Tropical Ponds Research Articles

Higher alpha and gamma, but not beta diversity in tropical than in Mediterranean temporary ponds: A multi‐taxon spatiotemporal approach

AbstractThe latitudinal diversity gradient predicts that tropical regions should have higher alpha, beta, and gamma diversity than temperate areas. However, only a few studies have assessed the temporal variability of the different components of diversity across climatic regions. In this study, we compare, using a spatial and temporal approach, the diversity of multiple taxa inhabiting tropical and Mediterranean temporary ponds. We sampled the biological communities of each set of ponds on three occasions during the same hydrological year. Under a spatial framework, we analyzed, alpha, beta, and gamma diversities. With a temporal approach, we compared the coefficients of variation in alpha diversity for each local community, and temporal beta diversity. Differences between regions and sampling periods were tested using generalized linear mixed models. We found higher gamma and alpha diversity in the tropical ponds, as expected given the latitudinal differences between them. However, phytoplankton and microinvertebrates from the Mediterranean region, matched or even exceeded tropical alpha diversity on some occasions. Spatial beta diversity did not differ between regions, and it showed lower values at the middle or the end of the hydroperiod in bacteria, micro‐ and macroinvertebrates and amphibians. Thus, processes homogenizing and heterogenising pond metacommunities must be balanced in both studied regions. Temporal variation in alpha and beta diversity was similar for ponds in both regions, except for macroinvertebrates and amphibians, suggesting differential effects on community variation observable only in animals with longer life‐spans, at our temporal scale of analysis.

Intra-specific variation in the morphometry of freshwater prawn (Caridina: Atyidae) from tropical ponds of South India

Intra-specific variation in the morphometry of freshwater prawn (Caridina: Atyidae) from tropical ponds of South India

Inconsistent response of taxonomic groups to space and environment in mediterranean and tropical pond metacommunities.

The metacommunity concept provides a theoretical framework that aims at explaining organism distributions by a combination of environmental filtering, dispersal, and drift. However, few works have attempted a multitaxon approach and even fewer have compared two distant biogeographical regions using the same methodology. We tested the expectation that temperate (mediterranean-climate) pond metacommunities would be more influenced by environmental and spatial processes than tropical ones, because of stronger environmental gradients and a greater isolation of waterbodies. However, the pattern should be different among groups of organisms depending on their dispersal abilities. We surveyed 30 tropical and 32 mediterranean temporary ponds from Costa Rica and Spain, respectively, and obtained data on 49 environmental variables. We characterized the biological communities of bacteria and archaea (from the water column and the sediments), phytoplankton, zooplankton, benthic invertebrates, amphibians and birds, and estimated the relative role of space and environment on metacommunity organization for each group and region, by means of variation partitioning using generalized additive models. Purely environmental effects were important in both tropical and mediterranean ponds, but stronger in the latter, probably due to their larger limnological heterogeneity. Spatially correlated environment and pure spatial effects were greater in the tropics, related to higher climatic heterogeneity and dispersal processes (e.g., restriction, surplus) acting at different scales. The variability between taxonomic groups in the contribution of spatial and environmental factors to metacommunity variation was very wide, but higher in active, compared with passive, dispersers. Higher environmental effects were observed in mediterranean passive dispersers, and higher spatial effects in tropical passive dispersers. The unexplained variation was larger in the tropical setting, suggesting a higher role for stochastic processes, unmeasured environmental factors, or biotic interactions in the tropics, although this difference affected some actively dispersing groups (insects and birds) more than passive dispersers. These results, despite our limitations in comparing only two regions, provide support, for a wide variety of aquatic organisms, for the classic view of stronger abiotic niche constraints in temperate areas compared with the tropics. The heterogeneous response of taxonomic groups between regions also points to a stronger influence of regional context than organism adaptations on metacommunity organization.

Effects of a Popular Aquatic Pest Control Agent among Carp Aqua-culturists on Aquatic Microfauna Dynamics

Cypermethrin is gaining popularity among fish farmers community to control aquatic insect pests and ectoparasites. Effect of cypermethrin application at farmer select dose (@0.003 ppm) on aquaculture pests (Notonecta & small prawn) commonly found in tropical ponds along with fish fry was assessed. Effect of cypermethrin application on the composition and survivability dynamics of aquatic microfauna namely rotifer, copepod and cladocera for 8 days was studied in tropical pond conditions. Cypermethrin cause significantly higher mortality to notonecta and prawn compared to fish fry within 24 h of exposure (P<0.05).

The environmental framework of temporary ponds: A tropical-mediterranean comparison

Temporary ponds are distributed worldwide, providing significant ecological services. Their limnological features are influenced by a set of regional (mainly climate) and local (natural or anthropogenic) factors. To evaluate the differences in their ecological functioning in distant geographic regions, we analysed the main features of 90 temporary ponds located in three distinct areas: two mediterranean-climate regions (Eastern Iberian Peninsula and Central Chile) and a tropical setting in Costa Rica. Each pond was surveyed thrice during the hydrological cycle of 2017–2018, and five sets of parameters were obtained: limnological, hydrogeomorphological, biotic, landscape and climatic variables. Through multivariate analyses, we determined the environmental heterogeneity of each region and the main environmental differences among them. As expected, hydrogeomorphological factors did not differ between regions, but climate variables showed marked differences between the tropical and the two mediterranean regions. We also detected clear differences between mediterranean and tropical ponds in terms of their mineralization patterns (mainly conductivity and alkalinity), natural vegetation cover and land use. Despite the regional similarities between mediterranean regions, some strong differences were found concerning vegetation cover, nutrient concentration and trophic state, probably associated to human activities (agriculture and extensive stockbreeding).

Developmental Twists: Only Human.

I first heard the news while sunning myself in the glasshouse. A call came through, informing me I'd been elected to the Academy's Developmental Biology Division. I nearly fell off my bench! I was being invited to attend the ceremony to accept the honour. Why me? I'd been highly recommended by a colleague.I could hardly contain my excitement when the day came. The arena was already heaving with famous scientists by the time I'd ported myself there. Everyone seemed to know everyone. To avoid gawping at them like an imbecile, I turned to study the portraits of past presidents. I was perusing a fine depiction, set in the Bay of Naples, when I heard: “An excellent resemblance, don't you think?” I turned to see the portrait's subject, Strongylocentrotus, inspecting the picture alongside me. “Those were the days,” said my companion, flexing her spines. “Morning bathe in the Med, then drop into the institute for an afternoon display. Not a bad life, eh?” I told her how I'd always admired her classic demonstration of totipotency. “Very kind of you to say so. Yes, amazing what can be conveyed through a simple routine.” Strongylocentrotus prodded me gently with one of her spikes. “Do I know you?” I introduced myself and explained that I'd just been elected. “Congratulations! I've never met a liverwort before”.We were soon approached by two others. “Ah, Xenopus and Gallus, this is Marchantia, the first liverwort to join us,” said Strongylocentrotus.“Welcome to the fold,” said Xenopus.“How's your audience getting on Xenopus?” asked Strongylocentrotus. “Still having trouble with interpretations?”I knew how tricky dealing with audiences could be. Audiences wanted to know whether their ideas might be right or not. But you couldn't tell them directly. Instead they had to play a guessing game. You gave a staged performance in the hope that they would glean the answer from your antics. If all went well, you got a joint publication. But it could go awry in so many ways – badly formulated ideas, poorly designed stage sets, lacklustre performances (one of my friends got stage fright while under a microscope objective), failures in interpretation.“I'm displaying the coolest expression patterns,” said Xenopus, “but my audience is so stuck in its ways it can't see their significance. So frustrating not being able to tell it what the patterns mean. We'll never publish at this rate”.“Mine's a washout,” said Gallus. “I mean, I send these magnificent eggs onto the stage, but the sets are lousy and the audience is continually dozing off or checking messages during the show”.Strongylocentrotus gave me a gentle prod. “How's yours doing?”The question took me by surprise. I'd been so absorbed in perfecting my routines recently, I'd hardly noticed my audience. “I'm not sure,” I said.“Well you'll have to do better than that if you are going to help them”.“Help them?”“They're like children finding their way. You can assist by giving them a little nudge every so often. Try a flamboyant gesture. Might trigger a new question or idea, if they're receptive that is.”“Mine's more of an obstinate brat than an inquisitive child,” said Xenopus.“I suppose we're lucky they chose us to put on stage,” I said.Xenopus inflated her throat to twice her body size and released a deafening croak: “Chose us? You've got it completely the wrong way round my friend! We're the ones who chose them, by putting ourselves in their path. Our audiences are so lazy they just go for whatever is around: Drosophila from garbage bins, Mus and Rattus from dirty dwellings, Arabidopsis from weedy gardens, Caenorhabditis from any old soil, Strongylocentrotus from swimming resorts and me from tropical ponds. And you're the common liverwort if I'm not mistaken?”Gallus, who had been nodding her head so vigorously it seemed in danger of dislocating, steadied herself and added “Not to mention those of us who put food on their plates, provide alcoholic beverages or flowers for their table. Zea, Pisum, Lycopersicon, Antirrhinum, Petunia, the yeast sisters, to mention just a few. And me of course.”The conversation was interrupted by an announcement that the admission ceremony was about to begin. I stood in line, observing those ahead of me going up to be anointed. I hoped I wouldn't wilt. Finally, my turn came: “For services in the understanding the evolution of morphogenesis.” I accepted the elevation on behalf of my kind.Since returning from the ceremony, I've been observing my audience more closely. It puts in long hours and takes endless recordings but doesn't seem to spend enough time thinking about what each performance means. I've decided to grow exaggerated curves in the hope of triggering its curiosity. Of course, there's no guarantee of success. It's only human after all.

Phosphorus balance in a tropical shallow urban pond in Southeast Brazil: implications for eutrophication management

ABSTRACT A detailed mass balance that evaluates nutrient inputs and outputs is fundamental to determining the most promising strategies to mitigate eutrophication and its undesirable effects. However, such analyses are rare in Brazilian urban ponds where water quality impairment remains a significant issue. We performed a mass balance to identify the main phosphorus (P) sources in a hypereutrophic tropical shallow urban pond. We used the PCLake model to estimate the P loading required to reduce phytoplankton biomass. The water column was considered the primary unit in the model. The P balance was calculated from external inputs, internal inputs from bed sediment to the water column, and outputs from the water column through surface water outflow and to the bed sediments over a full hydrological year. The total P input into the pond water (external and internal) was 35.3 mg m−2 d−1 and the output was 35.2 mg m−2 d−1. The P balance revealed that contributions to the water column from external and internal sources were 82.5% and 17.5%, respectively. Birds were the main contributor to P input (76.0%). The highest P loss from the water column was to the sediment (97.6%). Most of the P leaving the water column to the sediment was retained in the sediment, and part was returned to the water column through internal loading. Measures to reduce eutrophication in this pond should focus on integrated management to decrease both the external and internal P sources by managing birds and avoiding P release from sediment, and to decrease water residence time in the pond.

Environment and Space Rule, but Time Also Matters for the Organization of Tropical Pond Metacommunities

Metacommunities are dynamic systems, but the influence of time independently of environmental change in their configuration has been rarely considered. Temporary ponds are excellent ecosystem models, as they have well-defined boundaries in time and space; their communities are relatively isolated through a landscape matrix, and the progress of time leads to major changes through ecological succession and in habitat suitability related to hydroperiod dynamics. Therefore, strong temporal effects are expected to influence their metacommunity structure. We surveyed 30 temporary ponds along the dry tropical region of western Costa Rica and Nicaragua at three different moments of their hydroperiod: shortly after the infilling of the water bodies, at the middle of the hydroperiod and just before desiccation. We obtained data on 56 environmental variables (including limnological, climatic, landscape, hydrogeomorphological and conservation state), and used geographic coordinates to build spatial variables (Moran Eigenvector Maps). We collected biological samples and estimated the specific abundance of phytoplankton, zooplankton and benthic invertebrates. To evaluate the relative role of environmental, spatial and temporal (sequential sampling season) effects in metacommunity organization of the 646 species found, we used variation partitioning with distance-based redundancy analyses for each group of organisms. We repeated the analyses for selected taxonomic groups, separately for each sampling season, to check how the variance explained by spatial and environmental factors varied between sampling periods. The inclusion of time in the analysis highlighted that pure temporal effects explained part of metacommunity variance in almost every group, being as important as spatial or even environmental effects for some groups of organisms. In contrast to the assumed low environmental constraints in tropical areas (i.e. high and stable temperatures), we found strong environmental effects. Passive dispersers were more influenced by environmental factors than active ones. We also found a positive relationship between the body size of the different groups of organism and the magnitude of the temporal effect, interpreted as related to generation time. Finally, when analyzing each sampling period separately, we found differences in the relative role of environment and space at different sampling periods, showing that snapshot surveys may not be representative of highly dynamic metacommunities.

Interactions of fish, algae, and abiotic factors in a shallow, tropical pond

Protecting and restoring shallow tropical lakes and wetlands requires a knowledge of what shapes and controls algal dynamics and primary productivity in these systems. Algal community structure and composition can be regulated either through biotic or abiotic controls. Large-scale changes in fish populations can affect algal communities by altering food web dynamics and the physical and chemical properties of the aquatic environment. A reduction in fish biomass can lead to a reduction in algal biomass because of increased grazing by zooplankton and reduced availablity of nutrients. However, the omnivorous fish common in tropical systems often consume algae, and their reduction can increase algal biomass. There is a need for more information on the effect of fish removals/reductions in tropical systems. In a five-year study of a shallow, tropical pond in Hawaii, I investigated the water quality effects of tilapia removal following the occurrence of two natural fish die-offs. I describe the concurrent impacts of water-level fluctuations and the fish die-offs on the physical and chemical conditions of the pond and the subsequent changes in the algal community. Overall, nutrients, suspended sediment, organic matter, and algal biomass were significantly reduced and light availability significantly increased in the absence of tilapia.

Effect of nutrient alteration on pCO2(water) and chlorophyll-a dynamics in a tropical aquaculture pond situated within a Ramsar site: a microcosm approach.

Tropical sewage-fed aquaculture ponds of East Kolkata Wetlands (EKW), a Ramsar site, act as deposition center of organic matter and nutrient-rich sewage from the Kolkata metropolis, which in turn is utilized as fish feed in aquaculture ponds. Increasing nutrient load due to multifarious anthropogenic activities usually alters the chlorophyll-a (chl-a) and the partial pressure of carbon dioxide in water [pCO2(water)] dynamics in such aquatic systems. In this regard, the effect of nutrient level alteration [8 times and 24 times, dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) in addition, respectively] on chl-a and pCO2(water) was tested upon waters of EKW aquaculture ponds in three different seasons by means of microcosm for 8 consecutive days. In both DIN 8× and DIP 8× treatments, an overall increase in chl-a concentrations was observed by the end of experiment; however, in DIN 24× and DIP 24× treatments, chl-a in most of the seasons was found to diminish after a steep rise in its concentration during 4th or 5th day. In all the seasons, the surface waters were supersaturated with CO2 under in situ conditions. The extent of supersaturation enhanced with nutrient addition during monsoon; however, in post-monsoon and pre-monsoon, nutrient addition led to undersaturation of CO2. Though chl-a concentration exhibited substantial variability during the microcosm experiments, the variation in trophic state index was not that much remarkable. In DIN-treated microcosms, uptake rate of DIP was significantly high compared to the reverse scenario, which implied that DIP has a more limiting character than DIN. In P-enriched treatments, the lack of N supplies probably limit production of autotrophic biomass. Thus it can be concluded that the nature of sewage and its DIN/DIP content can significantly alter the primary productivity the CO2 dynamics of such aquaculture ponds in future.

New Pond—Indicator Bacteria to Complement Routine Monitoring in a Wet/Dry Tropical Wastewater Stabilization System

Bacteria monitoring is a critical part of wastewater management. At tropical wastewater stabilization ponds (WSPs) in north Australia, sanitation is assessed using the standard fecal indicator bacteria (FIB) Escherichia coli and Enterococci. However, these bacteria are poor surrogates for enteric pathogens. A focus on FIB misses the majority of pond-bacteria and how they respond to the tropical environment. Therefore, we aimed to identify the unknown pond bacteria and indicators that can complement E. coli to improve monitoring. Over two years, we measured the bacterial community in 288 wastewater samples during the wet and dry seasons. The WSP community was spatially and temporally dynamic. Standard pond-water physicochemical measures like conductivity poorly explained these community shifts. Cyanobacteria represented >6% of the WSP bacterial population, regardless of sample timing and location. Fecal bacteria were abundant in the first pond. However, in downstream ponds, these bacteria were less abundant, and instead, environmental taxa were common. For each pond, we identified a bacterial fingerprint that included new candidate bacterial indicators of fecal waste and processes like nitrogen removal. Combining the new indicators with standard FIB monitoring represents a locally relevant approach to wastewater monitoring that facilitates new tests for human fecal pollution within tropical climates.

Detection of the oil-producing microalga Botryococcus braunii in natural freshwater environments by targeting the hydrocarbon biosynthesis gene SSL-3

The green microalga Botryococcus braunii produces hydrocarbon oils at 25–75% of its dry weight and is a promising source of biofuel feedstock. Few studies have examined this species’ ecology in natural habitats, and few wild genetic resources have been collected due to difficulties caused by its low abundance in nature. This study aimed to develop a real-time PCR assay for specific detection and quantification of this alga in natural environments and to quantify spatiotemporal variations of wild B. braunii populations in a tropical pond. We designed PCR primers toward the hydrocarbon biosynthesis gene SSL-3 and examined amplification specificity and PCR efficiency with 70 wild strains newly isolated from various environments. The results demonstrated that this PCR assay specifically amplified B. braunii DNA, especially that of B-race strains, and can be widely used to detect wild B. braunii strains in temperate and tropical habitats. Field-testing in a tropical pond suggested a diurnal change in the abundance of B. braunii in surface water and found B. braunii not only in surface water, but also at 1–1.5 m deep and in bottom sediments. This method can contribute to efficient genetic resource exploitations and may also help elucidate the unknown ecology of B. braunii.

Trait-Environment Relationship of Aquatic Vegetation in a Tropical Pond Complex System

The relationship between organisms’ traits and the characteristics of their habitats has been a central theme in ecology. Using two complementary approaches to analyze three-matrices of species composition, functional trait, and environment data (RLQ and fourth-corner analyses), we tested if environmental gradient determines aquatic plant traits in ponds in the Pantanal wetland. Furthermore, we tried to understand if plant composition is spatially structured and if environmental gradient is correlated with taxonomic and functional community properties. We sampled aquatic plants coverage in 20 ponds and measured pond size, depth and pH to represent the environmental gradient. We found significant turnover of several traits of aquatic plants along the environmental gradient, being niche partitioning the most probable process structuring plant communities. There was no evidence of spatial autocorrelation determining species composition in the scale of the study, which may indicate that the annual flooding can act as homogenizing factor that promotes species co-occurrence along the ponds. Taxonomic abundance and functional richness were positively related with environmental gradient. Larger and deeper ponds provide higher resource availability thus supporting more functional attributes and vegetation cover. Our results support the hypothesis that niche process is the main driver of aquatic plants in the Pantanal.

Skin bacterial communities of neotropical treefrogs vary with local environmental conditions at the time of sampling.

The amphibian skin microbiome has been the focus of recent studies aiming to better understand the role of these microbial symbionts in host defense against disease. However, host-associated microbial communities are complex and dynamic, and changes in their composition and structure can influence their function. Understanding temporal variation of bacterial communities on amphibian skin is critical for establishing baselines from which to improve the development of mitigation techniques based on probiotic therapy and provides long-term host protection in a changing environment. Here, we investigated whether microbial communities on amphibian skin change over time at a single site. To examine this, we collected skin swabs from two pond-breeding species of treefrogs, Agalychnis callidryas and Dendropsophus ebraccatus, over 4 years at a single lowland tropical pond in Panamá. Relative abundance of operational taxonomic units (OTUs) based on 16S rRNA gene amplicon sequencing was used to determine bacterial community diversity on the skin of both treefrog species. We found significant variation in bacterial community structure across long and short-term time scales. Skin bacterial communities differed across years on both species and between seasons and sampling days only in D. ebraccatus. Importantly, bacterial community structures across days were as variable as year level comparisons. The differences in bacterial community were driven primarily by differences in relative abundance of key OTUs and explained by rainfall at the time of sampling. These findings suggest that skin-associated microbiomes are highly variable across time, and that for tropical lowland sites, rainfall is a good predictor of variability. However, more research is necessary to elucidate the significance of temporal variation in bacterial skin communities and their maintenance for amphibian conservation efforts.

Low cross-taxon congruence among aquatic organisms in artificial tropical ponds: implications for biomonitoring

The use of biodiversity surrogates is often suggested to increase the cost-effectiveness of biomonitoring programs, as this demands less time and taxonomic expertise. In addition, the detection of multi-taxon associations is a first step toward a better understanding of how organisms interact with each other. Such a multi-taxon association is termed a congruence, and can be detected through measuring the similarity in the distributional patterns shown by different biological groups. To assess the ability of different taxa to serve as surrogates for others, we carried out a Procrustes analysis on the beta diversity patterns of seven biological groups (aquatic birds, Amphibians, Macrophytes, Coleoptera, Odonata, Heteroptera and phytoplankton) in 35 ponds of the Cerrado biome. We found that: (i) the values of congruence in the studied ponds were weak; (ii) among all the biological groups compared, the highest congruence was found between amphibians and macrophytes; (iii) amphibians were congruent with the Coleoptera, Heteroptera, and macrophytes; (iv) the different taxa studied had different responses to environmental conditions; and (v) although they showed relatively weak congruence with the other taxa in each pond environment, amphibian communities were the most strongly influenced by environment variables. Almost all the communities observed in these systems showed unique pattern and thus should be studied and monitored in their entirety.

Effect of Physico-chemical Factors and Plankton Abundance in Selected Tropical Fish Earthen Ponds' Water

The study investigated the plankton diversity and abundance of three selected on-farm research fish ponds in Nigerian Institute for Oceanography and Marine Research, Lagos. Samples were taken from three ponds using standard procedure and physico- chemical features of the water bodies were measured. Plankton of class ( Bacillariophyceae, Chlorophyceae, Cyanophyceae and Euglenophyceae I) and Zooplanktons of ( Cladocera, Rotifera and Copepoda ) family were found. There were varying results for the phytoplaktons and zooplaktons respectively during the study. The highest percentage composition for phytoplankton was recorded in Pond 1 (94.11%), and the highest Shannon-Weaner diversity (1.265%) in pond 2. The highest percentage of zooplankton was recorded in pond 2 (91.67%). Utilizing the parameter of Shannon index value, the abundance value for zooplaktons was not remarkable. Statistical association between parameters and abundance reflected that abundance was positively correlated with temperature, and negatively correlated with pH while the levels of dissolved oxygen (DO) were positively correlated. The low densities and plankton diversity in pond 3 was an indication of low pH and high transparency as a result of nutrient depletion. Keywords : Abundance; physico-chemical factors; phytoplankton; zooplankton; fish ponds

Evaluation of the Ecological Integrity and Microalgae Carbon Sequestration Potential Across the Sewage Effluent Gradient of Tropical Waste Stabilization Pond System

Evaluation of the Ecological Integrity and Microalgae Carbon Sequestration Potential Across the Sewage Effluent Gradient of Tropical Waste Stabilization Pond System

Interactions of water levels with water quality, endemic waterbirds, and invasive species in a shallow, tropical pond

This study responds to a need for baseline physical and chemical data in shallow tropical water bodies. We investigated the degree to which water level fluctuations affected water quality and biota in a shallow tropical pond, Keālia Pond National Wildlife Refuge in Hawaii. We observed strong interactions among climate, water levels, salinity, DO, turbidity, waterbirds, fish, and invertebrates. Seasonal precipitation and air temperature patterns led to higher pond levels in winter and lower pond levels in summer. Low water levels in summer were associated with very high salinity and turbidity, and low DO. Endemic waterbirds were favored by lower water levels. Extremely low DO concentrations at minimum water levels caused fish die-offs, primarily non-native tilapia. The fish die-offs temporarily resulted in lower turbidities, clearer water, and a large increase in invertebrates, specifically a native rotifer but also a non-native chironomid midge. Nuisance emergences of midge only occurred in winters following summer fish die-offs but only if there was sufficient winter streamflow to lower salinity and create brackish conditions in the pond. The study results were used to assess restoration and management options to promote endemic waterbirds and other natives and suppress invasive species.

Influence of water quality on plankton in tropical ponds: A multivariate analysis approach

AbstractPlankton are highly sensitive to environmental changes, therefore being excellent water indicators. This study was conducted to classify water and sediment quality characteristics and different genera of phytoplankton and zooplankton in three ponds. The prominent water and sediment quality characteristics responsible for the occurrence of phytoplankton and zooplankton were also studied. The nutrient pollution factor is mainly responsible for the abundance of Cyanophyceae and for reduction in Rotifera, Cladocera, Copepoda and Ostracoda. The organic pollution factor is responsible for the abundance of Bacillariophyceae and Protozoa. The products of mineralization have more influence on the decreased Chlorophyceae. Thus, it is essential to control the disposal of pollutants into the study pond system.

Trophic plasticity, environmental gradients and food‐web structure of tropical pond communities

Summary Freshwater pond communities exhibit strong patterns in species composition in response to environmental gradients such as ecosystem size, disturbance and productivity, serving as excellent systems for studies of food‐web structure. We surveyed 13 ponds that varied along environmental gradients of canopy cover, pond size and hydroperiod at the beginning and end of the rainy season in the semi‐arid thorn forests of the Gran Chaco ecoregion of Bolivia. We collected basal resources and consumers (tadpoles, macroinvertebrates and fishes) from these ponds and used stable isotope ratios of carbon (13C/12C) and nitrogen (15N/14N), to quantify the spatiotemporal dynamics of the food webs in these tropical ponds. There were no relationships between vertical structure of the food webs and the environmental gradients associated with the ponds. Consumers within these ponds exhibited high trophic variability, with multiple taxa occupying more than one trophic position across space or time. Consumers from larger ponds had a greater degree of trophic redundancy. More shaded ponds supported food webs that had lower trophic diversity. More permanent ponds had significantly greater trophic diversity as well as a greater range of basal resource diversity. The breeding ponds utilised by tadpoles and macroinvertebrates are patchily distributed across space and time. In these dynamic habitats, a feeding strategy of trophic generalism and plasticity enables consumers to exploit a broad range of resources and promote species coexistence. These results suggest that high diversity in tropical ponds does not necessarily translate into specialisation of trophic function.