Differential response to climatic variation of free‐floating and submerged macrophytes in ditches

1. Experimental studies have indicated in freshwater ecosystems that a shift in dominance from submerged to free‐floating macrophytes may occur with climate change because of increased water surface temperatures and eutrophication. Field evidence is, however, rare. 2. Here, we analysed long‐term (26 years) dynamics of macrophyte cover in Dutch ditches in relation to Dutch weather variables and the North Atlantic Oscillation (NAO) winter index. The latter appears to be a good proxy for Dutch weather conditions. 3. Cover of both free‐floating macrophytes and evergreen overwintering submerged macrophytes was positively related to mild winters (positive NAO winter index). On the other hand, high cover of submerged macrophytes that die back in winter coincided with cold winters (negative NAO winter index). Our results therefore suggest that the effect of weather on macrophyte species depends strongly on their overwintering strategy. 4. The positive relation of free‐floating macrophytes with the NAO winter index was significantly stronger in ditches in organic soil than in those in inorganic soil. This may be because of increased nutrient loading associated with increased decomposition of organic matter and increased run‐off to these ditches during mild wet winters. 5. Our results suggest that mild winters in a changing climate may cause submerged macrophytes with an evergreen overwintering strategy and free‐floating macrophytes to outcompete submerged macrophytes that die back in winter.     

西太湖水生植物时空变化

水生植物在浅水湖泊生态系统中具有十分重要的作用。根据中国科学院太湖湖泊生态系统研究站1989年以来的常规监测资料,将西太湖（除东太湖以外的湖区）划分为9个区,采用点截法（point intercept method）,于2002～2005年对各区水生植物的种类、生物量和空间分布情况进行了6次调查。结果表明：西太湖现有水生植物16种,分属于11科12属;水生植物总面积约10220hm^2,其中沉水植物分布面积约占64．58％;挺水植物约占0．29％;漂浮植物约占38．16％。各个种之间生物量差异显著,马来眼子菜、荇菜、芦苇的生物量在所有水生植物中居前3位。多样性分析表明,水生植物种类4a来未发生明显变化,但种类和生物量季节性差异较大。水生植物呈环状分布在距湖岸5km以内的水域和部分岛屿周围,东岸和南岸为水生植物的主要集中分布区域,分布区连续性好,且水草种类齐全。挺水植物种类单一,仅有芦苇（Phragmites communis）一种,分布区域多限于水深小于1．6m的湖岸;沉水植物共有8种,为水生植物的主要组成部分,马来眼子菜（Potamogeton malaianus）的分布频度最高,在西山岛周围水域逐年扩张,成为该区域的先锋种;漂浮植物3种,主要以荇菜（Nymphoides peltata）为主,在七都水域有逐渐扩张的趋势。马来眼子菜、芦苇、荇菜表现出对水环境较强的适应能力,目前为西太湖的3个优势种。20世纪50年代以来,西太湖水生植物种类减少了50种,其中水质下降是导致水生植物种类不断减少甚至消失的一个重要原因。围网养殖和不合理的捕捞方式也对局部水域的植物造成极大的破坏。水生植物生存环境日益严峻,种群单一化趋势日益明显。     

Simple pond restoration measures increase dragonfly (Insecta: Odonata) diversity

Ponds are home to a diverse community of specialized plants and animals and are hence of great conservation concern. Through land-use changes, ponds have been disappearing rapidly and remaining ponds are often threatened by contamination and eutrophication, with negative consequences for pond-dependent taxa like amphibians or dragonflies (Odonata: Anisoptera and Zygoptera). Increasingly, restoration measures such as removal of shading terrestrial vegetation or submerged organic matter are implemented to counteract current threats, but how these measures affect the target taxa is rarely assessed. We tested if and how simple pond restoration measures affectionate diversity. We propose that pond restoration influences the light regime, which promotes aquatic and riparian vegetation important for different dragonfly life stages, thus increasing their diversity. Additionally, we assume that this changes dragonfly species composition between restored and unrestored ponds. We surveyed exuviae in the riparian and aquatic vegetation along the shore of 29 (12 restored, 17 unrestored) man-made ponds in southwest Germany and assessed environmental variables known to affect dragonfly diversity. We identified the cover of tall sedges and submerged macrophytes as the driving biotic variables for dragonfly diversity and species composition, with restoration measures affecting submerged macrophyte cover directly but tall sedges indirectly via available sunlight. This study demonstrates that simple restoration measures not only have a positive effect on overall dragonfly diversity, but also increase habitat suitability for several species that would otherwise be absent. We therefore propose dragonflies as a suitable flagship group for pond conservation.     

The relative importance of dispersal and the local environment for species richness in two aquatic plant growth forms

Local species richness can be affected by both the dispersal process and by environmental conditions (species sorting process). The evaluation of the relative roles of these two processes contributes not only to further understanding of the mechanisms determining species richness but also to biodiversity conservation. We studied the relative importance of hydrological dispersal and water chemistry for species richness of submerged and floating‐leaved macrophytes using 31 sets of interconnected ponds with different numbers of component ponds (defined as connection class). Connection class was slightly more important than, or equally important to, water chemistry in determining species richness of floating‐leaved macrophytes. In contrast, submerged macrophyte richness was much more influenced by water chemistry than by connection class, although increasing connection class had some positive effect. Similarly, the occurrence of a particular species of submerged macrophyte was better explained by pond water chemistry than by the occurrence of the same species in the pond immediately upstream. The reverse was true for floating‐leaved macrophytes; the presence of a given species was better explained by its presence in the pond immediately upstream than by water chemistry. These results indicated that the relative importance of the two processes that shape the species richness of aquatic plants is a consequence of the growth form of the plants. However, both the dispersal process via hydrologic connection and species sorting by water chemistry play some role in determining the species richness of both floating‐leaved and submerged macrophytes.     

Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition,species richness and functional diversity

1. The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2. In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara– tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3. Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free‐floating species was positively affected. 4. Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free‐floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5. Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity.     

Comparative feeding selectivity of herbivorous insects on water lilies: aquatic vs. semi‐terrestrial insects and submersed vs. floating leaves

1. The rate of grazing damage experienced by submersed and floating leaves of water lilies (Nuphar variegata and Nymphaea odorata) was monitored in lakes in the Upper Peninsula of Michigan, U.S.A. Herbivores damaged 0.2–1.7% of the leaf surface of water lilies per day. These grazing rates differed between plant species, between submersed and floating leaves, and between lakes. Some leaves had more than 60% of their surface damaged and an overall mean of 16% damage occurred during the 2–3 week monitoring period of this study. 2. Snapshot measurements of grazing damage on randomly collected submersed and floating leaves of Nuphar showed that submersed leaves were more damaged (11.0 ± 1.6%, n = 84) than floating leaves (3.8 ± 0.6%, n = 92). Overall, these 176 Nuphar leaves had 7.2% of their area damaged. 3. Five species of herbivorous insects were commonly found on water lilies (Nymphaeacea). One primarily aquatic insect (sensu 1 ), a caddisfly larva (Trichoptera: Limniphilidae), had a generalized diet of water lilies, other macrophytes, algae, and detritus. Four of the five insects were from primarily terrestrial insect groups (Coleoptera and Diptera;‘secondary invaders’, sensu 1 ) and consumed only water lilies in food preference experiments. 4. The feeding preferences of the generalist trichopteran were altered when the macrophytes were freeze-dried, ground into a powder, and reconstituted in an alginate gel. This suggests that plant structure may be an important feeding determinant for this insect. In contrast, a specialist weevil preferred its host plant in choice assays, regardless of whether fresh tissue or reconstituted macrophytes were used, suggesting this insect cued on a unique, non-structural property of its host plant. 5. These results suggest that herbivory on freshwater macrophytes is of a similar magnitude to that on terrestrial plants. The findings of this study are consistent with the hypothesis that herbivorous insects of primarily terrestrial groups have a narrower diet breadth than insects of primarily aquatic groups.     

Factors affecting abundance and distribution of submerged and floating macrophytes in Lake Naivasha, Kenya

Macrophytes have been shown to perform important ecological roles in Lake Naivasha. Consequently, various studies regarding the impact of biotic factors on the macrophytes have been advanced but related studies on environmental parameters have lagged behind. In an attempt to address this gap, sampling on floating species and submergents was carried out in eight sampling sites in 2003 to investigate how they were influenced by a set of environmental factors. Soil texture (sandy sediments; P  < 0.05, regression coefficient = −0.749) and wind were the most important environmental parameters influencing the distribution and abundance of floating macrophytes. Combination of soil texture and lake-bed slope explained the most (86.3%) variation encountered in the submergents. Continuous translocation of the floating dominant water hyacinth to the western parts by wind has led to displacement of the submergents from those areas. In view of these findings, the maintenance and preservation of the steep Crescent Lake basin whose substratum is dominated by sand thus hosting most submergents remain important, if the whole functional purpose of the macrophytes is to be sustained.     

On body size and habitat selection in rotifers in a macrophye-dominated lake Budzyńskie,Poland

Lake Budzyńskie is shallow, freshwater lake with a well-developed and differentiated macrophytic vegetation. Zooplankton samples were collected from five stations: two of them in submerged macrophytes (Chara and Myriophyllum), one in the zone of floating leaves (Potamogeton), a rush station (Typha) and one in the open water surrounding the vegetation beds. The mean Rotifera densities differed significantly between the lake parts. Furthermore, different habitats were characterised by differences in body size with the exception of the middle body size group (Keratella cochlearis, Polyarthra vulgaris and Trichocerca similis), which was dominated by limnetic representatives. However, in all the other size-dependent groups both stands of submerged macrophytes were characterised by much higher densities than other zones. Additionally, body size within the examined habitats significantly differed. Thus, the size structure of Rotifera communities was directly related to morphological and spatial structures of the substrata. Two groups of habitats were distinguished: the first one consisting of open water and two vegetated zones of less complicated structure (Potamogeton and Typha), and the second of more complex submerged macrophyte species (Chara and Myriophyllum). The differentiation of the architecture of macrophytes affected the nutritional conditions and refuge effectiveness of these habitats.     

Development of the Concept of ‘Core Resident Species’ for Quality Assurance of an Insect Reserve

Awareness in the eyes of the public is important for involving the wider community in conservation. A dragonfly awareness trail was developed and implemented in the year 2000 at a national botanical garden in South Africa. Such a trail is not likely to always have the same number of dragonfly species either throughout the year or from one year to the next. The aim was to assess dragonfly assemblage changes that occurred along the trail over 3 years, so as to fine-tune expectations that the public may have as regards species to be seen at any particular time. A cumulative species variance for species and speciesenvironmental relations, strongly indicated that certain measured site variables were responsible for the main variation in dragonfly species patterns over time. Habitat requirements of an odonate species may be defined primarily in terms of marginal grasses, floating and submerged vegetation, marginal herbs, sedges and reeds, and pH. Additional variables were percentage shade, exposed rock, marginal forest and water flow characteristics. Both dragonfly species richness and abundance changed over the 3 years. One of the reasons for this was a single, major disturbance, in the form of dredging the reservoir site to reverse ecological succession in 2002. Despite an impact such as this, and after accounting for vagrancy, there were in all 24 ‘core resident species’ still to be seen along the trail from January to May. Another 11 species, including two migrants and one species lost temporarily to dredging disturbance, can be considered only as ‘possibilities’ on any one visit. Assurance that the 24 core species can be seen in the summer months (although only three in winter) is essential for maintaining the bona fide of such a trail, and hence conservation awareness, in the eyes of the public.     

Effects of aquatic vegetation type on denitrification

In a microcosm ¹⁵N enrichment experiment we tested the effect of floating vegetation (Lemna sp.) and submerged vegetation (Elodea nuttallii) on denitrification rates, and compared it to systems without macrophytes. Oxygen concentration, and thus photosynthesis, plays an important role in regulating denitrification rates and therefore the experiments were performed under dark as well as under light conditions. Denitrification rates differed widely between treatments, ranging from 2.8 to 20.9 ??mol N m^?2 h^?1, and were strongly affected by the type of macrophytes present. These differences may be explained by the effects of macrophytes on oxygen conditions. Highest denitrification rates were observed under a closed mat of floating macrophytes where oxygen concentrations were low. In the light, denitrification was inhibited by oxygen from photosynthesis by submerged macrophytes, and by benthic algae in the systems without macrophytes. However, in microcosms with floating vegetation there was no effect of light, as the closed mat of floating plants caused permanently dark conditions in the water column. Nitrate removal was dominated by plant uptake rather than denitrification, and did not differ between systems with submerged or floating plants.     

Effects of land use on aquatic macrophyte diversity and water quality of ponds

1. Aquatic macrophyte diversity and water quality of 55 ponds in western Japan were related to land use and morphometric variables to identify the environmental factors that sustain biodiversity and the spatial extent at which these factors operate. 2. The relevant spatial extent for floating‐leaved macrophyte richness (500 m from pond edge) was larger than that for submerged macrophyte occurrence (10, 75 and 100 m), whereas emergent macrophyte richness was best explained at much larger extents (1000 m). Total macrophyte richness was explained at the extent of 500, 750 and 1000 m. The extents relevant for explaining the physicochemical condition of pond water (100 and 250 m) were similar to those for submerged and floating‐leaved macrophytes, suggesting that these two growth forms are more sensitive to water quality compared to emergent macrophytes. 3. Diversity of all three growth forms and that of total macrophytes collectively were inversely related to turbidity and nutrient concentration; among the three growth forms, submerged macrophytes were most affected by water quality. 4. Negative relationships were found between the proportion of urban area and the diversity of the three growth forms and that of total macrophytes and water quality. Species richness of emergent, floating‐leaved and total macrophytes decreased with depth and increased with surface area up to about 5000 m², above which it declined. 5. Urbanisation and enlargement of ponds were the two main factors that decreased aquatic macrophyte diversity in irrigation ponds. To alleviate the adverse effects of urban areas on aquatic macrophyte diversity, our results suggest that management efforts should focus on the creation of buffer zones within the relevant spatial extent from the pond edge.     

Promoting dragonfly diversity in cities: major determinants and implications for urban pond design

Urbanisation is increasing and it is essential to integrate biodiversity into the spatial planning of urban areas. This requires deeper understanding of biodiversity patterns in cities. We investigated which habitat variables are major determinants of dragonfly diversity and species assemblage structure in the municipal area of Dortmund (Germany). We sampled dragonfly larvae in 33 ponds situated in city parks, commercial, residential and agricultural areas. We recorded 30 autochthonous dragonfly species with species richness ranging from zero to 17. Additionally, we surveyed a set of environmental variables including habitat size, water level, pond structures and vegetation as well as surrounding landscape and potential disturbances like waterfowl and fish. Multivariate methods were used to identify the major determinants of dragonfly diversity, abundance and assemblage structure. Analysis indicated that diversity of aquatic and terrestrial vegetation affected dragonfly diversity positively. City park ponds had low diversity, but Ischnura elegans was obviously promoted by the specific park pond conditions, including high waterfowl density. We found five assemblages mostly determined by generalistic species which were related to different pond types. Moderately disturbed ruderal and pioneer ponds in residential and agricultural areas also contained increased numbers of rare species. Our results indicate that urban ponds may have a great value for maintaining biodiversity, but various disturbances have negative impact. To promote urban biodiversity we suggest a natural design of well-vegetated ponds as well as a high diversity of different pond types and particularly a more-natural redesign of city park ponds.     

The Influence of Invertebrate Predators on Daphnia Spatial Distribution and Survival in Laboratory Experiments: Support for Daphnia Horizontal Migration in Shallow Lakes

The behavioural response of Daphnia cucullata to the presence of the pelagic invertebrate predator Leptodora kindtii, and the predation rate of littoral dragonfly nymphs on this species were investigated under laboratory conditions. Results of this study revealed a strong hiding response of Daphnia cucullata in the presence of the predatory cladoceran, L. kindtii, which was similar to the response of Daphnia in the presence of juvenile perch. This suggests that pelagic invertebrate predators may cause Daphnia to hide in the littoral zone which could result in increased exposure to predation by littoral invertebrates. A strong influence of dragonfly nymphs on D. cucullata, both in the presence and absence of macrophytes, was found. The average predation rate of Odonata larvae was about 5 prey ind^–1 h^–1 and did not differ significantly between treatments. Quantification of dragonfly pressure on Daphnia populations will require cross‐verification with field experiments since in the natural conditions Daphnia seeks a shelter in the vegetation stands against predation by Leptodora, despite the occurrence of odonates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vegetation structure and ecology of the Cufada Lagoon (Guinea-Bissau)

The Cufada Lagoon, in the southern part of Guinea‐Bissau, West Africa, is a shallow lagoon with a surface area of 190 ha in the rainy season. The vascular flora and physico‐chemical characteristics of the lagoon were studied in December 1997 (end of the wet season) and May 1998 (dry season). The lagoon water is soft, with acid pH, low conductivity and low transparency. The maximum depth is 2.25 m in the rainy season and 1.20 m in the dry season. A total of 46 vascular plant species were recorded, 32 being emergent macrophytes, mostly Gramineae and Cyperaceae, five floating‐leaved, three submerged, one surface‐floating and also five shrubs. Cluster analysis of the floristic data shows two main groups of inventories in both seasons, grouping almost nine‐tenths of the vegetation samples. The inventories in these groups correspond to two main vegetation types and can be spatially arranged. In the deepest inner part of the lagoon, Nymphaea lotus is the most important species, while Oryza longistaminata dominates in the shallower part. In spite of the shallow depth, the middle of the lagoon remains uncolonized by macrophytes. The main factors limiting the colonization by plants of the lagoon seem to be the low mineral and nutrient content of the water and its low transparency.     

Management of Laguna Alalay: a case study of lake restoration in Andean valleys in Bolivia

We describe the limnological changes between 1989 and 2006 in an urban, shallow lake, Laguna Alalay, located in the Andean valley of Cochabamba (Bolivia). Until 1960, water diversion to the lake was used to lower the inundation risk of Cochabamba city. In the 1980s and 1990s, the high waterfowl diversity and recreational services provided by the lake increased its conservation value. However, the population increase and the discharge of wastewater rich in nutrients increased eutrophication, and the lake became characterized by an annual alternation of submerged macrophytes and phytoplankton. The main aim of the present study is to analyze the response of the lake to manipulations implemented by local authorities: (a) sediment removal and accidental introduction of the exotic fish species Odontesthes bonariensis in 1997 and (b) manual mass removal of floating macrophytes during 2004–2006. The sediment removal and species introduction had several unpredictable consequences for the functioning of the lake, namely the transition to a permanent turbid water state and the persistent dominance of floating macrophytes. A general conclusion of our study is that any lake recovery measures in Bolivia should consider not only ecological, but also socio-economic and political aspects. Taking these into account, restoration of the submerged macrophyte-dominated state may not be that universally desirable as is widely held.     

Transport and deposition of macrophytes to the dysphotic bottom of coastal waters

Some macrophytes are transported to the deep-sea bottom and are utilized by heterotrophs in the deep-sea as a food source. We inferred the transport route of macrophytes toward the deep-sea based on similarity in the species compositions of macrophyte pieces collected from the dysphotic bottom off the Izu Peninsula and the drifting macroalgae reported for the study area. We also examined whether or not the macrophytes are buried in the sediment, based on stable isotope distributions of organisms. Macrophytes collected by dredging at a depth of 100-300 m included 93 species, whereas 43 species were found by trawling at depths from 200 to 400 m. Only 15 of 76 dredged species (19.7%) that were identified to the species level were identical to the drifting macroalgal species reported for this area, whereas 15 of the 29 trawled species (51.7%) that were identified to the species level were identical to the reported drifting species. It was thus inferred that macrophytes were mainly transported through sliding along the sea bottom for the macrophytes collected by dredging and through sinking from the surface water for the macrophytes collected by trawling. The δ¹³C of sedimentary organic matter (SOM) from the 200-300 m zone was similar to the δ¹³C distribution of particulate organic matter in the surface water reported for the study area. The SOM in the zone likely originated from almost exclusively phytoplankton. In contrast, the ¹³C of SOM was significantly more enriched in shallow areas ≤100 m deep. We infer that not only phytoplankton but also macrophytes could supply organic matter to heterotrophs on the shallow bottom.     

A comparison of flooded forest and floating meadow fish assemblages in an upper Amazon floodplain

Matched sets of gillnets of different mesh-sizes were used to evaluate the degree to which contiguous and connected flooded forest and floating meadow habitats are characterized by distinct fish faunas during the flooding season in the Peruvian Amazon. For fishes between 38–740 mm standard length ( L _S) (the size range captured by the gear), an overriding pattern of faunal similarity emerged between these two habitats. The mean species richness, diversity, abundance, fish mass, mean and maximum L _S, and maximum mass did not differ significantly between flooded forest and floating meadows. Species abundances followed a log-normal distribution in which three species accounted for 60–70% of the total abundance in each habitat. Despite these similarities, multivariate analyses demonstrated subtle differences in species composition between flooded forest and adjacent floating macrophytes. In addition, the absolute number of species was higher in flooded forest, reflecting a higher percentage of rare species. The day–night species turnover was found to be greater in flooded forests than floating meadows. Further, nocturnal samples had higher abundances and greater species richness than diurnal samples in both habitats. Differences in habitat structural complexity between flooded forest and floating meadows may result in a higher abundance and species richness of day-active species in floating meadows.     

Deconstructing responses of dragonfly species richness to area,nutrients, water plant diversity and forestry

Understanding large-scale variation in species richness in relation to area, energy, habitat heterogeneity and anthropogenic disturbance has been a major task in ecology. Ultimately, variation in species richness results from variation in individual species occupancies. We studied whether the individual species occupancy patterns are determined by the same candidate factors as total species richness. We sampled 26 boreal forest ponds for dragonflies (Odonata) and studied the effects of shoreline length, water vascular plant species density (WVPSD), availability of nutrients, intensity of forestry, amount of Sphagnum peat cover and pH on dragonfly species richness and individual dragonfly species. WVPSD and pH had a strong positive effect on species richness. Removal of six dragonfly species experiencing strongest responses to WVPSD cancelled the relationship between species richness and WVPSD. By contrast, removal of nine least observed species did not affect the relationship between WVPSD and species richness. Thus, our results showed that relatively common species responding strongly to WVPSD shaped the observed species richness pattern whereas the effect of least observed, often rare, species was negligible. Also, our results support the view that, despite of the great impact of energy on species richness at large spatial scales, habitat heterogeneity can still have an effect on species richness in smaller scales, even overriding the effects of area.     

Artificial ponds increase local dragonfly diversity in a global biodiversity hotspot

Human demands have led to an increased number of artificial ponds for irrigation of crops year-round. Certain insect species have established in these ponds, including dragonflies (Insecta: Odonata). There has been discussion around the value of artificial ponds for encouraging dragonfly diversity, with little work in biodiversity hotspots rich in rare and endemic species. We focus here on the Cape Floristic Region (CFR) global biodiversity hotspot, which has many endemic dragonfly species but has few natural ponds. Yet it has many artificial ponds mostly used for irrigation on local farms. This leads to an interesting question: to what extent do these artificial ponds provide habitats for dragonflies in this biologically rich, agriculturally fragmented landscape? To answer this, we recorded dragonfly species richness and abundances from 17 artificial ponds and 13 natural stream deposition pools as reference, in an area of the CFR where there are no local, natural, perennial ponds. Thirteen environmental and physical variables were recorded at the ponds and pools. We found that although ponds attracted no rare or threatened dragonfly species, they increased the area of occupancy and population sizes of many generalist species. These came from nearby natural deposition pools or from unknown sources elsewhere in the region, so providing refuges which otherwise would not be there. Interestingly, some CFR endemic species were also recorded at our artificial ponds. Overall dragonfly assemblages and those of true dragonflies (Anisoptera) and damselflies (Zygoptera) differed between artificial ponds and deposition pools, suggesting that artificial ponds are to some extent a novel ecosystem. Habitat type, elevation and temperature were significant drivers in structuring overall species assemblages. For the Anisoptera, riparian vegetation and level of landscape connectivity was important, while temperature was not. In contrast, Zygoptera species were most affected by river catchment, habitat type and temperature. In sum, these artificial ponds are stepping stone habitats across an increasingly fragmented landscape. Managing these ponds with perennial water, constant water levels, and maximum complexity and heterogeneity of habitats in terms of vegetation will conserve a wide range of generalists and some specialists.     

Floating meadow epiphyton: biological and chemical features of epiphytic material in an Amazon floodplain lake

SUMMARY. 1. Quantities and the chemical composition of epiphyton on the roots of floating aquatic macrophytes were measured in Lake Calado, an Amazon floodplain lake. Growth of epiphytic algae following physical disturbance and losses of epiphyton due to grazing and storms were investigated.
2. Deposition of silt from invading river water decreased chlorophyll and nutrient content (%C, %N, %P) of epiphyton during rising water. N:P ratios of epiphyton indicated that proximity to the river increased supplies of phosphorus. Attached algal biomass per unit root tissue was higher overall during the falling water period, when light was greater, storms less frequent, and new host plant tissue produced more slowly.
3. Epiphytic algal biomass at the margins of floating meadows exceeded that of the phytoplankton in the open water on a per unit area basis. Increases in attached algal chlorophyll ranged from two- to ten-fold over 1 week. Artificial denudation of roots was followed by rapid regrowth of attached algae, leading, after I week, to four-fold increases in chlorophyll over the pre-denuded state.
4. Wind-blown macrophytes experienced an episodic loss of 70% of epiphytic material in less than 1 h. Particulate material lost from roots grazed by snails included root tissue and contained significantly more carbon than material lost from ungrazed roots.