Odour emissions from anaerobic piggery ponds. 2: improving estimates of emission rate through recognition of spatial variability

Odour emission rates were measured for seven different anaerobic ponds treating piggery wastes at six to nine discrete locations across the surface of each pond on each sampling occasion over a thirteen month period. Significant variability in emission rates were observed for each pond. Measurement of a number of water quality variables in pond liquor samples collected at the same time and from the same locations as the odour samples indicated that the composition of the pond liquor was also variable. The results indicated that spatial variability was a real phenomenon and could have a significant impact on odour assessment practices. Considerably more odour samples would be required to characterise pond emissions than currently recommended by most practitioners, or regulatory agencies.     

A comparative study of phenotypic traits related to resource utilization in anuran communities

Larval anuran communities vary along a gradient of pond permanency. The families Hylidae, Ranidae, and Bufonidae have each diversified into multiple pond types. Species using ponds that dry seasonally (vernal ponds) must compete well to metamorphose before pond drying, while permanent ponds, which contain more predators, produce weaker selection for competitive ability. Quantifying phenotypic traits related to resource acquisition in 14 anuran species provides insight into the mechanistic underpinnings of adaptive radiation in anuran lineages. Under controlled laboratory conditions and at both early and late developmental stages, relative growth rate, relative consumption rate, assimilation efficiency and production efficiency varied significantly among species. As predicted, vernal pond species had high growth rates relative to species using more than one pond type. However, within a pond type, families frequently differed in phenotype. In species using permanent ponds with fish predators, hylids had high growth rates while ranids had low growth rates, and in species using vernal ponds, bufonids had higher assimilation efficiencies than hylids. Differences also occurred between stages; hylids and ranids in permanent, but fishless, ponds were similar at an early stage, but late stage hylids in the same pond type had lower growth and consumption rates, and higher assimilation efficiencies than ranids. Functional relationships between phenotypic traits also differed among species and developmental stage. Negative correlations between evolutionary change (independent contrast values) in both mass and growth rate (both stages), and mass and consumption rate (late stage), suggest the presence of trade-offs. These results indicate that different lineages have diversified in different ways into the same pond types.     

The effects of acid episodes on Lepomis sunfish recruitment and growth in two ponds in Massachusetts, U.S.A.

1. The effects of transient acidity on the recruitment of Lepomis sunfish were examined in two ponds in Plymouth County, Massachusetts with on-site monitoring systems. One pond had low buffering capacity and was sensitive to acidification and acid spikes, the other had better buffering with no acid spikes. Pond pH was continuously monitored over 3 years.
2. Young-of-the-year (YOY) sunfish were collected and through otolith analysis aged in days since larval metamorphosis. Day-classes were constructed from these age data. The YOY swim-up day-class distribution was more irregular with pronounced gaps in Maquan Pond than in the better-buffered Furnace Pond.
3. The poorly buffered pond, Maquan, experienced irregular acid spikes, defined as a sudden lowering of pond pH from about 6.6 to below 5.3 for an hour or more. These spikes were associated with rainfall ( P < 0.005). Acid spikes were not found at Furnace Pond.
4. The occurrence of acid spikes and diminished day-classes from expected swim-up values were significantly associated, based on pooled data from 3 years at Maquan Pond.
5. Transient acid spikes at Maquan Pond appear to harm Lepomis YOY at the vulnerable stage of metamorphosis, when their gills become fully functional and exposed to the environment.
6. Growth rates of Lepomis YOY were also studied. Length–age and weight–length growth relationships were examined for differences in instantaneous growth coefficients between years and between ponds. Length–age instantaneous growth coefficients ranged from 0.0114 to 0.0176 over five pond-years. The slowest growth rates were in a warm, dry spawning season with the earliest average metamorphosis date.     

Cyanobacteria as indicators of organic contamination

In two Costa Rican rivers used as receptors for domestic sewage, treated by primary stabilization ponds, were taken a total of 28 samplings located at the pond exit and at three different sites in each river: 100 m before the ponds discharge, at the discharge and 100 m after the discharge. These sampling were done for a five and a half years including dry and rainy seasons. In each sampling site, samples were collected of five different substrates: stones, submerge and semi submerge vegetation, tree trunks or sticks, water and artificial substrates. For each sample were used two types of artificial cultures, WC and BG110. A total of 55 cyanobacteria species isolations were obtained, belonging to a 26 genera, between these the most common were Phormidium with nine species, Microcystis with five species, Leptolyngbya and Pseudanabaena with four species each and Oscillatoria with three species. More cyanobacteria species were isolated in water substrate and less isolations in tree trunks and submerge vegetation. Konvophoron, Cyanarcus and Pilgeria only were isolate from water samples inoculated in culture media WC and in few opportunities, while three Leptolyngbya species and four Phormidium species were isolated very often. At the stabilization ponds Phormidium sp4 was dominant in 25 of 28 sampling while in the last others were the chlorophycea I. In this study were observed an increase in the frequency of cyanobacteria at the higher contamination places, and a species substitution between different sampling points. There were no biomass studies, therefore is not possible to relate between different cyanobacteria species and some specific types of water quality.     

The effects of acid episodes on Lepomis sunfish recruitment and growth in two ponds in Massachusetts, U.S.A.

1. The effects of transient acidity on the recruitment of Lepomis sunfish were examined in two ponds in Plymouth County, Massachusetts with on-site monitoring systems. One pond had low buffering capacity and was sensitive to acidification and acid spikes, the other had better buffering with no acid spikes. Pond pH was continuously monitored over 3 years.
2. Young-of-the-year (YOY) sunfish were collected and through otolith analysis aged in days since larval metamorphosis. Day-classes were constructed from these age data. The YOY swim-up day-class distribution was more irregular with pronounced gaps in Maquan Pond than in the better-buffered Furnace Pond.
3. The poorly buffered pond, Maquan, experienced irregular acid spikes, defined as a sudden lowering of pond pH from about 6.6 to below 5.3 for an hour or more. These spikes were associated with rainfall ( P < 0.005). Acid spikes were not found at Furnace Pond.
4. The occurrence of acid spikes and diminished day-classes from expected swim-up values were significantly associated, based on pooled data from 3 years at Maquan Pond.
5. Transient acid spikes at Maquan Pond appear to harm Lepomis YOY at the vulnerable stage of metamorphosis, when their gills become fully functional and exposed to the environment.
6. Growth rates of Lepomis YOY were also studied. Length–age and weight–length growth relationships were examined for differences in instantaneous growth coefficients between years and between ponds. Length–age instantaneous growth coefficients ranged from 0.0114 to 0.0176 over five pond-years. The slowest growth rates were in a warm, dry spawning season with the earliest average metamorphosis date.     

Local and Landscape Factors Driving the Structure of Tropical Anuran Communities: Do Ephemeral Ponds have a Nested Pattern?

The sets of species in animal and plant communities often comprise nested subsets of the species in broader communities. Although most mechanisms causing nested patterns are known and have been demonstrated for different environments and taxa, how amphibian communities are structured in ephemeral ponds in tropical disturbed landscapes remains unknown. We investigated if pond size, duration, presence of trees (local factors), and the proportion of forest cover surrounding ponds (landscape factor) affect anuran species richness and composition, and if pond assemblages showed a nested pattern. We sampled 11 ephemeral ponds in a pasture matrix near a large Atlantic Forest remnant in Brazil and measured local and landscape variables inside two buffer zones around each pond (100 and 500 m). We marked 1514 individuals from 23 anuran species, and found that richness in ponds ranged from 3–14 species. Both local and landscape factors explained frog species richness in the sampled ponds, and seemed to affect community composition. Frog communities occurred in a non‐nested pattern, contrary to our expectations: species found in poor subsets were not found in larger, more complex ponds. Local and landscape characteristics create a variety of environments in ephemeral ponds, even in impoverished ones; these characteristics restrict pond occupancy for some species, and result in a non‐nested pattern.     

Invertebrate communities and turnover in wetland ponds affected by drought

1. Changes to the macroinvertebrate fauna found in small ponds on a freshwater marsh (Aberlady Bay, Scotland) in 1986, 1987 and 1992 were used to assess the impact of the 1988–92 drought on taxon turnover in pond communities. 2. Permanent ponds accumulated taxa over the study period. Ponds that were wet throughout 1986–87 but dried in 1992 lost some of the many taxa associated with permanent water but acquired a reduced fauna typical of temporary ponds. Ponds that were temporary in 1986–87 were dry during most of 1992 and lost almost all aquatic taxa. 3. Faunal turnover was considerable even in permanent ponds. Extinction rates were high for taxa typical of permanent or temporary ponds. Colonization rates were poor for the taxa from permanent water, but high for the taxa from temporary ponds. 4. The importance of colonization and extinction rates as main predictors of the distribution of species between the ponds was looked at using metapopulation incidence functions, where observed incidence of a taxon can be used to predict colonization and extinction rates. Predicted rates were then compared with observed rates. Incidence functions gave reasonable predictions of observed colonization rates but were poor predictors of extinction, even for taxa that appeared likely to be true metapopulations. 5. For the pond fauna, including fugitive species adapted to temporary ponds, whilst colonization may well depend on environmental stochasricity (how long a pond holds water), subsequent survival depends on other, demographic, processes (e.g. finding a mate, predation) rather than the pond drying out.     

Temporal dynamics of aquatic communities and implications for pond conservation

Conservation through the protection of particular habitats is predicated on the assumption that the conservation value of those habitats is stable. We test this assumption for ponds by investigating temporal variation in macroinvertebrate and macrophyte communities over a 10-year period in northwest England. We surveyed 51 ponds in northern England in 1995/6 and again in 2006, identifying all macrophytes (167 species) and all macroinvertebrates (221 species, excluding Diptera) to species. The alpha-diversity, beta-diversity and conservation value of these ponds were compared between surveys. We find that invertebrate species richness increased from an average of 29.5 species to 39.8 species between surveys. Invertebrate gamma-diversity also increased between the two surveys from 181 species to 201 species. However, this increase in diversity was accompanied by a decrease in beta-diversity. Plant alpha-, beta- and gamma-diversity remained approximately constant between the two periods. However, increased proportions of grass species and a complete loss of charophytes suggests that the communities are undergoing succession. Conservation value was not correlated between sampling periods in either plants or invertebrates. This was confirmed by comparing ponds that had been disturbed with those that had no history of disturbance to demonstrate that levels of correlation between surveys were approximately equal in each group of ponds. This study has three important conservation implications: (i) a pond with high diversity or high conservation value may not remain that way and so it is unwise to base pond conservation measures upon protecting currently-speciose habitats; (ii) maximising pond gamma-diversity requires a combination of late and early succession ponds, especially for invertebrates; and (iii) invertebrate and plant communities in ponds may require different management strategies if succession occurs at varying rates in the two groups.     

A field study of larval development in a dragonfly assemblage in African desert ponds (Odonata)

Aquatic animals distributed along a 'habitat-permanence' gradient (HPG), differ in life history (Wellborn et al., 1996. Annual Revue of Ecology and Systematics 27: 337--363). Dragonflies that occur in hot arid regions often occur in temporary waters and consequently perform direct and rapid development. Dragonfly species of the Namibian desert do differ in their selection of habitats along the HPG and therefore may also differ in life cycle. Here, we attempt to monitor colonisation, larval growth and emergence in a temporary pond of known history. We studied the development of dragonfly species that laid eggs in artificial ponds constructed by us in March 2001. The assemblage consisted of species that originate from different habitats along the HPG. To obtain data on larval development we took samples from the ponds at 10-day intervals. Most species showed rapid development. By regressing the maximum sizes attained by larvae on each sampling date against time we estimated growth rates for five species and were thereby able to estimate that total duration of development from oviposition to emergence ranged between 38 and 70 days. Observation of first oviposition and first emergence for three of these species corroborated our estimates based on growth rate. Of few species, which laid eggs in the ponds no larvae or adults were found. For some this may have been the result of predation whereas others may not have grown fast enough to emerge before the ponds dried up. Our results indicate that dragonflies cannot recognise whether a pond will retain water long enough for full larval development and oviposit in waters that will not allow larval development.     

Long-term assessment of efficacy of permeable pond covers for odour reduction

Three anaerobic ponds used to store and treat piggery wastes were fully covered with permeable materials manufactured from polypropylene geofabric, polyethylene shade cloth and supported straw. The covers were assessed in terms of efficacy in reducing odour emission rates over a 40-month period. Odour samples were collected from the surface of the covers, the surface of the exposed liquor and from the surface of an uncovered (control) pond at one of the piggeries. Relative to the emission rate of the exposed liquor at each pond, the polypropylene, shade cloth and straw covers reduced average emission rates by 76%, 69% and 66%, respectively. At the piggery with an uncovered control pond, the polypropylene covers reduced average odour emission rates by 50% and 41%, respectively. A plausible hypothesis, consistent with likely mechanisms for the odour reduction and the olfactometric method used to quantifying the efficacy of the covers, is offered.     

Dispersal characteristics of seven odonate species in an agricultural landscape

Dispersal is an ecological phenomenon which is of fundamental importance to population biology. While dispersal behaviour of many orders of winged insects has received a great deal of attention, the dispersal characteristics of odonates have been poorly documented. We used capture-mark-recapture techniques to study dispersal behaviour of seven species of odonates breeding on a network of 11 small ponds in Cheshire, U.K. The ponds ranged in size from 615 to 1300 m²- and varied from 30 to 860 m apart. We found surprisingly high rates of dispersal between ponds, with 10–47% per species of recaptured individuals moving from their natal pond. The mean probability of dispersal differed significantly among species but the relationship between the probability of dispersal and distance moved consistently followed a simple negative exponential curve for all species. Most individuals stayed at their natal pond, but a few moved long distances. Neither the age at which an individual was marked (teneral vs sexually mature) nor its sex significantly affected its tendency to disperse. The negative exponential relationship suggests that dispersal should be relatively easy to incorporate in more complex models of odonate spatio-temporal dynamics. To our knowledge, this is the first large-scale, multi-species study to assess dispersal behaviour of odonates by direct observation.     

A quantitative study of the summer phytoplankton in four Central North Carolina ponds

Summary The phytoplankton of four ponds in the lower Piedmont and upper Coastal Plain of North Carolina was studied to find a possible correlation between bound phosphorus plankton numbers. No correlation was apparent therefore this paper reports a detailed study in relation to other habitat factors.The ponds are all shallow (2 m.). The Piedmont ponds are high in colloidal clay while the Coastal Plain ponds are much lower. The pH ranged around 7.0 except for one Coastal Plain pond which remained close to pH 6.4. Water temperature ranged from 30° C in June to 23° C near the end of August.Phytoplankton numbers were determined by the standard Sedgwick-Rafter method. Populations were low except for brief pulses. One Coastal Plain pond was typical of a fertilized pond and had several tremendous blooms of blue-green algae. The others supported a seemingly typical Caledonian flora, rich in species but low in number of individual organisms.There was no clear correlation between phytoplankton populations and any habitat factor except pH. This correlation is probably not direct but only an indication of water quality.This work was aided by Contract No. AT-(40-1) 2100 with the Division of Biology and Medicine, U. S. Atomic Energy Commission.     

Photobioreactor design: Mixing, carbon utilization, and oxygen accumulation

Photobioreactor design and operation are discussed in terms of mixing, carbon utilization, and the accumulation of photosynthetically produced oxygen. The open raceway pond is the primary type of reactor considered; however small diameter (1-5 cm) horizontal glass tubular reactors are compared to ponds in several respects. These are representative of the diversity in photobioreactor design: low capital cost, open systems and high capital cost, closed systems. Two 100-m(2) raceways were operated to provide input data and to validate analytical results. With a planktonic Chlorella sp., no significant difference in productivity was noted between one pond mixed at 30 cm/s and another mixed from 1 to 30 cm/s. Thus, power consumption or CO(2) outgassing limits maximal mixing velocities. Mixing power inputs measured in 100-m(2) ponds agreed fairly well with those calculated by the use of Manning's equation. A typically configured tubular reactor flowing full (1 cm diameter, 30 cm/s) consumes 10 times as much energy as a typical pond (20 cm deep flowing at 20 cm/s). Tubular reactors that flow only partially full would be limited by large hydraulic head losses to very short sections (as little as 2 m length at 30 cm/s flow) or very low flow velocities. Open ponds have greater CO(2) storage capacity than tubular reactors because of their greater culture volume per square meter (100-300 L/m(2) vs. 8-40 L/m(2) for 1-5-cm tubes). However, after recarbonation, open ponds tend to desorb CO(2) to the atmosphere. Thus ponds must be operated at higher pH and lower alkalinity than would be possible with tubular reactors if cost of carbon is a constraint. The mass transfer coefficient, K(L), for CO(2) release through the surface of a 100-m(2) pond was determined to be 0.10 m/h. Oxygen buildup would be a serious problem with any enclosed reactor, especially small-diameter tubes. At maximal rates of photosynthesis, a 1-cm tubular reactor would accumulate 8-10 mg O(2)/L/min. This may result in concentrations of oxygen reaching 100 mg/L, even with very frequent gas exchange. In an open pond, dissolved oxygen rises much more slowly as a consequence of the much greater volume per unit surface area and the outgassing of oxygen to the atmosphere. The maximum concentration of dissolved oxygen is typically 25-40 mg/L. The major advantage of enclosed reactors lies in the potential for aseptic operation, a product value which justifies the expense. For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements of such systems, provided desirable species can be maintained.     

不同草鱼池塘混养系统结构优化的实验研究

研究采用陆基围隔实验法,对草鱼(Ctenopharyngodon idellus)、鲢鱼(Hypophythalmichthys molitrix)、鲤鱼(Cyprinus carpio)和凡纳滨对虾(Litopenaeus vannamei)不同混养系统的养殖产量、投入产出比、氮磷利用率和综合养殖效果进行了研究。实验设置6个处理组,分别为草鱼单养(G)、草鱼和鲢鱼二元混养(GS)、草鱼、鲢鱼和鲤鱼按照不同比例放养的三元混养(GSC1和GSC2)和草鱼、鲢鱼和凡纳滨对虾按照不同比例放养的三元混养(GSL1和GSL2)。研究结果表明,各处理组总产量在770480—11492.50 kg/hm2之间;饲料系数在1.00—1.38之间,以GSC1最低,各处理组之间差异显著(P<0.05)。N、P总相对利用率在2.01—7.37之间,以GSL2最高,G最低;投入产出比在1:1.41—1:2.12之间,以GSL2最高,G最低;综合效果指标在0.59—1.39之间,以GSL2最高,G最小。研究结果表明,混养组能显著提高养殖系统的产量,降低饲料系数,提高N、P利用率,从而有效提高草鱼养殖的经济效益和生态效益。     

Multispecies coexistence of branchiopods (Anostraca,Notostraca & Spinicaudata) in temporary ponds of Chaouia plain (western Morocco): sympatry or syntopy between usually allopatric species

The study of the structure of communities of Crustacean branchiopods Anostraca, Notostraca and Spinicaudata of temporary ponds in Morocco revealed the existence of a geographical area with a particularly diversified number of species. Over a few hectares, 11 species, among the 18 known in Morocco, are present. While most of them are usually allopatric and belong to distinct associations, indicative of particular ecological and climatic conditions, they can coexist in Chaouia plain, either in adjoining ponds (sympatric species) or in the same pond (syntopic species). In one pond we could find up to 10 phyllopods: 6 Anostraca, 2 Notostraca and 2 Spinicaudata.This faunistic diversity may result from abiotic features (the location of the ponds at the boundary of two climatic areas) and from a heterogeneous geological substratum, creating a patchwork of temporary ponds with various mesologic conditions.Secondarily, this diversity may result from different life history characteristics of each coexisting species. As all species hatch synchronically, coexistence is only possible if their growth rates and life span are different. This implies that horizontal and vertical distribution, and exploitation of food supplies in the habitat differ for each ecophase of the syntopic species (spatial and trophic exclusion).     

Flexible antipredator behavior in a dragonfly species that coexists with different predator types

Two of the main predators of dragonfly larvae, insectivorous fish in communities with fish and large dragonfly species in communities without fish, differ markedly in their mode of predation. In general, dragonfly species coexist successfully with one predator or the other, but larvae of the dragonfly Pachydiplax longipennis can coexist successfully with both. I examined the behavioral response of these larvae to a simulated predator attack to determine whether their response (1) differs between the two communities, and (2) is sensitive to waterborne cues about the type of predator present. I compared larvae from two different communities: fish ponds where insectivorous fish were the top predators, and fish-free ponds where large dragonflies were the top predators. Larvae from fish-free ponds actively moved away from an attack significantly more than did larvae from fish ponds, provided each was attacked in its native pond water. Larvae collected from a fish-free pond but then attacked in fish water moved less than did controls (larvae attacked in fish-free water). Likewise, larvae collected from a fish pond but attacked in fish-free water moved more than did controls (larvae attacked in fish water). Larvae attacked first in water from their native pond and then in water from the contrasting pond changed their response in the expected direction. These results indicate that escape behavior in P. longipennis differs between communities with different predator types and is sensitive to waterborne cues in a manner consistent with the mode of predation employed by each predator.     

池塘养殖匙吻鲟与鳙胃肠道饵料生物的比较

通过对同一试验池中匙吻鲟（Polyodon spathala）和鳙（Aristichthys nobilis）胃肠道内含物的连续3次分析,揭示他们滤食的天然饵料生物组成及差异。首先根据物种鉴定结果对2种鱼的胃肠道内饵料生物组成进行了UPGMA聚类分析,结果显示:相同采样时间同一池塘内2种鱼饵料生物组成存在差异,分别聚为不同的分枝;分析匙吻鲟和鳙胃肠道内饵料生物种类时还发现不同采样时间前者枝角类和桡足类种类数均多于后者。同时对2种鱼胃肠道内各饵料生物的生物量进行分析,结果显示:当大型饵料生物充足时,枝角类和桡足类的生物量在2种鱼胃肠道内没有显著差异（P0.05）;当大型饵料生物减少时,匙吻鲟摄食强度减小,但其枝角类和桡足类的生物量仍显著较大（P0.05）;当大型饵料生物消失后,轮虫生物量在匙吻鲟胃肠道内显著增加 （P0.05）;相比较,鳙在各采样期则主要滤食较小型的浮游动物和浮游植物。另外,当动物性饵料减少后,匙吻鲟和鳙均通过大量滤食植物絮团来补充能量。综上,同一试验池养殖的匙吻鲟和鳙存在摄食竞争压力,该压力的大小与环境中大型饵料生物的丰富度密切相关。       

Mechanisms for Parasites Removal in a Waste Stabilisation Pond

A waste stabilisation pond (WSP) system formed by two anaerobic ponds, a facultative pond and a maturation pond was studied from December 2003 to September 2004 in north-western Spain in order to evaluate its efficiency in the removal of faecal indicator bacteria (total coliforms, Escherichia coli, faecal streptococci), coliphages, helminth eggs and protozoan (oo)cysts (Cryptosporidium and Giardia). Furthermore, sediment samples were collected from the bottom of the ponds to assess the settling rates and thus determine the main pathogen removal mechanisms in the WSPs system. The overall removal ranged from 1.4 log units for coliphages in the cold period to 5.0 log units for E. coli in the hot period. Cryptosporidium oocysts were reduced by an average of 96%, Giardia cysts by 98% and helminth eggs by 100%. The anaerobic ponds showed significantly higher surface removal rates (4.6, 5.2 and 3.7 log (oo)cysts/eggs removed m⁻² day⁻¹, respectively) than facultative and maturation ponds. Sunlight and water physicochemical conditions were the main factors influencing C. parvum oocysts removal both in the anaerobic and maturation ponds, whereas other factors like predation or natural mortality were more important in the facultative pond. Sedimentation, the most commonly proposed mechanism for cyst removal had, therefore, a negligible influence in the studied ponds.     

不同水深条件下刺参养殖池塘大型底栖动物群落结构季节性变化特征

于2012年7月至2013年4月调查了荣成靖海湾3个不同水深的刺参(Apostichopus japonicus)养殖池塘内大型底栖动物的构成,以了解不同水深对刺参养殖池塘环境条件的影响以及由此引起的大型底栖生物群落结构的改变。结果表明:3个不同水深梯度池塘(1#浅水位、2#正常水位和3#高水位)底部光照强度、叶绿素a(Chla)和总有机物(TOM)含量存在显著差异,各池塘水温差异不显著。光强、Chla和TOM含量在夏季、冬季和春季均表现为1#池塘显著高于3#池塘;秋季各池塘间光强和TOM含量差异不显著,Chla含量则表现为3#池塘显著高于1#池塘。各季节3个池塘间大型底栖动物在种类组成、丰度、生物量和多样性指数上均存在显著性差异。大型底栖动物丰度和生物量夏季均表现为1#池塘显著高于3#池塘,秋季和冬季则相反;春季1#池塘丰度显著高于3#池塘,生物量则差异不显著。这些差异主要与其各自优势种及其优势度指数大小有关。大型底栖动物多样性指数夏季和秋季均表现为1#池塘高于3#池塘,春季则相反,冬季各池塘间多样性指数差异不显著。单因子相似性分析(ANOSIM)表明,各季节3个池塘间大型底栖动物群落结构均存在显著差异,表明水深梯度对刺参养殖池塘大型底栖动物群落结构造成显著性影响。相似性百分比分析(SIMPER)显示,各季节对3个池塘间大型底栖动物群落差异起主要作用的物种为各个池塘的优势种。典范对应分析(CCA)表明,水深、Chla和TOM含量为影响大型底栖动物群落的主要环境因子。     

POLYPHENISM IN SPADEFOOT TOAD TADPOLES AS A LOCALLY ADJUSTED EVOLUTIONARILY STABLE STRATEGY

I examined the evolutionary factors maintaining two environmentally induced morphs in ponds of variable duration. Larvae of New Mexico spadefoot toads (Scaphiopus multiplicatus) often occur in the same pond as a large, rapidly developing carnivorous morph and as a smaller, more slowly developing omnivorous morph. Previous studies revealed that carnivores can be induced by feeding tadpoles live fairy shrimp and that morph determination is reversible. Field and laboratory experiments indicated that the ability of an individual to become a carnivore or an omnivore is maintained evolutionarily as a response to variability in pond longevity and food abundance. Carnivores survived better in highly ephemeral artificial ponds, because they developed faster. Omnivores survived better in longer-duration artificial ponds, because their larger fat reserves enhanced postmetamorphic survival. The two morphs also occupy different trophic niches. Experimental manipulations of morph frequency in ponds of intermediate duration revealed that increased competition for food among individuals of the more common morph made the rarer form more successful. Morph frequency within each pond was stabilized at an equilibrium by frequency-dependent morph reversal, which reflected frequency-dependent natural selection on size at metamorphosis: larger metamorphs had higher survival, and individuals reared at a frequency above the pond's equilibrium frequency were smaller at metamorphosis than were individuals of that morph reared at a frequency below the pond's equilibrium. Because neighboring ponds often differed in pond longevity and food abundance, each pond possessed a unique equilibrium morph frequency. This implies that morph determination in Scaphiopus is a locally adjusted evolutionarily stable strategy (ESS).