稳定性起到至关重要的作用。选取贵州典型喀斯特流域为研究对象,通过对DSi湿沉降过程,基流过程及降雨径流过程的动态变化进行全年监测分析,探讨DSi在旱雨季交替下的输送特征及河流DSi浓度变化引起的环境效应。结果表明：①湿沉降过程降雨量越大,DSi浓度越小,河流DSi浓度变化有明显的旱、雨季特征,雨季DSi浓度较高,旱季较低,地表水径流量及DSi浓度对降雨径流过程的响应比地下水明显。②DSi沉降通量及输出通量呈明显的旱、雨季差异,雨季DSi湿沉降通量占全年的69.5%,地表水雨季DSi输出负荷占全年的98.1%,地下水占51.4%。③流域硅酸盐岩风化过程不强烈,主要受到碳酸盐岩及蒸发岩控制。流域DSi浓度受人为水库影响明显,经过水库后河流中DSi浓度旱季下降29.0%、雨季下降70.9%。研究为全面认识硅在陆地生态系统中的生物地球化学循环提供科学依据。     

The impacts of changes in vegetation cover on dry season flow in the Kikuletwa River, northern Tanzania

While the decrease in flow is obvious in the Kikuletwa River, the mechanism leading to the decrease is unclear. We assessed the influence of vegetation cover change on dry season flow in the Kikuletwa River. The combined cover of closed and open forests decreased by 68% while closed and open forests decreased by 56% and 64% respectively. Land under agroforestry decreased by 25%, while that under annual crops increased by 41%. Grasslands increased by 116% and riverine vegetation decreased by 53%. Daily dry season flow showed a slightly decreasing trend in one of the stations despite all of them receiving water from the Rundugai natural springs. On the other hand, low flow indices indicated no statistically significant changes in the long-term average flow and there was no identifiable change in the rainfall amount. The majority (93%) of the local people perceived a changing rainfall pattern and decline in dry season flow in the Kikuletwa River. Changes in the dry season flow then can be associated with the identified land cover changes. Further research to substantiate the local people perceptions is important as indigenous knowledge may be good evidence for ascertaining changes in the natural environment.     

Bot fly myiasis of the cottontail rabbit, Sylvilagus floridanus mallurus in Virginia with some biology of the parasite, Cuterebra buccata

Twenty four percent of 2,643 cottontail rabbits (Sylvilagus floridanus) collected in Virginia from 1949-1975 showed evidence of Cuterebra parasitism. Occurrence was seasonal with greatest prevalence from July to November. Some Oryctolagus cuniculus, S. palustris and one S. transitionalis also showed Cuterebra myiasis. Juvenile rabbits had higher infection rates (28%) than did adult rabbits 14.5%, P less than .001). Juveniles had greater numbers of larvae per host than adults, with means of 2.14 and 1.62, respectively. Larval development sites were in the genital region of most hosts. Twenty flies reared from wild cottontails were identified as C. buccata. Duration of induced infections in Oryctalagus was 30-33 days. Minimal generation time for C. buccata is concluded to be 11 weeks, allowing up to four generations of flies to occur annually in the southern and one generation to occur in the northern distributional limits of this bot fly. Peromyscus hosts were refractory to C. buccata infections. C. buccata fecundity averaged 1316 eggs. Field observations of adult flies are described.     

El Niño and dry season rainfall influence hostplant phenology and an annual butterfly migration from Neotropical wet to dry forests

We censused butterflies flying across the Panama Canal at Barro Colorado Island (BCI) for 16 years and butterfly hostplants for 8 years to address the question: What environmental factors influence the timing and magnitude of migrating Aphrissa statira butterflies? The peak migration date was earlier when the wet season began earlier and when soil moisture content in the dry season preceding the migration was higher. The peak migration date was also positively associated with peak leaf flushing of one hostplant (Callichlamys latifolia) but not another (Xylophragma seemannianum). The quantity of migrants was correlated with the El Niño Southern Oscillation, which influenced April soil moisture on BCI and total rainfall in the dry season. Both hostplant species responded to El Niño with greater leaf flushing, and the number of adults deriving from or laying eggs on those new leaves was greatest during El Niño years. The year 1993 was exceptional in that the number of butterflies migrating was lower than predicted by the El Niño event, yet the dry season was unusually wet for an El Niño year as well. Thus, dry season rainfall appears to be a primary driver of larval food production and population outbreaks for A. statira. Understanding how global climate cycles and local weather influence tropical insect migrations improves the predictability of ecological effects of climate change.     

Grass seed production in the central Monte desert during successive wet and dry years

In desert regions, water availability triggers primary production, which determines seed production, the composition and size of soil seed reserves and the abundance and behaviour of seed-eating animals. In the central Monte desert, large precipitation events (≥10 mm) account for a high proportion of growing season’s rainfall. Our first objective here was to assess whether and how timing and amount of seed production of C₃ and C₄ perennial grasses are linked to spring and summer precipitation pulses and to estimate the seasonal and year-to-year variability in seed production. Our second aim was to calculate grass seed production and compare it with seed requirements by granivorous animals to infer whether the animals can exert top-down effects on plant populations. Seed production of C₃ and C₄ species was triggered by significant spring and summer rainfall, respectively. Such distinct response may be associated with the effect of precipitation during flower development and seed set in both functional groups. In all species, seed production varied among years. Rainfall pulses in the summer triggered and positively affected the magnitude of seed production in most C₄ grasses. However, all perennial grasses were able to produce high amount of seeds even during a year subjected to extreme drought, suggesting that perenniality would allow these species to make large reproductive investment despite harsh environmental conditions. The comparative assessment of seed production and consumer demands suggests that it is unlikely that granivory exerts a top−down control on grasses in the Monte desert.     

Field study of the relationship between skin-sensitizing antibody production in the cottontail rabbit, Sylvilagus floridanus, and infestation by the rabbit tick, Haemaphysalis leporispalustris (Acri: Ixodidae)

The resistance of cottontail rabbits to tick feeding appears correlated with the rabbits' development of skin-sensitizing antibodies. Resistance appeared to be greatest in adult rabbits which had been repeatedly infested with ticks. Rabbits with little exposure to ticks, usually the young cottontails, showed little or no skin-sensitizing antibody present in their blood and usually had relatively high tick loads when compared with adult rabbits. Models used to interpret the data show promise as tools for predicting tick population fluctuations and, perhaps, incidence of vector borne disease outbreaks. The existence of resistance to tick attachment has important implications for the host-parasite relationship. The research lends support to the hypothesis that the resistance may function as a homeostatic regulatory mechanism capable of maintaining the size of the tick population in equilibrium with the size of the rabbit population. In this way, host resistance may be advantageous to the parasite as well as to the host.     

岷江上游干旱河谷岷江柏的光合与水分生理特征干湿季对比研究

岷江柏（Cupressus chengiana）是干旱河谷地区的重要生态恢复物种,为探讨岷江柏对干旱河谷环境的适应策略,以生长于岷江上游干旱河谷自然生境中的岷江柏为研究对象,研究分析了其在湿季（7月）和干季（11月）的水分生理特征和光合生理特征。结果表明：（1）水分生理方面,相较于湿季,干季岷江柏的脯氨酸（Pro）、可溶性糖（SS）、过氧化物酶（POD）显著增加（P<0.05）,比叶重（LMA）、黎明水势（Ψ_pl）、正午水势（Ψ_ml）则显著下降（P<0.05）;（2）光合生理方面,相较于湿季,岷江柏在干季的气孔导度（G_s）、蒸腾速率（T_r）、饱和光下最大净光合速率（P_nmax）、初始羧化效率（CE）、光合能力（A_max）、CO₂补偿点（Γ）、光呼吸速率（R_p）、最大羧化速率（V_cmax）、最大电子传递速率（J_max）、磷酸丙糖利用率（TPU）、J_max/V_cmax、光能捕获效率（F_v''/F_m''）、PSII实际光化学效率（Ф_PSII）、光化学猝灭系数（qP）、电子传递效率（ETR）均显著下降（P<0.05）,而暗呼吸速率（R_d）、水分利用效率（WUE）、非光化学猝灭系数（NPQ）则显著上升（P<0.05）。干季,岷江柏采取增加水分获取能力并降低水分散失的水分利用策略、增加光合产物消耗策略、增加热耗散的光合器官保护策略等,以适应干季干旱、低温等环境胁迫,进而表现出较强的环境适应性。     

Soil factors determining the change in forests between dry and wet Chacos

This work consists of an extensive study of soil properties and floristic composition of the Paraguayan Chacoan forests. The role of the soil factors was determined conditioning the classical landscape differentiation between the dry western Chaco and the wet eastern Chaco. Soil horizon A best explains the previous classification of the forests. It highlights the soil differences between the eastern and western Chaco. CCA ordination including all forest, soil and geographical factors primarily arranged the plant associations along a W-E gradient. A significant relationship was found between the composition of the northern Paraguayan Chaco forest and geographic longitude, drainage and altitude. CCA ordination focusing on alluvial forests and soil features identified clay content as the primary soil factor discriminating forest types; it also underlined the importance of cation exchange and the content of exchange bases in the soil for differentiating dry and wet Chacoan forests.     

Analysis of fern spore banks from the soil of three vegetation types in the central region of Mexico

The vertical structure of fern spore banks was studied in a xerophilous shrubland, montane rain forest, and pine-oak forest in Hidalgo, Mexico, using the emergence method. Soil samples were collected in April 1999 at depths of 0-10, 10-20, and 20-30 cm. Viable spores decreased significantly with depth in all vegetation types, and the highest number of prothallia and sporophytes was found in the uppermost layer. The montane rain forest and the xerophilous shrubland had the largest and the richest banks, respectively. Twenty-three fern taxa were registered in the aboveground vegetation, 12 in the soil banks, and 43.5% were in both. Aboveground and in the soil bank, the xerophilous shrubland, the montane rain forest, and the pine-oak forest had, 17 and 7, 1 and 6, and 7 and 3 taxa, respectively. These were distributed differentially in relation to depth. The S?rensen index indicated a similarity of 61.5% between the xerophilous shrubland and the montane rain forest, and the Czeckanovsky index indicated 19.75%. The presence of viable spores in the soil of all vegetation types confirmed the existence of natural spore banks. Long-distance dispersal was an important factor determining the specific composition of the xerophilous shrubland and the pine-oak forest.     

Bird species richness in vegetation fences and in strips of residual rain forest vegetation at Los Tuxtlas, Mexico

Fragmentation of the lowland tropical rain forest has resulted in loss of animal and plant species and isolation of remaining populations that puts them at risk. At Los Tuxtlas, Mexico, lowland rain forests are particularly diverse in the avian fauna they contain and while most of the forests have been fragmented by human activity, many of the fragments still harbor diverse assemblages of bird species. In these landscapes, linear strips of residual rain forest vegetation along streams as well as linear strips of vegetation fences (live fences) crossing the pastures might provide some connectivity to bird populations existed in forest fragments. We investigated bird species richness and relative abundance in one 6-km long section of live fences (LF) bordering a dirt road and in two 6-km long sections of residual forest vegetation along a river (MR) and one permanent stream (BS). We used point count procedures which resulted in the count of 2984 birds representing 133 species. At the LF site we detected 74% of the species, 72% at the BS site and 57% at the MR site. Only 38% of the species were common among sites. Neotropical migratory birds accounted for 34–41% of the species counted at all sites. While edge and open habitat birds accounted for 6–10% of the species and for 50% of the records at the three vegetation strips, about 90% of the species were forest birds. Distance to forest fragments and degree of disturbance of the vegetation seemed to negatively influence bird species presence at the BS and MR strips. Rarefaction analysis indicated that the LF strip was richer in species than the other two sites, but the occurrence of the three vegetation strips in the landscape seem to favor the presence of many more species. We discuss the value of these vegetation strips to birds as stepping stones in the fragmented landscape.